Polarization and alignment of nucleus fission fragments
International Nuclear Information System (INIS)
Barabanov, A.L.; Grechukhin, D.P.
1987-01-01
Correlation of fragment orientation with orientation axis of fissile nucleus and with n-vector f vector of fragment divergence is considered. Estimations of polarization and alignment of fission fragments of preliminarily oriented nuclei in correlation (with n-vector f recording) and integral (with n-vector f averaging) experiments were conducted. It is shown that high sensitivity of polarization and fragment alignment to the character of nucleus movement at the stage of descent from barrier to rupture point exists
On angular distribution of nucleus fission fragments by fast neutrons
International Nuclear Information System (INIS)
Barabanov, A.L.; Grechukhin, D.P.
1987-01-01
Evaluation of amplitudes of quadrupole and hexadecapole components of angular distribution of nucleus fission fragments by neutrons with the energies E n < or approx. 6 MeV is conducted. Stability of this amplitude to permeability optical coefficient variations for neutrons is revealed. It is shown, that the ratio of these amplitudes as well as the character of their dependence on the target nucleus orientation degree are sensitive to the type of fission probability distribution along K projection if fissile nucleus J spin to the fragment scattering axis. This sensitivity may be used for fragment angular distribution anisotropy formation statistical model verification
International Nuclear Information System (INIS)
Barabanov, A.L.; Grechukhin, D.P.
1985-01-01
General analysis is conducted, and formulae for fission cross section and angular distribution of fission fragments of oriented nuclei by fast neutrons are presented. Geometrical coefficients making up the formulae permitting to carry out calculations for target nuclei with spins I=3/2, 5/2, 7/2 at interaction energies epsilon < or approximately 1 MeV are tabulated. Results of demonstrative calculation of fission fragment angular distribution of oriented sup(235)U nuclei by 0.1 <= epsilon <= 1.0 MeV neutrons reveal that angular distribution weakly depends on the set of permeability factors of neutron waves applied in the calculations
Fission fragment angular momentum
International Nuclear Information System (INIS)
Frenne, D. De
1991-01-01
Most of the energy released in fission is converted into translational kinetic energy of the fragments. The remaining excitation energy will be distributed among neutrons and gammas. An important parameter characterizing the scission configuration is the primary angular momentum of the nascent fragments. Neutron emission is not expected to decrease the spin of the fragments by more than one unit of angular momentum and is as such of less importance in the determination of the initial fragment spins. Gamma emission is a suitable tool in studying initial fragment spins because the emission time, number, energy, and multipolarity of the gammas strongly depend on the value of the primary angular momentum. The main conclusions of experiments on gamma emission were that the initial angular momentum of the fragments is large compared to the ground state spin and oriented perpendicular to the fission axis. Most of the recent information concerning initial fragment spin distributions comes from the measurement of isomeric ratios for isomeric pairs produced in fission. Although in nearly every mass chain isomers are known, only a small number are suitable for initial fission fragment spin studies. Yield and half-life considerations strongly limit the number of candidates. This has the advantage that the behavior of a specific isomeric pair can be investigated for a number of fissioning systems at different excitation energies of the fragments and fissioning nuclei. Because most of the recent information on primary angular momenta comes from measurements of isomeric ratios, the global deexcitation process of the fragments and the calculation of the initial fragment spin distribution from measured isomeric ratios are discussed here. The most important results on primary angular momentum determinations are reviewed and some theoretical approaches are given. 45 refs., 7 figs., 2 tabs
Non-compound nucleus fission in actinide and pre-actinide regions
Indian Academy of Sciences (India)
Abstract. In this article, some of our recent results on fission fragment/product angular distri- butions are discussed in the context of non-compound nucleus fission. Measurement of fission fragment angular distribution in 28Si+176Yb reaction did not show a large contribution from the non-compound nucleus fission. Data on ...
Non-compound nucleus fission in actinide and pre-actinide regions
Indian Academy of Sciences (India)
2015-07-22
Jul 22, 2015 ... In this article, some of our recent results on fission fragment/product angular distributions are discussed in the context of non-compound nucleus fission. Measurement of fission fragment angular distribution in 28Si+176Yb reaction did not show a large contribution from the non-compound nucleus fission.
Antiproton Induced Fission and Fragmentation of Nuclei
2002-01-01
The annihilation of slow antiprotons with nuclei results in a large highly localized energy deposition primarily on the nuclear surface. \\\\ \\\\ The study of antiproton induced fission and fragmentation processes is expected to yield new information on special nuclear matter states, unexplored fission modes, multifragmentation of nuclei, and intranuclear cascades.\\\\ \\\\ In order to investigate the antiproton-nucleus interaction and the processes following the antiproton annihilation at the nucleus, we propose the following experiments: \\item A)~Measurement of several fragments from fission and from multifragmentation in coincidence with particle spectra, especially neutrons and kaons. \\item B)~Precise spectra of $\\pi$, K, n, p, d and t with time-of-flight techniques. \\item C)~Installation of the Berlin 4$\\pi$ neutron detector with a 4$\\pi$ Si detector placed inside for fragments and charged particles. This yields neutron multiplicity distributions and consequently distributions of thermal excitation energies and...
The spectroscopy of fission fragments
International Nuclear Information System (INIS)
Phillips, W.R.
1998-01-01
High-resolution measurements on γ rays from fission fragments have provided a rich source of information, unobtainable at the moment in any other way, on the spectroscopy of neutron-rich nuclei. In recent years important data have been obtained on the yrast- and near yrast-structure of neutron-rich fission fragments. We discuss the scope of measurements which can be made on prompt gamma rays from secondary fission fragments, the techniques used in the experiments and some results recently obtained. (author)
The spectroscopy of fission fragments
Energy Technology Data Exchange (ETDEWEB)
Phillips, W.R. [Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL (United Kingdom); Collaboration: La Direction des Sciences de la Matiere du CEA (FR); Le Fonds National de la Recherche Scientifique de Belgique (BE)
1998-12-31
High-resolution measurements on {gamma} rays from fission fragments have provided a rich source of information, unobtainable at the moment in any other way, on the spectroscopy of neutron-rich nuclei. In recent years important data have been obtained on the yrast- and near yrast-structure of neutron-rich fission fragments. We discuss the scope of measurements which can be made on prompt gamma rays from secondary fission fragments, the techniques used in the experiments and some results recently obtained. (author) 24 refs., 8 figs., 1 tab.
Fission fragment mass distributions via prompt γ-ray spectroscopy
Indian Academy of Sciences (India)
2015-07-24
Jul 24, 2015 ... The distribution of fragment masses formed in nuclear fission is one of the most striking features of the process. Such measurements are very important to understand the shape evolution of the nucleus from ground state to scission through intermediate saddle points. The fission fragment mass distributions, ...
Fission fragment mass distributions via prompt γ-ray spectroscopy
Indian Academy of Sciences (India)
Abstract. The distribution of fragment masses formed in nuclear fission is one of the most strik- ing features of the process. Such measurements are very important to understand the shape evolu- tion of the nucleus from ground state to scission through intermediate saddle points. The fission fragment mass distributions ...
International Nuclear Information System (INIS)
Barabanov, A.L.
1985-01-01
Experimental data on dependence of fission cross section Σsub(f) (epsilon) and angular anisotropy W(epsilon, 0 deg)/W(epsilon, 90 deg) of sup(235)U fission fragment escape by neutrons with energy epsilon=100 and 200 keV on orientation of target nuclei are analyzed. 235 U (Isup(πsub(0))=7/2sup(-)) nuclei were orientated at the expense of interaction of quadrupole nucleus momenta with nonuniform electric field of uranyl-rubidium nitrate crystal at crystal cooling to T=0.2 K. The analysis was carried out with three different sets of permeability factors T(epsilon). Results of the analysis weakly depend on T(epsilon) choice. It is shown that a large number of adjusting parameters (six fissionabilities γsup(f)(Jsup(π), epsilon) and six momenta sub(Jsup(π))) permit to described experimental data on Σsub(f)(epsilon) and W(epsilon, 0 deg)/W(epsilon, 90 deg), obtained at epsilon=200 keV by introducing essential dependence of γsup(f)(Jsup(π), epsilon) and sub(Jsup(π)) on Jsup(π). Estimations of fission cross sections Σsub(f)(epsilon) and angular distribution W(epsilon, n vector) up to T approximately equal to 0.01 K in two geometries of the experiment: the orientation axis is parallel and perpendicular to momentum direction p vector of incident neutrons, are conducted
The VERDI fission fragment spectrometer
International Nuclear Information System (INIS)
Fregeau, M. O.; Brys, T.; Gamboni, T.; Geerts, W.; Oberstedt, S.; Oberstedt, A.; Borcea, R.
2013-01-01
The VERDI time-of-flight spectrometer is dedicated to measurements of fission product yields and of prompt neutron emission data. Pre-neutron fission-fragment masses will be determined by the double time-of-flight (TOF) technique. For this purpose an excellent time resolution is required. The time of flight of the fragments will be measured by electrostatic mirrors located near the target and the time signal coming from silicon detectors located at 50 cm on both sides of the target. This configuration, where the stop detector will provide us simultaneously with the kinetic energy of the fragment and timing information, significantly limits energy straggling in comparison to legacy experimental setup where a thin foil was usually used as a stop detector. In order to improve timing resolution, neutron transmutation doped silicon will be used. The high resistivity homogeneity of this material should significantly improve resolution in comparison to standard silicon detectors. Post-neutron fission fragment masses are obtained form the time-of-flight and the energy signal in the silicon detector. As an intermediary step a diamond detector will also be used as start detector located very close to the target. Previous tests have shown that poly-crystalline chemical vapour deposition (pCVD) diamonds provides a coincidence time resolution of 150 ps not allowing complete separation between very low-energy fission fragments, alpha particles and noise. New results from using artificial single-crystal diamonds (sCVD) show similar time resolution as from pCVD diamonds but also sufficiently good energy resolution. (authors)
Fission fragment anisotropy of 235U measured with the fissionTPC
Hensle, David; Greife, Uwe; Niffte Collaboration
2017-09-01
The fissionTPC, built for the purpose of making neutron-induced fission cross section measurements with unprecedented precision, is a two-chamber MICROMEGAS time projection chamber that allows for three-dimensional tracking of charged particles. This three-dimensional tracking capability also provides a direct measurement of fission fragment angular distributions for neutron-induced fission. Fragment angular anisotropy is an important experimental observable for understanding the quantum mechanical state of the fissioning nucleus and a parameter required to determine detection efficiency for cross section measurements. Preliminary results for 235U fission fragment anisotropy as a function of neutron energies in the range 130 keV - 100 MeV will be presented.
Geppert-Kleinrath, V.; Tovesson, F.; Barrett, J. S.; Bowden, N. S.; Bundgaard, J.; Casperson, R. J.; Cebra, D. A.; Classen, T.; Cunningham, M.; Duke, D. L.; Gearhart, J.; Greife, U.; Guardincerri, E.; Hagmann, C.; Heffner, M.
2017-01-01
Fission fragment angular distributions can provide insights into the quantum mechanical state of the transition nucleus at the saddle point and are therefore an important constraint on fission theory. Available anisotropy data is sparse, especially at neutron energies above 5 MeV. For the first time, a three-dimensional tracking detector is employed to study fragment emission angles and provide a direct measurement of angular anisotropy. The Neutron Induced Fission Fragment Tracking Experimen...
Reexamination of fission fragment angular distributions and the fission process: Formalism
International Nuclear Information System (INIS)
Bond, P.D.
1985-01-01
The theory of fission fragment angular distributions is examined and the universally used expression is found to be valid only under restrictive assumptions. A more general angular distribution formula is derived and applied to recent data of high spin systems. At the same time it is shown that the strong anisotropies observed from such systems can be understood without changing the essential basis of standard fission theory. The effects of reaction mechanisms other than complete fusion on fission fragment angular distributions are discussed and possible angular distribution signatures of noncompound nucleus formation are mentioned
Fission fragment angular distribution in heavy ion induced fission
Directory of Open Access Journals (Sweden)
S. Soheyli
2006-06-01
Full Text Available We have calculated the fission fragment angular anisotropy for 16O + 232Th,12C + 236U , 11B + 237 Np , 14 N + 232 Th , 11B + 235U , 12C + 232Th systems with the saddle point statistical model and compared the fission fragment angular anisotropy for these systems. This comparison was done with two methods a without neutron correction and b with neutron correction. Also we studied normal and anomalous behavior of the fission fragment angular anisotropy. Finally, we have predicted the average emitted neutron from compound nuclei considering the best fit for each system.
Fission fragment angular distribution in heavy ion induced fission
S. Soheyli; I. Ziaeian
2006-01-01
We have calculated the fission fragment angular anisotropy for 16O + 232Th,12C + 236U , 11B + 237 Np , 14 N + 232 Th , 11B + 235U , 12C + 232Th systems with the saddle point statistical model and compared the fission fragment angular anisotropy for these systems. This comparison was done with two methods a) without neutron correction and b) with neutron correction. Also we studied normal and anomalous behavior of the fission fragment angular anisotropy. Finally, we have predicted the averag...
Observation for really cold fragmentation of heavy nucleus
International Nuclear Information System (INIS)
Goverdovskij, A.A.; Ketlerov, V.V.; Mitrofanov, V.F.; Ostapenko, Yu.B.; Khryachkov, V.A.
1998-01-01
The results of the detailed study on mass-energy charged correlations of the thorium-232 fission fragments, produced by the 5 MeV neutrons are presented. The event of the thorium nucleus really cold fragmentation into tellurium-134 and strontium-99 at the basic quantum states is identified. It is shown that the whole reaction energy is exhausted by the motion kinetic energy of the fragments in the mutual field
Angular distribution of oriented nucleus fission neutrons
International Nuclear Information System (INIS)
Barabanov, A.L.; Grechukhin, D.P.
1982-01-01
Calculations of anisotropy of angular distribution of oriented 235 U nuclei thermal fission neutrons have been carried out. the neutrons were assumed to evaporate isotropically by completely accelerated fragements in the fragment system with only its small part, i. e. fission-producing neutrons, emitted at the moment of neck break. It has been found out that at low energies of neutrons Esub(n)=1-2 MeV the sensitivity of the angular distribution anisotropy to variations of spectrum of neutron evaporation from fragments and the magnitude of a share of fission-producing neutrons reaches approximately 100%, which at high energies, Esub(n) > 5 MeV it does not exceed approximately 20%. Therefore the angular distribution of fast neutrons to a greater degree of confidence may be used for restoring the angular distribution anisotropy of fragments while the angular distribution of low energy neutrons may be used for deriving information on the fission process, but only in case 6f the experiment accuracy is better than approximately 3%
Khryachkov, Vitaly; Goverdovskii, Andrei; Ketlerov, Vladimir; Mitrofanov, Vecheslav; Sergachev, Alexei
2018-03-01
Binary fission of 232Th and 238U induced by fast neutrons were under intent investigation in the IPPE during recent years. These measurements were performed with a twin ionization chamber with Frisch grids. Signals from the detector were digitized for further processing with a specially developed software. It results in information of kinetic energies, masses, directions and Bragg curves of registered fission fragments. Total statistics of a few million fission events were collected during each experiment. It was discovered that for several combinations of fission fragment masses their total kinetic energy was very close to total free energy of the fissioning system. The probability of such fission events for the fast neutron induced fission was found to be much higher than for spontaneous fission of 252Cf and thermal neutron induced fission of 235U. For experiments with 238U target the energy of incident neutrons were 5 MeV and 6.5 MeV. Close analysis of dependence of fission fragment distribution on compound nucleus excitation energy gave us some explanation of the phenomenon. It could be a process in highly excited compound nucleus which leads the fissioning system from the scission point into the fusion valley with high probability.
Directory of Open Access Journals (Sweden)
Khryachkov Vitaly
2018-01-01
Full Text Available Binary fission of 232Th and 238U induced by fast neutrons were under intent investigation in the IPPE during recent years. These measurements were performed with a twin ionization chamber with Frisch grids. Signals from the detector were digitized for further processing with a specially developed software. It results in information of kinetic energies, masses, directions and Bragg curves of registered fission fragments. Total statistics of a few million fission events were collected during each experiment. It was discovered that for several combinations of fission fragment masses their total kinetic energy was very close to total free energy of the fissioning system. The probability of such fission events for the fast neutron induced fission was found to be much higher than for spontaneous fission of 252Cf and thermal neutron induced fission of 235U. For experiments with 238U target the energy of incident neutrons were 5 MeV and 6.5 MeV. Close analysis of dependence of fission fragment distribution on compound nucleus excitation energy gave us some explanation of the phenomenon. It could be a process in highly excited compound nucleus which leads the fissioning system from the scission point into the fusion valley with high probability.
Dynamical Model of Fission Fragment Angular Distribution
Drozdov, V. A.; Eremenko, D. O.; Fotina, O. V.; Platonov, S. Yu.; Yuminov, O. A.; Giardina, G.; Taccone, A.
2002-01-01
A dynamical model of fission fragment angular distributions is suggested. The model allows one to calculate fission fragment angular distributions, prescission light particle multyplicities, evaporation residue cross sections etc. for the cases of decay of hot and rotating heavy nuclei. The experimental data on angular anisotropies of fission fragments and prescission neutron multiplicities are analyzed for the 16O + 208Pb, 232Th, 248Cm and 238U reactions at the energies of the incident 16O ions ranging from 90 to 160 MeV. This analysis allows us to extract both the nuclear friction coefficient value and the relaxation time for the tilting mode. It is also demonstrated that the angular distributions are sensitive to the deformation dependence of the nuclear friction.
Brownian shape motion: Fission fragment mass distributions
Directory of Open Access Journals (Sweden)
Sierk Arnold J.
2012-02-01
Full Text Available It was recently shown that remarkably accurate fission-fragment mass distributions can be obtained by treating the nuclear shape evolution as a Brownian walk on previously calculated five-dimensional potential-energy surfaces; the current status of this novel method is described here.
Fission probability of nucleus of sup(232)Th mesoatom
International Nuclear Information System (INIS)
Cojocaru, V.; Gavrilov, Yu.K.; Kim Si wan; Krogulski, T.; Kuznetsov, V.D.; Ortlepp, H.-G.; Polikanov, S.M.
1975-01-01
The fission probability of the nucleus of the sup(232)Th muonic atom has been measured. The fission yield was measured simultaneously with the intensity of 5g-4f transition in the muonic atom sup(232)Th. A good agreement with previous result obtained in measurements with the fission chamber and evident disagreement with the photoemulsion data have been obtained
Fission fragment angular distributions and fission cross section validation
International Nuclear Information System (INIS)
Leong, Lou Sai
2013-01-01
The present knowledge of angular distributions of neutron-induced fission is limited to a maximal energy of 15 MeV, with large discrepancies around 14 MeV. Only 238 U and 232 Th have been investigated up to 100 MeV in a single experiment. The n-TOF Collaboration performed the fission cross section measurement of several actinides ( 232 Th, 235 U, 238 U, 234 U, 237 Np) at the n-TOF facility using an experimental set-up made of Parallel Plate Avalanche Counters (PPAC), extending the energy domain of the incident neutron above hundreds of MeV. The method based on the detection of the 2 fragments in coincidence allowed to clearly disentangle the fission reactions among other types of reactions occurring in the spallation domain. I will show the methods we used to reconstruct the full angular resolution by the tracking of fission fragments. Below 10 MeV our results are consistent with existing data. For example in the case of 232 Th, below 10 MeV the results show clearly the variation occurring at the first (1 MeV) and second (7 MeV) chance fission, corresponding to transition states of given J and K (total spin and its projection on the fission axis), and a much more accurate energy dependence at the 3. chance threshold (14 MeV) has been obtained. In the spallation domain, above 30 MeV we confirm the high anisotropy revealed in 232 Th by the single existing data set. I'll discuss the implications of this finding, related to the low anisotropy exhibited in proton-induced fission. I also explore the critical experiments which is valuable checks of nuclear data. The 237 Np neutron-induced fission cross section has recently been measured in a large energy range (from eV to GeV) at the n-TOF facility at CERN. When compared to previous measurements, the n-TOF fission cross section appears to be higher by 5-7 % beyond the fission threshold. To check the relevance of n-TOF data, we simulate a criticality experiment performed at Los Alamos with a 6 kg sphere of 237 Np. This
Anisotropic Neutron Evaporation from Spinning Fission Fragments
Stuttgé, L.; Dorvaux, O.; Gönnenwein, F.; Mutterer, M.; Kopatch, Yu.; Chernysheva, E.; Hanappe, F.; Hambsch, F.-J.
2011-10-01
Neutron evaporation anisotropy in the centre of mass of the rotating fission fragments in the spontaneous fission of 252Cf has been investigated within the CORA experiments. If it is well accepted that the bulk of emitted neutrons originate from an isotropic evaporation in the centre of mass of the moving fragments, discrepancies in experimental as well as in theoretical energy and angular distributions appear throughout many attempts performed by various authors. Scission neutrons most probably contribute but don't allow to explain totally the observed anisotropy. Due to its weak contribution to the total anisotropy, the centre of mass anisotropy is very difficult to be highlighted. A novel experimental approach has been developed to extract this effect and will be presented as well as some first results.
Binary fragmentation based studies for the near super-heavy compound nucleus {sup 256}Rf
Energy Technology Data Exchange (ETDEWEB)
Thakur, Meenu; Behera, B.R.; Mahajan, Ruchi; Kaur, Gurpreet; Sharma, Priya; Kapoor, Kushal; Rani, Kavita [Panjab University, Department of Physics, Chandigarh (India); Saneesh, N.; Dubey, R.; Yadav, A.; Sugathan, P.; Jhingan, A.; Chatterjee, A.; Chatterjee, M.B. [Inter University Accelerator Centre, New Delhi (India); Kumar, Neeraj; Mandal, S. [University of Delhi, Department of Physics and Astrophysics, Delhi (India); Kumar, S. [Andhra University, Department of Nuclear Physics, Visakhapatnam (India); Saxena, A.; Kailas, S. [Bhabha Atomic Research Centre, Nuclear Physics Division, Mumbai (India); Pal, Santanu [CS, Kolkata (India); Nasirov, Avazbek [JINR, Bogoliubov Laboratory of Theoretical Physics, Dubna (Russian Federation); National University, Department of Physics, Tashkent (Uzbekistan); Kayumov, Bakhodir [National University, Department of Physics, Tashkent (Uzbekistan)
2017-06-15
Binary fragmentation of the near super-heavy compound nucleus {sup 256}Rf has been studied through the reaction {sup 48}Ti + {sup 208}Pb at a bombarding energy well above the Coulomb barrier. For a better understanding of its reaction dynamics, the mass distribution, mass-energy distribution and mass-angle distribution of the fission fragments produced from {sup 256}Rf have been investigated thoroughly. The masses and kinetic energies of the fission fragments were reconstructed event-by-event from their measured velocities and emission angles. From the mass-energy analysis, a sizeable contribution from the asymmetric fission was observed on the edges of symmetric mass distribution. Evidence of asymmetric fission was also clued from the observed correlation between the masses and emission angles of the fission fragments. Contribution of the quasi-fission products has also been estimated by performing the theoretical dinuclear system calculations. (orig.)
Measurement of fission fragments energy loss
Benetti, P; Calligarich, E; Cesana, A; Dolfini, R; Ioppolo, T; Raselli, G L; Terrani, M
2002-01-01
The mean energy of sup 2 sup 5 sup 2 Cf fission fragments emerging from an absorber and the determination of the capture rate in the absorber itself have been measured using two independent and complementary nuclear techniques. The results can be applied to the measurement of the energy self-absorption in a non-zero thickness source and can be used to validate simulation programs.
Langevin description of fission fragment charge distribution from excited nuclei
Karpov, A V
2002-01-01
A stochastic approach to fission dynamics based on a set of three-dimensional Langevin equations was applied to calculate fission-fragment charge distribution of compound nucleus sup 2 sup 3 sup 6 U. The following collective coordinates have been chosen - elongation coordinate, neck-thickness coordinate, and charge-asymmetry coordinate. The friction coefficient of charge mode has been calculated in the framework of one-body and two-body dissipation mechanisms. Analysis of the results has shown that Langevin approach is appropriate for investigation of isobaric distribution. Moreover, the dependences of the variance of the charge distribution on excitation energy and on the two-body viscosity coefficient has been studied
Inverse kinematics technique for the study of fission-fragment isotopic yields at GANIL energies
International Nuclear Information System (INIS)
Delaune, O.
2012-01-01
The characteristics of the fission-products distributions result of dynamical and quantum properties of the deformation process of the fissioning nucleus. These distributions have also an interest for the conception of new nuclear power plants or for the transmutation of the nuclear wastes. Up to now, our understanding of the nuclear fission remains restricted because of experimental limitations. In particular, yields of the heavy fission products are difficult to get with precision. In this work, an innovative experimental technique is presented. It is based on the use of inverse kinematics coupled to the use of a spectrometer, in which a 238 U beam at 6 or 24 A MeV impinges on light targets. Several actinides, from 238 U to 250 Cf, are produced by transfer or fusion reactions, with an excitation energy ranges from ten to few hundreds MeV depending on the reaction and the beam energy. The fission fragments of these actinides are detected by the VAMOS spectrometer or the LISE separator. The isotopic yields of fission products are completely measured for different fissioning systems. The neutron excess of the fragments is used to characterise the isotopic distributions. Its evolution with excitation energy gives important insights on the mechanisms of the compound-nucleus formation and its deexcitation. Neutron excess is also used to determine the multiplicity of neutrons evaporated by the fragments. The role of the proton and neutron shell effects into the formation of fission fragments is also discussed. (author) [fr
Light fragment preformation in cold fission of {sup 282}Cn
Energy Technology Data Exchange (ETDEWEB)
Poenaru, D.N.; Gherghescu, R.A. [Horia Hulubei National Institute of Physics and Nuclear Engineering (IFIN-HH), P.O. Box MG-6, Bucharest-Magurele (Romania); Johann Wolfgang Goethe University, Frankfurt Institute for Advanced Studies (FIAS), Frankfurt am Main (Germany)
2016-11-15
In a previous article, published in Phys. Rev. C 94, 014309 (2016), we have shown for the first time that the best dynamical trajectory during the deformation toward fission of the superheavy nucleus {sup 286}Fl is a linearly increasing radius of the light fragment, R{sub 2}. This macroscopic-microscopic result reminds us about the α or cluster preformation at the nuclear surface, assumed already in 1928, and proved microscopically many times. This time we give more detailed arguments for the nucleus {sup 282}Cn. Also similar figures are presented for heavy nuclei {sup 240}Pu and {sup 252} Cf. The deep minimum of the total deformation energy near the surface is shown for the first time as a strong argument for cluster preformation. (orig.)
Mass distribution of fission fragments within the Born-Oppenheimer approximation
Pomorski, K.; Ivanyuk, F. A.; Nerlo-Pomorska, B.
2017-03-01
The fission fragments mass-yield of 236 U is obtained by an approximate solution of the eigenvalue problem of the collective Hamiltonian that describes the dynamics of the fission process whose degrees of freedom are: the fission (elongation), the neck and mass-asymmetry modes. The macroscopic-microscopic method is used to evaluate the potential energy surface. The macroscopic energy part is calculated using the liquid drop model and the microscopic corrections are obtained using a Woods-Saxon single-particle levels. The four-dimensional modified Cassini ovals shape parametrization is used to describe the shape of the fissioning nucleus. The mass tensor is taken within a cranking-type approximation. The final fragment mass distribution is obtained by weighting the adiabatic density distribution in the collective space with the neck-dependent fission probability. The neck degree of freedom is found to play a significant role in determining the final fragment mass distribution.
The Munich accelerator for fission fragments MAFF
Habs, D.; Groß, M.; Assmann, W.; Ames, F.; Bongers, H.; Emhofer, S.; Heinz, S.; Henry, S.; Kester, O.; Neumayr, J.; Ospald, F.; Reiter, P.; Sieber, T.; Szerypo, J.; Thirolf, P. G.; Varentsov, V.; Wilfart, T.; Faestermann, T.; Krücken, R.; Maier-Komor, P.
2003-05-01
The Munich Accelerator for Fission Fragments MAFF has been designed for the new Munich research reactor FRM-II. It will deliver several intense beams (˜3×10 11 s -1) of very neutron-rich fission fragments with a final energy of 30 keV (low-energy beam) or energies between 3.7 and 5.9 MeV· A (high-energy beam). Such beams are of interest for the creation of super-heavy elements by fusion reactions, nuclear spectroscopy of exotic nuclei, but they also have a potential for applications, e.g. in medicine. Presently the Munich research reactor FRM-II is ready for operation, but authorities delay the final permission to turn the reactor critical probably till the end of 2002. Only after this final permission the financing of the major parts of MAFF can start. On the other hand all major components have been designed and special components have been tested in separate setups.
Alkaline glass as induced fission fragment detectors
International Nuclear Information System (INIS)
Amorim, A.M.M.
1986-01-01
The slide glass, registered trade marks INLAB, INVICT and PERFECTA were compared. For the three kinds of glasses the following studies were done: chemical composition; general dissolution rate for hydrofluoric acid solutions of concentrations between 1 and 10M, at 30 0 C and ultrasound shaking; relative efficiency for recording fission fragment tracks from 252 Cf. The INLAB glass was selected due to the better quality of its surface after chemical etching. The HF concentration 2.5M was determined for chemical etching of INLAB glass, and the optimum etching time was chosen between 8 and 10 minutes. The thermal attenuation of latent tracks in the environmental temperature was observed for intervals uo to 31 days between the detector exposure to the fission fragment source and etching of tracks. Several methods were used for determining the detector parameters, such as: critical angle, angle of the cone and efficiency of etching. The effects of gamma irradiation from 60 Co and reactor neutrons in material properties as track detector were studied. Attenuation of latent tracks and saturation of color centers were observed for doses over 100M Rad. Since this kind of material contains uranium as impurity, uniformely distributed, slide glass were calibrated to be applied as a monitor of thermal neutron flux in nuclear reactor. (Author) [pt
The Munich accelerator for fission fragments MAFF
International Nuclear Information System (INIS)
Habs, D.; Gross, M.; Assmann, W.; Ames, F.; Bongers, H.; Emhofer, S.; Heinz, S.; Henry, S.; Kester, O.; Neumayr, J.; Ospald, F.; Reiter, P.; Sieber, T.; Szerypo, J.; Thirolf, P.G.; Varentsov, V.; Wilfart, T.; Faestermann, T.; Kruecken, R.; Maier-Komor, P.
2003-01-01
The Munich Accelerator for Fission Fragments MAFF has been designed for the new Munich research reactor FRM-II. It will deliver several intense beams (∼3x10 11 s -1 ) of very neutron-rich fission fragments with a final energy of 30 keV (low-energy beam) or energies between 3.7 and 5.9 MeV·A (high-energy beam). Such beams are of interest for the creation of super-heavy elements by fusion reactions, nuclear spectroscopy of exotic nuclei, but they also have a potential for applications, e.g. in medicine. Presently the Munich research reactor FRM-II is ready for operation, but authorities delay the final permission to turn the reactor critical probably till the end of 2002. Only after this final permission the financing of the major parts of MAFF can start. On the other hand all major components have been designed and special components have been tested in separate setups
Formation and distribution of fragments in the spontaneous fission of 240Pu
Sadhukhan, Jhilam; Zhang, Chunli; Nazarewicz, Witold; Schunck, Nicolas
2017-12-01
Background: Fission is a fundamental decay mode of heavy atomic nuclei. The prevalent theoretical approach is based on mean-field theory and its extensions where fission is modeled as a large amplitude motion of a nucleus in a multidimensional collective space. One of the important observables characterizing fission is the charge and mass distribution of fission fragments. Purpose: The goal of this Rapid Communication is to better understand the structure of fission fragment distributions by investigating the competition between the static structure of the collective manifold and the stochastic dynamics. In particular, we study the characteristics of the tails of yield distributions, which correspond to very asymmetric fission into a very heavy and a very light fragment. Methods: We use the stochastic Langevin framework to simulate the nuclear evolution after the system tunnels through the multidimensional potential barrier. For a representative sample of different initial configurations along the outer turning-point line, we define effective fission paths by computing a large number of Langevin trajectories. We extract the relative contribution of each such path to the fragment distribution. We then use nucleon localization functions along effective fission pathways to analyze the characteristics of prefragments at prescission configurations. Results: We find that non-Newtonian Langevin trajectories, strongly impacted by the random force, produce the tails of the fission fragment distribution of 240Pu. The prefragments deduced from nucleon localizations are formed early and change little as the nucleus evolves towards scission. On the other hand, the system contains many nucleons that are not localized in the prefragments even near the scission point. Such nucleons are distributed rapidly at scission to form the final fragments. Fission prefragments extracted from direct integration of the density and from the localization functions typically differ by more than
New fission-fragment detector for experiments at DANCE
Rusev, G.; Roman, A. R.; Daum, J. K.; Springs, R. K.; Bond, E. M.; Jandel, M.; Baramsai, B.; Bredeweg, T. A.; Couture, A.; Favalli, A.; Ianakiev, K. D.; Iliev, M. L.; Mosby, S.; Ullmann, J. L.; Walker, C. L.
2015-10-01
A fission-fragment detector based on thin scintillating films has been built to serve as a veto/trigger detector in neutron-induced fission measurements at DANCE. The fissile material is surrounded by scintillating films providing a 4 π detection of the fission fragments. The scintillation events caused by the fission fragment interactions in the films are registered with silicon photomultipliers. Design of the detector and test measurements are described. Work supported by the U.S. Department of Energy through the LANL/LDRD Program and the U.S. Department of Energy, Office of Science, Nuclear Physics under the Early Career Award No. LANL20135009.
Fission fragment mass distributions via prompt γ-ray spectroscopy
Indian Academy of Sciences (India)
fragment mass distributions, generally obtained via conventional methods (i.e., by measuring the energy and/or the velocity of the correlated fission fragments) are limited to a mass resolution of 4–. 5 units. On the other hand, by employing the γ-ray spectroscopy, it is possible to estimate the yield of individual fission ...
Delayed β ray spectrum of 235U fission fragments
International Nuclear Information System (INIS)
Pascholati, P.R.
1973-01-01
The time-dependent electron spectra of fission fragments from the thermal-neutron-induced fission of 235 U are calculated. The Gross theory of nuclear beta decay is used to obtain the decay constant and individual electron spectra. The mean energy per fission carried by the electrons and the number of electrons per fission are also calculated. Comparison of these calculated spectra to experimental ones shows good agreements. (Author) [pt
Eslamizadeh, H.; Ahadi, E.
2017-09-01
The evaporation residue cross section, the anisotropy of the fission fragments angular distribution, the fission probability, the mass-energy distribution of the fission fragments, and the average prescission neutron multiplicity have been calculated for the compound nucleus 210Rn by using four-dimensional Langevin equations with dissipation generated through the chaos-weighted wall and window friction formula. Three collective shape coordinates plus the projection of the total spin of the compound nucleus to the symmetry axis K were considered in the four-dimensional dynamical model. In the dynamical calculations dissipation coefficient of K ,γk was considered as a free parameter, and its magnitude was inferred by fitting measured data on the evaporation residue cross section and the anisotropy of the fission fragments angular distribution for the compound nucleus 210Rn. It was shown that the results of the calculations are in good agreement with the experimental data by using values of the dissipation coefficient of K , equal to γk=(0 .185 -0 .200 ) (MeVzs) -1 /1 22 . It also was shown that the influence of the dissipation coefficient of K on the results of the calculations of the fission probability, the mass-energy distribution of the fission fragments, and the average prescission neutron multiplicity for the compound nucleus 210Rn is small.
Rossner, H.; Hinde, D. J.; Leigh, J. R.; Lestone, J. P.; Newton, J. O.; Wei, J. X.; Elfström, S.
1992-02-01
Neutrons have been measured in coincidence with fission fragments of the reaction 208Pb(16O,f) at bombarding energies ranging between 80 and 130 MeV. Pre-scission and post-scission multiplicities were deduced from the neutron spectra by application of a moving source fit procedure. Particles evaporated before the saddle point configuration of the fissioning nucleus will reduce the nuclear temperature of the transition nucleus. This effect of higher chance fission increases the anisotropies of fission fragment angular distributions compared to the assumption of first chance fission. Compound nuclei with nuclear temperatures considerably smaller than the fission barrier have statistical fission decay times that are much longer than saddle-to-scission times. With these conditions it is plausible that most of the particles evaporated from the fissioning nucleus are emitted before the saddle. Fission fragment angular distributions for 208Pb(16O,f) analyzed with the transition state model including the nuclear temperature reduction caused by pre-fission particle emission show ``normal'' anisotropies at low and near barrier energies.
Angular momenta of fission fragments in the {alpha}-accompanied fission of {sup 252}Cf
Energy Technology Data Exchange (ETDEWEB)
Jandel, M.; Kliman, J.; Krupa, L.; Morhac, M. [Slovak Academy of Sciences, Department of Nuclear Physics, Bratislava (Slovakia); Joint Institute for Nuclear Research, Flerov Laboratory for Nuclear Reactions, Dubna (Russian Federation); Hamilton, J.H.; Kormicki, J.; Ramayya, A.V.; Hwang, J.K.; Luo, Y.X.; Fong, D.; Gore, P. [Vanderbilt University, Department of Physics, Nashville, TN (United States); Ter-Akopian, G.M.; Oganessian, Yu.Ts.; Rodin, A.M.; Fomichev, A.S.; Popeko, G.S. [Joint Institute for Nuclear Research, Flerov Laboratory for Nuclear Reactions, Dubna (Russian Federation); Daniel, A.V. [Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Rasmussen, J.O.; Macchiavelli, A.O.; Stoyer, M.A. [Lawrence Livermore National Laboratory, Livermore, CA (United States); Donangelo, R.; Cole, J.D.
2005-06-01
For the first time, average angular momenta of the ternary fission fragments {sup 100,102}Zr, {sup 106}Mo, {sup 144,146}Ba and {sup 138,140,142}Xe from the {alpha}-accompanied fission of {sup 252}Cf were obtained from relative intensities of prompt {gamma}-ray transitions with the use of the statistical model calculation. Average values of the angular momenta were compared with the corresponding values for the same fission fragments from the binary fission of {sup 252}Cf. Results indicate the presence of a decreasing trend in the average values of angular momenta induced in ternary fission fragments compared to the same binary fission fragments. On the average, the total angular momentum extracted for ternary fission fragments is {proportional_to}1.4{Dirac_h} lower than in binary fission. Consequently, results indicate that the mechanism of the ternary {alpha}-particles emission may directly effect an induction of angular momenta of fission fragments, and possible scenarios of such mechanisms are discussed. Further, the dependence of the angular momenta of {sup 106}Mo and {sup 140}Xe on the number of emitted neutrons from correlated pairs of primary fragments was obtained also showing a decreasing dependence of average angular momenta with increasing number of emitted neutrons. Consequences are briefly discussed. (orig.)
Fission fragment mass and angular distributions
Indian Academy of Sciences (India)
2015-07-22
Jul 22, 2015 ... Synthesis of heavy and superheavy elements is severely hindered by fission and fission-like processes. The probability of these fission-like, non-equilibrium processes strongly depends on the entrance channel parameters. This article attempts to summarize the recent experimental findings and classify the ...
Fusion – fission dynamics: fragment mass distribution studies
Directory of Open Access Journals (Sweden)
Bhattacharya S.
2015-01-01
Full Text Available Using the major accelerator facilities available in India, detailed experimental studies have been made to understand the mechanism of quasi-fission and role of nuclear shell effect in heavy nuclei. Fission fragment mass distribution has been used as the probe to explore the role of entrance channel effects on fusion-fission and quasifission dynamics. Fission fragment mass distribution has also been demonstrated to be useful to identify the phenomenon of ‘washing out’ of nuclear shell effect with excitation energy.
Fission Fragment Yield Data in Support of Advanced Reactor Technology
Energy Technology Data Exchange (ETDEWEB)
Hecht, Adam [Univ. of New Mexico, Albuquerque, NM (United States)
2017-11-21
Within the 3 year POP we propose to continue to test and further develop the fission spectrometers, to do development tests and full data acquisition run at the national laboratory neutron beam facilities, to measure correlated fission fragment yields at low neutron energies with 235 U fission targets, and make these data available to the nuclear community. The spectrometer development will be both on the university based r\\prototype and on the National Laboratory Spectrometer, and measurements will be performed with both. Over the longer time frame of the collaboration, we will take data over a range of low energies, and use other fission targets available to the laboratory. We will gather energy specific fragment distributions and reaction cross sections. We will further develop the data acquisition capabilities to take correlated fission fragment'gamma ray/neurton data, all on an event-by-event basis. This really is an enabling technology.
Fission fragments transport by gaseous flow with aerosols
Gangrskij, Y P; Zhemenik, V I; Myshinskij, G V; Penionzhkevich, Yu E; Selesh, O
2002-01-01
Paper describes a pilot facility for fission fragment transport by gaseous flow with aerosols. This facility designed for fragment transport consists of a reaction chamber with irradiated target, receipt chamber to collect fragments, aerosol generator, roughing pump to pump put gas and a capillary connecting these units of facility. Paper presents the results of facility testing with fragments of sup 2 sup 3 sup 8 U photofission by microtron Bremsstrahlung. The obtained parameters of facility (up to 70% efficiency of transport, up to 0.1 s time of transport at 1 m distance) enable to use it efficiently in experiments dealing with heavy nuclei fission and with investigation in properties of fission fragments
Compound Nucleus Reactions in LENR, Analogy to Uranium Fission
Hora, Heinrich; Miley, George; Philberth, Karl
2008-03-01
The discovery of nuclear fission by Hahn and Strassmann was based on a very rare microanalytical result that could not initially indicate the very complicated details of this most important process. A similarity is discussed for the low energy nuclear reactions (LENRs) with analogies to the yield structure found in measurements of uranium fission. The LENR product distribution measured earlier in a reproducible way in experiments with thin film electrodes and a high density deuteron concentration in palladium has several striking similarities with the uranium fission fragment yield curve.ootnotetextG.H. Miley and J.A. Patterson, J. New Energy 1, 11 (1996); G.H. Miley et al, Proc ICCF6, p. 629 (1997).This comparison is specifically focussed to the Maruhn-Greiner local maximum of the distribution within the large-scale minimum when the fission nuclei are excited. Implications for uranium fission are discussed in comparison with LENR relative to the identification of fission a hypothetical compound nuclear reaction via a element ^306X126 with double magic numbers.
A fission fragment detector for correlated fission output studies
Energy Technology Data Exchange (ETDEWEB)
Mosby, S., E-mail: smosby@lanl.gov [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Tovesson, F.; Couture, A. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Duke, D.L. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Colorado School of Mines, Golden, CO 80401 (United States); Kleinrath, V. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Idaho State University, Pocatello, ID 83201 (United States); Meharchand, R.; Meierbachtol, K.; O' Donnell, J.M.; Perdue, B.; Richman, D. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Shields, D. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Colorado School of Mines, Golden, CO 80401 (United States)
2014-09-01
A digital data acquisition system has been combined with a double Frisch gridded ionization chamber for use at both moderated and unmoderated neutron sources at the Los Alamos Neutron Science (LANSCE) facility. The high efficiency of the instrument combined with intense LANSCE beams and new acquisition system permits fission output measurements across 11 orders of magnitude incident neutron energy. The acquisition and analysis system is presented along with the first in-beam performance tests of the setup.
No influence of a N =126 neutron-shell closure in fission-fragment mass distributions
Chaudhuri, A.; Ghosh, T. K.; Banerjee, K.; Bhattacharya, S.; Sadhukhan, Jhilam; Kundu, S.; Bhattacharya, C.; Meena, J. K.; Mukherjee, G.; Saha, A. K.; Asgar, Md. A.; Dey, A.; Manna, S.; Pandey, R.; Rana, T. K.; Roy, P.; Roy, T.; Srivastava, V.; Bhattacharya, P.; Biswas, D. C.; Joshi, B. N.; Mahata, K.; Shrivastava, A.; Vind, R. P.; Pal, S.; Behera, B. R.; Singh, Varinderjit
2015-10-01
Mass distributions of the fragments in the fission of 206Po and the N =126 neutron shell closed nucleus 210Po have been measured. No significant deviation of mass distributions has been found between 206Po and 210Po, indicating the absence of shell correction at the saddle point in both the nuclei, contrary to the reported angular anisotropy and prescission neutron multiplicity results. This result provides benchmark data to test the new fission dynamical models to study the effect of shell correction on the potential energy surface at saddle point.
Fission times studies of the Z=124 superheavy nucleus by X-ray fluorescence
International Nuclear Information System (INIS)
Airiau, Maud
2016-01-01
Since the 1960's nuclear structure model have predicted the existence of an island of stability of superheavy elements. It should be located around the next magic numbers expected at N=172 or 184 and between Z=114 and 126 depending on the model. Very high fission barrier of a few MeV are predicted to be generated by microscopic effects for those nuclei for which large fission times distributions extended to very high fission times are induced. Fission time measurements of the superheavy element Z=124 have been made by us using the X-ray fluorescence technique, a method based on the filling of inner-shell electronic vacancies created during the collision leading to the formation of the compound nucleus. The aim of this experiment was to detect in coincidence both fission fragments and characteristic X-rays from the Z=124, created by the reaction 238 U+ 70,76 Ge. The main difficulty was to identify those X-rays due to the fact that gamma-rays from fission fragments were emitted in the same energy range, which affected our photon multiplicities for any fragment selection. This new difficulty brings an important limitation to the study of some particular superheavy elements by the X-ray fluorescence method. K X-rays spectra have been simulated using MCDF (Multi-Configuration-Dirac-Fock) and then compared to the experimental ones in order to get a maximal K X-ray multiplicity compatible with our data. The extracted results were about 6-7% for 76 Ge and from 12 to 14% for 70 Ge. Those values remain compatible with the experimental signature of long lifetime component observed for the same system but using a blocking technique in single crystals. (author) [fr
A fission-fragment-sensitive target for X-ray spectroscopy in neutron-induced fission
Ethvignot, T; Giot, L; Casoli, P; Nelson, R O
2002-01-01
A fission-fragment-sensitive detector built for low-energy photon spectroscopy applications at the WNR 'white' neutron source at Los Alamos is described. The detector consists of eight layers of thin photovoltaic cells, onto which 1 mg/cm sup 2 of pure sup 2 sup 3 sup 8 U is deposited. The detector serves as an active target to select fission events from background and other reaction channels. The fairly small thickness of the detector with respect to transmission of 20-50 keV photons permits the measurement of prompt fission-fragment X-rays. Results with the GEANIE photon spectrometer are presented.
Modeling the Fission Fragment Detection Efficiency of the NIFFTE fissionTPC
Bowden, Nathaniel; Niffte Collaboration
2017-09-01
The goal of the Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) is to measure neutron-induced fission cross section ratios with unprecedented precision. The NIFFTE Collaboration has designed and built a Time Projection Chamber, the fissionTPC, for this purpose. The detector enables charged particle tracking with full three-dimensional charge cloud reconstruction, allowing for the characterization of fission fragments originating from a thin central target. Quantifying the fission fragment detection efficiency is a central element of these cross section ratio measurements. Here we describe how the wealth of data captured for every fission event allows us to build and validate a detailed Monte Carlo efficiency model. Effects such as anisotropy, fission fragment energy degradation, and target thickness, composition, and roughness must all be taken into account. LLNL-ABS-733618. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Jia, Ying; Bao, Jing-Dong
2007-03-01
The anisotropy of the fission fragment angular distribution defined at the saddle point and the neutron multiplicities emitted prior to scission for fissioning nuclei Th224, Np229, Cf248, and Fm254 are calculated simultaneously by using a set of realistic coupled two-dimensional Langevin equations, where the {c,h,α=0} nuclear parametrization is employed. In comparison with the one-dimensional stochastic model without neck variation, our two-dimensional model produces results that are in better agreement with the experimental data, and the one-dimensional model is available only for low excitation energies. Indeed, to determine the temperature of the nucleus at the saddle point, we investigate the neutron emission during nucleus oscillation around the saddle point for different friction mechanisms. It is shown that the neutrons emitted during the saddle oscillation cause the temperature of a fissioning nuclear system at the saddle point to decrease and influence the fission fragment angular distribution.
Analysis of fission-fragment mass distribution within the quantum-mechanical fragmentation theory
Singh, Pardeep; Kaur, Harjeet
2016-11-01
The fission-fragment mass distribution is analysed for the 208Pb(18O, f) reaction within the quantum-mechanical fragmentation theory (QMFT). The reaction potential has been calculated by taking the binding energies, Coulomb potential and proximity potential of all possible decay channels and a stationary Schrödinger equation has been solved numerically to calculate the fission-fragment yield. The overall results for mass distribution are compared with those obtained in experiment. Fine structure dips in yield, corresponding to fragment shell closures at Z = 50 and N=82, which are observed by Bogachev et al., are reproduced successfully in the present calculations. These calculations will help to estimate the formation probabilities of fission fragments and to understand many related phenomena occurring in the fission process.
Neutron detection methods based on fission fragment track counting
International Nuclear Information System (INIS)
Posta, S.
2004-12-01
The report deals with the development and application of a simple computer-controlled videomicroscope for fission fragment track counting. The principle of the SSFTD (Solid State Fission Track Detector) method, development of image processing methods, and track counting principles are outlined. Focus is on the application of the method to neutron flux density and fluence determination in reactor dosimetry. The procedures developed were applied to neutron parameter measurements in a VVER-1000 mockup in the LR-0 research reactor. (author)
High precision measurements on fission-fragment de-excitation
Oberstedt, Stephan; Gatera, Angélique; Geerts, Wouter; Göök, Alf; Hambsch, Franz-Josef; Vidali, Marzio; Oberstedt, Andreas
2017-11-01
In recent years nuclear fission has gained renewed interest both from the nuclear energy community and in basic science. The first, represented by the OECD Nuclear Energy Agency, expressed the need for more accurate fission cross-section and fragment yield data for safety assessments of Generation IV reactor systems. In basic science modelling made much progress in describing the de-excitation mechanism of neutron-rich isotopes, e.g. produced in nuclear fission. Benchmarking the different models require a precise experimental data on prompt fission neutron and γ-ray emission, e.g. multiplicity, average energy per particle and total dissipated energy per fission, preferably as function of fission-fragment mass and total kinetic energy. A collaboration of scientists from JRC Geel (formerly known as JRC IRMM) and other institutes took the lead in establishing a dedicated measurement programme on prompt fission neutron and γ-ray characteristics, which has triggered even more measurement activities around the world. This contribution presents new advanced instrumentation and methodology we use to generate high-precision spectral data and will give a flavour of future data needs and opportunities.
Sputtering yield of Pu bombarded by fission Fragments from Cf
Energy Technology Data Exchange (ETDEWEB)
Danagoulian, Areg [Los Alamos National Laboratory; Klein, Andreas [Los Alamos National Laboratory; Mcneil, Wendy V [Los Alamos National Laboratory; Yuan, Vincent W [Los Alamos National Laboratory
2008-01-01
We present results on the yield of sputtering of Pu atoms from a Pu foil, bombarded by fission fragments from a {sup 252}Cf source in transmission geometry. We have found the number of Pu atoms/incoming fission fragments ejected to be 63 {+-} 1. In addition, we show measurements of the sputtering yield as a function of distance from the central axis, which can be understood as an angular distribution of the yield. The results are quite surprising in light of the fact that the Pu foil is several times the thickness of the range of fission fragment particles in Pu. This indicates that models like the binary collision model are not sufficient to explain this behavior.
Coincident measurements of prompt fission γ rays and fission fragments at DANCE
Walker, C. L.; Baramsai, B.; Jandel, M.; Rusev, G.; Couture, A.; Mosby, S.; Ullmann, J.; Kawano, T.; Stetcu, I.; Talou, P.
2015-10-01
Modern statistical approaches to modeling fission involve the calculation of not only average quantities but also fully correlated distributions of all fission products. Applications such as those involving the detection of special nuclear materials also rely on fully correlated data of fission products. Experimental measurements of correlated data are thus critical to the validation of theory and the development of important applications. The goal of this experiment was to measure properties of prompt fission gamma-ray emission as a function of fission fragments' total kinetic energy in the spontaneous fission of 252Cf. The measurement was carried out at the Detector for Advanced Neutron Capture Experiments (DANCE), a 4 π γ-ray calorimeter. A prototype design consisting of two silicon detectors was installed in the center of DANCE, allowing simultaneous measurement of fission fragments and γ rays. Effort has been taken to simulate fragment kinetic energy losses as well as γ-ray attenuation in DANCE using such tools as GEANT4 and SRIM. Theoretical predictions generated by the code CGMF were also incorporated as input for these simulations. Results from the experiment and simulations will be presented, along with plans for future measurements.
International Nuclear Information System (INIS)
Heinrich, S.
2006-01-01
Nucleus fission process is a very complex phenomenon and, even nowadays, no realistic models describing the overall process are available. The work presented here deals with a theoretical description of fission fragments distributions in mass, charge, energy and deformation. We have reconsidered and updated the B.D. Wilking Scission Point model. Our purpose was to test if this statistic model applied at the scission point and by introducing new results of modern microscopic calculations allows to describe quantitatively the fission fragments distributions. We calculate the surface energy available at the scission point as a function of the fragments deformations. This surface is obtained from a Hartree Fock Bogoliubov microscopic calculation which guarantee a realistic description of the potential dependence on the deformation for each fragment. The statistic balance is described by the level densities of the fragment. We have tried to avoid as much as possible the input of empirical parameters in the model. Our only parameter, the distance between each fragment at the scission point, is discussed by comparison with scission configuration obtained from full dynamical microscopic calculations. Also, the comparison between our results and experimental data is very satisfying and allow us to discuss the success and limitations of our approach. We finally proposed ideas to improve the model, in particular by applying dynamical corrections. (author)
Anisotropic annealing of fission fragments in synthetic quartz
Sawamura, T; Narita, M
1999-01-01
A study on the thermal annealing behavior of fission fragments in synthetic quartz crystals was performed for application of synthetic quartz to track detectors under high temperature circumstances: x-, y-, and z-cut quartz plates were exposed to fission fragments from sup 2 sup 5 sup 2 Cf and were annealed up to 750 deg. C. It was found that track retention depended on the crystallographic structure: the annealing temperature, where the number of etched tracks was sharply reduced, was 550 deg. C for the x- and y-cut plates and 750 deg. C for z-cut plates. Track sizes decrease and disperse with reductions in the track retention.
Prompt particle emission in correlation with fission fragments
Directory of Open Access Journals (Sweden)
Litaize Olivier
2017-01-01
Full Text Available The de-excitation process of primary fission fragments can be simulated with the FIFRELIN Monte Carlo code leading to an estimation of prompt fission observables such as neutron/gamma multiplicities and spectra in correlation with fission fragments. De-excitation cascades are simulated using the notion of nuclear realization following Becvar terminology generalized to neutron/gamma coupled emission. A nuclear realization is a random set of nuclear levels (energy, spin, parity in association with partial widths for neutron, gamma or electron emission. Experimental data related to electromagnetic transitions in the discrete level region are taken from RIPL-3 database. When nuclear level structure is completely unknown (in the continuum region, level density and strength function models are used. In between these regions, our partial knowledge of nuclear structure is completed by models up to a fixed maximum level density. In this way the whole available experimental information is accounted for. FIFRELIN is ruled by five free input parameters driving the excitation energy sharing, the rotational energy and the spin distribution of primary fission fragments. These five free parameters are determined to match a target observable such as the average total prompt neutron multiplicity (ν. Once this procedure is completed, the whole set of fission observables can be compared with experimental results. Obviously the number of observables obtained within this code is higher than what is available from measurements. This code can therefore provide useful insights into the compatibility between models and a whole set of fission observables. In the present work the influence of shell corrections is reported on level densities and prompt fission neutron spectra (PFNS. The impact of the input data such as primary fission fragment total kinetic energy (TKE is also addressed. Average prompt neutron multiplicity as a function of TKE is also estimated for each
Fission-fragment properties in 238U(n ,f ) between 1 and 30 MeV
Duke, D. L.; Tovesson, F.; Laptev, A. B.; Mosby, S.; Hambsch, F.-J.; Bryś, T.; Vidali, M.
2016-11-01
The fragment mass and kinetic energy in neutron-induced fission of 238U has been measured for incident energies from 1 to 30 MeV at the Los Alamos Neutron Science Center. The change in mass distributions over this energy range were studied, and the transition from highly asymmetric to more symmetric mass distributions is observed. A decrease in average total kinetic energy (TKE ¯) with increasing excitation energy is observed, consistent with previous experimental work. Additional structure at multichance fission thresholds is present in the TKE ¯ data. The correlations between fragment masses and total kinetic energy and how that changes with excitation energy of the fissioning compound nucleus were also measured. The fission mass yields and average total kinetic energy are important for fission-based technologies such as nuclear reactors to understand nuclear waste generation and energy output when developing new and advanced concepts. The correlations between fragment mass and kinetic energy are needed both as input for theoretical calculations of the deexcitation process in fission fragments by prompt radiation emission and for validating advanced theoretical fission models describing the formation of the primordial fragments.
Nuclear structure via isomer tagging of fission fragments
Wu, C. Y.; Cline, D.; Simon, M. W.; Stoyer, M. A.
1997-10-01
The high efficiency for detecting high-fold γ rays by large Ge arrays makes it possible to study the detailed spectroscopy of many neutron-rich nuclei produced by fission. Major progress has been made using sealed spontaneous fission sources. Considerable improvement in selectivity is provided, with an open source, both by gating on isomers and by detection of both fission fragments in coincidence with the deexcitation γ rays (see the preceding contribution). The reconstructed kinematics allows a measure of fragment mass and the Doppler shift correction of γ rays. In a recent experiment, fission fragments were detected using half of the CHICO array and an annular PPAC in coincidence with deexcitation γ rays detected by the Rochester array of eight Compton-suppressed Ge detectors. The annular PPAC was located only 1.0" from a 3.7 μCi ^252Cf source for efficient isomer tagging. The correlation was studied between delayed, within a time window between 150 ns and 10 μs after a fission occurring, and prompt γ rays. Several prominent feeding patterns to isomers in the mass region around 100 and 130 are identified by such correlation study. Experimental details and results will be presented.
Neutron emission and fragment yield in high-energy fission
International Nuclear Information System (INIS)
Grudzevich, O. T.; Klinov, D. A.
2013-01-01
The KRIS special library of spectra and emission probabilities in the decays of 1500 nuclei excited up to energies between 150 and 250 MeV was developed for correctly taking into account the decay of highly excited nuclei appearing as fission fragments. The emission of neutrons, protons, and photons was taken into account. Neutron emission fromprimary fragments was found to have a substantial effect on the formation of yields of postneutron nuclei. The library was tested by comparing the calculated and measured yields of products originating from the fission of nuclei that was induced by high-energy protons. The method for calculating these yields was tested on the basis of experimental data on the thermal-neutroninduced fission of 235 U nuclei
Effectiveness in detecting fission fragments with ionization chambers
International Nuclear Information System (INIS)
Manrique Garcia, J.; Monne, G.
1991-01-01
Detection of fission fragments is important in nuclear measurements. When a high detection accuracy is required it is necessary to take in account the detection losses due to the absorption of fragments in the fissionable material. The losses corrections might change the final results in 2-3%. The traditional expression used in the calculation of the detection efficiency does not consider neither the density variation of the fissionable substance with its width, because it depends on the target material. That's why actually in many labs it is being searched new methods that allow to find the efficiency for each target. In this work a new method for determination of absorption efficiency is presented. The obtained results are analyzed
Spectroscopy of fission fragments using prompt-delayed ...
