International Nuclear Information System (INIS)
Excitation functions have been measured for complex fragment emission from the compound nucleus 98Mo, produced by the reaction of 86Kr with 12C. Mass asymmetric fission barriers have been obtained by fitting the excitation functions with a transition state formalism. The extracted barriers are ∼ 5.7 MeV higher, on average, than the calculations of the Rotating Finite Range Model (RFRM). These data clearly show an isospin dependence of the conditional barriers when compared with the extracted barriers from 90Mo and 94Mo. Eleven different liquid/liquid extractants were synthesized based upon the chelating moieties 3,2-HOPO and 3,4-HOPO; additionally, two liquid/liquid extractants based upon the 1,2-HOPO chelating moiety were obtained for extraction studies. The Pu(IV) extractions, quite surprisingly, yielded results that were very different from the Fe(III) extractions. The first trend remained the same: the 1,2-HOPOs were the best extractants, followed closely by the 3,2-HOPOs, followed by the 3,4-HOPOs; but in these Pu(IV) extractions the 3,4-HOPOs performed much better than in the Fe(III) extractions. 129 refs
Energy Technology Data Exchange (ETDEWEB)
Veeck, A.C. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Livermore National Lab., CA (United States). Glenn T. Seaborg Inst. for Transactinium Science]|[Lawrence Berkeley National Lab., CA (United States). Nuclear Science Div.
1996-08-01
Excitation functions have been measured for complex fragment emission from the compound nucleus {sup 98}Mo, produced by the reaction of {sup 86}Kr with {sup 12}C. Mass asymmetric fission barriers have been obtained by fitting the excitation functions with a transition state formalism. The extracted barriers are {approximately} 5.7 MeV higher, on average, than the calculations of the Rotating Finite Range Model (RFRM). These data clearly show an isospin dependence of the conditional barriers when compared with the extracted barriers from {sup 90}Mo and {sup 94}Mo. Eleven different liquid/liquid extractants were synthesized based upon the chelating moieties 3,2-HOPO and 3,4-HOPO; additionally, two liquid/liquid extractants based upon the 1,2-HOPO chelating moiety were obtained for extraction studies. The Pu(IV) extractions, quite surprisingly, yielded results that were very different from the Fe(III) extractions. The first trend remained the same: the 1,2-HOPOs were the best extractants, followed closely by the 3,2-HOPOs, followed by the 3,4-HOPOs; but in these Pu(IV) extractions the 3,4-HOPOs performed much better than in the Fe(III) extractions. 129 refs.
Fission barriers in a macroscopic-microscopic model
International Nuclear Information System (INIS)
In the framework of the macroscopic-microscopic model, this study investigates fission barriers in the region of actinide nuclei. A very effective four-dimensional shape parametrization for fissioning nuclei is proposed. Taking, in particular, the left-right mass asymmetric and nonaxial shapes into account is demonstrated to have a substantial effect on fission barrier heights. The influence of proton versus neutron deformation differences on the potential energy landscape of fissioning nuclei is also discussed
Superheavy nuclei and fission barriers
Lu, Bing-Nan; Zhao, Jie; Zhao, En-Guang; Zhou, Shan-Gui
In this chapter, we will present relativistic mean field (RMF) description of heavy and superheavy nuclei (SHN). We will discuss the shell structure and magic numbers in the mass region of SHN, binding energies and α decay Q values, shapes of ground states and potential energy surfaces and fission barriers. We particularly focus on the multidimensionally-constrained covariant density functional theories (CDFT) and the applications of CDFT to the study of exotic nuclear shapes and fission barriers.
Thermal fission rates with temperature dependent fission barriers
Zhu, Yi
2016-01-01
\\item[Background] The fission processes of thermal excited nuclei are conventionally studied by statistical models which rely on inputs of phenomenological level densities and potential barriers. Therefore the microscopic descriptions of spontaneous fission and induced fission are very desirable for a unified understanding of various fission processes. \\item[Purpose] We propose to study the fission rates, at both low and high temperatures, with microscopically calculated temperature-dependent fission barriers and mass parameters. \\item[Methods] The fission barriers are calculated by the finite-temperature Skyrme-Hartree-Fock+BCS method. The mass parameters are calculated by the temperature-dependent cranking approximation. The thermal fission rates can be obtained by the imaginary free energy approach at all temperatures, in which fission barriers are naturally temperature dependent. The fission at low temperatures can be described mainly as a barrier-tunneling process. While the fission at high temperatures ...
Thermal fission rates with temperature dependent fission barriers
Zhu, Yi; Pei, Junchen
2016-01-01
The fission processes of thermal excited nuclei are conventionally studied by statistical models which rely on inputs of phenomenological level densities and potential barriers. Therefore the microscopic descriptions of spontaneous fission and induced fission are very desirable for a unified understanding of various fission processes. We propose to study the fission rates, at both low and high temperatures, with microscopically calculated temperature-dependent fission barriers and collective ...
Possible origin of transition from symmetric to asymmetric fission
Paşca, H.; Andreev, A. V.; Adamian, G. G.; Antonenko, N. V.
2016-09-01
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 barriers and half-lives
International Nuclear Information System (INIS)
The authors briefly review the development of theoretical models for the calculation of fission barriers and half-lives. They focus on how results of actual calculations in a unified macroscopic-microscopic approach provide an interpretation of the mechanisms behind some of the large number of phenomena observed in fission. As instructive examples they choose studies of the rapidly varying fission properties of elements at the end of the periodic system
Fission Barriers of Compound Superheavy Nuclei
Pei, J C; Nazarewicz, W.; Sheikh, J. A.; Kerman, A. K.
2009-01-01
The dependence of fission barriers on the excitation energy of the compound nucleus impacts the survival probability of superheavy nuclei synthesized in heavy-ion fusion reactions. In this work, we investigate the isentropic fission barriers by means of the self-consistent nuclear density functional theory. The relationship between isothermal and isentropic descriptions is demonstrated. Calculations have been carried out for $^{264}$Fm, $^{272}$Ds, $^{278}$112, $^{292}$114, and $^{312}$124. F...
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.
Role of the second barrier upon mass division in the spontaneous fission of the heaviest elements
International Nuclear Information System (INIS)
In the region where theorists had earlier predicted the disappearance of the outer fission barrier or of it dropping below the ground-state, we have measured the mass and total-kinetic-energy distributions from spontaneous fission of 252No, 254No, 256[104], and 258[104]. The results, in combination with earlier measurements for 256No, 258No, and 262No, show a sharp transition from asymmetrical mass division in 256No to symmetrical ones for 258No and 262No. On-the-other-hand, all isotopes of element 104 including 260[104] appear to yield broadly symmetrical mass distributions. The total-kinetic energies around 200 MeV for the 104 isotopes indicate they fission by the low-energy mode of bimodal fission. Based on the hypothesis that the second barrier is responsible for asymmetrical mass distributions and when it disappears, for symmetrical ones, these observations for the isotopes of element 104 are in accord with 1976 calculations of the heights of the second fission barrier relative to the ground-state. Some recent calculations of static potential-energy surfaces and of barrier heights deduced from half-lives for spontaneous fission indicate the second barrier is from 0 to 2.9 MeV above the ground-state for the No and 104 isotopes. However, shape degrees-of-freedom have been limited in these calculations so that they fail to provide realistic heights for the outer fission barrier. For the few cases where higher-order asymmetrical deformations are included, this barrier height is well below the ground-state and, for these nuclides, we observe symmetric mass division only. Without more extensive calculations of potential-energy surfaces for comparison with our findings, we are unable reach a firm conclusion on the role of the second barrier upon mass division in fission
Putting in evidence the asymmetric fission in the desexcitation process of 47V nuclei
International Nuclear Information System (INIS)
The fusion-fission, which reflects the instability of the nuclei against the deformation and leads to a binary break up into nearly equal mass nuclei, have been considered as a general feature of the heavy ions (A>80). For lighter systems the fission decay of the compound nucleus is predicted by the rotating liquid drop model to be minor process and the fully-damped products observed in reactions between light heavy ions (A35 Cl+12 C, 31 P+16 O and 23 Na+24 Mg reactions used in order to populate the 47 V system at two excitation energies E = 59 and 64 MeV. This study shows that these fragments are the result of the emission from a source and their elemental distributions are asymmetric independently to the entrance channel asymmetry. The absence of entrance channel effect is a signature of the asymmetric fission process of the 47 V nucleus. The comparison of the experimental observations to the statistical model shows that the fission barriers in this mass region are lower than those predicted by the rotating liquid drop model and the need of introducing their angular momentum and mass asymmetry dependence is clearly shown. In conclusion, it is well established that the evidence of the asymmetric fission break up into the desexcitation process of the 47 V nucleus should be taken into account in the statistical calculations describing the complete fusion of light heavy ions
Probing the time scale of asymmetric fission
International Nuclear Information System (INIS)
The author describes the measurement of the mass-energy distributions of fission fragments in the reactions 197Au(14N,X) at 34 A.MeV and 232Th(7Li,X) at 43 A.MeV. He presents results on the mass-asymmetry and excitation energy sharing. (HSI)
Cluster radioactivity and very asymmetric fission through quasi-molecular shapes
Energy Technology Data Exchange (ETDEWEB)
Royer, G. [Centre National de la Recherche Scientifique, 44 - Nantes (France). Lab. de Physique Subatomique et des Technologies Associees; Gupta, R.K. [Panjab Univ., Chandigarh (India). Dept. of Physics; Denisov, V.Yu. [Akademyiya Nauk Ukrayini, Kiev (Ukraine)
1997-12-31
The decay of radioactive nuclei which emit heavy clusters like C, O, Ne, Mg and Si has been studied in the fission valley which leads one spherical nucleus towards two spherical touching nuclei before crossing the barrier. Assuming volume conservation, the deformation energy has been calculated within a generalized liquid drop model taking into account the proximity effects between the cluster and the daughter nucleus. The theoretical partial half-lives obtained within the WKB barrier penetration probability are in good agreement with the experimental data for the heaviest clusters. The Ne, Mg and Si emission looks like a very-asymmetric spontaneous fission. The {sup 14}C radioactivity is not correctly described within the fission hypothesis. The {sup 14}C and apparently also the {sup 20}O are probably pre-born in the parent nucleus, the emission being similar to the {alpha} decay process. (author). 27 refs.
Cluster radioactivity and very asymmetric fission through quasi-molecular shapes
International Nuclear Information System (INIS)
The decay of radioactive nuclei which emit heavy clusters like C, O, Ne, Mg and Si has been studied in the fission valley which leads one spherical nucleus towards two spherical touching nuclei before crossing the barrier. Assuming volume conservation, the deformation energy has been calculated within a generalized liquid drop model taking into account the proximity effects between the cluster and the daughter nucleus. The theoretical partial half-lives obtained within the WKB barrier penetration probability are in good agreement with the experimental data for the heaviest clusters. The Ne, Mg and Si emission looks like a very-asymmetric spontaneous fission. The 14C radioactivity is not correctly described within the fission hypothesis. The 14C and apparently also the 20O are probably pre-born in the parent nucleus, the emission being similar to the α decay process. (author)
Transition States at the Fission Barrier
International Nuclear Information System (INIS)
The current knowledge of the transition states that a nucleus traverses en route to fission is reviewed, together with the relevant theory of fission-fragment anisotropy. Theoretical progress in understanding this kind of data in terms of nuclear superfluidity is summarized. The evidence indicates that nuclear pairing effects play an important role in determining the transition state spectrum. Recent (d, pf) experimental data are noted, and their statistical analysis in terms of a pairing Hamiltonian considered in the fixed-energy ensemble appropriate for finite nuclei is presented. The results indicate that such pairing effects lead in Pu240 to an energy gap in the transition spectrum nearly twice that which occurs at the ground state shape of the same nucleus. Such a result is quite significant from the point of view of nuclear many-body physics, suggesting that the nuclear surface plays an important role in the pairing of nucleons in the finite nuclei. The significance for nuclear fission is also broad. Such a large energy gap forces reassessment of certain detailed conjectures that have been put forward concerning fission widths and mass asymmetry associated with capture resonances of specific spin and parity. The new situation suggests that the even-even and odd-odd spin-parity correlation that rules in the low energy spectra of deformed even-even nuclei does not prevail in the transition state spectrum. A possible explanation in terms of low energy mass- asymmetric and bending vibrations of the fissioning nucleus is discussed. Possible experimental studies that could support or negate the validity of this viewpoint are mentioned. (author)
Fission barrier heights in the A ∼ 200 mass region
Indian Academy of Sciences (India)
K Mahata
2015-08-01
Statistical model analysis is carried out for - and -induced fission reactions using a consistent description for fission barrier and level density in A ∼ 200 mass region. A continuous damping of shell correction with excitation energy is considered. Extracted fission barriers agree well with the recent microscopic–macroscopic model. The shell corrections at the saddle point were found to be insignificant.
Adiabatic fission barriers in superheavy nuclei
Jachimowicz, P.; Kowal, M; Skalski, J.
2016-01-01
Using the microscopic-macroscopic model based on the deformed Woods-Saxon single-particle potential and the Yukawa-plus-exponential macroscopic energy we calculated static fission barriers $B_{f}$ for 1305 heavy and superheavy nuclei $98\\leq Z \\leq 126$, including even - even, odd - even, even - odd and odd - odd systems. For odd and odd-odd nuclei, adiabatic potential energy surfaces were calculated by a minimization over configurations with one blocked neutron or/and proton on a level from ...
Asymmetrically deformed states of thorium isotopes during fission process
International Nuclear Information System (INIS)
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 230Th(n,f) and 232Th(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 230Th(n,f) and 232Th(n,f) reactions is exposed. Result interpretation show new aspects of nuclei rotational spectra and new nuclear forms
Microscopic Description of Nuclear Fission: Fission Barrier Heights of Even-Even Actinides
McDonnell, J; Schunck, N; Nazarewicz, W.
2013-01-01
We evaluate the performance of modern nuclear energy density functionals for predicting inner and outer fission barrier heights and energies of fission isomers of even-even actinides. For isomer energies and outer barrier heights, we find that the self-consistent theory at the HFB level is capable of providing quantitative agreement with empirical data.
International Nuclear Information System (INIS)
It is now well known that many reactions giving measurable fusion cross-sections also show a fission of the compound system formed, similar to the low energy fission of the known fissioning nuclei. Recently, both the fusion excitation functions and the mass equilibration in the fragmentation of the composite system were measured for a large number of systems with 94208Pb on different targets of 26Mg, 48Ca, 50Ti, 52Cr, 58Fe and 64Ni. From a theoretical point of view, it is relevant to ask the question: how do the colliding nuclei fuse and then why does the compound system formed fission instead of going to the ground state to give a stable system. In this Letter, we attempt to show that the fusion of asymmetric colliding nuclei is due to the overcoming of the interaction barriers in adiabatic potentials and the fission of the compound system should perhaps occur as a sudden process, like the one in the spontaneous fission phenomenon. We have made our calculations for the compound systems with 102<=Z<=110 and for the asymmetric target-projectile combinations of the experiments of Ref. 1, using the fragmentation theory whose basis is the asymmetric two-centre shell model
Sub-library of Updated Fission Barrier Parameters(CENPL-FBP2)
Institute of Scientific and Technical Information of China (English)
2001-01-01
The fission barrier parameters are important to determine the fission character of a nucleus. The fission barrier parameters and fission level densities are key ingredients in calculations of not only fission cross section but also various cross sections, and spectra for the fissile nuclides, even heavy nuclides at higher incident energies. It is necessaries that the accuracy of fission barrier parameters requires even higher, and nuclides with fission barrier parameters can cover even wider nuclear range.
Global calculations of fission barriers and beta-decay properties of neutron-rich nuclei
Energy Technology Data Exchange (ETDEWEB)
Moller, P. (Peter); Sierk, A. J. (Arnold J.); Ichikawa, Takatoshi; Iwamoto, A. (Akira)
2004-01-01
Recently we have performed large-scale calculations of fission barriers in the actinide region based on five-dimensional deformation spaces with more than 3,000,000 deformation points for each potential-energy surface. We have determined new model constants. We have also extended our model to axially asymmetric shapes. We apply these techniques to the calculations of fission barriers of heavy nuclei from the line of beta stability to the r-process line. The aim is to study fission near the end of the r-process. We have also extended our model of {beta}-decay so that allowed Gamow-Teller transitions are treated in a quasi-particle random-phase approximation as earlier, but we now also consider first-forbidden transitions in the statistical gross theory. We discuss the properties of this enhanced model and present results of global calculations.
Adiabatic fission barriers in superheavy nuclei
Jachimowicz, P; Skalski, J
2016-01-01
Using the microscopic-macroscopic model based on the deformed Woods-Saxon single-particle potential and the Yukawa-plus-exponential macroscopic energy we calculated static fission barriers $B_{f}$ for 1305 heavy and superheavy nuclei $98\\leq Z \\leq 126$, including even - even, odd - even, even - odd and odd - odd systems. For odd and odd-odd nuclei, adiabatic potential energy surfaces were calculated by a minimization over configurations with one blocked neutron or/and proton on a level from the 10-th below to the 10-th above the Fermi level. The parameters of the model that have been fixed previously by a fit to masses of even-even heavy nuclei were kept unchanged. A search for saddle points has been performed by the "Imaginary Water Flow" method on a basic five-dimensional deformation grid, including triaxiality. Two auxiliary grids were used for checking the effects of the mass asymmetry and hexadecapole non-axiallity. The ground states were found by energy minimization over configurations and deformations...
Fission barrier heights and lifetimes for heavy and superheavy nuclei
International Nuclear Information System (INIS)
Ground-state masses, fission barrier heights and α lifetimes for actinide and trans-actinide nuclei are determined in the framework of the macroscopic-microscopic model with the Lublin-Strasbourg Drop, the Strutinsky shell-correction method and the Modified Funny-Hills shape parametrization accounting for elongation, neck formation, left-right asymmetry and non-axiality together with the Yukawa folding procedure. Fission barrier height are nicely reproduced in our approach which contains no adjustable parameter. (authors)
Modelling with uncertainties: The role of the fission barrier
Directory of Open Access Journals (Sweden)
Lü Hongliang
2013-12-01
Full Text Available Fission is the dominant decay channel of super-heavy elements formed in heavy ions collisions. The probability of synthesizing heavy or super-heavy nuclei in fusion-evaporation reactions is then very sensitive to the height of their fission barriers. This contribution will firstly address the influence of theoretical uncertainty on excitation functions. Our second aim is to investigate the inverse problem, i.e., what information about the fission barriers can be extracted from excitation functions? For this purpose, Bayesian methods have been used with a simplified toy model.
International Nuclear Information System (INIS)
We present fission-barrier-height calculations for nuclei throughout the periodic system based on a realistic theoretical model of the multi-dimensional potential-energy surface of a fissioning nucleus. This surface guides the nuclear shape evolution from the ground state, over inner and outer saddle points, to the final configurations of separated fission fragments. We have previously shown that our macroscopic-microscopic nuclear potential-energy model yields calculated 'outer' fission-barrier heights (EB) for even-even nuclei throughout the periodic system that agree with experimental data to within about 1.0 MeV. We present final results of this work. Just recently we have enhanced our macroscopic-microscopic nuclear potential-energy model to also allow the consideration of axially asymmetric shapes. This shape degree of freedom has a substantial effect on the calculated height (EA) of the inner peak of some actinide fission barriers. We present examples of fission-barrier calculations by use of this model with its redetermined constants. Finally we discuss what the model now tells us about fission barriers at the end of the r-process nucleosynthesis path. (author)
Microscopic determinations of fission barriers (mean-field and beyond)
International Nuclear Information System (INIS)
With a help of the selfconsistent Hartree-Fock-Bogoliubov (HFB) approach with the D1S effective Gogny interaction and the Generator Coordinate Method (GCM) we incorporate the transverse collective vibrations to the one-dimensional model of the fission-barrier penetrability based on the traditional WKB method. The average fission barrier corresponding to the least-energy path in the two-dimensional potential energy landscape as function of quadrupole and octupole degrees of freedom is modified by the influence of the transverse collective vibrations along the nuclear path to fission. The set of transverse vibrational states built in the fission valley corresponding to a successively increasing nuclear elongation produces the new energy barrier which is compared with the least-energy barrier. These collective states are given as the eigensolutions of the GCM purely vibrational Hamiltonian. In addition, the influence of the collective inertia on the fission properties is displayed, and it turns out to be the decisive condition for the possible transitions between different fission valleys. (author)
Primary fragment mass-yield distributions for asymmetric fission path of heavy nuclei
International Nuclear Information System (INIS)
The primary fragment mass-yield distribution for the asymmetric fission path in heavy nuclei, 233Pa, 239Np, 245Am and 249Bk at the excitation energy of ∼20 MeV are experimentally constructed based on the intensities of total kinetic energies for individual mass splits. The results revealed an interesting phenomenon: in all the studied fissioning systems, the inner wings of the mass-yield distributions in the asymmetric fission path appear along the same mass-wall of A = 130 fragment mass. The asymmetric mass-yield distribution indicates the strong effect of structural shells in fragments on the final mass division process of the asymmetric fission path. (author)
Evaluation of Nuclear Fission Barrier Parameters for 17 Nuclei
Institute of Scientific and Technical Information of China (English)
2001-01-01
As well know that modern nuclear installations and applications have reached a high degree of sophistication. The effective safe and economical design of these technologies require detailed and reliable design calculations. The accuracy of these calculations is largely determined by the accuracy of the basic nuclear and atomic input parameters. In order to meet the needs on high energy fission cross section, fission spectra in waste disposal, transmutation, radioactive beams physics and so on, 17 nuclei fission barrier parameters were collected from the literature based on different experiments and
Spontaneous Fission Barriers Based on a Generalized Liquid Drop Model
Guo, Shu-Qing; Bao, Xiao-Jun; Li, Jun-Qing; Zhang, Hong-Fei
2014-05-01
The barrier against the spontaneous fission has been determined within the Generalized Liquid Drop Model (GLDM) including the mass and charge asymmetry, and the proximity energy. The shell correction of the spherical parent nucleus is calculated by using the Strutinsky method, and the empirical shape-dependent shell correction is employed during the deformation process. A quasi-molecular shape sequence has been defined to describe the whole process from one-body shape to two-body shape system, and a two-touching-ellipsoid is adopted when the superdeformed one-body system reaches the rupture point. On these bases the spontaneous fission barriers are systematically studied for nuclei from 230Th to 249Cm for different possible exiting channels with the different mass and charge asymmetries. The double, and triple bumps are found in the fission potential energy in this region, which roughly agree with the experimental results. It is found that at around Sn-like fragment the outer fission barriers are lower, while the partner of the Sn-like fragment is in the range near 108Ru where the ground-state mass is lowered by allowing axially symmetric shapes. The preferable fission channels are distinctly pronounced, which should be corresponding to the fragment mass distributions.
Remarks on the fission barriers of super-heavy nuclei
Hofmann, S.; Heinz, S.; Mann, R.; Maurer, J.; Münzenberg, G.; Antalic, S.; Barth, W.; Dahl, L.; Eberhardt, K.; Grzywacz, R.; Hamilton, J. H.; Henderson, R. A.; Kenneally, J. M.; Kindler, B.; Kojouharov, I.; Lang, R.; Lommel, B.; Miernik, K.; Miller, D.; Moody, K. J.; Morita, K.; Nishio, K.; Popeko, A. G.; Roberto, J. B.; Runke, J.; Rykaczewski, K. P.; Scheidenberger, C.; Shaughnessy, D. A.; Stoyer, M. A.; Thörle-Pospiech, P.; Tinschert, K.; Trautmann, N.; Uusitalo, J.; Yeremin, A. V.