Indian Academy of Sciences (India)
2015-08-02
Aug 2, 2015 ... Home; Journals; Pramana – Journal of Physics; Volume 85; Issue 3. Spectroscopy of fission fragments using prompt-delayed coincidence technique ... Author Affiliations. R Palit1 S Biswas1. Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai 400 005, India ...
Efficiency of SSNTD Spark Counters with fission fragment angular distribution
International Nuclear Information System (INIS)
Lopes, R.T.; Rogers, J.D.
1982-01-01
Fission fragments from a 252 Cf source were detected in 10 μm thick Makrofol KG plastic. Measurements were done of observed track densities less than 100 tracks/cm 2 . The efficiency of the counter was determined as a function of the actual track density for each angle of incidence and correction factors analysed of the resulting counting losses. (author) [pt
Spectroscopy of fission fragments using prompt-delayed ...
Indian Academy of Sciences (India)
2015-08-02
Aug 2, 2015 ... The physics focus of INGA is to investigate the emergent properties of nuclear many- body system under varying rotational stress.These experimental ..... prompt spectrum are due to de-excitations from another fission fragment (a contaminant) having an isomer of similar half-life. To confirm the prompt γ-rays ...
The SOFIA experiment: Measurement of 236U fission fragment yields in inverse kinematics
Directory of Open Access Journals (Sweden)
Grente L.
2016-01-01
Full Text Available The SOFIA (Studies On FIssion with Aladin experiment aims at measuring fission-fragments isotopic yields with high accuracy using inverse kinematics at relativistic energies. This experimental technique allows to fully identify the fission fragments in nuclear charge and mass number, thus providing very accurate isotopic yields for low energy fission of a large variety of fissioning systems. This report focuses on the latest results obtained with this set-up concerning electromagnetic-induced fission of 236U.
Energy Technology Data Exchange (ETDEWEB)
Moeller, Peter [Los Alamos National Laboratory, Theoretical Division, Los Alamos, NM (United States); Schmitt, Christelle [CEA/DSM-CNRS/IN2P3, Grand Accelerateur National d' Ions Lourds, Caen (France)
2017-01-15
We use the Brownian shape-motion model, with its recent extensions, which allow modeling of odd-even staggering, to calculate the evolution of fission-fragment charge distributions with neutron number for the compound-system sequence {sup 234}U, {sup 236}U, {sup 238}U, and {sup 240}U. We compare to experimental data where available, for neutron- and electromagnetic-induced fission over a compound-nucleus excitation energy range from about 6 to 20 MeV. A notable result of the study is that the evolution of the location of the peak charge yield from Z = 54 in {sup 234}U towards Z = 52 in heavier isotopes, seen in the experimental data, is present also in the calculated yields. We further show that to describe yields at higher compound-nucleus excitation energies, then, already at 20 MeV, it is necessary to take multi-chance fission into account. (orig.)
Upgrading DRACULA setup to be used for light products - fission fragments coincidence measurements
International Nuclear Information System (INIS)
Simion, V.; Petrovici, M.; Pop, A.; Berceanu, I.; Duma, M.; Moisa, D.; Pagano, A.; Geraci, E.
1999-01-01
At low bombarding energy (E/A 238 U give rise to a number of fission processes, all leading to very similar fission products. Therefore, in order to understand the fission processes in this energy domain it is of interest to determine the amount of fission occurring after a peripheral interaction relative to that originating from compound nucleus formation. Although the detection of a projectile residue (PLF) in coincidence with the fission fragments is a very promising probe for the macroscopic features of the mechanism of induced fission, at incident energies in the vicinity of the Coulomb barrier (E/A 2 cross section area uses the phoswich technique by coupling a thin fast NE102A plastic scintillator to a 10 cm long BaF 2 crystal of hexagonal section. The BaF 2 crystal detectors have been successfully used in modular multielement detector ARGOS in the context of GANCT and HOTCT researches at LNS. The light response of the phoswich configuration as a function of the plastic thickness and of the energy and charge of the incident ion has been studied at Tandem energies. Both arrays will be placed in separate vacuum chambers attached to the remaining large angular opening windows of the reaction chamber. By rotating the whole device the fission fragment detection arrays will cover a range of 96 angle in the horizontal plane. The main advantage of this setup is that it allows to perform continuous measurements in energy and angle of the reaction products. The geometry of the whole device has been tested by Monte Carlo calculations using the code ELPHIC. The coincidence condition is completely fulfilled for the first two positions of the setup and partially for the third one. Measurements are intended to be performed at the SMP Tandem from LNS-Catania using light beams ( 16 O, 19 F, 20 Ne, 32 S) at ∼ 6 MeV/A on high fissility parameter targets. (authors)
Pomorski, K.; Nerlo-Pomorska, B.; Bartel, J.; Schmitt, C.
2018-03-01
The fission-fragment mass and total kinetic energy (TKE) distributions are evaluated in a quantum mechanical framework using elongation, mass asymmetry, neck degree of freedom as the relevant collective parameters in the Fourier shape parametrization recently developed by us. The potential energy surfaces (PES) are calculated within the macroscopic-microscopic model based on the Lublin-Strasbourg Drop (LSD), the Yukawa-folded (YF) single-particle potential and a monopole pairing force. The PES are presented and analysed in detail for even-even Plutonium isotopes with A = 236-246. They reveal deep asymmetric valleys. The fission-fragment mass and TKE distributions are obtained from the ground state of a collective Hamiltonian computed within the Born-Oppenheimer approximation, in the WKB approach by introducing a neck-dependent fission probability. The calculated mass and total kinetic energy distributions are found in good agreement with the data.
Naderi, D.; Pahlavani, M. R.; Alavi, S. A.
2013-05-01
Using the Langevin dynamical approach, the neutron multiplicity and the anisotropy of angular distribution of fission fragments in heavy ion fusion-fission reactions were calculated. We applied one- and two-dimensional Langevin equations to study the decay of a hot excited compound nucleus. The influence of the level-density parameter on neutron multiplicity and anisotropy of angular distribution of fission fragments was investigated. We used the level-density parameter based on the liquid drop model with two different values of the Bartel approach and Pomorska approach. Our calculations show that the anisotropy and neutron multiplicity are affected by level-density parameter and neck thickness. The calculations were performed on the 16O+208Pb and 20Ne+209Bi reactions. Obtained results in the case of the two-dimensional Langevin with a level-density parameter based on Bartel and co-workers approach are in better agreement with experimental data.
Energy Technology Data Exchange (ETDEWEB)
Duke, Dana Lynn [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-11-12
This Ph.D. dissertation describes a measurement of the change in mass distributions and average total kinetic energy (TKE) release with increasing incident neutron energy for fission of ^{235}U and ^{238}U. Although fission was discovered over seventy-five years ago, open questions remain about the physics of the fission process. The energy of the incident neutron, En, changes the division of energy release in the resulting fission fragments, however, the details of energy partitioning remain ambiguous because the nucleus is a many-body quantum system. Creating a full theoretical model is difficult and experimental data to validate existing models are lacking. Additional fission measurements will lead to higher-quality models of the fission process, therefore improving applications such as the development of next-generation nuclear reactors and defense. This work also paves the way for precision experiments such as the Time Projection Chamber (TPC) for fission cross section measurements and the Spectrometer for Ion Determination in Fission (SPIDER) for precision mass yields.
Spatial- and Time-Correlated Detection of Fission Fragments
Directory of Open Access Journals (Sweden)
Platkevic M.
2012-02-01
Full Text Available With the goal to measure angular correlations of fission fragments in rare fission decay (e.g. ternary and quaternary fission, a multi-detector coincidence system based on two and up to four position sensitive pixel detectors Timepix has been built. In addition to the high granularity, wide dynamic range and per pixel signal threshold, these devices are equipped with per pixel energy and time sensitivity providing more information (position, energy, time, enhances particle-type identification and selectivity of event-by-event detection. Operation of the device with the integrated USB 2.0 based readout interface FITPix and the control and data acquisition software tool Pixelman enables online visualization and flexible/adjustable operation for a different type of experiments. Spatially correlated fission fragments can be thus registered in coincidence. Similarly triggered measurements are performed using an integrated spectrometric module with analogue signal chain electronics. The current status of development together with demonstration of the technique with a 252Cf source is presented.
Energy Technology Data Exchange (ETDEWEB)
Vandenbosch, R.; Bierman, J.D.; Lestone, J.P.; Liang, J.F.; Prindle, D.J.; Sonzogni, A.A. [University of Washington, Nuclear Physics Laboratory, Seattle, Washington 98195 (United States); Kailas, S.; Nadkarni, D.M.; Kapoor, S.S. [Nuclear Physics Division, Bhabha Atomic Research Centre, Bombay-400085 (India)
1996-09-01
Fission fragment anisotropies have been measured to energies extending well above the barrier for three entrance channels leading to the same compound nucleus {sup 248}Cf. For the {sup 12}C + {sup 236}U and {sup 16}O + {sup 232}Th systems, lying on either side of the Businaro-Gallone critical asymmetry, the mean square angular momentum is matched at an excitation energy of 62 MeV. The anisotropies, although different at lower energies, are in agreement within experimental errors at this excitation energy and thus show no entrance channel dependence. {copyright} {ital 1996 The American Physical Society.}
Fission of heavy nuclei: microscopic study of fission barriers and fragments angular momentum
International Nuclear Information System (INIS)
Bonneau, L.
2003-11-01
A lot of experimental data on nuclear fission has been being collected for the last 65 years, allowing theoreticians to confront their models with reality. The first part of this work is dedicated to the computation of fission barriers. We have extended the HF + BCS (Hartree Fock + Bandeen-Cooper-Schrieffer) method in order to include a new set of polynomials on which wave functions can be broken to, more accurately than on Hermite's polynomials in the 2 fragment configuration. The fission barriers of 26 heavy nuclei from Thorium-230 to Nobelium-256 have been assessed and compared to experimental data, it appears that differences are no greater than 1 MeV. We have discovered a neat correlation between the variation of the experimental fission lifetimes of even Fermium isotopes and the computed heights of second barriers. Moreover our model reproduces the hyper-deformed well of Thorium-230 with a good agreement on the well depth. The second part deals with the scission region. We have performed Hartree-Fock calculations in order to explore different ways of fragmentation. We have shown that the harmonic oscillator gives a valid description of such ways. In order to compute the mean value of J 2 in the fragments we have been driven to propose an adequate definition of that quantity consistent with the non-locality property of the J 2 operator. (A.C.)
Hirose, K.; Nishio, K.; Tanaka, S.; Léguillon, R.; Makii, H.; Nishinaka, I.; Orlandi, R.; Tsukada, K.; Smallcombe, J.; Vermeulen, M. J.; Chiba, S.; Aritomo, Y.; Ohtsuki, T.; Nakano, K.; Araki, S.; Watanabe, Y.; Tatsuzawa, R.; Takaki, N.; Tamura, N.; Goto, S.; Tsekhanovich, I.; Andreyev, A. N.
2017-12-01
Fission-fragment mass distributions were measured for U 237 - 240 , Np 239 - 242 , and Pu 241 - 244 populated in the excitation-energy range from 10 to 60 MeV by multinucleon transfer channels in the reaction O 18 +U 238 at the Japan Atomic Energy Agency tandem facility. Among them, the data for U 240 and Np 240 ,241 ,242 were observed for the first time. It was found that the mass distributions for all the studied nuclides maintain a double-humped shape up to the highest measured energy in contrast to expectations of predominantly symmetric fission due to the washing out of nuclear shell effects. From a comparison with the dynamical calculation based on the fluctuation-dissipation model, this behavior of the mass distributions was unambiguously attributed to the effect of multichance fission.
El-Hajje, Refaat
2000-10-01
Simultaneous measurements of the angular distribution, mass distribution and average total kinetic energy of fission fragments produced by the neutron-induced fission of 235U and 232Th have been made using a gridded ionisation chamber. The neutron energy range used was thermal to 1.9 MeV for 235U and 1.4 to 1.7 MeV for 232Th. The following topics were investigated: the interdependence of the fission fragment angular and mass distribution; the anomalous behaviour of fragment anisotropy for 235U(n,f) at neutron energies En below 150 keV; the possible existence of a third symmetric mass peak for 232Th(n,f); the mass fine structure in 235 U(n,f) and 232Th(n,f); and the dependence of the fission fragment average total kinetic energy on the excitation energy of the fissioning nucleus. For this study, mono-energetic neutrons were produced by the L73i( p,n)74 Be and H31( p,n)31 He reactions. Four signals produced by the fission chamber were fed into a data acquisition system and processed by a specially modified comprehensive computer program. The results indicate that there is no interdependence between the angular and mass distributions of fragments for 235U(n,f) and for 232Th(n,f). The angular distribution of 235U fission fragments showed an anisotropy of less than one for En below 150 keV. For 232Th, the expected minimum in the anisotropy near En = 1.6 MeV was confirmed. No evidence for a third peak in the mass symmetry region of 232Th(n,f) was observed, within the yield sensitivity limitation of the chamber. Fine structure was observed in the mass yield distributions for 235U(n,f) and 232Th(n,f) at mass locations predicted by theory. The fission fragment average total kinetic energy for 235U(n,f) and 232Th(n,f) showed no significant dependence on the excitation energy of the fissioning nucleus. Possible reasons for some of these results are advanced.
Study for fusion-fission and quasifission in reactions using {sup 238}U target nucleus
Energy Technology Data Exchange (ETDEWEB)
Nishio, Katsuhisa, E-mail: nishio.katsuhisa@jaea.go.jp [Advanced Science Reserch Center, Japan Atomic Energy Agency, Tokai, Ibraki 319-1195 (Japan)
2011-02-01
Fragment mass distributions for fission after full momentum transfer (FMT) were measured for the {sup 30}Si,{sup 31}P,{sup 34,36}S,{sup 40}Ar + {sup 238}U reactions at bombarding energies around the Coulomb barrier. The experiment was carried out at the JAEA tandem accelerator facility. We observed strong variation of the mass distribution on beam energy and projectile nucleus. In the reaction of {sup 36}S +{sup 238}U we observed a transition from symmetry to asymmetry mass distributions when the beam energies were decreased from the above-barrier to sub-barrier values. The mass asymmetry was A{sub L} /A{sub H} = 74/200, which corresponds to the fission valley leading to the nuclei close to the doubly closed-shell nuclei {sup 78}Ni /{sup 208}Pb. The fission channel is populated by quasifission, which is the disintegration without forming the compound nucleus. The incident-energy dependence is strongly correlated with the prolate deformation of {sup 238}U and the orientation at the initial impact. The results indicate that the reaction starting at the polar collisions on {sup 238}U has larger quasifission probability. The mass distributions are nicely reproduced by a model calculation using Langevin equation. The {sup 40}Ar + {sup 238}U reaction also has the similar mass asymmetry (A{sub L}/A{sub H} {approx} 78/200) in quasifission. In the reactions of {sup 31}P + {sup 238}U and {sup 30}Si + {sup 238}U, mass asymmetries are A{sub L}/A{sub H} 81/188 and 90/178, respectively. The results suggest that the system produced by the reaction using lighter projectile approaches closer to the shape of the compound nucleus even when quasifission occurs. In the reactions of {sup 30}Si +{sup 238}U and {sup 34}S+ {sup 238}U, we also measured the evaporation residue (ER) cross sections to obtain information on the fusion probability. From the ER cross sections for the {sup 34}S+{sup 238}U reaction it was suggested that the symmetric fission is also dominated by quasifission.
Projectile fission of 238U relativistic ions in a Pb target and discovery of new fission fragments
International Nuclear Information System (INIS)
Bernas, M.; Donzaud, C.; Dessagne, Ph.; Miehe, Ch.; Hanelt, E.; Heinz, A.
1994-01-01
With the 238 U beam accelerated at relativistic energies by the heavy ion synchrotron (SIS) at GSI, fission was investigated using inverse kinematics. This geometry is well suited for analyzing fragments with the fragment separator. The fragments are identified by in flight measurements of their energy loss and time of flight signals. More than forty new isotopes have been discovered focusing on the light branch of fission products. (K.A.) 12 refs., 5 figs., 1 tab
Koglin, J. D.; Burke, J. T.; Fisher, S. E.; Jovanovic, I.
2017-05-01
The Direct Excitation Angular Tracking pHotovoltaic-Silicon Telescope ARray (DEATH-STAR) combines a series of 12 silicon detectors in a ΔE - E configuration for charged particle identification with a large-area array of 56 photovoltaic (solar) cells for detection of fission fragments. The combination of many scattering angles and fission fragment detectors allows for an angular-resolved tool to study reaction cross sections using the surrogate method, anisotropic fission distributions, and angular momentum transfers through stripping, transfer, inelastic scattering, and other direct nuclear reactions. The unique photovoltaic detectors efficiently detect fission fragments while being insensitive to light ions and have a timing resolution of 15.63±0.37 ns. Alpha particles are detected with a resolution of 35.5 keV 1σ at 7.9 MeV. Measured fission fragment angular distributions are also presented.
International Nuclear Information System (INIS)
Bogdzel, A.A.; Furman, W.I.
1996-01-01
The results of the experiment on measuring the energy dependence of fission fragment angular anisotropy in resonance neutron induced fission of 235 U aligned target in energy region up to 42 eV are presented. The agreement with the data of Pattenden and Postma in resonances is good enough, while the theoretical curve, calculated using the R-matrix multilevel two fission channel approach, does not seem to describe the energy dependence of fission fragment angular anisotropy property. The necessity of taking into account the interference between levels with different spins is discussed. 11 refs., 2 figs
Non-compound nucleus fission in actinide and pre-actinide regions
Indian Academy of Sciences (India)
Data on the evaporation residue cross-sections, in addition to those on mass and angular distributions, are necessary for better understanding of the contribution from non-compound nucleus fission in the pre-actinide region. Measurement of mass-resolved angular distribution of fission products in 20Ne+232Th reaction ...
Fission dynamics of the compound nucleus 213 Fr formed in heavy ...
Indian Academy of Sciences (India)
A stochastic approach based on one-dimensional Langevin equations was used to calculate the average pre-fission multiplicities of neutrons, light charged particles and the fission probabilities for the compound nucleus 213Fr and the results are compared with the experimental data. In these calculations, a modified wall ...
Nucleus fragmentation induced by a high-energy hadron
International Nuclear Information System (INIS)
Zielinski, P.
1982-10-01
The author presents a review about the spallation in hadron reactions. Especially he considers proton-proton correlations at low relative momentum, angular distributions of 30-100 MeV protons, emission of fast deuterons, the vanishing of the Coulomb barrier, fission-like processes, the rise of the heavy fragment yield with energy transfer, proton-deuteron breakup reactions, and the backward emission of fast protons. (HSI)
Yields of correlated fragment pairs and neutron multiplicity in spontaneous fission of {sup 242}Pu
Energy Technology Data Exchange (ETDEWEB)
Veselsky, M.; Kliman, J.; Morhaccaron, M. [Institute of Physics of Slovak Academy of Sciences, Dubravska 9, 84228 Bratislava (Slovakia); Ramayya, A.V.; Kormicki, J.; Daniel, A.V. [Physics Department, Vanderbilt University, Nashville (United States)] Rasmussen, J.O. [Lawrence Berkeley National Laboratory, Berkeley (United States)] Stoyer, M.A. [Lawrence Livermore National Laboratory, Livermore (United States); Daniel, A.V.; Popeko, G.S.; Oganessian, Yu. Ts. [Joint Institute for Nuclear Research, Dubna (Russia)] Greiner, W. [Institut fur Theoretische Physik, J. W. Goethe Universitaet, Frankfurt a. M. (Germany); Aryaeinejad, R. [Idaho National Engineering Laboratory, Idaho Falls (United States)
1998-10-01
Yields of correlated fragment pairs were obtained in spontaneous fission of {sup 242}Pu. Charge, mass and neutron multiplicity distributions of fragment pairs were determined and compared to available data. The yield of cold fission without neutron emission was determined to about 10{percent} for the set of observed correlated fragment pairs. {copyright} {ital 1998 American Institute of Physics.}
Statistical emission of complex fragments from highly excited compound nucleus
International Nuclear Information System (INIS)
Matsuse, T.
1991-01-01
A full statistical analysis has been given in terms of the Extended Hauser-Feshbach method. The charge and kinetic energy distributions of 35 Cl+ 12 C reaction at E lab = 180, 200 MeV and 23 Na+ 24 Mg reaction at E lab = 89 MeV which form the 47 V compound nucleus are investigated as a prototype of the light mass system. The measured kinetic energy distributions of the complex fragments are shown to be well reproduced by the Extended Hauser-Feshbach method, so the observed complex fragment production is understood as the statistical binary decay from the compound nucleus induced by heavy-ion reaction. Next, this method is applied to the study of the complex production from the 111 In compound nucleus which is formed by the 84 Kr+ 27 Al reaction at E lab = 890 MeV. (K.A.) 18 refs., 10 figs
Target conception for the Munich fission fragment accelerator
Maier, H J; Gross, M L; Grossmann, R; Kester, O; Thirolf, P
1999-01-01
For the new high-flux reactor FRM II, the fission fragment accelerator MAFF is under design. MAFF will supply intense mass-separated radioactive ion beams of very neutron-rich nuclei with energies around the Coulomb barrier. A central part of this accelerator is the ion source with the fission target, which is operated at a neutron flux of 1.5x10 sup 1 sup 4 cm sup - sup 2 s sup - sup 1. The target consists of typically 1 g of sup 2 sup 3 sup 5 U dispersed in a cylindrical graphite matrix, which is encapsulated in a Re container. To enable diffusion and extraction of the fission products, the target has to be maintained at a temperature of up to 2400 deg. C during operation. It has to stand this temperature for at least one reactor cycle of 1250 h. Comprehensive tests are required to study the long-term behaviour of the involved materials at these conditions prior to operation in the reactor. The present paper gives details of the target conception and the projected tests.
Furman, W. I.; Kopach, Yu. N.; Popov, A. B.; Gonin, N. N.; Kozlovsky, L. K.; Tambovtsev, D. I.; Kliman, J.; Postma, H.
1998-10-01
New results of the analysis of experimental data on angular anisotropy of fission fragments in the neutron induced fission of aligned 235U nuclei are reported. A new approach to the theoretical description of the fission process led to the modified formulate for the differential fission cross sections. An R-matrix formalism was applied for the data analysis using the modified code SAMMY and the original code on the basis of the FUMILI procedure. The obtained values of the angular anisotropy coefficients A2(E) were analyzed together with the total neutron, total fission and spin separated fission cross sections in dependence on neutron energy E. Three fission channels were taken into account for the spin J=3 (K=0,1,2) and two for the spin J=4 (K=1,2).
From ground state to fission fragments: A complex, multi-dimensional multi-path problem
Energy Technology Data Exchange (ETDEWEB)
Moeller, P. [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan); Nix, J.R. [Los Alamos National Lab., NM (United States); Swiatecki, W.J. [Lawrence Berkeley Lab., CA (United States)
1992-03-01
Experimental results on the fission properties of nuclei close to {sup 264}Fm show sudden and large changes with a change of only one or two neutrons or protons. The nucleus {sup 258}Fm, for instance, undergoes symmetric fission with a half-life of about 0.4 ms and a kinetic-energy distribution peaked at about 235 MeV whereas {sup 256}Fm undergoes asymmetric fission with a half-life of about 3 h and a kinetic-energy distribution peaked at about 200 MeV. Qualitatively, these sudden changes have been postulated to be due to the emergence of fragment shells in symmetric-fission products close to {sup 132}Sn. Here we present a quantitative calculation that shows where high-kinetic-energy symmetric fusion occurs and why it is associated with a sudden and large decrease in fission half-lives. We base our study on calculations of potential-energy surfaces in the macroscopic-microscopic model and a semi-empirical model for the nuclear inertia. We use the three-quadratic-surface parameterization to generate the shapes for which the potential-energy surfaces are calculated. The use of this parameterization and the use of the finite-range macroscopic model allows for the study of two touching spheres and similar shapes. Since these shapes are thought to correspond to the scission shapes for the high-kinetic-energy events it is of crucial importance that a continuous sequence of shapes leading from the nuclear ground state to these configurations can be studied within the framework of the model. We present the results of the calculations in terms of potential-energy surfaces and fission half-lives for heavy even nuclei. The surfaces are displayed in the form of contour diagrams as functions of two moments of the shape. They clearly show the appearance of a second fission valley, which leads to scission configurations close to tow touching spheres, for fissioning systems in the vicinity of {sup 264}Fm.
Saxena, A.; Kailas, S.; Karnik, A.; Kapoor, S. S.
1993-01-01
Earlier calculations of fission fragment anisotropies made with the use of the standard saddle point statistical model have been corrected to include the effects of prefission neutron emission. These calculations are compared with the data reported earlier for the fissioning systems formed by projectile-target combinations of 10B, 12C, 16O, and 19F on 232Th and 237Np and 9Be on 232Th. It is seen that for these systems the conclusions reached earlier regarding the entrance channel dependence of the fission fragment anisotropy as a function of mass (charge) asymmetry are not affected by the inclusion of corrections due to prefission neutron emission.
Fragment angular momenta and descent dynamics in sup 2 sup 5 sup 2 Cf spontaneous fission
Popeko, J S; Ter-Akopian, G M
2002-01-01
Average angular momentum values of primary fission fragments as a function of neutron multiplicity and neutron-to-proton ratio were extracted for the first time for the Mo-Ba and Zr-Ce charge splittings of sup 2 sup 5 sup 2 Cf. The results are discussed in terms of the energy balance occurring at the scission point. For the first time we show that for large fragment elongation associated with larger numbers of evaporated neutrons (v sub t sub o sub t >=6), essentially only zero point bending oscillation takes places, i.e. T = 0 for this degree of freedom. For the major part of the fission events, with v sub t sub o sub t = 2-5, the banding oscillation is excited to a temperature of 2-3 MeV. Such a high bending temperature implies that the coupling between the collective and internal degrees of freedom is weak at the descent of the even-even nucleus of sup 2 sup 5 sup 2 Cf to the scission point. The dipole oscillations occurring at the descent take away some 2.5 - 3.0 MeV from the release energy. A correlation...
Metastable decay of photoionized niobium clusters: Evaporation vs fission fragmentation
International Nuclear Information System (INIS)
Cole, S.K.; Liu, K.; Riley, S.J.
1986-01-01
The metastable decay of photoionized niobium clusters (Nb/sub n/ + ) has been observed in a newly constructed cluster beam machine. The decay manifests itself in the time-of-flight (TOF) mass spectrum as an asymmetric broadening of daughter ion peaks. Pulsed ion extraction has been used to measure the decay rate constants and to establish the mechanism of the fragmentation, evaporation and/or fission of the photoionized clusters. It is found that within the experimental time window evaporation dominates for the smaller clusters (n 6 sec -1 . The average kinetic energy release is also determined and is found to be on the order of 5 MeV. 8 refs., 3 figs., 1 tab
Isotopic resolution of fission fragments from 238U + 12C transfer and fusion reactions
International Nuclear Information System (INIS)
Caamano, M.; Rejmund, F.; Derkx, X.; Schmidt, K. H.; Andouin, L.; Bacri, C. O.; Barreau, G.; Benlliure, J.; Casarejos, E.; Fernandez-Dominguez, B.; Gaudefroy, L.; Golabek, C.; Jurado, B.; Lemasson, A.; Navin, A.; Rejmund, M.; Roger, T.; Shrivastava, A.; Schmitt, C.; Taieb, J.
2010-01-01
Recent results from an experiment at GANIL, performed to investigate the main properties of fission-fragment yields and energy distributions in different fissioning nuclei as a function of the excitation energy, in a neutron-rich region of actinides, are presented. Transfer reactions in inverse kinematics between a 238 U beam and a 12 C target produced different actinides, within a range of excitation energy below 30 MeV. These fissioning nuclei are identified by detecting the target-like recoil, and their kinetic and excitation energy are determined from the reconstruction of the transfer reaction. The large-acceptance spectrometer VAMOS was used to identify the mass, atomic number and charge state of the fission fragments in flight. As a result, the characteristics of the fission-fragment isotopic distributions of a variety of neutron-rich actinides are observed for the first time over the complete range of fission fragments. (authors)
Dependence of Fission-Fragment Properties On Excitation Energy For Neutron-Rich Actinides
Directory of Open Access Journals (Sweden)
Ramos D.
2016-01-01
Isotopic fission yields of 250Cf, 244Cm, 240Pu, 239Np and 238U are presented in this work. With this information, the average number of neutrons as a function of the atomic number of the fragments is calculated, which reflects the impact of nuclear structure around Z=50, N=80 on the production of fission fragments. The characteristics of the Super Long, Standard I, Standard II, and Standard III fission channels were extracted from fits of the fragment yields for different ranges of excitation energy. The position and contribution of the fission channels as function of excitation energy are presented.
Orientations of fragments emitted in binary cold fission of sup 2 sup 5 sup 2 Cf
Misicu, S
2002-01-01
The dependence of the driving potential on the orientation of fragments at scission is investigated for the case of cold fission of sup 2 sup 5 sup 2 Cf. It is shown that in the case of cold fission the fragments exclusively emerge at scission in the pole-pole configuration. However, quantum fluctuations enable small deviations from this configuration during the tunnelling process. The mass yields of fission fragment pairs in the cold fission of sup 2 sup 5 sup 2 Cf are computed for pole-pole and equator-equator orientations and are compared to the experimental data.
A multiple parallel-plate avalanche counter for fission-fragment detection
Energy Technology Data Exchange (ETDEWEB)
Wu, C.Y., E-mail: wu24@llnl.gov [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); Henderson, R.A. [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); Haight, R.C.; Lee, H.Y.; Taddeucci, T.N. [Los Alamos National Laboratory, Los Alamos, MN 87545 (United States); Bucher, B.; Chyzh, A. [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); Devlin, M.; Fotiades, N. [Los Alamos National Laboratory, Los Alamos, MN 87545 (United States); Kwan, E. [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); National Superconducting Cyclotron Laboratory, East Lansing, MI 48824 (United States); O’Donnell, J.M.; Perdue, B.A.; Ullmann, J.L. [Los Alamos National Laboratory, Los Alamos, MN 87545 (United States)
2015-09-11
A new low-mass multiple gas-filled parallel-plate avalanche counter for the fission-fragment detection has been developed to mark the fission occurrence in measurements of the prompt fission neutron energy spectrum as a function of incident neutron energy. It was used successfully for the neutron-induced fission of {sup 235}U and {sup 239}Pu with a total mass near 100 mg each and the spontaneous fission of {sup 252}Cf. Both the incident neutron energy and the prompt fission neutron energy are measured by using the time-of-flight method. The design and performance of this avalanche counter are described.
International Nuclear Information System (INIS)
Benetti, P.; Raselli, G.L.; Tigliole, A. Borio di; Cagnazzo, M.; Cesana, A.; Mongelli, S.; Terrani, M.
2002-01-01
The transfer facility of the LENA laboratory allows the direct neutron irradiation of fissionable material in the D channel of the TRIGA reactor. A test measurement carried out with a ionization chamber and a 239 Pu sample shows the possibility to use this tool for the study of the transport effects of the fission fragment emerging from thin layers of fissile materials. (author)
Eslamizadeh, H.
2016-10-01
Abstract. A stochastic approach based on four-dimensional Langevin equations was applied to calculate the anisotropy of fission fragment angular distributions, average prescission neutron multiplicity, and the fission probability in a wide range of fissile parameters for the compound nuclei 197Tl,225Pa,248Cf , and 264Rf produced in fusion reactions. Three collective shape coordinates plus the projection of total spin of the compound nucleus to the symmetry axis K were considered in the four-dimensional dynamical model. In the dynamical calculations, nuclear dissipation was generated through the chaos-weighted wall and window friction formula. Furthermore, in the dynamical calculations the dissipation coefficient of K ,γk was considered as a free parameter, and its magnitude inferred by fitting measured data on the anisotropy of fission fragment angular distributions for the compound nuclei 197Tl,225Pa,248Cf , and 264Rf. Comparison of the calculated results for the anisotropy of fission fragment angular distributions with the experimental data showed that the results of the calculations are in good agreement with the experimental data by using values of the dissipation coefficient of K equal to (0.185-0.205), (0.175-0.192), (0.077-0.090), and (0.075-0.085) (MeVzs ) -1 /2 for the compound nuclei 197Tl,225Pa,248Cf , and 264Rf, respectively. It was also shown that the influence of the dissipation coefficient of K on the results of the calculations of the prescission neutron multiplicity and fission probability is small.
International Nuclear Information System (INIS)
Karamyan, S.A.; Adam, J.; Belov, A.G.; Chaloun, P.; Norseev, Yu.V.; Stegajlov, V.I.
1997-01-01
Fission-fragment mass distribution has been measured by the cumulative yields of radionuclides detected in the 232 Th(γ,f)-reaction at the Bremsstrahlung endpoint energies of 12 and 24 MeV. The yield upper limits have been estimated for the light nuclei 24 Na, 28 Mg, 38 S etc. at the Th and Ta targets exposure to the 24 MeV Bremsstrahlung. The results are discussed in terms of the multimodal fission phenomena and cluster emission >from a deformed fissioning system or from a compound nucleus
Directory of Open Access Journals (Sweden)
Kaplan Abdullah
2015-01-01
Full Text Available Implementation of projects of new generation nuclear power plants requires the solving of material science and technological issues in developing of reactor materials. Melts of heavy metals (Pb, Bi and Pb-Bi due to their nuclear and thermophysical properties, are the candidate coolants for fast reactors and accelerator-driven systems (ADS. In this study, α, γ, p, n and 3He induced fission cross section calculations for 209Bi target nucleus at high-energy regions for (α,f, (γ,f, (p,f, (n,f and (3He,f reactions have been investigated using different fission reaction models. Mamdouh Table, Sierk, Rotating Liquid Drop and Fission Path models of theoretical fission barriers of TALYS 1.6 code have been used for the fission cross section calculations. The calculated results have been compared with the experimental data taken from the EXFOR database. TALYS 1.6 Sierk model calculations exhibit generally good agreement with the experimental measurements for all reactions used in this study.
Energy Technology Data Exchange (ETDEWEB)
Nishio, Katsuhisa; Yamamoto, Hideki; Kimura, Itsuro; Nakagome, Yoshihiro [Kyoto Univ. (Japan)
1997-03-01
Simultaneous measurement of fission fragments and prompt neutrons following the thermal neutron induced fission of U-235 has been performed in order to obtain the neutron multiplicity (v) and its emission energy ({eta}) against the specified mass (m{sup *}) and the total kinetic energy (TKE). The obtained value of -dv/dTKE(m{sup *}) showed a saw-tooth distribution. The average neutron energy <{eta}>(m{sup *}) had a distribution with a reflection symmetry around the half mass division. The measurement also gave the level density parameters of the specified fragment, a(m{sup *}), and this parameters showed a saw-tooth trend too. The analysis by a phenomenological description of this parameters including the shell and collective effects suggested the existence of a collective motion of the fission fragments. (author)
International Nuclear Information System (INIS)
Moharram, B.M.
2000-01-01
The induced fission reactions of 235 U (n, f), 238 U (n,f) and 232 Th (n, f) based on the activation of natural uranium and thorium in samples with 252 Cf, neutron source, have been evaluated. The obtained results are the average of three samples from each test material (SRM 2710 Montana soil and Zirconia). The prepared samples have been configured in the so-called c ompensated - beam geometry i n which both gamma spectrometry jointly with solid state nuclear track detector techniques, revealed the fission rate sensitivity of 4.64 x 10 7 fission per gram per second per neutron (F.h 1 . S 1 .n 1 ), for zirconia as obtained by gamma activity arising from 134 I fission product (as a good monitor which is produced only from fissions), and the related value for SRM 2710 soil is 5.22 x 10 8 (F.g 1 S 1 .n 1 ). while the obtained values of the mean fission fragment ranges in SRM 2710 and zirconia as estimated from the fission track densities (by CR-39) and fission rates (by gamma spectrometry) are 3.97 x 10 3 g. cm 2 respectively which reveal good agreement with experiments and calculations done hitherto
Gamma ray transitions in de-excitation of 252Cf spontaneous fission fragments
International Nuclear Information System (INIS)
Khan, N.A.; Rashid, K.; Ahmad, M.; Qureshi, I.E.; Alam, G.D.; Ali, A.; Bhatti, N.; Horsch, F.
1983-11-01
Gamma rays in the range from 60 keV to 730 keV have been observed following the spontaneous fission of 252 Cf, with high resolution Ge(Li) detector, full width at half maximum (FWHM) of 700 eV at 122 keV, in coincidence with the two fission fragments observed with surface barrier detectors. A total number of 18, 636, 549 events were recorded over a run period of about 150 hours stretching over three weeks. The events were sorted to generate gamma ray spectra belonging to 2 amu intervals gamma of the fragment masses and 6 MeV intervals of the total kinetic energy released. Some of the prominent gamma lines belonging to various masses of the fission fragments have been identified. For some gamma lines, the intensities have been evaluated as a function of the total kinetic energy of the fission fragments. (authors)
Study of fission fragments produced by 14N + 235U reaction
International Nuclear Information System (INIS)
Yalcinkaya, M.; Erduran, M.N.; Ganioglu, E.; Akkus, B.; Bostan, M.; Gurdal, G.; Erturk, S.; Balabanski, D.; Minkova, A.; Danchev, M.
2005-01-01
This work was performed to understand the structure of neutron rich fission fragments around ∼ 130 region. A thin metallic 235 U target was bombarded by 14 N beam with 10 MeV/A from the Separated Sector Cyclotron at the National Accelerator Centre, Cape Town, South Africa. The main goal to detect and identify fission fragments and to obtain their mass distribution was achieved by using Solar Cell detectors in the AFRODITE (African Omnipurpose Detector for Innovative Techniques and Experiments) spectrometer. The X-rays emitted from fission fragments were detected by LEP detectors and γ rays emitted from excited states of the fission fragments were detected by CLOVER detectors in the spectrometer. (author)
National Aeronautics and Space Administration — A new technology, the Fission Fragment Rocket Engine (FFRE), requires small amounts of readily available, energy dense, long lasting fuel, significant thrust at...
Al-Adili, A.; Tarrío, D.; Hambsch, F.-J.; Göök, A.; Jansson, K.; Solders, A.; Rakopoulos, V.; Gustafsson, C.; Lantz, M.; Mattera, A.; Oberstedt, S.; Prokofiev, A. V.; Vidali, M.; Österlund, M.; Pomp, S.
2016-06-01
This paper presents the ongoing analysis of two fission experiments. Both projects are part of the collaboration between the nuclear reactions group at Uppsala and the JRC-IRMM. The first experiment deals with the prompt fission neutron multiplicity in the thermal neutron induced fission of 235U(n,f). The second, on the fission fragment properties in the thermal fission of 234U(n,f). The prompt fission neutron multiplicity has been measured at the JRC-IRMM using two liquid scintillators in coincidence with an ionization chamber. The first experimental campaign focused on 235U(nth,f) whereas a second experimental campaign is foreseen later for the same reaction at 5.5 MeV. The goal is to investigate how the so-called sawtooth shape changes as a function of fragment mass and excitation energy. Some harsh experimental conditions were experienced due to the large radiation background. The solution to this will be discussed along with preliminary results. In addition, the analysis of thermal neutron induced fission of 234U(n,f) will be discussed. Currently analysis of data is ongoing, originally taken at the ILL reactor. The experiment is of particular interest since no measurement exist of the mass and energy distributions for this system at thermal energies. One main problem encountered during analysis was the huge background of 235U(nth,f). Despite the negligible isotopic traces in the sample, the cross section difference is enormous. Solution to this parasitic background will be highlighted.
International Nuclear Information System (INIS)
Enqvist, T.; Benlliure, J.; Farget, F.; Schmidt, K.H.; Armbruster, P.; Bernas, M.; Tassan-Got, L.; Boeckstiegel, C.; Jong, M. de; Dufour, J.P.
1999-03-01
Projectile fragmentation and fission, induced in collisions of 238 U at 1 A GeV with lead, have systematically been studied. A complete survey on the isotopic production cross sections of all elements between vanadium (Z = 23) and rhenium (Z = 75) down to a cross section of 0.1 mb is given. About 600 isotopes produced in fragmentation and about 600 isotopes produced in fission were identified in the GSI fragment separator FRS from magnetic rigidities, time-of-flight values, and the energy loss in an ionisation chamber. In addition, the velocity distributions of all these reaction products have been mapped, and the products are unambiguously attributed to the different reaction mechanisms due to their kinematical properties. The results are compared with empirical systematics and previous data. The velocity of the fragments obtained in the fission process by the Coulomb repulsion allows to reconstruct the TKE-value of the break-up and to identify the atomic number of the fissioning nucleus in hot fission. The mean velocities of light projectile fragments were found to be higher than the beam velocity. (orig.)
SOFIA: An innovative setup to measure complete isotopic yield of fission fragments
Directory of Open Access Journals (Sweden)
Pellereau E.
2013-12-01
Full Text Available We performed an experiment dedicated to the accurate isotopic yield measurement of fission fragments over the whole range. SOFIA exploits the inverse kinematics technique: using heavy ion beams at relativistic energies, fission is induced by Coulomb excitation in a high-Z target. The fragments are emitted forward and both of them are identified in charge and mass. The setup will be presented, as well as preliminary spectra.
On the use of Makrofol KG to study fission fragment angular distributions
Chekirine, M
1999-01-01
Makrofol KG nuclear track detector processing and analysis is carefully regulated and assessed to reveal fission fragments' tracks and their angular distributions. For this purpose, foils of this detector are irradiated by a thin sup 2 sup 5 sup 2 Cf source and are subjected to chemical etching followed by a two-step sparking process. The detector efficiency as a function of fission fragment incidence angle and different etching parameters is carried out with a good reproducibility.
The GEM code. A simulation program for the evaporation and the fission process of an excited nucleus
Energy Technology Data Exchange (ETDEWEB)
Furihata, Shiori [Mitsubishi Research Institute Inc., Tokyo (Japan); Niita, Koji [Research Organization for Information Science and Technology, Tokai, Ibaraki (Japan); Meigo, Shin-ichiro; Ikeda, Yujiro; Maekawa, Fujio [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
2001-03-01
The GEM code is a simulation program which describes the de-excitation process of an excited nucleus, which is based on the Generalized Evaporation Model and the Atchison fission model. It has been shown that the combination of the Bertini intranuclear cascade model and GEM accurately predicts the cross sections of light fragments, such as Be produced from the proton-induced reactions. It has also been shown that the use of the reevaluated parameters in the Atchison model improves predictions of cross sections of fission fragments produced from the proton-induced reaction on Au. In this report, we present details and the usage of the GEM code. Furthermore, the results of benchmark calculations are shown by using the combination of the Bertini intranuclear cascade model and the GEM code (INC/GEM). Neutron spectra and isotope production cross sections from the reactions on various targets irradiated by protons are calculated with INC/GEM. Those results are compared with experimental data as well as the calculation results with LAHET. INC/GEM reproduces the experiments of double differential neutron emissions from the reaction on Al and Pb. The isotopic distributions for He, Li, and Be produced from the reaction on Ag are in good agreement with experimental data within 50%, although INC/GEM underestimates those of heavier nuclei than O. It is also shown that the predictions with INC/GEM for isotope production of light fragments, such as Li and Be, are better than those calculation with LAHET, particularly for heavy target. INC/GEM also gives better estimates of the cross sections of fission products than LAHET. (author)
Indian Academy of Sciences (India)
the energy minimization of all possible ternary breakups of a heavy radioactive nucleus. Further, within the TCM we have analysed the competition between different geometries as well as different positioning of the fragments. Also, an attempt was made to calculate the mass distribution of ternary fission process within the ...
Energy Technology Data Exchange (ETDEWEB)
Bonneau, L
2003-11-01
A lot of experimental data on nuclear fission has been being collected for the last 65 years, allowing theoreticians to confront their models with reality. The first part of this work is dedicated to the computation of fission barriers. We have extended the HF + BCS (Hartree Fock + Bandeen-Cooper-Schrieffer) method in order to include a new set of polynomials on which wave functions can be broken to, more accurately than on Hermite's polynomials in the 2 fragment configuration. The fission barriers of 26 heavy nuclei from Thorium-230 to Nobelium-256 have been assessed and compared to experimental data, it appears that differences are no greater than 1 MeV. We have discovered a neat correlation between the variation of the experimental fission lifetimes of even Fermium isotopes and the computed heights of second barriers. Moreover our model reproduces the hyper-deformed well of Thorium-230 with a good agreement on the well depth. The second part deals with the scission region. We have performed Hartree-Fock calculations in order to explore different ways of fragmentation. We have shown that the harmonic oscillator gives a valid description of such ways. In order to compute the mean value of J{sup 2} in the fragments we have been driven to propose an adequate definition of that quantity consistent with the non-locality property of the J{sup 2} operator. (A.C.)
Fission-fragment detector for DANCE based on thin scintillating films
Rusev, G.; Roman, A. R.; Daum, J. K.; Springs, R. K.; Bond, E. M.; Jandel, M.; Baramsai, B.; Bredeweg, T. A.; Couture, A.; Favalli, A.; Ianakiev, K. D.; Iliev, M. L.; Mosby, S.; Ullmann, J. L.; Walker, C. L.
2015-12-01
A fission-fragment detector based on thin scintillating films has been built to serve as a trigger/veto detector in neutron-induced fission measurements at DANCE. The fissile material is surrounded by scintillating films providing 4 π detection of the fission fragments. The scintillation photons were registered with silicon photomultipliers. A measurement of the 235U (n , f) reaction with this detector at DANCE revealed a correct time-of-flight spectrum and provided an estimate for the efficiency of the prototype detector of 11.6(7)%. Design and test measurements with the detector are described.
Anomalies in the Charge Yields of Fission Fragments from the ^{238}U(n,f) Reaction.
Wilson, J N; Lebois, M; Qi, L; Amador-Celdran, P; Bleuel, D; Briz, J A; Carroll, R; Catford, W; De Witte, H; Doherty, D T; Eloirdi, R; Georgiev, G; Gottardo, A; Goasduff, A; Hadyńska-Klęk, K; Hauschild, K; Hess, H; Ingeberg, V; Konstantinopoulos, T; Ljungvall, J; Lopez-Martens, A; Lorusso, G; Lozeva, R; Lutter, R; Marini, P; Matea, I; Materna, T; Mathieu, L; Oberstedt, A; Oberstedt, S; Panebianco, S; Podolyák, Zs; Porta, A; Regan, P H; Reiter, P; Rezynkina, K; Rose, S J; Sahin, E; Seidlitz, M; Serot, O; Shearman, R; Siebeck, B; Siem, S; Smith, A G; Tveten, G M; Verney, D; Warr, N; Zeiser, F; Zielinska, M
2017-06-02
Fast-neutron-induced fission of ^{238}U at an energy just above the fission threshold is studied with a novel technique which involves the coupling of a high-efficiency γ-ray spectrometer (MINIBALL) to an inverse-kinematics neutron source (LICORNE) to extract charge yields of fission fragments via γ-γ coincidence spectroscopy. Experimental data and fission models are compared and found to be in reasonable agreement for many nuclei; however, significant discrepancies of up to 600% are observed, particularly for isotopes of Sn and Mo. This indicates that these models significantly overestimate the standard 1 fission mode and suggests that spherical shell effects in the nascent fission fragments are less important for low-energy fast-neutron-induced fission than for thermal neutron-induced fission. This has consequences for understanding and modeling the fission process, for experimental nuclear structure studies of the most neutron-rich nuclei, for future energy applications (e.g., Generation IV reactors which use fast-neutron spectra), and for the reactor antineutrino anomaly.
Goodness of isospin in neutron rich systems from the fission fragment distribution
Garg, Swati; Jain, Ashok Kumar
2017-09-01
We present the results of our calculations for the relative yields of neutron-rich fission fragments emitted in 208Pb (18O, fission) reaction by using the concept of the conservation of isospin and compare with the experimental data. We take into account a range of isospin values allowed by the isospin algebra and assume that the fission fragments are formed in isobaric analog states. We also take into account the neutron multiplicity data for various neutron-emission channels in each partition, and use them to obtain the weight factors in calculating the yields. We then calculate the relative yields of the fission fragments. Our calculated results are able to reproduce the experimental trends reasonably well. This is the first direct evidence of the isospin conservation in neutron-rich systems and may prove a very useful tool in their studies.
James, G. D.; Syme, D. B.; Grainger, J.
1983-01-01
The determination of fission fragment angular distribution for 230Th and 228Th by monokinetic neutrons from a Van de Graaff generator has been carried out using a Makrofol fission fragment detector in a geometry different from any used previously. This change in geometry was deliberately introduced with the aim of resolving certain discrepancies in existing data. It also enables measurements to be made with safety on radiologically hazardous fissionable targets. The Makrofol Processing and analysis was carefully assessed and rigidly controlled. The detector efficiency as a function of reaction angle was calculated and the results confirmed experimentally. Finally, the neutron energy and fragment angle resolution functions, and their correlation, were investigated and adequately represented for the computer broadening of differential neutron-induced fission cross-section data.
Kailas, S.; Singh, P.
1994-12-01
The data of fission fragment anisotropies measured for the system16O +209Bi in the centre of mass energy region of 73 to 95 MeV have been compared with the saddle point statistical model calculations. The corrections to the nuclear temperature and the spin distribution arising due to pre-fission neutron emission have been made. While the resultant calculations reproduce very well the data in the near- and sub-barrier energy regions, they deviate from the data at higher energies. This observation is similar to what was already reported for16O +208Pb system.
Vorobyev, A. S.; Gagarski, A. M.; Shcherbakov, O. A.; Vaishnene, L. A.; Barabanov, A. L.
2015-08-01
Angular distributions of fission fragments from the neutron-induced fission of 232Th, 235U, and 238U have been measured in the energy range 1-200 MeV at the neutron time-of-flight (TOF) spectrometer GNEIS using position sensitive multiwire proportional counters as fission fragment detector. A short description of the experimental equipment and measurement procedure is given. The anisotropy of fission fragments deduced from the data on measured angular distributions is presented in comparison with experimental data of other authors.
Studies of fission fragment properties at the Los Alamos Neutron Science Center (LANSCE)
Tovesson, Fredrik; Mayorov, Dmitriy; Duke, Dana; Manning, Brett; Geppert-Kleinrath, Verena
2017-09-01
Nuclear data related to the fission process are needed for a wide variety of research areas, including fundamental science, nuclear energy and non-proliferation. While some of the relevant data have been measured to the required accuracies there are still many aspects of fission that need further investigation. One such aspect is how Total Kinetic Energy (TKE), fragment yields, angular distributions and other fission observables depend on excitation energy of the fissioning system. Another question is the correlation between mass, charge and energy of fission fragments. At the Los Alamos Neutron Science Center (LANSCE) we are studying neutron-induced fission at incident energies from thermal up to hundreds of MeV using the Lujan Center and Weapons Neutron Research (WNR) facilities. Advanced instruments such as SPIDER (time-of-flight and kinetic energy spectrometer), the NIFFTE Time Projection Chamber (TPC), and Frisch grid Ionization Chambers (FGIC) are used to investigate the properties of fission fragments, and some important results for the major actinides have been obtained.
Studies of fission fragment properties at the Los Alamos Neutron Science Center (LANSCE
Directory of Open Access Journals (Sweden)
Tovesson Fredrik
2017-01-01
Full Text Available Nuclear data related to the fission process are needed for a wide variety of research areas, including fundamental science, nuclear energy and non-proliferation. While some of the relevant data have been measured to the required accuracies there are still many aspects of fission that need further investigation. One such aspect is how Total Kinetic Energy (TKE, fragment yields, angular distributions and other fission observables depend on excitation energy of the fissioning system. Another question is the correlation between mass, charge and energy of fission fragments. At the Los Alamos Neutron Science Center (LANSCE we are studying neutron-induced fission at incident energies from thermal up to hundreds of MeV using the Lujan Center and Weapons Neutron Research (WNR facilities. Advanced instruments such as SPIDER (time-of-flight and kinetic energy spectrometer, the NIFFTE Time Projection Chamber (TPC, and Frisch grid Ionization Chambers (FGIC are used to investigate the properties of fission fragments, and some important results for the major actinides have been obtained.
Study of fission fragment mass distributions for the reaction 18O + 197Au
International Nuclear Information System (INIS)
Appannababu, S.; Jhingan, A.; Sugathan, P.; Negi, D.; Golda, K.S.; Gehlot, J.; Nayak, B.K.; Thomas, R.G.; Choudhury, R.K.; Prasad, E.; Rath, P.K.; Mukherjee, S.
2011-01-01
The study of fusion fission dynamics in medium mass nuclei is of great interest due to the observation of many interesting and exciting results. Recent experimental results on 19 F + 197 Au shows that mass equilibration is slower than the K degrees of equilibration. These results are some what contradictory to the results observed in heavier and highly fissile systems. In order to understand the relaxation mechanism of various degrees of freedom in less fissile systems one has to study both fission fragment angular and mass distributions. The complete K equilibration for the reaction 18 O + 197 Au through fission fragment angular distribution studies have been reported previously. The entrance channel mass asymmetry of the reaction 18 O + 197 Au is very much similar to that of the reaction 19 F + 197 Au, where fission fragment angular distributions show no evidence of pre-equilibrium fission. In order to investigate complete mass equilibration is taking place or not in this reaction, fission fragment mass distributions for the reaction 18 O + 197 Au around the coulomb barrier have been studied
Energy Technology Data Exchange (ETDEWEB)
Shetty, D.V.; Choudhury, R.K.; Nayak, B.K.; Nadkarni, D.M.; Kapoor, S.S. [Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)
1997-08-01
Measurements of fission fragment gamma ray multiplicity distributions were carried out at near and sub-barrier energies in {sup 12}C, {sup 16}O + {sup 232}Th reactions. The results were analyzed to determine the average values of the total fragment spin, which were used to deduce the average spin of the compound nucleus {l_angle}l{r_angle}{sub CN}. It is observed that {l_angle}l{r_angle}{sub CN} decreases smoothly with decreasing bombarding energy and saturates as the energy falls through the barrier, thereby resembling features analogous to those predicted by various fusion models. The present results do not indicate any anomalous feature in the {l_angle}l{r_angle}{sub CN} at the sub-barrier energies, which imply that the recently observed anomalous fragment anisotropies in these systems are not due to anomalous broadening of fusion l distributions but may result from the narrowing of K distribution in the fission process. {copyright} {ital 1997} {ital The American Physical Society}
Fission fragment mass and angular distributions: Probes to study ...
Indian Academy of Sciences (India)
C 71, 014602 (2005). [18] A J Sierk, Phys. Rev. C 33, 2039 (1986). [19] R Rafiei, R G Thomas, D J Hinde, M Dasgupta, C R Morton, L R Gasques, M L Brown and. M D Rodriguez, Phys. Rev. C 77, 024606 (2008). [20] R Vandenbosch and J R Huizenga, Nuclear fission (Acadamic, New York, 1973). [21] B B Back et al, Phys.
MAFF – The Munich accelerator for fission fragments
Indian Academy of Sciences (India)
CERN, Genf, Switzerland. Abstract. At the new high flux reactor FRM-II in Munich the accelerator MAFF (Munich accel- erator for fission ..... 16th Int. Conf. on the Application of Accelerators in Research and Industry,. CAARI 2000, Denton, Texas. [12] M Cavenago, Rev. Sci. Instrum. 71, 663 (2000). [13] H-J Maier et al, Nucl.
Fission fragment mass and angular distributions: Probes to study ...
Indian Academy of Sciences (India)
cesses (often commonly called quasifission in the literature) differ subtly in terms of the observables which are measured in a reaction, and disentangling the contributions of each of these processes is very challenging. While FF is observed when the fission barrier becomes vanishingly small at very high angular momenta, ...
Fission Fragment Angular Distributions measured with a Time Projection Chamber
International Nuclear Information System (INIS)
Kleinrath, Verena
2015-01-01
The subject is presented in a series of slides with the following organization: Introduction (What is anisotropy? Relevance (Theory and ratio cross section), Previous measurements); Experiment (Particle tracking in the fissionTPC, Neutron time of flight, Data analysis & uncertainty calculation, Preliminary result for 235 U); and Future Work (Refine 235 U result, Process 239 Pu data).
Fission fragment mass distribution in the 13C+182W and 176Yb reactions
International Nuclear Information System (INIS)
Ramachandran, K.; Hinde, D.J.; Dasgupta, M.; Williams, E.; Wakhle, A.; Luong, D.H.; Evers, M.; Carter, I.P.; Das, S.
2014-01-01
Fission fragment mass distributions have been measured for many systems and found to be asymmetric in the fission of nuclei with nucleon number A in the range 228-258 and proton number Z in the range 90-100. For lighter systems, it has been observed that fission fragment mass distributions are usually symmetric. At high excitation energies the shell effects are expected to vanish and the nuclei are expected to behave like a charged liquid drop; hence, only symmetric fission is expected for all the nuclei. Even after much experimental and theoretical work in this field, the rate of damping of shell effects with excitation energy is not well known. This abstract reports our measurements with 13 C beams on 182 W and 176 Yb targets
Directory of Open Access Journals (Sweden)
Oberstedt S.
2013-03-01
Full Text Available The correlation between the sub-barrier resonant behaviour of fission crosssection of non-fissile actinides (pre-scission stage and the visible fluctuations of their fission fragment and prompt neutron data (post-scission stage around the incident energies of sub-barrier resonances is outlined and supported by quantitative results for two fissioning systems 234,238U(n,f. These quantitative results refer to both stages of the fission process: a The pre-scission stage including the calculation of neutron induced cross-sections with focus on fission. Calculations are done in the frame of the refined statistical model for fission with sub-barrier effects also extended to take into account the multi-modal fission. b The post-scission stage including the prompt neutron emission treated in the frame of the Point-by-Point model. Total quantities characterizing the fission fragments and the prompt neutrons obtained by averaging the Point-by-Point results as a function of fragment over the fission fragment distributions reveal variations around the energies of sub-barrier resonances in the fission crosssection.
Fission and nuclear fragmentation of silver and bromine nuclei by photons of 1-6 GeV
International Nuclear Information System (INIS)
Pinheiro Filho, J.D.
1983-01-01
The studies of fission and fragmentation of silver and bromine nuclei by Bremsstrahlung photons of 1.6 GeV energy range are presented. The Il ford-KO nuclear emulsion submitted to Bremsstrahlung beams in Deutsches Elektronen Synchrotron (DESY) with total doses of 10'' equivalent photons, was used for nuclear fragment detection. The discrimination of fission and fragmentation events was done analysing angular distribution, range and angles between fragments. The results of fragment range distributions, angular distributions, distributions of angles between fragments, distributions of ratio between range, velocity distributions forward/backward ratio, cross sections of fission and fragmentation, nuclear fissionability and ternary fission frequency are presented and discussed. (M.C.K.)
Development of a thin scintillation films fission-fragment detector and a novel neutron source
Rusev, G.; Jandel, M.; Baramsai, B.; Bond, E. M.; Bredeweg, T. A.; Couture, A.; Daum, J. K.; Favalli, A.; Ianakiev, K. D.; Iliev, M. L.; Mosby, S.; Roman, A. R.; Springs, R. K.; Ullmann, J. L.; Walker, C. L.
2015-08-01
Investigation of prompt fission and neutron-capture Υ rays from fissile actinide samples at the Detector for Advanced Neutron Capture Experiments (DANCE) requires use of a fission-fragment detector to provide a trigger or a veto signal. A fission-fragment detector based on thin scintillating films and silicon photomultipliers has been built to serve as a trigger/veto detector in neutron-induced fission measurements at DANCE. The fissile material is surrounded by scintillating films providing a 4π detection of the fission fragments. The scintillations were registered with silicon photomultipliers. A measurement of the 235U(n,f) reaction with this detector at DANCE revealed a correct time-of-flight spectrum and provided an estimate for the efficiency of the prototype detector of 11.6(7)%. Design and test measurements with the detector are described. A neutron source with fast timing has been built to help with detector-response measurements. The source is based on the neutron emission from the spontaneous fission of 252Cf and the same type of scintillating films and silicon photomultipliers. Overall time resolution of the source is 0.3 ns. Design of the source and test measurements with it are described. An example application of the source for determining the neutron/gamma pulse-shape discrimination by a stilbene crystal is given.