2016-04-01
Shell-correction energies of super-heavy nuclei are approximated by using Q_{α} values of measured decay chains. Five decay chains were analyzed, which start at the isotopes 285Fl, 294118, 291Lv, 292Lv and 293Lv. The data are compared with predictions of macroscopic-microscopic models. Fission barriers are estimated that can be used to eliminate uncertainties in partial fission half-lives and in calculations of evaporation-residue cross-sections. In that calculations, fission probability of the compound nucleus is a major factor contributing to the total cross-section. The data also provide constraints on the cross-sections of capture and quasi-fission in the entrance channel of the fusion reaction. Arguments are presented that fusion reactions for synthesis of isotopes of elements 118 and 120 may have higher cross-sections than assumed so far.
Temperature-Dependent Fission Barriers of Superheavy Nuclei
Pei, J C; Sheikh-Javid, A; Kerman, A K
2009-01-01
The dependence of fission barriers on the excitation energy of the compound nucleus impacts the survival probability of superheavy nuclei synthesized in heavy-ion fusion reactions. We study the temperature-dependent fission barriers by means of the self-consistent nuclear density functional theory. The equivalence of isothermal and isentropic descriptions is demonstrated. The effect of the particle gas is found to be negligible in the range of temperatures studied. Calculations have been carried out for $^{264}$Fm, $^{272}$Ds, $^{278}$112, $^{292}$114, and $^{312}$124. For nuclei around $^{278}$112 produced in "cold fusion" reactions, we predict a more rapid decrease of fission barriers with temperature as compared to the nuclei around $^{292}$114 synthesized in "hot fusion" experiments. This is explained in terms of the difference between the ground-state and fission-barrier temperatures. Our calculations are consistent with the long survival probabilities of the superheavy elements produced in Dubna with th...
The sub-library of fission barrier parameters
International Nuclear Information System (INIS)
The first edition of fission barrier parameters sub-library, constitutes one part of the Chinese Evaluated Nuclear Parameter Library (CENPL), including data file and management-retrieval code system, has been finished. The introduction for its contents and usage of the retrieval system is presented. (1 fig.)
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.
Fission barriers and probabilities of spontaneous fission for elements with Z ≥ 100
Baran, A.; Kowal, M.; Reinhard, P.-G.; Robledo, L. M.; Staszczak, A.; Warda, M.
2015-12-01
This paper briefly reviews recent progress in theoretical studies on fission barriers and fission half-lives of even-even superheavy nuclei. We compare and discuss results obtained in the semi-classical macroscopic-microscopic approach, the self-consistent mean-field models with the Skyrme and Gogny energy density functionals and in the relativistic mean-field theory. A short part of the paper is devoted to the calculation of the mass parameters and nuclear fission dynamics. We also discuss the predictive power of Skyrme energy density functionals applied to key properties of the fission path of 266Hs. Standard techniques of error estimates in the framework of a χ2 analysis are applied.
Fission barrier, damping of shell correction and neutron emission in the fission of A$\\sim$200
Mahata, K; Kailas, S; S. S. Kapoor
2015-01-01
Decay of $^{210}$Po compound nucleus formed in light and heavy-ion induced fusion reactions has been analyzed simultaneously using a consistent prescription for fission barrier and nuclear level density incorporating shell correction and its damping with excitation energy. Good description of all the excitation functions have been achieved with a fission barrier of 21.9 $\\pm$ 0.2 MeV. For this barrier height, the predicted statistical pre-fission neutrons in heavy-ion fusion-fission are much ...
Fission barriers in covariant density functional theory: extrapolation to superheavy nuclei
Abusara, H.; Afanasjev, A. V.; Ring, P.
2012-01-01
Systematic calculations of fission barriers allowing for triaxial deformation are performed for even-even superheavy nuclei with charge number $Z=112-120$ using three classes of covariant density functional models. The softness of nuclei in the triaxial plane leads to an emergence of several competing fission pathes in the region of the inner fission barrier in some of these nuclei. The outer fission barriers are considerably affected by triaxiality and octupole deformation. General trends of...
Masses and fission barriers of nuclei in the LSD model
International Nuclear Information System (INIS)
Recently developed Lublin-Strasbourg Drop (LSD) model together with the microscopic corrections taken r is very successful in describing many features of nuclei. In addition to the classical liquid drop model the LSD contains the curvature term proportional to the A1/3. The r.m.s. deviation of the LSD binding energies of 2766 isotopes with Z,N>7 from the experimental ones is 0.698 MeV only. It turns out that the LSD model gives also a satisfactory prediction of the fission barrier heights. In addition, it was found in that taking into account the deformation dependence of the congruence energy proposed by Myers and Swiatecki significantly approaches the LSD-model barrier-heights to the experimental data in the case of light isotopes while the fission barriers for heavy nuclei remain nearly unchanged and agree well with experiment. It was also shown in that the saddle point masses of transactinides from 232Th to 250Cf evaluated using the LSD differ by less than 0.67 MeV from the experimental data.
Fission fragment mass reconstruction from Si surface barrier detector measurement
Velkovska, J.; McGrath, R. L.
1998-01-01
A method for plasma delay and pulse-height defect corrections for Si surface barrier detectors (SBD) is presented. Based on known empirical formulae, simple approximations involving the measured time-of-flight (TOF) and energy of the ions were found and a mass reconstruction procedure was developed. The procedure was applied for obtaining the fission fragment mass and angular distributions from the $^{64}$ Ni+$^{197}$Au reaction at 418 MeV and 383 MeV incident energy using an array of eight S...
Fission barriers at the end of the chart of the nuclides
Möller, Peter; Sierk, Arnold J.; Ichikawa, Takatoshi; Iwamoto, Akira; Mumpower, Matthew
2015-02-01
We present calculated fission-barrier heights for 5239 nuclides for all nuclei between the proton and neutron drip lines with 171 ≤A ≤330 . The barriers are calculated in the macroscopic-microscopic finite-range liquid-drop model with a 2002 set of macroscopic-model parameters. The saddle-point energies are determined from potential-energy surfaces based on more than 5 000 000 different shapes, defined by five deformation parameters in the three-quadratic-surface shape parametrization: elongation, neck diameter, left-fragment spheroidal deformation, right-fragment spheroidal deformation, and nascent-fragment mass asymmetry. The energy of the ground state is determined by calculating the lowest-energy configuration in both the Nilsson perturbed-spheroid (ɛ ) and the spherical-harmonic (β ) parametrizations, including axially asymmetric deformations. The lower of the two results (correcting for zero-point motion) is defined as the ground-state energy. The effect of axial asymmetry on the inner barrier peak is calculated in the (ɛ ,γ ) parametrization. We have earlier benchmarked our calculated barrier heights to experimentally extracted barrier parameters and found average agreement to about 1 MeV for known data across the nuclear chart. Here we do additional benchmarks and investigate the qualitative and, when possible, quantitative agreement and/or consistency with data on β -delayed fission, isotope generation along prompt-neutron-capture chains in nuclear-weapons tests, and superheavy-element stability. These studies all indicate that the model is realistic at considerable distances in Z and N from the region of nuclei where its parameters were determined.
Particle Transport with Asymmetric Unbiased Forces and Entropic Barrier
Institute of Scientific and Technical Information of China (English)
XIE Hui-Zhang; AI Bao-Quan; LIU Xue-Mei; CHENG xiao-Bo; LIU Liang-Gang; LI Zhi-Bing
2007-01-01
Transport of a Brownian particle moving along the axis of a three-dimensional(3D)symmetric and periodic tube is investigated in the presence of asymmetric unbiased forces.It is found that in the presence of entropic barrier,the asymmetry of the unbiased forces is a way of inducing a net particle current.The particle current is a peaked function of temperature,which jndicares that the thermaJ noise may facilitate the transport even in the presence of entropic barrier.There exists an optimized radius at the bottleneck at which the particle current takes its maximum value.The current can be influenced by the slope of tube walls and there exists an optimized slope for which the particle current takes its maximum value.
Experimental evidence of the third minimum in the fission barrier
International Nuclear Information System (INIS)
Theoretical calculations predict that the fission barrier of the actinides exhibits three minima, the third one corresponding to a nucleus with an unusual elongated pear-shape deformation. In order to get an experimental evidence of such configurations, a program of high resolution measurements of the fission cross-section coupled with angular distribution determinations was undertaken on several isotopes of thorium and uranium. For the compound nuclei 231Th and 233Th, both (n,f) and (d,pf) reactions indicate the presence of two almost degenerate bands of rotational levels with opposite parities and a very high moment of inertia, all properties which characterize a nucleus with the third minimum deformation. Compound nuclei 230Th, 234U and 237U were studied via the (d,pf) reaction alone. The results obtained for 230Th lead to the same conclusion as for the other two thorium isotopes, while for the uraniums, the intrusion of second well states in the fission cross-section precludes a proper identification of the third well ones
Study of asymmetric fission yield behavior from neutron-deficient Hg isotope
Energy Technology Data Exchange (ETDEWEB)
Perkasa, Y. S. [Department of Physics, Sunan Gunung Djati State Islamic University Bandung, Jl. A.H Nasution No. 105 Cibiru, Bandung (Indonesia); Waris, A., E-mail: awaris@fi.itb.ac.id; Kurniadi, R., E-mail: awaris@fi.itb.ac.id; Su' ud, Z., E-mail: awaris@fi.itb.ac.id [Nuclear Physics and Biophysics Research Division, Department of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesa No. 10 Bandung 40132 (Indonesia)
2014-09-30
A study of asymmetric fission yield behavior from a neutron-deficient Hg isotope has been conducted. The fission yield calculation of the neutron-deficient Hg isotope using Brownian Metropolis shape had showed unusual result at decreasing energy. In this paper, this interesting feature will be validated by using nine degree of scission shapes parameterization from Brosa model that had been implemented in TALYS nuclear reaction code. This validation is intended to show agreement between both model and the experiment result. The expected result from these models considered to be different due to dynamical properties that implemented in both models.
35Cl + 12C asymmetrical fission excitation functions
International Nuclear Information System (INIS)
The fully energy-damped yields from the 35Cl + 12C reaction have been systematically investigated using particle-particle coincidence techniques at a 35Cl bombarding energy of ∼ 8 MeV/nucleon. The fragment-fragment correlation data show that the majority of events arises from a binary-decay process with rather large numbers of secondary light-charged particles emitted from the two excited exit fragments. No evidence is observed for ternary breakup events. The binary-process results of the present measurement, along with those of earlier, inclusive experimental data obtained at several lower bombarding energies are compared with predictions of two different kinds of statistical model calculations. The methods give comparable predictions and are both in good agreement with the experimental results thus confirming the fusion-fission origin of the fully-damped yields. (author)
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 proposed experiment [1] at the HIE-ISOLDE, using the ACTAR TPC, will thus provide the experimental information, which is not available at the moment and which is highly interesting for nuclear theory.
Fission barriers in neutron-proton isospin plane for heavy neutron-rich nuclei
Minato, F.; Hagino, K.
2008-01-01
We discuss the sensitivity of fission barrier for heavy neutron-rich nuclei to fission paths in the two dimensional neutron-proton quadrupole plane. To this end, we use the constrained Skyrme-Hartree-Fock + BCS method, and examine the difference of fission barriers obtained with three constraining operators, that is, the neutron, proton, and mass quadrupole operators. We investigate $^{220}$U, $^{236}$U, and $^{266}$U, %from proton-rich to neutron-rich uranium isotopes, that is relevant to r-...
Statistical model calculations with a double-humped fission barrier GIVAB computer code
International Nuclear Information System (INIS)
Neutron and gamma emission probabilities and fission probabilities are computed, taking into account the special feature of the actinide fission barriers with two maxima. Spectra and cross sections are directly deduced from these probabilities. Populations of both wells are followed step by step. For each initial E and J, decay rates are computed and normalized in order to obtain the de-excitation probabilities imposed by the two-humped fission barrier
Exploring the multi-humped fission barrier of 238U via sub-barrier photofission
Csige, L; Glodariu, T; Gulyás, J; Günther, M M; Habs, D; Karwowski, H J; Krasznahorkay, A; Rich, G C; Sin, M; Stroe, L; Tesileanu, O; Thirolf, P G
2013-01-01
The photofission cross-section of 238U was measured at sub-barrier energies as a function of the gamma-ray energy using, for the first time, a monochromatic, high-brilliance, Compton-backscattered gamma-ray beam. The experiment was performed at the High Intensity gamma-ray Source (HIgS) facility at beam energies between E=4.7 MeV and 6.0 MeV and with ~3% energy resolution. Indications of transmission resonances have been observed at gamma-ray beam energies of E=5.1 MeV and 5.6 MeV with moderate amplitudes. The triple-humped fission barrier parameters of 238U have been determined by fitting EMPIRE-3.1 nuclear reaction code calculations to the experimental photofission cross section.
Exploring the multihumped fission barrier of 238U via sub-barrier photofission
Csige, L.; Filipescu, D. M.; Glodariu, T.; Gulyás, J.; Günther, M. M.; Habs, D.; Karwowski, H. J.; Krasznahorkay, A.; Rich, G. C.; Sin, M.; Stroe, L.; Tesileanu, O.; Thirolf, P. G.
2013-04-01
The photofission cross section of 238U was measured at sub-barrier energies as a function of the γ-ray energy using a monochromatic, high-brilliance, Compton-backscattered γ-ray beam. The experiment was performed at the High Intensity γ-ray Source (HIγS) facility at beam energies between Eγ=4.7 MeV and 6.0 MeV and with ˜3% energy resolution. Indications of transmission resonances have been observed at γ-ray beam energies of Eγ=5.1 MeV and 5.6 MeV with moderate amplitudes. The triple-humped fission barrier parameters of 238U have been determined by fitting empire-3.1 nuclear reaction code calculations to the experimental photofission cross section.
Analysis of microdischarges in asymmetric dielectric barrier discharges in argon
International Nuclear Information System (INIS)
Theoretical and experimental studies of two different discharge modes in asymmetric dielectric barrier discharges in argon at atmospheric pressure have been performed. The first mode appears to be the well-known filamentary microdischarge with non-striated positive column whereas the second mode is characterized by discharge instabilities and the appearance of striations. Both experiment and model calculations predict a transition from the first mode to the second mode when the applied voltage amplitude is increased above approximately 2 kV. The reliability of the employed fluid model is confirmed by comparison of the current–voltage characteristics obtained by model calculations and measurements for different applied voltage amplitudes. The results of the model calculations point out that in the second discharge mode the ionization of excited argon atoms prevents the total recombination of charge carriers between two subsequent discharge events. This leads to the occurrence of the memory from one discharge to the following one, which plays an important role in mode transition. (paper)
Fission barrier in even-even superheavy nuclei
International Nuclear Information System (INIS)
In this work, the ground state properties of even-even superheavy nuclei (Z=112-120) are studied. The work has given emphasis on the role of deformation on the structure of superheavy nuclei. The problem of superdeformed ground state, their deformation energy curves and the potential energy surface of these nuclei is addressed. Both the nonrelativistic Skyrme-Hartree-Fock SHF and the deformed Relativistic Mean Field RMF models have been used in a constrained calculation. The systematic investigations of fission barriers in even-even superheavy nuclei with charge number Z=112-120 within relativistic mean field theory including the triaxial shapes and octupole shapes with axial symmetry. The improved version of NL3 parameter set (NL3), standard NL3, SkI4 and SLy4 parameter sets are used for the calculations. The pairing correlations are treated using the BCS approximation using the seniority pairing forces adjusted to empirical values of the gap parameters. The investigations for potential energy surface (PES), and the deformation energy curves for several isotopes with charge number Z=112, 114, 116, 118 and 120 nuclei obtained with the NL3 parameterization of the RMF Lagrangian is presented. The results will be for the case of axial solution with reflection symmetry, triaxial solutions with reflection symmetry, and octupole deformation solutions with axial symmetry
Exploring the stability of super heavy elements: First Measurement of the Fission Barrier of 254No
Directory of Open Access Journals (Sweden)
Henning G.
2014-03-01
Full Text Available The gamma-ray multiplicity and total energy emitted by the heavy nucleus 254No have been measured at 2 different beam energies. From these measurements, the initial distributions of spin I and excitation energy E∗ of 254No were constructed. The distributions display a saturation in excitation energy, which allows a direct determination of the fission barrier. 254No is the heaviest shell-stabilized nucleus with a measured fission barrier.
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.)
International Nuclear Information System (INIS)
Evaporation-residue excitation functions for 16O and 12C+197Au reactions were measured by means of the activation technique. The competition between evaporation and fission of the compound nuclei was studied by comparing the observed evaporation-residue data with the published fission excitation functions. A newly devised analysis was applied in order to deduce a fission barrier height at a specified angular momentum and determine the relevant fissioning nucleus as well. We found the fission barriers to be 8.2 MeV for the 211Fr nucleus at 16 ℎ and 8.2 MeV for the 207At nucleus at 27 ℎ. (orig.)
Fission barriers for r-process nuclei and implications for astrophysics
International Nuclear Information System (INIS)
The authors present calculations of fission-barrier heights, beta decay energies, and neutron separation energies for nuclei with 76 ≤ Z ≤ 100 and 140 ≤ N ≤ 184. For these nuclear-structure calculations they use the macroscopic-microscopic method with a Yukawa-plus-exponential macroscopic model and a folded-Yukawa microscopic model. The barrier-heights they finda re higher than those calculated in previous studies using the droplet macroscopic model. They discuss the implications of the new results on fission-barrier heights for astrophysics
Stability of trans-fermium elements at high spin: Measuring the fission barrier of 254No
International Nuclear Information System (INIS)
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 Bf(I), which gives information on the shell energy E(shell)(I). Theoretical calculations predict different fission barrier heights from Bf(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 Bf 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 254No, there is no suitable target for a transfer reaction. We therefore rely on the complementary decay widths ratio Γγ/Γ(fission) and its spin dependence, deduced from the entry distribution (I, E*).Measurements of the gamma-ray multiplicity and total energy for 254No have been performed with beam energies of 219 and 223 MeV in the reaction 208Pb(48Ca,2n) at ATLAS (Argonne Tandem Linac Accelerator System). The 254No 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 254No gamma rays from those from fission fragments, which are ≥ 106 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 MeV of beam energy
International Nuclear Information System (INIS)
Recently, direct measurements of fission cross-sections for 233Pa (n, f) reaction are available which stimulated the calculation of fission cross-sections for this reaction. For this calculation we have derived an analytical barrier formula based on microscopic-macroscopic description by fitting the actinide fission barrier data for the double humped barrier. Pairing effects have also been taken into account. The cross sections calculated for using the analytical barrier formula with the code EMPIRE 2.19 give better agreement with the available measurements. (author)
A new approach to barrier-top fission dynamics
Bertsch, G F
2015-01-01
We proposed a calculational framework for describing induced fission that avoids the Bohr-Wheeler assumption of well-defined fission channels. The building blocks of our approach are configurations that form a discrete, orthogonal basis and can be characterized by both energy and shape. The dynamics is to be determined by interaction matrix elements between the states rather than by a Hill-Wheeler construction of a collective coordinate. Within our approach, several simple limits can be seen: diffusion; quantized conductance; and ordinary decay through channels. The specific proposal for the discrete basis is to use the $K^\\pi$ quantum numbers of the axially symmetric Hartree-Fock approximation to generate the configurations. Fission paths would be determined by hopping from configuration to configuration via the residual interaction. We show as an example the configurations needed to describe a fictitious fission decay $^{32}{\\rm S} \\rightarrow ^{16}{\\rm O} + ^{16}{\\rm O}$. We also examine the geometry of th...
International Nuclear Information System (INIS)
The correlation between the sub-barrier resonant behaviour of fission cross-section 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 cross-section. (authors)
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.
Transition from asymmetric to symmetric fission in 45-69 MeV proton induced fission of 238U
Directory of Open Access Journals (Sweden)
H. Noshad
2007-03-01
Full Text Available Thin targets of 238U were bombarded with 45, 55, 65 and 69 MeV protons at the Cyclotron and Radioisotope Center (CYRIC of Tohoku University in Japan. Gamma rays emitted from the fission products were recorded and analyzed by using gamma spectroscopy. Then, the cross sections for the formation of fission products, fragment mass distributions, and total fission cross sections were measured. Special care was taken to make this measurement precisely. The experimental results show that for 238U(p, f reaction at Ep > 65 MeV, the asymmetry component in the mass distribution is eliminated, and the symmetric fission remains the dominant fission mode.
A new approach to barrier-top fission dynamics
Directory of Open Access Journals (Sweden)
Bertsch G.F.
2016-01-01
Full Text Available We proposed a calculational framework for describing induced fission that avoids the Bohr-Wheeler assumption of well-defined fission channels. The building blocks of our approach are configurations that form a discrete, orthogonal basis and can be characterized by both energy and shape. The dynamics is to be determined by interaction matrix elements between the states rather than by a Hill-Wheeler construction of a collective coordinate. Within our approach, several simple limits can be seen: diffusion; quantized conductance; and ordinary decay through channels. The specific proposal for the discrete basis is to use the Kπ quantum numbers of the axially symmetric Hartree-Fock approximation to generate the configurations. Fission paths would be determined by hopping from configuration to configuration via the residual interaction. We show as an example the configurations needed to describe a fictitious fission decay 32S → 16 O + 16 O. We also examine the geometry of the path for fission of 236U, measuring distances by the number of jumps needed to go to a new Kπ partition.
A new approach to barrier-top fission dynamics
Bertsch, G. F.; Mehlhaff, J. M.
2016-06-01
We proposed a calculational framework for describing induced fission that avoids the Bohr-Wheeler assumption of well-defined fission channels. The building blocks of our approach are configurations that form a discrete, orthogonal basis and can be characterized by both energy and shape. The dynamics is to be determined by interaction matrix elements between the states rather than by a Hill-Wheeler construction of a collective coordinate. Within our approach, several simple limits can be seen: diffusion; quantized conductance; and ordinary decay through channels. The specific proposal for the discrete basis is to use the Kπ quantum numbers of the axially symmetric Hartree-Fock approximation to generate the configurations. Fission paths would be determined by hopping from configuration to configuration via the residual interaction. We show as an example the configurations needed to describe a fictitious fission decay 32S → 16 O + 16 O. We also examine the geometry of the path for fission of 236U, measuring distances by the number of jumps needed to go to a new Kπ partition.
Oberstedt S.; Hambsch F.-J.; Tudora A.
2013-01-01
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 calculat...
Five-Dimensional Fission-Barrier Calulations from Se-70 to Cf-252
Moller, Peter; Sierk, Arnold J.; Iwamoto, Akira
2004-01-01
We present fission-barrier-height calculations for nuclei throught the Periodic Table based on a realistic macroscopic-microscopic model. Compared to other calculations: (1) we use a deformation space of sufficiently high dimension, sampled densely enough to describe the relevant topography of the fission potential, (2) we unambiguously find the physically relevant saddle points in this space, and (3) we formulate our model so that we obtain continuity of the potential energy at the division ...
International Nuclear Information System (INIS)
The fusion cross sections and fragment angular distributions for the complete fusion-fission reactions of 11B+238U, 237Np, 12C+237Np, 16O+232Th, 238U, and 19F+23Th at near- and sub-barrier energies have been measured by the fragment folding angle technique. It is revealed that the anomalous anisotropies of fission fragments in latter three systems are existence. Based on the experimental observations and Dressing and Randrup's theory, a new version model of preequilibrium fission is put forward to explain the anomaly. (author)
Transition from asymmetric to symmetric fission in 45-69 MeV proton induced fission of 238U
H. Noshad
2007-01-01
Thin targets of 238U were bombarded with 45, 55, 65 and 69 MeV protons at the Cyclotron and Radioisotope Center (CYRIC) of Tohoku University in Japan. Gamma rays emitted from the fission products were recorded and analyzed by using gamma spectroscopy. Then, the cross sections for the formation of fission products, fragment mass distributions, and total fission cross sections were measured. Special care was taken to make this measurement precisely. The experimental results show that for 238U(p...
Velásquez, Rober
2003-04-01
In this work we report on field-induced features appearing in the tunneling current traces of a biased asymmetric triple barrier resonant tunneling device in the presence of an in-plane magnetic field. A theoretical model that satisfactorily explains the origin of these features is discussed. The reported data evidences the localized nature of the quantum states in thin layer asymmetric double-quantum-well structures.
Fusion-Fission of $^{16}O+^{197}Au$ at Sub-Barrier Energies
Back, B B; Janssens, R V F; Henderson, D J; Shumard, B R; Lister, C J; Peterson, D; Rehm, K E; Tanihata, I; Tang, X; Wang, X; Zhu, S
2006-01-01
The recent discovery of heavy-ion fusion hindrance at far sub-barrier energies has focused much attention on both experimental and theoretical studies of this phenomenon. Most of the experimental evidence comes from medium-heavy systems such as Ni+Ni to Zr+Zr, for which the compound system decays primarily by charged-particle evaporation. In order to study heavier systems, it is, however, necessary to measure also the fraction of the decay that goes into fission fragments. In the present work we have, therefore, measured the fission cross section of 16O+197Au down to unprecedented far sub-barrier energies using a large position sensitive PPAC placed at backward angles. The preliminary cross sections will be discussed and compared to earlier studies at near-barrier energies. No conclusive evidence for sub-barrier hindrance was found, probably because the measurements were not extended to sufficiently low energies.
Fission barriers of super-heavy nuclei produced in cold-fusion reactions
Energy Technology Data Exchange (ETDEWEB)
Peter, J. [LPC Caen, ENSICAEN, Caen cedex (France)
2004-11-01
Excitation functions of super-heavy evaporation residues formed in cold-fusion reactions were analyzed with the aim of getting information on the fission barrier height of these nuclei. The method uses the location of the maximum of 1n and 2n excitation functions. The results obtained on nuclei from Z=104 to 112 are compared to three theoretical predictions. (orig.)
Intermediate energy nuclear fission
International Nuclear Information System (INIS)
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)
Experimental survey of the potential energy surfaces associated with fission
International Nuclear Information System (INIS)
Progress in the experimental determination of the properties of the potential energy surface associated with fission is reviewed. The importance of nuclear symmetry effects on the calculation of fission widths is demonstrated. Evidence is presented for the fragmentation of the mass-asymmetric second barrier in the thorium region and the axial asymmetric first barrier in the californium region. Detailed analyses of experimental data suggest the presence of two parallel second barriers; the normal mass-asymmetric, axial-symmetric barrier and a slightly higher mass-symmetric, axial-asymmetric barrier. Experimental barrier parameters are determined systematically and compared with calculations from various theoretical models. Techniques for expanding fission probability measurements to higher energies are discussed. (author)
Fission excitation function for 19F + 194,196,198Pt at near and above barrier energies
Directory of Open Access Journals (Sweden)
Singh Varinderjit
2015-01-01
Full Text Available Fission excitation functions for 19F + 194,196,198Pt reactions populating 213,215,217Fr compound nuclei are reported. Out of these three compound nuclei, 213Fr is a shell closed (N=126 compound nucleus and the other two are away from the shell closure. From a comparison of the experimental fission cross-sections with the statistical model predictions, it is observed that the fission cross-sections are underestimated by the statistical model predictions using shell corrected finite range rotating liquid drop model (FRLDM fission barriers. Further the FRLDM fission barriers are reduced to fit the fission cross-sections over the entire measured energy range.
Excitation Functions of Fusion and Fission for 32S+170Er at Energies Near and Below Coulomb Barrier
Institute of Scientific and Technical Information of China (English)
BAO; Peng-fei; LIN; Cheng-jian; YANG; Feng; JIA; Hui-ming; XU; Xin-xing; YANG; Lei; SUN; Li-jie; MA; Nan-ru; ZHANG; Huan-qiao; LIU; Zu-hua
2013-01-01
Excitation functions of fusion evaporation residue(ER)and fission for 32S+170Er system at near barrier energy region were measured,respectively.With the comparison to the calculations of coupledchannels effects,it is accessible to investigate the impacts on the fusion and fission processes of target deformation and the dependence on the entrance-channel.The experiment was performed at Beijing HI-13 Tandem Accelerator.Fission and fusion evaporation
Fission barriers of 237 to 240 plutonium isotopes with the 236U(α,xn) reactions
International Nuclear Information System (INIS)
Excitation functions for the reactions 236U(α,xn)sup(240-x)Pu have been measured for x=2, 3, 4. The production of 236U targets as well as the chemical separation of Pu from the irradied targets are given. Experimental results have been analysed using the preequilibrium mechanism (PREEQ code) and the statistical model description of fission through a double humped barrier (GIVAB code)
Systematic analysis of fission cross sections of uranium and plutonium isotopes
International Nuclear Information System (INIS)
Neutron induced fission cross section of 10 actinide nuclei is analyzed in terms of the double humped fission barrier model to deduce the barrier heights. Good fits were obtained by assuming the inner barrier axially-asymmetric and the outer one mass asymmetric. The obtained values of barrier heights are compared to other results. Systematic trends were observed in the barrier heights of the isotopes studied, their isotopical dependence presents the odd-even fluctuations. The difference EA-EB with increasing of neutron number is also analyzed. The level density is calculated in the frame of Semimicroscopical Combined Method (SCM) for all extreme points of fission path
Plasma propagation of a 13.56 MHz asymmetric surface barrier discharge in atmospheric pressure air
Energy Technology Data Exchange (ETDEWEB)
Dedrick, J; Boswell, R W; Charles, C [Space Plasma, Power and Propulsion Group, Research School of Physics and Engineering, The Australian National University, ACT 0200 (Australia); Audier, P; Rabat, H; Hong, D, E-mail: james.dedrick@anu.edu.au [GREMI - UMR6606 CNRS/Universite d' Orleans, Polytech' Orleans, 14, rue d' Issoudun - BP6744, 45067 ORLEANS Cedex 2 (France)
2011-05-25
The propagation of an rf asymmetric surface barrier discharge in atmospheric pressure air has been investigated. Measurements of the pulse-modulated 13.56 MHz voltage and current together with ICCD images of the plasma were recorded to study the visible plasma structure with respect to the rf pulses, time within the pulses and the rf waveforms. When exposing images over full rf pulses, which comprise over 150 oscillations of the applied voltage, clearly defined filamentary structures are observed indicating a strong memory effect. The discharge intensity decreases exponentially with distance from the electrode edge, and the average propagation length increases linearly with the applied voltage. Similar to some lower frequency asymmetric surface dielectric barrier discharges, two distinct breakdown events occur during one period of the voltage waveform. The number of filaments is found to be the same for both breakdown events, and collective effects are observed in both discharges.
Electron Transport through Magnetic Superlattices with Asymmetric Double-Barrier Units in Graphene
International Nuclear Information System (INIS)
We investigate the transport properties through magnetic superlattices with asymmetric double-barrier units in monolayer graphene. In N-periodic asymmetric double-barrier units, there is (N − 1)-fold resonant peak splitting for transmission, but the splitting is (2N − 1)-fold in N-periodic symmetric units. The transmission depends not only on the value of incident wavevectors but also on the value and the direction of transverse wavevectors. This renders the structure's efficient wavevector filters. In addition, the conductance of standard electrons with a parabolic energy spectrum is suppressed more strongly than that of Dirac electrons, whereas the resonances are more pronounced for Dirac electrons than for standard ones. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Han, Jie
2014-01-01
We investigate time-dependent probability for a Brownian particle passing over the barrier to stay at a metastable potential pocket against escaping over the barrier. This is related to whole fusion-fission dynamical process and can be called the reverse Kramers problem. By the passing probability over the saddle point of inverse harmonic potential multiplying the exponential decay factor of a particle in the metastable potential, we present an approximate expression for the modified passing probability over the barrier, in which the effect of reflection boundary of potential is taken into account. Our analytical result and Langevin Monte-Carlo simulation show that the probability passing and against escaping over the barrier is a non-monotonous function of time and its maximal value is less than the stationary result of passing probability over the saddle point of inverse harmonic potential.
Useinov, Arthur
2012-06-01
In this paper, we study the value of the tunnel magnetoresistance (TMR) as a function of the applied voltage in double barrier magnetic tunnel junctions (DMTJs) with the left and right ferromagnetic (FM) layers being pinned and numerically estimate the possible difference of the TMR curves for negative and positive voltages in the homojunctions (equal barriers and electrodes). DMTJs are modeled as two single barrier junctions connected in series with consecutive tunneling (CST). We investigated the asymmetric voltage behavior of the TMR for the CST in the range of a general theoretical model. Significant asymmetries of the experimental curves, which arise due to different annealing regimes, are mostly explained by different heights of the tunnel barriers and asymmetries of spin polarizations in magnetic layers. © (2012) Trans Tech Publications.
Henning, Greg; Khoo, T L; Lopez-Martens, A; Seweryniak, D; Alcorta, M; Asai, M; Back, B B; Bertone, P F; Boilley, D; Carpenter, M P; Chiara, C J; Chowdhury, P; Gall, B; Greenlees, P T; Gürdal, G; Hauschild, K; Heinz, A; Hoffman, C R; Janssens, R V F; Karpov, A V; Kay, B P; Kondev, F G; Lakshmi, S; Lauritsen, T; Lister, C J; McCutchan, E A; Nair, C; Piot, J; Potterveld, D; Reiter, P; Rogers, A M; Rowley, N; Zhu, S
2014-12-31
We report on the first measurement of the fission barrier height in a heavy shell-stabilized nucleus. The fission barrier height of 254No is measured to be Bf=6.0±0.5 MeV at spin 15ℏ and, by extrapolation, Bf=6.6±0.9 MeV at spin 0ℏ. This information is deduced from the measured distribution of entry points in the excitation energy versus spin plane. The same measurement is performed for 220Th and only a lower limit of the fission barrier height can be determined: Bf(I)>8 MeV. Comparisons with theoretical fission barriers test theories that predict properties of superheavy elements. PMID:25615317
Fusability and fissionability in 86Kr induced reactions near and below the fusion barrier
International Nuclear Information System (INIS)
Evaporation-residue excitation functions for the reactions 86Kr + sup(70,76)Ge, sup(92,100)Mo, sup(99,102,104)Ru have been measured using activation methods and the velocity filter SHIP. The data span the region from well below the fusion barrier up to and beyond the energy where limitation by fission competition takes place. The data are shown to be compatible with the concept of complete fusion followed by the statistical decay of the equilibrated compound nucleus. Information on both the fusion probability at and below the fusion threshold and the fissionability of the compound nuclei formed is extracted. The model dependence of the extracted fission barriers is discussed in detail. In analogy to studies involving lighter projectiles, strong correlations between the low-energy nuclear-structure properties of the nuclei and the subbarrier fusion probability are found. A relative shift of the fusion barrier to higher energies, that increases with the number of valence neutrons in the target nuclei, is observed. (orig.)
DEFF Research Database (Denmark)
Zubov, F. I.; Zhukov, A. E.; Shernyakov, Yu M.;
2015-01-01
Current-voltage and light-current characteristics of quantum-well lasers have been studied at high drive currents. The introduction of asymmetric barrier layers adjacent to the active region caused a significant suppression of the nonlinearity in the light-current characteristic and an increase in...... the external differential efficiency. As a result, the maximum wallplug efficiency increased by 9%, while the output optical power increased by 29%....
Lateral current density fronts in asymmetric double-barrier resonant-tunneling structures
Rodin, Pavel; Schoell, Eckehard
2003-01-01
We present a theoretical analysis and numerical simulations of lateral current density fronts in bistable resonant-tunneling diodes with Z-shaped current-voltage characteristics. The bistability is due to the charge accumulation in the quantum well of the double-barrier structure. We focus on asymmetric structures in the regime of sequential incoherent tunneling and study the dependence of the bistability range, the front velocity and the front width on the structure parameters. We propose a ...
Useinov, Arthur
2011-10-22
In this paper we study the asymmetric voltage behavior (AVB) of the tunnel magnetoresistance (TMR) for single and double barrier magnetic tunnel junctions (MTJs) in range of a quasi-classical free electron model. Numerical calculations of the TMR-V curves, output voltages and I-V characteristics for negative and positive values of applied voltages were carried out using MTJs with CoFeB/MgO interfaces as an example. Asymmetry of the experimental TMR-V curves is explained by different values of the minority and majority Fermi wave vectors for the left and right sides of the tunnel barrier, which arises due to different annealing regimes. Electron tunneling in DMTJs was simulated in two ways: (i) Coherent tunneling, where the DMTJ is modeled as one tunnel system and (ii) consecutive tunneling, where the DMTJ is modeled by two single barrier junctions connected in series. © 2012 Elsevier B.V. All rights reserved.
International Nuclear Information System (INIS)
Fission and total level densities modelling approach was developed. Neutron-induced fission cross section data for incident energies from 10 keV up to emissive fission threshold were employed to extract level density and fission barrier parameters. In particular, fission barrier parameters (inner barrier height, outer barrier height, curvatures) were extracted for altogether 49 isotopes of Th, Pa, U, Np, Pu, Am, Cm, Bk, and Cf. The adopted level density modelling approach and fission barrier parametrization was supported by calculations of fission cross section data above the emissive fission threshold, up to 20 MeV neutron incident energy. (author)
International Nuclear Information System (INIS)
The fission fragment mass distribution followed by neutron emission is studied for the 238U(18O,f) reaction using the asymmetric two-center shell model. Within the thermodynamic approach, excitation energy carried by the compound nucleus is dissipated in the emission of a pair of neutrons in several consecutive steps. Therefore, we have considered 2-12 (in step of 2) neutron emission channels in our formalism. The mass distribution corresponding to 8-neutron emission channel compares reasonably well with the experimental data. The observed fine structure dips corresponding to shell closure (Z = 50 and N = 82) of individual fission fragment arise mainly due to shell structure in the mass parameters. However, an exact location and magnitude of the dip at A = 124 in the mass distribution depends on how the temperature modifies masses and, also, on the precise information of pre- and post-neutron emission data. This suggests a possible importance of extending these calculations to get new insight into an understanding of the dynamical behaviour of fragment formation in the fission process. (orig.)
Hidden systematics of fission channels
Directory of Open Access Journals (Sweden)
Schmidt Karl-Heinz
2013-12-01
of the fissioning system obey a hidden systematics that can be explained by the number of states in the vicinity of the outer fission barrier as a function of mass asymmetry, if the potential is constructed as the sum of the macroscopic contribution of the compound nucleus and empirically determined fragment shells. This hidden systematics also explains the transition from asymmetric to symmetric fission around 226Th and around 258Fm.
Numerical and analytical super-asymmetric fission model for exotic cluster decays. Chapter 17
International Nuclear Information System (INIS)
One has to keep in touch with any experimental new finding in the field, trying to improve the fundamental understanding and description of various decay modes within different theoretical approaches. As an example, new experimental results are awaited in the island of cluster emitters above Sn, particularly 12C radioactivity of 114Ba, from which different nuclear properties of intermediate mass proton-rich nuclei can be determined. Also a new experiment on the fine structure of 14C decay of 223Ra should determine the hindrance factor of the transition to the fourth (1/2+) excited state of the daughter 209Pb. At present it is not known whether this transition is hindered or not. The fission theory of the fine structure, and more generally of cluster emission from nuclei with odd number of protons and/or neutrons, has to be elaborated up to the point of predicting some other interesting cases which could be measured in the near future. In the same time one has to think about the cold fission of heavy nuclei which can be experimentally studied with the technique of large arrays of gamma ray detectors already applied to the study of spontaneous fission of 252Cf in Oak Ridge. The best candidate for a cold fission process would certainly be 264Fm, decaying into two double magic 132Sn nuclei. Some other nuclei (perhaps longer lived) will be recommended to be measured. Interesting connections with the fission of atomic clusters could be made, by trying to see how far can be extrapolated to this new field of research the knowledge of nuclear phenomena
International Nuclear Information System (INIS)
V.M. STRUTINSKY's semi-classical method is the most precise to determine the energy of the different states along the fission way. The double-humped fission barrier explains fission isomerism. V.M. STRUTINSKY's barrier explains the ''intermediate structure'' observed in the cross section under the threshold; it provides also the observed effect of ''vibrational resonances'' with an interpretation. Taking an asymmetry parameter in consideration, a triple-humped fission barrier seems to be essential now for the light actinides. There is still a microscopic fission barrier to be explained
Effects of nuclear orientation on fusion and fission in the reaction using 238U target nucleus
Hirose K.; Hofmann S.; Ohtsuki T.; Nagame Y.; Nishinaka I.; Mitsuoka S.; Ikezoe H.; Nishio K.
2011-01-01
Fission fragment mass distributions in the reaction of 30Si+238U were measured around the Coulomb barrier. At the above-barrier energies, the mass distribution showed a Gaussian shape. At the subbarrier energies, triple-humped distribution was observed, which consists of symmetric fission and asymmetric fission peaked at AL/AH ≈ 90/178. The asymmetric fission should be attributed to quasifission from the results of the measured evaporation residue (ER) cross-sections for 30Si+238U. Th...
Some spectroscopic properties of fine structures observed near the 231Pa(n,f) fission threshold
International Nuclear Information System (INIS)
The 231Pa neutron-induced fission cross section from 140 to 400 keV was resolved into finer structures. For some of the fractionated vibrational resonances in this energy region, the assignment of spectroscopic parameters may support evidence for an asymmetrically deformed third minimum in the 232Pa fission barrier. Also, for the first time, narrow fission resonances are observed above 1.3 eV exhibiting an average fission width /sub obs/ = 8meV
The nucleon phase of binary fission
International Nuclear Information System (INIS)
Full text: The main step of the fission process is a sharing-out of nucleons, within a 'nucleon-phase', between the valence shells of the primordial cluster of the internally-dissociated fissioning system and the valence shells of the 'A =126 nucleon core' of the nascent heavy fragment. The formation of an 'A = 82 nucleon core' in the nascent light fragment explains the asymmetric fission mode of the light actinide nuclei. The nucleon partition in the nucleon phase can be understood in the framework of chemical thermodynamics. The formation of an 'A = 126 nucleon core' in the nascent light fragment of heavier fissioning systems explains the symmetric fission mode of 258Fm and that of heavier nuclei. But the new phenomenon of 'barrier-free' fission, discovered in 258Fm (s.f.), plays in this system and all symmetrically fissioning superheavy nuclei a very important role. (author)
Energy Technology Data Exchange (ETDEWEB)
Pons, Jerome; Moreau, Eric; Touchard, Gerard [LEA, University of Poitiers/CNRS/ENSMA, Bd. Curie, Teleport 2, BP 30179, 86962 Futuroscope Cedex (France)
2005-10-07
The electrical properties of an asymmetric surface dielectric barrier discharge in atmospheric air have been investigated experimentally. The discharge is used for airflow production close to the dielectric surface, and the time-averaged flow velocity spatial profiles have been measured. Velocities of up to 3.5 m s{sup -1} at heights of 1-2 mm are reached when filamentary discharges with current peaks up to 20 mA are produced along the surface. In terms of powers, mechanical powers (output) of a few milliwatts are obtained for electrical powers (input) up to 10 W. Variation laws or behaviour with several discharge parameters (applied voltage waveform, distance between electrodes, dielectric thickness and permittivity) have been experimentally determined.
Zhang, Jin-Ju; Montgomery, Benjamin R; Huang, Shuang-Quan
2016-01-01
Interspecific hybridization is widespread among plants; nevertheless, pre- and post-zygotic isolating mechanisms may maintain species integrity for interfertile species in sympatry despite some gene flow. Interspecific hybridization and potential isolating barriers were evaluated between co-flowering Silene asclepiadea and Silene yunnanensis in an alpine community in southwest China. We investigated morphological and molecular (nuclear microsatellites and chloroplast gene sequence) variation in sympatric populations of S. asclepiadea and S. yunnanensis. Additionally, we analyzed pollinator behaviour and compared reproductive success between the putative hybrids and their parental species. Both the molecular and morphological data indicate that there were putative natural hybrids in the field, with S. asclepiadae the ovule parent and S. yunnanensis the pollen parent. Bumblebees were the primary visitors to S. asclepiadae and putative hybrids, while butterflies were the primary visitors to S. yunnanensis Pollen production and viability were significantly lower in putative hybrids than the parental species. The direction of hybridization is quite asymmetric from S. yunnanensis to S. asclepiadea Protandry combined with later peak flowering of S. yunnanensis, and pollinator preference may have contributed to the asymmetric pattern of hybridization, but putative hybrids were rare. Our results thus suggest that despite gene flow, S. asclepiadea and S. yunnanensis can maintain species boundaries, perhaps as a result of floral isolation and low fecundity of the hybrids. PMID:27178066
Effects of nuclear orientation on fusion and fission in the reaction using 238U target nucleus
Directory of Open Access Journals (Sweden)
Hirose K.
2010-03-01
Full Text Available Fission fragment mass distributions in the reaction of 30Si+238U were measured around the Coulomb barrier. At the above-barrier energies, the mass distribution showed a Gaussian shape. At the subbarrier energies, triple-humped distribution was observed, which consists of symmetric fission and asymmetric fission peaked at AL/AH ≈ 90/178. The asymmetric fission should be attributed to quasifission from the results of the measured evaporation residue (ER cross-sections for 30Si+238U. The cross-section for 263Sg at the abovebarrier energy agree with the statistical model calculation which assumes that the measured fission cross-section originates from fusion-fission, whereas the one for 264 Sg measured at the sub-barrier energy is smaller than the calculation, which suggests the presence of quasifission.
Tuning of terahertz intrinsic oscillations in asymmetric triple-barrier resonant tunneling diodes
Wójcik, Paweł; Spisak, Bartłomiej J.; Wołoszyn, Maciej; Adamowski, Janusz
2012-06-01
Intrinsic terahertz oscillations of the electronic current in the asymmetric triple-barrier resonant tunneling diode are investigated by means of the time-dependent Wigner-Poisson method. The current-voltage characteristics calculated for the nanodevice exhibits four separate bias voltage windows with the current oscillations, which are caused by two different mechanisms. One of these bias voltage windows, for which the electronic current oscillations stem from the negative feedback between the electronic current and the coupled quasi-bound states in the quantum wells embedded in the active region of the nanodevice, is considered in detail. It is demonstrated that the amplitude and frequency of the current oscillations in this bias voltage window depend on the coupling between the quasi-bound states formed in the quantum wells. Strength of this coupling is controlled by the thickness of the central barrier separating the quantum wells, which allows to tune the amplitude and frequency of the terahertz oscillations. Additionally, it was shown that the amplitude of the current oscillations can be tuned by shifting up or down the energy of the bottom of the wider quantum well. These properties suggest that the considered nanodevice may be of interest because of its possible application as tunable terahertz generator.