Correlated spins of complementary fragment pairs in the spontaneous fission of 252Cf
International Nuclear Information System (INIS)
Smith, A. G.; Simpson, G. S.; Billowes, J.; Dagnall, P. J.; Durell, J. L.; Freeman, S. J.; Leddy, M.; Phillips, W. R.; Roach, A. A.; Smith, J. F.
1999-01-01
A study of the γ-ray decay of low-lying excited states in fragments produced in the spontaneous fission of 252 Cf has revealed a significant correlation between the angles of emission of the 2 1 + →0 1 + transitions of complementary fragment pairs. Calculations of the amount of dealignment that is needed to reproduce the measured a 2 values, and a comparison with the results of previous fragment-γ angular distribution measurements, suggests that at scission there may be significant population of m≠0 substates associated with the projection of the fragment spin vector on the fission axis. Fragments from the spontaneous fission of 248 Cm emit 2 1 + →0 1 + γ rays that show markedly reduced interfragment correlations, suggesting that either a larger role is played by the relative angular momentum of the fragments, or that the dealignment introduced by the neutron emission and statistical γ decay to the 2 1 + state is larger in 248 Cm than 252 Cf fission. (c) 1999 The American Physical Society
Theoretical energy straggling of /sup 252/Cf fission fragments in various absorbers
Energy Technology Data Exchange (ETDEWEB)
Al-Bedri, M.B.; Al-Hindawi, K.A.A. (Baghdad Univ. (Iraq). Dept. of Physics)
1982-07-15
A new theoretical formula of energy straggling for heavy ions such as /sup 252/Cf fission fragments in various stopping media has been calculated in terms of incident heavy ion energy, differential scattering cross-section, electronic and nuclear stopping cross-section. However, no theory yet exists which is cabable of predicting straggling behaviour of fission fragments. Comparison between our theoretical predictions and the previous work of Al-Bedri and Sykes has been made. Good agreement has been achieved at the beginning of the range of fission fragments but towards the end of the range our theoretical results were greater than the experimental results by about 10-20%. This discrepancy could be caused by the stopping cross-section, because the experimental stopping cross-section is greater than the theoretical data by about 0-30%.
Nuclear energy: fusion and fission - From the atomic nucleus to energy
International Nuclear Information System (INIS)
2002-09-01
Matter is made up of atoms. In 1912, the English physicist Ernest Rutherford (who had shown that the atom had a nucleus), and the Danish physicist Niels Bohr developed a model in which the atom was made up of a positively charged nucleus surrounded by a cloud of electrons. In 1913, Rutherford discovered the proton, and in 1932, the English physicist Chadwick discovered the neutron. In 1938, Hahn and Strassmann discovered spontaneous fission and the French physicist Frederic Joliot-Curie, assisted by Lew Kowarski and Hans Von Halban, showed in 1939 that splitting uranium nuclei caused an intense release of heat. The discovery of the chain reaction would enable the exploitation of nuclear energy. 'It was the Second World War leaders who, by encouraging research for military purposes, contributed to the development of nuclear energy'. During the Second World War, from 1939 to 1945, studies of fission continued in the United States, with the participation of emigre physicists. The Manhattan project was launched, the aim of which was to provide the country with a nuclear weapon (used at Hiroshima and Nagasaki in 1945). After the war ended, research into energy production by the nuclear fission reaction continued for civil purposes. CEA (the French Atomic Energy Commission) was set up in France in 1945 under the impetus of General de Gaulle. This public research body is responsible for giving France mastery of the atom in the research, health, energy, industrial, safety and defense sectors. (authors)
Kleinrath, Verena
2014-09-01
Fission fragment angular distributions can lend insights into fission barrier shapes and level densities at the scission point, both important for fission theory development. Fragment emission anisotropies are also valuable for precision cross section ratio measurements, if the distributions are different for the two isotopes used in the ratio. Available angular data is sparse for 235U and even more so for 239Pu, especially at neutron energies above 5 MeV. The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) time projection chamber, which enables precise tracking of charged particles, can be used to study angular distributions and emission anisotropies of fission fragments in neutron-induced fission. Analysis of in-beam data collected at the Los Alamos Neutron Science Center with a 239Pu/235U target will provide angular distributions as a function of incident neutron energy for these isotopes. Preliminary angular distributions for 235U and 239Pu using the NIFFTE time projection chamber will be presented. Fission fragment angular distributions can lend insights into fission barrier shapes and level densities at the scission point, both important for fission theory development. Fragment emission anisotropies are also valuable for precision cross section ratio measurements, if the distributions are different for the two isotopes used in the ratio. Available angular data is sparse for 235U and even more so for 239Pu, especially at neutron energies above 5 MeV. The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) time projection chamber, which enables precise tracking of charged particles, can be used to study angular distributions and emission anisotropies of fission fragments in neutron-induced fission. Analysis of in-beam data collected at the Los Alamos Neutron Science Center with a 239Pu/235U target will provide angular distributions as a function of incident neutron energy for these isotopes. Preliminary angular distributions for 235U and
Fission Fragment Angular Distributions measured with a Time Projection Chamber
Energy Technology Data Exchange (ETDEWEB)
Kleinrath, Verena [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-04-28
The subject is presented in a series of slides with the following organization: Introduction (What is anisotropy? Relevance (Theory and ratio cross section), Previous measurements); Experiment (Particle tracking in the fissionTPC, Neutron time of flight, Data analysis & uncertainty calculation, Preliminary result for ^{235}U); and Future Work (Refine ^{235}U result, Process ^{239}Pu data).
International Nuclear Information System (INIS)
Birtcher, R.C.; Blewitt, T.H.
1981-01-01
Damage production and saturation has been monitored in copper by simultaneous electrical resistivity- and length-change measurements. Damage was introduced by 235 U fission fragments at either 7 or 85 K. At both temperatures, the resistivity and length changes were linearly related to each other for resistivity changes less than 80% saturation resistivity. The linear relationship was the same for both irradiation temperatures and was the same as that observed previously for 10 B fission fragment irrations at 4 K. These results are interpreted to show that the resistivity change per defect is unaffected by irradiation under conditions which lead to interstitial clustering. (orig.)
New fission fragments discovered in collisions of relativistic 238U ions with Pb target nuclei
International Nuclear Information System (INIS)
Bernas, M.; Donzaud, C.; Dessagne, Ph.; Miehe, Ch.; Hanelt, E.; Heinz, A.
1994-01-01
Projectile fission of 238 U was investigated at a bombarding energy of 750 AMeV using a Pb target. Forward emitted fragments from 80 Zn up to 155 Ce were analyzed with the Fragment Separator (FrS) and unambiguously identified by their energy-loss and time-of-flight. The magnetic selection of the largest momenta acted as a trigger of low energy fission component. More than forty new nuclear species were identified. The related isotopic production cross-sections are presented. (authors). 13 refs., 4 figs., 1 tab
MAFF–The Munich accelerator for fission fragments
Indian Academy of Sciences (India)
Research reactors; linear accelerator; beam transport; particle sources and targets; ion sources. Abstract. At the new high ﬂux reactor FRM-II in Munich the accelerator MAFF (Munich accelerator for ﬁssion fragments) is under design. In the high neutron ﬂux of 1014 n/cm2 s up to 1014 neutron-rich ﬁssion fragments per ...
Pion production and fragmentation of nuclei in high energy nucleus-nucleus collisions
International Nuclear Information System (INIS)
Oskarsson, A.
1983-01-01
In collisions between nuclei at high energies one can study the behaviour of nuclear matter under extreme conditions, regarding nuclear density and temperature. The Bevalac and the CERN SC beams have been used and nuclear emulsion and scintillation telescopes have measured the reaction products. Collisions at 50A-200A MeV and at 2A GeV have been investigated. Proton spectra from 12 C induced reactions at 85A MeV have been recorded for different targets. Energetic protons at large angles can be assumed to be emitted from a source moving with half the beam velocity and a temperature between 13 and 17 MeV, depending on the target. In collisions between nuclei, pions can be produced below 290A MeV due to the internal Fermi motion of the nucleons. Subthreshold pion production has been studied for 12 C induced reactions at 85A and 75A Mev. The cross-sections are consistent with a quasi-free nucleon-nucleon scattering picture, involving Fermi motion, Pauli blocking and pion reabsorption. 16 C induced reactions in emulsion have been studied at 75A, 175A and 2000A MeV. It is shown that the excitation of the parts of the nuclei which are not overlapping (the spectators) increases with the beam energy. The 16 O projectile frequently breaks up into multiple He fragments. These events are associated with large impact parameters. Central collisions with Ag, Br target at 50A-110A MeV have been analysed separately. It is shown that the momentum transfer to the target nucleus is limited to a value considerably lower than the full momentum transfer in a fusion reactions. Events are observed where there are numerous fragments with 3< Z<8. These multifragmentation events cannot be understood in a thermal approach. (author)
Total Kinetic Energy and Fragment Mass Distribution of Neutron-Induced Fission of U-233
Energy Technology Data Exchange (ETDEWEB)
Higgins, Daniel James [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Schmitt, Kyle Thomas [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Mosby, Shea Morgan [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Tovesson, Fredrik [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-09-29
Properties of fission in U-233 were studied at the Los Alamos Neutron Science Center (LANSCE) at incident neutron energies from thermal to 40 MeV at both the Lujan Neutron Scattering Center flight path 12 and at WNR flight path 90-Left from Dec 2016 to Jan 2017. Fission fragments are observed in coincidence using a twin ionization chamber with Frisch grids. The average total kinetic energy (TKE) released from fission and fragment mass distributions are calculated from observations of energy deposited in the detector and conservation of mass and momentum. Accurate experimental measurements of these parameters are necessary to better understand the fission process and obtain data necessary for calculating criticality. The average TKE released from fission has been well characterized for several isotopes at thermal neutron energy, however, few measurements have been made at fast neutron energies. This experiment expands on previous successful experiments using an ionization chamber to measure TKE and fragment mass distributions of U-235, U-238, and Pu-239. This experiment requires the full spectrum of neutron energies and can therefore only be performed at a small number of facilities in the world. The required full neutron energy spectrum is obtained by combining measurements from WNR 90L and Lujan FP12 at LANSCE.
International Nuclear Information System (INIS)
Bao Shanglian; Liu Jinquan; Batenkov, O.I.; Blinov, M.V.; Smirnov, S.N.
1994-09-01
The 252 Cf spontaneous prompt fission neutron spectrum at 0 degree and 180 degree relative to the motion direction of corresponding fission fragments was measured. High angular resolution for fragment measurements and high energy resolution for neutron measurements were obtained using multi-parameter TOF spectrometer. The results showed that there is a symmetric distribution of 'forward' and 'backward' for low energy in C.M.S. neutrons, which was an evidence of nonequilibrium neutrons existed in fission process
Time-zero fission-fragment detector based on low-pressure multiwire proportional chambers
International Nuclear Information System (INIS)
Assamagan, K.; Baker, K.; Bayatyan, G.; Carlini, R.; Danagoulian, S.; Eden, T.; Egiyan, K.; Ent, R.; Fenker, H.; Gan, L.; Gasparian, A.; Grigoryan, N.; Greenwood, Z.; Gueye, P.; Hashimoto, O.; Johnston, K.; Keppel, C.; Knyazyan, S.; Majewski, S.; Margaryan, A.; Margaryan, Yu.; Marikyan, G.; Martoff, J.; Mkrtchyan, H.; Parlakyan, L.; Sato, Y.; Sawafta, R.; Simicevic, N.; Tadevosyan, V.; Takahashi, T.; Tang, L.; Vartanyan, G.; Vulcan, W.; Wells, S.; Wood, S.
1999-01-01
A time-zero fission fragment (FF) detector, based on the technique of low-pressure multiwire proportional chambers (LPMWPC), has been designed and constructed for the heavy hypernuclear lifetime experiment (E95-002) at Thomas Jefferson National Accelerator Facility. Its characteristics and the method of time-zero reconstruction were investigated using fission fragments from a 252 Cf spontaneous fission source. The influence of the ionization energy loss was also studied. It is shown that Heptane, Hexane, and Isobutane gases at a pressure of 1-2 Torr are all suitable for such a FF detector. As desired by experiment, a timing resolution of about 200 ps (FWHM) for a chamber size of 21x21 cm 2 was achieved
Time-zero fission-fragment detector based on low-pressure multiwire proportional chambers
Assamagan, Ketevi A; Bayatyan, G L; Carlini, R; Danagulyan, S; Eden, T; Egiyan, K; Ent, R; Fenker, H; Gan, L; Gasparian, A; Grigoryan, N K; Greenwood, Z; Gueye, P; Hashimoto, O; Johnston, K; Keppel, C; Knyazyan, S; Majewski, S; Margaryan, A; Margaryan, Yu L; Marikian, G G; Martoff, J; Mkrtchyan, H G; Parlakyan, L; Sato, Y; Sawafta, R; Simicevic, N; Tadevosyan, V; Takahashi, T; Tang, L; Vartanian, G S; Vulcan, W; Wells, S; Wood, S
1999-01-01
A time-zero fission fragment (FF) detector, based on the technique of low-pressure multiwire proportional chambers (LPMWPC), has been designed and constructed for the heavy hypernuclear lifetime experiment (E95-002) at Thomas Jefferson National Accelerator Facility. Its characteristics and the method of time-zero reconstruction were investigated using fission fragments from a sup 2 sup 5 sup 2 Cf spontaneous fission source. The influence of the ionization energy loss was also studied. It is shown that Heptane, Hexane, and Isobutane gases at a pressure of 1-2 Torr are all suitable for such a FF detector. As desired by experiment, a timing resolution of about 200 ps (FWHM) for a chamber size of 21x21 cm sup 2 was achieved.
Prokhorova, E.; Gönnenwein, F.; Kopatch, Yu.; Mutterer, M.; Hanappe, F.; Kinnard, V.; Stuttgé, L.; Dorvaux, O.; Wollersheim, H.-J.
2007-05-01
A novel method to search for the anisotropic emission of prompt neutrons in the center-of-mass system of fission fragments is presented. The anisotropy is conjectured to be due to the large spins of fission fragments are known to carry. Triple neutron- neutron-fragment correlations in spontaneous fission of 252Cf were investigated in an exploratory experiment dubbed CORA-DEMON experiment. Fission fragments were intercepted in a double ionization chamber while neutrons were spotted in 2 two-dimensional cylindrical walls of Demon detectors with the target on the vertical cylinder axis. A new method of analysis of triple angular correlations between 2 neutrons and a fission fragment was applied. Preliminary results are reported.
Mass distribution of fission-like fragments formed in 20Ne + 165Ho system at Elab≈ 8.2 MeV/A
International Nuclear Information System (INIS)
Singh, D.; Linda, Sneha Bharti; Giri, Pankaj K.
2017-01-01
In the present work, an attempt has been made to study CFF and IFF in 20 Ne + 165 Ho system at projectile energy ≈ 8.2 MeV/A. Twelve fission like fragments (FLF) produced through complete fusion-fission (CFF) and/or incomplete fusion-fission (IFF) in the present system have been identified. The production cross-sections of identified fission like fragments have been measured and the mass distribution of fission like fragments studied
MAFF–The Munich accelerator for fission fragments
Indian Academy of Sciences (India)
At the new high ﬂux reactor FRM-II in Munich the accelerator MAFF (Munich accelerator for ﬁssion fragments) is under design. In the high neutron ﬂux of 1014 n/cm2 s up to 1014 ... The through-going beam tube has been installed in the heavy water tank of the reactor. Tests of the target ion source in a special oven to test ...
Feasibility of Traveling Wave Direct Energy Conversion of Fission Reaction Fragments
Tarditi, A. G.; George, J. A.; Miley, G. H.; Scott, J. H.
2013-01-01
Fission fragment direct energy conversion has been considered in the past for the purpose of increasing nuclear power plant efficiency and for advanced space propulsion. Since the fragments carry electric charge (typically in the order of 20 e) and have 100 MeV-range kinetic energy, techniques utilizing very high-voltage DC electrodes have been considered. This study is focused on a different approach: the kinetic energy of the charged fission fragments is converted into alternating current by means of a traveling wave coupling scheme (Traveling Wave Direct Energy Converter, TWDEC), thereby not requiring the utilization of high voltage technology. A preliminary feasibility analysis of the concept is introduced based on a conceptual level study and on a particle simulation model of the beam dynamics.
Neutron-induced fission fragment angular distribution at CERN n TOF: The Th-232 case
Tarrio, Diego; Paradela, Carlos
This thesis work was done in the frame of the study of the neutron-induced fission of actinides and subactinides at the CERN n TOF facility using a fast Parallel Plate Avalanche Counters (PPACs) setup. This experimental setup provide us with an intense neutron beam with a white spectrum from thermal to 1 GeV and with an outstanding high resolution provided by its flight path of 185 m. In our experiment, fission events were identified by detection of both fission fragments in time coincidence in the two PPAC detectors flanking the corresponding target. This technique allowed us to discriminate the fission events from the background produced by α disintegration of radioactive samples and by particles produced in spallation reactions. Because PPAC detectors are insensitive to the γ flash, it is possible to reach energies as high as 1 GeV. The stripped cathodes provide the spatial position of the hits in the detectors, so that the emission angle of the fission fragments can be measured. Inside the reaction cham...
Tovesson, F.; Duke, D.; Geppert-Kleinrath, V.; Manning, B.; Mayorov, D.; Mosby, S.; Schmitt, K.
2018-03-01
Different aspects of the nuclear fission process have been studied at Los Alamos Neutron Science Center (LANSCE) using various instruments and experimental techniques. Properties of the fragments emitted in fission have been investigated using Frisch-grid ionization chambers, a Time Projection Chamber (TPC), and the SPIDER instrument which employs the 2v-2E method. These instruments and experimental techniques have been used to determine fission product mass yields, the energy dependent total kinetic energy (TKE) release, and anisotropy in neutron-induced fission of U-235, U-238 and Pu-239.
Vorobyev Alexander S.; Gagarski Alexei M.; Shcherbakov Oleg A.; Vaishnene Larisa A.; Barabanov Alexei L.
2017-01-01
Angular distributions of fission fragments from the neutron-induced fission of 232Th, 233U, 235U, 238U and 209Bi have been measured in the energy range 1–200 MeV at the neutron TOF spectrometer GNEIS based on the spallation neutron source at 1 GeV proton synchrocyclotron of the PNPI (Gatchina, Russia). The multiwire proportional counters have been used as a position sensitive fission fragment detector. A description of the experimental equipment and measurement procedure is given. The anisotr...
Fission throughout the periodic table
International Nuclear Information System (INIS)
Moretto, L.G.; Wozniak, G.J.
1989-04-01
The dualistic view of fission and evaporation as two distinct compound nucleus processes is substituted with a unified view in which fission, complex fragment emission, and light particle evaporation are seen as different aspects of a single process. 47 refs., 22 figs
Influence of primary fragment excitation energy and spin distributions on fission observables
Litaize, Olivier; Thulliez, Loïc; Serot, Olivier; Chebboubi, Abdelaziz; Tamagno, Pierre
2018-03-01
Fission observables in the case of 252Cf(sf) are investigated by exploring several models involved in the excitation energy sharing and spin-parity assignment between primary fission fragments. In a first step the parameters used in the FIFRELIN Monte Carlo code "reference route" are presented: two parameters for the mass dependent temperature ratio law and two constant spin cut-off parameters for light and heavy fragment groups respectively. These parameters determine the initial fragment entry zone in excitation energy and spin-parity (E*, Jπ). They are chosen to reproduce the light and heavy average prompt neutron multiplicities. When these target observables are achieved all other fission observables can be predicted. We show here the influence of input parameters on the saw-tooth curve and we discuss the influence of a mass and energy-dependent spin cut-off model on gamma-rays related fission observables. The part of the model involving level densities, neutron transmission coefficients or photon strength functions remains unchanged.
Lifetime measurements on fission fragments in the A ∼ 100 region
International Nuclear Information System (INIS)
Grente, L.; Salsac, M. D.; Korten, W.; Goergen, A.; Hagen, T. W.; Braunroth, T.; Bruyneel, B.; Celikovic, I.; Clement, E.; Delaune, O.; Dijon, A.; Drouart, A.; Ertuerk, S.; Farget, F.; De France, G.; Gottardo, A.; Hackstein, M.; Jacquot, B.; Libert, J.; Litzinger, J.; Ljungvall, J.; Louchart, C.; Michelagnoli, C.; Napoli, D. R.; Navin, A.; Pillet, N.; Pipidis, A.; Recchia, F.; Rejmund, M.; Rother, W.; Sahin, E.; Schmitt, C.; Siem, S.; Sulignano, B.; Valiente-Dobon, J. J.; Zell, K. O.
2013-01-01
Lifetimes of first 4 + and 6 + states have been measured in neutron-rich isotopes of Zr, Mo, Ru and Pd using the recoil distance Doppler shift method at GANIL. The nuclei were produced through a fusion-fission reaction in inverse kinematics. The fission fragments were fully identified in the large-acceptance VAMOS spectrometer and γ-rays were detected in coincidence with the EXOGAM germanium array. Lifetimes of excited states in the range of 1-100 ps were measured with the Cologne plunger. Preliminary lifetime results are presented as well as a discussion on the evolution of the collectivity in this region. (authors)
Influence of pre-saddle neutrons on the fission fragment angular distribution
Fröbrich, P.; Rossner, H.
1994-06-01
In the present note it is shown that distinguishing between pre-saddle and saddle-to-scission neutrons removes a discrepancy previously found [2 4] between data for the fission fragment anisotropy and an analysis in the framework of the transition state theory in which it has been assumed that all pre-scission neutrons influence the temperature at the saddle point. The analysis of the present paper requires a fairly weak (β=2 * 1021 s -1) friction at compact shapes, in agreement with a previous [9,10] analysis of prescission neutron multiplicities and fission probabilities.
Energy Technology Data Exchange (ETDEWEB)
Gaudefroy, L., E-mail: laurent.gaudefroy@cea.fr [CEA, DAM, DIF, F-91297 Arpajon (France); Roger, T., E-mail: roger@ganil.fr [GANIL, CEA/DSM-CNRS/IN2P3, BP 55027, F-14076 Caen (France); Pancin, J., E-mail: pancin@ganil.fr [GANIL, CEA/DSM-CNRS/IN2P3, BP 55027, F-14076 Caen (France); Spitaels, C. [GANIL, CEA/DSM-CNRS/IN2P3, BP 55027, F-14076 Caen (France); Aupiais, J. [CEA, DAM, DIF, F-91297 Arpajon (France); Mottier, J. [Institut de Physique Nucléaire, Université Paris-Sud-11-CNRS-IN2P3, F-91406 Orsay (France)
2017-05-21
We present a twin Frisch-grid ionization chamber. The detector is meant to provide high selective power for the study of delayed gamma-ray spectroscopy of fission fragments produced via {sup 252}Cf spontaneous fission. A mean energy resolution on the kinetic energy of fission fragments of 675 keV (FWHM) is achieved and allows us to resolve masses of fragments for fission events where neutron emission is not energetically possible. The mean mass resolution measured for these particular events amounts to 0.54 mass units (FWHM). For fission events with neutron emission a resolution of 4 mass units (FWHM) is reported. Information on fragment emission angle is measured with a resolution of 0.1 on the difference of the cosines determined for both halves of the detector. A charge resolution of 4.5 charge units (FWHM) is also demonstrated.
Fission and fragmentation of silver and bromine nuclei by 1-6 GeV energy photons
International Nuclear Information System (INIS)
Pinheiro Filho, J. de D.
1983-01-01
Fission and fragmentation of silver and bromine nuclei induced by bremsstrahlung photons in the maximum energy range of 1-6 GeV are studied. A special technique of nuclear emulsion for the highly ionizing nuclear fragment detection is used in the discrimination between nuclear fission and fragmentation events. Films of Ilford-KO nuclear emulsion (approximatelly 10 20 atoms/cm 2 of Ag, Br) which had been exposed to bremsstrahlung beams in 'Deutsches Elektronen Synchrotron' (DESY, Hamburg) with total doses of approximatelly 10 11 equivalent photons are used. Through a detailed analysis of range, angular and angle between fragment distributions, and empirical relations which permit to estimate nuclear fragment energy, range and velocity, the discrimination between fission and fragmentation events is made. Results related to fragment range distribution, angular distribution, distribution of angle between fragments, distribution of ratio between ranges, velocity distributions, forward/backward ratio, fission and fragmentation cross sections, nuclear fissionability and ternary fission frequency are presented and discussed. The results show that the mean photofragmentation cross section in the internal 1-6 GeV (0,09+-0,02mb) is significant when compared to the photofission (0,29+-0,05mb). It is also shown that the mean photofission cross section between 1 and 6 GeV is great by a factor of approximatelly 10 when compared to the foreseen by the cascade-evaporation nuclear model for monoenergetic photons of 0,6 GeV. (L.C.) [pt
Vorobyev, Alexander S.; Gagarski, Alexei M.; Shcherbakov, Oleg A.; Vaishnene, Larisa A.; Barabanov, Alexei L.
2017-09-01
Angular distributions of fission fragments from the neutron-induced fission of 232Th, 233U, 235U, 238U and 209Bi have been measured in the energy range 1-200 MeV at the neutron TOF spectrometer GNEIS based on the spallation neutron source at 1 GeV proton synchrocyclotron of the PNPI (Gatchina, Russia). The multiwire proportional counters have been used as a position sensitive fission fragment detector. A description of the experimental equipment and measurement procedure is given. The anisotropy of fission fragments deduced from the data on measured angular distributions is presented in comparison with experimental data of other authors, first of all, the recent data from WNR at LANSCE (Los Alamos, USA) and n_TOF(CERN).
Directory of Open Access Journals (Sweden)
Vorobyev Alexander S.
2017-01-01
Full Text Available Angular distributions of fission fragments from the neutron-induced fission of 232Th, 233U, 235U, 238U and 209Bi have been measured in the energy range 1–200 MeV at the neutron TOF spectrometer GNEIS based on the spallation neutron source at 1 GeV proton synchrocyclotron of the PNPI (Gatchina, Russia. The multiwire proportional counters have been used as a position sensitive fission fragment detector. A description of the experimental equipment and measurement procedure is given. The anisotropy of fission fragments deduced from the data on measured angular distributions is presented in comparison with experimental data of other authors, first of all, the recent data from WNR at LANSCE (Los Alamos, USA and n_TOF(CERN.
Neutron-fragment and Neutron-neutron Correlations in Low-energy Fission
Energy Technology Data Exchange (ETDEWEB)
Lestone, J.P., E-mail: lestone@lanl.gov
2016-01-15
A computational method has been developed to simulate neutron emission from thermal-neutron induced fission of {sup 235}U and from spontaneous fission of {sup 252}Cf. Measured pre-emission mass-yield curves, average total kinetic energies and their variances, both as functions of mass split, are used to obtain a representation of the distribution of fragment velocities. Measured average neutron multiplicities as a function of mass split and their dependence on total kinetic energy are used. Simulations can be made to reproduce measured factorial moments of neutron-multiplicity distributions with only minor empirical adjustments to some experimental inputs. The neutron-emission spectra in the rest-frame of the fragments are highly constrained by ENDF/B-VII.1 prompt-fission neutron-spectra evaluations. The n-f correlation measurements of Vorobyev et al. (2010) are consistent with predictions where all neutrons are assumed to be evaporated isotropically from the rest frame of fully accelerated fragments. Measured n-f and n-n correlations of others are a little weaker than the predictions presented here. These weaker correlations could be used to infer a weak scission-neutron source. However, the effect of neutron scattering on the experimental results must be studied in detail before moving away from a null hypothesis that all neutrons are evaporated from the fragments.
Fission fragment mass distribution in the 13C+182W and 176Yb reactions
International Nuclear Information System (INIS)
Ramachandran, K.; Hinde, D. J.; Dasgupta, M.; Williams, E.; Wakhle, A.; Luong, D. H.; Evers, M.; Carter, I. P.; Das, S.
2013-01-01
Shell effects can play a prominent role in fission fragment mass distributions. For lighter systems in the region of A∼180-200, mass distributions were generally expected to be symmetric. However, a recent experiment showed that fission of 180 Hg following electron capture of 180 Tl leads to an asymmetric mass split. Recent calculations by various groups indicate that the mechanism of asymmetric fission could be very different in this mass region compared to the actinide region. To investigate the role of shell effects in this mass region, we have measured the fission fragment mass distribution for the 13 C+ 182 W, 176 Yb reactions forming the compound nuclei 195 Hg and 189 Os respectively, at lab bombarding energies of 60, 63 and 66 MeV using the CUBE detector setup located at the ANU Heavy Ion Accelerator Facility. The experimental data were fitted with single and double Gaussian distributions. The results indicate an asymmetric mass split for 195 Hg, whereas for 189 Os, the mass distribution is well fitted with a single Gaussian distribution. (authors)
Imaging technique for detection of leaf surface contaminations with fission fragments
International Nuclear Information System (INIS)
Furuta, Etsuko
2011-01-01
Fission fragments by the Fukushima Daiichi catastrophe were scattered over a large area. Between Tokyo and Fukushima, leaves were gathered up from March to June and measured their radioactivities by HPGe. Radionuclides of 129m Tc, 131 I, 134 Cs and 137 Cs were rightly detected. Also the leaf surface contaminations were shown as images by imaging technique which detected beta- and gamma-rays exposure. The clear images were gotten within 24 h exposure though a normal leaf image needs at least one week exposure in a shield box. The total PSL values of leaves depend on their activities of sampling points, so the imaging technique is able to use for detection of the spread of fission fragments and the relative concentration. Also the rain effect to leaves could be shown by imaging technique when leaves were washed in running water. The imaging technique is easy and useful for the nuclear catastrophe. (author)
Measurement of the angular distribution of fission fragments using a PPAC assembly at CERN n_TOF
Tarrío, D; Audouin, L; Duran, I; Paradela, C; Tassan-Got, L; Le Naour, C; Bacri, C O; Petitbon, V; Mottier, J; Caamano, M; Altstadt, S; Andrzejewski, J; Barbagallo, M; Bécares, V; Bečvář, F; Belloni, F; Berthoumieux, E; Billowes, J; Boccone, V; Bosnar, D; Brugger, M; Calviani, M; Calviño, F; Cano-Ott, D; Carrapiço, C; Cerutti, F; Chiaveri, E; Chin, M; Colonna, N; Cortés, G; Cértes-Giraldo, M A; Diakaki, M; Domingo-Pardo, C; Dzysiuk, N; Eleftheriadis, C; Ferrari, A; Fraval, K; Ganesan, S; García, A R; Giubrone, G; Gómez-Hornillos, M B; Gonçalves, I F; González-Romero, E; Griesmayer, E; Guerrero, C; Gunsing, F; Gurusamy, P; Jenkins, D G; Jericha, E; Kadi, Y; Käppeler, F; Karadimos, D; Koehler, P; Kokkoris, M; Krtička, M; Kroll, J; Langer, C; Lederer, C; Leeb, H; Losito, R; Manousos, A; Marganiec, J; Martínez, T; Massimi, C; Mastinu, P F; Mastromarco, M; Meaze, M; Mendoza, E; Mengoni, A; Milazzo, P M; Mingrone, F; Mirea, M; Mondalaers, W; Pavlik, A; Perkowski, J; Plompen, A; Praena, J; Quesada, J M; Rauscher, T; Reifarth, R; Riego, A; Roman, F; Rubbia, C; Sarmento, R; Schillebeeckx, P; Schmidt, S; Tagliente, G; Tain, J L; Tsinganis, A; Valenta, S; Vannini, G; Variale, V; Vaz, P; Ventura, A; Versaci, R; Vermeulen, M J; Vlachoudis, V; Vlastou, R; Wallner, A; Ware, T; Weigand, M; Weiß, C; Wright, T J; Žugec, P
2014-01-01
A fission reaction chamber based on Parallel Plate Avalanche Counters (PPACs) was built for measuring angular distributions of fragments emitted in neutron-induced fission of actinides at the neutron beam available at the Neutron Time-Of-Flight (n_TOF) facility at CERN. The detectors and the samples were tilted 45 1 with respect to the neutron beam direction to cover all the possible values of the emission angle of the fission fragments. The main features of this setup are discussed and results on the fission fragment angular distribution are provided for the 232 Th(n,f) reaction around the fission threshold. The results are compared with the available data in the literature, demonstrating the good capabilities of this setup
Prasad, E.; Varier, K. M.; Thomas, R. G.; Vinodkumar, A. M.; Mahata, K.; Appannababu, S.; Sugathan, P.; Golda, K. S.; Babu, B. R. S.; Saxena, A.; John, B. V.; Kailas, S.
2012-05-01
Fission fragment angular distributions have been measured for 16O + 194Pt reaction forming the compound system 210Rn, in the laboratory energy range from 79 to 90 MeV. The measured fission fragment anisotropies as a function of E/VB are compared with the predictions of standard saddle point statistical model (SSPM). Anisotropies calculated using the average excitation energy and angular momentum values could not reasonably fit the experimental data. Statistical model calculations were performed using the PACE with modified fission barrier and level density parameters. Fission probability, evaporation residue cross section and neutron multiplicity were simultaneously used to fix the statistical parameters. Model calculations incorporating the chance nature of fission decay and scaled values of the rotating finite range model (RFRM) moment of inertia could reasonably fit the fragment angular anisotropies.
Burnout and gate rupture of power MOS transistors with fission fragments of 252Cf
International Nuclear Information System (INIS)
Tang Benqi; Wang Yanping; Geng Bin; Chen Xiaohua; He Chaohui; Yang Hailiang
2000-01-01
A study to determine the single event burnout (SEB) and single event gate rupture (SEGR) sensitivities of power MOSFET devices is carried out by exposure to fission fragments from 252 Cf source. The test method, test results, a description of observed burnout current waveforms and a discussion of a possible failure mechanism are presented. The test results include the observed dependence upon applied drain or gate to source bias and effect of external capacitors and limited resistors
Ability of Accelerator-Driven Systems (ADS) to Transmute Long Lived Fission Fragments
International Nuclear Information System (INIS)
Nguyen Mong Giao; Nguyen Thi Ai Thu; Tu Thanh Danh; Tran Thanh Dung; Huynh, Thi Kim Chi
2010-12-01
This paper presents the research results of the possibility to transmute the long-lived radioactive isotopes into stable or short-lived, mainly the long-lived fission fragments as 99 Tc, 127 I, 129 I, 181 Ta, 107 Ag, 109 Ag by accelerator-driven systems. We use semi-empirical formulas to establish our calculating code with the support of computer programs. (author)
Deformation energy of a toroidal nucleus and plane fragmentation barriers
International Nuclear Information System (INIS)
Fauchard, C.; Royer, G.
1996-01-01
The path leading to pumpkin-like configurations and toroidal shapes is investigated using a one-parameter shape sequence. The deformation energy is determined within the analytical expressions obtained for the various shape-dependent functions and the generalized rotating liquid drop model taking into account the proximity energy and the temperature. With increasing mass and angular momentum, a potential well appears in the toroidal shape path. For the heaviest systems, the pocket is large and locally favourable with respect to the plane fragmentation barriers which might allow the formation of evanescent toroidal systems which would rapidly decay in several fragments to minimize the surface tension. (orig.)
New insight on the high radiation resistance of UO{sub 2} against fission fragments
Energy Technology Data Exchange (ETDEWEB)
Szenes, G., E-mail: szenesgyorgy@caesar.elte.hu
2016-12-15
Track radii are derived for semiconductors from a temperature distribution Θ(r) in which the width of the distribution is the only materials parameter. Analysis of track data for GeS, InP, GaAs and GaN show that the projectile velocity has no effect on track radii in semiconductors. Due to the missing velocity effect, the threshold for track formation, S{sub et} = 20 keV/nm is high in semiconducting UO{sub 2} in the whole range of projectile velocities. This is the origin of the high radiation resistance for fission fragments. Consequences for the simulation experiments with insulating CeO{sub 2} are discussed. It is verified that sputtering is described accurately by the Arrhenius equation for various materials including UO{sub 2}. The ion-induced surface potential has a strong effect on the activation energy. - Highlights: • Uniform features of track formation are demonstrated. • Semiconductors are more stable than insulators against fission fragments. • Melting point and width of the thermal spike control the track size. • High threshold for tracks S{sub et} = 20 keV/nm for fission fragments in semiconducting UO{sub 2}. • An Arrhenius equation describes the inelastic sputtering in UO{sub 2} and other solids.
Seregina, E. A.; Seregin, A. A.
2013-02-01
The characteristics of radioluminescence of Nd3+ : Y3Al5O12 crystals and laser glasses under excitation by plutonium-239 (239Pu) α-particles, as well as by α-particles and spontaneous fission fragments of californium-252 (252Cf), are studied. The radioluminescence branching ratios βij for the transition from the 2F25/2 level to the 2S+1LJ levels in Nd3+ : Y3Al5O12 crystals are measured. Radioluminescence from the 2P3/2 level to low-lying levels is observed. The βij ratios for transitions from the high-lying 2F25/2, 4D3/2, and 2P3/2 levels are theoretically calculated. The lifetimes of metastable levels of Nd3+ excited by 252Cf fission fragments are measured. The efficiency of the conversion of energy of α-particles and fission fragments to the energy of optical radiation of Nd3+ : Y3Al5O12 crystals and laser glasses is determined.
Charge distributions of fission fragments of low- and high-energy fission of Fm, No, and Rf isotopes
Paşca, H.; Andreev, A. V.; Adamian, G. G.; Antonenko, N. V.
2018-03-01
The charge (mass) distributions of fission fragments resulting from low- and high-energy fission of the even-even nuclei 254 -260 ,264Fm , 258 -264No , and 262 -266Rf are studied with the statistical scission-point model. The calculated results are compared with the available experimental data. In contrast to the experimental data, the calculated mass distribution for 258Fm (s.f.) is strikingly similar to the experimental one for 257Fm (s.f.). The transformation of the shape of charge distribution with increasing isospin and excitation energy occurs gradually and in a similar fashion like that of the mass distribution, but slower. For 254Fm(i.f.), 257Fm(nt h,f), and 260Fm (s.f.), the unexpected difference (symmetric or asymmetric) between the shapes of charge and mass distributions is predicted for the first time. At some critical excitation energy, the saturation of the symmetric component of charge (mass) yields is demonstrated.
International Nuclear Information System (INIS)
Spaggiari, E.R.V.
1978-01-01
The results of measuments of the disintegration constant for spontaneous fission in 238 U are presented, with a discussion on the method used for the detection of fission tracks in muscovite mica. Samples of muscovite mica sandwiched between two natural uranium dioxide cylinders were irradiated with fragments of spontaneous fission and the etched tracks counted with projetion optical microscope. The effective thickness of the UO 2 layer which contributed to the observed tracks was measured through irradiation of mica samples, in contact with the UO 2 cylinder with 14,0 MeV neutrons from a (d,t) reaction. (Author) [pt
A high-resolution time-of-flight spectrometer for fission fragments and ion beams
International Nuclear Information System (INIS)
Kosev, Krasimir Milchev
2007-01-01
For the purpose of fission-fragment detection a double time-of-flight (TOF) spectrometer has been developed. The key component of the TOF spectrometer is a TOF detector consisting of multichannel-plate (MCP) detectors with a position-sensitive readout, a foil for secondary electron (SE) production and an electrostatic mirror. The fission fragments are detected by measuring the SEs impinging on the position-sensitive anode after emission from the foil, acceleration and deflection by the electrostatic mirror. The functionality of the different detector components is proven in detail. Optimised schemes for the high-voltage supplies of the MCP detectors have been implemented successfully. In order to process the multichannel-plate detector signals optimally, a new state-of-the-art constant-fraction discriminator based on the amplitude and rise time compensated technique with very low threshold capabilities and optimised walk properties has been developed and incorporated into the setup. In a setup consisting of two mirror MCP detectors, we could successfully observe the TOF spectrum of a mixed ( 226 Ra, 222 Rn, 210 Po, 218 Po, 214 Po) α-source. Testing photo-fission experiments were performed at the bremsstrahlung facility at the ELBE accelerator. The setup consisted of two mirror detectors (first arm) and a 80 mm diameter MCP detector (second arm) with a 238 U target positioned in between. TOF measurements with two bremsstrahlung end-point energies of 12.9 and 16.0 MeV were carried out. A clear cut separation of the TOF peaks for the medium-mass and heavy fission fragments was observed. (orig.)
A high-resolution time-of-flight spectrometer for fission fragments and ion beams
Energy Technology Data Exchange (ETDEWEB)
Kosev, Krasimir Milchev
2007-07-01
For the purpose of fission-fragment detection a double time-of-flight (TOF) spectrometer has been developed. The key component of the TOF spectrometer is a TOF detector consisting of multichannel-plate (MCP) detectors with a position-sensitive readout, a foil for secondary electron (SE) production and an electrostatic mirror. The fission fragments are detected by measuring the SEs impinging on the position-sensitive anode after emission from the foil, acceleration and deflection by the electrostatic mirror. The functionality of the different detector components is proven in detail. Optimised schemes for the high-voltage supplies of the MCP detectors have been implemented successfully. In order to process the multichannel-plate detector signals optimally, a new state-of-the-art constant-fraction discriminator based on the amplitude and rise time compensated technique with very low threshold capabilities and optimised walk properties has been developed and incorporated into the setup. In a setup consisting of two mirror MCP detectors, we could successfully observe the TOF spectrum of a mixed ({sup 226}Ra,{sup 222}Rn,{sup 210}Po,{sup 218}Po,{sup 214}Po) {alpha}-source. Testing photo-fission experiments were performed at the bremsstrahlung facility at the ELBE accelerator. The setup consisted of two mirror detectors (first arm) and a 80 mm diameter MCP detector (second arm) with a {sup 238}U target positioned in between. TOF measurements with two bremsstrahlung end-point energies of 12.9 and 16.0 MeV were carried out. A clear cut separation of the TOF peaks for the medium-mass and heavy fission fragments was observed. (orig.)
Application of the dinuclear system model to fission process
Andreev, A. V.; Shneidman, T. M.; Ventura, A.
2016-01-01
A theoretical evaluation of the collective excitation spectra of nucleus at large deformations is possible within the framework of the dinuclear system model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two-cluster configurations in a dynamical way, permitting exchange of nucleons between clusters. In this work the method of calculation of the potential energy and the collective spectrum of fissioning nucleus at scission point is presented. Combining the DNS model calculations and the statistical model of fission we calculate the mass, total kinetic energy, and angular distribution of fission fragments for the neutron-induced fission of 239Pu.
Application of the dinuclear system model to fission process
Directory of Open Access Journals (Sweden)
Andreev A. V.
2016-01-01
Full Text Available A theoretical evaluation of the collective excitation spectra of nucleus at large deformations is possible within the framework of the dinuclear system model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two-cluster configurations in a dynamical way, permitting exchange of nucleons between clusters. In this work the method of calculation of the potential energy and the collective spectrum of fissioning nucleus at scission point is presented. Combining the DNS model calculations and the statistical model of fission we calculate the mass, total kinetic energy, and angular distribution of fission fragments for the neutron–induced fission of 239Pu.
Accurate measurements of fission-fragment yields in 234,235,236,238U(γ,f) with the SOFIA set-up
International Nuclear Information System (INIS)
Chatillon, A.; Taieb, J.; Martin, J.F.; Pellereau, E.; Boutoux, G.; Gorbinet, T.; Grente, L.; Belier, G.; Laurent, B.; Alvarez-Pol, H.; Ayyad, Y.; Benlliure, J.; Caamano, M.; Cortina-Gil, D.; Fernandez-Dominguez, B.; Paradela, C.; Ramos, D.; Rodriguez-Sanchez, J.L.; Vargas, J.; Audouin, L.; Tassan-Got, L.; Yan, Y.; Casarejos, E.; Farget, F.; Rodriguez-Tajes, C.; Heinz, A.; Lindberg, S.; Jurado, B.; Kelic-Heil, A.; Kurz, N.; Loeher, B.; Nociforo, C.; Pietri, S.; Rossi, D.; Schmidt, K.H.; Simon, H.; Voss, B.; Weick, H.; Toernqvist, H.
2016-01-01
SOFIA (Studies On Fission with Aladin) is a new experimental set-up dedicated to accurate measurement of fission-fragments isotopic yields. It is located at GSI, the only place to use inverse kinematics at relativistic energies in order to study the (γ,f) electromagnetic-induced fission. The SOFIA set-up is a large-acceptance magnetic spectrometer, which allows to fully identify both fission fragments in coincidence on the whole fission-fragment range. This paper will report on fission yields obtained in 234,235,236,238 U(γ,f) reactions. (authors)
Directory of Open Access Journals (Sweden)
V. Yu. Denisov
2017-11-01
Full Text Available The influence for various parameterizations of the nuclear part of the interaction potential to the mass yields of fission fragments of highly excited nuclei for the reaction α+197Au → fission was studied. It is shown that using of various nuclear potentials leads to small changes in the yields of fission fragments of the nuclei.
Non-adiabatic transition of the fissioning nucleus at scission: the time scale
International Nuclear Information System (INIS)
Carjan, N.; Rizea, M.
2012-01-01
The sudden approximation has been recently used to calculate the microscopic scission-properties during low-energy fission of 236 U. In this approach the scission process, i.e., the transition from two fragments connected by a thin neck to two separated fragments was considered to happen suddenly. The approach is stationary (the time evolution is not explicitly treated) and it only involves the two sets of neutron eigenstates for the two nuclear configurations considered: just before scission (α i ) and immediately after scission (α f ). The purpose of the present paper is to go beyond this mathematical approximation considering the real physical situation in which the above mentioned transition takes place in a time interval ΔT ≠ 0. For this we need to follow the evolution from α i to αf of all occupied neutron states by solving numerically the two-dimensional time-dependent Schroedinger equation with time-dependent potential. Calculations are performed for mass divisions from A L = 70 to A L = 118 (A L being the light fragment mass) taking into account all the neutron states (Ω = 1/2, 3/2,..., 11/2) that are bound in 236 U at α i . The diabatic-dissipative dynamics of the neck rupture is very complicated and its exact duration is un-known. ΔT is therefore taken as parameter having values from 0.25 x 10 -22 to 6 x 10 -22 sec. The resulting scission neutron multiplicities - sc and primary fragments' excitation energies E sc * are compared with those obtained in the frame of the sudden approximation (that corresponds to ΔT = 0). As expected, shorter is the transition time more excited are the fragments and more neutrons are emitted, the sudden approximation being an upper limit. For ΔT = 10 -22 sec, which is a realistic value, the time dependent results are 20% below this limit. For transition times longer than 5 x 10 -22 sec the adiabatic limit is reached: no scission neutrons are emitted anymore and the excitation energy at α f is negligible. The
Fission Fragment Angular Distribution of 232Th(n,f) at the CERN n_TOF Facility
Tarrío, D; Audouin, L; Duran, I.; Paradela, C.; Tassan-Got, L; Altstadt, S; Andrzejewski, J; Barbagallo, M; Bécares, V; Bečvář, F; Belloni, F; Berthoumieux, E; Billowes, J; Boccone, V; Bosnar, D; Brugger, M; Calviani, M; Calviño, F; Cano-Ott, D; Carrapiço, C; Cerutti, F; Chiaveri, E; Chin, M; Colonna, N; Cortés, G; Cortés-Giraldo, M A; Diakaki, M; Domingo-Pardo, C; Dzysiuk, N; Eleftheriadis, C; Ferrari, A; Fraval, K; Ganesan, S; García, A R; Giubrone, G; Gómez-Hornillos, M B; Gonçalves, I F; González-Romero, E; Griesmayer, E; Guerrero, C; Gunsing, F; Gurusamy, P; Jenkins, D G; Jericha, E; Kadi, Y; Käppeler, F; Karadimos, D; Koehler, P; Kokkoris, M; Krtička, M; Kroll, J; Langer, C; Lederer, C; Leeb, H; Losito, R; Manousos, A; Marganiec, J; Martínez, T; Massimi, C; Mastinu, P F; Mastromarco, M; Meaze, M; Mendoza, E; Mengoni, A; Milazzo, P M; Mingrone, F; Mirea, M; Mondalaers, W; Pavlik, A; Perkowski, J; Plompen, A; Praena, J; Quesada, J M; Rauscher, T; Reifarth, R; Riego, A; Roman, F; Rubbia, C; Sarmento, R; Schillebeeckx, P; Schmidt, S; Tagliente, G; Tain, J L; Tsinganis, A; Valenta, S; Vannini, G; Variale, V; Vaz, P; Ventura, A; Versaci, R; Vermeulen, M J; Vlachoudis, V; Vlastou, R; Wallner, A; Ware, T; Weigand, M; Weiß, C; Wright, T J; Žugec, P
2014-01-01
The angular distribution of fragments emitted in neutron-induced fission of Th-232 was measured in the white spectrum neutron beam at the n\\_TOF facility at CERN. A reaction chamber based on Parallel Plate Avalanche Counters (PPAC) was used, where the detectors and the targets have been tilted 45 degrees with respect to the neutron beam direction in order to cover the full angular range of the fission fragments. A GEANT4 simulation has been developed to study the setup efficiency. The data analysis and the preliminary results obtained for the Th-232(n,f) between fission threshold and 100 MeV are presented here.
International Nuclear Information System (INIS)
Tanaka, E.M.
1979-01-01
The Fission Fragment Track Registration Technique is developed to measure the uranium concentration about microgram of uranium per litre of liquid samples. The drying method of drops on the detector (Makrofol KG) and a special sampling procedure to avoid the cumbersome high density of tracks formation at the edge of the deposition surface as a 'ring' is adopted. The samples are irradiated by neutrons produced by the IEA-R1 Reactor (thermal neutron flux about 10 12 neutrons/cm 2 .s) inducing the uranium fission. The tracks registered by the fission fragments in the detector are chemically enlarged and counted by an automatic couting system. By this method the uranium concentrations ranging from 0,9 to 7,6 microgram of uranium per litre, can be determined with precisions between 2,7% the greater and 23% to the lower concentration. The uranium concentration measurements in human hair and urine are made showing that this method is very useful to control and detect eventual uranium contamination [pt
Light nuclides observed in the fission and fragmentation of 238U
International Nuclear Information System (INIS)
Ricciardi, M.V.; Schmidt, K.H.; Benlliure, J.
2001-05-01
Light nuclides produced in collisions of 1 A.GeV 238 U with protons and titanium have been fully identified with a high-resolution forward magnetic spectrometer, the fragment separator (FRS), at GSI, and for each nuclide an extremely precise determination of the velocity has been performed. The so-obtained information on the velocity shows that the very asymmetric fission of uranium, in the 238 U + p reaction, produces neutron-rich isotopes of elements down to around charge 10. New important features of the fragmentation of 238 U, concerning the velocity and the N/Z-ratio of these light fragments, and a peculiar even-odd structure in N=Z nuclei, have also been observed. (orig.)
International Nuclear Information System (INIS)
Pellereau, Eric
2013-01-01
The isotopic fission yields of U 238 following the SOFIA experiment, conducted at the GSI facility (Darmstadt), are presented here. This experiment takes advantage of the inverse kinematics technique at relativistic energies. Benefits are several: fission fragments are highly focused (high geometrical efficiency) and are also completely stripped, which greatly simplifies their nuclear charge measurement. The first detector of the SOFIA setup is an active target in which fission occurs via electromagnetic excitation, followed by an ionization chamber to measure the nuclear charge and the horizontal angle of both fission fragments. The masses are deduced by the bending radius measurement of the fragments, deflected by a strong magnet (ALADIN), thanks to two position detectors (MWPC), and also by a highly resolved time-of-flight measurement (40 ps FWHM) so that heavy neighboring isotopes can be separated. The data analysis shows that the main goals are achieved since the isotopic separation is reached over the whole range of the fission fragments. A strong even-odd effect is seen in the charge spectrum, which also exhibits a mean heavy charge close to Z = 54. Surprisingly, the neutron even-odd effect of the light region is seen to be very close to the one in thermal neutron induced fission. The peak-to-valley ratio of the mass spectrum confirms that the mean excitation energy at fission is close to the expected one (14 MeV). The GEF code is used for comparison and always gives results very close to ours. (author) [fr
International Nuclear Information System (INIS)
Sawamura, Teruko; Baba, Satoshi; Narita, Masakuni; Yamazaki, Hatsuo
1994-01-01
The etching behavior of fission fragment tracks in synthetic quartz plates concerning to +x, y and z planes was studied using NaOH solution as an etchant. Systematic experiments gave an optimum etching condition of 65% NaOH at 150degC suitable for track detection. Under this etching condition, following several properties were studied; the bulk etching rate, the etched track opening shape and its growth rate, the critical angle of track etching, and the irradiation effect of low LET radiation. All of three different cuts were demonstrated to be useful for plates as fission track detectors. An application to neutron detection was studied for the +x-plane of an x-cut plate. The detection sensitivity of the plane in close contact with a Th-radiator was 2.7x10 -6 tracks/fluence for 14 MeV neutrons. (author)
International Nuclear Information System (INIS)
Wagemans, C.
1991-01-01
Since its discovery in 1946, light (charged) particle accompanied fission (ternary fission) has been extensively studied, for spontaneous as well as for induced fission reactions. The reason for this interest was twofold: the ternary particles being emitted in space and time close to the scission point were expected to supply information on the scission point configuration and the ternary fission process was an important source of helium, tritium, and hydrogen production in nuclear reactors, for which data were requested by the nuclear industry. Significant experimental progress has been realized with the advent of high-resolution detectors, powerful multiparameter data acquisition systems, and intense neutron and photon beams. As far as theory is concerned, the trajectory calculations (in which scission point parameters are deduced from the experimental observations) have been very much improved. An attempt was made to explain ternary particle emission in terms of a Plateau-Rayleigh hydrodynamical instability of a relatively long cylindrical neck or cylindrical nucleus. New results have also been obtained on the so-called open-quotes trueclose quotes ternary fission (fission in three about-equal fragments). The spontaneous emission of charged particles has also clearly been demonstrated in recent years. This chapter discusses the main characteristics of ternary fission, theoretical models, light particle emission probabilities, the dependence of the emission probabilities on experimental variables, light particle energy distributions, light particle angular distributions, correlations between light particle accompanied fission observables, open-quotes trueclose quotes ternary fission, and spontaneous emission of heavy ions. 143 refs., 18 figs., 8 tabs
Detection of fission fragments and alpha particles using the solid trace detector CR-39
International Nuclear Information System (INIS)
Santos, R.C.
1988-01-01
The technique of detecting charged particles using the solid track detector CR-39 is employed to establish some characteristics of fission fragments and alpha particles emitted from a Cf-252 source. Results are presented and discussed on the following aspects i) distribution of the track diameters; ii) variations on the track diameters to the chemical attack; iii) variations of the chemical attack velocity with respect to concentration and temperature. iv) activation energy of the developping process; v) induction time; vi) critical angle and efficiency on track developping. (A.C.A.S.) [pt
Hiryanov, R. M.; Karpov, A. V.; Adeev, G. D.
2008-08-01
The anisotropy of angular distributions of fission fragments and the average multiplicity of prescission neutrons were calculated within a stochastic approach to fission dynamics on the basis of three-dimensional Langevin equations. This approach was combined with a Monte Carlo algorithm for the degree of freedom K (projection of the total angular momentum I onto the fission axis). The relaxation time τ K in the coordinate K was considered as a free parameter of the model; it was estimated on the basis of a fit to experimental data on the anisotropy of angular distributions. Specifically, the relaxation time τ K was estimated at 2 × 10-21 s for the compound nuclei 224Th and 225Pa and at 4 × 10-21 s for the heavier nuclei 248Cf, 254Fm, and 264Rf. The potential energy was calculated on the basis of the liquid-drop model with allowance for finiteness of the range of nuclear forces and for the diffuseness of the nuclear surface. A modified one-body viscosity mechanism featuring a coefficient k s that takes into account the reduction of the contribution from the wall formula was used to describe collective-energy dissipation. The coefficient k s was also treated as a free parameter and was estimated at 0.5 on the basis of a fit to experimental data on the average prescission multiplicity of neutrons.
International Nuclear Information System (INIS)
Goennenwein, F.; Boersig, B.
1991-01-01
Cold fission is defined to be the limiting case of nuclear fission where virtually all of the available energy is converted into the total kinetic energy of the fragments. The fragments have, therefore, to be born in or at least close to their respective ground states. Starting from the viewpoint that cold fission corresponds to most compact scission configurations, energy constraints have been exploited to calculate minimum tip distances between the two nascent fragments in binary fission. Crucial input parameters to this tip model of cold fission are the ground-state deformations of fragment nuclei. It is shown that the minimum tip distances being compatible with energy conservation vary strongly with both the mass and charge fragmentation of the fission prone nucleus. The tip distances refer to nuclei with equivalent sharp surfaces. In keeping with the size of the surface width of leptodermous nuclei, only configurations where the tip distances are smaller than a few fm may be considered as valid scission configurations. From a comparison with experimental data on cold fission this critical tip distance appears to be 3.0 fm for the model parameters chosen. Whenever the model calculation yields tip distances being smaller than the critical value, a necessary condition for attaining cold fission is considered to be fulfilled. It is shown that this criterion allows to understand in fair agreement with experiment which mass fragmentations are susceptible to lead to cold fission and which fragment-charge divisions are the most favored in each isobaric mass chain. Being based merely on energy arguments, the model cannot aim at predicting fragment yields in cold fission. However, the tip model proposed appears well suited to delineate the phase space where cold fission phenomena may come into sight. (orig.)
Final report: Accelerated beta decay for disposal of fission fragment wastes
International Nuclear Information System (INIS)
Reiss, Howard R.
2000-01-01
The fundamental theory of the interaction of intense, low-frequency electromagnetic fields with certain radioactive nuclei has been fully formulated. The nuclei are of the type that exists in high-level radioactive wastes that are end products of the production of energy from nuclear fission. The basic physical mechanisms that underlie the coupling of the applied field to the nucleus have been identified. Both the basic theory and numerical predictions that stem from it support the conclusion that high-level radioactive wastes can be disposed of by substantially accelerating the rate of radioactive decay. Some old experiments on the acceleration of this type of radioactivity, with results that were not understood at the time, have been re-examined. Their interpretation is now clear, and the experiments are found to be in agreement with the theory
International Nuclear Information System (INIS)
Carlsson, Magnus
2004-06-01
Areas ranging from nuclear structure models to accelerator-driven systems benefit from improved neutron-induced fission data in the intermediate energy region. In this Master's degree thesis, the fragment angular distribution from fission of 238 U, induced by 21-MeV neutrons, has been analysed from an experiment performed with the Medley/DIFFICILE setup at the The Svedberg Laboratory in Uppsala. The data have been corrected for low energy neutrons in the beam. The results agree with other experiments, as well as with model calculations. The data should be a starting point for further analysis with a goal to deduce the fission cross-section of 238 U
Zhang, Huanqiao; Liu, Zuhua; Xu, Jincheng; Qian, Xing; Qiao, Yu; Lin, Chengjian; Xu, Kan
1994-02-01
Using the fragment folding angle technique, the complete fusion-fission is separated from the transfer-induced fission. The cross sections of the complete fusion-fission and fragment angular distributions for the systems of 16O+232Th, 19F+232Th, and 16O+238U at near- and sub-barrier energies have been measured. The observed fission excitation functions can be fitted very well by coupled-channels theory calculations. It is found that fragments from complete fusion fission show a smaller angular anisotropy as compared with our previous measurements in which the transfer-induced fission component was not excluded. However, the measured angular anisotropies of complete fusion-fission are obviously greater than expected on the basis of theoretical models in which the effect of prefission neutron emission was taken into account. Also the peak in the variation of the anisotropy with incident energy still persists in the 19F+232Th case.