International Nuclear Information System (INIS)
Large-scale structures in the fission cross sections of the lower-charge actinides are commonly interpreted as pure vibrational (transmission) resonances associated with a well in the fission barrier. This well is often hypothesised to be a tertiary well, the secondary well of a double-humped barrier being too deep (according to most theoretical models) to allow undampled vibrational modes at the excitation energies involved. The present paper considers the possible width and strength ratios of low-lying states associated with secondary and tertiary wells, investigating the deviation, due to coupling of single-particle and vibrational motions, of these properties from the simple expectations of a simple transmission model; this deviation is found to be considerable. Comparison of the calculated resonance properties with experimental data is made; this slightly favours the tertiary well hypothesis. Overall, the results indicate that more detailed fission cross section and angular distribution measurements in conjunction with more realistic model calculations of the type outlined in this paper could help bring a definitive answer to the problem of the structure of the light actinide fission barriers. (author)
Fission barriers and half-lives of actinides in the quasimolecular shape valley
Royer, G.; Jaffré, M.; Moreau, D.
2012-10-01
The energy of actinide nuclei in the fusionlike deformation valley has been determined from a liquid-drop model, taking into account the proximity energy, the mass and charge asymmetries, and the shell and pairing energies. Double-humped potential barriers appear. The saddle point corresponds to the second maximum and to the transition from compact one-body shapes with a deep neck to two touching ellipsoids. The scission point, where the effects of the nuclear attractive forces between the fragments vanish, lies at the end of an energy plateau below the saddle point and corresponds to two well-separated fragments. The kinetic and excitation energies of the fragments come from the energy on this plateau. The shell and pairing effects play a main role to decide the most probable decay path. The heights of the potential barriers roughly agree with the experimental data and the calculated half-lives follow the trend of the experimental values. A shallow third minimum and a third peak appear in specific asymmetric exit channels where one fragment is close to a double magic quasispherical nucleus, while the other one evolves from oblate to prolate shapes.
Benchmarking Nuclear Fission Theory
G. F. Bertsch(INT, Seattle, USA); Loveland, W.; Nazarewicz, W.; Talou, P.
2015-01-01
We suggest a small set of fission observables to be used as test cases for validation of theoretical calculations. The purpose is to provide common data to facilitate the comparison of different fission theories and models. The proposed observables are chosen from fission barriers, spontaneous fission lifetimes, fission yield characteristics, and fission isomer excitation energies.
Energy Dependence of Plutonium Fission-Product Yields
International Nuclear Information System (INIS)
A method is developed for interpolating between and/or extrapolating from two pre-neutron-emission first-chance mass-asymmetric fission-product yield curves. Measured 240Pu spontaneous fission and thermal-neutron-induced fission of 239Pu fission-product yields (FPY) are extrapolated to give predictions for the energy dependence of the n + 239Pu FPY for incident neutron energies from 0 to 16 MeV. After the inclusion of corrections associated with mass-symmetric fission, prompt-neutron emission, and multi-chance fission, model calculated FPY are compared to data and the ENDF/B-VII.1 evaluation. The ability of the model to reproduce the energy dependence of the ENDF/B-VII.1 evaluation suggests that plutonium fission mass distributions are not locked in near the fission barrier region, but are instead determined by the temperature and nuclear potential-energy surface at larger deformation.
Energy Dependence of Plutonium Fission-Product Yields
Lestone, J. P.
2011-12-01
A method is developed for interpolating between and/or extrapolating from two pre-neutron-emission first-chance mass-asymmetric fission-product yield curves. Measured 240Pu spontaneous fission and thermal-neutron-induced fission of 239Pu fission-product yields (FPY) are extrapolated to give predictions for the energy dependence of the n + 239Pu FPY for incident neutron energies from 0 to 16 MeV. After the inclusion of corrections associated with mass-symmetric fission, prompt-neutron emission, and multi-chance fission, model calculated FPY are compared to data and the ENDF/B-VII.1 evaluation. The ability of the model to reproduce the energy dependence of the ENDF/B-VII.1 evaluation suggests that plutonium fission mass distributions are not locked in near the fission barrier region, but are instead determined by the temperature and nuclear potential-energy surface at larger deformation.
The fusion-fission process in the reaction {sup 34}S+{sup 186}W near the interaction barrier
Energy Technology Data Exchange (ETDEWEB)
Harca, I. M. [Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, (FLNR JINR) Dubna, Russia and Faculty of Physics, University of Bucharest - P.O. Box MG 11, RO 77125, Bucharest-Magurele (Romania); Dmitriev, S.; Itkis, J.; Kozulin, E. M.; Knyazheva, G.; Loktev, T.; Novikov, K. [Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, (FLNR JINR) Dubna (Russian Federation); Azaiez, F.; Gottardo, A.; Matea, I.; Verney, D. [IPN, CNRS/IN2P3, Univ. Paris-Sud, 91405 Orsay (France); Chubarian, G. [Cyclotron Institute, Texas A and M University, College Station, TX 77843-3366 (United States); Hanappe, F. [Universite Libre de Bruxelles (ULB), Bruxelles (Belgium); Piot, J.; Schmitt, C. [GANIL, CEA/DSM-CNRS/IN2P3, Bd Henri Becquerel, BP 55027, F-14076 Caen Cedex 5 (France); Trzaska, W. H. [Accelerator Laboratory of University of Jyväskylä (JYFL), Jyväskylä (Finland); Vardaci, E. [Dipartamento di Scienze Fisiche and INFN (INFN-Na), Napoli (Italy)
2015-02-24
The reaction {sup 34}S+{sup 186}W at E{sub lab}=160 MeV was investigated with the aim of diving into the features of the fusion-fission process. Gamma rays in coincidence with binary reaction fragments were measured using the high efficiency gamma-ray spectrometer ORGAM at the TANDEM Accelerator facility of I.P.N., Orsay, and the time-of-flight spectrometer for fission fragments (FF) registration CORSET of the Flerov Laboratory of Nuclear Reactions (FLNR), Dubna. The coupling of the ORGAM and CORSET setups offers the unique opportunity of extracting details for characterizing the fusion-fission process and gives information regarding production of neutron-rich heavy nuclei. The FF–γ coincidence method is of better use then the γ – γ coincidence method when dealing with low statistic measurements and also offers the opportunity to precisely correct the Dopler shift for in-flight emitted gamma rays. Evidence of symmetric and asymmetric fission modes were observed in the mass and TKE distributions, occurring due to shell effects in the fragments. Coincident measurements allow for discrimination between the gamma rays by accepting a specific range within the mass distribution of the reaction products. Details regarding the experimental setup, methods of processing the acquisitioned data and preliminary results are presented.
Energy Technology Data Exchange (ETDEWEB)
Singh, K P [Computational Plasma Dynamics Laboratory, Mechanical Engineering, Kettering University, Flint, Michigan 48504 (United States); Roy, Subrata [Computational Plasma Dynamics Laboratory, Mechanical Engineering, Kettering University, Flint, Michigan 48504 (United States); Gaitonde, Datta V [Computational Sciences Branch, Air Vehicles Directorate, Air Force Research Laboratory, Wright Patterson AFB, Ohio 45433 (United States)
2006-11-01
Separation mitigation using asymmetric dielectric barrier discharges is studied by considering the neutral gas flow past a flat plate at an angle of attack. A self-consistent plasma actuator model is employed to couple the electric force field to the momentum of the neutral gas. The equations governing the motion of electrons, ions and neutrals are solved with Poisson's equation to study effective control of flow separation. The impact of select parameters such as amplitude of the excitation, dielectric constants, the initial ionization level and the electrode shape is elucidated. It is found that the dielectric surface just downstream of the exposed electrode becomes negatively charged during part of the cycle for the chosen work parameters and a time averaged force acts on the plasma predominantly downstream, with a transverse component towards the wall. The momentum of the plasma couples to neutral gas through collisions, which results in the enhancement of near-wall momentum yielding a wall-jet feature that effectively eliminates the separation bubble.
Gas breakdown mechanism in pulse-modulated asymmetric ratio frequency dielectric barrier discharges
Energy Technology Data Exchange (ETDEWEB)
Wang, Qi; Sun, Jizhong, E-mail: jsun@dlut.edu.cn; Ding, Zhenfeng; Ding, Hongbin; Wang, Dezhen [School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116023 (China); Nozaki, Tomohiro [Department of Mechanical Sciences and Engineering, Tokyo Institute of Technology, Tokyo 152-8550 (Japan); Wang, Zhanhui [Southwestern Institute of Physics, Chengdu 610041 (China)
2014-08-15
The gas breakdown mechanisms, especially the roles of metastable species in atmospheric pressure pulse-modulated ratio frequency barrier discharges with co-axial cylindrical electrodes, were studied numerically using a one dimensional self-consistent fluid model. Simulation results showed that in low duty cycle cases, the electrons generated from the channels associated with metastable species played a more important role in initializing next breakdown than the direct ionization of helium atoms of electronic grounded states by electron-impact. In order to quantitatively evaluate the contribution to the discharge by the metastables, we defined a “characteristic time” and examined how the value varied with the gap distance and the electrode asymmetry. The results indicated that the lifetime of the metastable species (including He*and He{sub 2}{sup *}) was much longer than that of the pulse-on period and as effective sources of producing electrons they lasted over a period up to millisecond. When the ratio of the outer radius to the inner radius of the cylindrical electrodes was far bigger than one, it was found that the metastables distributed mainly in a cylindrical region around the inner electrode. When the ratio decreased as the inner electrode moved outward, the density of metastables in the discharge region near the outer electrode became gradually noticeable. As the discharging gap continued to decrease, the two hill-shaped distributions gradually merged to one big hill. When the discharge spacing was fixed, asymmetric electrodes facilitated the discharge.
Intrinsic current oscillations in an asymmetric triple-barrier resonant tunnelling diode
International Nuclear Information System (INIS)
The electronic transport characteristics of an asymmetric triple-barrier resonant tunnelling diode are calculated by the time-dependent Wigner–Poisson method. The intrinsic current oscillations are found in two separate bias voltage ranges. The first one is located below the resonant current peak, and the second lies in the negative differential resistance region. We provide the explanation of the current density oscillations in these two separate bias voltage ranges based on the analysis of the self-consistent potential profiles and changes of electron density. We have shown that two different formation mechanisms are responsible for the current density oscillations in these two bias voltage ranges. In the bias voltage range below the resonant current peak in the current–voltage characteristics, the current density oscillations are caused by the coupling between quasi-bound states in the left and right quantum wells. On the other hand, the current density oscillations in the negative differential resistance region result from the coupling between quasi-bound states in the left quantum well and the quantum well formed in the region of the left contact
Ghosh, T.K.; Bhattacharya, P
2005-01-01
A critical re-analysis of the experimental data to reject transfer fission component did not change the fragment mass widths and hence the conclusion regarding abrupt rise in mass widths with decreasing energy around Coulomb barrier remains unchanged
International Nuclear Information System (INIS)
The fission process in which heavy nuclei fragment into three large charged panicles, in place of the usual two, has been studied in the case of thermal-neutron-induced fission of U235 and the spontaneous fission of Cf252. Solid-state detectors, a fast triple coincidence system and a three-coincident-parameter analyser were used to measure the three fission fragment energies parallel with the detection of each ternary fission event. Experimental evidence is presented supporting the existence of ternary fission by specifically excluding recoil phenomena and accidental events as contributing to the observed three-fold coincidence events. Mass-energy-angular correlations of ternary fission have been determined and are summarized as follows: The total kinetic energy release in ternary fission appears to be slightly higher (by approximately 10 MeV) than that for binary fission. In the case of the spontaneous ternary fission of Cf252, the frequency of occurrence is observed to be greater than 2.2 x 10-6 ternary fission events per binary fission event. Tripartition of Cf252 results preferentially in division into two medium mass particle (one of which has a mass number near 56) and one larger mass. In the case of thermal-neutron-induced fission of U235, the frequency of occurrence is observed to be greater than 1.2 x 10-6 ternary fission events per binary fission event. Ternary fission of U236: results in the formation of one light fragment (near mass 36) and two large fragments or, as in the case of Cf252, two medium fragments and one large one. These results indicate that axially asymmetric distortion modes are possible in the pre-scission configurations of the fissioning nucleus. A description is given of experiments designed to radiochemically detect the light fragment resulting from ternary fission. (author)
Energy Technology Data Exchange (ETDEWEB)
Chuenkov, V. A., E-mail: v.a.chuenkov@mail.ru [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)
2013-12-15
The theory of the interaction of a monoenergetic flow of injected electrons with a strong high-frequency ac electric field in resonant-tunneling diode (RTD) structures with asymmetric barriers of finite height and width is generalized. In the quasi-classical approximation, electron wavefunctions and tunneling functions in the quantum well and barriers are found. Analytical expressions for polarization currents in RTDs are derived in both the general case and in a number of limiting cases. It is shown that the polarization currents and radiation power in RTDs with asymmetric barriers strongly depend on the ratio of the probabilities of electron tunneling through the emitter and collector barriers. In the quantum mode, when δ = ε − ε{sub r} = ħω ≪ Γ (ε is the energy of electrons injected in the RTD, ħ is Planck’s constant, ω is the ac field frequency, ε{sub r} and Γ are the energy and width of the resonance level, respectively), the active polarization current in a field of E ≈ 2.8ħω/ea (e is the electron charge and a is the quantum-well width) reaches a maximum equal in magnitude to 84% of the direct resonant current, if the probability of electron tunneling through the emitter barrier is much higher than that through the collector barrier. The radiation-generation power at frequencies of ω = 10{sup 12}–10{sup 13} s{sup −1} can reach 10{sup 5}–10{sup 6} W/cm{sup 2} in this case.
Mass distribution in 19F induced fission of 232Th
International Nuclear Information System (INIS)
Formation cross sections of several fission products have been determined using the recoil catcher technique followed by γ-ray spectrometry in 19F induced fission of 232Th at Elab=95 and 112 MeV. The data show significant admixture of fission from compound nuclei formed by complete fusion as well as targetlike nuclei formed by transfer reactions. Mass distributions for both the fissioning systems have been obtained using the systematics of charge distribution in low and medium energy fission. Mass distribution for complete fusion fission is broad Gaussian whereas it is asymmetric for transfer induced fission. At 95 MeV the transfer fission constitutes about 28% of total fission cross section while at 112 MeV it is about 14%, showing that the transfer fission fraction decreases with increasing projectile energy across the barrier. The evaporation residue cross sections of the targetlike nucleus formed in the 232Th (19F, 18O) 233Pa reaction were also measured. The evaporation residue cross sections and the calculated decay probabilities of the targetlike nucleus 233Pa by PACE2 have been used to estimate the fraction of proton and α transfer fission in the total transfer fission cross section. copyright 1996 The American Physical Society
Excitation-energy dependence of the nuclear fission characteristics
Energy Technology Data Exchange (ETDEWEB)
Baba, H.; Saito, T.; Takahashi, N. [Osaka City Univ. (Japan). Faculty of Science] [and others
1996-03-01
It is known that the width parameter of the fragment mass yield distribution follows a beautiful systematics with respect to the excitation energy. According to this systematics, the fission characteristics following the systematics should disappear when the excitation energy Ex goes down to 14 MeV. The present purpose is to elucidate if, where, how and why a transition takes place in the fission characteristics of the asymmetric fission of light actinide elements. Two types of experiments are performed, one is the double-energy measurement of the kinetic energies of complementary fragments in the thermal-neutron fission of {sup 235,233}U and proton-induced fission of {sup 238}U at 13.3- and 15.7-MeV excitations, and the other is the radiochemical study of proton-induced fission and photofission of {sup 238}U at various excitation energies. In conclusion, it has demonstrated that there are two distinctive fission mechanisms in the low-energy fission of light actinide elements and the transition between them takes place around 14-MeV excitation. The characteristics of proton fission and photofission in the energy range lower than the above transition point are the essentially the same as those of thermal-neutron fission and also spontaneous fission. The results of GDR fission indicates the fission in the high-energy side starts from the nuclear collective states, whereas the lower-energy fission is of non-collective nature. It is likely that thermal-neutron fission is rather of the barrier-penetrating type like spontaneous fission than the threshold fission. (S.Y.)
Examination of the fission time of the Z =120 nucleus
Sikdar, A. K.; Ray, A.; Chatterjee, A.
2016-04-01
We show that the large difference in the measured lifetime for asymmetric fission of the highly excited (T ≈1.5 -MeV ) Z =120 nucleus as measured by the atomic techniques (crystal blocking and x-ray methods) with those measured by the nuclear techniques (mass-angle distribution and prefission neutron multiplicity) cannot be due to the different sensitivities of the atomic and nuclear techniques in different time domains. The claim of formation of a superheavy Z =120 nucleus with a high fission barrier on the basis of an observed long fission time by the atomic techniques is in direct conflict with all other available measurements and calculations.
Fission barriers of odd-mass nuclei within the HF-BCS and HTDA approaches
International Nuclear Information System (INIS)
Within two mean-field plus correlation descriptions (Hartree-Fock plus BCS or plus Highly Truncated Diagonalization Approaches) we study here some static properties of two odd-neutron nuclei (235U, 239Pu) from the ground-state deformation to the fission isomeric well, using three different Skyrme force parametrizations. A specific study of the polarization effects due to the account of relevant time-odd density functions is performed. (authors)
Fission investigations and evaluation activities at IRMM
International Nuclear Information System (INIS)
The IRMM has a longstanding tradition in the field of neutron induced fission physics studies. It is especially well equipped with world-class facilities as the high resolution neutron time-of-flight spectrometer GELINA and the 7 MV Van de Graaff accelerator for the quasi-monoenergetic neutron production. During the past decade several neutron induced fission reactions have been studied in the energy range from eV up to 6 MeV and spontaneous fission. The isotopes under investigation were 235,238 U(n,f), 239 Pu(n,f), 237 Np(n,f), 252 Cf(SF) and 233 Pa(n,f). For all isotopes but 233 Pa, the fission fragment mass-yield and total kinetic energy distributions were measured. 233 Pa was only investigated for the fission cross-section. The results have been described within the multi-modal fission model. The three most dominant fission modes, the two asymmetric standard I (S1) and standard II (S2) as well as the the symmetric superlong mode were used for all the isotopes but 252 Cf. For this isotope at least one other fission mode had to be taken into account, the so--called standard III (S3) mode. Since the theoretical interpretation of experimental results was rather successful also an attempt was made to improve the evaluation of the respective fission cross-section as well as their neutron multiplicities and spectra. Here, the statistical model for fission cross-section evaluation was extended by including the multi-modality concept for fission. Based on the underlying model, separate outer fission barriers have been considered for each mode, while the inner barriers and isomeric wells are assumed to be the same. The self-consistent calculations of the fission cross-section as well as total, capture, elastic and inelastic cross-sections were in good agreement with the experimental data and evaluated nuclear data libraries. As a side product, also fission fragment mass yield distributions have been deduced at incident neutron energies hitherto unaccessible. Very
Prokhorova, E. V.; 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.; Pashkevich, V. V.; Rusanov, A. Ya.
2008-04-01
Mass-energy distributions (MEDs) and capture-fission cross sections have been measured in the reaction 48Ca + 208Pb → 256No at the energies E=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 256No and quasi-fission "shoulders" corresponding to the light fragment masses ˜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=130-135 u and the TKE of ≈233 MeV.
International Nuclear Information System (INIS)
Mass-energy distributions (MEDs) and capture-fission cross sections have been measured in the reaction 48Ca + 208Pb →256No at the energies Elab=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 256No and quasi-fission 'shoulders' corresponding to the light fragment masses ∼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 MH=130-135 u and the TKE of ∼233 MeV
Poenaru, D N; Greiner, W
2005-01-01
Complex fission phenomena can be studied in a unified way. Very general reflection asymmetrical equilibrium (saddle-point) nuclear shapes, may be obtained by solving an integro-differential equation without being necessary to specify a certain parametrization. The mass asymmetry in cold fission phenomena can be explained as the result of adding a phenomenological shell correction to the liquid drop model deformation energy. Applications to binary, ternary, and quaternary fission are outlined. Predictions of two alpha accompanied fission are experimentally confirmed.
DEFF Research Database (Denmark)
Zhukov, A. E.; Asryan, L. V.; Semenova, Elizaveta;
2015-01-01
Band offsets at the heterointerface are calculated for various combinations of InAlGaAs/AlGaAs heteropairs that can be synthesized on GaAs substrates in the layer-by-layer pseudomorphic growth mode. Patterns which make it possible to obtain an asymmetric barrier layer providing the almost...
International Nuclear Information System (INIS)
Fission probabilities and the angular distribution of the fission fragments have been measured for six even-even compound nuclear systems using the (t, pf) reaction. Angular correlations of fission fragments obtained in these experiments provide information about the low-lying collective excitations or transition states at the fission barrier. The (t, p) reaction in particular leads to neutron-rich residual nuclei unobtainable by other methods. The absence of spin coupling for (t, p) reactions on even-even targets provides angular distributions with well defined structure in the region of the fission barrier. The experimental data were obtained using an 18-MeV triton beam on targets of 242Pu, 240Pu, 238U, 236U, 232Th and 230Th at Los Alamos Van-de-Graaff accelerator facility. Outgoing protons were detected at 140 deg relative to the incident triton beam. Excitation energies ranging from 3.0 to 9.0 MeV were obtained in these experiments. Fission fragment angular distributions were measured at 24 angles from 0 deg to 140 deg relative to the kinematic recoil angle. The data were fitted to a series of even Legendre polynomials W(θ) = A0 [1 + ΣL gL PL (cos θ)] and the coefficients g2 through g12 and A0 were determined as a function of excitation energy. The fission probability Pf was obtained from the ratio of A0 to the (t, p) cross-section for the target nucleus. The results exhibit well defined structure in the angular coefficients which correlates with structure in the fission probability for most of the nuclei studied. In an attempt to interpret this observed structure the experimentally determined fitting parameters Pf and g are compared with calculated results of a microscopic model. This model takes into consideration the penetrability and angular dependence of fission through each member of the various transition bands at the saddle point and appropriately sums the results for comparison with the data. The effects of barrier penetration through a two
Low frequency noise in asymmetric double barrier magnetic tunnel junctions with a top thin MgO layer
Guo, Hui-Qiang; Tang, Wei-Yue; Liu, Liang; Wei, Jian; Li, Da-Lai; Feng, Jia-Feng; Han, Xiu-Feng
2015-07-01
Low frequency noise has been investigated at room temperature for asymmetric double barrier magnetic tunnel junctions (DBMTJs), where the coupling between the top and middle CoFeB layers is antiferromagnetic with a 0.8-nm thin top MgO barrier of the CoFeB/MgO/CoFe/CoFeB/MgO/CoFeB DBMTJ. At enough large bias, 1/f noise dominates the voltage noise power spectra in the low frequency region, and is conventionally characterized by the Hooge parameter αmag. With increasing external field, the top and bottom ferromagnetic layers are aligned by the field, and then the middle free layer rotates from antiparallel state (antiferromagnetic coupling between top and middle ferromagnetic layers) to parallel state. In this rotation process αmag and magnetoresistance-sensitivity-product show a linear dependence, consistent with the fluctuation dissipation relation. With the magnetic field applied at different angles (θ) to the easy axis of the free layer, the linear dependence persists while the intercept of the linear fit satisfies a cos(θ) dependence, similar to that for the magnetoresistance, suggesting intrinsic relation between magnetic losses and magnetoresistance. Project supported by the National Basic Research Program of China (Grant Nos. 2011CBA00106, 2012CB927400, 2010CB934401, and 2014AA032904), the National High Technology Research and Development Program of China (Grant No. 2014AA032904), and the National Natural Science Foundation of China (Grant Nos. 11434014 and 11104252).
Janjua, Bilal
2014-04-01
We study the enhanced hole confinement by having a large bandgap AlGaN monolayer insertion (MLI) between the quantum well (QW) and the quantum barrier (QB). The numerical analysis examines the energy band alignment diagrams, using a self-consistent 6 × 6 k ·p method and, considering carrier distribution, recombination rates (Shockley-Reed-Hall, Auger, and radiative recombination rates), under equilibrium and forward bias conditions. The active region is based on AlaGa1-aN (barrier)/AlbGa1-bN (MLI)/AlcGa1-cN (well)/AldGa1-dN (barrier), where b > d > a > c. A large bandgap AlbGa1-bN mono layer, inserted between the QW and QB, was found to be effective in providing stronger hole confinement. With the proposed band engineering scheme, an increase of more than 30% in spatial overlap of carrier wavefunction was obtained, with a considerable increase in carrier density and direct radiative recombination rates. The single-QW-based UV-LED was designed to emit at 280 nm, which is an effective wavelength for water disinfection.
International Nuclear Information System (INIS)
An analytically solvable model is used to study the potential barrier penetrability in the case when the gap parameter Δ is treated as a dynamical variable governed by the least action principle. It is found that, as compared to the standard (BCS) approach, the dynamical treatment of pairing results in a considerably weakened dependence of the fission barrier penetrability on the intensity of pairing correlations in the initial state (Δ0), on the barrier height, and on the energy of the initial state. On this basis, a more adequate explanation is proposed for typical order-of-magnitude values of the empirical hidrance factors for groun-state spontaneous fission of odd nuclei. It is also shown that a large enhancement of superfluidity in tunneling - the inherent effect of the dynamical treatment of pairing - strongly facilitates deeply subbarier fusion of complex nuclei. Finally, an analysis is given for the probability of spontaneous fission from K-isomeric quasiparticle (q-p) states in even-even heavy nuclei. The relative change of the partial spontaneous fission half-life in going from the ground-state to a high-spin q-p isomeric state, T*sf/Tsf, is found to be strongly dependent on whether or not there takes place the dynamically induced enhancement of superfluidity in tunneling. Measurements of T*sf/Tsf provide thus a unique possibility of verifying theoretical predictions about the strong, inverse-square dependence of the effective inertia associated with large-scale subbarrier rearrangements of nuclei
Fission dynamics within time-dependent Hartree-Fock. II. Boost-induced fission
Goddard, Philip; Stevenson, Paul; Rios, Arnau
2016-01-01
Background: Nuclear fission is a complex large-amplitude collective decay mode in heavy nuclei. Microscopic density functional studies of fission have previously concentrated on adiabatic approaches based on constrained static calculations ignoring dynamical excitations of the fissioning nucleus and the daughter products. Purpose: We explore the ability of dynamic mean-field methods to describe induced fission processes, using quadrupole boosts in the nuclide 240Pu as an example. Methods: Following upon the work presented in Goddard et al. [Phys. Rev. C 92, 054610 (2015)], 10.1103/PhysRevC.92.054610, quadrupole-constrained Hartree-Fock calculations are used to create a potential energy surface. An isomeric state and a state beyond the second barrier peak are excited by means of instantaneous as well as temporally extended gauge boosts with quadrupole shapes. The subsequent deexcitation is studied in a time-dependent Hartree-Fock simulation, with emphasis on fissioned final states. The corresponding fission fragment mass numbers are studied. Results: In general, the energy deposited by the quadrupole boost is quickly absorbed by the nucleus. In instantaneous boosts, this leads to fast shape rearrangements and violent dynamics that can ultimately lead to fission. This is a qualitatively different process than the deformation-induced fission. Boosts induced within a finite time window excite the system in a relatively gentler way and do induce fission but with a smaller energy deposition. Conclusions: The fission products obtained using boost-induced fission in time-dependent Hartree-Fock are more asymmetric than the fragments obtained in deformation-induced fission or the corresponding adiabatic approaches.
Segre, Emilio
1950-11-22
The first attempt to discover spontaneous fission in uranium was made by [Willard] Libby, who, however, failed to detect it on account of the smallness of effect. In 1940, [K. A.] Petrzhak and [G. N.] Flerov, using more sensitive methods, discovered spontaneous fission in uranium and gave some rough estimates of the spontaneous fission decay constant of this substance. Subsequently, extensive experimental work on the subject has been performed by several investigators and will be quoted in the various sections. [N.] Bohr and [A.] Wheeler have given a theory of the effect based on the usual ideas of penetration of potential barriers. On this project spontaneous fission has been studied for the past several years in an effort to obtain a complete picture of the phenomenon. For this purpose the spontaneous fission decay constants {lambda} have been measured for separated isotopes of the heavy elements wherever possible. Moreover, the number {nu} of neutrons emitted per fission has been measured wherever feasible, and other characteristics of the spontaneous fission process have been studied. This report summarizes the spontaneous fission work done at Los Alamos up to January 1, 1945. A chronological record of the work is contained in the Los Alamos monthly reports.
Ghosh, T.K.
2005-01-01
The thesis presents investigations on the angular and mass distribution of fission fragments on heavy ion induced fission reactions. The present investigations address current issues in heavy ion induced fission reactions like finding the optimum entrance channel for the synthesis of super heavy elements (SHE). A double arm time of flight spectrometer over long flight path was used to measure the precise masses of complementary fission fragments. Necessary large area position sensitive gas de...
Evolution of fusion hindrance for asymmetric systems at deep sub barrier energies
Shrivastavaa, A; Pandit, S K; Nanal, V; Ichikawa, T; Hagino, K; Navin, A; Palshetkar, C S; Parkar, V V; Ramachandran, K; Rout, P C; Kumar, Abhinav; Chatterjee, A; Kailas, S
2016-01-01
Measurements of fusion cross-sections of 7Li and 12C with 198Pt at deep sub-barrier energies are reported to unravel the role of the entrance channel in the occurrence of fusion hindrance. The onset of fusion hindrance has been clearly observed in 12C + 198Pt system but not in 7Li + 198Pt system, within the measured energy range. Emergence of the hindrance, moving from lighter (6,7Li) to heavier (12C,16O) projectiles is explained employing a model that considers a gradual transition from a sudden to adiabatic regime at low energies. The model calculation reveals a weak effect of the damping of coupling to collective motion for the present systems as compared to that obtained for systems with heavier projectiles.
Calculation of fission product behavior in a multiple reactor barriers in case of an accident
International Nuclear Information System (INIS)
Radiation protection of the population in case of a reactor accident utilizes reference levels which are based on doses values. Therefore, adequate provisions for effective and timely dose assessment for population in case of accidents at nuclear power plant (NPP) are important. Developing the background for such provisions is the objective of this study. In particular, an exponential model has been developed and utilized to calculate the release rate of the most volatile gaseous materials from different reactor barriers. Calculation has been performed for noble gases (133Xe, 135Xe, 138Xe, 85Kr, 87Kr, 88Kr) and the halogens(1'31I, 132I, 133I, 1'34I, 135I). The effective dose rate equivalent is calculations in the nearly stage of a reactor accident. Calculations are performed using the MCNP-4C code. The results are comparable with the final analysis report which utilizes different codes. Results of our calculation shows no excessive dose in populated regions and it is recommended to use secondary containment barrier for highly reduction of the release rate to the environment. (Author)
Montoya, Modesto
2015-01-01
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 235U. 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...
International Nuclear Information System (INIS)
This Letter deals with the effect of a delta-potential barrier on the one-dimensional and asymmetric Aharonov-Bohm ring with Rashba spin-orbit interaction. The analytic expressions of the transmission amplitude and conductance are derived by applying the transfer matrix method in the one-electron scattering formalism. Resorting to an adequate tuning of the Aharonov-Bohm magnetic flux and Rashba coupling strength, a control of the conductance can be done by varying the strength and the location of the barrier. This may be useful in the design of further mesoscopic spin filters by using suitable asymmetry configurations. -- Highlights: → An asymmetric Aharonov-Bohm ring with Rashba spin-orbit interaction is considered. → The effect of a delta-potential barrier on this ring is examined. → The analytic expression of the transmission amplitude is derived. → The conductance can be controlled by varying the barrier parameters. → The asymmetric ring can acts like a spin filter device.
Interplay of fission modes in mass distribution of light actinide nuclei 225,227Pa
Directory of Open Access Journals (Sweden)
R. Dubey
2016-01-01
Full Text Available Fission-fragment mass distributions were measured for 225,227Pa nuclei formed in fusion reactions of 19F+206,208Pb around fusion barrier energies. Mass-angle correlations do not indicate any quasi-fission like events in this bombarding energy range. Mass distributions were fitted by Gaussian distribution and mass variance extracted. At below-barrier energies, the mass variance was found to increase with decrease in energy for both nuclei. Results from present work were compared with existing data for induced fission of 224,226Th and 228U around barrier energies. Enhancement in mass variance of 225,227Pa nuclei at below-barrier energies shows evidence for presence of asymmetric fission events mixed with symmetric fission events. This is in agreement with the results of mass distributions of nearby nuclei 224,226Th and 228U where two-mode fission process was observed. Two-mode feature of fission arises due to the shell effects changing the landscape of the potential-energy surfaces at low excitation energies. The excitation-energy dependence of the mass variance gives strong evidence for survival of microscopic shell effects in fission of light actinide nuclei 225,227Pa with initial excitation energy ∼30–50 MeV.
Interplay of fission modes in mass distribution of light actinide nuclei 225,227Pa
Dubey, R.; Sugathan, P.; Jhingan, A.; Kaur, Gurpreet; Mukul, Ish; Mohanto, G.; Siwal, D.; Saneesh, N.; Banerjee, T.; Thakur, Meenu; Mahajan, Ruchi; Kumar, N.; Chatterjee, M. B.
2016-01-01
Fission-fragment mass distributions were measured for 225,227Pa nuclei formed in fusion reactions of 19F + 206,208Pb around fusion barrier energies. Mass-angle correlations do not indicate any quasi-fission like events in this bombarding energy range. Mass distributions were fitted by Gaussian distribution and mass variance extracted. At below-barrier energies, the mass variance was found to increase with decrease in energy for both nuclei. Results from present work were compared with existing data for induced fission of 224,226Th and 228U around barrier energies. Enhancement in mass variance of 225,227Pa nuclei at below-barrier energies shows evidence for presence of asymmetric fission events mixed with symmetric fission events. This is in agreement with the results of mass distributions of nearby nuclei 224,226Th and 228U where two-mode fission process was observed. Two-mode feature of fission arises due to the shell effects changing the landscape of the potential-energy surfaces at low excitation energies. The excitation-energy dependence of the mass variance gives strong evidence for survival of microscopic shell effects in fission of light actinide nuclei 225,227Pa with initial excitation energy ∼30-50 MeV.
Poenaru, Dorin N.; Gherghescu, Radu A.; Greiner, Walter
2005-01-01
Complex fission phenomena are studied in a unified way. Very general reflection asymmetrical equilibrium (saddle point) nuclear shapes are obtained by solving an integro-differential equation without being necessary to specify a certain parametrization. The mass asymmetry in binary cold fission of Th and U isotopes is explained as the result of adding a phenomenological shell correction to the liquid drop model deformation energy. Applications to binary, ternary, and quaternary fission are ou...
International Nuclear Information System (INIS)
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
International Nuclear Information System (INIS)
Band offsets at the heterointerface are calculated for various combinations of InAlGaAs/AlGaAs heteropairs that can be synthesized on GaAs substrates in the layer-by-layer pseudomorphic growth mode. Patterns which make it possible to obtain an asymmetric barrier layer providing the almost obstruction-free transport of holes and the highest possible barrier height for electrons are found. The optimal compositions of both compounds (In0.232Al0.594Ga0.174As/Al0.355Ga0.645As) at which the flux of electrons across the barrier is at a minimum are determined with consideration for the critical thickness of the indium-containing quaternary solid solution
Interplay of fission modes in mass distribution of light actinide nuclei 225,227Pa
Dubey, R; Jhingan, A; Kaur, Gurpreet; Mukul, Ish; Mohanto, G; Siwal, D; Saneesh, N; Banerjee, T; Thakur, Meenu; Mahajan, Ruchi; Kumar, N; Chatterjee, M B
2015-01-01
Fission-fragment mass distributions were measured for 225,227Pa nuclei formed in fusion reactions of 19F + 206, 208Pb around fusion barrier energies. Mass-angle correlations do not indicate any quasi-fission like events in this bombarding energy range. Mass distributions were fitted by Gaussian distribution and mass variance extracted. At below-barrier energies, the mass variance was found to increase with decrease in energy for both nuclei. Results from present work were compared with existing data for induced fission of 224, 226Th and 228U around barrier energies. Enhancement in mass variance of 225, 227Pa nuclei at below-barrier energies shows evidence for presence of asymmetric fission events mixed with symmetric fission events. This is in agreement with the results of mass distributions of nearby nuclei 224, 226Th and 228U where two-mode fission process was observed. Two-mode feature of fission arises due to the shell effects changing the landscape of the potential energy surfaces at low excitation energ...
International Nuclear Information System (INIS)
The results of experiments carried out at GSI Darmstadt, LBNL Berkeley and RIKEN Tokyo on the synthesis of superheavy nuclei of Z = 104–113 in cold fusion reactions have been analyzed within the fusion-by-diffusion (FBD) model by using the fission barriers, ground-state masses, shell effects and deformations calculated with the Warsaw macroscopic–microscopic model. An empirical parametrization of the injection-point distance has been established for this new theoretical input to the FBD model that enables one to reproduce existing data with reasonable accuracy and predict synthesis cross sections and optimum bombarding energies in as yet unexplored cold fusion reactions. (paper)
Protactinium neutron-induced fission up to 200 MeV
International Nuclear Information System (INIS)
The theoretical evaluation of 230-233Pa(n,F) cross sections is based on direct data, 230-234Pa fission probabilities and ratios of fission probabilities in first-chance and emissive fission domains, surrogate for neutron-induced fission. First chance fission cross sections trends of Pa are based on consistent description of 232Th(n,F), 232Th(n,2n) and 238U(n,F), 238U(n,xn) data, supported by the ratio surrogate data by Burke et al., 2006, for the 237U(n,F) reaction. Ratio surrogate data on fission probabilities of 232Th(6Li,4He)234Pa and 232Th(6Li,d)236U by Nayak et al., 2008, support the predicted 233Pa(n,F) cross section at En=11.5-16.5 MeV. The predicted trends of 230-232Pa(n,F) cross section up to En=20 MeV, are consistent with fissile properties of Pa nuclides, extracted by 232Th(p,F) (Isaev et al., 2008) and 232Th(p,3n) (Morgenstern et al., 2008) data analysis. The excitation energy and nucleon composition dependence of the transition from asymmetric to symmetric scission for fission observables of Pa nuclei is defined by analysis of p-induced fission of 232Th at Ep=1-200 MeV. Predominantly symmetric fission in 232Th(p,F) at En(p)=200 MeV as revealed by experimental branching ratios (Dujvestijn et al., 1999) is reproduced. Steep transition from asymmetric to symmetric fission with increase of nucleon incident energy is due to fission of neutron-deficient Pa (A≤229) nuclei. A structure of the potential energy surface (a drop of symmetric and asymmetric fission barriers difference (Ef(SYM) - Ef(ASYM)) from about 3.5 MeV to 1 MeV) of N-deficient Pa nuclides (A≤226) and available phase space at outer fission saddles, are shown to be responsible for the sharp increase with En(p) of the symmetric fission component contribution for 232Th(p,F) and 230-233Pa(n,F) reactions. That is a strong evidence of emissive fission nature of moderately excited Pa nuclides, reliably quantified only up to En(p) about 20(30) MeV. Predicted fission cross section of 232Pa
Protactinium neutron-induced fission up to 200 MeV
Directory of Open Access Journals (Sweden)
Maslov V.
2010-03-01
Full Text Available The theoretical evaluation of 230-233Pa(n,F cross sections is based on direct data, 230-234Pa fission probabilities and ratios of fission probabilities in first-chance and emissive fission domains, surrogate for neutroninduced fission. First chance fission cross sections trends of Pa are based on consistent description of 232Th(n,F, 232Th(n,2n and 238U(n,F, 238U(n,xn data, supported by the ratio surrogate data by Burke et al., 2006, for the 237U(n,F reaction. Ratio surrogate data on fission probabilities of 232Th(6 Li,4 He234Pa and 232 Th(6 Li,d236U by Nayak et al., 2008, support the predicted 233Pa(n, F cross section at En=11.5-16.5 MeV. The predicted trends of 230-232Pa(n, F cross section up to En=20 MeV, are consistent with fissilities of Pa nuclides, extracted by 232Th(p,F (Isaev et al., 2008 and 232Th(p,3n (Morgenstern et al., 2008 data analysis. The excitation energy and nucleon composition dependence of the transition from asymmetric to symmetric scission for fission observables of Pa nuclei is defined by analysis of p-induced fission of 232Th at Ep=1-200 MeV. Predominantly symmetric fission in 232Th(p,F at En( p=200 MeV as revealed by experimental branching ratios (Dujvestijn et al., 1999 is reproduced. Steep transition from asymmetric to symmetric fission with increase of nucleon incident energy is due to fission of neutron-deficient Pa (A≤229 nuclei. A structure of the potential energy surface (a drop of f f symmetric and asymmetric fission barriers difierence (EfSYM - EfASYM from ~3.5 MeV to ~1 MeV of N-deficient Pa nuclides (A≤226 and available phase space at outer fission saddles, are shown to be responsible for the sharp increase with En( p of the symmetric fission component contribution for 232Th(p,F and 230-233 Pa(n, F reactions. That is a strong evidence of emissive fission nature of moderately excited Pa nuclides, reliably quantified only up to En( p~20(30 MeV. Predicted fission cross section of 232Pa(n,F coincides with
Fission modes of mercury isotopes
Warda, M; Nazarewicz, W
2012-01-01
Recent experiments on beta-delayed fission in the mercury-lead region and the discovery of asymmetric fission in $^{180}$Hg [1] have stimulated renewed interest in the mechanism of fission in heavy nuclei. Here we study fission modes and fusion valleys in $^{180}$Hg and $^{198}$Hg using the self-consistent nuclear density functional theory employing Skyrme and Gogny energy density functionals. We show that the observed transition from asymmetric fission in $^{180}$Hg towards more symmetric distribution of fission fragments in $^{198}$Hg can be explained in terms of competing fission modes of different geometries that are governed by shell effects in pre-scission configurations. The density distributions at scission configurations are studied and related to the experimentally observed mass splits.
Siwek-Wilczynska, K; Kowal, M; Sobiczewski, A; Wilczynski, J
2012-01-01
A complete set of existing data on hot fusion reactions leading to synthesis of superheavy nuclei of Z =114-118, obtained in a series of experiments in Dubna and later in GSI Darmstadt and LBNL Berkeley, was analyzed in terms of a new angular-momentum dependent version of the Fusion by Diffusion (FBD) model with fission barriers and ground-state masses taken from the Warsaw macroscopic-microscopic model (involving non-axial shapes) of Kowal et al. The only empirically adjustable parameter of the model, the injection-point distance (sinj), has been determined individually for all the reactions and very regular systematics of this parameter have been established. The regularity of the obtained sinj systematics indirectly points at the internal consistency of the whole set of fission barriers used in the calculations. Having fitted all the experimental excitation functions for elements Z = 114-118, the FBD model (with the new sinj systematics) was used to predict cross sections for synthesis of elements Z = 119 ...
Microscopic Description of Induced Fission
Schunck, N
2013-01-01
Selected aspects of the description of neutron-induced fission in 240Pu in the framework of the nuclear energy density functional theory at finite temperature are presented. In particular, we discuss aspects pertaining to the choice of thermodynamic state variables, the evolution of fission barriers as function of the incident neutron energy, and the temperatures of the fission fragments.
Conductance in Co/Al2O3/Si/Al2O3 permalloy with asymmetrically doped barrier
Guerrero, R.; Aliev, F. G.; Villar, R.; Santos, T.; Moodera, J.; Dugaev, V. K.; Barnas, J.
2010-01-01
Permalloy magnetic tunnel junctions. Complementary low frequency noise measurements are used to understand the conductance results. The obtained data indicate the breakdown of the Coulomb blockade for thickness of the asymmetric silicon layer exceeding 1.2\\AA . The crossover in the conductance, the dependence of the tunnelling magnetoresistance with the bias voltage and the noise below 80K correspond to 1 monolayer coverage. Interestingly, the zero bias magnetoresistance remains nearly unaffe...
Dynamics of fission and heavy ion reactions
International Nuclear Information System (INIS)
Recent advances in a unified macroscopic-microscopic description of large-amplitude collective nuclear motion such as occurs in fission and heavy ion reactions are discussed. With the goal of finding observable quantities that depend upon the magnitude and mechanism of nuclear dissipation, one-body dissipation and two-body viscosity within the framework of a generalized Fokker-Planck equation for the time dependence of the distribution function in phase space of collective coordinates and momenta are considered. Proceeding in two separate directions, the generalized Hamilton equations of motion for the first moments of the distribution function with a new shape parametrization and other technical innovations are first solved. This yields the mean translational fission-fragment kinetic energy and mass of a third fragment that sometimes forms between the two end fragments, as well as the energy required for fusion in symmetric heavy-ion reactions and the mass transfer and capture cross section in asymmetric heavy-ion reactions. In a second direction, we specialize to an inverted-oscillator fission barrier and use Kramers' stationary solution to calculate the mean time from the saddle point to scission for a heavy-ion-induced fission reaction for which experimental information is becoming available. 25 references
Energy Technology Data Exchange (ETDEWEB)
Schaeffer, A.
2011-02-15
A fission experiment performed at CERN on mercury nuclei produced an unexpected asymmetric reaction. The study of the potential energy surface shows that this asymmetric reaction minimized the energy consumed in the reactions but led to 2 different elements (ruthenium-100 and krypton-80) far less stable than zirconium-90 that is the element expected in a symmetric fission. (A.C.)
Isoscaling of the Fission Fragments with Langevin Equation
Institute of Scientific and Technical Information of China (English)
WANG Kun; TIAN Wen-Dong; ZHONG Chen; ZHOU Xing-Fei; MA Yu-Gang; WEI Yi-Bin; CAI Xiang-Zhou; CHEN Jin-Gen; FANG De-Qing; GUO Wei; MA Guo-Liang; SHEN Wen-Qing
2005-01-01
@@ The Langevin equation is used to simulate the fission process of 112Sn + 112Sn and 116Sn + 116Sn. The mass distribution of the fission fragments are given by assuming the process of symmetric fission or asymmetric fission with the Gaussian probability sampling. The isoscaling behaviour has been observed from the analysis of fission fragments of both the reactions, and the isoscaling parameter α seems to be sensitive to the width of fission probability and the beam energy.