International Nuclear Information System (INIS)
Fernandez-Dominguez, B.
2003-03-01
The aim of this work is the study of the fission fragments produced in the spallation reaction 208 Pb + p at 500 AMeV. The fission fragments from Z=23 up to Z=59 have been detected and identified by using the inverse kinematics technique with the high-resolution spectrometer FRS. The production cross sections and the recoil velocities of 430 nuclei have been measured. The measured data have been compared with previous data. The isotopic distributions show a high precision. However, the absolute value of the fission cross section is higher than expected. From the experimental data the characteristics of the average fissioning system have been reconstructed (Z fis , A fis , E* fis ). In addition, the number of post-fission neutrons emitted from the fission fragments, v post , has been determined by using a new method. The experimental data have been compared to the two-steps models describing the spallation reaction. The impact of the model parameters on the observables has been analysed and the reasons Leading to the observed differences between the codes are also presented. This analyse shows a good agreement with the INCL4+ABLA code. (author)
Directory of Open Access Journals (Sweden)
Porta A.
2016-01-01
Full Text Available Beta decay of fission products is at the origin of decay heat and antineutrino emission in nuclear reactors. Decay heat represents about 7% of the reactor power during operation and strongly impacts reactor safety. Reactor antineutrino detection is used in several fundamental neutrino physics experiments and it can also be used for reactor monitoring and non-proliferation purposes. 92,93Rb are two fission products of importance in reactor antineutrino spectra and decay heat, but their β-decay properties are not well known. New measurements of 92,93Rb β-decay properties have been performed at the IGISOL facility (Jyväskylä, Finland using Total Absorption Spectroscopy (TAS. TAS is complementary to techniques based on Germanium detectors. It implies the use of a calorimeter to measure the total gamma intensity de-exciting each level in the daughter nucleus providing a direct measurement of the beta feeding. In these proceedings we present preliminary results for 93Rb, our measured beta feedings for 92Rb and we show the impact of these results on reactor antineutrino spectra and decay heat calculations.
Multiplicity and energy of neutrons from {sup 233}U(n{sub th},f) fission fragments
Energy Technology Data Exchange (ETDEWEB)
Nishio, Katsuhisa; Kimura, Itsuro; Nakagome, Yoshihiro [Kyoto Univ. (Japan)
1998-03-01
The correlation between fission fragments and prompt neutrons from the reaction {sup 233}U(n{sub th},f) was measured with improved accuracy. The results determined the neutron multiplicity and emission energy as a function of fragment mass and total kinetic energy. The average energy as a function of fragment mass followed a nearly symmetric distribution centered about the equal mass-split and formed a remarkable contrast with the saw-tooth distribution of the average neutron multiplicity. The neutron multiplicity from the specified fragment decreases linearly with total kinetic energy, and the slope of multiplicity with kinetic energy had the minimum value at about 130 u. The level density parameter versus mass determined from the neutron data showed a saw-tooth structure with the pronounced minimum at about 128 and generally followed the formula by Gilbert and Cameron, suggesting that the neutron emission process was very much affected by the shell-effect of the fission fragment. (author)
Energy Technology Data Exchange (ETDEWEB)
Heinrich, S
2006-07-01
Nucleus fission process is a very complex phenomenon and, even nowadays, no realistic models describing the overall process are available. The work presented here deals with a theoretical description of fission fragments distributions in mass, charge, energy and deformation. We have reconsidered and updated the B.D. Wilking Scission Point model. Our purpose was to test if this statistic model applied at the scission point and by introducing new results of modern microscopic calculations allows to describe quantitatively the fission fragments distributions. We calculate the surface energy available at the scission point as a function of the fragments deformations. This surface is obtained from a Hartree Fock Bogoliubov microscopic calculation which guarantee a realistic description of the potential dependence on the deformation for each fragment. The statistic balance is described by the level densities of the fragment. We have tried to avoid as much as possible the input of empirical parameters in the model. Our only parameter, the distance between each fragment at the scission point, is discussed by comparison with scission configuration obtained from full dynamical microscopic calculations. Also, the comparison between our results and experimental data is very satisfying and allow us to discuss the success and limitations of our approach. We finally proposed ideas to improve the model, in particular by applying dynamical corrections. (author)
Energy Technology Data Exchange (ETDEWEB)
Paul, Debasish; Ghose, Debasis; Sastri, R.C. E-mail: res@juphys.ernet.in
2001-04-01
During the course of investigations on the radon and stable gas migration around the hot spring zone at Bakreswar, Birbhum in India, it was noticed that CR-39 plastic detectors used for the detection of radon revealed tracks with much bigger diameters than usual for alpha particle tracks. Exposed CR-39 detectors etched adapting sequential etching technique confirmed the presence of bigger diameter tracks similar in nature to the tracks formed by spontaneous fission fragments. This paper presents the results of these observations along with the histogram plots of the track number versus track diameter that indicate an asymmetric distribution as was seen for mass distribution of spontaneous fission fragments.
International Nuclear Information System (INIS)
Moraes, O.M.G. de.
1984-01-01
A systematic study about the registration characteristics of synthetic fused quartz 'Suprasil I' use as a detector of fission fragments under high flux of reactor neutrons and the effects of irradiation on it was performed. Fission fragments of 252 Cf, gamma radiation doses of of 60 Co up to 150 MGy, and integrated neutrons fluxes up to 10 20 n/cm 2 were used. A model to explain the effects on track registration and development characteristics of 'Suprasil I' irradiated on reactors were proposed, based on the obtained results for efficiency an for annealing. (C.G.C.) [pt
Dynamic effect analysis in 240Pu fission at low energy
International Nuclear Information System (INIS)
Patin, Y.; Lachkar, J.; Sigaud, J.
1975-01-01
The variations of kinetic and excitation energies and fragment masses have been analyzed as a function of the fissioning nucleus excitation energy. Most interest has been taken in the fission of 240 Pu where many experimental data have been reported. The results tend, in the whole, to illustrate the existence of two modes of fission; the first one is superfluid, the other is strongly damped in the last stage of the fission process [fr
Gönnenwein, F.; Bunakov, V.; Dorvaux, O.; Gagarski, A.; Guseva, I.; Hanappe, F.; Kadmensky, S.; von Kalben, J.; Khlebnikov, S.; Kinnard, V.; Kopatch, Yu.; Mutterer, M.; Nesvizhevsky, V.; Petrov, G.; Prokhorova, E.; Rubchenya, V.; Sillanpää, M.; Simpson, G.; Sokolov, V.; Soldner, T.; Stuttgé, L.; Tiourine, G.; Trzaska, W.; Tsekhanovich, I.; Wagemans, C.; Wollersheim, H.-J.; Zavarukhina, T.; Zimmer, O.
2008-04-01
Three novel experiments in spontaneous and thermal neutron induced fission all with a bearing on angular momentum in fission are reviewed. In the first experiment it was observed that, in the reaction 235U(n, f) with incident polarized cold neutrons, the nucleus undergoing scission is rotating. This was inferred from the shift in angular distributions of ternary particles being dependent on the orientation of neutron spin. In the second study the properties of the angular momentum of spherical fission fragments was investigated. Current theories trace the spin of fragments to their deformations allowing for collective rotational vibrations at scission. However, in particular the spherical 132Te isotope exhibits a large spin at variance with theory. Exploiting the specific properties of cold deformed fission it could be proven that, for 132Te, single particle excitations instead of collective modes are responsible for the large spin observed. In a third project a pilot study was exploring the possibility to search for an evaporation of neutrons from fragments being anisotropic in their own cm-system. Due to fragment spin this anisotropy is claimed since decades to exist. It was so far never observed. A scheme has been devised and tested were triple coincidences between a fragment and two neutrons are evaluated in a way to bring the cm-anisotropy into the foreground while getting rid of the kinematical anisotropy in the lab-system due to evaporation from moving fragments. The test was run for spontaneous fission of 252Cf.
Concept Assessment of a Fission Fragment Rocket Engine (FFRE) Propelled Spacecraft
Werka, Robert; Clark, Rod; Sheldon, Rob; Percy, Tom
2012-01-01
The March, 2012 issue of Aerospace America stated that ?the near-to-medium prospects for applying advanced propulsion to create a new era of space exploration are not very good. In the current world, we operate to the Moon by climbing aboard a Carnival Cruise Lines vessel (Saturn 5), sail from the harbor (liftoff) shedding whole decks of the ship (staging) along the way and, having reached the return leg of the journey, sink the ship (burnout) and return home in a lifeboat (Apollo capsule). Clearly this is an illogical way to travel, but forced on Explorers by today's propulsion technology. However, the article neglected to consider the one propulsion technology, using today's physical principles that offer continuous, substantial thrust at a theoretical specific impulse of 1,000,000 sec. This engine unequivocally can create a new era of space exploration that changes the way spacecraft operate. Today's space Explorers could travel in Cruise Liner fashion using the technology not considered by Aerospace America, the novel Dusty Plasma Fission Fragment Rocket Engine (FFRE). This NIAC study addresses the FFRE as well as its impact on Exploration Spacecraft design and operation. It uses common physics of the relativistic speed of fission fragments to produce thrust. It radiatively cools the fissioning dusty core and magnetically controls the fragments direction to practically implement previously patented, but unworkable designs. The spacecraft hosting this engine is no more complex nor more massive than the International Space Station (ISS) and would employ the successful ISS technology for assembly and check-out. The elements can be lifted in "chunks" by a Heavy Lift Launcher. This Exploration Spacecraft would require the resupply of small amounts of nuclear fuel for each journey and would be an in-space asset for decades just as any Cruise Liner on Earth. This study has synthesized versions of the FFRE, integrated one concept onto a host spacecraft designed for
Directory of Open Access Journals (Sweden)
R. Léguillon
2016-10-01
Full Text Available It is shown that the multinucleon transfer reactions is a powerful tool to study fission of exotic neutron-rich actinide nuclei, which cannot be accessed by particle-capture or heavy-ion fusion reactions. In this work, multinucleon transfer channels of the 18O+232Th reaction are used to study fission of fourteen nuclei 231,232,233,234Th, 232,233,234,235,236Pa, and 234,235,236,237,238U. Identification of fissioning nuclei and of their excitation energy is performed on an event-by-event basis, through the measurement of outgoing ejectile particle in coincidence with fission fragments. Fission fragment mass distributions are measured for each transfer channel, in selected bins of excitation energy. In particular, the mass distributions of 231,234Th and 234,235,236Pa are measured for the first time. Predominantly asymmetric fission is observed at low excitation energies for all studied cases, with a gradual increase of the symmetric mode towards higher excitation energy. The experimental distributions are found to be in general agreement with predictions of the fluctuation–dissipation model.
Energy Technology Data Exchange (ETDEWEB)
Kleinrath, Verena [NIFFTE collaboration, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
2015-07-01
Fission fragment angular distributions can lend insights into fission barrier shapes and level densities at the scission point, both important for fission theory development. Fragment emission anisotropies are also valuable for precision cross section ratio measurements, if the distributions are different for the two isotopes used in the ratio. Available angular data is sparse for {sup 235}U and even more so for {sup 239}Pu, especially at neutron energies above 5 MeV. The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) time projection chamber, which enables precise tracking of charged particles, can be used to study angular distributions and emission anisotropies of fission fragments in neutron-induced fission. In-beam data collected at the Los Alamos Neutron Science Center with a {sup 235}U/{sup 239}Pu target during the 2014 run-cycle will provide angular distributions as a function of incident neutron energy for these isotopes. (LA-UR-1426972). (authors)
A theoretical framework is described, allowing to determine the fission barrier height using the observed cross sections of fission induced by the (d,p)-transfer with accuracy, which is not achievable in another type of low-energy fission of neutron-deficient nuclei, the $\\beta$-delayed fission. The primary goal is to directly determine the fission barrier height of proton-rich fissile nuclei, preferably using the radio-active beams of isotopes of odd elements, and thus confirm or exclude the low values of fission barrier heights, typically extracted using statistical calculations in the compound nucleus reactions at higher excitation energies. Calculated fission cross sections in transfer reactions of the radioactive beams show sufficient sensitivity to fission barrier height. In the probable case that fission rates will be high enough, mass asymmetry of fission fragments can be determined. Results will be relevant for nuclear astrophysics and for production of super-heavy nuclei. Transfer induced fission of...
International Nuclear Information System (INIS)
Kasilov, V.I.; Lapin, N.N.
1981-01-01
An enhancement is detected under the angle of 90 deg in the fission fragment yield from 238 U nuclei produced by photons emitted by high-energy electrons passing through a silicon monocrystal. The results enable one to select the most optimal conditions to obtain maximal yields of nuclear particles [ru
Energy Technology Data Exchange (ETDEWEB)
Montoya, M.; Rojas, J. [Instituto Peruano de Energia Nuclear, Av. Canada 1470, Lima 41 (Peru); Saettone, E. [Facultad de Ciencias, Universidad Nacional de lngenieria, Av. Tupac Amaru 210, Apartado 31-139, Lima (Peru)
2007-07-01
The mass and kinetic energy distribution of nuclear fragments from the thermal neutron-induced fission of {sup 235}U have been studied using a Monte Carlo simulation. Besides reproducing the pronounced broadening on the standard deviation of the final fragment kinetic energy distribution ({sigma}{sub e}(m)) around the mass number m = 109, our simulation also produces a second broadening around m = 125 that is in agreement with the experimental data obtained by Belhafaf et al. These results are a consequence of the characteristics of the neutron emission, the variation in the primary fragment mean kinetic energy, and the yield as a function of the mass. (Author)
Leal Cidoncha, Esther
2017-01-01
This thesis work focuses on the measurement of the fission fragment angular distribution (FFAD) and fission cross section of the reactions 234U(n,f) y 235U(n,f) using PPAC (Parallel Plate Avalanche Counter) detectors at the n_ TOF facility (CERN). This faci lity is characterised by a wide neutron spectrum from thermal to 1 GeV with a high energy resolution. This measurement has been performed using the tilted configuration of targets and detectors, which unlike the perpendicular configuration...
Measurement of the fission fragment angular distribution for 232Th(n,f) at the CERN n-TOF facility
Tarrío, D; Audouin, L; Duran, I; Leong, L S; Paradela, C; Altstadt, S; Andrzejewski, J; Barbagallo, M; Bécares, V; Bečvář, F; Belloni, F; Berthoumieux, E; Billowes, J; Boccone, V; Bosnar, D; Brugger, M; Calviani, M; Calviño, F; Cano-Ott, D; Carrapiço, C; Cerutti, F; Chiaveri, E; Chin, M; Colonna, N; Cortés, G; Cortés-Giraldo, M A; Diakaki, M; Domingo-Pardo, C; Dzysiuk, N; Eleftheriadis, C; Ferrari, A; Fraval, K; Ganesan, S; Garcìa, A R; Giubrone, G; Gómez-Hornillos, M B; Gonçalves, I F; González-Romero, E; Griesmayer, E; Guerrero, C; Gunsing, F; Gurusamy, P; Jenkins, D G; Jericha, E; Kadi, Y; Käppeler, F; Karadimos, D; Koehler, P; Kokkoris, M; Krtička, M; Kroll, J; Langer, C; Lederer, C; Leeb, H; Losito, R; Manousos, A; Marganiec, J; Martìnez, T; Massimi, C; Mastinu, P F; Mastromarco, M; Meaze, M; Mendoza, E; Mengoni, A; Milazzo, P M; Mingrone, F; Mirea, M; Mondalaers, W; Pavlik, A; Perkowski, J; Plompen, A; Praena, J; Quesada, J M; Rauscher, T; Reifarth, R; Riego, A; Roman, F; Rubbia, C; Sarmento, R; Schillebeeckx, P; Schmidt, S; Tagliente, G; Tain, J L; Tsinganis, A; Valenta, S; Vannini, G; Variale, V; Vaz, P; Ventura, A; Versaci, R; Vermeulen, M J; Vlachoudis, V; Vlastou, R; Wallner, A; Ware, T; Weigand, M; Weiß, C; Wright, T J; Žugec, P
2012-01-01
A fission reaction chamber was designed to measure the angular distribution of the fragments emitted in neutron-induced fission reactions at n_TOF. Up to ten Parallel Plate Avalanche Counters can be included and kept at controlled low-pressure gas. Counters are tilted 45º with respect to the neutron beam direction and up to nine targets can be interleaved in between. A first measurement of the 232Th(n,f) was recently done and preliminary experimental results demonstrating the suitability of the setup are presented here.
Soheyli, Saeed; Khanlari, Marzieh Varasteh
2016-04-01
Effects of the various neutron emission energy spectra, as well as the influence of the angular momentum of pre-scission neutrons on theoretical predictions of fission fragment angular anisotropies for several heavy-ion induced fission systems are considered. Although theoretical calculations of angular anisotropy are very sensitive to neutron emission correction, the effects of the different values of kinetic energy of emitted neutrons derived from the various neutron emission energy spectra before reaching to the saddle point on the prediction of fission fragment angular distribution by the model are not significant and can be neglected, since these effects on angular anisotropies of fission fragments for a wide range of fissility parameters and excitation energies of compound nuclei are not more than 10%. Furthermore, the theoretical prediction of fission fragment angular anisotropy is not sensitive to the angular momentum of emitted neutrons.
(d,p)-transfer induced fission of heavy radioactive beams
Veselsky, Martin
2012-01-01
(d,p)-transfer induced fission is proposed as a tool to study low energy fission of exotic heavy nuclei. Primary goal is to directly determine the fission barrier height of proton-rich fissile nuclei, preferably using the radio-active beams of isotopes of odd elements, and thus confirm or exclude the low values of fission barrier heights, typically extracted using statistical calculations in the compound nucleus reactions at higher excitation energies. Calculated fission cross sections in transfer reactions of the radioactive beams show sufficient sensitivity to fission barrier height. In the probable case that fission rates will be high enough, mass asymmetry of fission fragments can be determined. Results will be relevant for nuclear astrophysics and for production of super-heavy nuclei. Transfer induced fission offers a possibility for systematic study the low energy fission of heavy exotic nuclei at the ISOLDE.
Zhang, Huanqiao; Liu, Zuhua; Xu, Jincheng; Qian, Xing; Chen, Shaolin; Lu, Lixing
1992-06-01
Fission fragment angular distributions have been measured for the reactions 11B+238U, 12C+237Np at near- and sub-barrier energies, and 16O+238U at 90 MeV. The complete fusion-fission and transfer-fission were separated as components in the whole energy region in this experiment. The influence of prescission neutron emission on fragment anisotropies has been considered. This effect leads to increase of the anisotropies when compared with the results obtained under the assumption of first chance fission. However, the anomalous anisotropies still persist.
Influence of nuclear dissipation on fission dynamics of the excited ...
Indian Academy of Sciences (India)
2016-05-31
May 31, 2016 ... where r is the dimensionless fission coordinate and is defined as the ratio of half of the distance between the centre of mass of the future fission fragments and the radius of the compound nucleus, p is the conjugate momentum, m is the inertia parameter, η is the friction coefficient, R(t) is a random force with ...
Influence of nuclear dissipation on fission dynamics of the excited ...
Indian Academy of Sciences (India)
A stochastic approach to fission dynamics based on two-dimensional Langevin equations was applied to calculate the anisotropy of the fission fragments angular distribution and average pre-scission neutron multiplicities for the compound nucleus 248Cf formed in the $${16}$O+$^{232}$Th reactions. Postsaddle nuclear ...
Energy Technology Data Exchange (ETDEWEB)
Carlsson, Magnus
2004-06-01
Areas ranging from nuclear structure models to accelerator-driven systems benefit from improved neutron-induced fission data in the intermediate energy region. In this Master's degree thesis, the fragment angular distribution from fission of {sup 238}U, induced by 21-MeV neutrons, has been analysed from an experiment performed with the Medley/DIFFICILE setup at the The Svedberg Laboratory in Uppsala. The data have been corrected for low energy neutrons in the beam. The results agree with other experiments, as well as with model calculations. The data should be a starting point for further analysis with a goal to deduce the fission cross-section of {sup 238}U.
Fission fragment yield distribution in the heavy-mass region from the 239Pu (nth,f ) reaction
Gupta, Y. K.; Biswas, D. C.; Serot, O.; Bernard, D.; Litaize, O.; Julien-Laferrière, S.; Chebboubi, A.; Kessedjian, G.; Sage, C.; Blanc, A.; Faust, H.; Köster, U.; Ebran, A.; Mathieu, L.; Letourneau, A.; Materna, T.; Panebianco, S.
2017-07-01
The fission fragment yield distribution has been measured in the 239Pu(nth,f ) reaction in the mass region of A =126 to 150 using the Lohengrin recoil-mass spectrometer. Three independent experimental campaigns were performed, allowing a significant reduction of the uncertainties compared to evaluated nuclear data libraries. The long-standing discrepancy of around 10% for the relative yield of A =134 reported in JEF-2.2 and JEFF-3.1.1 data libraries is finally solved. Moreover, the measured mass distribution in thermal neutron-induced fission does not show any significant dip around the shell closure (A =136 ) as seen in heavy-ion fission data of 208Pb(18O, f ) and 238U(18O, f ) reactions. Lastly, comparisons between our experimental data and the predictions from Monte Carlo codes (gef and fifrelin) are presented and discussed.
Continuous in-situ measurements of fission fragment irradiation induced void swelling in Ni
International Nuclear Information System (INIS)
Lefakis, H.
1980-01-01
A novel simulation technique has been developed to study the early stages of irradiation induced void formation in metals. The technique makes use of fission fragment irradiation produced by doping with 235 U and irradiating in a thermal neutron flux under highly controlled irradiation-environmental conditions. Employment of a computer and a high temperature radiation resistant LVDT resulted in a high volumetric sensitivity and the production of continuous, in-situ void swelling data for bulk specimens. Results for Ni, used as a test-metal served to corroborate the technique in a number of ways including comparisons with (a) reactor data, (b) direct post-irradiation specimen length measurements and (c) TEM examinations of irradiated samples. The technique has several unique advantages and, in conjunction with other conventional methods, it offers the possibility of detailed evaluation of void nucleation and growth theories. In view of the present results no definitive answer may be given on the issue of the incubation period while checks with two theoretical models have yielded an order-of-magnitude agreement
Pahlavani, M. R.; Naderi, D.; Mirfathi, S. M.
The three-dimensional Langevin equation (LE) and Transition State Model (TSM) are applied to calculate prescission neutron multiplicity and anisotropy of fission fragment angular distribution for 16O+181Ta and 16O+208Pb systems. Dynamical calculations were carried out considering one-body dissipation. Theoretical results of pre-scission neutron multiplicity and anisotropy have been compared with experimental data for given systems. Calculations show that the results of anisotropy based on dynamical approach are in better agreement with the experimental data as compared with the TSM (in saddle point).
Change over from compound nuclear fission to quasi-fission
International Nuclear Information System (INIS)
Ghosh, T. K.; Banerjee, K.; Bhattacharya, C.; Bhattacharya, S.; Kundu, S.; Meena, J. K.; Mukherjee, G.; Mukhopadhyay, S.; Rana, T. K.; Golda, K. S.; Bhattacharya, P.
2010-01-01
Fission fragment mass distribution has been measured from the decay of 246 Bk nucleus populating via two entrance channels with slight difference in mass asymmetries but belonging on either side of the Businaro Gallone mass asymmetry parameter. Both the target nuclei were deformed. Near the Coulomb barrier, at similar excitation energies the width of the fission fragment mass distribution was found to be drastically different for the 14 N+ 232 Th reaction compared to the 11 B+ 235 U reaction. The entrance channel mass asymmetry was found to affect the fusion process sharply. (authors)
Change over from compound nuclear fission to quasi-fission
Directory of Open Access Journals (Sweden)
Bhattacharya P.
2010-03-01
Full Text Available Fission fragment mass distribution has been measured in two reactions to populate compound nucleus 246Bk. Both the target nuclei were deformed. However, entrance channel mass asymmetry of the two systems was on the either side of the Businaro Gallone mass asymmetry parameter. Near the Coulomb barrier, at similar excitation energies, the width of the fission fragment mass distribution was found to be significantly different for the 14N+232Th reaction compared to the 11B+235U reaction. The entrance channel mass asymmetry was found to play a significant role in deciding the fusion process.
A new fission-fragment detector to complement the CACTUS-SiRi setup at the Oslo Cyclotron Laboratory
Energy Technology Data Exchange (ETDEWEB)
Tornyi, T.G., E-mail: tornyitom@atomki.hu [Department of Physics, University of Oslo (Norway); Institute of Nuclear Research of the Hungarian Academy of Sciences (MTA Atomki), Debrecen (Hungary); Görgen, A.; Guttormsen, M.; Larsen, A.C.; Siem, S. [Department of Physics, University of Oslo (Norway); Krasznahorkay, A. [Institute of Nuclear Research of the Hungarian Academy of Sciences (MTA Atomki), Debrecen (Hungary); Csige, L. [Institute of Nuclear Research of the Hungarian Academy of Sciences (MTA Atomki), Debrecen (Hungary); Max-Planck-Institute for Quantum Optics, D-85748 Garching (Germany)
2014-02-21
An array of Parallel Plate Avalanche Counters (PPAC) for the detection of heavy ions has been developed. The new device, NIFF (Nuclear Instrument for Fission Fragments), consists of four individual detectors and covers 60% of 2π. It was designed to be used in conjunction with the SiRi array of ΔE−E silicon telescopes for light charged particles and fits into the CACTUS array of 28 large-volume NaI scintillation detectors at the Oslo Cyclotron Laboratory. The low-pressure gas-filled PPACs are sensitive for the detection of fission fragments, but are insensitive to scattered beam particles of light ions or light-ion ejectiles. The PPAC detectors of NIFF have good time resolution and can be used either to select or to veto fission events in in-beam experiments with light-ion beams and actinide targets. The powerful combination of SiRi, CACTUS, and NIFF provides new research opportunities for the study of nuclear structure and nuclear reactions in the actinide region. The new setup is particularly well suited to study the competition of fission and γ decay as a function of excitation energy.
International Nuclear Information System (INIS)
Singh, Arvind; Santra, S.; Topkar, Anita; Mahata, K.; Mukhopadhyay, P.K.; Chatterjee, A.; Pithawa, C.K.; Rath, P.K.; Parihari, A.
2012-01-01
Thin ΔE detectors with thickness of a few microns are used for study of nuclear reactions involving heavy charged particles such as fission fragments. Such detectors are difficult to fabricate using conventional silicon etching techniques and are also difficult to handle as they are very fragile. To overcome these problems, a novel detector in which the E and ΔE detectors are integrated on the same silicon chip has been developed. The performance of the first prototype has been presented earlier. In this paper, the performance of the second prototype with light charged particles (measured in 7 Li + 12 C reaction) and fission fragments (measured in 19 F + 209 Bi reaction) has been presented. The results presented in this paper demonstrate that the integrated detector has performance as good as that of a silicon detector telescope which incorporates commercially available physically separate E and ΔE detectors
Fusion-fission study at IUAC: Recent results
Pullanhiotan, Sugathan
2016-10-01
Several properties observed in heavy ion induced fission led to the conclusion that fission is not always originated from fully equilibrated compound nucleus. Soon after the collision of two nuclei, it forms a di-nuclear system than can fission before a compound nucleus is formed. This process termed quasi-fission is a major hurdle to the formation of heavier elements by fusion. Fission originated before complete equilibration showed anomalously large angular anisotropy and mass distribution wider than what is expected from compound nucleus fission. The standard statistical model fails to predict the outcome of quasi-fission and currently no dynamical model is fully developed to predict all the features of quasi-fission. Though much progress has been made in recent times, a full understanding of the fission dynamics is still missing. Experiments identifying the influence of entrance channel parameters on dynamics of fusion-fission showed contrasting results. At IUAC accelerator facility many experiments have been performed to make a systematic study of fission dynamics using mass distribution, angular distribution and neutron multiplicity measurements in mass region around A ∼ 200. Recent measurement on mass distribution of fission fragment from reaction 19 F +206,208 Pb around fusion barrier energy showed the influence of multi-mode fission in enhancing the mass variance at low excitation energy. In this talk I will present some of these results.
Ryzhov, I. V.; Onegin, M. S.; Tutin, G. A.; Blomgren, J.; Olsson, N.; Prokofiev, A. V.; Renberg, P.-U.
2005-10-01
Fission fragment angular distributions have been measured for the 232Th( n,f) and 238U( n,f) reactions in the neutron energy range 20-100 MeV. The fragment angular anisotropy for 232Th was found to be systematically larger than that for 238U. The obtained results have been analyzed in the framework of the statistical saddle-point model combined with pre-equilibrium and Hauser-Feshbach calculations of partial fission cross sections. The calculations have revealed that fission following multiple neutron emission takes place in both reactions, resulting in a considerable contribution of high chances to the total fission fragment angular anisotropy. This gives grounds to expect that the observed difference is mainly due to nuclei fissioning at the end of the neutron evaporation chain.
International Nuclear Information System (INIS)
Simutkin, V.D.
2008-01-01
Conceptual analysis of accelerator-driven systems assumes extensive use of nuclear data on neutron-induced reactions at intermediate energies. In particular, information about the fission fragment yields from the 238 U(n,f) and 232 Th(n,f) reactions is of particular interest at neutron energies from 10 to 200 MeV. However, there is a lack of such data for both 238 U and 232 Th. Up to now, the intermediate energy measurements have been performed for 238 U only, and there are no data for the 232 Th(n,f) reaction. The aim of the work is to provide such data. Fission fragment mass distributions for the 232 Th(n,f) and 238 U(n,f) reactions have been measured for the incident neutron energies 32.8 MeV, 45.3 MeV and 59.9 MeV. The experiments have been performed at the neutron beam facility of the Universite Catholique de Louvain, Belgium. A multi-section Frisch-gridded ionization chamber has been used as a fission fragment detector. The data obtained have been interpreted in terms of the multimodal random neck-rupture model (MMRNRM). (authors)
International Nuclear Information System (INIS)
Montoya, M.; Rojas, J.; Saetone, E.
2007-01-01
The mass and kinetic energy distribution of nuclear fragments from thermal neutron-induced fission of 235 U(n th ,f) have been studied using a Monte-Carlo simulation. Besides reproducing the pronounced broadening in the standard deviation of the kinetic energy at the final fragment mass number around m = 109, our simulation also produces a second broadening around m = 125. These results are in good agreement with the experimental data obtained by Belhafaf et al. and other results on yield of mass. We conclude that the obtained results are a consequence of the characteristics of the neutron emission, the sharp variation in the primary fragment kinetic energy and mass yield curves. We show that because neutron emission is hazardous to make any conclusion on primary quantities distribution of fragments from experimental results on final quantities distributions
Mass and Charge Distribution in Low-Energy Fission
International Nuclear Information System (INIS)
Wahl, A.C.
1965-01-01
The mass and charge distributions for thermal-neutron fission of U 235 are discussed in considerable detail and compared with the corresponding distributions in other low-energy fission processes. Points discussed in connection with the mass distributions for binary fission include the positions of the peaks, valley and fine structure in a mass yield curve with respect to filled nuclear shells and the changes in the positions that occur with changing fissioning nucleus and excitation energy. The mass distribution from ternary fission is discussed also. For both binary and ternary fission comments are made concerning the mass distributions of primary fragments (before neutron evaporation) and of fission products (after neutron evaporation). Charge distribution is discussed in terms of charge dispersion among fission products with the same mass number and the variation with mass number of Zp, the ''most probable charge'' (non-integral) for a given mass number. Although direct information about charge distribution is limited to fission products, estimates are presented of charge distribution for primary fission fragments. Knowledge and estimates of mass and charge distribution for a fission process allow estimation of primary yields of all fission products or fragments. Although many estimated primary yields are quite uncertain mainly because of lack of knowledge of charge distribution, especially for fission products formed in low yield; some estimates of primary yields are presented to illustrate the need for and possible practicality of further experimentation. Fission processes other than thermal-neutron fission of U 235 that are discussed include thermal-neutron fission of U 233 and Pu 239 , spontaneous fission of Pu 240 and Cf 252 , 14-MeV neutron fission of U 235 and U 238 , 11-MeV proton fission of Ra 226 and 22-MeV deuteron fission of Bi 209 . (author) [fr
Fission dynamics of the compound nucleus Fr formed in heavy-ion ...
Indian Academy of Sciences (India)
The phenomenological friction turned out to be smaller than the standard wall formula value for .... in the frame of the Werner–Wheeler approach and the nuclear temperature is defined as T = √ ... z-axis and zN is the position of the neck plane. The surface of a nucleus of mass number A with elongation c can be defined as.
International Nuclear Information System (INIS)
Montoya, M.; Rojas, J.; Lobato, I.
2010-01-01
The average of fragment kinetic energy (E-bar sign*) and the multiplicity of prompt neutrons (ν(bar sign)) as a function of fragment mass (m*), as well as the fragment mass yield (Y(m*)) from thermal neutron-induced fission of 239 Pu have been measured by Tsuchiya et al.. In that work the mass and kinetic energy are calculated from the measured kinetic energy of one fragment and the difference of time of flight of the two complementary fragments. However they do not present their results about the standard deviation σ E *(m*). In this work we have made a numerical simulation of that experiment which reproduces its results, assuming an initial distribution of the primary fragment kinetic energy (E(A)) with a constant value of the standard deviation as function of fragment mass (σ E (A)). As a result of the simulation we obtain the dependence σ E *(m*) which presents an enhancement between m* = 92 and m* = 110, and a peak at m* = 121.
Studies of fission fragment yields via high-resolution γ-ray spectroscopy
Directory of Open Access Journals (Sweden)
Wilson J.N.
2018-01-01
Full Text Available Precise spectroscopic information on the fast neutron induced fission of the 238U(n,f reaction was recently gained using a new technique which involved coupling of the Miniball high resolution y-ray spectrometer and the LICORNE directional neutron source. The experiment allowed measurement of the isotopic fission yields for around 40 even-even nuclei at an incident neutron energy of around 2 MeV where yield data are very sparse. In addition spectroscopic information on very neutron-rich fission products was obtained. Results were compared to models, both the JEFF-3.1.1 data base and the GEF code, and large discrepancies for the S1 fission mode in the Sn/Mo isotope pair were discovered. This suggests that current models are overestimating the role played by spherical shell effects in fast neutron induced fission. In late 2017 and 2018 the nu-ball hybrid spectrometer will be constructed at the IPN Orsay to perform further experimental investigations with directional neutrons coupled to a powerful hybrid Ge/LaBr3 detector array. This will open up new possibilities for measurements of fission yields for fast-neutron-induced fission using the spectroscopic technique and will be complimentary to other methods being developed.
Dynamic effects in neutron induced fission of 230Th and 232Th
International Nuclear Information System (INIS)
Trochon, J.; Frehaut, J.; Pranal, Y.; Simon, G.; Boldeman, J.W.
1982-09-01
The fission fragment characteristics of the two thorium isotopes 230 Th and 232 Th have been measured in an attempt to study the evolution of the fissioning nucleus from saddle point to scission. The partial fission channel at the saddle point have been deduced from a fission fragment angular distribution and fission cross section analysis. Changes with energy in the average number of prompt neutron (νsub(p)) emitted per fission and the total fragment kinetic energy (TKE) have been observed in the fission threshold region. A rather good fit of νsub(p) and TKE values has been obtained on the basis of a correlation of these quantities and the partial fission channel ratios. This leads to expect for these isotopes a passage from saddle point to scission sufficiently rapid for the coupling between collective and intrinsic excitation to be very weak [fr
International Nuclear Information System (INIS)
Harrison, K.G.; Hancock, I.B.; Holt, P.D.; Wylie, J.W.
1977-10-01
A new type of personal neutron dosimeter, in which neutron-induced fissions in a thin 237 Np foil are detected by a polycarbonate track-detector, is under development at Harwell for use in a nuclear-fuel reprocessing plant. As part of the development programme, an experimental dosimeter, etching facility and spark counter have been used to study the spark-counting method for counting fission-fragment tracks in polycarbonate. Emphasis has been placed on developing operating procedures for the counter consistent with good overall reproducibility. Existing methods for the optimizing and testing of spark counters is briefly reviewed and a practical operational testing procedure is devised. The optimized system is found to be relatively foolproof in operation and gives good results in unskilled use as well as under carefully-controlled laboratory conditions. (author)
Fission Fragment Angular Distributions in the $^{234}$U(n,f) and $^{236}$U(n,f) reactions
We propose to measure the fission fragment angular distribution (FFAD) of the $^{234}$U(n,f) and $^{236}$U (n,f) reactions with the PPAC detection setup used in previous n_TOF-14 experiment. This experiment would take advantage of the high resolution of the n_TOF facility to investigate the FFAD behaviour in the pronounced vibrational resonances that have been observed between 0.1 and 2 MeV for the thorium cycle isotopes. In addition, the angular distribution of these isotopes will be measured for the first time beyond 14 MeV. Furthermore, the experiment will also provide the fission cross section with reduced statistical uncertainty, extending the $^{236}$U(n,f) data up to 1 GeV
Nuclear fission studies: from LOHENGRIN to FIPPS
International Nuclear Information System (INIS)
Chebboubi, Abdelaziz
2015-01-01
Nuclear fission consists in splitting a nucleus, in general an actinide, into smaller nuclei. Despite nuclear fission was discovered in 1939 by Hahn and Strassman, fission models cannot predict the fission observables with an acceptable accuracy for nuclear fuel cycle studies for instance. Improvement of fission models is an important issue for the knowledge of the process itself and for the applications. To reduce uncertainties of the nuclear data used in a nuclear reactor simulation, a validation of the models hypothesis is mandatory. In this work, two features of the nuclear fission were investigated in order to test the resistance of the theories. One aspect is the study of the symmetric fission fragments through the measurement of their yield and kinetic energy distribution. The other aspect is the study of the fission fragment angular momentum.Two techniques are available to assess the angular momentum of a fission fragment. The first one is to look at the properties of the prompt gamma. The new spectrometer FIPPS (Fission Product Prompt gamma-ray Spectrometer), is currently under development at the ILL and will combine a fission filter with a large array of gamma and neutron detectors in order to respond to these issues. The first part of this work is dedicated to the study of the properties of a Gas Filled Magnet (GFM) which is the type of fission filter considered for the FIPPS project.The second part of this work deals with the measurement of isomeric yields and evaluations of the angular momentum distribution of fission fragments. The study of the spherical nucleus 132 Sn shed the light on the current limits of fission models. Finally, the last part of this work is about the measurement of the yields and kinetic energy distributions of symmetric fission fragments. Since models predict the existence of fission modes, the symmetry region is a suitable choice to investigate this kind of prediction. In parallel with all these studies, an emphasis on the
Duke, D. L.; Tovesson, F.; Brys, T.; Geppert-Kleinrath, V.; Hambsch, F.-J.; Laptev, A.; Meharchand, R.; Manning, B.; Mayorov, D.; Meierbachtol, K.; Mosby, S.; Perdue, B.; Richman, D.; Shields, D.; Vidali, M.
2017-09-01
The average Total Kinetic Energy (TKE) release and fission-fragment yields in neutron-induced fission of 235U and 238U was measured using a Frisch-gridded ionization chamber. These observables are important nuclear data quantites that are relevant to applications and for informing the next generation of fission models. The measurements were performed a the Los Alamos Neutron Science Center and cover En = 200 keV - 30 MeV. The double-energy (2E) method was used to determine the fission-fragment yields and two methods of correcting for prompt-neutron emission were explored. The results of this study are correlated mass and TKE data.
Directory of Open Access Journals (Sweden)
Duke D.L.
2017-01-01
Full Text Available The average Total Kinetic Energy (TKE release and fission-fragment yields in neutron-induced fission of 235U and 238U was measured using a Frisch-gridded ionization chamber. These observables are important nuclear data quantites that are relevant to applications and for informing the next generation of fission models. The measurements were performed a the Los Alamos Neutron Science Center and cover En = 200 keV – 30 MeV. The double-energy (2E method was used to determine the fission-fragment yields and two methods of correcting for prompt-neutron emission were explored. The results of this study are correlated mass and TKE data.
Energy Technology Data Exchange (ETDEWEB)
Ibrahim, F
2005-06-15
The study of nuclei far from stability is constitutive of the history of nuclear physics at its very beginning and has been making considerable great strides since then. The study of these nuclei give the opportunity to reach new information on the nuclear structure and thus to measure the solidity of our knowledge on nuclear matter and its validity when it is pushed to its limits. The reaction selected for the production of exotic nuclei in the framework of the PARRNe program is the fission of uranium 238. The nuclei produced have an intermediate mass and are very rich in neutrons. The technique to recover them in order to accelerate them is the thick target method called also the Isol technique. The installation of the ancient Lep injector at the Tandem line in Orsay (IPN) is expected to increase by a factor 100 the production rate of exotic nuclei in the PARRNe program, it is the Alto project. The work presented here concerns studies carried out at the Lohengrin spectrometer installed at the ILL in Grenoble, and at the Tandem installation in Orsay. This document is divided into 4 parts: 1) in flight techniques at Lohengrin, 2) the Isol technique, 3) magic numbers in the domain N=50, and 4) the Alto project.
Collective spectra along the fission barrier
Directory of Open Access Journals (Sweden)
Pigni M. T.
2012-12-01
Full Text Available Discrete and continuous spectra of fissioning nuclei at the humps of fission barriers (Bohr transition states and in the intermediate wells (superdeformed and hyperdeformed states play a key role in the calculation of fission cross sections. A theoretical evaluation of the collective parts of the spectra is possible within the framework of the dinuclear system model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two–cluster configurations in a dynamical way, permitting exchange of upper–shell nucleons between clusters. The impact of theoretical spectra on neutron–induced fission cross sections and, in combination with an improved version of the scission–point model, on angular distribution of fission fragments is evaluated for plutonium isotopes of interest to nuclear energy applications.
Collective spectra along the fission barrier
Shneidman, T. M.; Andreev, A. V.; Pigni, M. T.; Massimi, C.; Vannini, G.; Ventura, A.
2012-12-01
Discrete and continuous spectra of fissioning nuclei at the humps of fission barriers (Bohr transition states) and in the intermediate wells (superdeformed and hyperdeformed states) play a key role in the calculation of fission cross sections. A theoretical evaluation of the collective parts of the spectra is possible within the framework of the dinuclear system model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two-cluster configurations in a dynamical way, permitting exchange of upper-shell nucleons between clusters. The impact of theoretical spectra on neutron-induced fission cross sections and, in combination with an improved version of the scission-point model, on angular distribution of fission fragments is evaluated for plutonium isotopes of interest to nuclear energy applications.
Fission-fragment attachment to aerosols and their transport through capillary tubes
International Nuclear Information System (INIS)
Novick, V.J.; Alvarez, J.L.; Greenwood, R.C.
1981-01-01
The transport of radioactive aerosols was studied using equipment, collectively called the Helium jet, that has been constructed to provide basic nuclear physics data on fission product nuclides. The transport of the fission products in the system depends on their attachment to aerosol particles. The system consists of 1) a tube furnace which generates aerosols by the sublimation or evaporation of source material, 2) a helium stream used to transport the aerosols, 3) a 25 m settling tube to eliminate the larger aerosols and smaller aerosols that would deposit in the capillary, 4) a Californium-252 self-fissioning source of fission product nuclides, and 5) a small capillary to carry the radioactive aerosols from the hot cell to the laboratory. Different source materials were aerosolized but NaCl is generally used because it yielded the highest transport efficiencies through the capillary. Particle size measurments were made with NaCl aerosols by using a cascade impactor, an optical light scattering device, and the capillary itself as a diffusion battery by performing radiation measurements and/or electrical conductivity measurements. Both radioactive and nonradioactive aerosols were measured in order to investigate the possibility of a preferential size range for fission product attachment. The measured size distributions were then used to calculate attachment coefficients and finally an attachment time
Paul, D; Sastri, R C; Ghose, D
1999-01-01
The SSNTD has come a long way in its application for the study of nuclear phenomena. Spontaneous fission of transuranic elements is one such phenomena wherein use of SSNTD offers easy registration of the signature of the fission fragments. The object of the present study is to explore whether any one of the track parameters such as the diameter can be used to estimate the atomic mass ratios of the spontaneous fission fragments. The spontaneous fission data from sup 2 sup 5 sup 2 Cf recorded almost at the end of one and four half-life periods for alpha decay are analysed, taking a plot of the number of tracks versus the track diameter. From these plots it is seen that initially, when significant alpha activity of sup 2 sup 5 sup 2 Cf persists, the fission fragments appear to cluster into two predominant groups as indicated by two peaks. The ratio of the diameters at these peak positions appear to be related to the ratio of average mass numbers of the light and heavy groups of fission fragments. However, absenc...
Vorobyev, A. S.; Gagarski, A. M.; Shcherbakov, O. A.; Vaishnene, L. A.; Barabanov, A. L.
2016-09-01
New results of the neutron-induced fission experiments carried out at the neutron time-of-flight spectrometer GNEIS of the PNPI are given. Angular distributions of fission fragments from the neutron-induced fission of 233U and 209Bi nuclei have been measured in the energy range 1-200 MeV using position sensitive multiwire proportional counters as fission fragment detector. The recent improvements of the measurement and data processing procedures are described. The data on anisotropy of fission fragments deduced from the measured angular distributions are presented in comparison with the experimental data of other authors.
International Nuclear Information System (INIS)
Katsuma, Masahiko; Kobayashi, Hiroshi; Sawada, Tetsuo; Sasa, Toshinobu
2005-01-01
The 1 GeV proton induced reaction on 208 Pb targets is analyzed by using the percolation model combined with the Atchison fission model. The fragment mass distribution and the isotopic production cross sections obtained from our model are compared with the experimental data. The trends of the fragment mass distribution for the 1 GeV proton induced reaction can be reproduced by our calculation in some degree. The order of magnitude for the calculated isotopic production cross sections at the calculated peak positions is similar to that of the experimental peak values. The calculated peak positions of the isotopic production cross sections are shifted to the heavier region than those of the experimental data. (author)
New type of asymmetric fission in proton-rich nuclei
Andreyev, A N; Huyse, M; Van Duppen, P; Antalic, S; Barzakh, A; Bree, N; Cocolios, T E; Comas, V F; Diriken, J; Fedorov, D; Fedosseev, V; Franchoo, S; Heredia, J A; Ivanov, O; Koster, U; Marsh, B A; Nishio, K; Page, R D; Patronis, N; Seliverstov, M; Tsekhanovich, I; Van den Bergh, P; Van De Walle, J; Venhart, M; Vermote, S; Veselsky, M; Wagemans, C; Ichikawa, T; Iwamoto, A; Moller, P; Sierk, A J
2010-01-01
A very exotic process of ${\\beta}$-delayed fission of $^{180}$Tl is studied in detail by using resonant laser ionization with subsequent mass separation at ISOLDE (CERN). In contrast to common expectations, the fission-fragment mass distribution of the post-${\\beta}$-decay daughter nucleus $^{180}$Hg (N/Z=1.25) is asymmetric. This asymmetry is more surprising since a mass-symmetric split of this extremely neutron-deficient nucleus would lead to two $^{90}$Zr fragments, with magic N=50 and semimagic Z=40. This is a new type of asymmetric fission, not caused by large shell effects related to fragment magic proton and neutron numbers, as observed in the actinide region. The newly measured branching ratio for $\\beta$-delayed fission of $^{180}$Tl is 3.6(7)×10$^{-3}$%, approximately 2 orders of magnitude larger than in an earlier study.
Pereira, J; Wlazlo, W; Benlliure, J; Casarejos, E; Armbruster, P; Bernas, M; Enqvist, T; Legrain, R; Leray, S; Rejmund, F; Mustapha, B; Schmidt, K.-H; Stéphan, C; Taïeb, J; Tassan-Got, L; Volant, C; Boudard, A; Czajkowski, S; 10.1103/PhysRevC.75.014602
2007-01-01
Fission fragments of 1A GeV 238U nuclei interacting with a deuterium target have been investigatedwith the Fragment Separator (FRS) at GSI (Darmstadt) by measuring their isotopicproduction cross-sections and recoil velocities. The results, along with those obtained recently forspallation-evaporation fragments, provide a comprehensive analysis of the spallation nuclear productionsin the reaction 238U(1A GeV)+d. Details about experiment performance, data reductionand results will be presented.
More detailed study of fission dynamics in fusion-fission reactions within a stochastic approach
Nadtochy, P. N.; Adeev, G. D.; Karpov, A. V.
2002-06-01
A stochastic approach based on three-dimensional Langevin equations was applied to a more detailed study of fission dynamics in fusion-fission reactions. The dynamical model has been developed and extended to investigate fission characteristics of light fissioning nuclei at low excitation energies. The energy dependences of an anisotropy of the fission fragment angular distribution, an evaporation residue cross section, a fission cross section, mean prescission neutron, and giant dipole γ multiplicities have been analyzed for the 16O+208Pb-induced fission of 224Th. Also, dependence of the prescission neutron multiplicity on the fragment mass asymmetry and total kinetic energy have been calculated. Analysis of the results shows that not only characteristics of the mass-energy distribution of fission fragments, but also the mass and kinetic-energy dependence of the prescission neutron multiplicity, the angular anisotropy, and fission probability can be reproduced using a modified one-body mechanism for nuclear dissipation with a reduction coefficient of the contribution from a wall formula ks=0.25 0.5 for compound nuclei 172Yb, 205Fr, 215Fr, and 224Th. Decrease of the prescission neutron multiplicities with fragment mass asymmetry is due to a decrease of the fission time. The results obtained show that prescission neutrons are evaporated predominantly from the nearly spherical compound nucleus at an early stage of fission process before the saddle point is reached. From performed analysis one can conclude that coordinate-independent reduction coefficient ks is not compatible with simultaneous description of the main fission characteristics for heavy fissioning systems 256Fm and 252Fm.
Choice of initial conditions in dynamical calculations of distributions of nuclear fission fragments
International Nuclear Information System (INIS)
Kosenko, G.I.
1993-01-01
The distribution function in the coordinates and momenta for a fissioning system traversing a barrier is determined in terms of Langevin fluctuation-dissipation dynamics. It is shown that this distribution is best described by the Kramers distribution. The equilibrium distribution can be used as the initial condition, provided that the system is in the overdamping regime. 28 refs., 5 figs., 3 tabs
Miss Piggy, a californium-252 fission fragment source as a generator of short-lived radionuclides
Düllmann, Ch. E.; Eichler, B.; Eichler, R.; Gäggeler, H. W.; Jost, D. T.; Kindler, U.; Piguet, D.; Soverna, S.; Thörle, P.; Trautmann, N.; Türler, A.
2003-10-01
Carrier-free short-lived nuclides are employed in many different fields of modern nuclear chemistry. The two main production strategies are either thermal neutron-induced fission of 235U or 239Pu at nuclear reactors or spallation neutron sources or charged particle-induced nuclear reactions at accelerator facilities. An alternative method is to use a spontaneously fissioning nuclide. A facility applying this technique ("Miss Piggy") was built at the University of Berne (Switzerland). Californium-252 ( 252Cf), which has a 3% fission branch and a half-life of 2.645 a, is used for the production of short-lived fission products that are stopped in an adjacent recoil chamber. Short-lived nuclides are transported out of the recoil chamber using the well-known gas-jet technique. Over 100 nuclides have been identified so far and used in different applications. Since such a device does not require any large facility and is easy to operate it serves well the needs of typical university laboratories.
Nolen, J A; Hassanein, A; Novick, V J; Plotkin, P; Specht, J R
2003-01-01
The driver linac of the proposed rare isotope accelerator facility is designed to deliver 2x10 sup 1 sup 3 uranium ions per second at 400 MeV/u on target for radionuclide production via the fission and fragmentation mechanisms. The ion optics of the large acceptance, high-resolution fragment separators that follow the production target require primary beam spot widths of 1 mm. To cope with the resulting high power densities, windowless liquid lithium targets are being developed. The present designs build on existing experience with liquid lithium and liquid sodium systems that have been used for fusion and fission applications. However, no completely windowless systems have been developed or tested to date. For the beam power indicated above (400 kW), the flow requirements are up to about 20 m/s and 10 l/s linear and volume flow rates, respectively. The required target thickness is 1-1.5 g/cm sup 2 (2-3 cm lithium thickness). At this time a prototype windowless system with a lithium thickness of 1-2 cm is und...
Physics and chemistry of fission
International Nuclear Information System (INIS)
1979-01-01
models, the nucleus is imagined to be a very small drop of liquid; the theorist then devises many schemes that lead to its splitting into two smaller drops. It is surprising how many detailed features theorists can predict, based on such simple models, and how well these predictions have been confirmed by experiments. The symposium summarized the progress in this field, and indicated how many intricate details can be introduced into a simple liquid drop model to give better agreement with experimental results. Step by step, a picture is emerging and being continuously improved, coming closer and closer to the truth. However, the liquid drop model has several competitors of which the most prominent is the shell model. This model assumes that the constituents of the nucleus are sorted into well defined energy levels, or shells; the distribution of protons and neutrons in these shells, and their movements from one shell to another, can provide an explanation for many experimentally observed facts New theoretical results drawn from these models were reported at the symposium, together with some efforts to combine different theoretical concepts, thereby trying to create a unified picture of nuclear fission. The nucleus is too small for the scientist to be able to observe directly what is happening inside it. There is really only one way for an experimenter to study a process in a nucleus, he must measure the energies of the particles coming out of it. In the case of fission, these 'messengers' can be the fission fragments, i.e. nuclei of elements that are being created from the splitting atom, but they can also be the neutrons or gamma rays which emerge during and after the fission process. Several sessions in the symposium were devoted to reports of such studies. With the help of sophisticated electronics systems, or complicated radiochemical methods, experimenters have measured the energies of fission fragments, neutrons, gamma and X-rays, and other particles emerging from
International Nuclear Information System (INIS)
Takagi, F.
1985-01-01
Constituent quark model for projectile fragmentation in hadron-hadron and hadron-nucleus collisions is reformulated by taking into account (i) quark-antiquark annihilation, (ii) quark flavour content in the central region and (iii) quark shadowing effect. The model provides a satisfactory explanation of strong long range correlations observed in the projectile fragmentation regions of inclusive reaction πsup(+-)+p-> or anti p + anything, πsup(+-)+A->p,anti p,Λ or anti Λ + anything p+p->Λ or Δ ++ + anything and anti p+p->anti Λ or Δ ++ + anything. (orig.)
Fireball on 6 July 2002 over the Mediterranean Sea is a fragment of the comet's nucleus
Churyumov, Klim; Kruchinenko, Vitaly G.; Churyumova, Tetyana; Mozgova, Alyona
2015-03-01
Today has been known for a considerable number of cases, the explosion of large meteoroids in Earth's atmosphere. This is confirmed by the data of registrations of fireballs by devices and the results of measurements in the atmosphere of bright light flashes by photodiodes Corporation ``Sandia Laboratories", which were installed on geostationary satellites of the United States, and also by data of measurements of acoustic-gravitational waves from the thermal explosions of meteoroids [ReVelle D.O. Historical detection of atmospheric impacts by large bolides using acoustic-gravity waves, Near-Earth Objects, Ed. Remo J. Annals of the New York Academy of Sciences 882, 284-302, 1997]. The work [Brown P., Spalding R.E., ReVelle D.O. et al. The flux of small near-Earth objects colliding with the Earth, Nature 420, 314-316, 2002.] shows the results of processing the observations of flashes of large meteoroids in Earth's atmosphere, obtained with the help of geostationary satellites of the United States. Over 8.5 years (from February 1994 to September 2002) 300 such events were registered. On July 6, 2002 r over the Mediterranean Sea a bright fireball was registered. The energy of the meteoroid explosion that caused the phenomenon of the car, was 26 kilotons of TNT [Brown et al., 2002]. We believe that this energy refers to the height of the full bracking of the meteoroid. At a speed of 20.3 km/s adopted by the authors, body mass at this height is 5 × 108 g, and when entering the Earth's atmosphere, it was about 7 × 108 g. Based on the obtained values of the mass, we conclude that the exploded meteoroid, causing a phenomenon of the fireball was a fragment of the comet nucleus. In processing the density of the body were taken 1 g/cm 3 and the initial velocity (~30 km/s).
Energy Technology Data Exchange (ETDEWEB)
Zhao, Yunmei [Institute of Mechanics and Computational Engineering, Department of Aeronautics and Astronautics, Fudan University, Shanghai 200433 (China); Ding, Shurong, E-mail: dsr1971@163.com [Institute of Mechanics and Computational Engineering, Department of Aeronautics and Astronautics, Fudan University, Shanghai 200433 (China); Zhang, Xunchao; Wang, Canglong; Yang, Lei [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China)
2016-12-15
The micro-scale finite element models for CERCER pellets with different-sized fuel particles are developed. With consideration of a grain-scale mechanistic irradiation swelling model in the fuel particles and the irradiation creep in the matrix, numerical simulations are performed to explore the effects of the particle size and the fission-fragment-enhanced irradiation creep on the thermo-mechanical behavior of CERCER pellets. The enhanced irradiation creep effect is applied in the 10 μm-thick fission fragment damage matrix layer surrounding the fuel particles. The obtained results indicate that (1) lower maximum temperature occurs in the cases with smaller-sized particles, and the effects of particle size on the mechanical behavior in pellets are intricate; (2) the first principal stress and radial axial stress remain compressive in the fission fragment damage layer at higher burnup, thus the mechanism of radial cracking found in the experiment can be better explained. - Highlights: • A grain-scale gas swelling model considering the development of recrystallization and resolution is adopted for particles. • The influence of fission-gas-induced porosity is considered in the constitutive relations for particles. • A simulation method is developed for the multi-scale thermo-mechanical behavior. • The effects of fuel particle size and fission-fragment-enhanced irradiation creep are investigated in pellets.
Prompt muon-induced fission: A probe for nuclear friction in large-amplitude collective motion
International Nuclear Information System (INIS)
Oberacker, V.E.; Umar, A.S.; Wells, J.C.; Strayer, M.R.; Maruhn, J.A.; Reinhard, P.G.
1998-01-01
Excited muonic atoms in the actinide region may induce prompt fission by inverse internal conversion, i.e. the excitation energy of the muonic atom is transferred to the nucleus. The authors solve the time dependent Dirac equation for the muonic spinor wave function in the Coulomb field of the fissioning nucleus on a 3-dimensional lattice and demonstrate that the muon attachment probability to the light fission fragment is a measure of the nuclear energy dissipation between the outer fission barrier and the scission point
Electron microscopic investigations of tracks of Cf252 fission fragments in quartz glass
International Nuclear Information System (INIS)
Werba, T.; Granzer, F.