Isoscaling of the Fission Fragments with Langevin Equation
Wang, K.; Ma, Y. G.; Wei, Y. B.; Cai, X. Z.; Chen, J. G.; Fang, D Q; Guo, W; Ma, G. L.; Shen, W.Q.(Shanghai Institute of Applied Physics, Shanghai, 201800, China); Tian, W.D.; Zhong, C.; Zhou, X. F.
2004-01-01
Langevin equation is used to simulate the fission process of $^{112}$Sn + $^{112}$Sn and $^{116}$Sn + $^{116}$Sn. The mass distribution of the fission fragments are given by assuming the process of symmetric fission or asymmetric fission with the Gaussian probability sampling. Isoscaling behavior has been observed from the analysis of fission fragments of both reactions and the isoscaling parameter $\\alpha$ seems to be sensitive to the width of fission probability and the beam energy.
Calculations of fission rates for r-process nucleosynthesis
Panov, I. V.; Kolbe, E.; Pfeiffer, B.; Rauscher, T.; Kratz, K.-L.; Thielemann, F. -K.
2004-01-01
Fission plays an important role in the r-process which is responsible not only for the yields of transuranium isotopes, but may have a strong influence on the formation of the majority of heavy nuclei due to fission recycling. We present calculations of beta-delayed and neutron-induced fission rates, taking into account different fission barriers predictions and mass formulae. It is shown that an increase of fission barriers results naturally in a reduction of fission rates, but that neverthe...
Nuclear fission in covariant density functional theory
International Nuclear Information System (INIS)
The current status of the application of covariant density functional theory to microscopic description of nuclear fission with main emphasis on superheavy nuclei (SHN) is reviewed. The softness of SHN in the triaxial plane leads to an emergence of several competing fission paths in the region of the inner fission barrier in some of these nuclei. The outer fission barriers of SHN are considerably affected both by triaxiality and octupole deformation. (authors)
Nuclear fission in covariant density functional theory
Afanasjev A.V.; Abusara H.; Ring P.
2013-01-01
The current status of the application of covariant density functional theory to microscopic description of nuclear fission with main emphasis on superheavy nuclei (SHN) is reviewed. The softness of SHN in the triaxial plane leads to an emergence of several competing fission pathes in the region of the inner fission barrier in some of these nuclei. The outer fission barriers of SHN are considerably affected both by triaxiality and octupole deformation.
Fission in Rapidly Rotating Nuclei
Directory of Open Access Journals (Sweden)
A. K. Rhine Kumar
2014-02-01
Full Text Available We study the effect of rotation in fission of the atomic nucleus 256Fm using an independent-particle shell model with the mean field represented by a deformed Woods-Saxon potential and the shapes defined through the Cassinian oval parametrization. The variations of barrier height with increasing angular momentum, appearance of double hump in fission path are analysed. Our calculations explain the appearance of double hump in fission path of 256Fm nucleus. The second minimum vanishes with increase in angular momentum which hints that the fission barrier disappears at large spin.
Qi, Haicheng; Fan, Zhihui; Liu, Yidi; Ren, Chunsheng
2016-05-01
Atmospheric pressure dielectric barrier discharge plasma is produced in airflow by applying nanosecond high voltage pulses with peak voltage about 35 kV and rising time about 40 ns on a plate-to-plate electrode arrangement. The effects of airflow rate (0-50 m/s) on the discharge characteristics are investigated under different barrier conditions (the bare anode case and the bare cathode case). For both cases, the breakdown voltage and the time lag increase distinctly and the discharge intensity decreases sharply when the airflow rate increases from 0 to 30 m/s, and then keep almost constant until the airflow rate is further increased to 50 m/s. For the bare anode case (the cathode is covered by dielectric plate), the discharge mode transforms gradually from filamentary to diffuse discharge with the increasing airflow rate. While for the bare cathode case, some micro-discharge channels are still excited, though the discharge becomes more diffuse when the airflow rate is higher than 30 m/s. By acquiring the time-resolved images of the discharge, it is proved that it is the primary discharge which becomes diffuse when airflow is introduced and the following two discharges of the same voltage pulse occur principally at the positions where the primary discharge is more intense. And in both cases, the plasma temperatures are reduced, but the degree is different. All the phenomena can be explained mainly by the variation of the space charge distribution when the airflow is introduced into the discharge gap. And it is indicated that the bare anode case has an advantage in obtaining diffuse discharge.
Extended optical model for fission
Sin, M.; Capote, R.; Herman, M. W.; Trkov, A.
2016-03-01
A comprehensive formalism to calculate fission cross sections based on the extension of the optical model for fission is presented. It can be used for description of nuclear reactions on actinides featuring multi-humped fission barriers with partial absorption in the wells and direct transmission through discrete and continuum fission channels. The formalism describes the gross fluctuations observed in the fission probability due to vibrational resonances, and can be easily implemented in existing statistical reaction model codes. The extended optical model for fission is applied for neutron induced fission cross-section calculations on 234,235,238U and 239Pu targets. A triple-humped fission barrier is used for U,235234(n ,f ) , while a double-humped fission barrier is used for 238U(n ,f ) and 239Pu(n ,f ) reactions as predicted by theoretical barrier calculations. The impact of partial damping of class-II/III states, and of direct transmission through discrete and continuum fission channels, is shown to be critical for a proper description of the measured fission cross sections for 234,235,238U(n ,f ) reactions. The 239Pu(n ,f ) reaction can be calculated in the complete damping approximation. Calculated cross sections for U,238235(n ,f ) and 239Pu(n ,f ) reactions agree within 3% with the corresponding cross sections derived within the Neutron Standards least-squares fit of available experimental data. The extended optical model for fission can be used for both theoretical fission studies and nuclear data evaluation.
Spontaneous fission of superheavy nucleus $^{286}$Fl
Poenaru, Dorin N
2016-01-01
The decimal logarithm of spontaneous fission half-life of the superheavy nucleus $^{286}$Fl experimentally determined is $\\log_{10} T_f^{exp} (s) = -0.632$. We present a method to calculate the half-life based on the cranking inertia and the deformation energy, functions of two independent surface coordinates, using the best asymmetric two center shell model. In the first stage we study the statics. At a given mass asymmetry up to about $\\eta=0.5$ the potential barrier has a two hump shape, but for larger $\\eta$ it has only one hump. The touching point deformation energy versus mass asymmetry shows the three minima, produced by shell effects, corresponding to three decay modes: spontaneous fission, cluster decay and $\\alpha$~decay. The least action trajectory is determined in the plane $(R,\\eta)$ where $R$ is the separation distance of the fission fragments and $\\eta$ is the mass asymmetry. We may find a sequence of several trajectories one of which gives the least action. The parametrization with two deforma...
General view on the progress in nuclear fission : a review
Schmidt, Karl-Heinz; Jurado, Beatriz
2016-01-01
An overview is given on some of the main advances in experimental methods, experimental results and theoretical models and ideas of the last years in the field of nuclear fission. New approaches extended the availability of fissioning systems for experimental studies of nuclear fission considerably and provided a full identification of all fission products in A and Z for the first time. In particular, the transition from symmetric to asymmetric fission around 226 Th and some unexpected struct...
Hidden systematics of fission channels
Schmidt Karl-Heinz; Jurado Beatriz
2013-01-01
It is a common procedure to describe the fission-fragment mass distributions of fissioning systems in the actinide region by a sum of at least 5 Gaussian curves, one for the symmetric component and a few additional ones, together with their complementary parts, for the asymmetric components. These components have been attributed to the influence of fragment shells, e.g. in the statistical scission-point model of Wilkins, Steinberg and Chasman. They have also been associated with valleys in th...
Institute of Scientific and Technical Information of China (English)
赵瑞娟; 安盼龙; 许丽萍; 杨艳
2012-01-01
非对称多势垒可获得比双势垒更大的共振隧穿电流及更良好的峰谷比。通过分析单电子对任意势垒透射的理论模型,建立了任意非对称三势垒模型,研究了不同偏压和温度对透射系数的影响,并得出结论,为进一步设计非对称量子器件提供理论指导。%Asymmetric multi-barrier can obtain larger resonant tunneling current and better peak-valley ratio than double barrier. By analyzing the theoretical models of single-electron transmission on any harrier, an arbitrary asymmetric three-barrier model was established. Effects of different bias and temperatures on the transmission coefficient were studied. It provides a theoretical guidance for the further design of asymmetric quantum devices.
International Nuclear Information System (INIS)
Delayed fission is a nuclear process that couples beta decay and fission. In the delayed fission process, a parent nucleus undergoes beta decay or electron capture and thus populates excited states in the daughter nucleus. This review covers experimental methods for detecting and measuring delayed fission. Experimental results (ECDF activities and beta-DF activities) and theory are presented. The future prospects for study of delayed fission are discussed. 50 refs., 8 figs., 2 tabs
Fission dynamics within time-dependent Hartree-Fock: Deformation-induced fission
Rios Huguet, A; Stevenson, PD; Goddard, P.
2015-01-01
Background: Nuclear fission is a complex large-amplitude collective decay mode in heavy nuclei. Microscopic density functional studies of fission have previously concentrated on adiabatic approaches based on constrained static calculations ignoring dynamical excitations of the fissioning nucleus, and the daughter products. Purpose: To explore the ability of dynamic mean-field methods to describe fast fission processes beyond the fission barrier, using the nuclide $^{240}$Pu as an example. Met...
Prokhorova, E. V.; Cherepanov, E. A.; Itkis, M.G.; Kondratiev, N. A.; Kozulin, E. M.; Krupa, L.; Oganessian, Yu.Ts.; Pashkevich, V. V.; Pokrovsky, I. V.; Rusanov, A. Ya.
2003-01-01
The capture-fission cross-sections in an energy range of 206-242 MeV of 48Ca-projectiles and mass-energy distributions (MEDs) of reaction products in an energy range of 211-242 MeV have been measured in the 48Ca+208Pb reaction using the double-arm time-of-flight spectrometer CORSET. The MEDs of fragments for heated fission were shown to consist of two components. One component, which is due to classical fusion-fission, is associated with the symmetric fission of the 256No compound nucleus. Th...
The stunning nuclear fission of the mercury nucleus
International Nuclear Information System (INIS)
A fission experiment performed at CERN on mercury nuclei produced an unexpected asymmetric reaction. The study of the potential energy surface shows that this asymmetric reaction minimized the energy consumed in the reactions but led to 2 different elements (ruthenium-100 and krypton-80) far less stable than zirconium-90 that is the element expected in a symmetric fission. (A.C.)
Shell effects and fission fragments angular anisotropy
International Nuclear Information System (INIS)
The impact of the shell corrections attenuation effect with growth of the fissionable nuclei temperature on the angular anisotropy of the fission fragments is considered. The experimental data on the anisotropy of the fission fragments angular distributions of the compound nucleus, formed in the 4He + 238U reactions, are analyzed within the frames of the transition states model in the fission barriers saddle point and statistic theory of nuclear reactions. The obvious kind of the shell corrections attenuation function is obtained
International Nuclear Information System (INIS)
The nuclear fission process is pedagogically reviewed from a macroscopic-microscopic point of view. The Droplet model is considered. The fission dynamics is discussed utilizing path integrals and semiclassical methods. (L.C.)
Mass asymmetry of fusion and fission processes induced in heavy ion reaction
International Nuclear Information System (INIS)
Simple parametrisations of nuclear shapes able to describe the essential features of the fission and fusion processes were introduced. The Myers-Swiatecki (1967) liquid drop model and its generalisations: the Krape-Nix (1974) finite range of nuclear forces model and the Krappe-Nix-Sierk (1979) folded Yukawa-plus-exponential model, were extended for the nuclear systems with different charge densities. Some information concerning the interaction barrier (Esub(I)) the energy release (Q) and the fission barrier (Esub(b)) trends of variation with mass and charge asymmetry were obtained from the energy at infinite separation distance between ions (or fission fragments), at the touching point and at the fused spherical system. Good agreement with experimental data was obtained and an empirical relationship for the estimation of the interaction barriers was derived. The reaction parteners, for which it is important to take into account the charge density difference, were identified and the orders of magnitude of the errors on Esub(I), Q and Esub(b) made if this difference is ignored, were estimated. The nonaxiality of the nuclear shape at the first saddle point was demonstrated on a simple model allowing to decrease the computer running time by 3 orders of magnitude. The asymmetric spheroidal oscillator, introduced by the author, can be used to study the fission process. The fission theory was successfully applied to compute the Q-values and the life-times of the alpha decay. Good agreement (within +-0.8 orders of magnitude) of the theoretical half-lives with experimental ones, over a range of 24 orders of magnitude was obtained. This is a strong argument that the alpha decay could be considered a fission process with very high mass asymmetry and charge density asymmetry. (author)
Fission dynamics within time-dependent Hartree-Fock: deformation-induced fission
Goddard, P M; Rios, A
2015-01-01
Background: Nuclear fission is a complex large-amplitude collective decay mode in heavy nuclei. Microscopic density functional studies of fission have previously concentrated on adiabatic approaches based on constrained static calculations ignoring dynamical excitations of the fissioning nucleus, and the daughter products. Purpose: To explore the ability of dynamic mean-field methods to describe fast fission processes beyond the fission barrier, using the nuclide $^{240}$Pu as an example. Methods: Time-dependent Hartree-Fock calculations based on the Skyrme interaction are used to calculate non-adiabatic fission paths, beginning from static constrained Hartree-Fock calculations. The properties of the dynamic states are interpreted in terms of the nature of their collective motion. Fission product properties are compared to data. Results: Parent nuclei constrained to begin dynamic evolution with a deformation less than the fission barrier exhibit giant-resonance-type behaviour. Those beginning just beyond the ...
The contrasting fission potential-energy structure of actinides and mercury isotopes
Ichikawa, Takatoshi; Iwamoto, Akira; Möller, Peter; Sierk, Arnold J.
2012-01-01
Fission-fragment mass distributions are asymmetric in fission of typical actinide nuclei for nucleon number $A$ in the range $228 \\lnsim A \\lnsim 258$ and proton number $Z$ in the range $90\\lnsim Z \\lnsim 100$. For somewhat lighter systems it has been observed that fission mass distributions are usually symmetric. However, a recent experiment showed that fission of $^{180}$Hg following electron capture on $^{180}$Tl is asymmetric. We calculate potential-energy surfaces for a typical actinide ...
Calculations of fission rates for r-process nucleosynthesis
Panov, I V; Pfeiffer, B; Rauscher, T; Kratz, K L; Thielemann, F K
2005-01-01
Fission plays an important role in the r-process which is responsible not only for the yields of transuranium isotopes, but may have a strong influence on the formation of the majority of heavy nuclei due to fission recycling. We present calculations of beta-delayed and neutron-induced fission rates, taking into account different fission barriers predictions and mass formulae. It is shown that an increase of fission barriers results naturally in a reduction of fission rates, but that nevertheless fission leads to the termination of the r-process. Furthermore, it is discussed that the probability of triple fission could be high for $A>260$ and have an effect on the formation of the abundances of heavy nuclei. Fission after beta-delayed neutron emission is discussed as well as different aspects of the influence of fission upon r-process calculations.
Change over from compound nuclear fission to quasi-fission
Bhattacharya P; Golda K. S.; Rana T. K.; Mukhopadhyay S; Mukherjee G; Meena J. K.; Kundu S.; Bhattacharya S; Bhattacharya C.; Banerjee K; Ghosh T. K.
2010-01-01
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. T...
International Nuclear Information System (INIS)
Recent experimental results for spontaneous fission half-lives and fission fragment mass and kinetic-energy distributions and other properties of the fragments are reviewed and compared with recent theoretical models. The experimental data lend support to the existence of the predicted deformed shells near Z = 108 and N = 162. Prospects for extending detailed studies of spontaneous fission properties to elements beyond hahnium (element 105) are considered. (orig.)
Velocity fluctuations of fission fragment.
Llanes Estrada, Felipe José; Martínez Carmona, Belén; Muñoz Martínez, José L.
2016-01-01
We propose event by event velocity fluctuations of nuclear fission fragments as an additional interesting observable that gives access to the nuclear temperature in an independent way from spectral measurements and relates the diffusion and friction coefficients for the relative fragment coordinate in Kramers-like models (in which some aspects of fission can be understood as the diffusion of a collective variable through a potential barrier). We point out that neutron emission by the heavy fr...
Fission of actinides through quasimolecular shapes
Royer, Guy; Zhang, Hongfei; Eudes, Philippe; Moustabchir, Rachid; Moreau, Damien; Jaffré, Muriel; Morabit, Youssef; Particelli, Benjamin
2013-12-01
The potential energy of heavy nuclei has been calculated in the quasimolecular shape path from a generalized liquid drop model including the proximity energy, the charge and mass asymmetries and the microscopic corrections. The potential barriers are multiple-humped. The second maximum is the saddle-point. It corresponds to the transition from compact one-body shapes with a deep neck to two touching ellipsoids. The scission point lies at the end of an energy plateau well below the saddle-point and where the effects of the nuclear attractive forces between two separated fragments vanish. The energy on this plateau is the sum of the kinetic and excitation energies of the fragments. The shell and pairing corrections play an essential role to select the most probable fission path. The potential barrier heights agree with the experimental data and the theoretical half-lives follow the trend of the experimental values. A third peak and a shallow third minimum appear in asymmetric decay paths when one fragment is close to a double magic quasi-spherical nucleus, while the smaller one changes from oblate to prolate shapes.
Fission of actinides through quasimolecular shapes
Directory of Open Access Journals (Sweden)
Royer Guy
2013-12-01
Full Text Available The potential energy of heavy nuclei has been calculated in the quasimolecular shape path from a generalized liquid drop model including the proximity energy, the charge and mass asymmetries and the microscopic corrections. The potential barriers are multiple-humped. The second maximum is the saddle-point. It corresponds to the transition from compact one-body shapes with a deep neck to two touching ellipsoids. The scission point lies at the end of an energy plateau well below the saddle-point and where the effects of the nuclear attractive forces between two separated fragments vanish. The energy on this plateau is the sum of the kinetic and excitation energies of the fragments. The shell and pairing corrections play an essential role to select the most probable fission path. The potential barrier heights agree with the experimental data and the theoretical half-lives follow the trend of the experimental values. A third peak and a shallow third minimum appear in asymmetric decay paths when one fragment is close to a double magic quasi-spherical nucleus, while the smaller one changes from oblate to prolate shapes.
Spontaneous fission of the superheavy nucleus 286Fl
Poenaru, D. N.; Gherghescu, R. A.
2016-07-01
The decimal logarithm of spontaneous fission half-life of the superheavy nucleus 286Fl experimentally determined is log10Tfexp(s ) =-0.632 . We present a method to calculate the half-life based on the cranking inertia and the deformation energy, functions of two independent surface coordinates, using the best asymmetric two center shell model. Spherical shapes are assumed. In the first stage we study the statics. At a given mass asymmetry up to about η =0.5 the potential barrier has a two hump shape, but for larger η it has only one hump. The touching point deformation energy versus mass asymmetry shows the three minima, produced by shell effects, corresponding to three decay modes: spontaneous fission, cluster decay, and α decay. The least action trajectory is determined in the plane (R ,η ) , where R is the separation distance of the fission fragments and η is the mass asymmetry. We may find a sequence of several trajectories one of which gives the least action. The parametrization with two deformation coordinates (R ,η ) and the radius of the light fragment, R2, exponentially or linearly decreasing with R is compared with the simpler one, in which R2=constant and with a linearly decreasing or linearly increasing R2. The latter is closer to the reality and reminds us about the α or cluster preformation at the nuclear surface.
Fission properties of Po isotopes in different macroscopic-microscopic models
Bartel, J.; Pomorski, K.; Nerlo-Pomorska, B.; Schmitt, Ch
2015-11-01
Fission-barrier heights of nuclei in the Po isotopic chain are investigated in several macroscopic-microscopic models. Using the Yukawa-folded single-particle potential, the Lublin-Strasbourg drop (LSD) model, the Strutinsky shell-correction method to yield the shell corrections and the BCS theory for the pairing contributions, fission-barrier heights are calculated and found in quite good agreement with the experimental data. This turns out, however, to be only the case when the underlying macroscopic, liquid-drop (LD) type, theory is well chosen. Together with the LSD approach, different LD parametrizations proposed by Moretto et al are tested. Four deformation parameters describing respectively elongation, neck-formation, reflectional-asymmetric, and non-axiality of the nuclear shape thus defining the so called modified Funny Hills shape parametrization are used in the calculation. The present study clearly demonstrates that nuclear fission-barrier heights constitute a challenging and selective tool to discern between such different macroscopic approaches.
Studies of exotic modes of fission in the lead region
International Nuclear Information System (INIS)
In a series of complementary experiments at the tandem of JAEA and at the mass-separator ISOLDE (CERN), new fission phenomena in the lead region of the chart of nuclei were investigated. At ISOLDE, the low-energy fission of 194,196Po was studied via the process of beta-delayed fission of the parent 194,196At nuclei. A multi-modal fission fragment mass split was observed for 194,196Po. At JAEA the higher-energy fusion-fission studies of 198Hg, 191,193Ir were performed in reactions with protons and 7Li. In the JAEA experiment, we observed a transition from mass-symmetric to mass asymmetric fission between 189Ir and 193Ir. By studying fission in these regions, we investigate the new evolution of shell structure to regulate fission (as far as fission is concerned) of the chart of nuclides. (author)
Fission dynamics within time-dependent Hartree-Fock: Deformation-induced fission
Goddard, Philip; Stevenson, Paul; Rios, Arnau
2015-11-01
Background: Nuclear fission is a complex large-amplitude collective decay mode in heavy nuclei. Microscopic density functional studies of fission have previously concentrated on adiabatic approaches based on constrained static calculations ignoring dynamical excitations of the fissioning nucleus and the daughter products. Purpose: We explore the ability of dynamic mean-field methods to describe fast fission processes beyond the fission barrier, using the nuclide Pu240 as an example. Methods: Time-dependent Hartree-Fock calculations based on the Skyrme interaction are used to calculate nonadiabatic fission paths, beginning from static constrained Hartree-Fock calculations. The properties of the dynamic states are interpreted in terms of the nature of their collective motion. Fission product properties are compared to data. Results: Parent nuclei constrained to begin dynamic evolution with a deformation less than the fission barrier exhibit giant-resonance-type behavior. Those beginning just beyond the barrier explore large-amplitude motion but do not fission, whereas those beginning beyond the two-fragment pathway crossing fission to final states which differ according to the exact initial deformation. Conclusions: Time-dependent Hartree-Fock is able to give a good qualitative and quantitative description of fast fission, provided one begins from a sufficiently deformed state.
Superfluid dynamics of 258Fm fission
Scamps, Guillaume; Simenel, Cédric; Lacroix, Denis
2015-01-01
Theoretical description of nuclear fission remains one of the major challenges of quantum many-body dynamics. The slow, mostly adiabatic motion through the fission barrier is followed by a fast, non-adiabatic descent of the potential between the fragments. The latter stage is essentially unexplored. However, it is crucial as it generates most of the excitation energy in the fragments. The superfluid dynamics in the latter stage of fission is obtained with the time-dependent Hartree-Fock theor...