1977-01-01
Using a single stage carbon replication technique, track pits of Cf 252 -fission products in quartz glass could be revealed by transmission electron microscopy with a high degree of resolution. From the shape of the track pits the angles of incidence of the nuclear particles were determined down to extremely small angles. In addition track pits on the fracture surface of irradiated quartz glass samples have been investigated by scanning electron microscopy. (author)
Energy Technology Data Exchange (ETDEWEB)
Montoya, M.; Rojas, J. [Instituto Peruano de Energia Nuclear, Av. Canada 1470, Lima 41 (Peru); Lobato, I. [Facultad de Ciencias, Universidad Nacional de Ingenieria, Av. Tupac Amaru 210, Apartado Postal 31-139, Lima (Peru)]. e-mail: mmontoya@ipen.gob.pe
2008-07-01
The standard deviation of the final kinetic energy distribution ({sigma}{sub e}) as a function of mass of final fragments (m) from low energy fission of {sup 234}U, measured with the Lohengrin spectrometer by Belhafaf et al., presents a peak around m = 109 and another around m = 122. The authors attribute the first peak to the evaporation of a large number of neutrons around the corresponding mass number, i.e. there is no peak on the standard deviation of the primary kinetic energy distribution ({sigma}{sub E}) as a function of primary fragment mass (A). The second peak is attributed to a real peak on {sigma}{sub E}(A). However, theoretical calculations related to primary distributions made by H.R. Faust and Z. Bao do not suggest any peak on {sigma}{sub E}(A). In order to clarify this apparent controversy, we have made a numerical experiment in which the masses and the kinetic energy of final fragments are calculated, assuming an initial distribution of the kinetic energy without structures on the standard deviation as function of fragment mass. As a result we obtain a pronounced peak on {sigma}{sub e} (m) curve around m = 109, a depletion from m = 121 to m = 129, and an small peak around m = 122, which is not as great as that measured by Belhafaf et al. Our simulation also reproduces the experimental results on the yield of the final mass Y(m), the average number of emitted neutrons as a function of the provisional mass (calculated from the values of the final kinetic energy of the complementary fragments) and the average value of fragment kinetic energy as a function of the final mass. From our results we conclude that there are no peaks on the {sigma}{sub E} (A) curve, and the observed peaks on {sigma}{sub e} (m) are due to the emitted neutron multiplicity and the variation of the average fragment kinetic energy as a function of primary fragment mass. (Author)
Tambovtsev, D. I.
2008-04-01
Statistical distributions of the coefficients measured for the angular distribution of fragments originating from the fission of 235U oriented nuclei that was induced by resonance neutrons obtained by using booster targets at the electron accelerator in Harwell and at a pulsed reactor in Dubna were approximated by a curve that was calculated under the assumption of a normal distribution of partial-wave fission amplitudes. A cutoff from below at a level of one-half of the average partial-wave width was introduced in this distribution. The calculation was performed with allowance for the K = 0, 1 and 2 channels for J = 3 and the K = 1 and 2 channels for J =4. The contributions of the K channels to the total probability were in the ratio 0.15 : 0.53 : 0.32 for J = 3 and in the ratio 0.625 : 0.375 for J = 4. A strong suppression of the K = 0 channel in the J = 3 spin subsystem in contrast to the situation observed in photofission can be interpreted as an indication of the possible partial conservation of K in resonance states formed from the entrance channel, which features only maximum values of K equal to J and J - 1.
Energy Technology Data Exchange (ETDEWEB)
Léguillon, R. [Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan); Nishio, K., E-mail: nishio.katsuhisa@jaea.go.jp [Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan); Hirose, K.; Makii, H.; Nishinaka, I.; Orlandi, R.; Tsukada, K. [Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan); Smallcombe, J. [Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan); TRIUMF, Vancouver, British Columbia V6T 2A3 (Canada); Chiba, S. [Laboratory for Advanced Nuclear Energy, Institute for Innovative Research, Tokyo Institute of Technology, N1-9, 2-12-1 Ookayama, Meguro, Tokyo 152-8550 (Japan); Aritomo, Y. [Faculty of Science and Engineering, Kindai University, Higashi-Osaka, 577-8502 (Japan); Ohtsuki, T. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennangun, Osaka 590-0494 (Japan); Tatsuzawa, R.; Takaki, N. [Graduate School of Engineering, Tokyo City University, Tokyo 158-8557 (Japan); Tamura, N.; Goto, S. [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan); Tsekhanovich, I. [University of Bordeaux, 351 Cours de la Libration, 33405 Talence Cedex (France); Petrache, C.M. [Centre des Sciences Nucléaire et des Sciences de la Matière, Université Paris-Saclay, CNRS/IN2P3, 91406 Orsay (France); Andreyev, A.N. [Department of Physics, University of York, Heslington, York, YO10 5DD (United Kingdom); Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan)
2016-10-10
It is shown that the multinucleon transfer reactions is a powerful tool to study fission of exotic neutron-rich actinide nuclei, which cannot be accessed by particle-capture or heavy-ion fusion reactions. In this work, multinucleon transfer channels of the {sup 18}O + {sup 232}Th reaction are used to study fission of fourteen nuclei {sup 231,232,233,234}Th, {sup 232,233,234,235,236}Pa, and {sup 234,235,236,237,238}U. Identification of fissioning nuclei and of their excitation energy is performed on an event-by-event basis, through the measurement of outgoing ejectile particle in coincidence with fission fragments. Fission fragment mass distributions are measured for each transfer channel, in selected bins of excitation energy. In particular, the mass distributions of {sup 231,234}Th and {sup 234,235,236}Pa are measured for the first time. Predominantly asymmetric fission is observed at low excitation energies for all studied cases, with a gradual increase of the symmetric mode towards higher excitation energy. The experimental distributions are found to be in general agreement with predictions of the fluctuation–dissipation model.
Directory of Open Access Journals (Sweden)
K. Nishio
2015-09-01
Full Text Available Mass distributions of fission fragments from the compound nuclei 180Hg and 190Hg formed in fusion reactions 36Ar + 144Sm and 36Ar + 154Sm, respectively, were measured at initial excitation energies of E⁎(Hg180=33–66 MeV and E⁎(Hg190=48–71 MeV. In the fission of 180Hg, the mass spectra were well reproduced by assuming only an asymmetric-mass division, with most probable light and heavy fragment masses A¯L/A¯H=79/101. The mass asymmetry for 180Hg agrees well with that obtained in the low-energy β+/EC-delayed fission of 180Tl, from our earlier ISOLDE(CERN experiment. Fission of 190Hg is found to proceed in a similar way, delivering the mass asymmetry of A¯L/A¯H=83/107, throughout the measured excitation energy range. The persistence as a function of excitation energy of the mass-asymmetric fission for both proton-rich Hg isotopes gives strong evidence for the survival of microscopic effects up to effective excitation energies of compound nuclei as high as 40 MeV. This behavior is different from fission of actinide nuclei and heavier mercury isotope 198Hg.
International Nuclear Information System (INIS)
Thackray, M.
1976-01-01
A method is described for producing a photographic image on a normally non-photo-receptive surface comprising the steps of 1) toning the photograph with substances which combine with or replace the silver grains so that the photograph emits either spontaneously or indirectly fission fragments or alpha particles in amounts related to the distribution of the silver grains in the photograph, 2) placing the toned photograph contiguous with the surface on which the image is to be reproduced, for sufficient time for the emissions from the photograph to reproduce the image as a radiation-damage image on the surface, the damage areas having a close positional relationship to the silver grains in the original photograph. (author)
Energy Technology Data Exchange (ETDEWEB)
Pant, L.M.; Saxena, A.; Choudhury, R.K.; Nadkarni, D.M. [Nuclear Physics Division, Bhabha Atomic Research Centre, Bombay 400085 (India)
1996-10-01
Measurements were carried out on mass, energy correlations of fission fragments for the systems of {sup 11}B+{sup 237}Np at {ital E}{sub lab}=76 MeV and {sup 16}O+{sup 209}Bi at {ital E}{sub lab}=100 MeV at forward and perpendicular angles of emission with respect to the beam direction. The fragment anisotropy averaged over all fragment masses matches well for both the systems with the standard saddle point statistical model calculations. Variation of the angular anisotropy and total kinetic energy of fragments were studied as a function of the mass of the fragment pair. For the {sup 11}B+{sup 237}Np system, the fragment anisotropy is seen to be nearly independent of the fragment mass, whereas for the {sup 16}O+{sup 209}Bi system, the anisotropy is seen to decrease with increasing fragment mass asymmetry. The results are discussed on the basis of the statistical model of fragment angular distributions and mass division in the fission process. {copyright} {ital 1996 The American Physical Society.}
ISOLDE experiment explores new territory in nuclear fission
CERN Bulletin
2011-01-01
An international collaboration led by the University of Leuven, Belgium, exploiting ISOLDE’s radioactive beams, has recently discovered an unexpected new type of asymmetric nuclear fission, which challenges current theories. The surprising result opens the way for new nuclear structure models and further theories to elucidate the question. Resonance Ionization Laser Ion Source (RILIS) in action at ISOLDE. RILIS was instrumental in providing the pure beam necessary for the successful nuclear fission experiment. In nuclear fission, the nucleus splits into two fragments (daughter nuclei), releasing a huge amount of energy. Nuclear fission is exploited in power plants to produce energy. From the fundamental research point of view, fission is not yet fully understood decades after its discovery and its properties can still surprise nuclear physicists. The way the process occurs can tell us a lot about the internal structure of the nucleus and the interactions taking place inside the com...
International Nuclear Information System (INIS)
Tamagno, Pierre
2015-01-01
The work presented here aims to improve models used in the fission cross section evaluation. The results give insights for a significant breakthrough in this field and yielded large extensions of the evaluation code CONRAD. Partial cross sections are inherently strongly correlated together as of the competition of the related reactions must yield the total cross section. Therefore improving fission cross section benefits to all partial cross sections. A sound framework for the simulation of competitive reactions had to be settled in order to further investigate on the fission reaction; this was implemented using the TALYS reference code as guideline. After ensuring consistency and consistency of the framework, focus was made on fission. Perspective resulting from the use of macroscopic-microscopic models such as the FRDM and FRLDM were analyzed; these models have been implemented and validated on experimental data and benchmarks. To comply with evaluation requirements in terms of computation time, several specific numerical methods have been used and parts of the program were written to run on GPU. These macroscopic-microscopic models yield potential energy surfaces that can be used to extract a one-dimensional fission barrier. This latter can then be used to obtained fission transmission coefficients that can be used in a Hauser-Feshbach model. This method has been finally tested for the calculation of the average fission cross section for 239 Pu(n,f). (author) [fr
Fragment angular momentum and descent dynamics in {sup 252}Cf spontaneous fission
Energy Technology Data Exchange (ETDEWEB)
Popeko, G.S.; Ter-Akopian, G.M.; Daniel, A.V.; Oganessian, Y.T.; Kliman, J. [JINR, Dubna, 141980 (Russia); Ter-Akopian, G.M.; Hamilton, J.H.; Kormicki, J.; Daniel, A.V.; Ramayya, A.V.; Hwang, J.K.; Sandulescu, A.; Florescu, A.; Greiner, W. [Vanderbilt University, Nashville, Tennessee 37235 (United States); Ter-Akopian, G.M.; Daniel, A.V.; Florescu, A.; Greiner, W. [JIHIR, Oak Ridge, Tennessee 37831 (United States); Greiner, W. [ITP, J.W. Goethe University, D-60054, Frankfurt am Main (Germany); Florescu, A. [IAP, Bucharest, P.O. Box MG-6, (Russian Federation); Kliman, J.; Morhac, M. [IP SASc, Bratislava (Slovak Republic); Rasmussen, J.O. [LBNL, Berkeley, California 94720 (United States); Stoyer, M.A. [LLNL, Livermore , California 94550 (United States); Cole, J.D. [INEL, Idaho Falls, Idaho 83415 (United States)
1998-12-01
Fragment angular momenta as a function of neutron multiplicity were extracted for the first time for the Mo-Ba and Zr-Ce charge splits of {sup 252}Cf by studying prompt coincident {gamma}-rays. The obtained primary fragment angular momenta do not continuously rise with the increase in the number of neutrons evaporated. In frame of the scission point bending oscillation model such regularity is explained due the decrease of the bending temperature. Adiabatic bending oscillations (T=0) are obtained at large ({nu}{sub tot}{gt}5) and small ({nu}{sub tot}=0) scission point elongation. These oscillations are excited to the temperature of 2{endash}3 MeV for the most probable scission configurations indicating a weak coupling between collective and internal degrees of freedom. A strong coupling between the collective bending and dipole oscillations was found. {copyright} {ital 1998 American Institute of Physics.}
Sequential character of low-energy ternary and quaternary nuclear fission
Kadmensky, S. G.; Bulychev, A. O.
2016-09-01
An analysis of low-energy true ternary (quaternary) nuclear fission leads to the conclusion that these fission modes have a sequential two-step (three-step) character such that the emission of a third particle (third and fourth particles) and the separation of fission fragments occur at distinctly different instants, in contrast to the simultaneous emergence of all fission products in the case of onestep ternary (quaternary) fission. This conclusion relies on the following arguments. First, the emission of a third particle (third and fourth particles) from a fissile nucleus is due to a nonevaporative mechanism associated with a nonadiabatic character of the collective deformation motion of this nucleus at the stages preceding its scission. Second, the axial symmetry of the deformed fissile compound nucleus and the direction of its symmetry axis both remain unchanged at all stages of ternary (quaternary) fission. This circumstancemakes it possible to explain themechanism of the appearance of observed anisotropies and T — odd asymmeries in the angular distributions of products of ternary (quaternary) nuclear fission. Third, the T —odd asymmetry discovered experimentally in ternary nuclear fission induced by cold polarized neutrons obeys the T —invariance condition only in the case of a sequential two-step (three-step) character of true ternary (quaternary) nuclear fission. At the same time, this asymmetry is not a T —invariant quantity in the case of the simultaneous emission of products of true ternary (quaternary) nuclear fission from the fissile compound nucleus.
Energy Technology Data Exchange (ETDEWEB)
Fernandez-Dominguez, B
2003-03-01
The aim of this work is the study of the fission fragments produced in the spallation reaction {sup 208}Pb + p at 500 AMeV. The fission fragments from Z=23 up to Z=59 have been detected and identified by using the inverse kinematics technique with the high-resolution spectrometer FRS. The production cross sections and the recoil velocities of 430 nuclei have been measured. The measured data have been compared with previous data. The isotopic distributions show a high precision. However, the absolute value of the fission cross section is higher than expected. From the experimental data the characteristics of the average fissioning system have been reconstructed (Z{sub fis}, A{sub fis}, E*{sub fis}). In addition, the number of post-fission neutrons emitted from the fission fragments, v{sub post}, has been determined by using a new method. The experimental data have been compared to the two-steps models describing the spallation reaction. The impact of the model parameters on the observables has been analysed and the reasons Leading to the observed differences between the codes are also presented. This analyse shows a good agreement with the INCL4+ABLA code. (author)
Energy Technology Data Exchange (ETDEWEB)
Reiter, Moritz Pascal
2015-07-01
High precision experiments and decay spectroscopy of exotic nuclei are of great interest for nuclear structure and nuclear astro-physics. They allow for studies of the nuclear structure far from stability, test of fundamental interactions and symmetries and give important input for the understanding of the nuclear synthesis in the universe. In the context of this work a second generation stopping cell for the low energy branch of the Super-FRS was commissioned at the FRS at GSI and significant improvements were made to the device. The prototype stopping cell is designed as a cryogenic stopping cell (CSC), featuring enhanced cleanliness and high area density. The CSC was brought into full operation and its performance characteristics were investigated including the maximal area density, extraction times, cleanliness and extraction efficiencies. In three commissioning experiments at the current GSI FRS facility in 2011, 2012 and 2014 up to 22 isotopes from 14 elements produced by in-flight projectile fragmentation and fission of {sup 238}U could be thermalized and extracted with high efficiency. For the first time projectile and fission fragmentation produced at 1000 MeV/u could be thermalized in a stopping cell and provided as a low-energy beam of high brilliance for high precision experiments. The technical improvements of the CSC, such as an improved RF carpet, new cryocooler-based cooling system, a monitoring system of the cleanliness and the high density operation, made it possible to thermalize heavy {sup 238}U projectile fragments with total efficiencies of about 20% in the 2014 experiment. In addition the improvements lead to an increase in the stability and reliability of the CSC and the performance of the CSC during online experiments at the FRS Ion Catcher showed that the utilized techniques are ready for the final CSC for the low-energy branch of the Super-FRS at FAIR. The CSC was operated with an area density of up to 6.3 mg/cm{sup 2} helium during
International Nuclear Information System (INIS)
Fiorentino, J.
1983-01-01
The nuclear fission process considering initially the formation of compound nucleus and finishing with radioactive decay of fission products is studied. The process is divided in three parts which consist of the events associated to the nucleus of intermediate transitional state, the scission configuration, and the phenomenum of post scission. (M.C.K.) [pt
Neutron emission as a probe of fusion-fission and quasi-fission dynamics
International Nuclear Information System (INIS)
Hinde, D.J.
1991-01-01
Pre- and post scission neutron yeilds have been measured as a function of projectile mass, compound nucleus fissility, and fission mass-split and total kinetic energy (TKE) for 27 fusion-fission and quasi-fission reactions induced by beams of 16,18 O, 40 Ar and 64 Ni. A new method of interpretation of experimental pre-scission neutron multiplicities ν-pre and mean kinetic energies ε ν allows the extraction of fission time scales with much less uncertainty than previously, all fusion-fission results being consistent with a dynamical time scale of (35±15) x 10 -21 s for symmetric fission. All reactions show that ν-pre falls quite rapidly with increasing mass-asymmetry; evidence is presented that for fusion-fission reactions this is partly due to a reduction of the dynamical fission time scale with mass-asymmetry. For quasi-fission, the data indicate that the pre-scission multiplicity and mean neutron kinetic energy are very sensitive to the final mass-asymmetry, but that the time scale is virtually independent of mass-asymmetry. It is concluded that for fusion-fission there is no dependence of ν-pre on TKE, whilst for 64 Ni-induced quasi-fission reactions, a strong increase of ν-pre with decreasing TKE is observed, probably largely caused by neutron emission during the acceleration time of the fission fragments in these fast reactions. Interpretation of post-scission multiplicities in terms of fragment excitation energies leads to deduced time scales consistent with those determined from the pre-scission data. 54 refs., 17 tabs., 25 figs
International Nuclear Information System (INIS)
Modesto, Montoya
2014-01-01
The Coulomb effects hypothesis is used to interpret even-odd effects of maximum total kinetic energy as a function of mass and charge of fragments from thermal neutron induced fission of 235 U. Assuming spherical fragments at scission, the Coulomb interaction energy between fragments (C sph ) is higher than the Q-value, the available energy. Therefore at scission the fragments must be deformed, so that the Coulomb interaction energy does not exceed the Q-value. The fact that the even-odd effects in the maximum total kinetic energy as a function of the charge and mass, respectively, are lower than the even-odd effects of Q is consistent with the assumption that odd mass fragments are softer than the even-even fragments. Even-odd effects of charge distribution in super asymmetric fragmentation also are interpreted with the Coulomb effect hypothesis. Because the difference between C sph and Q increases with asymmetry, fragmentations require higher total deformation energy to occur. Higher deformation energy of the fragments implies lower free energy to break pairs of nucleons. This explains why in the asymmetric fragmentation region, the even-odd effects of the distribution of proton number and neutron number increases with asymmetry. (author).
Directory of Open Access Journals (Sweden)
Minato Futoshi
2016-01-01
Full Text Available Nuclear β-decay and delayed neutron (DN emission is important for the r-process nucleosynthesis after the freeze-out, and stable and safe operation of nuclear reactors. Even though radioactive beam facilities have enabled us to measure β-decay and branching ratio of neutron-rich nuclei apart from the stability line in the nuclear chart, there are still a lot of nuclei which one cannot investigate experimentally. In particular, information on DN is rather scarce than that of T1/2. To predict T1/2 and the branching ratios of DN for next JENDL decay data, we have developed a method which comprises the quasiparticle-random-phase-approximation (QRPA and the Hauser-Feshbach statistical model (HFSM. In this work, we calculate fission fragments with T1/2 ≤ 50 sec. We obtain the rms deviation from experimental half-life of 3:71. Although the result is still worse than GT2 which has been adopted in JENDL decay data, DN spectra are newly calculated. We also discuss further subjects to be done in future for improving the present approach and making next generation of JENDL decay data.
Energy Technology Data Exchange (ETDEWEB)
Espinosa, G.; Golzarri, J. I. [UNAM, Instituto de Fisica, Circuito Exterior, Ciudad Universitaria, 04510 Mexico D. F. (Mexico); Castano, V. M. [UNAM, Centro de Fisica Aplicada y Tecnologia Avanzada, Boulevard Juriquilla 3001, Santiago de Queretaro, 76230 Queretaro (Mexico); Gaso, I. [ININ, Carretera Mexico-Toluca s/n, Ocoyoacac 52750, Estado de Mexico (Mexico); Mena, M.; Segovia, N. [UNAM, Instituto de Geofisica, Circuito de la Investigacion Cientifica, Ciudad Universitaria, 04510 Mexico D. F. (Mexico)
2010-02-15
The energy spectrum of {sup 252}Cf fission fragments was measured using nuclear track detectors and digital image analysis system. The detection material was fused silica glass. The detectors were chemically etched in an 8% HF solution. After experimenting with various etching time, it was found that the best resolution of the track diameter distribution was obtained after 30 minutes of etching. Both Gaussian and Lorentzian curves were fit to the track diameter distribution histograms and used to determine the basic parameters of the distribution of the light (N{sub L}) and heavy (N{sub H}) formed peaks and the minimum of the central valley (N{sub V}). Advantages of the method presented here include the fully-automated analysis process, the low cost of the nuclear track detectors and the simplicity of the nuclear track method. The distribution resolution obtained by this method is comparable with the resolution obtained by electronic analysis devices. The descriptive variables calculated were very close to those obtained by other methods based on the use of semiconductor detectors. (Author)
Sukhodub, L F; Chivanov, V D; Grebenik, L I; Bondarenko, P V; Zubarev, R A; Knysh, A N
1992-01-01
Study of interaction of the antitumor alkylating drug triethylenethiophosphoramide (thioTEPA) with nucleotides (dGMP and dCMP) suggests highly perspective employment of 252-Cf fission fragment induced desorption mass spectrometry (252-Cf PDMS) in biochemical pharmacology. Using the 252-Cf PDMS the molecular masses of the unstable, unvolatile, high-molecular substances of biological origin and the chemical adducts or complexes with drugs can be used to establish some structural-functional parameters of the above mentioned biomolecules and their derivatives in microvolumes of the incubation medium. The resulting data may be used for modelling chemotherapeutic processes of "drug-biomolecule-target" type. Using 252-Cf PDMS the complexes (dGMP (thioTEPA) n), n = 1, 2, 3 and (dCMP (thioTEPA) n), n = 1, were obtained. Some quantitative parameters and stability of these complexes were studied. Binding of dGMP with drug in the presence of dCMP was shown preferential. The data are compatible with the predictions concerning the mechanism of the antitumor property of the thioTEPA which can be manifested in the impairment structure of DNA of the malignant cells.
Energy Technology Data Exchange (ETDEWEB)
Simutkin, V.D. [Uppsala University, P.O Box 525, SE-751 20 Uppsala (Sweden)
2008-07-01
Conceptual analysis of accelerator-driven systems assumes extensive use of nuclear data on neutron-induced reactions at intermediate energies. In particular, information about the fission fragment yields from the {sup 238}U(n,f) and {sup 232}Th(n,f) reactions is of particular interest at neutron energies from 10 to 200 MeV. However, there is a lack of such data for both {sup 238}U and {sup 232}Th. Up to now, the intermediate energy measurements have been performed for {sup 238}U only, and there are no data for the {sup 232}Th(n,f) reaction. The aim of the work is to provide such data. Fission fragment mass distributions for the {sup 232}Th(n,f) and {sup 238}U(n,f) reactions have been measured for the incident neutron energies 32.8 MeV, 45.3 MeV and 59.9 MeV. The experiments have been performed at the neutron beam facility of the Universite Catholique de Louvain, Belgium. A multi-section Frisch-gridded ionization chamber has been used as a fission fragment detector. The data obtained have been interpreted in terms of the multimodal random neck-rupture model (MMRNRM). (authors)
Energy Technology Data Exchange (ETDEWEB)
Knoebel, R.; Litvinov, Yu.A.; Weick, H.; Bosch, F.; Boutin, D.; Dimopoulou, C.; Dolinskii, A.; Franczak, B.; Franzke, B.; Kozhuharov, C.; Kurcewicz, J.; Litvinov, S.A.; Matos, M.; Mazzocco, M.; Muenzenberg, G.; Nociforo, C.; Nolden, F.; Stadlmann, J.; Steck, M.; Winkler, M. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Diwisch, M. [Justus-Liebig-Universitaet Giessen, II. Physikalisches Institut, Giessen (Germany); Geissel, H.; Plass, W.R.; Scheidenberger, C.; Chen, L. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Justus-Liebig-Universitaet Giessen, II. Physikalisches Institut, Giessen (Germany); Patyk, Z. [National Centre for Nuclear Research - NCBJ Swierk, Warszawa (Poland); Sun, B. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Beihang University, School of Physics and Nuclear Energy Engineering, Beijing (China); Hausmann, M. [Michigan State University, East Lansing, MI (United States); Nakajima, S.; Suzuki, T.; Yamaguchi, T. [Saitama University, Department of Physics, Saitama (Japan); Ohtsubo, T. [Niigata University, Department of Physics, Niigata (Japan); Ozawa, A. [University of Tsukuba, Institute of Physics, Ibaraki (Japan); Walker, P.M. [University of Surrey, Department of Physics, Guildford (United Kingdom)
2016-05-15
Masses of uranium fission fragments have been measured with the FRagment Separator (FRS) combined with the Experimental Storage Ring (ESR) at GSI. A 410-415 MeV/u {sup 238}U projectile beam was fast extracted from the synchrotron SIS-18 with an average intensity of 10{sup 9}/spill. The projectiles were focused on a 1g/cm{sup 2} beryllium target at the entrance of the FRS to create neutron-rich isotopes via abrasion-fission. The fission fragments were spatially separated with the FRS and injected into the isochronous storage ring ESR for fast mass measurements without applying cooling. The Isochronous Mass Spectrometry (IMS) was performed under two different experimental conditions, with and without B ρ-tagging at the high-resolution dispersive central focal plane of the FRS. The evaluation has been done for the combined data sets from both experiments with a new method of data analysis. The use of a correlation matrix has provided experimental mass values for 23 different neutron-rich isotopes for the first time and 6 masses with improved values. The new masses were obtained for nuclides in the element range from Se to Ce. The applied analysis has given access even to rare isotopes detected with an intensity of a few atoms per week. The novel data analysis and systematic error determination are described and the results are compared with extrapolations of experimental values and theoretical models. (orig.)
Dissipative effects in fission investigated with proton-on-lead reactions
Directory of Open Access Journals (Sweden)
Rodríguez-Sánchez J. L.
2016-01-01
Full Text Available The complete kinematic measurement of the two fission fragments permitted us to investigate dissipative effects at large deformations, between the saddle-point and the corresponding scission configurations. Up to now, this kind of study has only been performed with fusionfission reactions using a limited number of observables, such as the mass distribution of the fission fragments or the neutron multiplicities. However, the large angular momenta gained by the compound nucleus could affect the conclusions drawn from such experiments. In this work, the use of spallation reactions, where the fissioning systems are produced with low angular momentum, small deformations and high excitation energies, favors the study of dissipation, and allowed us to define new observables, such as postscission neutron multiplicities and the neutron excess of the final fission fragments as a function of the atomic number of the fissioning system. These new observables are used to investigate the dissipation at large deformations.
Shimizu, Yohei; Kubo, Toshiyuki; Fukuda, Naoki; Inabe, Naohito; Kameda, Daisuke; Sato, Hiromi; Suzuki, Hiroshi; Takeda, Hiroyuki; Yoshida, Koichi; Lorusso, Giuseppe; Watanabe, Hiroshi; Simpson, Gary S.; Jungclaus, Andrea; Baba, Hidetada; Browne, Frank; Doornenbal, Pieter; Gey, Guillaunme; Isobe, Tadaaki; Li, Zhihuan; Nishimura, Shunji; Söderström, Pär-Anders; Sumikama, Toshiyuki; Taprogge, Jan; Vajta, Zsolt; Wu, Jin; Xu, Zhengyu; Odahara, Atsuko; Yagi, Ayumi; Nishibata, Hiroki; Lozeva, Radomira; Moon, Changbum; Jung, HyoSoon
2018-01-01
The search for new isotopes using the in-flight fission of a 238U beam has been conducted concurrently with decay measurements, during the so-called EURICA campaigns, at the RIKEN Nishina Center RI Beam Factory. Fission fragments were analyzed and identified in flight using the BigRIPS separator. We have identified the following 36 new neutron-rich isotopes: 104Rb, 113Zr, 116Nb, 118,119Mo, 121,122Tc, 125Ru, 127,128Rh, 129,130,131Pd, 132Ag, 134Cd, 136,137In, 139,140Sn, 141,142Sb, 144,145Te, 146,147I, 149,150Xe, 149,150,151Cs, 153,154Ba, and 154,155,156,157La.
Sharp change-over from compound nuclear fission to quasifission
International Nuclear Information System (INIS)
Ghosh, T. K.; Banerjee, K.; Bhattacharya, C.; Bhattacharya, S.; Kundu, S.; Mali, P.; Meena, J. K.; Mukherjee, G.; Mukhopadhyay, S.; Rana, T. K.; Bhattacharya, P.; Golda, K. S.
2009-01-01
Fission fragment mass distributions have been measured from the decay of the compound nucleus 246 Bk that has been populated via two entrance channels. These entrance channels have a slight difference in their mass asymmetries that puts them on either side of the Businaro Gallone mass asymmetry parameter. Both target nuclei were deformed. Near the Coulomb barrier, at similar excitation energies, the width of the fission fragment mass distribution was found to be drastically different for the 14 N+ 232 Th reaction compared to the 11 B+ 235 U reaction. The entrance channel mass asymmetry was found to affect the fusion process sharply.
Investigation of exotic fission modes
International Nuclear Information System (INIS)
Poenaru, D. N.; Gherghescu, R. A.; Greiner, W.; Nagame, Y.; Hamilton, J. H.; Ramayya, A. V.
2002-01-01
Fission approach to the cluster radioactivities and α-decay has been systematically developed during the last two decades. A more complex process, the ternary fission, was observed since 1946 both in neutron-induced and spontaneous fission. We obtained interesting results concerning the binary fission saddle-point reflection asymmetric nuclear shapes, and we can explain how a possible nuclear quasimolecular state is formed during the 10 Be accompanied cold fission of 252 Cf. The equilibrium nuclear shapes in fission theory are usually determined by minimizing the deformation energy for a given surface equation. We developed a method allowing to obtain a very general saddle-point shape as a solution of a differential equation without an a priori introduction of a shape parametrization. In the approach based on a liquid drop model (LDM), saddle-point shapes are always reflection symmetric: the deformation energy increases with the mass-asymmetry parameter η = (A 1 - A 2 )/(A 1 + A 2 ). By adding the shell corrections to the LDM deformation energy, we obtained minima at a finite mass asymmetry for parent nuclei 238 U, 232,228 Th in agreement with experiments. This correction was calculated phenomenologically. A technique based on the fragment identification by using triple γ coincidences in the large arrays of Ge-detectors, like GAMMASPHERE, was employed at Vanderbilt University to discover new characteristics of the fission process, and new decay modes. The possibility of a whole family of new decay modes, the multicluster accompanied fission, was envisaged. Besides the fission into two or three fragments, a heavy or superheavy nucleus spontaneously breaks into four, five or six nuclei of which two are asymmetric or symmetric heavy fragments and the others are light clusters, e.g. α-particles, 10 Be, 14 C, or combinations of them. Examples were presented for the two-, three- and four cluster accompanied cold fission of 252 Cf and 262 Rf, in which the emitted
Hora, H.; Miley, G. H.
2007-12-01
One of the most convincing facts about LENR due to deuterons of very high concentration in host metals as palladium is the measurement of the large scale minimum of the reaction probability depending on the nucleon number A of generated elements at A = 153 where a local maximum was measured. This is similar to the fission of uranium at A = 119 where the local maximum follows from the Maruhn-Greiner theory if the splitting nuclei are excited to about MeV energy. The LENR generated elements can be documented any time after the reaction by SIMS or K-shell X-ray excitation to show the very unique distribution with the local maximum. An explanation is based on the strong Debye screening of the Maxwellian deuterons within the degenerate rigid electron background especially within the swimming electron layer at the metal surface or at interfaces. The deuterons behave like neutrals at distances of about 2 picometers. They may form clusters due to soft attraction in the range above thermal energy. Clusters of 10 pm diameter may react over long time probabilities (megaseconds) with Pd nuclei leading to a double magic number compound nucleus which splits like in fission to the A = 153 element distribution.
International Nuclear Information System (INIS)
Tarantin, N.I.
2001-01-01
Data on nuclear masses provide a basis for creating and testing various nuclear models. A tandem system of FLNR comprised of the U-400M cyclotron, the COMBAS magnetic separator and the mass-spectrometric ion trap of an 'in-flight capture' type is considered as a possible complex for producing of the short-lived nuclei in fragmentation reactions by heavy ions and for precise mass measurement of these nuclei. The plan of scientific and technical FLNR research includes a project DRIBs for producing beams of accelerated radioactive nuclear reaction products and photofission fragments. This project proposes also precise mass measurements of the fission fragment with the help of the ion trap. The in-flight entrance of the ions and their capture in the mass-spectrometric ion trap using the monochromatizing degrader, the static electric and magnetic fields and a new invention, a magnetic unidirectional transporting ventil, is considered
Indian Academy of Sciences (India)
2015-08-05
Aug 5, 2015 ... We present the ternary fission of 252Cf and 236U within a three-cluster model as well as in a level density approach. The competition between collinear and equatorial geometry is studied by calculating the ternary fragmentation potential as a function of the angle between the lines joining the stationary ...
Energy Technology Data Exchange (ETDEWEB)
Mulgin, S.I. [Institute of Nuclear Physics, National Nuclear Center, 050032 Almaty (Kazakhstan); Zhdanov, S.V. [Institute of Nuclear Physics, National Nuclear Center, 050032 Almaty (Kazakhstan)], E-mail: zhdanov@inp.kz; Kondratiev, N.A. [Flerov' s Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, 141980 Dubna, Moscow region (Russian Federation); Kovalchuk, K.V.; Rusanov, A.Ya. [Institute of Nuclear Physics, National Nuclear Center, 050032 Almaty (Kazakhstan)
2009-06-01
Mass and energy distributions of fragments from fission of target nuclei {sup 232}Th and {sup 235}U induced by the 10.3-30.0 MeV protons have been measured with surface-barrier silicon detectors. A new method for decomposition of experimental distributions into fragment mass and energy yields of four independent fission modes has been proposed. Main characteristics of fission modes such as distinct mode mass yields, mean masses and kinetic energies as well as variances in fragment masses and energies have been studied in relation with energy of protons. Revealed regularities in these quantities for given energy range of incident protons support the assumption that the modes S1 and S2 are initially formed in a unified asymmetric fission valley.
Dynamical processes at the final stage of nuclear fission
International Nuclear Information System (INIS)
Rubchenya, V.A.; Yavshits, S.G.
1984-01-01
A model of the final stage of fission near the scission point is proposed. The processes of nucleon exchange through sub-barrier transitions between the fragments are considered within the framework of this model in the diffusion approximation. For the determination of the initial conditions a method by which the transition from the one-center configuration of the nucleus before scission to a fragment-system configuration can be made, and which relates the stage in question to the stage at which the descent from the saddle point occurs, is formulated. The model parameters, the transport coefficients, and the mass distributions of the fragments are found for two cases: the low- and high-energy fission of the 236 U compound nucleus. The results are compared with the experimental data
Angular distribution in the neutron-induced fission of actinides
Directory of Open Access Journals (Sweden)
Leong L.S.
2013-12-01
Full Text Available Above 1 MeV of incident neutron energy the fission fragment angular distribution (FFAD has generally a strong anisotropic behavior due to the combination of the incident orbital momentum and the intrinsic spin of the fissioning nucleus. This effect has to be taken into account for the efficiency estimation of devices used for fission cross section measurements. In addition it bears information on the spin deposition mechanism and on the structure of transitional states. We designed and constructed a detection device, based on Parallel Plate Avalanche Counters (PPAC, for measuring the fission fragment angular distributions of several isotopes, in particular 232Th. The measurement has been performed at n_TOF at CERN taking advantage of the very broad energy spectrum of the neutron beam. Fission events were recognized by back to back detection in coincidence in two position-sensitive detectors surrounding the targets. The detection efficiency, depending mostly on the stopping of fission fragments in backings and electrodes, has been computed with a Geant4 simulation and validated by the comparison to the measured case of 235U below 3 keV where the emission is isotropic. In the case of 232Th, the result is in good agreement with previous data below 10 MeV, with a good reproduction of the structures associated to vibrational states and the opening of second chance fission. In the 14 MeV region our data are much more accurate than previous ones which are broadly scattered.
International Nuclear Information System (INIS)
2009-01-01
This conference is dedicated to the last achievements in experimental and theoretical aspects of the nuclear fission process. The topics include: mass, charge and energy distribution, dynamical aspect of the fission process, nuclear data evaluation, quasi-fission and fission lifetime in super heavy elements, fission fragment spectroscopy, cross-section and fission barrier, and neutron and gamma emission. This document gathers the program of the conference and the slides of the presentations
Directory of Open Access Journals (Sweden)
Al-Adili A.
2010-03-01
Full Text Available Fission Research at JRC-IRMM has a longstanding tradition. The present paper is discussing recent investigations of fission fragment properties of 238 U(n,f, 234 U(n,f, prompt neutron emission in fission of 252 Cf(SF as well as the prompt fission neutron spectrum of 235 U(n,f and is presenting the most important results.
$\\beta$-delayed fission in proton-rich nuclei in the lead region
AUTHOR|(CDS)2085005; Huyse, Mark; Popescu, Lucia
Nuclear fission is the breakup of an atomic nucleus into two (sometimes three) fragments, thereby releasing a large amount of energy. Soon after its discovery in the late 1930’s, the gross properties of the fission phenomenon were explained by macroscopic nuclear models. Certain features however, such as asymmetric fission-fragment mass distributions in the actinide region, require the inclusion of microscopic effects. This interplay of the microscopic motion of individual nucleons on this macroscopic process is, until today, not yet fully understood. The phenomenon of fission has therefore been of recurring interest for both theoretical and experimental studies. This thesis work focuses on the $\\beta$-delayed fission ($\\beta$DF) process, an excellent tool to study low-energy fission of exotic nuclei, which was discovered in 1966 in the actinide region. In this two-step process, a precursor nucleus first undergoes $\\beta$-decay to an excited level in the daughter nucleus, which may subsequently fission. Rec...
Theoretical approaches to the emission of α particles during nuclear fission
International Nuclear Information System (INIS)
Carjan, N.
1986-05-01
Recent models as well as new trajectory calculations used to interpret the experimental data on α-accompanied fission are presented and experimental hints towards the emission mechanism are pointed out. The important question of the distribution of the emission points and moments is brought up: are these particles coming only from the region between the fragments (the neck) or, are they coming with comparable probability, from any point of the surface of the fissioning system and: are they emitted just at scission or at any sufficiently deformed stage of the fission process. The simultaneous division of the nucleus into three fragments (the true ternary fission) is discussed in terms of the dynamical liquid-drop model. It is suggested that this process occurs in the tail (corresponding to overelongated shapes) of the distribution of the fission probability in the multidimensional space of the collective coordinates
Fission-fragment angular distributions and total kinetic energies for 235U(n,f) from .18 to 8.83 MeV
International Nuclear Information System (INIS)
Meadows, J.W.; Budtz-Joergensen, C.
1982-01-01
A gridded ion chamber was used to measure the fission fragment angular distribution and total kinetic energy for the 235 U(n,f) reaction from 0.18 to 8.81 MeV neutron energy. The anisotropies are in generally good agreement with earlier measurements. The average total kinetic energy is approx. 0.2 MeV greater than the thermal value at neutron energies < 2 MeV and shows a sudden decrease of approx. 0.8 MeV between 4 and 5 MeV neutron energy, well below the (n, n'f) threshold. Possible causes of this decrease are a change in the mass distribution or decreased shell effects in the heavy fragment
Rupture of the neck in nuclear fission
International Nuclear Information System (INIS)
Davies, K.T.R.; Managan, R.A.; Nix, J.R.; Sierk, A.J.
1977-01-01
We introduce a degree of freedom to describe the rupture of the neck in nuclear fission and calculate the point at which the neck ruptures as the nucleus descends dynamically from its fission saddle point. This is done by mentally slicing the system into two portions at its minimum neck radius and calculating the force required to separate the two portions while keeping their shapes fixed. This force is obtained by differentiating with respect to separation the sum of the Coulomb and nuclear interaction energies between the two portions. For nuclei throughout the Periodic Table we calculate this force along dynamical paths leading from the fission saddle point. The force is initially attractive but becomes repulsive when the neck reaches a critical size. For actinide nuclei the neck radius at which rupture occurs is about 2 fm. This increases the calculated translational kinetic energy of the fission fragments at infinity relative to that calculated for scission occurring at zero neck radius. With the effect of neck rupture taken into account, we calculate and compare with experimental results fission-fragment kinetic energies for two types of nuclear dissipation: ordinary two-body viscosity and one-body dissipation
Energy Technology Data Exchange (ETDEWEB)
Montoya, M. [Universidad Nacional de Ingeniería, Av. Túpac Amaru 210, Rímac, Lima (Peru)
2016-07-07
Even-odd effects of the maximal total kinetic energy (K{sub max}) as a function of charge (Z) and mass (A) of fragments from thermal neutron induced fission of actinides are questioned by other authors. In this work, visiting old results on thermal neutron induced fission of {sup 235}U, those even-odd effects are reconfirmed. The cases seeming to contradict even-odd effects are interpreted with the Coulomb effect hypothesis. According to Coulomb effect hypothesis, K{sub max} is equal to the Coulomb interaction energy of the most compact scission configuration. As a consequence, between two isobaric charge splits with similar Q-values, the more asymmetrical one will get the more compact scission configuration and then it will reach the higher K{sub max}-value. In some cases, the more asymmetrical charge split corresponds, by coincidence, to an odd charge split; consequently its higher K{sub max}-value may be misinterpreted as anti-even-odd effect. Another experimental result reported in the literature is the increasing of even-odd effects on charge distribution on the more asymmetrical fragmentations region. In this region, the difference between K{sub max} and Q-values increases with asymmetry, which means that the corresponding scission configuration needs higher total deformation energy to occur. Higher deformation energy of the fragments implies lower free energy to break nucleon pairs. Consequently, in the asymmetric fragmentation region, the even-odd effects of the distribution of proton number and neutron number must increase with asymmetry.
Multidimensional Langevin approach to describing the 18O + 208Pb fusion-fission reaction
International Nuclear Information System (INIS)
Kosenko, G.I.; Ivanyuk, F.A.; Pashkevich, V.V.
2002-01-01
The fusion-fission reaction is treated as a multistep process. Langevin equations are used to describe the evolution of the system at each reaction stage. The parameters of the fusion process are calculated at the first stage. The results obtained in the input channel are employed as initial conditions in calculating the features of the fission process. The cross sections for fusion and fission are successfully described, and the cross sections for the formation of evaporation residues are estimated. In addition, the procedure used makes it possible to describe the mass distribution of fission fragments and the fragment-mass dependence of the multiplicity of prefission neutrons and to determine the mass-energy distribution of fission fragments. From the calculations, it follows that all the fission features of the reaction in question can be reproduced without considering the formation of a classical compound nucleus. The reaction times are so long that it is impossible to separate experimentally such events from the case of true fission through a compound nucleus
International Nuclear Information System (INIS)
Vijayaraghavan, K.R.; Balasubramaniam, M.; Oertzen, W. von
2014-01-01
Splitting of heavy radioactive nucleus into three fragments is known as ternary fission. If the size of the fragments are almost equal it is referred to as true ternary fission. Recently, Yu. V. Pyatkov et al observed/reported the experimental observation of true ternary fission in 252 Cf. In this work, the possibilities of different true ternary fission modes of 252 Cf through potential energy surface (PES) calculations based on three cluster model (TCM) are discussed. In TCM a condition on the mass numbers of the fission fragments is implied as A 1 ≥ A 2 ≥ A 3 in order to avoid repetition of combinations. Due to this condition, the values of Z 3 vary from 0 to 36 and Z 2 vary from 16 to 51. Of the different pairs having similar (Z 2 , Z 3 ) with different potential energy, a pair possessing minimum potential energy is chosen. Thus identified favourable combinations are plotted. For the PES calculations the arrangement of the fragments is considered in the order of A 1 +A 2 +A 3 . i.e. the heavy and the lightest fragments are kept at the ends. It is seen that the deepest minimum in the PES occurs for Z 3 =2 labelled as (Z 2 ; 2) indicating He accompanied breakup as the most favourable one. Of which, the breakup with Z 2 around 46 to 48 is the least (shown by dashed (Z 1 = 50) and dotted (Z 1 = 52) lines indicating a constant Z 1 value). The other notable minima in the PES are labelled and they correspond to the (Z 2 , Z 3 ) pairs viz., (20, 20), (28, 20), (28, 28) and (32, 32). Of these four minima, the first three are associated with the magic numbers 20 and 28. For Z 3 =20, there are two minimums at (20,20) and (28,20) among them (28,20) is the lowest minimum through which the minimum-path passes, and it is the ternary decay observed by Yu. V. Pyatkov et al. The fourth minima is the most interesting due to the fact that it corresponds to true ternary fission mode with Z 2 =32, Z 3 =32 and Z 1 =34. The minimum potential energy path also goes through this true
International Nuclear Information System (INIS)
Strugalski, Z.
1985-01-01
Shapes and sizes of the regions in target-nuclei in which reactions leading to the nucleon emission, particle production and fragment evaporation occur are determined. The region of nucleon emission is of cylindrical shape, with the diameter as large as two nucleon diameters, centered on the incident hadron course. The reactions leading to the particle production happen predominantly along the incident hadron course in nuclear matter. The fragment evaporation goes from the surface layer of the part of the target-nucleus damaged in nucleon emission process
International Nuclear Information System (INIS)
Madland, D.G.
1988-01-01
An improved calculation is presented for the prompt fission neutron spectrum N(E) from the spontaneous fission of /sup 252/Cf. In this calculation the fission-spectrum model of Madland and Nix is used, but with several improvements leading to a physically more accurate representation of the spectrum. Specifically, the contributions to N(E) from the entire fission-fragment mass and charge distributions will be calculated instead of calculating on the basis of a seven- point approximation to the peaks of these distributions as has been done in the past. Therefore, values of the energy release in fission, fission-fragment kinetic energy, and compound nucleus cross section for the inverse process will be considered on a point-by-point basis over the fragment yield distributions instead of considering averages of these quantities over the peaks of the distributions. Preliminary results will be presented and compared with a measurement, an earlier calculation, and a recent evaluation of the spectrum. 14 refs., 4 figs
Fission Fragment Angular Distribution measurements of 235U and 238U at CERN n_TOF facility
Directory of Open Access Journals (Sweden)
Leal-Cidoncha E.
2016-01-01
In order to measure the FFAD of neutron-induced reactions, a fission detection setup based on parallel-plate avalanche counters (PPACs has been developed and successfully used at the CERN-n_TOF facility. In this work, we present the preliminary results on the analysis of new 235U(n,f and 238U(n,f data in the extended energy range up to 200 MeV compared to the existing experimental data.
Energy Technology Data Exchange (ETDEWEB)
Majumdar, N.; Bhattacharya, P. [Saha Institute of Nuclear Physics, 1/AF, Bidhannagar Calcutta 700 064 (India); Biswas, D.C.; Choudhury, R.K.; Nadkarni, D.M.; Saxena, A. [Bhabha Atomic Research Centre, Bombay 400 085 (India)
1996-12-01
Fission fragment angular distributions have been measured for fission following full momentum transfer in {sup 11}B, {sup 12}C, {sup 16}O, and {sup 19}F+{sup 232}Th systems from above barrier to below sub-barrier energies. The fragment anisotropies are found to exhibit an anomalous peaklike structure below the fusion barrier in all the systems. This structure has a universal behavior independent of the entrance channel mass asymmetry. With some refinement in the quasifission hypothesis it is possible to explain qualitatively the experimental results reasonably well. {copyright} {ital 1996 The American Physical Society.}
Even-odd effects in the prompt fission emission of even Z actinides
Directory of Open Access Journals (Sweden)
Tudora Anabella
2016-01-01
Full Text Available The investigation of even-odd effects in the prompt emission of even Z actinides showed a sawtooth shape of ν(Z with staggering in the asymmetric fission region. Average prompt emission quantities as a function of A, e.g. ν(A, of even Z fragmentations are higher than those of odd Z fragmentations and they exhibit oscillations with a periodicity of about 5 mass units in the asymmetric fission region. This periodicity is not due to the Z even-odd effect in fragment distributions. The even-odd effect in (TKE is increasing with increasing TKE and it decreases with increasing mass of the fissioning nucleus. The global even-odd effect in total average prompt emission quantities is decreasing with increasing mass of the fissioning nucleus. In the case of an even-odd fissioning nucleus, 234U(n,f, the global even-odd effect in prompt emission quantities exhibits a very slow variation with the incident neutron energy.
Insights into nuclear structure and the fission process from spontaneous fission
Energy Technology Data Exchange (ETDEWEB)
Hamilton, J.H.; Butler-Moore, K.; Ramayya, A.V. [Vanderbilt Univ., Nashville, TN (United States)] [and others
1993-12-31
The {gamma}-rays emitted following spontaneous and induced fission are rich sources of information about the structure of neutron-rich nuclei and about the fission process itself. The study of spontaneous fissioning isotopes with large Ge detector arrays are providing a wealth of such information as seen, for example, in recent reports. In this paper we present some of our most recent results on nuclear structure studies and conclusions on the fission process itself. In our work, we have employed in spontaneous fission, a triple gamma coincidence study for the first time and a high resolution, X-ray detector-{gamma}-coincidence study. These data provide powerful ways of separating the gamma rays which belong to a particular nucleus. The triple coincidence technique was used to uniquely identify the levels in {sup 136}Te and higher spin states in its N=84 isotones, {sup 138}Xe and {sup 140}Ba{sup 171}. Some other examples of the level structures observed in the low and high mass partners are presented, including a detailed analysis of the backbending of the moment of inertia in {sup 112,114,116}Pd. Finally, we present the first examples of how our analysis allows one to extract a detailed picture of the dependence of the angular momentum on the mass and atomic numbers of the fission fragments and of the long-sought neutron multiplicity distribution from zero-n to ten-n as a function of the charge and mass asymmetry.
General Description of Fission Observables: GEF Model Code
Schmidt, K.-H.; Jurado, B.; Amouroux, C.; Schmitt, C.
2016-01-01
The GEF ("GEneral description of Fission observables") model code is documented. It describes the observables for spontaneous fission, neutron-induced fission and, more generally, for fission of a compound nucleus from any other entrance channel, with given excitation energy and angular momentum. The GEF model is applicable for a wide range of isotopes from Z = 80 to Z = 112 and beyond, up to excitation energies of about 100 MeV. The results of the GEF model are compared with fission barriers, fission probabilities, fission-fragment mass- and nuclide distributions, isomeric ratios, total kinetic energies, and prompt-neutron and prompt-gamma yields and energy spectra from neutron-induced and spontaneous fission. Derived properties of delayed neutrons and decay heat are also considered. The GEF model is based on a general approach to nuclear fission that explains a great part of the complex appearance of fission observables on the basis of fundamental laws of physics and general properties of microscopic systems and mathematical objects. The topographic theorem is used to estimate the fission-barrier heights from theoretical macroscopic saddle-point and ground-state masses and experimental ground-state masses. Motivated by the theoretically predicted early localisation of nucleonic wave functions in a necked-in shape, the properties of the relevant fragment shells are extracted. These are used to determine the depths and the widths of the fission valleys corresponding to the different fission channels and to describe the fission-fragment distributions and deformations at scission by a statistical approach. A modified composite nuclear-level-density formula is proposed. It respects some features in the superfluid regime that are in accordance with new experimental findings and with theoretical expectations. These are a constant-temperature behaviour that is consistent with a considerably increased heat capacity and an increased pairing condensation energy that is
Asymmetric Fission in the 78Kr+40Ca reactions at 5.5 MeV/nucleon
Directory of Open Access Journals (Sweden)
Roy R.
2012-02-01
Full Text Available The cross section, kinetic energy distribution and angular distribution of fragments with atomic number 3 ≤ Z ≤ 28 emitted in the reaction 78Kr + 40Ca at the bombarding energy of 5.5 MeV/nucleon and coincidence between light charged particles and fragments were measured by means of the 4π-INDRA array to study the decay mechanism of medium mass excited nucleus. Global features indicate a high degree of relaxation and are compatible with a binary fission from compound nucleus. The mean value of the kinetic energy distributions of fragments indicates dominance of Coulomb interaction, while the width of the distribution signals large fluctuations. Inclusive cross-section distributions of fragments with charge 3 ≤ Z ≤ 28 are bell-shaped and a strong even-odd-staggering (o-es is observed for 3 ≤ Z ≤ 12. Coincidence measurements suggest that the light partners in very asymmetric fission are emitted at excitation energies below the particle emission thresholds. Data were confronted to the predictions of statistical model describing the decay of compound nuclei by emission of light particles and fragments. Calculations assuming spherical fission fragments and finite-range liquid drop fission barriers are not able to explain the experimental features. Attempts have been made to improve the agreement with experimental data. The analysis indicates the strong influence of the shape parameterization of the potential energy surface in describing the fission process of intermediate mass compound nuclei.
Intermediate energy nuclear fission
International Nuclear Information System (INIS)
Hylten, G.
1982-01-01
Nuclear fission has been investigated with the double-kinetic-energy method using silicon surface barrier detectors. Fragment energy correlation measurements have been made for U, Th and Bi with bremsstrahlung of 600 MeV maximum energy. Distributions of kinetic energy as a function of fragment mass are presented. The results are compared with earlier photofission data and in the case of bismuth, with calculations based on the liquid drop model. The binary fission process in U, Yb, Tb, Ce, La, Sb, Ag and Y induced by 600 MeV protons has been investigated yielding fission cross sections, fragment kinetic energies, angular correlations and mass distributions. Fission-spallation competition calculations are used to deduce values of macroscopic fission barrier heights and nuclear level density parameter values at deformations corresponding to the saddle point shapes. We find macroscopic fission barriers lower than those predicted by macroscopic theories. No indication is found of the Businaro Gallone limit expected to occur somewhere in the mass range A = 100 to A = 140. For Ce and La asymmetric mass distributions similar to those in the actinide region are found. A method is described for the analysis of angular correlations between complementary fission products. The description is mainly concerned with fission induced by medium-energy protons but is applicable also to other projectiles and energies. It is shown that the momentum and excitation energy distributions of cascade residuals leading to fission can be extracted. (Author)
Event-by-Event Simulation of Induced Fission
Vogt, Ramona; Randrup, Jørgen
2008-04-01
We are developing a novel code that treats induced fission by statistical (or Monte-Carlo) simulation of individual decay chains. After its initial excitation, the fissionable compound nucleus may either de-excite by evaporation or undergo binary fission into a large number of fission channels each with different energetics involving both energy dissipation and deformed scission pre-fragments. After separation and Coulomb acceleration, each fission fragment undergoes a succession of individual (neutron) evaporations, leading to two bound but still excited fission products (that may further decay electromagnetically and, ultimately, weakly), as well as typically several neutrons. (The inclusion of other possible ejectiles is planned.) This kind of approach makes it possible to study more detailed observables than could be addressed with previous treatments which have tended to focus on average quantities. In particular, any type of correlation observable can readily be extracted from a generated set of events. With a view towards making the code practically useful in a variety of applications, emphasis is being put on making it numerically efficient so that large event samples can be generated quickly. In its present form, the code can generate one million full events in about 12 seconds on a MacBook laptop computer. The development of this qualitatively new tool is still at an early stage and quantitative reproduction of existing data should not be expected until a number of detailed refinement have been implemented.
Event-by-Event Simulation of Induced Fission
International Nuclear Information System (INIS)
Vogt, Ramona; Randrup, Joergen
2008-01-01
We are developing a novel code that treats induced fission by statistical (or Monte-Carlo) simulation of individual decay chains. After its initial excitation, the fissionable compound nucleus may either de-excite by evaporation or undergo binary fission into a large number of fission channels each with different energetics involving both energy dissipation and deformed scission pre-fragments. After separation and Coulomb acceleration, each fission fragment undergoes a succession of individual (neutron) evaporations, leading to two bound but still excited fission products (that may further decay electromagnetically and, ultimately, weakly), as well as typically several neutrons. (The inclusion of other possible ejectiles is planned.) This kind of approach makes it possible to study more detailed observables than could be addressed with previous treatments which have tended to focus on average quantities. In particular, any type of correlation observable can readily be extracted from a generated set of events. With a view towards making the code practically useful in a variety of applications, emphasis is being put on making it numerically efficient so that large event samples can be generated quickly. In its present form, the code can generate one million full events in about 12 seconds on a MacBook laptop computer. The development of this qualitatively new tool is still at an early stage and quantitative reproduction of existing data should not be expected until a number of detailed refinement have been implemented
Binary and ternary fission yields induced by 12C and 20Ne ions on 238U targets
International Nuclear Information System (INIS)
Otto, R.J.
1974-01-01
Evidence for ternary fission of 250 Cf* and 258 No* compound nuclei has been found. Relative cross section data for nuclides with masses between 24 Na and 161 Tb have been determined for 12 C bombardments of natural uranium at laboratory energies of 122 MeV, 113 MeV and 105 MeV. Relative cross section data for 8 nuclides between 24 Na and 66 Ni were sought for 20 Ne bombardments of natural uranium at 150 MeV laboratory energies. The binary fission fragment mass distribution for 238 U( 12 C,f) was determined by analysis of fission fragment recoil collection foils using radiochemical techniques and high resolution gamma ray spectroscopy. The results indicated the existence of a ternary fission branch similar to mass distributions obtained for He induced fission of Th, U, and Pu nuclei at intermediate energies. Comparison of the data with He induced ternary fission data obtained previously in this laboratory indicated an increase in the ternary fission probability with increasing Z 2 /A of the compound nucleus and with excitation energy. A shift of the binary-ternary fission product intersection point to lower mass numbers with increasing Z 2 /A and excitation energy of the compound nucleus was also observed. (Diss. Abstr. Int., B)
Ternary fission of 184466,476X formed in U + U collisions
International Nuclear Information System (INIS)
Karthikraj, C.; Subramanian, S.; Selvaraj, S.
2016-01-01
Recently, the very rare process of nuclear ternary fission has been of great interest in nuclear dynamics. Based on the statistical theory of fission, we discuss here the ternary-fission mass distribution of 184 466,476 X formed in low-energy U + U collisions for different heavy third fragments at T = 1 and 2 MeV. The expected ternary configurations 208 Pb + 208 Pb + 50 Ca and 204 Hg + 204 Hg + 58 Cr are obtained from the ternary fission of 184 466 X at T = 2 MeV. In addition, for both the systems, various possible ternary modes are listed for different heavy third fragments. Our results clearly indicate that the favored ternary configurations have either proton and/or neutron shell closure nucleus as one of their partners. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Kadmensky, S. G., E-mail: kadmensky@phys.vsu.ru; Titova, L. V.; Bulychev, A. O. [Voronezh State University (Russian Federation)
2015-07-15
An analysis of basicmechanisms of binary and ternary fission of nuclei led to the conclusion that true ternary and quaternary fission of nuclei has a sequential two-step (three-step) character, where, at the first step, a fissile nucleus emits a third light particle (third and fourth light particles) under shakeup effects associated with a nonadiabatic character of its collective deformation motion, whereupon the residual nucleus undergoes fission to two fission fragments. Owing to this, the formulas derived earlier for the widths with respect to sequential two- and three-step decays of nuclei in constructing the theory of two-step twoproton decays and multistep decays in chains of genetically related nuclei could be used to describe the relative yields and angular and energy distributions of third and fourth light particles emitted in (α, α), (t, t), and (α, t) pairs upon the true quaternary spontaneous fission of {sup 252}Cf and thermal-neutron-induced fission of {sup 235}U and {sup 233}U target nuclei. Mechanisms that explain a sharp decrease in the yield of particles appearing second in time and entering into the composition of light-particle pairs that originate from true quaternary fission of nuclei in relation to the yields of analogous particles in true ternary fission of nuclei are proposed.