International Nuclear Information System (INIS)
The base of this experimental work is the study of the fusion-evaporation reactions for the compound nuclei 51Ni, 60Ni, 62Ni formed by symmetrical and asymmetrical entrance channels at energies near and below of the Coulomb barrier. The absolute cross sections were determined by means of in-beam γ-ray spectroscopy technique associated with the use of a turning target. Six fusion excitation functions have been established corresponding to the measurements of about 2000 absolute cross sections. The experimental errors are of the order of 10-20%. The excitation functions for complete fusion are analysed with a semi-classical model, and fusion barriers, radii and potential curvatures are extracted. The data are compared with the predictions of several heavy ion potentials. The enhancement of the fusion cross sections at sub-barrier energies can be reproduced either by one dimensional barrier penetration taking into account the zero point motion of the reaction partners, or by quantum mechanical calculations with two degrees of freedom indicating the presence of neck formation is sub-barrier fusion. It seems that the formation of these compound nuclei is limited neither by the entrance channels nor by the Yrast line. The Hauser-Feshbach statistical model (Cascade calculation) predictions for the deexcitation of the compound nuclei agree sufficiently with the data for the exit channels having an intensity superior to 10% of the fusion cross section. On the other hand, a systematic underestimation of the 2α decay mode is observed. A correct parametrization of the entrance channel transmission coefficients does not improve significantly the agreement between the measured and calculated evaporation residue cross sections
Proton-induced fission on 241Am, 238U and 237Np at intermediate energies
Deppman, A.; Andrade-II, E.; Guimaraes, V; Karapetyan, G. S.; Balabekyan, A. R.; Demekhina, N. A.
2013-01-01
Intermediate energy data of proton-induced fission on 241Am, 238U and 237Np targets were analysed and investigated using the computational simulation code CRISP. Inelastic interactions of protons on heavy nuclei and both symmetric and asymmetric fission are regarded. The fission probabilities are obtained from the CRISP code calculations by means of the Bohr-Wheeler model. The fission cross sections, the fissility and the number of nucleons evaporated by the nuclei, before and after fission, ...
Isotopic yield in cold binary fission of even-even 244-258Cf isotopes
Santhosh, K. P.; Cyriac, Annu; Krishnan, Sreejith
2016-05-01
The cold binary fission of even-even 244-258Cf isotopes has been studied by taking the interacting barrier as the sum of Coulomb and proximity potential. The favorable fragment combinations are obtained from the cold valley plot (plot of driving potential vs. mass number of fragments) and by calculating the yield for charge minimized fragments. It is found that for 244,246,248Cf isotopes highest yield is for the fragments with isotope of Pb (Z = 82) as one fragment, whereas for 250Cf and 252Cf isotopes the highest yield is for the fragments with isotope of Hg (Z = 80) as one fragment. In the case of 254,256,258Cf isotopes the highest yield is for the fragments with Sn (Z = 50) as one fragment. Thus, the fragment combinations with maximum yield reveal the role of doubly magic and near doubly magic nuclei in binary fission. It is found that asymmetric splitting is favored for Cf isotopes with mass number A ≤ 250 and symmetric splitting is favored for Cf isotopes with A > 252. In the case of Cf isotope with A = 252, there is an equal probability for asymmetric and symmetric splitting. The individual yields obtained for the cold fission of 252Cf isotope are compared with the experimental data taken from the γ- γ- γ coincidences technique using Gammasphere.
Fatigue in asymmetric-field-driven ferroelectric thin films
International Nuclear Information System (INIS)
The polarization fatigue problems in asymmetric-field-driven ferroelectric thin films is investigated in present Letter. The refreshment of fatigue induced by the application of asymmetric voltage to the top and bottom electrodes is modeled by asymmetric Schottky voltage barrier of a quantum well structure. The fatigue behavior under various asymmetric driving voltages and asymmetric driving pulses have been studied. Theoretical calculations are shown to be in agreement with experimental results
The effect of atomic electrons on nuclear fission
Dzuba, V. A.; Flambaum, V. V.
2008-01-01
We calculate correction to the nuclear fission barrier produced by the atomic electrons. The result presented in analytical form is convenient to use in future nuclear calculations. The atomic electrons have a small stabilizing effect on nuclei, increasing lifetime in nuclear fission channel. This effect gives a new instrument to study the fission process.
Fission Characteristics of Heavy Nuclei: Statics and Dynamics
Back, Birger B.
1999-01-01
This paper presents a selective historical perspective of fission research over the last thirty-five years while Ray Nix has made central contributions to the field. The emphasis is placed on early studies of the shell stabilized secondary minimum in the static fission barrier and on the dynamic properties of fission of hot nuclei, which have recently been the focus of intense study.
Bimodal fission in the Skyrme-Hartree-Fock approach
Staszczak, A.; Dobaczewski, J.; Nazarewicz, W.
2006-01-01
Spontaneous-fission properties of 256Fm, 258Fm, and 260Fm isotopes are studied within the Skyrme-Hartree-Fock+BCS framework. In the particle-hole channel we take the Skyrme SkM* effective force, while in the particle-particle channel we employ the seniority pairing interaction. Three static fission paths for all investigated heavy fermium isotopes are found. The analysis of these fission modes allows to describe observed asymmetric fission of 256Fm, as well as bimodal fission of 258Fm and sym...
Geometrical and statistical factors in fission of small metal clusters
Obolensky, O. I.; Lyalin, A. G.; Solov'yov, A. V.; Greiner, W.
2005-01-01
Fission of metastable charged univalent metal clusters has been studied on example of Na_{10}^{2+} and Na_{18}^{2+} clusters by means of density functional theory methods. Energetics of the process, i.e. dissociation energies and fission barriers, as well as its dynamics, i.e. fission pathways, have been analyzed. The dissociation energies and fission barriers have been calculated for the full range of fission channels for the Na_{10}^{2+} cluster. The impact of cluster structure on the fissi...
International Nuclear Information System (INIS)
The fission fragment properties of the reaction 238U(n,f) have been studied, at different incident neutron energies ranging from En=1.2 to 5.8 MeV. The pre-neutron emission mass, kinetic energy and fission fragment angular distributions have been investigated with a double Frisch-gridded ionization chamber. The influence of the subthreshold vibrational resonances and of the proton pairing effect on the fission fragment properties is clearly visible. The total kinetic energy averaged over all fission fragment masses TKEbar shows an increasing trend up to En=3.5 MeV with a sudden drop at roughly En=3.8 MeV which has been attributed to the onset of pair breaking at the barrier. Above En=3.8 MeV, the TKEbar is again continuously increasing. The changes in the mass yield and TKEbar(A) distributions have been studied as a function of the compound nuclear excitation energy and their contribution to the observed variations in the TKEbar have been determined. The two-dimensional mass-TKE distributions have been described in terms of fission modes and compared with theoretical calculations performed recently in the frame of the multi-modal random neck-rupture model. Although theoretically six asymmetric fission modes are predicted which all surpass individual outer barriers, an interpretation in terms of only two asymmetric modes has physical meaning. This points to an influence of shell structure effects to the observed distributions. In any case, the super-long symmetric mode has to be included, in order to explain the dip in TKEbar(A) distribution close to symmetry
Vivès, F.; Hambsch, F.-J.; Bax, H.; Oberstedt, S.
2000-01-01
The fission fragment properties of the reaction 238U(n,f) have been studied, at different incident neutron energies ranging from En=1.2 to 5.8 MeV. The pre-neutron emission mass, kinetic energy and fission fragment angular distributions have been investigated with a double Frisch-gridded ionization chamber. The influence of the subthreshold vibrational resonances and of the proton pairing effect on the fission fragment properties is clearly visible. The total kinetic energy averaged over all fission fragment masses ( overlineTKE) shows an increasing trend up to En=3.5 MeV with a sudden drop at roughly En=3.8 MeV which has been attributed to the onset of pair breaking at the barrier. Above En=3.8 MeV, the overlineTKE is again continuously increasing. The changes in the mass yield and overlineTKE( A) distributions have been studied as a function of the compound nuclear excitation energy and their contribution to the observed variations in the overlineTKE have been determined. The two-dimensional mass-TKE distributions have been described in terms of fission modes and compared with theoretical calculations performed recently in the frame of the multi-modal random neck-rupture model. Although theoretically six asymmetric fission modes are predicted which all surpass individual outer barriers, an interpretation in terms of only two asymmetric modes has physical meaning. This points to an influence of shell structure effects to the observed distributions. In any case, the super-long symmetric mode has to be included, in order to explain the dip in overlineTKE( A) distribution close to symmetry.
Zhao, Jie; Lu, Bing-Nan; Nikšić, Tamara; Vretenar, Dario; Zhou, Shan-Gui
2016-04-01
Background: Studies of fission dynamics, based on nuclear energy density functionals, have shown that the coupling between shape and pairing degrees of freedom has a pronounced effect on the nonperturbative collective inertia and, therefore, on dynamic (least-action) spontaneous fission paths and half-lives. Purpose: The aim is to analyze the effects of particle-number fluctuation degrees of freedom on symmetric and asymmetric spontaneous fission (SF) dynamics, and to compare the findings with the results of recent studies based on the self-consistent Hartree-Fock-Bogoliubov (HFB) method. Methods: Collective potentials and nonperturbative cranking collective inertia tensors are calculated using the multidimensionally-constrained relativistic-mean-field (MDC-RMF) model. Pairing correlations are treated in the BCS approximation using a separable pairing force of finite range. Pairing fluctuations are included as a collective variable using a constraint on particle-number dispersion. Fission paths are determined with the dynamic programming method by minimizing the action in multidimensional collective spaces. Results: The dynamics of spontaneous fission of 264Fm and 250Fm are explored. Fission paths, action integrals, and corresponding half-lives computed in the three-dimensional collective space of shape and pairing coordinates, using the relativistic functional DD-PC1 and a separable pairing force of finite range, are compared with results obtained without pairing fluctuations. Results for 264Fm are also discussed in relation with those recently obtained using the HFB model. Conclusions: The inclusion of pairing correlations in the space of collective coordinates favors axially symmetric shapes along the dynamic path of the fissioning system, amplifies pairing as the path traverses the fission barriers, significantly reduces the action integral, and shortens the corresponding SF half-life.
Effects of fissioning nuclei distributions on fragment mass distributions for high energy fission
Directory of Open Access Journals (Sweden)
Rossi P C R
2012-02-01
Full Text Available We study the effects of fissioning nuclei mass- and energy-distributions on the formation of fragments for fission induced by high energy probes. A Monte Carlo code called CRISP was used for obtaining mass distributions and spectra of the fissioning nuclei for reactions induced by 660 MeV protons on 241Am and on 239Np, by 500 MeV protons on 208Pb, and by Bremsstrahlung photons with end-point energies at 50 MeV and 3500 MeV on 238U. The results show that even at high excitation energies, asymmetric fission may still contribute significantly to the fission cross section of actinide nuclei, while it is the dominante mode in the case of lead. However, more precise data for high energy fission on actinide are necessary in order to allow definite conclusions.
Theoretical Description of the Fission Process
Energy Technology Data Exchange (ETDEWEB)
Witold Nazarewicz
2003-07-01
The main goals of the project can be summarized as follows: Development of effective energy functionals that are appropriate for the description of heavy nuclei. Our goal is to improve the existing energy density (Skyrme) functionals to develop a force that will be used in calculations of fission dynamics. Systematic self-consistent calculations of binding energies and fission barriers of actinide and trans-actinide nuclei using modern density functionals. This will be followed by calculations of spontaneous fission lifetimes and mass and charge divisions using dynamic adiabatic approaches based on the WKB approximation. Investigate novel microscopic (non-adiabatic) methods to study the fission process.
Theoretical Description of the Fission Process
International Nuclear Information System (INIS)
The main goals of the project can be summarized as follows: Development of effective energy functionals that are appropriate for the description of heavy nuclei. Our goal is to improve the existing energy density (Skyrme) functionals to develop a force that will be used in calculations of fission dynamics. Systematic self-consistent calculations of binding energies and fission barriers of actinide and trans-actinide nuclei using modern density functionals. This will be followed by calculations of spontaneous fission lifetimes and mass and charge divisions using dynamic adiabatic approaches based on the WKB approximation. Investigate novel microscopic (non-adiabatic) methods to study the fission process
Fission properties for r-process nuclei
Erler, J.; Langanke, K; Loens, H. P.; Martínez-Pinedo, G.; Reinhard, P.-G.
2011-01-01
We present a systematics of fission barriers and fission lifetimes for the whole landscape of super-heavy elements (SHE), i.e. nuclei with Z>100. The fission lifetimes are also compared with the alpha-decay half-lives. The survey is based on a self-consistent description in terms of the Skyrme-Hartree-Fock (SHF) approach. Results for various different SHF parameterizations are compared to explore the robustness of the predictions. The fission path is computed by quadrupole constrained SHF. Th...
Revisiting the even-odd staggering in fission fragment yields
Caamano, M.; Rejmund, F.; Schmidt, K. -H.
2009-01-01
The even-odd staggering observed in the experimental fission-fragment nuclear-charge yields is investigated over a wide systematics of fission fragments measured at Lohengrin in direct kinematics and at GSI in inverse kinematics. The general increase of the even-odd staggering in the fission-fragment charge yields towards asymmetric charge splits is explained by the absorption of the unpaired nucleons by the heavy fragment. As a consequence, the well established trend of evenodd staggering in...
Shaker, Ahmed; Ossaimee, Mahmoud; Zekry, A.
2016-08-01
In this paper, a proposed structure based on asymmetrical double pockets SB-TFET with gate-drain underlap is presented. 2D extensive modeling and simulation, using Silvaco TCAD, were carried out to study the effect of both underlap length and pockets' doping on the transistor performance. It was found that the underlap from the drain side suppresses the ambipolar conduction and doesn't enhance the high-frequency characteristics. The enhancement of the high-frequency characteristics could be realized by increasing the doping of the drain pocket over the doping of the source pocket. An optimum choice was found which gives the conditions of minimum ambipolar conduction, maximum ON current and maximum cut-off frequency. These enhancements render the device more competitive as a nanometer transistor.
Indian Academy of Sciences (India)
M Balasubramaniam; K R Vijayaraghavan; C Karthikraj
2015-09-01
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 middle fragment and the two end fragments. The obtained results for the 16O accompanying ternary fission indicate that collinear configuration is preferred to equatorial configuration. Further, for all the possible third fragments, the potential energy surface (PES) is calculated corresponding to an arrangement in which the heaviest and the lightest fragments are considered at the end in a collinear configuration. The PES reveals several possible ternary modes including true ternary modes where the three fragments are of similar size. The complete mass distributions of Si and Ca which accompanied ternary fission of 236U is studied within a level density picture. The obtained results favour several possible ternary combinations.
International Nuclear Information System (INIS)
In this work we are reporting the energy level spectrum for a quantum system consisting of an n-type double δ-doped quantum well with a Schottky barrier potential in a Gallium Arsenide matrix. The calculated states are taken as the basis for the evaluation of the linear and third-order nonlinear contributions to the optical absorption coefficient and to the relative refractive index change, making particular use of the asymmetry of the potential profile. These optical properties are then reported as a function of the Schottky barrier height (SBH) and the separation distance between the δ-doped quantum wells. Also, the effects of the application of hydrostatic pressure are studied. The results show that the amplitudes of the resonant peaks are of the same order of magnitude of those obtained in the case of single δ-doped field effect transistors; but tailoring the asymmetry of the confining potential profile allows the control the resonant peak positions
Energy Technology Data Exchange (ETDEWEB)
Rojas-Briseño, J.G.; Martínez-Orozco, J.C.; Rodríguez-Vargas, I. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad esquina con Paseo la Bufa S/N, C.P. 98060, Zacatecas, Zac. (Mexico); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico); Instituto de Física, Universidad de Antioquia, AA 1226, Medellín (Colombia); Duque, C.A., E-mail: cduque@fisica.udea.edu.co [Instituto de Física, Universidad de Antioquia, AA 1226, Medellín (Colombia)
2013-09-01
In this work we are reporting the energy level spectrum for a quantum system consisting of an n-type double δ-doped quantum well with a Schottky barrier potential in a Gallium Arsenide matrix. The calculated states are taken as the basis for the evaluation of the linear and third-order nonlinear contributions to the optical absorption coefficient and to the relative refractive index change, making particular use of the asymmetry of the potential profile. These optical properties are then reported as a function of the Schottky barrier height (SBH) and the separation distance between the δ-doped quantum wells. Also, the effects of the application of hydrostatic pressure are studied. The results show that the amplitudes of the resonant peaks are of the same order of magnitude of those obtained in the case of single δ-doped field effect transistors; but tailoring the asymmetry of the confining potential profile allows the control the resonant peak positions.
New results on the spectroscopy and dynamics of fission
International Nuclear Information System (INIS)
The present status of Coulomb fission experiments is discussed. Probabilities for fission induced by the purely electromagnetic interaction between heavy ions are compared for the systems Sm + U, W + U, W + Cm, and W + Th. Experimental results on the moments of inertia, spins, and quadrupole moments of fission isomers are summarized. Data are presented that prove their large deformation and thereby justify their interpretation as shape isomers in the second minimum of a double-humped fission barrier. 21 figures, 2 tables
The measurement of extreme nuclear deformation of fission isomers
International Nuclear Information System (INIS)
Existence and properties of spontaneously fissioning isomers are discussed as consequences of a double fission barrier. The measurement of the quadrupole moment of the fission-isomeric state by the new developed method for the determination of lifetimes of excited states yields to a prolate shape of the the nucleus. The deformation ratio is 2:1 in the second minimum of the fission potential. (orig./WL)
Exotic fission properties of highly neutron-rich Uranium isotopes
Satpathy, L.; Patra, S.K.; Choudhury, R. K.
2007-01-01
The series of Uranium isotopes with $N=154 \\sim 172$ around the magic number N=162/164 are identified to be thermally fissile. The thermal neutron fission of a typical representative $^{249}$U of this region amenable to synthesis in the radioactive ion beam facilities is considered here. Semiempirical study of fission barrier height and width shows this nucleus to be infinitely stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. Calculation of p...
Fission fragment mass distribution in the 13C+182W and 176Yb reactions
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 180Hg following electron capture of 180Tl 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 ...
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.
Bloch, F.; Staub, H.
1943-08-18
Measurements of the spectrum of the fission neutrons of 25 are described, in which the energy of the neutrons is determined from the ionization produced by individual hydrogen recoils. The slow neutrons producing fission are obtained by slowing down the fast neutrons from the Be-D reaction of the Stanford cyclotron. In order to distinguish between fission neutrons and the remaining fast cyclotron neutrons both the cyclotron current and the pusle amplifier are modulated. A hollow neutron container, in which slow neutrons have a lifetime of about 2 milliseconds, avoids the use of large distances. This method results in much higher intensities than the usual modulation arrangement. The results show a continuous distribution of neutrons with a rather wide maximum at about 0.8 MV falling off to half of its maximum value at 2.0 MV. The total number of netrons is determined by comparison with the number of fission fragments. The result seems to indicate that only about 30% of the neutrons have energies below .8 MV. Various tests are described which were performed in order to rule out modification of the spectrum by inelastic scattering. Decl. May 4, 1951
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 ostatní: 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
DEFF Research Database (Denmark)
Christiansen, Steen Ledet
materialisation of an ideological fission which attempts to excise certain ideological constructions, yet paradoxically casting them in a form that is recognizable and familiar. The monstrous metonomy which is used shows us glimpses of a horrid being, intended to vilify the attack on New York City. However, it is...
Fission dynamics study in 243Am and 254Fm
Banerjee, K.; Ghosh, T. K.; Roy, P.; Bhattacharya, S.; Chaudhuri, A.; Bhattacharya, C.; Pandey, R.; Kundu, S.; Mukherjee, G.; Rana, T. K.; Meena, J. K.; Mohanto, G.; Dubey, R.; Saneesh, N.; Sugathan, P.; Guin, R.; Das, S.; Bhattacharya, P.
2016-06-01
Fission fragment mass distributions in the reactions 11B + 232Th and 11B + 243Am were measured in an energy range around the barrier. No sudden change in the width of the mass distribution as a function of center-of-mass energy was observed at near-barrier energies, indicating no quasifission transition in the near-barrier energies. Interestingly, the previous measurements of fission fragment angular anisotropies for the same systems showed significant departure from the statistical saddle-point model predictions at near-barrier energies, indicating the presence of nonequilibrium fission processes.
Velocity fluctuations of fission fragments
Llanes-Estrada, Felipe J; Martinez, Jose L Muñoz
2015-01-01
We propose event by event velocity fluctuations of nuclear fission fragments as an additional interesting observable that gives access to the nuclear temperature in an independent way from spectral measurements and relates the diffusion and friction coefficients for the relative fragment coordinate in Kramer-like models (in which some aspects of fission can be understood as the diffusion of a collective variable through a potential barrier). We point out that neutron emission by the heavy fragments can be treated in effective theory if corrections to the velocity distribution are needed.
Velocity fluctuations of fission fragments
Llanes-Estrada, Felipe J.; Carmona, Belén Martínez; Martínez, Jose L. Muñoz
2016-02-01
We propose event by event velocity fluctuations of nuclear fission fragments as an additional interesting observable that gives access to the nuclear temperature in an independent way from spectral measurements and relates the diffusion and friction coefficients for the relative fragment coordinate in Kramers-like models (in which some aspects of fission can be understood as the diffusion of a collective variable through a potential barrier). We point out that neutron emission by the heavy fragments can be treated in effective theory if corrections to the velocity distribution are needed.
New formulas for TKE release in nuclear fission process
International Nuclear Information System (INIS)
New TKE formulas that will replace the previous existing ones are obtained. Recently, three types of the final deformation of fissioning nuclei were found for actinides out off which only one was observed. The final deformations of the fissioning nuclei was found to be constant and independent of the mass and temperature of the fissioning system. These hence allow to deduce a new formula for the TKE release in nuclear fission process based on the invariance of scission deformations of fissioning nuclei. They yield, TKE(sym) = 0.1173 x (Zf2/Af1/3)+7.5 MeV for the symmetric fission and TKE(asym) = 0.1217 x (Zf2/Af1/3)+3.5 MeV for the asymmetric fission. Details for the new formulas and their comparison with the experimental data are given. (author)
International Nuclear Information System (INIS)
In nuclear reactions where a compound nucleus is formed at high excitation energies, one is forced to use a statistical theory to explain the observables of the reaction. The statistical theory of fission of Weisskopf-Ewing-Newton and Ericson is applied to binary spallation of 16O, 20Ne, and 14N by protons in the proton energy range of 20 to 150 MeV, 0 to 105 MeV, and 0 to 41.9 MeV, respectively. The capture cross section of the incident proton is calculated from the reaction cross section using appropriate optical model potentials. The differential and total cross sections for binary fragmentation into near symmetric mass nuclei are calculated which are in reasonable agreement with experimental results. The kinetic energy spectrum and decay widths in the final channels are also calculated, however these have not been measured experimentally for comparison. All of these calculations are done using three different ion-ion optical potentials suggested by others. One then reformulated the statistical theory to include the second law of thermodynamics. Both theories are applied to neutron induced fission of 239Pu, 235U, 233U, 229Th, and 226Ra at several different neutron and alpha energies using the recently proposed external barrier between the saddle and the scission point. The transmission functions are calculated using a set of coupled equations in the exit channels. The computed results indicate that the model can account for the observed variation of the percentage mass yield spectra. Furthermore one calculated the most probable kinetic energy in the fission in all cases and found it to agree with the observation. The spontaneous and isomer fission half lives are calculated giving good agreement with experimental data. The kinetic energy spectrums are also computed for some representative daughter pairs. The inclusion of the second law of thermodynamics improves the agreement between theory and experiment
Properties of fission fragments for Z =112 -116 superheavy nuclei
Kaur, Gurjit; Sandhu, Kirandeep; Sharma, Manoj K.