Neutron induced fission of 234U
Directory of Open Access Journals (Sweden)
Pomp S.
2012-02-01
Full Text Available The fission fragment properties of 234U(n,f were investigated as a function of incident neutron energy from 0.2 MeV up to 5 MeV. The fission fragment mass, angular distribution and kinetic energy were measured with a double Frisch-grid ionization chamber using both analogue and digital data acquisition techniques. The reaction 234U(n,f is relevant, since it involves the same compound nucleus as formed after neutron evaporation from highly excited 236U*, the so-called second-chance fission of 235U. Experimental data on fission fragment properties like fission fragment mass and total kinetic energy (TKE as a function of incident neutron energy are rather scarce for this reaction. For the theoretical modelling of the reaction cross sections for Uranium isotopes this information is a crucial input parameter. In addition, 234U is also an important isotope in the Thorium-based fuel cycle. The strong anisotropy of the angular distribution around the vibrational resonance at En = 0.77 MeV could be confirmed using the full angular range. Fluctuations in the fragment TKE have been observed in the threshold region around the strong vibrational resonance at En = 0.77 MeV. The present results are in contradiction with corresponding literature values. Changes in the mass yield around the vibrational resonance and at En = 5 MeV relative to En = 2 MeV show a different signature. The drop in mean TKE around 2.5 to 3 MeV points to pair breaking as also observed in 235,238U(n,f. The measured two-dimensional mass yield and TKE distribution have been described in terms of fission modes. The yield of the standard 1 (S1 mode shows fluctuations in the threshold of the fission cross section due to the influence of the resonance and levels off at about 20% yield for higher incident neutron energies. The S2 mode shows the respective opposite behaviour. The mean TKE of both modes decreases with En. The decrease in mean TKE overrules the increase in S1 yield, so the mean
Neutron induced fission of 234U
Hambsch, F.-J.; Al-Adili, A.; Oberstedt, S.; Pomp, S.
2012-02-01
The fission fragment properties of 234U(n,f) were investigated as a function of incident neutron energy from 0.2 MeV up to 5 MeV. The fission fragment mass, angular distribution and kinetic energy were measured with a double Frisch-grid ionization chamber using both analogue and digital data acquisition techniques. The reaction 234U(n,f) is relevant, since it involves the same compound nucleus as formed after neutron evaporation from highly excited 236U*, the so-called second-chance fission of 235U. Experimental data on fission fragment properties like fission fragment mass and total kinetic energy (TKE) as a function of incident neutron energy are rather scarce for this reaction. For the theoretical modelling of the reaction cross sections for Uranium isotopes this information is a crucial input parameter. In addition, 234U is also an important isotope in the Thorium-based fuel cycle. The strong anisotropy of the angular distribution around the vibrational resonance at En = 0.77 MeV could be confirmed using the full angular range. Fluctuations in the fragment TKE have been observed in the threshold region around the strong vibrational resonance at En = 0.77 MeV. The present results are in contradiction with corresponding literature values. Changes in the mass yield around the vibrational resonance and at En = 5 MeV relative to En = 2 MeV show a different signature. The drop in mean TKE around 2.5 to 3 MeV points to pair breaking as also observed in 235,238U(n,f). The measured two-dimensional mass yield and TKE distribution have been described in terms of fission modes. The yield of the standard 1 (S1) mode shows fluctuations in the threshold of the fission cross section due to the influence of the resonance and levels off at about 20% yield for higher incident neutron energies. The S2 mode shows the respective opposite behaviour. The mean TKE of both modes decreases with En. The decrease in mean TKE overrules the increase in S1 yield, so the mean TKE is dropping
Danilyan, G. V.; Klenke, J.; Krakhotin, V. A.; Kopach, Yu. N.; Novitsky, V. V.; Pavlov, V. S.; Shatalov, P. B.
2011-05-01
Study of the T-odd three-vector correlation in the emission of prompt neutrons from 235U fission by polarized cold neutrons has been continued at the facility MEPHISTO of the FRM II reactor (Technical University of Munich). The sought correlation was not found within experimental error of 2.3 × 10-5. The upper limit for the asymmetry coefficient has been set to | D n | fission correlation coefficient D α = (170±20) × 10-5. This limit casts doubt on a model that explains the three-vector correlation in ternary fission by the Coriolis mechanism. At the same time, five-vector correlation in the emission of prompt fission neutrons has been measured, which describes the rotation of the fissioning nucleus at the moment it breaks (ROT effect). At the angle 22.5° to the fission axis, the correlation coefficient was found to be (1.57 ± 0.20) × 10-4, while at the angle of 67.5° it is zero within the experimental uncertainty. The existence of ROT effect in the emission of prompt fission neutrons can be explained by the anisotropy of neutron emission in the rest frame of the fragment (fission fragments are aligned with respect to the axis of deformation of the fissioning nucleus), similar to the mechanism of ROT effect in the emission of prompt γ-rays.
Contribution to the study of nuclear fission
International Nuclear Information System (INIS)
Serot, O.
2009-09-01
The author proposes an overview of his research activity during the past fifteen years and more particularly that dealing with nuclear fission. The first part reports works on nucleus physics at the scission via the investigation of ternary fission (experimental procedure, influence of fission modes, influence of resonance spin, influence of excitation energy of the fissioning nucleus, emission probabilities, energy spectra of ternary alphas and tritons, emission mechanism). The second part reports measurements and assessments of neutron-induced fission cross sections. The third part reports the investigation of some properties of fission products (efficiencies, branching ratios of the main delayed neutron precursors)
International conference on fifty years research in nuclear fission
International Nuclear Information System (INIS)
1989-02-01
These proceedings contain extended abstracts of the papers presented at the named conference. They deal with static properties of fission, instrumentation for fission studies, fission in compound-nucleus reactions, fission dynamics, fission-like heavy ion reactions, and fusion reactions. See hints under the relevant topics. (HSI)
Energy Technology Data Exchange (ETDEWEB)
Younes, W. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2016-10-26
A three-year theory project was undertaken to study the fission process in extreme astrophysical environments, such as the crust of neutron stars. In the first part of the project, the effect of electron screening on the fission process was explored using a microscopic approach. For the first time, these calculations were carried out to the breaking point of the nucleus. In the second part of the project, the population of the fissioning nucleus was calculated within the same microscopic framework. These types of calculations are extremely computer-intensive and have seldom been applied to heavy deformed nuclei, such as fissioning actinides. The results, tools and methodologies produced in this work will be of interest to both the basic-science and nuclear-data communities.
Coulex fission of 234U, 235U, 237Np, and 238Np studied within the SOFIA experimental program
International Nuclear Information System (INIS)
Martin, Julie-Fiona
2014-01-01
SOFIA (Studies On FIssion with Aladin) is an experimental project which aims at systematically measuring the fission fragments' isotopic yields as well as their total kinetic energy, for a wide variety of fissioning nuclei. The PhD work presented in this dissertation takes part in the SOFIA project, and covers the fission of nuclei in the region of the actinides: 234 U, 235 U, 237 Np and 238 Np. The experiment is led at the heavy-ion accelerator GSI in Darmstadt, Germany. This facility provides intense relativistic primary beam of 238 U. A fragmentation reaction of the primary beam permits to create a secondary beam of radioactive ions, some of which the fission is studied. The ions of the secondary beam are sorted and identified through the FR-S (Fragment Separator), a high resolution recoil spectrometer which is tuned to select the ions of interest.The selected - fissile - ions then fly further to Cave-C, an experimental area where the fission experiment itself takes place. At the entrance of the cave, the secondary beam is excited by Coulomb interaction when flying through an target; the de-excitation process involves low-energy fission. Both fission fragments fly forward in the laboratory frame, due to the relativistic boost inferred from the fissioning nucleus.A complete recoil spectrometer has been designed and built by the SOFIA collaboration in the path of the fission fragments, around the existing ALADIN magnet. The identification of the fragments is performed by means of energy loss, time of flight and deviation in the magnet measurements. Both fission fragments are fully (in mass and charge) and simultaneously identified.This document reports on the analysis performed for (1) the identification of the fissioning system, (2) the identification of both fission fragments, on an event-by-event basis, and (3) the extraction of fission observables: yields, TKE, total prompt neutron multiplicity. These results, concerning the actinides, are discussed, and
Study of the $^{234}$U(n,f) fission fragment angular distribution at the CERN n_TOF facility
Cidoncha-Leal, E; Paradela, C; Tarrío, D; Leong, L S; Audouin, L; Tassan-Got, L; Altstadt, S; Andrzejewski, J; Barbagallo, M; Bécares, V; Becvár, F; Belloni, F; Berthoumieux, E; Billowes, J; Boccone, V; Bosnar, D; Brugger, M; Calviani, M; Calviño, F; Cano-Ott, D; Carrapiço, C; Cerutti, F; Chiaveri, E; Chin, M; Colonna, N; Cortés, G; Cortés-Giraldo, M A; Diakaki, M; Domingo-Pardo, C; Dressler, R; Dzysiuk, N; Eleftheriadis, C; Ferrari, A; Fraval, K; Ganesan, S; García, A R; Giubrone, G; Gómez-Hornillos, M B; Gonçalves, I F; González-Romero, E; Griesmayer, E; Guerrero, C; Gunsing, F; Gurusamy, P; Hernández-Prieto, A; Jenkins, D G; Jericha, E; Kadi, Y; Käppeler, F; Karadimos, D; Kivel, N; Koehler, P; Kokkoris, M; Krticka, M; Kroll, J; Lampoudis, C; Langer, C; Lederer, C; Leeb, H; Losito, R; Mallick, A; Manousos, A; Marganiec, J; Martínez, T; Massimi, C; Mastinu, P F; Mastromarco, M; Meaze, M; Mendoza, E; Mengoni, A; Milazzo, P M; Mingrone, F; Mirea, M; Mondalaers, W; Pavlik, A; Perkowski, J; Plompen, A; Praena, J; Quesada, J M; Rauscher, T; Reifarth, R; Riego, A; Robles, M S; Roman, F; Rubbia, C; Sabaté-Gilarte, M; Sarmento, R; Saxena, A; Schillebeeckx, P; Schmidt, S; Schumann, D; Tagliente, G; Tain, J L; Tsinganis, A; Valenta, S; Vannini, G; Variale, V; Vaz, P; Ventura, A; Versaci, R; Vermeulen, M J; Vlachoudis, V; Vlastou, R; Wallner, A; Ware, T; Weigand, M; Weiß, C; Wright, T; Zugec, P
2014-01-01
The angular distribution of the f ssion fragments (FFAD) produced in neutron- induced reactions of actinides have been measured with a f ssion detection setup based on parallel-plate avalanche counters (PPACs) at the Neutron Time- Of-Flight (n_TOF) facility at CERN. The main features of the setup and pre- liminary results are reported here forthe 234 U(n,f)reaction measurement show- ing a high concordance with previous data, while providing new results up to 100 MeV.
Shell effects in fission and quasi-fission of heavy and superheavy nuclei
Energy Technology Data Exchange (ETDEWEB)
Itkis, M.G. E-mail: itkis@flnr.jinr.ru; Aeystoe, J.; Beghini, S.; Bogachev, A.A.; Corradi, L.; Dorvaux, O.; Gadea, A.; Giardina, G.; Hanappe, F.; Itkis, I.M.; Jandel, M.; Kliman, J.; Khlebnikov, S.V.; Kniajeva, G.N.; Kondratiev, N.A.; Kozulin, E.M.; Krupa, L.; Latina, A.; Materna, T.; Montagnoli, G.; Oganessian, Yu.Ts.; Pokrovsky, I.V.; Prokhorova, E.V.; Rowley, N.; Rubchenya, V.A.; Rusanov, A.Ya.; Sagaidak, R.N.; Scarlassara, F.; Stefanini, A.M.; Stuttge, L.; Szilner, S.; Trotta, M.; Trzaska, W.H.; Vakhtin, D.N.; Vinodkumar, A.M.; Voskressenski, V.M.; Zagrebaev, V.I
2004-04-05
Results of the experiments aimed at the study of fission and quasi-fission processes in the reactions {sup 12}C+{sup 204}Pb, {sup 48}Ca+{sup 144,154}Sm, {sup 168}Er, {sup 208}Pb, {sup 244}Pu, {sup 248}Cm; {sup 58}Fe+{sup 208}Pb, {sup 244}Pu, {sup 248}Cm, and {sup 64}Ni+{sup 186}W, {sup 242}Pu are presented in the work. The choice of the above-mentioned reactions was inspired by recent experiments on the production of the isotopes {sup 283}112, {sup 289}114 and {sup 283}116 at Dubna [1],[2] using the same reactions. The {sup 58}Fe and {sup 64}Ni projectiles were chosen since the corresponding projectile-target combinations lead to the synthesis of even heavier elements. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR, Russia), the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL, Italy) and the Accelerator of the Laboratory of University of Jyvaskyla (JYFL, Finland) using the time-of-flight spectrometer of fission fragments CORSET[3] and the neutron multi-detector DEMON[4],[5]. The role of shell effects and the influence of the entrance channel on the mechanism of the compound nucleus fusion-fission and the competitive process of quasi-fission are discussed.
Investigating fusion dynamics at high angular momentum via fission cross sections
Palshetkar, C. S.; Hinde, D. J.; Williams, E.; Ramachandran, K.; Dasgupta, M.; Cook, K. J.; Wakhle, A.; Jeung, D. Y.; Rafferty, D. C.; McNeil, S. D.; Carter, I. P.; Luong, D. H.
2017-11-01
A quantitative understanding of fusion dynamics at high angular momentum is attempted employing experimental fission cross sections as a probe and carrying out a simultaneous description of the fusion and fission cross sections at above barrier energies. For this, experimental fission fragment angular distributions for three systems: 16O+148Sm, 28Si+136Ba and 40Ca+124Sn, all forming the same compound nucleus 164Yb at similar excitation energies, have been measured at four beam energies above their respective capture barriers. A simultaneous description of the angle integrated fission cross sections and evaporation residue/fusion cross sections available in literature for the systems is carried out using coupled-channels and statistical model calculations. Fission cross sections, which are most sensitive to the changes in angular momentum, provide very stringent constraints for model calculations thus indicating the need of precision evaporation residue as well as fission cross sections in such studies. A large diffuseness (ao>0.65 fm) of the nuclear potential gives the best reproduction of the experimental data. In addition, different coupling schemes give very different angular momentum distributions, which, in turn, give very different fission cross section predictions. Both these observations hint at the explanation that depending on energy dissipation of the interacting nuclei occurring inside or outside the fusion pocket, very different fission cross sections can result due to heavily altered angular momentum and thus justifies the sensitivity of fission cross sections used as probes in the present work.
Mahata, K.; Kailas, S.; Shrivastava, A.; Chatterjee, A.; Singh, P.; Santra, S.; Tomar, B. S.
2002-03-01
Fission fragment angular distributions have been measured for 19F+194,198Pt systems in the laboratory energy range from 88 to 104 MeV and the fission fragment angular anisotropy data have been compared with the statistical saddle-point model calculations. The anisotropy data for 19F+198Pt (217Fr with compound nucleus neutron number Nc=130) are in good accord with the calculations over the entire range of bombarding energies except at the highest energy point. However, the data for 19F+194Pt (213Fr with Nc=126) though consistent on the average with the calculations, show noticeable deviation at a few energies.
Eslamizadeh, H.
2017-02-01
Evaporation residue cross section, fission probability, anisotropy of fission fragment angular distribution, mass and energy distributions of fission fragments and the pre-scission neutron multiplicity for the excited compound nuclei {}168{{Y}}{{b}}, {}172{{Y}}{{b}}, {}178{{W}} and {}227{{P}}{{a}} produced in fusion reactions have been calculated in the framework of the modified statistical model and multidimensional dynamical model. In the dynamical calculations, the dynamics of fission of excited nuclei has been studied by solving three- and four-dimensional Langevin equations with dissipation generated through the chaos-weighted wall and window friction formula. Three collective shape coordinates plus the projection of total spin of the compound nucleus to the symmetry axis, K, were considered in the four-dimensional dynamical model. A non-constant dissipation coefficient of K, {γ }k, was applied in the four-dimensional dynamical calculations. A comparison of the results of the three- and four-dimensional dynamical models with the experimental data showed that the results of the four-dimensional dynamical model for the evaporation residue cross section, fission probability, anisotropy of fission fragment angular distribution, mass and energy distributions of fission fragments and the pre-scission neutron multiplicity are in better agreement with the experimental data. It was also shown that the modified statistical model can reproduce the above-mentioned experimental data by choosing appropriate values of the temperature coefficient of the effective potential, λ , and the scaling factor of the fission-barrier height, {r}s.
International Nuclear Information System (INIS)
Engelmann, C.; Ameil, F.; Bernas, M.; Heinz, A.; Janas, Z.; Kozhuharov, C.; Miehe, C.; Pfuetzner, M.; Roehl, C.; Stephan, C.; Tassan-Got, L.; Voss, B.
1995-07-01
We report the first observation of the doubly magic nucleus 78 Ni 50 and the heavy isotopes 77 Ni, 73,74,75 Co, 80 Cu. The isotopes were produced by nuclear fission in collisions of 750 A.MeV projectiles of 238 U on Be target nuclei. The fully-stripped fission products were separated in-flight by the fragment separator FRS and identified event-by-event by measuring the magnetic rigidity, the trajectory, the energy deposit, and the time of flight. Production cross-sections and fission yields for the new Ni-isotopes are given. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Bentaleb, M.
1995-06-01
A search for octupole deformation in neutron rich Xe isotopes has been conducted through gamma-ray of secondary fragments produced in the spontaneous fission of {sup 248} Cm. The spectrometer consisted of Eurogam 1 array and a set of LEPS detectors. Clean one-dimensional spectra were extracted from a cubic data array and gated matrices. This technique enabled the construction of level schemes for Xe isotopes with masses ranging from 138 to 144. None of the level schemes exhibit an alternating parity quasimolecular band, a feature usually encountered in nuclei with stable octupole deformation. For several isotopes, structures are observed in the level schemes which indicates that the nuclei are octupole soft. (author). 48 refs., 52 figs., 4 tabs.
Event-by-Event Simulation of Induced Fission
Energy Technology Data Exchange (ETDEWEB)
Vogt, R; Randrup, J
2007-12-13
We are developing a novel code that treats induced fission by statistical (or Monte-Carlo) simulation of individual decay chains. After its initial excitation, the fissionable compound nucleus may either deexcite by evaporation or undergo binary fission into a large number of fission channels each with different energetics involving both energy dissipation and deformed scission prefragments. After separation and Coulomb acceleration, each fission fragment undergoes a succession of individual (neutron) evaporations, leading to two bound but still excited fission products (that may further decay electromagnetically and, ultimately, weakly), as well as typically several neutrons. (The inclusion of other possible ejectiles is planned.) This kind of approach makes it possible to study more detailed observables than could be addressed with previous treatments which have tended to focus on average quantities. In particular, any type of correlation observable can readily be extracted from a generated set of events. With a view towards making the code practically useful in a variety of applications, emphasis is being put on making it numerically efficient so that large event samples can be generated quickly. In its present form, the code can generate one million full events in about 12 seconds on a MacBook laptop computer. The development of this qualitatively new tool is still at an early stage and quantitative reproduction of existing data should not be expected until a number of detailed refinement have been implemented.
Event-by-Event Simulation of Induced Fission
International Nuclear Information System (INIS)
Vogt, R; Randrup, J
2007-01-01
We are developing a novel code that treats induced fission by statistical (or Monte-Carlo) simulation of individual decay chains. After its initial excitation, the fissionable compound nucleus may either deexcite by evaporation or undergo binary fission into a large number of fission channels each with different energetics involving both energy dissipation and deformed scission prefragments. After separation and Coulomb acceleration, each fission fragment undergoes a succession of individual (neutron) evaporations, leading to two bound but still excited fission products (that may further decay electromagnetically and, ultimately, weakly), as well as typically several neutrons. (The inclusion of other possible ejectiles is planned.) This kind of approach makes it possible to study more detailed observables than could be addressed with previous treatments which have tended to focus on average quantities. In particular, any type of correlation observable can readily be extracted from a generated set of events. With a view towards making the code practically useful in a variety of applications, emphasis is being put on making it numerically efficient so that large event samples can be generated quickly. In its present form, the code can generate one million full events in about 12 seconds on a MacBook laptop computer. The development of this qualitatively new tool is still at an early stage and quantitative reproduction of existing data should not be expected until a number of detailed refinement have been implemented
Indian Academy of Sciences (India)
Home; Journals; Resonance – Journal of Science Education; Volume 21; Issue 3. Story of Fission: Unlocking Power of the Nucleus. Amit Roy. General Article Volume 21 Issue 3 March 2016 pp 247-258. Fulltext. Click here to view fulltext PDF. Permanent link: http://www.ias.ac.in/article/fulltext/reso/021/03/0247-0258 ...
International Nuclear Information System (INIS)
McKay, H.A.C.
1978-01-01
In this article by the retired head of the Separation Processes Group of the Chemistry Division, Atomic Energy Research Establishment, Harwell, U.K., the author recalls what he terms 'an exciting drama, the unravelling of the nature of the atomic nucleus' in the years before the Second World War, including the discovery of fission. 12 references. (author)
Theory of nuclear fission: a review
International Nuclear Information System (INIS)
Mosel, U.
1976-01-01
General properties of nuclear fission are reviewed and related to our present knowledge of fission theory. For this purpose the basic reasons for the shape of the fission barriers are discussed and their consequences compared with experimental results on barrier shapes and structures. Special emphasis is put on the asymmetry of the fission barriers and mass-distributions and its relation to the shells of the nascent fragment shells. Finally the problem of calculating fission cross sections is discussed
Radiochemistry and the Study of Fission
Energy Technology Data Exchange (ETDEWEB)
Rundberg, Robert S. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-11-14
These are slides from a lecture given at UC Berkeley. Radiochemistry has been used to study fission since its discovery. Radiochemical methods are used to determine cumulative mass yields. These measurements have led to the two-mode fission hypothesis to model the neutron energy dependence of fission product yields. Fission product yields can be used for the nuclear forensics of nuclear explosions. The mass yield curve depends on both the fuel and the neutron spectrum of a device. Recent studies have shown that the nuclear structure of the compound nucleus can affect the mass yield distribution. The following topics are covered: In the beginning: the discovery of fission; forensics using fission products: what can be learned from fission products, definitions of R-values and Q-values, fission bases, K-factors and fission chambers, limitations; the neutron energy dependence of the mass yield distribution (the two mode fission hypothesis); the influence of nuclear structure on the mass yield distribution. In summary: Radiochemistry has been used to study fission since its discovery. Radiochemical measurement of fission product yields have provided the highest precision data for developing fission models and for nuclear forensics. The two-mode fission hypothesis provides a description of the neutron energy dependence of the mass yield curve. However, data is still rather sparse and more work is needed near second and third chance fission. Radiochemical measurements have provided evidence for the importance of nuclear states in the compound nucleus in predicting the mass yield curve in the resonance region.
Radiochemistry and the Study of Fission
International Nuclear Information System (INIS)
Rundberg, Robert S.
2016-01-01
These are slides from a lecture given at UC Berkeley. Radiochemistry has been used to study fission since its discovery. Radiochemical methods are used to determine cumulative mass yields. These measurements have led to the two-mode fission hypothesis to model the neutron energy dependence of fission product yields. Fission product yields can be used for the nuclear forensics of nuclear explosions. The mass yield curve depends on both the fuel and the neutron spectrum of a device. Recent studies have shown that the nuclear structure of the compound nucleus can affect the mass yield distribution. The following topics are covered: In the beginning: the discovery of fission; forensics using fission products: what can be learned from fission products, definitions of R-values and Q-values, fission bases, K-factors and fission chambers, limitations; the neutron energy dependence of the mass yield distribution (the two mode fission hypothesis); the influence of nuclear structure on the mass yield distribution. In summary: Radiochemistry has been used to study fission since its discovery. Radiochemical measurement of fission product yields have provided the highest precision data for developing fission models and for nuclear forensics. The two-mode fission hypothesis provides a description of the neutron energy dependence of the mass yield curve. However, data is still rather sparse and more work is needed near second and third chance fission. Radiochemical measurements have provided evidence for the importance of nuclear states in the compound nucleus in predicting the mass yield curve in the resonance region.
International Nuclear Information System (INIS)
Tudora, A.
2013-01-01
The experimental data of average prompt neutron multiplicity as a function of total kinetic energy of fragments <ν>(TKE) exhibit, especially in the case of 252 Cf(SF), different slopes dTKE/dν and different behaviours at low TKE values. The Point-by-Point (PbP) model can describe these different behaviours. The higher slope dTKE/dν and the flattening of <ν> at low TKE exhibited by a part of experimental data sets is very well reproduced when the PbP multi-parametric matrix ν(A,TKE) is averaged over a double distribution Y(A,TKE). The lower slope and the almost linear behaviour over the entire TKE range exhibited by other data sets is well described when the same matrix ν(A,TKE) is averaged over a single distribution Y(A). In the case of average prompt neutron energy in SCM as a function of TKE, different dTKE/dε slopes are also obtained by averaging the same PbP matrix ε(A,TKE) over Y(A,TKE) and over Y(A). The results are exemplified for 3 fissioning systems benefiting of experimental data as a function of TKE: 252 Cf(SF), 235 U(n th ,f) and 239 Pu(n th ,f). In the case of 234 U(n,f) for the first time it was possible to calculate <ν>(TKE) and <ε>(TKE) at many incident energies by averaging the PbP multi-parametric matrices over the experimental Y(A,TKE) distributions recently measured at IRMM for 14 incident energies in the range 0.3- 5 MeV. The results revealed that the slope dTKE/dν does not vary with the incident energy and the flattening of <ν> at low TKE values is more pronounced at low incident energies. The average model parameters dependences on TKE resulted from the PbP treatment allow the use of the most probable fragmentation approach, having the great advantage to provide results at many TKE values in a very short computing time compared to PbP and Monte Carlo treatments. (author)
Eslamizadeh, H.
2016-02-01
A stochastic approach based on one- and two-dimensional Langevin equations is applied to calculate the pre-scission neutron multiplicity, fission probability, anisotropy of fission fragment angular distribution, fission cross section and the evaporation cross section for the compound nuclei 188Pt, 227Pa and 251Es in an intermediate range of excitation energies. The chaos weighted wall and window friction formula are used in the Langevin equations. The elongation parameter, c, is used as the first dimension and projection of the total spin of the compound nucleus onto the symmetry axis, K, considered as the second dimension in Langevin dynamical calculations. A constant dissipation coefficient of K, γK = 0.077(MeV zs)-1/2, is used in two-dimensional calculations to reproduce the above mentioned experimental data. Comparison of the theoretical results of the pre-scission neutron multiplicity, fission probability, fission cross section and the evaporation cross section with the experimental data shows that the results of two-dimensional calculations are in better agreement with the experimental data. Furthermore, it is shown that the two-dimensional Langevin equations together with a dissipation coefficient of K, γK = 0.077(MeV zs)-1/2, can satisfactorily reproduce the anisotropy of fission fragment angular distribution for the heavy compound nucleus 251Es. However, a larger value of γK = 0.250(MeV zs)-1/2 is needed to reproduce the anisotropy of fission fragment angular distribution for the lighter compound nucleus 227Pa.
Nuclear Forensics and Radiochemistry: Fission
Energy Technology Data Exchange (ETDEWEB)
Rundberg, Robert S. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-11-07
Radiochemistry has been used to study fission since it’ discovery. Radiochemical methods are used to determine cumulative mass yields. These measurements have led to the two-mode fission hypothesis to model the neutron energy dependence of fission product yields. Fission product yields can be used for the nuclear forensics of nuclear explosions. The mass yield curve depends on both the fuel and the neutron spectrum of a device. Recent studies have shown that the nuclear structure of the compound nucleus can affect the mass yield distribution.
Collective spectra along the fission barrier
Pigni M. T.; Andreev A. V.; Shneidman T. M.; Massimi C.; Vannini G.; Ventura A.
2012-01-01
Discrete and continuous spectra of fissioning nuclei at the humps of fission barriers (Bohr transition states) and in the intermediate wells (superdeformed and hyperdeformed states) play a key role in the calculation of fission cross sections. A theoretical evaluation of the collective parts of the spectra is possible within the framework of the dinuclear system model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two–cluster co...
Study of the Fission Decay of Heavy Hypernuclei
2002-01-01
The purpose of the original experiment PS177 was to produce heavy hypernuclei using the annihilation at rest of antiprotons in heavy targets, and to measure their lifetime. \\\\ \\\\ Lambda hyperons can be produced, within a nucleus, in a 2-step process: p@*~@A~K&bar.K~+~X; &bar.KN~@A~@L@p; or in a direct 3-body interaction: @*NN~@A~K|+@L. In the first case, the kinematical conditions favour recoilless lambda with, consequently, a higher probability of attachment to the nucleus. In a heavy nucleus the lambda-hyperon decays weakly according to: @LN~@A~NN, and the &prop.170~MeV energy released induces fission.\\\\ \\\\ The identification of the hypernuclei and their lifetime measurements were performed through the detection of delayed fission using the recoil-distance-method (suitable for lifetimes in the expected region @=10|-|1|0s). The fission fragments were detected by parallel-plate avalanche counters. \\\\ \\\\ The new proposal aims at i) increasing the accuracy of the measured lifetimes, ii) having a str...
Nucleus spectroscopy: extreme masses and deformations
International Nuclear Information System (INIS)
Theisen, Ch.
2009-12-01
The author proposes a synthesis of research activities performed since 1995 in the field of experimental nuclear physics, and more particularly in the investigation of two nucleus extreme states: deformation on the one hand, heavy and very heavy nuclei on the other hand. After a presentation of the context of investigations on deformation, rotation, and heavy nuclei, he gives an overview of developments regarding instruments (gamma spectrometers, detection of fission fragments, and detection at the focal plane of spectrometers or separators) and analysis techniques. Experiments and results are then reported and discussed, concerning super-deformed states with a high angular moment, spectroscopy of neutron-rich nuclei, very heavy nuclei close to nucleus map borders. He finally draws perspectives for middle and long term studies on the heaviest nuclei
Studies of complex fragment emission in heavy ion reactions
International Nuclear Information System (INIS)
Sobotka, L.G.
1989-01-01
The production of large fragments, fragments with mass between light particles and fission fragments, in intermediate and high energy nuclear reactions has fostered the proposal of a number of novel reaction mechanisms. These include liquid-vapor equilibrium and nuclear shattering. Temporarily left in the wake of these exciting proposed mechanisms was the old standard, statistical decay of compound nuclei. To be sure, the standard treatment of compound nucleus decay did not deal with large fragment production. However, this omission was not due to any fundamental deficiency of statistical models, but rather an uncertainty concerning exactly how to splice large fragment emission into statistical models. A large portion of our program deals with this problem. Specifically, by studying the yields of large fragments produced in sufficiently low energy reactions we are attempting to deduce the asymmetry and l-wave dependence of large fragment emission from compound nuclear intermediates. This, however, is only half of the problem. Since the novel mechanisms proposed for large fragment emission were spawned by intermediate and high energy reaction data, we must also realize the relevance of the compound nucleus mechanisms at high energies. It is not unreasonable to suspect that compound nucleus-like objects are formed with less than complete momentum transfer and perhaps less than complete mass transfer. Therefore the study of energy, mass, and angular momentum transfer in incomplete fusion and non-compound reactions. This thread joins the apparently divergent subjects covered in this report
Mechanisms of fission neutron emission
International Nuclear Information System (INIS)
Maerten, H.
1991-01-01
The time evolution in fission is the starting point for discussing not only the main mechanism of fission neutron emission, the evaporation from fully accelerated fragments, but also possible secondary ones connected with dynamical features of nuclear fission. ''Asymptotic'' conditions as relevant for describing the particle release from highly excited, rapidly moving fragments are defined. Corresponding statistical model approaches to fission neutron emission, based on the adequate consideration of the intricate fragment occurrence probability, reproduce most of the experimental data. The remarkable influence of fission modes on neutron observables is analyzed in the framework of a macroscopic-microscopic scission point model consistent with energy conservation. Finally, chances and deficiencies for solving the mechanism puzzle are summarized. (author). 87 refs, 21 figs
Energy Technology Data Exchange (ETDEWEB)
Santhosh, K.P.; Krishnan, Sreejith [Kannur University, School of Pure and Applied Physics, Payyanur, Kerala (India)
2016-04-15
Within the unified ternary fission model (UTFM), the alpha accompanied ternary fission of even-even {sup 244-260}Cf isotopes has been studied by taking the interacting barrier as the sum of Coulomb and proximity potential. For the alpha accompanied ternary fission of the {sup 244}Cf isotope, the highest yield is obtained for the fragment combination {sup 108}Ru + {sup 4}He + {sup 132}Te, which contains the near doubly magic nucleus {sup 132}Te (N = 80, Z = 52). In the case of {sup 246}Cf and {sup 248}Cf isotopes, the highest yield is obtained for the fragment combinations with the near doubly magic nucleus {sup 134}Te (N = 82, Z = 52) as the heaviest fragment. The highest yield obtained for {sup 250}Cf, {sup 252}Cf, {sup 254}Cf, {sup 256}Cf, {sup 258}Cf and {sup 260}Cf isotopes is for the fragment combination with the doubly magic nucleus {sup 132}Sn (N = 82), Z = 50 as the heaviest fragment. We have included the effect of deformation and orientation of fragments and this has revealed that in addition to the closed shell effect, ground-state deformation also plays an important role in the calculation of the relative yield of favorable fragment combinations. The computed isotopic yields for the alpha accompanied ternary fission of the {sup 252}Cf isotope are found to be in agreement with the experimental data. The emission probability and kinetic energy of the long-range alpha particle is calculated for the various isotopes of Cf and are found to be in good agreement with the experimental data. (orig.)
Fission hindrance and nuclear viscosity
Indian Academy of Sciences (India)
viscosity in slowing down the diffusion rate in comparison to the decay rate without vis- cosity predicted by Bohr and ... revived Kramers' dynamical approach to understand nuclear fission at finite temperature and angular momentum. ... tor and (2) a compact seven-element array of BaF2 detectors. The fission fragments were.
Four-dimensional Langevin dynamics of heavy-ion-induced fission
Nadtochy, P. N.; Ryabov, E. G.; Gegechkori, A. E.; Anischenko, Yu. A.; Adeev, G. D.
2012-06-01
A four-dimensional dynamical model based on Langevin equations was developed and applied to calculate a wide set of experimental observables for the reactions 16O+208Pb→224Th and 16O+232Th→248Cf over a wide range of excitation energy. The fusion-fission and evaporation residue cross sections, fission fragment mass-energy distribution parameters, prescission neutron multiplicities, and anisotropy of angular distribution of fission fragments could be reasonably reproduced using a modified one-body mechanism for nuclear friction with a reduction coefficient of the contribution from a wall formula ks≃0.25 and a dissipation coefficient for the orientation degree of freedom (K coordinate) γK≃ 0.077 (MeVzs)-1/2. Inclusion of the K coordinate into calculation of potential energy changes the stiffness of the nucleus with respect to mass asymmetry coordinate for the values of K≠0 and results in a shift of the Businaro-Gallone point towards larger Z2/A values. The experimental data on the fission fragment mass-energy distribution parameters together with mean prescission neutron multiplicity for heavy fissioning nuclei are reproduced through the four-dimensional Langevin calculations more accurately than through three-dimensional calculations.
International Nuclear Information System (INIS)
Wagemans, C.
1991-01-01
Fifty years after its discovery, the nuclear fission phenomenon is of recurring interest. When its fundamental physics aspects are considered, fission is viewed in a very positive way, which is reflected in the great interest generated by the meetings and large conferences organized for the 50th anniversary of its discovery. From a purely scientific and practical point of view, a new book devoted to the (low energy) nuclear fission phenomenon was highly desirable considering the tremendous amount of new results obtained since the publication of the book Nuclear Fission by Vandenbosch and Huizenga in 1973 (Academic Press). These new results could be obtained thanks to the growth of technology, which enabled the construction of powerful new neutron sources, particle and heavy ion accelerators, and very performant data-acquisition and computer systems. The re-invention of the ionization chamber, the development of large fission fragment spectrometers and sophisticated multiparameter devices, and the production of exotic isotopes also contributed significantly to an improved understanding of nuclear fission. This book is written at a level to introduce graduate students to the exciting subject of nuclear fission. The very complete list of references following each chapter also makes the book very useful for scientists, especially nuclear physicists. The book has 12 chapters covering the fission barrier and the various processes leading to fission as well as the characteristics of the various fission reaction products. In order to guarantee adequate treatment of the very specialized research fields covered, several distinguished scientists actively involved in some of these fields were invited to contribute their expertise as authors or co-authors of the different chapters
Fission dynamics of 240Cf* formed in 34,36S induced reactions
Directory of Open Access Journals (Sweden)
Jain Deepika
2015-01-01
Full Text Available We have studied the entrance channel effects in the decay of Compound nucleus 240Cf* formed in 34S+206Pb and 36S+204Pb reactions by using energy density dependent nuclear proximity potential in the framework of dynamical cluster-decay model (DCM. At different excitation energies, the fragmentation potential and preformation probability of decaying fragments are almost identical for both the entrance channels, which seem to suggest that decay is independent of its formation and entrance channel excitation energy. It is also observed that, with inclusion of deformation effects upto quadrupole within the optimum orientation approach, the fragmentation path governing potential energy surfaces gets modified significantly. Beside this, the fission mass distribution of Cf* isotopes is also investigated. The calculated fission cross-sections using SIII force for both the channels find nice agreement with the available experimental data for deformed choice of fragments, except at higher energies. In addition to this, the comparative analysis with Blocki based nuclear attraction is also worked out. It is observed that Blocki proximity potential accounts well for the CN decay at all energies whereas the use of EDF based nuclear potential suggests the presence of some non-compound nucleus process (such as quasi-fission (qf at higher energies.
Capture and fission with DANCE and NEUANCE
Energy Technology Data Exchange (ETDEWEB)
Jandel, M.; Baramsai, B.; Bond, E.; Rusev, G.; Walker, C.; Bredeweg, T.A.; Chadwick, M.B.; Couture, A.; Fowler, M.M.; Hayes, A.; Kawano, T.; Mosby, S.; Stetcu, I.; Taddeucci, T.N.; Talou, P.; Ullmann, J.L.; Vieira, D.J.; Wilhelmy, J.B. [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)
2015-12-15
A summary of the current and future experimental program at DANCE is presented. Measurements of neutron capture cross sections are planned for many actinide isotopes with the goal to reduce the present uncertainties in nuclear data libraries. Detailed studies of capture gamma rays in the neutron resonance region will be performed in order to derive correlated data on the de-excitation of the compound nucleus. New approaches on how to remove the DANCE detector response from experimental data and retain the correlations between the cascade gamma rays are presented. Studies on {sup 235}U are focused on quantifying the population of short-lived isomeric states in {sup 236}U after neutron capture. For this purpose, a new neutron detector array NEUANCE is under construction. It will be installed in the central cavity of the DANCE array and enable the highly efficient tagging of fission and capture events. In addition, developments of fission fragment detectors are also underway to expand DANCE capabilities to measurements of fully correlated data on fission observables. (orig.)
Capture and fission with DANCE and NEUANCE
Jandel, M.; Baramsai, B.; Bond, E.; Rusev, G.; Walker, C.; Bredeweg, T. A.; Chadwick, M. B.; Couture, A.; Fowler, M. M.; Hayes, A.; Kawano, T.; Mosby, S.; Stetcu, I.; Taddeucci, T. N.; Talou, P.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.
2015-12-01
A summary of the current and future experimental program at DANCE is presented. Measurements of neutron capture cross sections are planned for many actinide isotopes with the goal to reduce the present uncertainties in nuclear data libraries. Detailed studies of capture gamma rays in the neutron resonance region will be performed in order to derive correlated data on the de-excitation of the compound nucleus. New approaches on how to remove the DANCE detector response from experimental data and retain the correlations between the cascade gamma rays are presented. Studies on 235U are focused on quantifying the population of short-lived isomeric states in 236U after neutron capture. For this purpose, a new neutron detector array NEUANCE is under construction. It will be installed in the central cavity of the DANCE array and enable the highly efficient tagging of fission and capture events. In addition, developments of fission fragment detectors are also underway to expand DANCE capabilities to measurements of fully correlated data on fission observables.
Energy Technology Data Exchange (ETDEWEB)
Majumdar, N.; Bhattacharya, P. [Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Calcutta 700 064 (India); Biswas, D.C.; Choudhury, R.K.; Nadkarni, D.M.; Saxena, A. [Nuclear Physics Division, Bhabha Atomic Research Centre, Bombay 400 085 (India)
1996-02-01
In the present work we have measured fission fragment angular distributions and fusion excitation functions for the systems {sup 12}C, {sup 16}O+{sup 232}Th at energies around the Coulomb barrier. These results along with the results of our earlier measurements on {sup 19}F + {sup 232}Th system were analyzed following Hinde {ital et} {ital al}. [Phys. Rev. Lett. {bold 74}, 1295 (1995)] where it was pointed out that the anomalous fission fragment angular distributions seen in heavy ion reactions below the Coulomb barrier can be due to possible occurrence of quasifission events caused by the interaction of the projectile with the tip of the deformed target nucleus. The present data do not show the expected saturation behavior of the fission fragment anisotropy at sub-barrier energies for the {sup 12}C+{sup 232}Th system which exhibits different behavior of the fission fragment anisotropy in the sub-barrier region as compared to the other two systems. The present measurements using different projectiles on the same target nucleus do not seem to conform to the expected behavior of the quasifission mechanism to be caused by the interaction of the projectile with the tip of the deformed target nucleus. {copyright} {ital 1996 The American Physical Society.}
True ternary fission in 310126X
International Nuclear Information System (INIS)
Banupriya, B.; Vijayaraghavan, K.R.; Balasubramaniam, M.
2015-01-01
All possible combinations are minimized by the two dimensional minimization process and minimized with respect to neutron numbers and proton numbers of the fragments. Potential energy is low and Q - value is high at true ternary fission region. It shows that true ternary mode is the dominant mode in the ternary fission of superheavy nuclei. Also, the results show that the fragments with neutron magic numbers are the dominant one in the ternary fission of superheavy nuclei whereas the fragments with proton magic numbers are the dominant one in the ternary fission of heavy nuclei
Fission of sup 2 sup 0 sup 9 Bi and sup 1 sup 9 sup 7 Au nuclei induced by 30 MeV protons
Noshad, H; Lamehi-Rachti, M
2002-01-01
Thin targets of sup 2 sup 0 sup 9 Bi and sup 1 sup 9 sup 7 Au were bombarded with 30 MeV protons at the Cyclotron Department of Nuclear Research Center for Agriculture and Medicine. Correlated measurements of kinetic energies of fission fragment pairs, and their time-of-flights were made by using pair spectrometry. The fission cross sections, fragment mass distributions, and total kinetic energy distributions of the fragments were measured in our experiment. The accurate values of cross sections for fission of sup 2 sup 0 sup 9 Bi and sup 1 sup 9 sup 7 Au nuclei with 30 MeV protons were obtained to be 1100+-100 and 62+-5.6 mu b, respectively. The cross section of sup 2 sup 0 sup 9 Bi fission with its associated error, by using this method, has not been reported previously. The interpretation in terms of liquid-drop model of fissioning nucleus sup 2 sup 1 sup 0 Po at the excitation energy of 35 MeV was confirmed by the dispersion of the distribution in fragment mass for bismuth fission.
Fission modelling with FIFRELIN
Energy Technology Data Exchange (ETDEWEB)
Litaize, Olivier; Serot, Olivier; Berge, Leonie [CEA, DEN, DER, SPRC, Saint Paul Lez Durance (France)
2015-12-15
The nuclear fission process gives rise to the formation of fission fragments and emission of particles (n,γ, e{sup -}). The particle emission from fragments can be prompt and delayed. We present here the methods used in the FIFRELIN code, which simulates the prompt component of the de-excitation process. The methods are based on phenomenological models associated with macroscopic and/or microscopic ingredients. Input data can be provided by experiment as well as by theory. The fission fragment de-excitation can be performed within Weisskopf (uncoupled neutron and gamma emission) or a Hauser-Feshbach (coupled neutron/gamma emission) statistical theory. We usually consider five free parameters that cannot be provided by theory or experiments in order to describe the initial distributions required by the code. In a first step this set of parameters is chosen to reproduce a very limited set of target observables. In a second step we can increase the statistics to predict all other fission observables such as prompt neutron, gamma and conversion electron spectra but also their distributions as a function of any kind of parameters such as, for instance, the neutron, gamma and electron number distributions, the average prompt neutron multiplicity as a function of fission fragment mass, charge or kinetic energy, and so on. Several results related to different fissioning systems are presented in this work. The goal in the next decade will be i) to replace some macroscopic ingredients or phenomenological models by microscopic calculations when available and reliable, ii) to be a support for experimentalists in the design of detection systems or in the prediction of necessary beam time or count rates with associated statistics when measuring fragments and emitted particle in coincidence iii) extend the model to be able to run a calculation when no experimental input data are available, iv) account for multiple chance fission and gamma emission before fission, v) account for
Post-scission fission theory: Neutron emission in fission
International Nuclear Information System (INIS)
Madland, D.G.
1997-01-01
A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N (E) and the average prompt neutron multiplicity bar ν p . Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N (E) and bar ν p upon the fissioning nucleus and its excitation energy are treated. Recent work in the calculation of the prompt fission neutron spectrum matrix N (E, E n ), where E n is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of our ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches
Pellereau, E.; Taïeb, J.; Chatillon, A.; Alvarez-Pol, H.; Audouin, L.; Ayyad, Y.; Bélier, G.; Benlliure, J.; Boutoux, G.; Caamaño, M.; Casarejos, E.; Cortina-Gil, D.; Ebran, A.; Farget, F.; Fernández-Domínguez, B.; Gorbinet, T.; Grente, L.; Heinz, A.; Johansson, H.; Jurado, B.; Kelić-Heil, A.; Kurz, N.; Laurent, B.; Martin, J.-F.; Nociforo, C.; Paradela, C.; Pietri, S.; Rodríguez-Sánchez, J. L.; Schmidt, K.-H.; Simon, H.; Tassan-Got, L.; Vargas, J.; Voss, B.; Weick, H.
2017-05-01
SOFIA (Studies On Fission with Aladin) is a novel experimental program, dedicated to accurate measurements of fission-fragment isotopic yields. The setup allows us to fully identify, in nuclear charge and mass, both fission fragments in coincidence for the whole fission-fragment range. It was installed at the GSI facility (Darmstadt), to benefit from the relativistic heavy-ion beams available there, and thus to use inverse kinematics. This paper reports on fission yields obtained in electromagnetically induced fission of 238U.
Mechanism of fission of neutron-deficient actinoids nuclides
Energy Technology Data Exchange (ETDEWEB)
Sueki, Keisuke; Nakahara, Hiromichi [Tokyo Metropolitan Univ., Hachioji (Japan). Faculty of Science; Tanase, Masakazu; Nagame, Yuichiro; Shinohara, Nobuo; Tsukada, Kazuaki
1996-01-01
A heavy ion reaction ({sup 19}F+{sup 209}Bi) is selected. The reaction produces neutron-deficient {sup 228}U which is compound nucleus with a pair of Rb(z=37) and Cs(Z=55). Energy dissipation problem of nucleus was studied by measuring the isotope distribution of two fissile nuclides. Bismuth metal evaporated on aluminium foil was irradiated by {sup 19}F with the incident energy of 105-128 MeV. We concluded from the results that the excess energy of reaction system obtained with increasing the incident energy is consumed by (1) light Rb much more than Cs and (2) about 60% of energy is given to two fission fragments and the rest 40% to the translational kinetic energy or unknown anomalous {gamma}-ray irradiation. (S.Y.)
Energy Technology Data Exchange (ETDEWEB)
Rentenier, A; Bordenave-Montesquieu, D; Moretto-Capelle, P; Bordenave-Montesquieu, A [Laboratoire CAR-IRSAMC, UMR 5589 CNRS - Universite Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse Cedex (France)
2003-04-28
Multifragmentation and asymmetric fission (AF) of the C{sub 60} molecule induced by H{sup +}, H{sub 2}{sup +}, H{sub 3}{sup +} and He{sup +} ions at medium collision energies (2-130 keV) are considered. Momenta and kinetic energies of C{sub n}{sup +} fragment ions (n = 1- 12) are deduced from an analysis of time-of-flight spectra. In multifragmentation processes, momenta are found to be approximately constant when n > 2, a behaviour which explains that the most probable kinetic energy, as well as the width of the kinetic energy distributions, is found to be inversely proportional to the fragment size n; both momenta and kinetic energies are independent of the velocity and nature of the projectile, and hence of the energy deposit. A specific study of the AF shows that the kinetic energies of C{sub 2}{sup +}, C{sub 4}{sup +} and C{sub 6}{sup +} fragments are also independent of the collision velocity and projectile species; a quantitative agreement is found with values deduced from kinetic energy release measurements by another group in electron impact experiments, and the observed decrease when the mass of the light fragment increases is also reproduced. A quantitative comparison of AF and multifragmentation for the n = 2, 4 and 6 fragment ions shows that kinetic energies in AF exceed that in multifragmentation, a result which explains the oscillations observed when momenta or kinetic energies of fragments are plotted against the n-value. The AF yield is also found to scale with the energy deposit in the collision velocity range extending below the velocity at the maximum of the electronic stopping power; except for protons, it remains negligible with respect to multifragmentation as soon as the total energy deposit exceeds about 100 eV.
Decay and fission of the oriented nuclei
Kadmenskij, S G
2002-01-01
The fragment angular distributions for binary decay of oriented spherical and deformed nuclei with taking into account the correct transformational properties of wave functions under time inversion have been investigated. It has been shown that for description of fragment angular distributions the adiabatic approximation for collective rotational nuclear degrees of freedom is not correct. It has been demonstrated that this approximation is valid for description of spontaneous and induced low-energy nuclear fission. The dependence of partial fission widths on the orientation of the internal axes spins, projections of spins, and relative angular moments of fission fragments has been analyzed. It has been shown that the adiabatic approximation results in coherent interference of wave functions of fragments relative movement. This interference forms fragments the universal angular distributions of fission fragments for oriented nuclei. For these distributions the deviations from A. Bohr's formula have been invest...
Challenging fission dynamics around the barrier: The case of {sup 34}S + {sup 186}W
Energy Technology Data Exchange (ETDEWEB)
Kozulin, E.M.; Itkis, I.; Knyazheva, G.; Novikov, K.; Bogachev, A.; Dmitriev, S.; Loktev, T. [Joint Institute for Nuclear Research, Flerov Laboratory of Nuclear Reactions, Dubna (Russian Federation); Vardaci, E. [Dipartamento di Scienze Fisiche, Napoli (Italy); INFN, Napoli (Italy); Harca, I.M. [Joint Institute for Nuclear Research, Flerov Laboratory of Nuclear Reactions, Dubna (Russian Federation); Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering (IFIN-HH), Bucharest - Magurele (Romania); Universitatea din Bucuresti, Facultatea de Fizica, Bucharest (Romania); Schmitt, C.; Piot, J. [GANIL, CEA/DSM-CNRS/IN2P3, Bd Henri Becquerel, BP 55027, Caen (France); Azaiez, F.; Matea, I.; Verney, D.; Gottardo, A. [Universite Paris-Saclay, IPN, CNRS/IN2P3, Orsay (France); Dorvaux, O. [Universite de Strasbourg, IPHC, CNRS/IN2P3, Strasbourg (France); Chubarian, G. [Texas A and M University, Cyclotron Institute, College Station, TX (United States); Trzaska, W.H. [Accelerator Laboratory of University of Jyvaskyla (JYFL), Jyvaskyla (Finland); Hanappe, F. [Universite Libre de Bruxelles (ULB), Bruxelles (Belgium); Borcea, C.; Calinescu, S.; Petrone, C. [Horia Hulubei National Institute for R and D in Physics and Nuclear Engineering (IFIN-HH), Bucharest - Magurele (Romania)
2016-09-15
The current status of fission dynamics studies in heavy-ion collisions around the Coulomb barrier is illustrated with the {sup 34}S + {sup 186}W reaction. The fission-fragment mass and total kinetic energy were measured at the ALTO facility at IPN Orsay, France, with a dedicated set-up using the (v, E) approach. The measurement reveals the presence of an asymmetric fission component on top of a predominantly symmetric distribution. The asymmetric structure, pointed out for the first time, is discussed along with results of previous experiments studying the same reaction. While these analyses suggested the contribution from either quasi-fission or pre-equilibrium fission, we offer an alternative interpretation, in terms of shell-driven compound-nucleus fission. The present measurement demonstrates the critical influence of resolution when addressing puzzling cases, situated at the crossroads of the various channels opened in a heavy-ion collision. Current status in the field clearly calls for innovative measurements involving manifold correlations and new observables. The outcome of the attempt done in this work in this direction, based on the coincident measurement of prompt γ-rays is reported, and encouraging perspectives are discussed. (orig.)
Charged particle-induced nuclear fission reactions – Progress and ...
Indian Academy of Sciences (India)
of fission process for nuclei at moderately high excitation energies with large angular momentum values. ... model analysis of these data, the fission barrier can be determined for the fissioning com- pound nucleus. .... qualitative understanding of the various features of mass division are understood in terms of scission point ...
Bimodal nature in low-energy fission of light actinides
International Nuclear Information System (INIS)
Nagame, Yuichiro; Nishinaka, Ichiro; Tsukada, Kazuaki; Ikezoe, Hiroshi; Otsuki, Tsutomu; Sueki, Keisuke; Nakahara, Hiromichi; Kudo, Hisaaki.
1995-01-01
To solve various problems in the mass division process of light actinoids, some experiments on the basis of bimodal fission were carried. Mass and kinetic energy distribution of Th-232 and U-238 were determined. Pa-225 (N= 134) and Pa-227 (N=136), fission nuclei, were produced by Bi-209 + 0-16 and Bi-209 + 0-18 heavy ion nucleus reactions, and the mass yield distribution were determined by the time-of-flight method and the radiochemical procedure. From the results, two independent deforming processes were proved in the fission process of light actinoid nuclei. On the deforming process through the low fission barrier, nucleus fissioned after small deformation under the influence of stabilization of the shell structure of fission product. In the case of process through the high barrier, however, the nucleus fissioned after large deformation. The unsymmetrical mass division was derived from the former and the symmetrical one from the latter. (S.Y.)
Directory of Open Access Journals (Sweden)
Furman W.I.
2012-02-01
Full Text Available Last data on angular correlations of fission fragments from slow (s-wave neutron induced binary fission of spin-aligned nuclei 235U are discussed in the context of JπK A. Bohrs channels. Special attention is paid to K = 0 channel. Reasons for its suppression are specified for compound nucleus states of negative parity. A brief overview of recent data on T-odd angular correlations in ternary and binary (with emission of a third particle, a neutron or γ-quantum fission induced by slow polarized neutrons is presented. On the basis of the developed theoretical approach it is shown that a valuable information on JπK fission channels at scission point can be inferred from these T-odd angular correlations.
International Nuclear Information System (INIS)
Baranov, I.; Jarmiychuk, S.; Kirillov, S.; Novikov, A.; Obnorskii, V.; Pchelintsev, A.; Wien, K.; Reimann, C.
1999-01-01
In this work the charge state of the negatively charged gold nanocluster ions (2-20 nm) that were desorbed from nanodispersed gold islet targets by 252 Cf fission fragments via electronic processes is studied. Mean cluster charge was calculated as a ratio of mean cluster mass to mean mass-to-charge ratio . Cluster masses were measured by means of a collector technique employing transmission electron microscopy and scanning force microscopy, while m/q was measured by means of a tandem TOF-spectrometer. It is shown that the nanocluster ions are mostly multiply charged (2-16e) and the charge increases non-linearly with the cluster size. The results are discussed
Intermediate mass fragments emission in binary fragmentation model
International Nuclear Information System (INIS)
Bhattacharya, C.; Bhattacharya, S.
1991-01-01
Intermediate mass fragments emission in intermediate-energy nucleus-nucleus collisions has been studied in the framework of a generalized model where the fragments are assumed to be emitted from binary fissionlike decay of the fully equilibrated compound nucleus. The present formulation, with a schematic exit channel shape configuration and simple rotating liquid-drop nuclear potential, has been found to explain most of the intermediate mass fragments emission cross sections reasonably well without incorporating any free parameters in the calculation
$\\bar{p}$-Induced Fission Studies with Plastic Track Detectors Using 4$\\pi$-Geometry
2002-01-01
% EMU20 \\\\ \\\\ The annihilation of a stopped antiproton on the surface of a target nucleus produces on the average five pions with a mean energy of 230~MeV. The high excitation of the nuclei with low angular momentum transfer can also be achieved by direct pion-nucleus interactions. The fission probabilities of highly excited nuclei can be explained on the basis of high energy limit of statistical theory. Previously the binary fission and higher multiplicity break-up of various nuclei caused by the absorption of pions has been studied by our group. The mechanism of nuclear excitation may still be the same when an antiproton annihilates in a nucleus and produces pions. It would be interesting to see whether the $\\bar{p}$ annihilation produces high enough excitation energies for nuclear phase-transition to take place. If so, then the fragmentation would overwhelm binary and ternary fission process. \\\\ \\\\The use of a highly sensitive plastic detector, CR-39, was made by our group in a number of studies involving ...
Application of the dinuclear system model to fission process
Andreev A. V.; Shneidman T. M.; Ventura A.
2016-01-01
A theoretical evaluation of the collective excitation spectra of nucleus at large deformations is possible within the framework of the dinuclear system model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two-cluster configurations in a dynamical way, permitting exchange of nucleons between clusters. In this work the method of calculation of the potential energy and the collective spectrum of fissioning nucleus at scission point...
The resonance neutron fission on heavy nuclei
Kopach, Yu N; Furman, V I; Alfimenkov, V P; Lason', L; Pikelner, L B; Gonin, N N; Kozlovskij, L K; Tambovtsev, D I; Gagarskij, A M; Petrov, G A; Sokolov, V E
2001-01-01
A new approach to the description of the fission, similar to the well-known reaction theory and based on the helicity representation for the exit fission channels, is briefly summarized. This approach allows one to connect the multimodal fission representation with A. Bohr's concept of the fission transition states and to obtain formulae for the partial and differential fission cross sections. The formulae are used for analysis of the angular anisotropy of fragments in the neutron resonance induced fission of aligned sup 2 sup 3 sup 5 U nuclei and of the P-even angular forward-backward and right-left correlations of fragments oe the P-odd correlations caused by the interference of s- and p-wave neutron resonances
The resonance neutron fission on heavy nuclei
International Nuclear Information System (INIS)
Kopach, Yu.N.; Popov, A.B.; Furman, V.I.; Alfimenkov, V.P.; Lason', L.; Pikel'ner, L.B.; ); Gonin, N.N.; Kozlovskij, L.K.; Tambovtsev, D.I.; Gagarskij, A.M.; Petrov, G.A.; Sokolov, V.E.
2001-01-01
A new approach to the description of the fission, similar to the well-known reaction theory and based on the helicity representation for the exit fission channels, is briefly summarized. This approach allows one to connect the multimodal fission representation with A. Bohr's concept of the fission transition states and to obtain formulae for the partial and differential fission cross sections. The formulae are used for analysis of the angular anisotropy of fragments in the neutron resonance induced fission of aligned 235 U nuclei and of the P-even angular forward-backward and right-left correlations of fragments oe the P-odd correlations caused by the interference of s- and p-wave neutron resonances [ru
Seventy-five years of nuclear fission
Indian Academy of Sciences (India)
the angular distribution of the fragments with the direction of the incident projectile caus- ing fission will depend on .... But in harnessing nuclear energy through the critical fission reactors, disposal of nuclear waste ... experimental technique based on a gridded ion chamber, emission spectra and angular distributions of the ...
International Nuclear Information System (INIS)
Er-Qin, Wang; Fu-Hu, Liu; Jian-Xin, Sun; Rahim, Magda A.; Fakhraddin, S.
2011-01-01
The multiplicity distributions of projectile fragments emitted in interactions of different nuclei with emulsion are studied by using a multi-source model. Our calculated results show that the projectile fragments can be described by the model and each source contributes an exponential distribution. As the weighted sum of the folding result of many exponential distributions, a multi-component Erlang distribution is used to describe the experimental data. The relationship between the height (or width) of the distribution and the mass of the incident projectile, as well as the dependence of projectile fragments on target groups, are investigated too. (nuclear physics)
Ree, J.M. van; Wolterink, G.; Fekete, M.; Wied, D. de
1982-01-01
Chronic treatment with des-enkephalin-γ-endorphin (DEγE, β-endorphin 6–17) twice daily for 10 days into the nucleus accumbens of rats resulted in hypoactivity, while similar treatment with γ-endorphin antiserum led to a marked hyperactivity. This enhanced activity persisted for at least 3 days
Eslamizadeh, H.
2015-09-01
The fission probability, pre-scission neutron, proton and alpha multiplicities, anisotropy of fission fragment angular distribution and the fission time have been calculated for the compound nuclei 200Pb and 197Tl based on the modified statistical model and four-dimensional dynamical model. In dynamical calculations, dissipation was generated through the chaos weighted wall and window friction formula. The projection of the total spin of the compound nucleus to the symmetry axis, K, was considered as the fourth-dimension in Langevin dynamical calculations. In our dynamical calculations, we have used a constant dissipation coefficient of K, {γ }K=0.077{({{MeV}} {{zs}})}-{1/2}, and a non-constant dissipation coefficient to reproduce the above-mentioned experimental data. Comparison of the theoretical results of the fission probability and pre-scission particle multiplicities with the experimental data showed that the difference between the results of both dynamical models is small whereas, for the anisotropy of fission fragment angular distribution, it is slightly large. Furthermore, comparison of the results of the modified statistical model with the above-mentioned experimental data showed that with choosing appropriate values of the temperature coefficient of the effective potential, λ , and the scaling factor of the fission-barrier height, {r}s, the experimental data were satisfactorily reproduced.
Heavy fragment radioactivity of /sup 238/Pu: Si and Mg emission
International Nuclear Information System (INIS)
Wang, S.; Snowden-Ifft, D.; Price, P.B.; Moody, K.J.; Hulet, E.K.
1989-01-01
In addition to its two known hadronic decay modes: alpha decay (half-life 88 yr) and spontaneous fission (5 x 10/sup 10/ yr): we have found that /sup 238/Pu also decays by emission of a Mg nucleus (/similar to/2 x 10/sup 18/ yr) and by emission of a Si nucleus (/similar to/6 x 10/sup 17/ yr). This extends to four (the other two being /sup 14/C emission and Ne emission) the number of known modes of decay by emission of a fragment of mass between that of an alpha particle and that resulting from fission. The branching ratios relative to alpha decay are the lowest yet observed: /similar to/6 x 10/sup -17/ for Mg emission and 1.4 x 10/sup -16/ for Si emission
SYMMETRICAL AND ASYMMETRIC TERNARY FISSION OF HOT NUCLEI
SIWEKWILCZYNSKA, K; WILCZYNSKI, J; LEEGTE, HKW; SIEMSSEN, RH; WILSCHUT, HW; GROTOWSKI, K; PANASIEWICZ, A; SOSIN, Z; WIELOCH, A
Emission of a particles accompanying fusion-fission processes in the Ar-40 + Th-232 reaction at E(Ar-40) = 365 MeV was studied in a wide range of in-fission-plane and out-of-plane angles. The exact determination of the emission angles of both fission fragments combined with the time-of-flight
Spontaneous fission of superheavy nuclei
Indian Academy of Sciences (India)
2015-08-02
Aug 2, 2015 ... ... nuclear configurations typical for fission processes. The deformed two-centre shell model is used to obtain single-particle energy levels for the transition region of two partially overlapped daughter and emitted fragment nuclei. The macroscopic part is obtained using the Yukawa-plus-exponential potential.
Neutron induced fission of 235sub(U)
International Nuclear Information System (INIS)
Straede, C.A.
1985-05-01
In order to achieve a better understanding of the fision process it is essential to get experimental data on the details of the mass, energy and angular distributions, and the mass versus energy and mass versus angular distribution correlations as function of excitation energy. The present work describes the result of such a measurement for 235 U(n,f) with thermal 235 U(n,f) reaction has a rather high cross section, especially for thermal neutrons. The changes in the average total kinetic energy relative to the thermal value have been measured at several neutron energies above thermal, and the angular anisotropy of the fission fragments averaged over all fragment masses has been determined in several measurements. Many of the thermal values, the average kinetic energy and average angular anisotropy values at higher neutron energies were compared with measurements using other techniques. Good agreement is found. It indicates that the chamber works as intended and it gives confidence to the data measured for the first time with the present setup. It furthermore allows to use the chamber with confidence in future measurements on less known fission reactions and at less explored excitation energies of the compound nucleus. (author)
Hinde, D. J.
1993-03-01
A compilation of currently available data on pre-scission neutron multiplicities shows clearly that the excitation energy in the fission fragments hardly increases with bombarding energy. This can be explained if fission is always a slow process, whilst evaporation becomes more and more rapid. The neutron clock-thermometer is introduced as a tool to deduce the dynamical timescale for fusion-fission, giving (35±15)×10-21 s. Quasi-fission is faster than fusion-fission because the equilibrium deformation is never reached (the mononucleus is thought to be always very deformed) thus fragment temperatures are higher, and the strong variation of vpre with TKE shows that a significant number of neutrons are emitted while the fragments are accelerating after scission. This appears not to be the case for fusion-fission. The fall in vpre for asymmetric mass-splits suggests that the dynamical time scale is shorter: this will influence fission mass-distributions.
On the mechanism of fission neutron emission
International Nuclear Information System (INIS)
Maerten, H.; Richter, D.; Seeliger, D.
1986-01-01
This review represents the present knowledge of the mechanism of prompt fission neutron emission. Starting with a brief fission process characterization related with neutron emission, possible emission mechanisms are discussed. It is emphasized that the experimental study of special mechanisms, i.e. scission neutron emission processes, requires a sufficiently correct description of emission probabilities on the base of the main mechanism, i.e. the evaporation from fully accelerated fragments. Adequate statistical-model approaches have to account for the complexity of nuclear fission reflected by an intricate fragment distribution. The present picture of scission neutron emission is not clarified neither experimentally nor theoretically. Deduced data are contradictory and depend on the used analysis procedures often involving rough discriptions of evaporated-neutron distributions. The contribution of two secondary mechanisms of fission neutron emission, i.e. the neutron evaporation during fragment acceleration and neutron emission due to the decay of 5 He after ternary fission, is estimated. We summarize the recent progress of the theoretical description of fission neutron spectra in the framework of statistical models considering the standard spectrum of 252 Cf(sf) neutrons especially. The main experimental basis for the study of fission neutron emission is the accurate measurement of emission probabilities as a function of emission energy and angle (at least) as well as fragment parameters (mass number ratio and kinetic energy). The present status is evaluated. (author)
Energy Technology Data Exchange (ETDEWEB)
Laget, M
2007-10-15
While the existence of an island of stability beyond Z=110 is theoretically acquired, the location of this island ranges from Z=114 to Z=126 depending on models. In this work, the stability of super-heavy nuclei is probed through the study of their fission time. The chosen experimental method, the crystal blocking method, is sensitive to the presence of possible long time components in the fission time distribution which indicates a fission mechanism occurring after the formation of a compound nucleus. The blocking dips were therefore constituted for the various products of the reaction U{sup 238} + Ni (6.6 MeV/A) {yields} 120, the experimental set-up allowing us to clearly identify and select the reaction mechanisms. The comparison of the blocking dip constituted for quasi-elastic scattering events with the one obtained for the fission fragments of a Z=120, combined with the study of kinematical properties of these fission fragments, give evidences of the existence of very long fission times (> 10{sup -18} s) only compatible with a fusion-fission mechanism implying a non vanishing fission barrier height for Z=120. The second part outlines microscopic calculations of fission barrier heights, carried out in the framework of the finite temperature of the Hartree-Fock-Bogoliubov (HFB) theory. Because of the progressive vanishing of the pairing correlation with T, which happens differently at the ground state and at the top of the barrier, B{sub f} first grows until T {approx_equal} 0.8 MeV before dropping with T owing to shell-effects damping with temperature. (author)
Mass dependence of positive pion-induced fission
International Nuclear Information System (INIS)
Khan, H.A.; Khan, N.A.; Peterson, R.J.
1991-01-01
Fission cross sections for a range of targets have been measured by solid-state track detectors following 80 and 100 MeV π + bombardment. Fission probabilities have been inferred by comparison to computed reaction cross sections. Fission probabilities for heavy targets agree with those for other probes of comparable energy and with statistical calculations. Probabilities for lighter targets are much above those previously observed or computed. Ternary fission cross sections and multiplicities of light fragments have also been determined
Czech Academy of Sciences Publication Activity Database
Smith, M. B.; Michl, Josef
2010-01-01
Roč. 110, č. 11 (2010), s. 6891-6936 ISSN 0009-2665 Grant - others:Department of Energy(US) DE- FG36 -08GO18017 Institutional research plan: CEZ:AV0Z40550506 Keywords : solar energy conversion * photovoltaics * singlet fission Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 33.033, year: 2010
Some aspects of the nuclear fission process
International Nuclear Information System (INIS)
Netter, F.
1961-01-01
In the following report one can find first a short general view on the present situation of our knowledge concerning the nuclear fission process, namely on the nucleus going through the saddle-point. Then there are some aspects connected with the excitation energy of the fissioning nucleus. The measurements made at Saclay on the fast neutron fission cross-section of U 233 , U 235 , Pu 239 , U 238 are described at the beginning of this work. It appears that for U 233 there is some characteristic shape modulation of the cross-section curve, in relation with the collective excited state of the deformed nucleus at the saddle-point. Good evidence of this is also given by the study of the relative fission rate with emission of long-range particles; it appears also that this ternary fission rate does not change substantially for neutron between thermal energy and 2 MeV, but that is very lower for the compound nucleus U 239 than for even-even compound nuclei. At the end there are some experiments on the strong 4,5 MeV gamma-ray originated by slow neutron absorption in U 235 . Time-of-flight device is used to establish that this 4,5 MeV gamma-ray seems mostly connected with radiative capture. (author) [fr
A model for particle emission from a fissioning system
International Nuclear Information System (INIS)
Milek, B.; Reif, R.; Revai, J.
1987-04-01
The differential emission probability for a neutron emitted in a binary fission process due to non-adiabatic effects in the coupling of the single particle degrees of freedom to the accelerated relative motion of the fragments is investigated wihtin a model, which represents each nucleus by a non-deformed one-term separable potential. The derivation of measurable quantities from the asymptotic solution of the time-dependent Schroedinger equation for the single particle wave function is examined. Numerical calculations were performed for parameter values, which correspond to 252 Cf(sf). The calculated energy spectra and angular distributions of the emitted particles are presented in dependence on the mass asymmetry. (author)
New fission-neutron-spectrum representation for ENDF
International Nuclear Information System (INIS)
Madland, D.G.
1982-04-01
A new representation of the prompt fission neutron spectrum is proposed for use in the Evaluated Nuclear Data File (ENDF). The proposal is made because a new theory exists by which the spectrum can be accurately predicted as a function of the fissioning nucleus and its excitation energy. Thus, prompt fission neutron spectra can be calculated for cases where no measurements exist or where measurements are not possible. The mathematical formalism necessary for application of the new theory within ENDF is presented and discussed for neutron-induced fission and spontaneous fission. In the case of neutron-induced fission, expressions are given for the first-chance, second-chance, third-chance, and fourth-chance fission components of the spectrum together with that for the total spectrum. An ENDF format is proposed for the new fission spectrum representation, and an example of the use of the format is given
Fragment Angular Anisotropies for Magic and Non-Magic Nuclei
Behkami, A. N.; Maroofi, S.; Esmailipour, A.; Rasooli, S.
2007-10-01
Fission fragment angular distributions have been studied for ^239 Pu (n, f) reaction at several neutron energies. Theoretical calculations have been utilized to determine the variance K0^2 at each bombarding energy from the observed angular anisotropies. The values of K0^2 show sharp rise from a value of 5-6 to about 13 for higher neutron energies. From the position of one of the breaks in the K0^2 value, the magnitude of the pairing gap 2δ in the highly deformed transition nucleus ^240 Pu is estimated to be 2.4 MeV. Fission fragment angular anisotropies from changed particle fission of ^208 Pb, ^209 Bi, ^235U and ^238U at laboratory energy of 43.0 MeV have also been analyzed using the traditional transition state model. In all these calculations, optical model transmission coefficients with spin-orbit interaction have been used. In the case of magic nuclei, ^208Pb and ^209 Bi it is found that the deduced values of K0^2 are very small as compared to their corresponding values for ^235U and ^238U nuclei. This interpreted as due to shell structure, since significant shell and pairing effects appear for the magic nuclei ^208 Pb and ^209 Bi.
Multifragmentation in peripheral nucleus-nucleus collisions
International Nuclear Information System (INIS)
Trautmann, W.; Adloff, J.C.; Bouissou, P.; Hubele, J.; Imme, G.; Iori, I.; Kreutz, P.; Leray, S.; Lindenstruth, V.; Liu, Z.; Lynen, U.; Meijer, R.J.; Milkau, U.; Moroni, A.; Mueller, W.F.J.; Ngo, C.; Ogilvie, C.A.; Pochodzalla, J.; Raciti, G.; Rudolf, G.; Schuettauf, A.; Stuttge, L.
1993-10-01
The complete fragmentation of highly excited nuclear systems into fragments of intermediate mass is observed in heavy-ion reactions at relativistic bombarding energies in the range of several hundreds of MeV per nucleon. Similar features are found for peripheral collisions between heavy nuclei and for more central collisions between a heavy and a light nucleus. The partition space explored in multifragment decays is well described by the statistical multifragmentation models. The expansion before breakup is confirmed by the analysis of the measured fragment energies of ternary events in their own rest frame. Collective radial flow is confined to rather small values in these peripheral-type reactions. Many conceptually different models seem to be capable of reproducing the charge correlations measured for the multifragment decays. (orig.)
Indian Academy of Sciences (India)
respectively, which are expressed in MeV and taken from [12]. The ternary fragmentation potential between the three (spherical) fragments (referred to as PES), within the TCM [1–6], is defined as the sum of the total Coulomb potential, total nuclear potential, ℓ-dependent potential and the sum of the mass excesses of ternary.
Fission dynamics with microscopic level densities
Randrup, Jørgen; Ward, Daniel; Carlsson, Gillis; Døssing, Thomas; Möller, Peter; Åberg, Sven
2018-03-01
Working within the Langevin framework of nuclear shape dynamics, we study the dependence of the evolution on the degree of excitation. As the excitation energy of the fissioning system is increased, the pairing correlations and the shell effects diminish and the effective potential-energy surface becomes ever more liquid-drop like. This feature can be included in the treatment in a formally well-founded manner by using the local level densities as a basis for the shape evolution. This is particularly easy to understand and implement in the Metropolis treatment where the evolution is simulated by means of a random walk on the five-dimensional lattice of shapes for which the potential energy has been tabulated. Because the individual steps between two neighboring lattice sites are decided on the basis of the ratio of the statistical weights, what is needed is the ratio of the local level densities for those shapes, evaluated at the associated local excitation energies. For this purpose, we adapt a recently developed combinatorial method for calculating level densities which employs the same single-particle levels as those that were used for the calculation of the pairing and shell contributions to the macroscopic-microscopic deformation-energy surface. For each nucleus under consideration, the level density (for a fixed total angular momentum) is calculated microscopically for each of the over five million shapes given in the three-quadratic-surface parametrization. This novel treatment, which introduces no new parameters, is illustrated for the fission fragment mass distributions for selected uranium and plutonium cases.
Fusion-fission dynamics at high excitation energies studied by neutron emission
Zank, W. P.; Hilscher, D.; Ingold, G.; Jahnke, U.; Lehmann, M.; Rossner, H.
1986-02-01
Neutron emission in coincidence with fusion-fission events and evaporation residues was measured in the heavy-ion reactions 141+(316 MeV) 40Ar and 175Lu+(192 MeV) 12C. Both reactions are leading to similar composite systems and excitation energies as the previously investigated reaction 165Ho+ 20Ne. In order to determine the lifetimes of the composite systems prior to scission and to study entrance channel and angular-momentum effects, the results for all three systems are compared. From measured cross sections of fission and evaporation residues, the angular momentum intervals leading to fission are deduced to be 50-109 ħ and 49-62 ħ for Pr+Ar and Lu+C, respectively. The corresponding prescission neutron multiplicities are deduced to be Mnpresc=3.6+/-0.6 and 6.3+/-0.8, whereas the respective postscission multiplicities are Mnpost=4.4+/-0.4 and 3.6+/-0.6. For the system 175Lu+ 12C it is found that 0.5+/-0.2 preequilibrium neutrons are emitted. In contrast to the evaporative neutrons, a strong anisotropy anPE=2.2+/-0.6 relative to the reaction plane defined by one fission fragment and the beam direction is observed. From the prescission neutron multiplicities, the evaporation time of the system prior to scission is deduced using the statistical model to ~=(3-12)×10-20 s. Nucleus deformation effects and neutron emission from not fully accelerated fission fragments are taken into account. The unexpected long prescission lifetimes can be explained as long transition times to the scission point caused by a large two-body viscosity. Under this assumption the viscosity parameter of the highly excited nuclei has been determined in a first approximation to μ~=0.1 TP. The results might be understood also assuming a mixture of a two-body and one-body friction.
Fission decay properties of ultra neutron-rich uranium isotopes
Indian Academy of Sciences (India)
The series of uranium isotopes around it with = 154-172 are identified to be thermally fissile on the basis of the fission barrier and neutron separation energy systematics; a manifestation of the close shell nature of = 162 (or 164). We consider here the thermal neutron fission of a typical representative 249U nucleus in ...
Fusion-Fission like studies from medium heavy to light compound systems
International Nuclear Information System (INIS)
Heusch, B.
1991-01-01
It has been shown that for systems as light as A CN = 47 up to systems just above the Businaro Gallone point in the mass region of 100 to 110 the probability for a system to deexcite by the fission channel, is not negligible. As predicted, the asymmetrical separation becomes dominant when the A CN mass is decreasing but the symmetrical mode remains measurable. The ambiguities in the measured outgoing fragment distributions arise from the competition with IMF emissions as well as dynamical fission processes which depend strongly on the studied system. Fully relaxed DIC has also be used to interpret the results. I tried to show that precise checks on the behavior of two neighbouring systems as well as search for entrance channel effect and/or energy dependence bring evidence enough that the deexcitation of the compound nucleus can account for the symmetric and asymmetric fission channels as well as IMF emissions. This is strongly supported by different recent calculations all done in this frame. These all conclusions indicate also that the RLDM fails in the data interpretation. The strength of the fission channel depends strongly on the possibilities a system has to deexcite. For very light systems especially the number of open channels available determines directly the flux repartition between direct or compound processes and therefore very large differences in the general behaviour of two neighbouring systems can be observed. 15 figs
Nuclear data for neutron emission in the fission process
International Nuclear Information System (INIS)
Ganesan, S.
1991-11-01
This document contains the proceedings of the IAEA Consultants' Meeting on Nuclear Data for Neutron Emission in the Fission Process, Vienna, 22 - 24 October 1990. Included are the conclusions and recommendations reached at the meeting and the papers presented by the meeting participants. These papers provide a review of the status of experimental and theoretical data on neutron emission in spontaneous and neutron induced fission with reference to the data needs for reactor applications oriented towards actinide burner studies. The specific topics covered are the following: experimental measurements and theoretical predictions and evaluations of fission neutron energy spectra, average prompt fission neutron multiplicity, correlation in neutron emission from complementary fragments, neutron emission during acceleration of fission fragments, statistical properties of neutron rich nuclei by study of emission spectra of neutrons from the excited fission fragments, integral qualification of nu-bar for the major fissile isotopes, nu-bar total of 239 Pu and 235 U, and related problems. Refs figs and tabs
International workshop on dynamical aspects of nuclear fission. Programme and abstracts
International Nuclear Information System (INIS)
1991-06-01
All 28 papers presented are within the scope of INIS and cover the following topics: dynamical aspects of ternary, binary and photofission, dynamics of fission-like processes, emission of fragments in fission of excited nuclei. (Z.S.)
Dynamic treatment of the fission mass asymmetry with the help of the two-centre-shell model
International Nuclear Information System (INIS)
Maruhn, J.A.
1973-01-01
In this work, a description of the distribution of the total mass of a fissioning nucleus on the fragments is proposed by means of a collective coordinate, and the applicability of the method is examined by various examples compared to the experiment. A quantitative agreement with the experiment cannot be expected in view of the necessary approximations and the relatively less accurate determination especially of the mass parameters. The experiments, however, exhibit good qualitative and semi-quantitative agreement with the experimental mass yields. (orig./LH) [de
Darnall, Robert A; Harris, Michael B; Gill, W Hugh; Hoffman, Jill M; Brown, Justin W; Niblock, Mary M
2005-09-07
Serotonergic receptor binding is altered in the medullary serotonergic nuclei, including the paragigantocellularis lateralis (PGCL), in many infants who die of sudden infant death syndrome (SIDS). The PGCL receives inputs from many sites in the caudal brainstem and projects to the spinal cord and to more rostral areas important for arousal and vigilance. We have shown previously that local unilateral nonspecific neuronal inhibition in this region with GABA(A) agonists disrupts sleep architecture. We hypothesized that specifically inhibiting serotonergic activity in the PGCL would result in less sleep and heightened vigilance. We analyzed sleep before and after unilaterally dialyzing the 5-HT1A agonist (+/-)-8-hydroxy-2-(dipropylamino)-tetralin (8-OH-DPAT) into the juxtafacial PGCL in conscious newborn piglets. 8-OH-DPAT dialysis resulted in fragmented sleep with an increase in the number and a decrease in the duration of bouts of nonrapid eye movement (NREM) sleep and a marked decrease in amount of rapid eye movement (REM) sleep. After 8-OH-DPAT dialysis, there were decreases in body movements, including shivering, during NREM sleep; body temperature and heart rate also decreased. The effects of 8-OH-DPAT were blocked by local pretreatment with N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexane-carboxamide, a selective 5-HT1A antagonist. Destruction of serotonergic neurons with 5,7-DHT resulted in fragmented sleep and eliminated the effects of subsequent 8-OH-DPAT dialysis on REM but not the effects on body temperature or heart rate. We conclude that neurons expressing 5-HT1A autoreceptors in the juxtafacial PGCL are involved in regulating or modulating sleep. Abnormalities in the function of these neurons may alter sleep homeostasis and contribute to the etiology of SIDS.
Fission dynamics in the proton induced fission of heavy nuclei
Energy Technology Data Exchange (ETDEWEB)
Rubchenya, V.A. E-mail: rubchen@phys.jyu.fi; Trzaska, W.H.; Itkis, I.M.; Itkis, M.G.; Kliman, J.; Kniajeva, G.N.; Kondratiev, N.A.; Kozulin, E.M.; Krupa, L.; Pokrovski, I.V.; Voskressenski, V.M.; Hanappe, F.; Materna, T.; Dorvaux, O.; Stuttge, L.; Chubarian, G.; Khlebnikov, S.V.; Vakhtin, D.N.; Lyapin, V.G
2004-04-05
Multi-parameter correlation study of the reaction {sup 242}Pu(p, f) at E{sub p} 13, 20 and 55 MeV has been carried out. Fission fragment mass and kinetic energy distributions and the double differential neutron spectra have been measured. It was observed that the two-humped shape of mass distributions prevailed up to highest proton energy. Manifestation of the nuclear shell Z 28 near fragment mass A{sub fr} = 70 has been detected. The experimental results were analyzed in the framework of a time-dependent statistical model with inclusion of nuclear friction effects in the fission process. The multi-parameter correlation study of the reaction.
Semiclassical approach to sequential fission in peripheral heavy-ion collisions
Directory of Open Access Journals (Sweden)
Strazzeri Andrea
2016-01-01
Full Text Available A closed-form theoretical approach describing in a single picture both the evaporation component and the fast nonequilibrium component of the sequential fission of projectilelike fragments in a semiperipheral heavy-ion collision is derived and then applied to the dynamical fission observed in the 124Sn+64Ni semiperipheral collision at 35A MeV. Information on opposite polarization effects of the fissioning projectilelike fragments and on their “formation-to-fast fission lifetimes” are obtained.
Different fission behavior induced by heavy ion central and peripheral collisions
International Nuclear Information System (INIS)
Wu Enjiu; Zheng Jiwen; Xiao Zhigang; Zhang Chun; Tan Jilian; Yin Shuzhi; Wang Sufang; Jin Genming; Yin Xu; Song Mingtao; Jin Weiyang; Peng Xingping; Li Zuyu; Wu Heyu; He Zhiyong; Jiang Dongxing; Qian Xing
2000-01-01
Correlated fission fragments from the 40 Ar + 209 Bi reaction and their further correlation with α particles have been studied for peripheral and central collisions simultaneously. The existence of different fission behavior of hot nuclei formed in central and peripheral collisions was found from the systematic analysis of the mass and energy distributions of fission fragments as a function of the initial temperature of hot fissioning nuclei
Seventy-five years of nuclear fission
Indian Academy of Sciences (India)
2015-07-19
Jul 19, 2015 ... ... fission related research has not only provided new insights in the physics of large scale motion, deformation and subsequent division of a heavy nucleus, but has also opened several new frontiers of research in nuclear physics. This article is a narrative giving an overview of the landmarks of the progress ...
Fifty years of nuclear fission: Nuclear data and measurements series
International Nuclear Information System (INIS)
Lynn, J.E.
1989-06-01
This report is the written version of a colloquium first presented at Argonne National Laboratory in January 1989. The paper begins with an historical preamble about the events leading to the discovery of nuclear fission. This leads naturally to an account of early results and understanding of the fission phenomena. Some of the key concepts in the development of fission theory are then discussed. The main theme of this discussion is the topography of the fission barrier, in which the interplay of the liquid-drop model and nucleon shell effects lead to a wide range of fascinating phenomena encompassing metastable isomers, intermediate-structure effects in fission cross-sections, and large changes in fission product properties. It is shown how study of these changing effects and theoretical calculations of the potential energy of the deformed nucleus have led to broad qualitative understanding of the nature of the fission process. 54 refs., 35 figs
14. International workshop on nuclear fission physics. Proceedings
International Nuclear Information System (INIS)
2000-01-01
The meetings on nuclear fission took place 12-15 October 1998 and was organized by Institute of Physics and Power Engineering. The aim of the workshop was to present and discuss main new both theoretical and experimental results obtained in the area of nuclear fission, dynamical feature, properties of fission fragments and complementary radiation. As usual the program of the workshop was designed to cover a wide range of physical phenomena - from low energy and spontaneous fission to fission of hot rotating nuclei and multifragmentation at intermediate and high energies. Reaction induced by slow and fast neutron, light and heavy ions were discussed [ru
Fission fragment pumping of CO gas mixtures
International Nuclear Information System (INIS)
McArthur, D.A.
1978-01-01
Some initial experiments on the spectral properties of the room-temperature CO nuclear pumped laser (NPL), and also the results of some parameter optimization experiments are presented. The parameter optimization has resulted in peak laser powers approximately 20 W and laser energies > or approximately equal to 1 mJ, which are greater than those reported thus far for any other room temperature NPL (however, the laser powers and energies of the low-temperature CO NPL are still much higher than those reported here). The spectral properties of the CO laser were studied because they may reveal how energy enters the vibrational level system of the CO molecule, and thus help quantify the amount of vibrational excitation which is occurring
Fission rate of nuclei at high excitation energy and emission of light particles
International Nuclear Information System (INIS)
Mersits, E.
1991-10-01
Light charged-particle emission has been measured for the reactions α + 238 U, 209 Bi, 232 Th at 118 MeV bombarding energies. The rate of particles detected in coincidence with fission fragments have been determined at high excitation energy. Modified precompound decay models and statistical models (program ALICE) have been used in an attempt to interpret the experimental data. The ratio of the level density parameter af/an was found to be 1.03 and 1.08, the temperature of neutron spectra was found to be 1.58 MeV and 1.33 MeV, for 238 U and 209 Bi, respectively. Analysing the experimental light-charged-particle spectra, there was no evidence for emission from the fission fragments which was in good agreement with calculations for the nucleus 209 Bi. On the other hand the theoretical emission spectra of 238 U predict great parts of such 'postfission' particles. Simplification in the model concerning the time of possible particle emission, that is, before the saddle-point and from the fragments, leads to the assumption of light particle emission between the saddle and the scission point
Development of a “Fission-proxy” Method for the Measurement of 14-MeV Neutron Fission Yields at CAMS
Energy Technology Data Exchange (ETDEWEB)
Gharibyan, Narek [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2016-10-25
Relative fission yield measurements were made for 50 fission products from 25.6±0.5 MeV alpha-induced fission of Th-232. Quantitative comparison of these experimentally measured fission yields with the evaluated fission yields from 14-MeV neutron-induced fission of U-235 demonstrates the feasibility of the proposed fission-proxy method. This new technique, based on the Bohr-independence hypothesis, permits the measurement of fission yields from an alternate reaction pathway (Th-232 + 25.6 MeV α → U-236* vs. U-235 + 14-MeV n → U-236*) given that the fission process associated with the same compound nucleus is independent of its formation. Other suitable systems that can potentially be investigated in this manner include (but are not limited to) Pu-239 and U-237.
Role of the excitation energy of the compound nucleus in binary decay processes
Directory of Open Access Journals (Sweden)
Paşca H.
2018-01-01
Full Text Available Employing the improved scission-point model, the isotopic and excitation energy trends of the charge distribution of fission fragments are studied in fission of even-even Th isotopes at low and high excitation energies.
Delayed fission of atomic nuclei (To the 50th anniversary of the discovery)
Skobelev, N. K.
2017-09-01
The history of the discovery of delayed nuclear fission is presented, and the retrospective of investigations into this phenomenon that were performed at various research centers worldwide is outlined. The results obtained by measuring basic delayed-fission features, including the fission probability, the total kinetic energy of fission fragments, and their mass distributions, are analyzed. Recommendations concerning further studies in various regions of nuclear map with the aim of searches for and investigation of atomic nuclei undergoing delayed fission are given. Lines of further research into features of delayed fission with the aim of solving current problems of fission physics are discussed.
International Nuclear Information System (INIS)
Ruben, A.; Maerten, H.; Seeliger, D.
1990-01-01
A complex statistical theory of fission neutron emission combined with a phenomenological fission model has been used to calculate fission neutron data for 238 U. Obtained neutron multiplicities and energy spectra as well as average fragment energies for incidence energies from threshold to 20 MeV (including multiple-chance fission) are compared with traditional data representations. (author). 19 refs, 6 figs
New experimental approaches to investigate the fission dynamics
Energy Technology Data Exchange (ETDEWEB)
Benlliure, J., E-mail: j.benlliure@usc.es; Rodríguez-Sánchez, J. L.; Alvarez-Pol, H.; Ayyad, Y.; Cortina-Gil, D.; Paradela, C.; Pietras, B.; Ramos, D.; Vargas, J. [Universidade de Santiago de Compostela, 15782 Santiago de Compostela (Spain); Audouin, L.; Boutoux, G. [Institut de Physique Nucléaire d’Orsay, F-91406 Orsay (France); Bélier, G.; Chatillon, A.; Gorbinet, T.; Laurent, B.; Martin, J.-F.; Pellereau, E.; Taïeb, J. [CEA, DAM, DIF, F-91297 Arpajon (France); Casarejos, E. [Universidad de Vigo, E-36200 Vigo (Spain); Heinz, A. [Chalmers University of Technology, SE-412 96 Gothenburg (Sweden); and others
2016-07-07
The first ever achieved full identification of both fission fragments, in atomic and mass number, made it possible to define new observables sensitive to the fission dynamics along the fission path up to the scission point. Moreover, proton-induced fission of {sup 208}Pb at high energies offers optimal conditions for the investigation of dissipative, and transient effects, because of the high-excitation energy of the fissioning nuclei, its low angular momentum, and limited shape distortion by the reaction. In this work we show that the charge distribution of the final fission fragments can constrain the ground-to-saddle dynamics while the mass distribution is sensitive to the dynamics until the scission point.
International Nuclear Information System (INIS)
Diwisch, Marcel
2015-01-01
In this work the basic features of isochronous mass spectroscopy (IMS) for the present facilities at GSI and also for the future experiments at FAIR have been experimentally and theoretically investigated. The prospects and limitations of IMS have been carefully studied with calculations and experiments. The data of two different previous IMS experiments at GSI have been combined and analyzed with a novel correlation-matrix method (CMM). Both experiments were performed with the fragment separator FRS and the experimental ion storage ring ESR. In both experiments fission fragments, created by 238 U projectiles in a beryllium target at the entrance of the FRS, were spatially separated and injected into the isochronous ESR. In the first experiment the full Bρ acceptance of the ESR was used whereas in the second one the Bρ of each fragment was defined by slits in the dispersive central focal plane of the FRS. In this way the magnetic rigidity was well-determined for all injected fragments to ΔBρ/Bρ=1.5.10 -4 . The harvest of this analysis is 25 new masses near and at the N=82 shell closure. The comparison of the experimental results with the AME extrapolation and different theoretical models reveal significant differences due to the low theoretical prediction power of the calculations in this mass range. In this respect one has to emphasize that due to the novel analysis method in this work these 25 new masses could be extracted additional to our previously already published results. It is almost needless to mention that the new mass values will contribute to improved r-process calculations which are in progress. In the present analysis the existing matrix method was extended with a variable scaling factor (s). The scaling factor was determined for each mass-to-charge ratio (m/q) of the measured ions and implemented as a function of m/q in the analysis. This has extended the accessible m/q range. The revolution time was determined via a 3rd-order fit of the time
Odd–even effect in fragment angular momentum in low-energy ...
Indian Academy of Sciences (India)
the experimental data for fragments in the mass number region of 130–140. The odd–even effect observed in the fragment angular momenta in the low-energy fission of actinides has been explained quantitatively for the first time. Keywords. Fission fragment angular momentum; scission point model; fragment defor- mation ...
Stability of trans-fermium elements at high spin: Measuring the fission barrier of 254No
International Nuclear Information System (INIS)
Henning, Greg
2012-01-01
Super heavy nuclei provide opportunities to study nuclear structure near three simultaneous limits: in charge Z, spin I and excitation energy E*. These nuclei exist only because of a fission barrier, created by shell effects. It is therefore important to determine the fission barrier and its spin dependence B f (I), which gives information on the shell energy E(shell)(I). Theoretical calculations predict different fission barrier heights from B f (I = 0) = 6.8 MeV for a macro-microscopic model to 8.7 MeV for Density Functional Theory calculations using the Gogny or Skyrme interactions. Hence, a measurement of B f provides a test for theories.To investigate the fission barrier, an established method is to measure the rise of fission with excitation energy, characterized by the ratio of decay widths Γ(fission)/Γ(total), using transfer reactions. However, for heavy elements such as 254 No, there is no suitable target for a transfer reaction. We therefore rely on the complementary decay widths ratio Γ γ /Γ(fission) and its spin dependence, deduced from the entry distribution (I, E*).Measurements of the gamma-ray multiplicity and total energy for 254 No have been performed with beam energies of 219 and 223 MeV in the reaction 208 Pb( 48 Ca,2n) at ATLAS (Argonne Tandem Linac Accelerator System). The 254 No gamma rays were detected using the Gammasphere array as a calorimeter - as well as the usual high resolution γ-ray detector. Coincidences with evaporation residues at the Fragment Mass Analyzer focal plane separated 254 No gamma rays from those from fission fragments, which are ≥ 10 6 more intense. From this measurement, the entry distribution - i.e. the initial distribution of I and E* - is constructed. Each point (I,E*) of the entry distribution is a point where gamma decay wins over fission and, therefore, gives information on the fission barrier. The measured entry distributions show an increase in the maximum spin and excitation energy from 219 to 223 Me
Nuclear fission: a review of experimental advances and phenomenology
Andreyev, A. N.; Nishio, K.; Schmidt, K.-H.
2018-01-01
In the last two decades, through technological, experimental and theoretical advances, the situation in experimental fission studies has changed dramatically. With the use of advanced production and detection techniques both much more detailed and precise information can now be obtained for the traditional regions of fission research and, crucially, new regions of nuclei have become routinely accessible for fission studies. This work first of all reviews the recent developments in experimental fission techniques, in particular the resurgence of transfer-induced fission reactions with light and heavy ions, the emerging use of inverse-kinematic approaches, both at Coulomb and relativistic energies, and of fission studies with radioactive beams. The emphasis on the fission-fragment mass and charge distributions will be made in this work, though some of the other fission observables, such as prompt neutron and γ-ray emission will also be reviewed. A particular attention will be given to the low-energy fission in the so far scarcely explored nuclei in the very neutron-deficient lead region. They recently became the focus for several complementary experimental studies, such as β-delayed fission with radioactive beams at ISOLDE(CERN), Coulex-induced fission of relativistic secondary beams at FRS(GSI), and several prompt fusion–fission studies. The synergy of these approaches allows a unique insight in the new region of asymmetric fission around {\\hspace{0pt}}180 Hg, recently discovered at ISOLDE. Recent extensive theoretical efforts in this region will also be outlined. The unprecedented high-quality data for fission fragments, completely identified in Z and A, by means of reactions in inverse kinematics at FRS(GSI) and VAMOS(GANIL) will be also reviewed. These experiments explored an extended range of mercury-to-californium elements, spanning from the neutron-deficient to neutron-rich nuclides, and covering both asymmetric, symmetric and transitional fission regions
Statistical and dynamical modeling of heavy-ion fusion-fission reactions
Eslamizadeh, H.; Razazzadeh, H.
2018-02-01
A modified statistical model and a four dimensional dynamical model based on Langevin equations have been used to simulate the fission process of the excited compound nuclei 207At and 216Ra produced in the fusion 19F + 188Os and 19F + 197Au reactions. The evaporation residue cross section, the fission cross section, the pre-scission neutron, proton and alpha multiplicities and the anisotropy of fission fragments angular distribution have been calculated for the excited compound nuclei 207At and 216Ra. In the modified statistical model the effects of spin K about the symmetry axis and temperature have been considered in calculations of the fission widths and the potential energy surfaces. It was shown that the modified statistical model can reproduce the above mentioned experimental data by using appropriate values of the temperature coefficient of the effective potential equal to λ = 0.0180 ± 0.0055, 0.0080 ± 0.0030 MeV-2 and the scaling factor of the fission barrier height equal to rs = 1.0015 ± 0.0025, 1.0040 ± 0.0020 for the compound nuclei 207At and 216Ra, respectively. Three collective shape coordinates plus the projection of total spin of the compound nucleus on the symmetry axis, K, were considered in the four dimensional dynamical model. In the dynamical calculations, dissipation was generated through the chaos weighted wall and window friction formula. Comparison of the theoretical results with the experimental data showed that two models make it possible to reproduce satisfactorily the above mentioned experimental data for the excited compound nuclei 207At and 216Ra.
Statistical and dynamical modeling of heavy-ion fusion–fission reactions
Directory of Open Access Journals (Sweden)
H. Eslamizadeh
2018-02-01
Full Text Available A modified statistical model and a four dimensional dynamical model based on Langevin equations have been used to simulate the fission process of the excited compound nuclei 207At and 216Ra produced in the fusion 19F + 188Os and 19F + 197Au reactions. The evaporation residue cross section, the fission cross section, the pre-scission neutron, proton and alpha multiplicities and the anisotropy of fission fragments angular distribution have been calculated for the excited compound nuclei 207At and 216Ra. In the modified statistical model the effects of spin K about the symmetry axis and temperature have been considered in calculations of the fission widths and the potential energy surfaces. It was shown that the modified statistical model can reproduce the above mentioned experimental data by using appropriate values of the temperature coefficient of the effective potential equal to λ=0.0180±0.0055, 0.0080±0.0030 MeV−2 and the scaling factor of the fission barrier height equal to rs=1.0015±0.0025, 1.0040±0.0020 for the compound nuclei 207At and 216Ra, respectively. Three collective shape coordinates plus the projection of total spin of the compound nucleus on the symmetry axis, K, were considered in the four dimensional dynamical model. In the dynamical calculations, dissipation was generated through the chaos weighted wall and window friction formula. Comparison of the theoretical results with the experimental data showed that two models make it possible to reproduce satisfactorily the above mentioned experimental data for the excited compound nuclei 207At and 216Ra.
Mechanism of intermediate mass fragment emission at low energy
International Nuclear Information System (INIS)
Dhara, A.K.; Bhattacharya, C.; Bhattacharya, S.; Krishan, K.
1993-01-01
The study of the dynamics of intermediate mass fragment emission in fusion-fission processes has been carried out. The average kinetic energies and relative yield ratio of different fragments are calculated and compared with experimental values
International Nuclear Information System (INIS)
Sobotka, L.G.
1988-01-01
The production of large fragments, fragments with mass between light particles and fission fragments, in intermediate and high energy nuclear reactions has fostered the proposal of a number of novel reaction mechanisms. These include liquid-vapor equilibrium and nuclear shattering. Temporarily left in the wake of these exciting proposed mechanisms was the old standard, statistical decay of compound nuclei. To be sure, the standard treatment of compound nucleus decay did not deal with large fragment production. However, this emission was not due to any fundamental deficiency of statistical models, but rather an uncertainty concerning exactly how to splice large fragment emission into statistical models. A large portion of our program deals with this problem. Specifically, by studying the yields of large fragments produced in sufficiently low energy reactions we are attempting to deduce the asymmetry and l-wave dependence of large fragment emission from compound nuclear intermediates. This, however, is only half of the problem. Since the novel mechanisms proposed for large fragment emission were spawned by intermediate and high energy reaction data, we must also realize the relevance of the compound nucleus mechanisms at high energies. It is not unreasonable to suspect that compound nucleus-like objects are formed with less than complete momentum transfer and perhaps less than complete mass transfer. Therefore the study of large fragment production in low energy reactions should go hand in hand with the study of energy, mass, and angular momentum transfer in incomplete fusion and non-compound reactions. This thread joins the apparently divergent subjects covered in this report
Application of pulse shape discrimination in Si detector for fission ...
Indian Academy of Sciences (India)
Pulse shape discrimination (PSD) with totally depleted transmission type Si surface barrier detector in reverse mount has been investigated to identify fission fragments in the presence of elastic background in heavy ion-induced fission reactions by both numerical simulation and experimental studies. The PSD method is ...
Fission anisotropy of Tl produced in fusion reactions in the ...
Indian Academy of Sciences (India)
Abstract. The anisotropy of fission fragment angular distribution, evaporation residue cross- section and the fission cross-section were calculated for 197Tl formed in 16O+181Ta reactions in the framework of the modified statistical model and the results were compared with the experimental data. The effects of temperature ...
Experimental Studies of quasi-fission reactions
International Nuclear Information System (INIS)
Back, B.B.
1989-01-01
A large number of recent experimental studies have shown that a substantial fraction of the total reaction cross section in heavy-ion reactions is found in fission-like processes, which do not result from the fission decay of a completely fused system. Following the suggestion of Swiatecki such processes, which represents a complete relaxation of the relative kinetic energy and a substantial amount of net mass transfer between the two fragments, are denoted quasi-fission reactions. They are distinct from compound fission reactions by bypassing the stage of a completely fused system. This typically means that they are associated with short reaction times, which results in several measurable characteristics such as broken forward-backward symmetries, large anisotropies of the angular distributions and increased widths of the fragment mass distributions. The distinction between quasi-fission and deep inelastic reactions is less stringent and has the character of a gradual evolution from one reaction type to the other, as found also as quasi-elastic reaction evolves into deeply inelastic processes as a function of the total kinetic energy loss. In the present paper some of the experimental data characterizing quasi-fission reactions are reviewed and discussed. (author)
A method to measure prompt fission neutron spectrum using gamma multiplicity tagging
Energy Technology Data Exchange (ETDEWEB)
Blain, E., E-mail: blaine2@rpi.edu; Daskalakis, A.; Block, R.C.; Barry, D.; Danon, Y.
2016-01-01
In order to improve on current prompt fission neutron spectrum measurements, a gamma multiplicity tagging method was developed at the Rensselaer Polytechnic Institute Gearttner Linear Accelerator Center. This method involves using a coincidence requirement on an array of BaF{sub 2} gamma detectors to determine the timing of a fission event. This allows for much larger fission samples to be used due to the higher penetrability of gammas compared to fission fragments. Additionally, since the method relies on gammas as opposed to fission fragments, the effects of the low level discriminator, used in fission chambers to eliminate alpha events, are not seen. A {sup 252}Cf fission chamber was constructed in order to determine the viability of this method as well as the efficiency when compared to a fission chamber. The implemented multiple gamma tagging method was found to accurately reproduce the prompt fission neutron spectrum for the spontaneous fission of {sup 252}Cf and to detect 30% of fission events. - Highlights: • A method measuring prompt fission neutron spectrum using gamma rays was proposed. • The method tags fission as reliably as a fission chamber and with better timing. • The gamma tag method shows good agreement with existing {sup 252}Cf data and models. • This eliminates the need of a fission chamber and allows larger samples to be measured.
Fission dynamics of excited nuclei within the liquid-drop model
Radionov, S V; Kolomietz, V M; Magner, A G
2002-01-01
The temperature T sub s sub c sub i sub s at the scission point and the saddle-to-scission time tau sub s sub c sub i sub s for the fission of heated nuclei is evaluated. The classical Lagrange-like equations of motion within the liquid-drop model are used. The nuclear surface is parametrized by the two-parametric family of the Lawrence shapes. Conservative forces are defined through the free energy of the nucleus at finite temperatures. The friction tensor derived from the Navier-Stokes momentum flux tensor taking into account the boundary conditions on the nuclear surface is used. The scission line is determined from the instability condition of the nuclear shape with respect to the variations of the neck radius. The numerical solution of the dynamical equations is performed for the nucleus sup 2 sup 3 sup 6 U. The viscosity coefficient mu was obtained from the comparison of the experimental data for the kinetic energy for the fission fragments with the computed one. A significant deviation of mu, obtained ...
Correlated prompt fission data in transport simulations
Talou, P.; Vogt, R.; Randrup, J.; Rising, M. E.; Pozzi, S. A.; Verbeke, J.; Andrews, M. T.; Clarke, S. D.; Jaffke, P.; Jandel, M.; Kawano, T.; Marcath, M. J.; Meierbachtol, K.; Nakae, L.; Rusev, G.; Sood, A.; Stetcu, I.; Walker, C.
2018-01-01
Detailed information on the fission process can be inferred from the observation, modeling and theoretical understanding of prompt fission neutron and γ-ray observables. Beyond simple average quantities, the study of distributions and correlations in prompt data, e.g., multiplicity-dependent neutron and γ-ray spectra, angular distributions of the emitted particles, n - n, n - γ, and γ - γ correlations, can place stringent constraints on fission models and parameters that would otherwise be free to be tuned separately to represent individual fission observables. The FREYA and CGMF codes have been developed to follow the sequential emissions of prompt neutrons and γ rays from the initial excited fission fragments produced right after scission. Both codes implement Monte Carlo techniques to sample initial fission fragment configurations in mass, charge and kinetic energy and sample probabilities of neutron and γ emission at each stage of the decay. This approach naturally leads to using simple but powerful statistical techniques to infer distributions and correlations among many observables and model parameters. The comparison of model calculations with experimental data provides a rich arena for testing various nuclear physics models such as those related to the nuclear structure and level densities of neutron-rich nuclei, the γ-ray strength functions of dipole and quadrupole transitions, the mechanism for dividing the excitation energy between the two nascent fragments near scission, and the mechanisms behind the production of angular momentum in the fragments, etc. Beyond the obvious interest from a fundamental physics point of view, such studies are also important for addressing data needs in various nuclear applications. The inclusion of the FREYA and CGMF codes into the MCNP6.2 and MCNPX - PoliMi transport codes, for instance, provides a new and powerful tool to simulate correlated fission events in neutron transport calculations important in
International Nuclear Information System (INIS)
James, M.F.
1969-05-01
The effective energy released in and following the fission of U-235, Pu-239 and Pu-241 by thermal neutrons, and of U-238 by fission spectrum neutrons, is discussed. The recommended values are: U-235 ... 192.9 ± 0.5 MeV/fission; U-238 ... 193.9 ± 0.8 MeV/fission; Pu-239 ... 198.5 ± 0.8 MeV/fission; Pu-241 ... 200.3 ± 0.8 MeV/fission. These values include all contributions except from antineutrinos and very long-lived fission products. The detailed contributions are discussed, and inconsistencies in the experimental data are pointed out. In Appendix A, the contribution to the total useful energy release in a reactor from reactions other than fission are discussed briefly, and in Appendix B there is a discussion of the variations in effective energy from fission with incident neutron energy. (author)
Fission products collecting devices
International Nuclear Information System (INIS)
Matsumoto, Hiroshi
1979-01-01
Purpose: To enable fission products trap with no contamination to coolants and cover gas by the provision of a fission products trap above the upper part of a nuclear power plant. Constitution: Upon fuel failures in a reactor core, nuclear fission products leak into coolants and move along the flow of the coolants to the coolants above the reactor core. The fission products are collected in a trap container and guided along a pipeline into fission products detector. The fission products detector monitors the concentration of the fission products and opens the downstream valve of the detector when a predetermined concentration of the fission products is detected to introduce the fission products into a waste gas processing device and release them through the exhaust pipe. (Seki, T.)
Second international conference on dynamical aspects of nuclear fission. Programme and abstracts
International Nuclear Information System (INIS)
1994-01-01
The proceedings contain 37 abstracts and short communications dealing with the fission of heavy nuclei. The fission is induced by neutrons or by reactions of heavy ions, or occurs spontaneously. Included are both theoretical and experimental studies. Particular attention was paid to the description of the fission mechanism and kinematics (fragments, neutrons, light ions). (S.P.)
Characteristic relation for the mass and energy distribution of the nuclear fission products
International Nuclear Information System (INIS)
Alexandru, G.
1977-01-01
The dispersion relation for nuclear fission is written in the two part fragmentation approach which allows to obtain the characteristic relation for the mass and energy distribution of the nuclear fission products. One explains the resonance approximation in the mass distribution of the fission products taking into account the high order resonances too. (author)
Is channeling of fission tracks taking place?
Yada, K
1999-01-01
A single crystal of natural zircon which is sliced to have (010) basal plane and thinned by ion thinning is electron microscopically observed after slow neutron irradiation to ascertain whether channeling of the nuclear fission fragments is taking place or not. A fairly large number of the induced fission tracks are recognized at low magnification images where a considerable number of them are parallel to low-index lattice planes such as 100, 001, 101, 301, 103 though their directions changed some time up to several degrees. High resolution images of fission tracks often show a variety of zigzag passing of the tracks along low-index lattice planes in atomistic level. The rate of the tracks which are parallel to these low-index lattice planes is fairly high as about 45%, which strongly suggests that channeling of the fission tracks is taking place.
Fission processes through compact and creviced shapes
International Nuclear Information System (INIS)
Royer, G.; Remaud, B.
1984-01-01
Using a one-parameter family of compact and creviced shapes the deformation energy of the liquid-drop model including the nuclear proximity energy has been calculated. The introduction of the proximity forces on such a shape sequence leads to the identification of fission and scission barriers since the rupture of the neck between the fragments is assumed before the barrier is crossed. The fission barrier heights are well reproduced and are much lower than those given by the liquid-drop model (without proximity) for the medium systems. It is shown that these low barriers are compatible with a strong enhancement of the critical angular momentum for cold fission. The translational kinetic energy of the fragments agrees with experimental data. Double-humped barriers are predicted for actinides; the inner barrier has essentially a microscopic origin while the outer one (which plays the role of a scission barrier) is governed mostly by the balance between Coulomb and nuclear forces. (author)
Probing the time scale of asymmetric fission
International Nuclear Information System (INIS)
Kamanin, D.
1999-12-01
The author describes the measurement of the mass-energy distributions of fission fragments in the reactions 197 Au( 14 N,X) at 34 A.MeV and 232 Th( 7 Li,X) at 43 A.MeV. He presents results on the mass-asymmetry and excitation energy sharing. (HSI)
Proceedings of the specialists' meeting on physics and engineering of fission and spallation, 1989
International Nuclear Information System (INIS)
Nakagome, Yoshihiro
1990-07-01
The third meeting was held on August 1, and the fourth meeting was held on December 12, 1989. The reports of the international conferences on 50 years research on nuclear fission in Germany and USA, and the reports on the nuclear data of fission-produced nuclei for evaluating reactor decay heat, the atomic mass formula considering proton-neutron interaction and unstable nuclei, research on short life fission fragments by on-line isotope separation process, the reactor physics on waste annihilation disposal and fuel breeding with an accelerator, the double differential cross section of back neutrons in nuclear spallation reaction, measurement of fission cross section and fission neutron spectra with fast neutrons, U-235 fission spectra by unfolding activation foil data and production mechanisms of intermediate mass fragments from hot nuclei-emission of complex and fission fragments for 84 Kr+ 27 Al at 10.6 MeV/u were made. (K.I.)
A new technique to measure fission-product diffusion coefficients in UO2 fuel
International Nuclear Information System (INIS)
Hocking, W.H.; Verrall, R.A.; Bushby, S.J.
1999-01-01
This paper describes a new out-reactor technique for the measurement of fission-product diffusion rates in UO 2 . The technique accurately simulates in-reactor fission-fragment effects: a thermal diffusion that is due to localized mixing in the fission track, radiation-enhanced diffusion that is due to point-defect creation by fission fragments, and bubble resolution. The technique utilizes heavy-ion accelerators - low energy (40 keV to 1 MeV) for fission-product implantation, high energy (72 MeV) to create fission-fragment damage effects, and secondary ion mass spectrometry (SIMS) for measuring the depth profile of the implanted species. Preliminary results are presented from annealing tests (not in the 72 MeV ion flux) at 1465 deg. C and 1650 deg. C at low and high concentrations of fission products. (author)
Ternary fission of spontaneously fissile uranium isomers excited by neutrons
International Nuclear Information System (INIS)
Makarenko, V.E.; Molchanov, Y.D.; Otroshchenko, G.A.; Yan'kov, G.B.
1989-01-01
Spontaneously fissile isomers (SFI) of uranium were excited in the reactions 236,238 U(n,n') at an average neutron energy 4.5 MeV. A pulsed electrostatic accelerator and time analysis of the fission events were used. Fission fragments were detected by the scintillation method, and long-range particles from fission were detected by an ionization method. The relative probability of fission of nuclei through a spontaneously fissile isomeric state was measured: (1.30±0.01)·10 -4 ( 236 U) and (1.48±0.02)·10 -4 ( 238 U). Half-lives of the isomers were determined: 121±2 nsec (the SFI 236 U) and 267±13 nsec (the SFI 238 U). In study of the ternary fission of spontaneously fissile isotopes of uranium it was established that the probability of the process amounts to one ternary fission per 163±44 binary fissions of the SFI 236 U and one ternary fission per 49±14 binary fissions of the SFI 238 U. The substantial increase of the probability of ternary fission of SFI of uranium in comparison with the case of ternary fission of nuclei which are not in an isomeric state may be related to a special nucleon configuration of the fissile isomers of uranium
Possible origin of transition from symmetric to asymmetric fission
Directory of Open Access Journals (Sweden)
H. Paşca
2016-09-01
Full Text Available The charged distributions of fragments produced in the electromagnetic-induced fission of the even–even isotopes of Rn, Ra, Th, and U are described within an improved scission-point model and compared with the available experimental data. The three-equal-peaked charge distributions are predicted for several fissioning nuclei with neutron number N=136. The possible explanation of the transition from a symmetric fission mode to an asymmetric one around N∼136 is presented. The excitation energy dependencies of the asymmetric and symmetric fission modes are anticipated.
Fission in Inverse Kinematics: A path to new experimental observables
Caamaño, Manuel; Farget, Fanny; Ramos, Diego
2017-11-01
Historically, experimental fission studies were based on reactions in direct kinematics with fixed target-like fissioning systems. Besides its advantages, this technique suffers from some drawbacks such as the difficulty of producing exotic fissioning systems and the seldom measurement of the fragment atomic number. Inverse kinematic provides an alternative to ease these issues and offers a new set of experimental observables that improves our level of information about the fission process, including an unprecedented access to the scission point. In this document, we review some of the observables obtained from the experimental campaign based on inverse kinematics, performed at VAMOS/GANIL.
Description of light charged particle emission in ternary fission
International Nuclear Information System (INIS)
Andreev, A. V.; Adamian, G. G.; Antonenko, N. V.; Kuklin, S. N.; Scheid, W.
2010-01-01
We consider the motion of three fragments starting from the scission point of ternary system. In the alpha-accompanied ternary fission the initial conditions are not the free parameters and determined by minimization of potential energy at scission point. In the trajectory calculations the angular distribution and mean value of the kinetic energy of the alpha-particles are well described in the spontaneous ternary fission of 252 Cf. In the Be- and C-accompanied ternary fission we found that the emission of the third particle occurs from one of the heavy fragments after their separation. (authors)
Monte Carlo Simulation for Statistical Decay of Compound Nucleus
Directory of Open Access Journals (Sweden)
Chadwick M.B.
2012-02-01
Full Text Available We perform Monte Carlo simulations for neutron and γ-ray emissions from a compound nucleus based on the Hauser-Feshbach statistical theory. This Monte Carlo Hauser-Feshbach (MCHF method calculation, which gives us correlated information between emitted particles and γ-rays. It will be a powerful tool in many applications, as nuclear reactions can be probed in a more microscopic way. We have been developing the MCHF code, CGM, which solves the Hauser-Feshbach theory with the Monte Carlo method. The code includes all the standard models that used in a standard Hauser-Feshbach code, namely the particle transmission generator, the level density module, interface to the discrete level database, and so on. CGM can emit multiple neutrons, as long as the excitation energy of the compound nucleus is larger than the neutron separation energy. The γ-ray competition is always included at each compound decay stage, and the angular momentum and parity are conserved. Some calculations for a fission fragment 140Xe are shown as examples of the MCHF method, and the correlation between the neutron and γ-ray is discussed.
Ternary Fission Studies by Correlation Measurements with Ternary Particles
Mutterer, Manfred
2011-10-01
The rare ternary fission process has been studied mainly by inclusive measurements of the energy distributions and fractional yields of the light charged particles (LCPs) from fission, or by experiments on the angular and energy correlation between LCPs and fission fragments (FFs). The present contribution presents a brief overview of more elaborate correlation measurements that comprise the emission of neutrons and γ rays with LCPs and FFs, or the coincident registration of two LCPs. These measurements have permitted identification of new modes of particle-accompanied fission, such as the population of excited states in LCPs, the formation of neutron-unstable nuclei as short-lived intermediate LCPs, as well as the sequential decay of particle-unstable LCPs and quaternary fission. Furthermore, the neutron multiplicity numbers bar ν (A) and distributions of fragment masses A, measured for the ternary fission modes with various LCP isotopes, give a valuable hint of the role played by nuclear shell structure in the fission process near scission. Finally, two different hitherto unknown asymmetries in ternary α-particle emission with respect to the fission axis, called the TRI and ROT effect, were studied in fission reactions induced by polarised cold neutrons.
Generalization of Kramer's formula: Fission over a multidimensional potential barrier
International Nuclear Information System (INIS)
Jing-Shang, Z.; Weidenmueller, H.A.
1983-01-01
We generalize Kramers's rate expression for diffusion over a potential barrier to the case of a diffusion problem for n degrees of freedom. These can be thought of as the shape degrees of freedom of a fissioning nucleus. We present our formula for the fission width and discuss its dependence on the parameters: the mass tensor, the friction tensor, and the shape of the potential landscape
Spontaneous fission of neutron-rich superheavy nuclei
International Nuclear Information System (INIS)
Gherghiescu, R.A.
1997-01-01
Neutron-rich isotopes of the superheavy elements 112, 114, and 116 have been studied for neutron numbers 184, 186, and 188. The spontaneous fission life-time calculations have been performed within the WKB method. Large values have been obtained due to the proton-shell closure 114. The maximum of the fission lifetime occurs for the double-magic superheavy nucleus (114,184). (author)
Characteristics of diallyl phthalate resin as a fission track detector
Tsuruta, T
1999-01-01
Diallyl phthalate (DAP) resin plates were irradiated with fission fragments, and then etched in aqueous solution of KOH. Etched tracks were observed and counted by using an optical microscope. The detection efficiency of fission fragments was about 100% for both perpendicular and random incidence. DAP plates were insensitive to alpha particles and fast neutrons. These characteristics are suitable for detecting selected fission fragments, which coexist with alpha particles or fast neutrons. DAP plates are valuable for quantitative analysis of fissionable materials and neutron dosimetry. DAP and allyl diglycol carbonate (CR-39) were formed into copolymers in various ratios. The copolymers showed intermediate characteristics between DAP and CR-39. The fabrication of the copolymers made it possible to control the discrimination level for detection of heavy charged particles.
Generalized Energy-Dependent Q Values for Fission
Energy Technology Data Exchange (ETDEWEB)
Vogt, R
2010-03-31
We extend Madland's parameterization of the energy release in fission to obtain the dependence of the fission Q value for major and minor actinides on the incident neutron energies in the range 0 {le} E{sub n} {le} 20 MeV. Our parameterization is based on the actinide evaluations recommended for the ENDF/B-VII.1 release. This paper describes the calculation of energydependent fission Q values based on the calculation of the prompt energy release in fission by Madland. This calculation was adopted for use in the LLNL ENDL database and then generalized to obtain the prompt fission energy release for all actinides. Here the calculation is further generalized to the total energy release in fission. There are several stages in a fission event, depending on the time scale. Neutrons and gammas may be emitted at any time during the fission event.While our discussion here is focussed on compound nucleus creation by an incident neutron, similar parameterizations could be obtained for incident gammas or spontaneous fission.
Spontaneous fission of the heaviest elements
Energy Technology Data Exchange (ETDEWEB)
Hoffman, D.C.
1989-04-01
Although spontaneous fission was discovered in /sup 238/U in 1940, detailed studies of the process were first made possible in the 1960's with the availability of milligram quantities of /sup 252/Cf. The advent of solid-state detectors made it possible to perform measurements of coincident fission fragments from even very short-lived spontaneous fission activities or those available in only very small quantities. Until 1971 it was believed that the main features of the mass and kinetic-energy distributions were essentially the same as those for thermal neutron-induced fission and that all low-energy fission proceeded via asymmetric mass division with total kinetic energies which could be derived by linear extrapolation from those of lighter elements. In 1971, measurements of /sup 257/Fm showed an increase in symmetric mass division with anomalously high TKE's. Subsequent experiments showed that in /sup 258/Fm and /sup 259/Fm, the most probable mass split was symmetric with very high total kinetic energy. Measurements for the heavier elements have shown symmetric mass distributions with both high and low total kinetic energies. Recent results for spontaneous fission properties of the heaviest elements are reviewed and compared with theory. 31 refs., 8 figs., 1 tab.
General Description of Fission Observables - JEFF Report 24. GEF Model
International Nuclear Information System (INIS)
Schmidt, Karl-Heinz; Jurado, Beatriz; Amouroux, Charlotte
2014-06-01
The Joint Evaluated Fission and Fusion (JEFF) Project is a collaborative effort among the member countries of the OECD Nuclear Energy Agency (NEA) Data Bank to develop a reference nuclear data library. The JEFF library contains sets of evaluated nuclear data, mainly for fission and fusion applications; it contains a number of different data types, including neutron and proton interaction data, radioactive decay data, fission yield data and thermal scattering law data. The General fission (GEF) model is based on novel theoretical concepts and ideas developed to model low energy nuclear fission. The GEF code calculates fission-fragment yields and associated quantities (e.g. prompt neutron and gamma) for a large range of nuclei and excitation energy. This opens up the possibility of a qualitative step forward to improve further the JEFF fission yields sub-library. This report describes the GEF model which explains the complex appearance of fission observables by universal principles of theoretical models and considerations on the basis of fundamental laws of physics and mathematics. The approach reveals a high degree of regularity and provides a considerable insight into the physics of the fission process. Fission observables can be calculated with a precision that comply with the needs for applications in nuclear technology. The relevance of the approach for examining the consistency of experimental results and for evaluating nuclear data is demonstrated. (authors)
Intermediate mass fragments emission in the reaction 96 MeV 19F on 12C
International Nuclear Information System (INIS)
Bhattacharya, C.; Bandyopadhyay, D.; Basu, S.K.; Bhattacharya, S.; Krishan, K.; Murthy, G.S.; Chatterjee, A.; Kailas, S.; Singh, P.
1996-01-01
The energy distributions of the complex fragments (3≤Z≤11) emitted in the reaction 19 F(96 MeV) + 12 C have been measured in the angular range 10 degree ≤θ lab ≤60 degree. The lighter fragments (3≤Z≤6) have been found to be emitted predominantly due to the asymmetric fissionlike decay of the compound nucleus, whereas the heavier fragments (Z≥10) have been identified as evaporation residues. The shapes of the fragment energy distributions, as well as the total elemental yields for the lighter fragments (3≤Z≤6) have been explained fairly well by the asymmetric binary fission model. The binary fragment yields from the reaction 19 F(96 MeV) + 12 C have been compared with those obtained in α(60 MeV) + 27 Al and 7 Li(47 MeV) + 24 Mg reactions, all producing the same composite 31 P at same excitation energy. No significant entrance channel asymmetry dependence has been observed. copyright 1996 The American Physical Society
Theoretical models of neutron emission in fission
International Nuclear Information System (INIS)
Madland, D.G.
1992-01-01
A brief survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity bar v p . Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the new models. In particular, the dependencies of N(E) and bar v p upon the fissioning nucleus and its excitation energy are treated. Recent work in the calculation of the prompt fission neutron spectrum matrix N(E,E n ), where E n is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of our ability to calculate these observables with confidence, the direction of future theoretical efforts, and limititations to current and future calculations. Finally, recommendations are presented as to which model should be used currently and which model should be pursued in future efforts
Theory of neutron emission in fission
International Nuclear Information System (INIS)
Madland, D.G.
1998-01-01
A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity bar ν p . Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and some examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N(E) and bar ν p upon the fissioning nucleus and its excitation energy are treated in detail for the Los Alamos model. Recent work in the calculation of the prompt fission neutron spectrum matrix N(E, E n ), where E n is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of the ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches. This paper is an extension of a similar paper presented at the International Centre for Theoretical Physics in 1996
Symmetric and asymmetric ternary fission of hot nuclei
International Nuclear Information System (INIS)
Siwek-Wilczynska, K.; Wilczynski, J.; Leegte, H.K.W.; Siemssen, R.H.; Wilschut, H.W.; Grotowski, K.; Panasiewicz, A.; Sosin, Z.; Wieloch, A.
1993-01-01
Emission of α particles accompanying fusion-fission processes in the 40 Ar + 232 Th reaction at E( 40 Ar) = 365 MeV was studied in a wide range of in-fission-plane and out-of-plane angles. The exact determination of the emission angles of both fission fragments combined with the time-of-flight measurements allowed us to reconstruct the complete kinematics of each ternary event. The coincident energy spectra of α particles were analyzed by using predictions of the energy spectra of the statistical code CASCADE . The analysis clearly demonstrates emission from the composite system prior to fission, emission from fully accelerated fragments after fission, and also emission during scission. The analysis is presented for both symmetric and asymmetric fission. The results have been analyzed using a time-dependent statistical decay code and confronted with dynamical calculations based on a classical one-body dissipation model. The observed near-scission emission is consistent with evaporation from a dinuclear system just before scission and evaporation from separated fragments just after scission. The analysis suggests that the time scale of fission of the hot composite systems is long (about 7x10 -20 s) and the motion during the descent to scission almost completely damped
Neutron angular distribution in plutonium-240 spontaneous fission
Energy Technology Data Exchange (ETDEWEB)
Marcath, Matthew J., E-mail: mmarcath@umich.edu [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 2355 Bonisteel Boulevard, Ann Arbor, MI 48109 (United States); Shin, Tony H.; Clarke, Shaun D. [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 2355 Bonisteel Boulevard, Ann Arbor, MI 48109 (United States); Peerani, Paolo [European Commission at the Joint Research Centre, Ispra (Italy); Pozzi, Sara A. [Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 2355 Bonisteel Boulevard, Ann Arbor, MI 48109 (United States)
2016-09-11
Nuclear safeguards applications require accurate fission models that exhibit prompt neutron anisotropy. In the laboratory reference frame, an anisotropic neutron angular distribution is observed because prompt fission neutrons carry momentum from fully accelerated fission fragments. A liquid organic scintillation detector array was used with pulse shape discrimination techniques to produce neutron-neutron cross-correlation time distributions and angular distributions from spontaneous fission in a {sup 252}Cf, a 0.84 g {sup 240}Pu{sub eff} metal, and a 1.63 g {sup 240}Pu{sub eff} metal sample. The effect of cross-talk, estimated with MCNPX-PoliMi simulations, is removed from neutron-neutron coincidences as a function of the angle between detector pairs. Fewer coincidences were observed at detector angles near 90°, relative to higher and lower detector angles. As light output threshold increases, the observed anisotropy increases due to spectral effects arising from fission fragment momentum transfer to emitted neutrons. Stronger anisotropy was observed in Cf-252 spontaneous fission prompt neutrons than in Pu-240 neutrons. - Highlights: • Pu-240 prompt fission fast-neutron anisotropy was quantified for the first time. • MCNPX-PoliMi and MPPost codes were used to remove cross-talk neutron detections from experiment results. • Cf-252 spontaneous fission neutrons were found to be more anisotropic than Pu-240 neutrons.
Energy Technology Data Exchange (ETDEWEB)
Prokhorova, E.V. [Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, 141980 Dubna, Moscow region (Russian Federation)], E-mail: elena.prokhorova@jinr.ru; Bogachev, A.A.; Itkis, M.G.; Itkis, I.M.; Knyazheva, G.N.; Kondratiev, N.A.; Kozulin, E.M.; Krupa, L.; Oganessian, Yu.Ts.; Pokrovsky, I.V. [Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, 141980 Dubna, Moscow region (Russian Federation); Pashkevich, V.V. [Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna, Moscow region (Russian Federation); Rusanov, A.Ya. [Institute of Nuclear Physics of the National Nuclear Center of Kazakhstan, 480082 Alma-Ata (Kazakhstan)
2008-04-01
Mass-energy distributions (MEDs) and capture-fission cross sections have been measured in the reaction {sup 48}Ca + {sup 208}Pb {yields}{sup 256}No at the energies E{sub lab}=206-242 MeV using a double-arm time-of-flight spectrometer CORSET. It has been observed that MED of the fragments consists of two parts, namely, the classical fusion-fission process corresponding to the symmetric fission of {sup 256}No and quasi-fission 'shoulders' corresponding to the light fragment masses {approx}60-90 u and complimentary heavy fragment masses. The quasi-fission 'shoulders' have a higher total kinetic energy (TKE) as compared with that expected for the classical fission. A mathematical formalism was employed for the MEDs fragment decomposition into fusion-fission and quasi-fission components. In the fusion-fission process a high-energy Super-Short mode has been discovered for the masses M{sub H}=130-135 u and the TKE of {approx}233 MeV.
International Nuclear Information System (INIS)
Le Brun, C.; Lecolley, J.F.; Lefebvres, F.; L'Haridon, M.; Osmont, A.; Patry, J.P.; Steckmeyer, J.C.; Chechik, R.; Guilbault, F.
We have measured the angular distribution of the target-like reaction product fission fragments emitted in coincidence with the light projectile like reaction product. For the first time, a sequential fission experiment in deeply inelastic collisions has observed an increase of the width of the out of plane angular distributions with the in-plane angle phi. The in-plane distribution exhibits an anisotropy centered in the recoil direction of the heavy fissionning nucleus, and shows up a dealignment mechanism of the transferred angular comparatively to the normal to the reaction plane. The de-aligned spin components have a gaussian distribution with a r.m.s width of about 10h and are lying preferentially in a plane perpendicular to the recoil direction. The mean value of the aligned component is of about 45h in agreement with the sticking limit with deformed nuclei. The dependence of the target-like reaction product fission probabilities on the total kinetic energy loss and Z of the projectile-like reaction product have been measured [fr
International Nuclear Information System (INIS)
Steckmeyer, J.C.
1984-10-01
Angular momentum transfer and spin dealignment mechanisms have been studied in the deep inelastic collisions Ar+Bi and Ni+Pb using the sequential fission method. This experimental technique consists to measure the angular distribution of the fission fragments of a heavy nucleus in coincidence with the reaction partner, and leads to a complete determination of the heavy nucleus spin distribution. High spin values are transferred to the heavy nucleus in the interaction and indicate that the dinuclear system has reached the rigid rotation limit. A theoretical model, taking into account the excitation of surface vibrations of the nuclei and the nucleon transfer between the two partners, is able to reproduce the high spin values measured in our experiments. The spin fluctuations are important, with values of the order of 15 to 20 h units. These fluctuations increase with the charge transfer from the projectile to the target and the total kinetic energy loss. The spin dealignment mechanisms act mainly in a plane approximately perpendicular to the heavy recoil direction in the laboratory system. These results are well described by a dynamical transport model based on the stochastic exchange of individual nucleons between the two nuclei during the interaction. The origin of the dealignment mechanisms in the spin transfer processes is then related to the statistical nature of the nucleon exchange. However other mechanisms can contribute to the spin dealignment as the surface vibrations, the nuclear deformations as well their relative orientations [fr
Contributions to the theory of fission neutron emission
International Nuclear Information System (INIS)
Seeliger, D.; Maerten, H.; Ruben, A.
1990-03-01
This report gives a compilation of recent work performed at Technical University, Dresden by D. Seeliger, H. Maerten and A. Ruben on the topic of fission neutron emission. In the first paper calculated fission neutron spectra are presented using the temperature distribution model FINESSE for fissioning actinide nuclei. In the second paper, starting from a general energy balance, Terrell's approach is generalized to describe average fragment energies as a function of incident energy; trends of fragment energy data in the Th-Pu region are well reproduced. In the third contribution, prompt fission neutron spectra and fragment characteristics for spontaneous fission of even Pu-isotopes are presented and discussed in comparison with experimental data using a phenomenological scission point model including temperature dependent shell effects. In the fourth paper, neutron multiplicities and energy spectra as well as average fragment energies for incident energies from threshold to 20 MeV (including multiple-chance fission) for U-238 are compared with traditional data representations. (author). Refs, figs and tabs
Fission product range effects on HEU fissile gas monitoring for UF6 gas
International Nuclear Information System (INIS)
Munro, J.K. Jr.; Valentine, T.E.; Perez, R.B.
1997-01-01
The amount of 235 U in UF 6 flowing in a pipe can be monitored by counting gamma rays emitted from fission fragments carried along by the flowing gas. Neutron sources are mounted in an annular sleeve that is filled with moderator material and surrounds the pipe. This provides a source of thermal neutrons to produce the fission fragments. Those fragments that remain in the gas stream following fission are carried past a gamma detector. A typical fragment will be quite unstable, giving up energy as it decays to a more stable isotope with a significant amount of this energy being emitted in the form of gamma rays. A given fragment can emit several gamma rays over its lifetime. The gamma ray emission activity level of a distribution of fission fragments decreases with time. The monitoring system software uses models of these processes to interpret the gamma radiation counting data measured by the gamma detectors
Geology behind nuclear fission technology
International Nuclear Information System (INIS)
Dhana Raju, R.
2005-01-01
Geology appears to have played an important role of a precursor to Nuclear Fission Technology (NFT), in the latter's both birth from the nucleus of an atom of and most important application as nuclear power extracted from Uranium (U), present in its minerals. NFT critically depends upon the availability of its basic raw material, viz., nuclear fuel as U and/ or Th, extracted from U-Th minerals of specific rock types in the earth's crust. Research and Development of the Nuclear Fuel Cycle (NFC) depends heavily on 'Geology'. In this paper, a brief review of the major branches of geology and their contributions during different stages of NFC, in the Indian scenario, is presented so as to demonstrate the important role played by 'Geology' behind the development of NFT, in general, and NFC, in particular. (author)
Prompt fission neutron emission in the reaction 235U(n,f)
Göök, Alf; Hambsch, Franz-Josef; Oberstedt, Stephan
2018-03-01
Experimental activities at JRC-Geel on prompt fission neutron (PFN) emission in response to OECD/NEA nuclear data requests are presented in this contribution. Specifically, on-going investigations of PFN emission from the reaction 235U(n,f) in the region of the resolved resonances, taking place at the GELINA facility, are presented. The focus of this contribution lies on studies of PFN correlations with fission fragment properties. The experiment employs a scintillation detector array for neutron detection, while fission fragment properties are determined via the double kinetic energy technique using a position sensitive twin ionization chamber. This setup allows us to study several correlations between properties of neutron and fission fragments simultaneously. Results on PFN correlations with fission fragment properties from the present study differ significantly from earlier studies on this reaction, induced by thermal neutrons.
A Time Projection Chamber for High Accuracy and Precision Fission Cross-Section Measurements
Energy Technology Data Exchange (ETDEWEB)
T. Hill; K. Jewell; M. Heffner; D. Carter; M. Cunningham; V. Riot; J. Ruz; S. Sangiorgio; B. Seilhan; L. Snyder; D. M. Asner; S. Stave; G. Tatishvili; L. Wood; R. G. Baker; J. L. Klay; R. Kudo; S. Barrett; J. King; M. Leonard; W. Loveland; L. Yao; C. Brune; S. Grimes; N. Kornilov; T. N. Massey; J. Bundgaard; D. L. Duke; U. Greife; U. Hager; E. Burgett; J. Deaven; V. Kleinrath; C. McGrath; B. Wendt; N. Hertel; D. Isenhower; N. Pickle; H. Qu; S. Sharma; R. T. Thornton; D. Tovwell; R. S. Towell; S.
2014-09-01
The fission Time Projection Chamber (fissionTPC) is a compact (15 cm diameter) two-chamber MICROMEGAS TPC designed to make precision cross-section measurements of neutron-induced fission. The actinide targets are placed on the central cathode and irradiated with a neutron beam that passes axially through the TPC inducing fission in the target. The 4p acceptance for fission fragments and complete charged particle track reconstruction are powerful features of the fissionTPC which will be used to measure fission cross-sections and examine the associated systematic errors. This paper provides a detailed description of the design requirements, the design solutions, and the initial performance of the fissionTPC.
A new prompt heavy-ion-induced fission mode
Indian Academy of Sciences (India)
2015-07-19
Jul 19, 2015 ... Home; Journals; Pramana – Journal of Physics; Volume 85; Issue 2. A new prompt ... Experimental evidence is presented in support of a new mode of prompt fission of the composite nucleus formed in central 78Kr+40Ca collisions at only a few MeV per nucleon above the interaction barrier. The new ...
Fission of highly excited nuclei investigated in complete kinematic measurements
International Nuclear Information System (INIS)
Rodriguez-Sanchez, J. L.; Benlliure, J.; Taieb, J.; Avarez-Pol, H.; Audouin, L.; Ayyad, Y.; Belier, G.; Boutoux, G.; Casarejos, E.; Chatillon, A.; Cortina-Gil, D.; Gorbinet, T.; Heinz, A.; Kelic-Heil, A.; Kurz, N.; Laurent, B.; Martin, J. F.; Paradela, C.; Pellereau, E.; Pietras, B.; Prochazka, A.; Ramos, D.; Rodriguez-Tajes, C.; Rossi, D.; Simon, H.; Tassan-Got, L.; Vargas, J.; Voss, B.
2013-01-01
Fission is an extremely complex mechanism that requires a dynamical approach to describe the evolution of the process in terms of intrinsic and collective excitations of the nuclear constituents. In order to determine these effects a complex experimental setup was mounted at GSI, which allowed us for the first time the full identification in charge and mass of all fission fragments thanks to a magnetic separation and the use of the inverse kinematic technique. Moreover, we also measured the neutron multiplicities and the light-charged particles emitted in coincidence with fission. These complete kinematic measurements will be used to define sensitive observables to dissipative and transient effects in fission. In this manuscript we present the first results for the total fission cross sections. (authors)
Fission, fusion and photonuclear physics. Chapter 2
International Nuclear Information System (INIS)
Berlanger, M.; Deleplanque, M.A.; Gerschel, C.; Hanappe, F.; Leblanc, M.; Mayault, J.F.; Ngo, C.; Paya, D.; Perrin, N.; Peter, J.; Tamain, B.; Valentin, L.
The γ-ray multiplicity has been measured for the quasi-fission events in the Cu + Au reaction at 443MeV. Using the usual assumption on the γ-ray multipolarity and estimating the angular momentum carried away by the evaporated particles, a value of 57h is obtained for the angular momentum transferred to the fragments, in agreement with the sticking hypothesis [fr
Fission Spectrum Related Uncertainties
Energy Technology Data Exchange (ETDEWEB)
G. Aliberti; I. Kodeli; G. Palmiotti; M. Salvatores
2007-10-01
The paper presents a preliminary uncertainty analysis related to potential uncertainties on the fission spectrum data. Consistent results are shown for a reference fast reactor design configuration and for experimental thermal configurations. However the results obtained indicate the need for further analysis, in particular in terms of fission spectrum uncertainty data assessment.
Recent progress in fission at saddle point and scission point
International Nuclear Information System (INIS)
Blons, J.; Paya, D.; Signarbieux, C.
High resolution measurements of 230 Th and 232 Th fission cross sections for neutrons exhibit a fine structure. Such a structure is interpreted as a superposition of two rotational bands in the third, asymmetric, well of the fission barrier. The fragment mass distribution in the thermal fission of 235 U and 233 U does not show any even-odd effect, even at the highest kinetic energies. This is the mark of a strong viscosity in the descent from saddle point to scission point [fr
Scission neutron emission and prompt fission neutron spectrum
Kornilov, N V
2001-01-01
The mass, energy and angular integrated spectra of prompt fission neutrons for sup 2 sup 3 sup 5 U induced fission in the energy range from thermal to 5 MeV were analyzed. It allows assume that about 0.362+-0.025 neutrons per fission are emitted due to another mechanism then neutron emission from excited fragments after full acceleration. The spectrum of scission neutrons consists of two components with average energy 0.98 MeV and 2.74 MeV. The share of scission neutrons and their spectrum shape estimated in this work does not contradict to results of differential experiments analyzed in previous papers.
Maglich, Bogdan; Hester, Tim; Calsec Collaboration
2015-10-01
Uranium-uranium colliding beam experiment1, used fully ionized 238U92+ at energy 100GeV --> accelerated through 3 MV accelerator, will collide beam 240 MeV --> 4 FF + 5n + 430 MeV. Using a simple model1 fission σf ~ 100 b. Suppression of Pu by a factor of 106 will be achieved because NO thermal neutron fission can take place; only fast, 1-3 MeV, where σabs is negligible. Direct conversion of 95% of 430 MeV produced is carried by electrically charged FFs which are magnetically funneled for direct conversion of energy of FFs via electrostatic decelerators4,11. 90% of 930 MeV is electrically recoverable. Depending on the assumptions, we project electric _ power density production of 20 to 200 MWe m-3, equivalent to Thermal 1.3 - 13 GWthm-3. If one-half of unburned U is used for propulsion while rest powers system, heavy FF ion mass provides specific impulse Isp = 106 sec., 103 times higher than current rocket engines.
Cohensedgh, Farhad
This research resolves two problems that have long been of important concern in experimental fission physics: (1) determination of pulse height distribution response of ionization chambers in fission fragment detection measurements, and (2) correction of "thick-foil effect" systematic errors in standard values of the fundamental parameters of fission physics--the average number of prompt neutrons per fission (=nu), absolute fission activity and true fission rate of samples (TFR), and isotopic fission cross sections (sigma _{f}). Results are obtained by a comprehensive digital simulation of the electrostatics and pulse height distribution response of the parallel-plate, ungridded, electron-pulse ionization fission chamber together with prompt neutron -fragment multiplicity and angular distribution correlations, neutron-fragment coincidence detection and related variations in the 4pi^here around the chamber for a wide range of the relevant factors--foil thickness, alpha particle interference bias level, fission detector configuration characteristics, fissile isotopes (^{252}Cf, ^{235}U, etc.) and other experimental parameters. Isotope-specific double-energy (E_1,E_2) natural variations in fragment spectrum, in fragment-specific range-energy (dE/dx) relations and in prompt neutron-fragment multiplicity (nu) and nuclear temperature dependent angular distribution correlations are simulated in detail. Detailed results are obtained for double-energy, fragment-specific count loss fractions resulting from in -foil fragment absorption and from alpha -interference discrimination as well as for chamber detection efficiency, fragment spectrum distortion and prompt neutron -fragment coincidence detection distribution variations. Decay alpha pulse pileup statistics are discussed, and the behavior of and factors affecting the fragment pulse height distribution tail are analyzed in detail. Fragment pairs and prompt neutrons issued from them are tracked in the 4pi^ace around the
Ree, J.M. van; Caffe, A.R.; Wolterink, G.
1982-01-01
The hypoactivity in rats induced by small doses of apomorphine, injected bilaterally into the nucleus accumbens area of the brain, could be antagonized by pretreatment with the neuroleptic-like neuropeptide des-enkephalin-γ-endorphin (DEγE, β-endorphin 6–17) as well as with the neuroleptic drugs
Ree, J.M. van; Király, I.
1984-01-01
Injection of small doses of apomorphine, bromocriptine and the new ergoline compound, GYKI-32887 into the nucleus accumbens decreased locomotor activity when rats were tested in a small open field. This effect was observed following injection of 1 pg of these substances; GYKI-32887 being more potent
Preliminary Results from the Triple Fission-Ejecta Correlations Trial (TRIFECTA) at ORNL
Peters, William; Smith, M. S.; Galindo-Uribarri, A.; Temanson, E.; Smith, K.; Paulauskas, S. V.; Thornsberry, C.; Jones, K. L.; Grzywacz, R.; Cizewski, J. A.
2017-09-01
Despite fission having been studied for almost 80 years, there is a shortage of data on the correlations of multiple fission products needed to benchmark advanced theoretical models of fission. A pioneering experiment underway at ORNL, the Triple Fission-Ejecta Correlations Trial (TRIFECTA), involves the measurement of energy and angular correlations between prompt 252Cf fission neutrons and gamma rays with respect to one fission fragment in time-coincidence. The mass of one fragment is determined, with 4 amu precision, by using 2 micro-channel plate timing detectors and a silicon total-energy detector. Time-coincident data from auxiliary detectors are also recorded: 6 NaI detectors to measure gamma-ray multiplicity, 1 HPGe detector to measure the high-resolution gamma-ray spectrum, and an array of 28 VANDLE modules to measure the neutron spectrum and multiplicity. For the first time, correlations between coincident fragment - gamma - neutron fission products can be studied, as a function of fragment mass. Utilizing certain unique gamma-ray transitions recorded by the HPGe detector, we were able to determine the neutron energy and angular correlations of specific fission fragments. Preliminary results on neutron - neutron angular correlations, gamma-ray vs. neutron multiplicity, and other correlations will be presented, along with plans for future improvements. Work supported in part by the Laboratory Directed Research and Development Program of ORNL, managed by UT-Battelle, LLC, for the U.S. Department of Energy. Done...processed 708 records...16:18:14
Langevin model of low-energy fission
Sierk, Arnold J.
2017-09-01
Background: Since the earliest days of fission, stochastic models have been used to describe and model the process. For a quarter century, numerical solutions of Langevin equations have been used to model fission of highly excited nuclei, where microscopic potential-energy effects have been neglected. Purpose: In this paper I present a Langevin model for the fission of nuclei with low to medium excitation energies, for which microscopic effects in the potential energy cannot be ignored. Method: I solve Langevin equations in a five-dimensional space of nuclear deformations. The macroscopic-microscopic potential energy from a global nuclear structure model well benchmarked to nuclear masses is tabulated on a mesh of approximately 107 points in this deformation space. The potential is defined continuously inside the mesh boundaries by use of a moving five-dimensional cubic spline approximation. Because of reflection symmetry, the effective mesh is nearly twice this size. For the inertia, I use a (possibly scaled) approximation to the inertia tensor defined by irrotational flow. A phenomenological dissipation tensor related to one-body dissipation is used. A normal-mode analysis of the dynamical system at the saddle point and the assumption of quasiequilibrium provide distributions of initial conditions appropriate to low excitation energies, and are extended to model spontaneous fission. A dynamical model of postscission fragment motion including dynamical deformations and separation allows the calculation of final mass and kinetic-energy distributions, along with other interesting quantities. Results: The model makes quantitative predictions for fragment mass and kinetic-energy yields, some of which are very close to measured ones. Varying the energy of the incident neutron for induced fission allows the prediction of energy dependencies of fragment yields and average kinetic energies. With a simple approximation for spontaneous fission starting conditions
Fission in the landscape of heaviest elements: Some recent examples
International Nuclear Information System (INIS)
Khuyagbaatar, J.; Yakushev, A.; Düllmann, Ch.E.; Ackermann, D.; Andersson, L.-L.; Block, M.; Brand, H.; Even, J.; Forsberg, University; Hartmann, W.; Herzberg, R.-D.; Heßberger, F.P.; Hoffmann, J.; Hübner, A.; Jäger, E.; Jeppsson, J.; Kindler, B.; Kratz, J.V.; Krier, J.; Kurz, N.; Lommel, B.; Maiti, M.; Minami, S.; Rudolph, D.; Runke, J.; Sarmiento, L.G.; Schädel, M.; Schausten, B.; Steiner, J.; Heidenreich, T. Torres De; Uusitalo, J.; Wiehl, N.; Yakusheva, V.
2016-01-01
The fission process still remains a main factor that determines the stability of the atomic nucleus of heaviest elements. Fission half-lives vary over a wide range, 10 −19 −10 24 s. Present experimental techniques for the synthesis of the superheavy elements that usually measure α-decay chains are sensitive only in a limited range of half-lives, often 10 −5 −10 3 s. In the past years, measurement techniques for very short-lived and very long-lived nuclei were significantly improved at the gas-filled recoil separator TASCA at GSI Darmstadt. Recently, several experimental studies of fission-related phenomena have successfully been performed. In this paper, results on 254−256 Rf and 266 Lr are presented and corresponding factors for retarding the fission process are discussed.
International Nuclear Information System (INIS)
Moehring, H.; Ranft, J.; Capella, A.; Tran Thanh Van, J.
1993-01-01
Λ, bar Λ, and K S 0 production is studied in a Monte Carlo dual parton model for hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions with an SU(3) symmetric sea for chain formation (chain ends) but strangeness suppression in the chain fragmentation process. Additionally, (qq)-(bar q bar q) production from the sea was introduced into the chain formation process with the same probability as for the q→qq branching within the chain decay process. With these assumptions, multiplicity ratios and Feynman-x distributions for strange particles in h-h and multiplicity ratios in heavy ion collisions are reasonably well reproduced
Eslamizadeh, H.
2015-05-01
The evaporation residue cross section anisotropy of the fission fragment angular distribution, pre-scission neutron multiplicity and the pre-saddle and post-saddle contributions of the pre-scission neutron multiplicity were analyzed within a stochastic approach based on one-, two- and three-dimensional Langevin equations for the compound nucleus 224Th formed via a complete fusion. In these calculations, dissipation was generated through the chaos weighted wall and window friction formula. Comparison of the theoretical results with the experimental data showed that three-dimensional Langevin equations with dissipation generated through the chaos weighted wall and window friction formula make it possible to reproduce satisfactorily the above-mentioned experimental data.
Vorobyev, A. S.; Shcherbakov, O. A.; Gagarski, A. M.; Val'Ski, G. V.; Petrov, G. A.
2010-10-01
A series of experiments has been performed to measure prompt neutron angular and energy distributions from thermal neutron-induced fission of 235,233U in correlation with the fission fragments. These distributions have been analyzed with the assumption of neutron isotropic emission from accelerated fission fragments. The performed analysis demonstrates that all obtained results can be described within 5% accuracy using this assumption. This discrepancy is approximately constant and doesn't depend on fragment mass and the total kinetic energy (TKE). Some minor peculiarities of angular distribution may be interpreted as a result of anisotropy of the fission neutron angular distribution in the fragment center-of-mass system.
Prediction of fission barrier height for induced fission reactions with 16O at several energies
Directory of Open Access Journals (Sweden)
S Soheyli
2009-09-01
Full Text Available We have calculated the fission barrier height for 16O+208Pb, 16O+209Bi, 16O+232Th, 16O+238U and 16O+248Cm systems in energy range between 90 MeV to 215 MeV. This method is based on the experimental data for angular anisotropies of fission fragments. In present work, we have used the transition state model (STM for two different cases: the first case is without neutron emission correction and the second case is with neutron emission correction. In this paper, we have predicted the fission barrier for the two super heavy nuclei that were not reported previously with experimental methods.
A uniform semi-classical approach to the Coulomb fission problem
International Nuclear Information System (INIS)
Levit, S.; Smilansky, U.
1978-01-01
A semi-classical theory based on the path integral formalism is applied to the description of Coulomb fission. Complex classical trajectories are used to compute the classically forbidden transitions from the target's ground state to fission. In a simple model the energy spectrum and angular distributions of the fragments are calculated for the Coulomb fission in the Xe + U collision. Theoretical predictions are made which may be checked experimentally. (author)
Parton Propagation and Fragmentation in QCD Matter
Energy Technology Data Exchange (ETDEWEB)
Alberto Accardi, Francois Arleo, William Brooks, David D' Enterria, Valeria Muccifora
2009-12-01
We review recent progress in the study of parton propagation, interaction and fragmentation in both cold and hot strongly interacting matter. Experimental highlights on high-energy hadron production in deep inelastic lepton-nucleus scattering, proton-nucleus and heavy-ion collisions, as well as Drell-Yan processes in hadron-nucleus collisions are presented. The existing theoretical frameworks for describing the in-medium interaction of energetic partons and the space-time evolution of their fragmentation into hadrons are discussed and confronted to experimental data. We conclude with a list of theoretical and experimental open issues, and a brief description of future relevant experiments and facilities.
Angular Correlations with γ-RAYS and Neutrons in Ternary Fission of 252Cf
Mutterer, M.; Kopatch, Yu. N.; Singer, P.; Klemens, M.; Hotzel, A.; Schwalm, D.; Thirolf, P.; Hesse, M.; Gönnenwein, F.
The following sections are included: * Experiment * Data analysis * Anisotropy of γ-Ray Emission in Binary and Ternary Fission * Anisotropy of γ-ray emission with respect to fragment motion * Anisotropy of γ-my emission with respect to a-particle motion * Gamma-ray angular correlations for other ternary fission modes * Neutron Decay of Ternary Particles * References
Bismuth-fission detectors for high energy nucleons: I. Registration characteristics
Czech Academy of Sciences Publication Activity Database
Zhou, D.; Cavaioli, M.; Jain, R. K.; Spurný, František; Teodori, R.; Tommasino, L.
1999-01-01
Roč. 31, - (1999), s. 455-458 ISSN 1350-4487 R&D Projects: GA AV ČR IAA3048606 Keywords : Spark counter * Fission cross section * Fission fragments Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 0.572, year: 1999
Dispersions and correlations of the distributions of products of 252Cf spontaneous fission
International Nuclear Information System (INIS)
Vidyakin, G.S.; Vyrodov, V.N.; Gurevich, I.I.; Kirillov, B.F.; Kozlov, Y.V.; Martem'yanov, V.P.; Sukhotin, S.V.; Tarasenkov, V.G.; Khakimov, S.K.
1982-01-01
We report the results of two experiments on study of the dispersions and correlations of the distributions of products of the spontaneous fission of 252 Cf. In each experiment about 10 8 fissions were recorded with simultaneous measurement of the number of neutrons produced and in one case the fragment kinetic energy and in the other case the energy of the prompt #betta# rays. The quantities obtained were the probabilities of production of a given number of neutrons per fission, the dispersions of the distributions of the number of neutrons produced and of the fragment kinetic energy, and the dependence of the average #betta#-ray energy and the average fragment kinetic energy on the number of neutrons produced. A calculation is made of the spectrum of the total energy carried away by fragments and neutrons, and its dispersion is determined. An estimate of the total energy release in the 252 Cf fission process is made
Possible Mechanisms of Ternary Fission in the 197Au+197 Au System at 15 AMeV
International Nuclear Information System (INIS)
Jun-Long, Tian; Xian, Li; Shi-Wei, Yan; Xi-Zhen, Wu; Zhu-Xia, Li
2009-01-01
Ternary fission in 197 Au+ 197 Au collisions at 15 A MeV is investigated by using the improved quantum molecular dynamical (ImQMD) model. The experimental mass distributions for each of the three fragments are reproduced for the first time without any freely adjusting parameters. The mechanisms of ternary fission in central and semi-central collisions are dynamically studied. In direct prolate ternary fission, two necks are found to be formed almost simultaneously and rupture sequentially in a very short time interval. Direct oblate ternary fission is a very rare fission event, in which three necks are formed and rupture simultaneously, forming three equally sized fragments along space-symmetric directions in the reaction plane. In sequential ternary fission a binary division is followed by another binary fission event after hundreds of fm/c. (nuclear physics)
a Study of Prompt Neutron Emission in Thermal Neutron-Induced Fission of URANIUM-235.
Franklyn, Christopher Barry
An original experiment was performed to measure the angular correlation of fission neutrons from thermal -neutron-induced fission of ('235)U, with respect to the light fission fragment direction, as a function of fragment mass division and neutron energy. A Monte Carlo model, with a realistic description of the fission fragment de -excitation process, was developed to simulate the observed neutron-fragment angular correlation data. The model was capable of investigating various possible forms of neutron emission which were classified into emission before, during and after full fragment acceleration, and correspondingly named scission acceleration and prompt neutron emission. Simulated neutron-fragment angular correlations displaying similar distributions with respect to the light fragment direction for different forms of neutron emission are shown to exhibit differing distributions when examined as a function of fragment mass division or neutron energy, thus illustrating the sensitivity of the experiment to the forms of neutron emission occurring in fission. A primary conclusion of the investigation was that neutron emission solely from fully accelerated fragments, whether isotropically or anisotropically emitted in the fragment centre of mass system, was unable to adequately describe the observed neutron-fragment angular correlations. Simulation of the fission process with some neutron emission before or during fragment acceleration exhibited a closer correspondence with observed phenomena. Within the scope of this work the form of neutron emission that produced the closest overall correspondence with experimental data was a simulation in which 20% of the emitted neutrons were isotropically emitted scission neutrons with a Maxwellian energy distribution of temperature 1.0 MeV. The remaining neutrons were emitted from fully accelerated fragments, being isotropic in the fragment centre of mass frame, except for the n-th(n > 1) neutrons from the light fragment, which
Neutron angular distribution in plutonium-240 spontaneous fission
Marcath, Matthew J.; Shin, Tony H.; Clarke, Shaun D.; Peerani, Paolo; Pozzi, Sara A.
2016-09-01
Nuclear safeguards applications require accurate fission models that exhibit prompt neutron anisotropy. In the laboratory reference frame, an anisotropic neutron angular distribution is observed because prompt fission neutrons carry momentum from fully accelerated fission fragments. A liquid organic scintillation detector array was used with pulse shape discrimination techniques to produce neutron-neutron cross-correlation time distributions and angular distributions from spontaneous fission in a 252Cf, a 0.84 g 240Pueff metal, and a 1.63 g 240Pueff metal sample. The effect of cross-talk, estimated with MCNPX-PoliMi simulations, is removed from neutron-neutron coincidences as a function of the angle between detector pairs. Fewer coincidences were observed at detector angles near 90°, relative to higher and lower detector angles. As light output threshold increases, the observed anisotropy increases due to spectral effects arising from fission fragment momentum transfer to emitted neutrons. Stronger anisotropy was observed in Cf-252 spontaneous fission prompt neutrons than in Pu-240 neutrons.
Radiological study of the calcanean ossification secondary nucleus development
International Nuclear Information System (INIS)
Carvalho Filho, Guaracy.
1994-01-01
This work describes the normal aspects of the calcanean ossification secondary nucleus radiological development, the appearing time, his form, localization, fragmentation and evolution of area, from a sample of normal individuals. (author). 14 refs., 16 figs., 8 tabs
Systematics of fission cross sections at the intermediate energy region
Energy Technology Data Exchange (ETDEWEB)
Fukahori, Tokio; Chiba, Satoshi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
1997-03-01
The systematics was obtained with fitting experimental data for proton induced fission cross sections of Ag, {sup 181}Ta, {sup 197}Au, {sup 206,207,208}Pb, {sup 209}Bi, {sup 232}Th, {sup 233,235,238}U, {sup 237}Np and {sup 239}Pu above 20 MeV. The low energy cross section of actinoid nuclei is omitted from systematics study, since the cross section has a complicated shape and strongly depends on characteristic of nucleus. The fission cross sections calculated by the systematics are in good agreement with experimental data. (author)
Neutron-multiplicity experiments for enhanced fission modelling
Al-Adili, Ali; Tarrío, Diego; Hambsch, Franz-Josef; Göök, Alf; Jansson, Kaj; Solders, Andreas; Rakapoulos, Vasileios; Gustavsson, Cecilia; Lantz, Mattias; Mattera, Andrea; Oberstedt, Stephan; Prokofiev, Alexander V.; Sundén, Erik A.; Vidali, Marzio; Österlund, Michael; Pomp, Stephan
2017-09-01
The nuclear de-excitation process of fission fragments (FF) provides fundamental information for the understanding of nuclear fission and nuclear structure in neutron-rich isotopes. The variation of the prompt-neutron multiplicity, ν(A), as a function of the incident neutron energy (En) is one of many open questions. It leads to significantly different treatments in various fission models and implies that experimental data are analyzed based on contradicting assumptions. One critical question is whether the additional excitation energy (Eexc) is manifested through an increase of ν(A) for all fragments or for the heavy ones only. A systematic investigation of ν(A) as a function of En has been initiated. Correlations between prompt-fission neutrons and fission fragments are obtained by using liquid scintillators in conjunction with a Frisch-grid ionization chamber. The proof-of-principle has been achieved on the reaction 235U(nth,f) at the Van De Graff (VdG) accelerator of the JRC-Geel using a fully digital data acquisition system. Neutrons from 252Cf(sf) were measured separately to quantify the neutron-scattering component due to surrounding shielding material and to determine the intrinsic detector efficiency. Prelimenary results on ν(A) and spectrum in correlation with FF properties are presented.
Fission of Polyanionic Metal Clusters
König, S.; Jankowski, A.; Marx, G.; Schweikhard, L.; Wolfram, M.
2018-04-01
Size-selected dianionic lead clusters Pbn2 -, n =34 - 56 , are stored in a Penning trap and studied with respect to their decay products upon photoexcitation. Contrary to the decay of other dianionic metal clusters, these lead clusters show a variety of decay channels. The mass spectra of the fragments are compared to the corresponding spectra of the monoanionic precursors. This comparison leads to the conclusion that, in the cluster size region below about n =48 , the fission reaction Pbn2 -→Pbn-10 -+Pb10- is the major decay process. Its disappearance at larger cluster sizes may be an indication of a nonmetal to metal transition. Recently, the pair of Pb10- and Pbn-10 - were observed as pronounced fragments in electron-attachment studies [S. König et al., Int. J. Mass Spectrom. 421, 129 (2017), 10.1016/j.ijms.2017.06.009]. The present findings suggest that this combination is the fingerprint of the decay of doubly charged lead clusters. With this assumption, the dianion clusters have been traced down to Pb212 -, whereas the smallest size for the direct observation was as high as n =28 .
Angular correlations in the prompt neutron emission in spontaneous fission of 252Cf
Kopatch Yuri; Chietera Andreina; Stuttgé Louise; Gönnenwein Friedrich; Mutterer Manfred; Gagarski Alexei; Guseva Irina; Dorvaux Olivier; Hanappe Francis; Hambsch Franz-Josef
2017-01-01
An experiment aiming at the detailed investigation of angular correlations in the neutron emission from spontaneous fission of 252Cf has been performed at IPHC Strasbourg using the angle-sensitive double ionization chamber CODIS for measuring fission fragments and a set of 60 DEMON scintillator counters for neutron detection. The main aim of the experiment is to search for an anisotropy of neutron emission in the center-of-mass system of the fragments. The present status of the data analysis ...
Compound nucleus studies withy reverse kinematics
International Nuclear Information System (INIS)
Moretto, L.G.
1985-06-01
Reverse kinematics reactions are used to demonstrate the compound nucleus origin of intermediate mass particles at low energies and the extension of the same mechanism at higher energies. No evidence has appeared in our energy range for liquid-vapor equilibrium or cold fragmentation mechanisms. 11 refs., 12 figs
Nuclear fission: What have we learned in 50 years?
International Nuclear Information System (INIS)
Vandenbosch, R.
1989-01-01
Nuclear fission has captured the imagination of chemists and physicists for half a century now. There are several reasons for this. One of course is that it represents the most drastic rearrangement of nuclear matter known, challenged only recently by collisions induced by very heavy ions. Another is that both statistical and dynamical features come into play. Perhaps one of the most compelling reasons is its never-ending capacity to surprise us: asymmetric mass distributions, the sawtooth dependence of neutron yields in fragment mass, spontaneously fissioning isomers and intermediate structure resonances. Finally, and perhaps most importantly, fission is a rich laboratory within which one can explore the delicate interplay between the macroscopic aspects of bulk nuclear matter and the quantal effects of a finite number of Fermions. It will of course be impossible for me to cover all aspects of fission. I have chosen a limited number of topics to cover, with particular topics being chosen either because the have been associated with persistent puzzles in fission or because they have, or hopefully will, tell us something special about how nuclei behave. After a brief historical note, I organize these topics sequentially according to the various stages of the fission process, starting first with the probability for fission to occur and ending with scission phenomena. 56 refs., 11 figs
Actinide Sputtering Induced by Fission with Ultra-cold Neutrons
Shi, Tan; Venuti, Michael; Fellers, Deion; Martin, Sean; Morris, Chris; Makela, Mark
2017-09-01
Understanding the effects of actinide sputtering due to nuclear fission is important for a wide range of applications, including nuclear fuel storage, space science, and national defense. A new program at the Los Alamos Neutron Science Center uses ultracold neutrons (UCN) to induce fission in actinides such as uranium and plutonium. By controlling the UCN energy, it is possible to induce fission at the sample surface within a well-defined depth. It is therefore an ideal tool for studying the effects of fission-induced sputtering as a function of interaction depth. Since the mechanism for fission-induced surface damage is not well understood, this work has the potential to deconvolve the various damage mechanisms. During the irradiation with UCN, NaI detectors are used to monitor the fission events and were calibrated by monitoring fission fragments with an organic scintillator. Alpha spectroscopy of the ejected actinide material is performed in an ion chamber to determine the amount of sputtered material. Actinide samples with various sample properties and surface conditions are irradiated and analyzed. In this talk, I will discuss our experimental setup and present the preliminary results from the testing of multiple samples. This work has been supported by Los Alamos National Laboratory and Seaborg Summer Research Fellowship.
Cold fission description with constant and varying mass asymmetries
International Nuclear Information System (INIS)
Duarte, S.B.; Rodriguez, O.; Tavares, O.A.P.; Goncalves, M.; Garcia, F.; Guzman, F.
1998-01-01
Different description for varying the mass asymmetry in the fragmentation process are used to calculate the cold fission barrier penetrability. The relevance of the appropriate choice for both the description of the pre-scission phase and inertia coefficient to unify alpha decay, cluster radioactivity, and spontaneous cold fission processes in the same theoretical framework is explicitly shown. We calculate the half-life of all possible partition modes of nuclei of A > 200 following the most recent Mass Table by Audi and Wapstra. It is shown that if one uses the description in which the mass asymmetry is maintained constant during the fragmentation process, the experimental half-life-values and mass yield of 234 U cold fission are satisfactorily reproduced. (author)
Statistical and dynamical aspects in fission process: The rotational ...
Indian Academy of Sciences (India)
process. In [12,13], the fragment mass and charge distributions in low energy fission were investigated in detail with realistic inputs for the nucleon transfer probabilities. However, angular momentum generation has not been explicitly treated. It is instructive to enumerate the translational and rotational degrees of freedom of ...
Overview of research by the fission group in Trombay
Indian Academy of Sciences (India)
In this overview, it will not be possible to do enough justice to all the different types of contributions made by the various .... dynamics as the projectile–target mass asymmetry is varied across the BG asymmetry. (see figure 4). 6. Fission fragment mass and kinetic energy correlations. One of the areas where extensive work ...
Perspective of ultrarelativistic nucleus-nucleus collisions
International Nuclear Information System (INIS)
Specht, H.J.
1985-01-01
The paper concerns the lectures given at the International School of nuclear physics, Erice, 1985, which survey the expectations for the field of ultrarelativistic nucleus-nucleus collisions. The primary motivation for the field, the organization of the lectures, and a description of the NA 34 experiment, are all briefly given. (U.K.)
Hambsch, F.-J.; Salvador-Castiñeira, P.; Oberstedt, S.; Göök, A.; Billnert, R.
2016-06-01
In recent years JRC-IRMM has been investigating fission cross-sections of 240,242Pu in the fast-neutron energy range relevant for innovative reactor systems and requested in the High Priority Request List (HPRL) of the OECD/Nuclear Energy Agency (NEA). In addition to that, prompt neutron multiplicities are being investigated for the major isotopes 235U, 239Pu in the neutron-resonance region using a newly developed scintillation detector array (SCINTIA) and an innovative modification of the Frisch-grid ionisation chamber for fission-fragment detection. These data are highly relevant for improved neutron data evaluation and requested by the OECD/Working Party on Evaluation Cooperation (WPEC). Thirdly, also prompt fission γ-ray emission is investigated using highly efficient lanthanide-halide detectors with superior timing resolution. Again, those data are requested in the HPRL for major actinides to solve open questions on an under-prediction of decay heat in nuclear reactors. The information on prompt fission neutron and γ-ray emission is crucial for benchmarking nuclear models to study the de-excitation process of neutron-rich fission fragments. Information on γ-ray emission probabilities is also useful in decommissioning exercises on damaged nuclear power plants like Fukushima Daiichi to which JRC-IRMM is contributing. The results on the 240,242Pu fission cross section, 235U prompt neutron multiplicity in the resonance region and correlations with fission fragments and prompt γ-ray emission for several isotopes will be presented and put into perspective.
Directory of Open Access Journals (Sweden)
Hambsch F.-J.
2016-01-01
Full Text Available In recent years JRC-IRMM has been investigating fission cross-sections of 240,242Pu in the fast-neutron energy range relevant for innovative reactor systems and requested in the High Priority Request List (HPRL of the OECD/Nuclear Energy Agency (NEA. In addition to that, prompt neutron multiplicities are being investigated for the major isotopes 235U, 239Pu in the neutron-resonance region using a newly developed scintillation detector array (SCINTIA and an innovative modification of the Frisch-grid ionisation chamber for fission-fragment detection. These data are highly relevant for improved neutron data evaluation and requested by the OECD/Working Party on Evaluation Cooperation (WPEC. Thirdly, also prompt fission γ-ray emission is investigated using highly efficient lanthanide-halide detectors with superior timing resolution. Again, those data are requested in the HPRL for major actinides to solve open questions on an under-prediction of decay heat in nuclear reactors. The information on prompt fission neutron and γ-ray emission is crucial for benchmarking nuclear models to study the de-excitation process of neutron-rich fission fragments. Information on γ-ray emission probabilities is also useful in decommissioning exercises on damaged nuclear power plants like Fukushima Daiichi to which JRC-IRMM is contributing. The results on the 240,242Pu fission cross section, 235U prompt neutron multiplicity in the resonance region and correlations with fission fragments and prompt γ-ray emission for several isotopes will be presented and put into perspective.
Nucleus behavior in violent collisions
International Nuclear Information System (INIS)
Lefort, M.; Galin, J.; Guerreau, D.
1985-01-01
Thanks to new heavy ion beams (Argon, Krypton...) accelerated at Ganil and Sara to velocities of about 0.2 to 0.5 times the light one, very violent collisions, between complex nuclei can be made. During peripheral collisions, the projectile is strongly heated in '' wearing away'' the target and follows its way at high velocity in loosing nucleons. Resulting fragments can present themselves as nuclei very different from usual stable nuclei, often at existence limit. In more central collisions, the energy transferred is such that fusion of both leads to a new type of very hot nucleus near the immediate boiling. Another existence limit is reached by this way: where the bound nucleon system tend to become nucleon gas or a bulk of little fragments [fr
Prompt gamma-ray multiplicity distributions in spontaneous fission of 252Cf
International Nuclear Information System (INIS)
Varma, R.; Mehta, G.K.; Choudhury, R.K.; Kapoor, S.S.; Nayak, B.K.; Ramamurthy, V.S.
1991-01-01
The mean and the standard deviation of the prompt gamma-ray multiplicity distribution in spontaneous fission of 252 Cf have been measured as a function of the charge ratio of the fission fragment pairs. While the variation of the mean multiplicity as a function of charge ratio is found to be nearly structureless, the standard deviation exhibits considerable variations. A statistical model analysis of the data was carried out to determine the contribution of the initial spin distribution widths of the fission fragments to the observed standard deviation of the gamma-ray multiplicity distribution
International Nuclear Information System (INIS)
Chung, K.C.
1989-01-01
An introduction to nuclear fragmentation, with emphasis in percolation ideas, is presented. The main theoretical models are discussed and as an application, the uniform expansion approximation is presented and the statistical multifragmentation model is used to calculate the fragment energy spectra. (L.C.)
Fission gas measuring technology
International Nuclear Information System (INIS)
Lee, Hyung Kwon; Kim, Eun Ka; Hwang, Yong Hwa; Lee, Eun Pyo; Chun, Yong Bum; Seo, Ki Seog; Park, Dea Gyu; Chu, Yong Sun; Ahn, Sang Bok.
1998-02-01
Safety and economy of nuclear plant are greatly affected by the integrity of nuclear fuels during irradiation reactor core. A series of post-irradiation examination (PIE) including non-destructive and destructive test is to be conducted to evaluate and characterize the nuclear performance. In this report, a principle of the examination equipment to measure and analyse fission gases existing nuclear fuels were described and features of the component and device consisting the fission gas measuring equipment are investigated. (author). 4 refs., 2 tabs., 6 figs
Fission gas measuring technology
Energy Technology Data Exchange (ETDEWEB)
Lee, Hyung Kwon; Kim, Eun Ka; Hwang, Yong Hwa; Lee, Eun Pyo; Chun, Yong Bum; Seo, Ki Seog; Park, Dea Gyu; Chu, Yong Sun; Ahn, Sang Bok
1998-02-01
Safety and economy of nuclear plant are greatly affected by the integrity of nuclear fuels during irradiation reactor core. A series of post-irradiation examination (PIE) including non-destructive and destructive test is to be conducted to evaluate and characterize the nuclear performance. In this report, a principle of the examination equipment to measure and analyse fission gases existing nuclear fuels were described and features of the component and device consisting the fission gas measuring equipment are investigated. (author). 4 refs., 2 tabs., 6 figs.
International Nuclear Information System (INIS)
Nifenecker, H.
1982-02-01
In these lectures we present the liquid drop model of fission and compare some of its prediction with experiment. The liquid drop analogy allows to define in a rather simple and intuitive way a number of useful concepts and possible observables. We then discuss, using the example of the oscillator model, the generality of shell effects. We show how a synthesis of the liquid drop model and of the shell model can be made using the Strutinsky shell averaging procedure. Some experimental data related to the existence of shape isomers are presented and discussed. We conclude by discussing some aspects, both experimental and theoretical, of fission dynamics
International Nuclear Information System (INIS)
Nifenecker, H.
1980-08-01
In these lectures the liquid drop model of fission is presented and some of its predictions compared with experiment. The liquid drop analogy allows to define in a rather simple and intuitive way a number of useful concepts and possible observables. It is shown how a synthesis of the liquid drop model and of the shell model can be made using the Strutinsky shell averaging procedure. Some experimental data related to the existence of shape isomers are presented and discussed. We conclude by discussing some aspects, both experimental and theoretical, of fission dynamics
Asymmetrically deformed states of thorium isotopes during fission process
International Nuclear Information System (INIS)
Blons, J.
1982-05-01
Some theoretical considerations are recalled on fission barriers calculated from macroscopic, microscopic or macroscopic-microscopic and ''thorium anomaly'' problem is set. Experimental techniques used to measure fission cross sections in (n,f) reactions near the threshold are described. Fission dectector is described; stray resonance problems and retrodiffused neutrons are discussed. Results obtained in experimental study of 230 Th(n,f) and 232 Th(n,f) reactions are presented. They are compared with results obtained in other laboratories. The analysis model which allows to describe a (n,f) reaction is exposed. The compound nucleus formation cross section and transmission coefficients in neutron and gamma output channel are presented according to neutron energy for each value of angular moment and parity. Cross-section analysis and angular distribution obtained respectively in 230 Th(n,f) and 232 Th(n,f) reactions is exposed. Result interpretation show new aspects of nuclei rotational spectra and new nuclear forms [fr
DEFF Research Database (Denmark)
Schrøder, H D
1981-01-01
in the length of the nucleus was observed. Based on the cytoarchitecture the nucleus could be divided in three parts, a cranial, a dorsomedial and a ventrolateral. All parts of the nucleus consisted of chromatin-rich medium-sized neurons, and apparent direct appositions between different cells bodies as well...
Discoveries of isotopes by fission
Indian Academy of Sciences (India)
2015-08-28
Aug 28, 2015 ... Of the about 3000 isotopes presently known, about 20% have been discovered in fission. The history of fission as it relates to the discovery of isotopes as well as the various reaction mechanisms leading to isotope discoveries involving fission are presented.
International Nuclear Information System (INIS)
Hilscher, D.
1989-01-01
The article tells the story of the discovery of nuclear fission in Berlin 50 years ago by Otto Hahn and Fritz Strassmann in cooperation with Lise Meitner. 50 years later nuclear fission is still a subject of research. Some question remain unanswered. Selected new research results are used to discuss the dynamics of the collective movement of the elementary nuclear fission process. (orig.) [de