2016-07-01
The dynamical cluster decay model (DCM) is applied to understand the dynamics of 48Ca+238U,244Pu,248Cm reactions at comparable excitation energies across the barrier. To understand the capture stage of *286112 ,*292114 , and *296116 nuclei, the compound nucleus formation probability is calculated. The indication of PC Nprocess such as quasifission may occur at the capture stage of the 48Ca induced reactions. To understand this further, the comparative decay analysis of *286112 ,*292114 and *296116 , nuclei is carried out using β2 i deformations within hot optimum orientation criteria, and the calculated fission cross sections find nice agreement with available data. The fission mass distribution shows a double humped structure where a symmetric peak observed around the Sn region appears to find its genesis in a symmetric quasifission component. On the other hand, the emergence of peaks around Pb in the decay of Z =112 , 114, and 116 nuclei signify the possible presence of asymmetric quasifission. Higher and broader asymmetric quasifission peaks are observed for *296116 and *292114 nuclei as compared to *286112 nucleus. Beside this, the total kinetic energy (TKE) distribution of the decay fragments is also explored by using different proximity potentials, such as Prox-77, Prox-88, and Prox-00. Prox-88 seems to perform better and the calculated TKE values find relatively better comparison at lower angular momentum states. The possible role of different radii of the decaying nuclei is also exercised to understand the TKE ¯ dynamics of 48Ca+238U,244Pu,248Cm reactions.
Rowland, Mark S.; Snyderman, Neal J.
2012-04-10
A neutron detector system for discriminating fissile material from non-fissile material wherein a digital data acquisition unit collects data at high rate, and in real-time processes large volumes of data directly into information that a first responder can use to discriminate materials. The system comprises counting neutrons from the unknown source and detecting excess grouped neutrons to identify fission in the unknown source.
International Nuclear Information System (INIS)
In order to highlight the sensitivity of the fission observables to the potential energy surface, we have carried out statistical model calculations with three different options: a. liquid drop mass (MLD) and liquid drop fission barrier (BLD), b. experimental mass (Mexp = MLD + Δn) along with a damping of the shell correction at the ground state (Δn) with excitation energy and shell corrected fission barrier (BLD-Δn), c. experimental mass and liquid drop fission barrier
Fission of heavy $\\Lambda$ hypernuclei with the Skyrme-Hartree-Fock approach
Minato, F.; Chiba, S.; Hagino, K.
2009-01-01
Fission-related phenomena of heavy $\\Lambda$ hypernuclei are discussed with the constraint Skyrme-Hartree-Fock+BCS (SHF+BCS) method, in which a similar Skyrme-type interaction is employed also for the interaction between a $\\Lambda$ particle and a nucleon. Assuming that the $\\Lambda$ particle adiabatically follows the fission motion, we discuss the fission barrier height of $^{239}_{\\Lambda}$U. We find that the fission barrier height increases slightly when the $\\Lambda$ particle occupies the...
Some aspects of fission and quasifission processes
Indian Academy of Sciences (India)
B B Back
2015-08-01
The discovery of nuclear fission in 1938–1939 had a profound influence on the field of nuclear physics and it brought this branch of physics into the forefront as it was recognized for having the potential for its seminal influence on modern society. Although many of the basic features of actinide fission were described in a ground-breaking paper by Bohr and Wheeler only six months after the discovery, the fission process is very complex and it has been a challenge for both experimentalists and theorists to achieve a complete and satisfactory understanding of this phenomenon. Many aspects of nuclear physics are involved in fission and it continues to be a subject of intense study even three quarters of a century after its discovery. In this talk, I will review an incomplete subset of the major milestones in fission research, and briefly discuss some of the topics that I have been involved in during my career. These include studies of vibrational resonances and fission isomers that are caused by the second minimum in the fission barrier in actinide nuclei, studies of heavy-ion-induced fission in terms of the angular distributions and the mass–angle correlations of fission fragments. Some of these studies provided evidence for the importance of the quasifission process and the attendant suppression of the complete fusion process. Finally, some of the circumstances around the establishment of large-scale nuclear research in India will be discussed.
Isotopic yield in cold binary fission of even-even $^{244-258}$Cf isotopes
Santhosh, K P; Krishnan, Sreejith
2016-01-01
The cold binary fission of even-even 244-258Cf isotopes has been studied by taking the interacting barrier as the sum of Coulomb and proximity potential. The favorable fragment combinations are obtained from the cold valley plot (plot of driving potential vs. mass number of fragments) and by calculating the yield for charge minimized fragments. It is found that highest yield for 244,246,248Cf isotopes are for the fragments with isotope of Pb (Z=82) as one fragment, whereas for 250Cf and 252Cf isotopes the highest yield is for the fragments with isotope of Hg (Z=80) as one fragment. In the case of 254,256,258Cf isotopes the highest yield is for the fragments with Sn (Z=50) as one fragment. Thus, the fragment combinations with maximum yield reveal the role of doubly magic and near doubly magic nuclei in binary fission. It is found that asymmetric splitting is favoured for Cf isotopes with mass number A 252. In the case of Cf isotope with A=252, there is an equal probability for asymmetric and symmetric splitti...
Fission dynamics within time-dependent Hartree-Fock: boost-induced fission
Goddard, P M; Rios, A
2015-01-01
Background: Nuclear fission is a complex large-amplitude collective decay mode in heavy nuclei. Microscopic density functional studies of fission have previously concentrated on adiabatic approaches based on constrained static calculations ignoring dynamical excitations of the fissioning nucleus, and the daughter products. Purpose: To explore the ability of dynamic mean-field methods to describe induced fission processes, using quadrupole boosts in the nuclide $^{240}$Pu as an example. Methods: Quadrupole constrained Hartree-Fock calculations are used to create a potential energy surface. An isomeric state and a state beyond the second barrier peak are excited by means of instantaneous as well as temporally extended gauge boosts with quadrupole shapes. The subsequent deexcitation is studied in a time-dependent Hartree-Fock simulation, with emphasis on fissioned final states. The corresponding fission fragment mass numbers are studied. Results: In general, the energy deposited by the quadrupole boost is quickl...
Above-threshold structure in {sup 244}Cm neutron-induced fission cross section
Energy Technology Data Exchange (ETDEWEB)
Maslov, V.M. [Radiation Physics and Chemistry Problems Inst., Minsk-Sosny (Belarus)
1997-03-01
The quasi-resonance structure appearing above the fission threshold in neutron-induced fission cross section of {sup 244}Cm(n,f) is interpreted. It is shown to be due to excitation of few-quasiparticle states in fissioning {sup 245}Cm and residual {sup 244}Cm nuclides. The estimate of quasiparticle excitation thresholds in fissioning nuclide {sup 245}Cm is consistent with pairing gap and fission barrier parameters. (author)
Role of the zero-point corrections in fission dynamics
International Nuclear Information System (INIS)
The way of evaluating spontaneous fission half-lives of nuclei in a multidimensional deformation space is discussed. The cranking as well as the generator coordinate method were used to obtain the collective inertia tensor and the 'zero-point' corrections to the fission barriers. The fission probability was evaluated within the WKB approximation along the least-action trajectory to fission. The influence on the fission life-times of the dynamics in the pairing degrees of freedom as well as the effect of the higher even-multipolarity shape parameters and the role of the reflection asymmetry is examined. (author)
Superfluid dynamics of 258Fm fission
Scamps, Guillaume; Lacroix, Denis
2015-01-01
Theoretical description of nuclear fission remains one of the major challenges of quantum many-body dynamics. The slow, mostly adiabatic motion through the fission barrier is followed by a fast, non-adiabatic descent of the potential between the fragments. The latter stage is essentially unexplored. However, it is crucial as it generates most of the excitation energy in the fragments. The superfluid dynamics in the latter stage of fission is obtained with the time-dependent Hartree-Fock theory including BCS dynamical pairing correlations. The fission modes of the 258Fm nucleus are studied. The resulting fission fragment characteristics show a good agreement with experimental data. Quantum shell effects are shown to play a crucial role in the dynamics and formation of the fragments. The importance of quantum fluctuations beyond the independent particle/quasi-particle picture is underlined and qualitatively studied.
Calculated medium energy fission cross sections
International Nuclear Information System (INIS)
An analysis has been made of medium-energy nucleon induced fission of 238U and 237Np using detailed models of fission, based upon the Bohr-Wheeler formalism. Two principal motivations were associated with these calculations. The first was determination of barrier parameters for proton-rich uranium and neptunium isotopes normally not accessible in lower energy reactions. The second was examination of the consistency between (p,f) experimental data versus new (n,f) data that has recently become available. Additionally, preliminary investigations were also made concerning the effect of fission dynamics on calculated fission cross sections at higher energies where neutron emission times may be significantly less than those associated with fission
Neutron emission prior to fission
International Nuclear Information System (INIS)
In recent years, many groups have measured neutrons and light charged particles in coincidence with fission fragments in heavy ion reactions. In most cases, particles emitted with an energy spectrum and angular distribution characteristic of that of compound nucleus evaporation have been measured in excess of statistical model predictions. They have chosen to investigate this effect in detail by studying neutron emission in the 158Er composite system. The advantage of this system is that it can be produced by a variety of projectile target combinations. They have chosen four combinations which form 158Er with similar critical angular momenta but varying excitation energy. The rationale is to form the same system with different neutron emission times; if the enhanced neutrons are being emitted during the fission process, the different emission time scales might possibly be used to time the fission process. In addition, they impose an additional constraint - that they have a significant fission barrier for most of the partial waves involved in the fission process. The reactions they have selected are 16O + 142Nd (207 MeV beam energy), 24Mg + 134Ba (180 MeV), 32S + 126Te (180 MeV), 50Ti + 108Pd (216 MeV)
Rearrangement of cluster structure during fission processes
DEFF Research Database (Denmark)
Lyalin, Andrey G.; Obolensky, Oleg I.; Solov'yov, Andrey V.;
2004-01-01
groups of atoms from the parent cluster is largely independent of the isomer form of the parent cluster. The importance of rearrangement of the cluster structure during the fission process is elucidated. This rearrangement may include transition to another isomer state of the parent cluster before actual......Results of molecular dynamics simulations of fission reactions $Na_10^2+ -->Na_7^++ Na_3^+ and Na_18^2+--> 2Na_9^+ are presented. The dependence of the fission barriers on the isomer structure of the parent cluster is analysed. It is demonstrated that the energy necessary for removing homothetic...
Asymmetry of fission fragment mass distribution for Po and Ir isotopes
Andreev, A. V.; Adamian, G. G.; Antonenko, N. V.
2016-03-01
Using the improved scission-point model, the mass distributions are calculated for induced fission of several Po and Ir isotopes. The calculated mass distributions and mean total kinetic energies of fission fragments are compared with the existing experimental data. The revealed coexistence of both symmetric and asymmetric modes in the β -delayed fission of At,196194 is in agreement with the experimental observations. The change of the shape of mass distribution with increasing A of fissioning AIr nucleus from asymmetric for 185Ir to symmetric for 193Ir is found.
International Nuclear Information System (INIS)
The study of CP violation in beauty decay is one of the key challenges facing high energy physics. Much work has not yielded a definitive answer how this study might best be performed. However, one clear conclusion is that new accelerator facilities are needed. Proposals include experiments at asymmetric electron-positron colliders and in fixed-target and collider modes at LHC and SSC. Fixed-target and collider experiments at existing accelerators, while they might succeed in a first observation of the effect, will not be adequate to study it thoroughly. Giomataris has emphasized the potential of a new approach to the study of beauty CP violation: the asymmetric proton collider. Such a collider might be realized by the construction of a small storage ring intersecting an existing or soon-to-exist large synchrotron, or by arranging collisions between a large synchrotron and its injector. An experiment at such a collider can combine the advantages of fixed-target-like spectrometer geometry, facilitating triggering, particle identification and the instrumentation of a large acceptance, while the increased √s can provide a factor > 100 increase in beauty-production cross section compared to Tevatron or HERA fixed-target. Beams crossing at a non-zero angle can provide a small interaction region, permitting a first-level decay-vertex trigger to be implemented. To achieve large √s with a large Lorentz boost and high luminosity, the most favorable venue is the high-energy booster (HEB) at the SSC Laboratory, though the CERN SPS and Fermilab Tevatron are also worth considering
Theoretical Description of the Fission Process
International Nuclear Information System (INIS)
Advanced theoretical methods and high-performance computers may finally unlock the secrets of nuclear fission, a fundamental nuclear decay that is of great relevance to society. In this work, we studied the phenomenon of spontaneous fission using the symmetry-unrestricted nuclear density functional theory (DFT). Our results show that many observed properties of fissioning nuclei can be explained in terms of pathways in multidimensional collective space corresponding to different geometries of fission products. From the calculated collective potential and collective mass, we estimated spontaneous fission half-lives, and good agreement with experimental data was found. We also predicted a new phenomenon of trimodal spontaneous fission for some transfermium isotopes. Our calculations demonstrate that fission barriers of excited superheavy nuclei vary rapidly with particle number, pointing to the importance of shell effects even at large excitation energies. The results are consistent with recent experiments where superheavy elements were created by bombarding an actinide target with 48-calcium; yet even at high excitation energies, sizable fission barriers remained. Not only does this reveal clues about the conditions for creating new elements, it also provides a wider context for understanding other types of fission. Understanding of the fission process is crucial for many areas of science and technology. Fission governs existence of many transuranium elements, including the predicted long-lived superheavy species. In nuclear astrophysics, fission influences the formation of heavy elements on the final stages of the r-process in a very high neutron density environment. Fission applications are numerous. Improved understanding of the fission process will enable scientists to enhance the safety and reliability of the nation's nuclear stockpile and nuclear reactors. The deployment of a fleet of safe and efficient advanced reactors, which will also minimize radiotoxic
Heavy ion fusion and fission reactions
International Nuclear Information System (INIS)
Various methods of probing the partial wave distribution are reviewed and new results using fission fragment angular distributions are discussed. Evidence that existing models of fusion reactions near-barrier and sub-barrier energies underestimate the mean-square spin values are presented. The dynamics of fusion reactions at higher energies are also discussed. The controversy over the interpretation of fission fragment and angular distributions are reviewed. Both statistical scission models and dynamical models with incomplete K mixing are discussed. New developments related to the effective moment of inertia of the saddlepoint shape are presented
Energy Technology Data Exchange (ETDEWEB)
Goeoek, Alf
2012-11-05
The photofission of {sup 232}Th, {sup 234}U and {sup 238}U at excitation energies in the barrier region has been studied. The goal has been to extract information on the mass, total kinetic energy (TKE) and angular distributions of the fission fragments. The experiments were performed using bremsstrahlung, produced by an electron beam in a copper radiator at the injector of the Superconducting Darmstadt linear accelerator (S-DALINAC). Mass and TKE distributions were determined by means of the double kinetic energy technique using a twin Frisch grid ionization chamber. The angular distributions were derived simultaneously by measuring the drift time of ionization electrons. Results show that this drift-time method is comparable in accuracy to other more commonly used methods, but with a simplified procedure for setting up the experiment. Mass, TKE and angular distributions have been obtained from bremsstrahlung-induced fission of {sup 232}Th at average excitation energies left angle E{sub x} right angle =6.68 MeV and 7.26 MeV, for {sup 234}U at left angle E{sub x} right angle =5.80 MeV, 6.49 MeV and 7.23 MeV, and for {sup 238}U at left angle E{sub x} right angle =5.90 MeV, 6.11 MeV and 6.93 MeV. Results on fission fragment characteristics from {sup 238}U({gamma},f) show good agreement with literature data, which verifies the experimental procedure. The correlated mass and TKE data have been analyzed in terms of fission modes within the multi-modal random-neck-rupture model. The result exhibits a dominant yield of the mass asymmetric standard-2 mode in all the investigated fissioning nuclei, with a relative yield of {proportional_to}77 % in {sup 232}Th, {proportional_to}75 % in {sup 234}U and {proportional_to}67 % in {sup 238}U. No strong fluctuation of the mode yields were found as a function of the excitation energy. Correlations between mass, TKE and angular distributions have been investigated in {sup 232}Th and {sup 234}U. The correlation takes the form of an
Detection efficiencies of solid state nuclear track detectors for fission fragments
International Nuclear Information System (INIS)
Detection efficiencies of solid state nuclear track detectors (SSNTDs) for fission fragments have been calibrated with the help of Au-Si surface barrier detector and fission chamber. The results obtained for thin fission source are given for muscovite mica; polycarbonate foil; polyester; phosphate glass; silicate glass; and quartz. Corrections have been made for the effect of backscattering of fission fragments by Au-Si surface barrier detector on the detection efficiencies with a special designed arrangement using SSNTD. The effects of backscattering of fission fragments on detection efficiencies range from 0 for silicate glass to 2.6% for polycarbonate foil (Chaoyan) for using Au-Si as backing material. A discussion was given to the effect of critical angles of SSNTDs on the correction for self absorption of fission fragments in thick fission sources. A formula is given to calculate the detection efficiency of SSNTDs for fission fragments from fission sources of various thickness. (author)
Al-Adili A.; Fabry I.; Borcea R.; Zeynalov S.; Kornilov N.; Hambsch F.-J.; Oberstedt S.
2010-01-01
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.
Geometrical and statistical factors in fission of small metal clusters
Obolensky, O I; Solovyov, A V; Greiner, W
2005-01-01
Fission of metastable charged univalent metal clusters has been studied on example of Na_{10}^{2+} and Na_{18}^{2+} clusters by means of density functional theory methods. Energetics of the process, i.e. dissociation energies and fission barriers, as well as its dynamics, i.e. fission pathways, have been analyzed. The dissociation energies and fission barriers have been calculated for the full range of fission channels for the Na_{10}^{2+} cluster. The impact of cluster structure on the fission process has been elucidated. The calculations show that the geometry of the smaller fragment and geometry of its immediate neighborhood in the larger fragment play a leading role in defining the fission barrier height. The present study demonstrates importance of rearrangement of the cluster structure during fission. It may include forming a neck between the two fragments or fissioning via another isomer state of the parent cluster; examples of such processes are given. For several low-lying isomers of Na_{10}^{2+} clu...
Active matter on asymmetric substrates
Olson Reichhardt, C. J.; Drocco, J.; Mai, T.; Wan, M. B.; Reichhardt, C.
2011-10-01
For collections of particles in a thermal bath interacting with an asymmetric substrate, it is possible for a ratchet effect to occur where the particles undergo a net dc motion in response to an ac forcing. Ratchet effects have been demonstrated in a variety of systems including colloids as well as magnetic vortices in type-II superconductors. Here we examine the case of active matter or self-driven particles interacting with asymmetric substrates. Active matter systems include self-motile colloidal particles undergoing catalysis, swimming bacteria, artificial swimmers, crawling cells, and motor proteins. We show that a ratchet effect can arise in this type of system even in the absence of ac forcing. The directed motion occurs for certain particle-substrate interaction rules and its magnitude depends on the amount of time the particles spend swimming in one direction before turning and swimming in a new direction. For strictly Brownian particles there is no ratchet effect. If the particles reflect off the barriers or scatter from the barriers according to Snell's law there is no ratchet effect; however, if the particles can align with the barriers or move along the barriers, directed motion arises. We also find that under certain motion rules, particles accumulate along the walls of the container in agreement with experiment. We also examine pattern formation for synchronized particle motion. We discuss possible applications of this system for self-assembly, extracting work, and sorting as well as future directions such as considering collective interactions and flocking models.
Modelisation of the fission cross section
International Nuclear Information System (INIS)
The neutron cross sections of four nuclear systems (n+235U, n+233U, n+241Am and n+237Np) are studied in the present document. The target nuclei of the first case, like 235U and 239Pu, have a large fission cross section after the absorption of thermal neutrons. These nuclei are called 'fissile' nuclei. The other type of nuclei, like 237Np and 241Am, fission mostly with fast neutrons, which exceed the fission threshold energy. These types of nuclei are called 'fertile'. The compound nuclei of the fertile nuclei have a binding energy higher than the fission barrier, while for the fissile nuclei the binding energy is lower than the fission barrier. In this work, the neutron induced cross sections for both types of nuclei are evaluated in the fast energy range. The total, reaction and shape-elastic cross sections are calculated by the coupled channel method of the optical model code ECIS, while the compound nucleus mechanism are treated by the statistical models implemented in the codes STATIS, GNASH and TALYS. The STATIS code includes a refined model of the fission process. Results from the theoretical calculations are compared with data retrieved from the experimental data base EXFOR. (author)
Sharp change over from compound nuclear fission to shape dependent quasi fission
Ghosh, T.K.; Banerjee, K.; C. Bhattacharya; Bhattacharya, S.(Brown University, Providence, USA); Kundu, S.; Mali, P.; Meena, J. K.; Mukherjee, G.; Mukhopadhyay, S.; Rana, T. K.; Bhattacharya, P; Golda, K. S.
2008-01-01
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...
Heavy-ion-induced fission reactions
International Nuclear Information System (INIS)
Fission-cross-section excitation functions were measured from near threshold to approx. 10 MeV/nucleon using heavy-ion beams from the Brookhaven National Laboratory three-stage Tandem Accelerator Facility. The systems studied included 210Po formed in 12C and 18O induced reactions, 186Os formed in 9Be, 12C, 16O, and 26Mg reactions, 158Er formed in 16O, 24Mg, 32S, and 64Ni reactions. In addition the composite systems 204206, 208Po formed with 16O and 18O projectiles were studied. The measured fission excitation functions along with previous data from 4He and 11B bombardments for the 186Os and 210Po systems and recent data on the 200Pb system are compared to predictions from a statistical model using recent fission-barrier calculations from A. Sierk. Comparisons of calculated and measured fission excitation functions show good overall agreement between data and calculations and between calculations with two different level-density functions. It is concluded that the barriers from Sierk give a good description of both the mass and angular momentum dependence of fission barriers in this region
Indian Academy of Sciences (India)
B K Nayak; E T Mirgule; R K Choudhury
2005-12-01
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 compared with the other conventional methods adopted to identify fission fragments with solid-state detectors such as - telescope and single thin detector and the data for the 10B + 232Th fission reaction are presented. Results demonstrate the usefulness of a single transmission-type surface barrier detector for the identification of fission fragments and projectiles like heavy ions.
International Nuclear Information System (INIS)
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)
Dynamical features of Coulomb-fission
International Nuclear Information System (INIS)
Fission following quasielastic scattering was investigated in the reactions 208Pb -> 238U below the Coulomb Barrier and 7.5 MeV/u 238U -> 238U at scattering angles forward of the grazing angle (870). A kinematically complete analysis of 3-body coincidences was carried out measuring position and time-of-flight of the scattered projectile-like particle and 2 fission fragments in large parallel plate detectors. In the reaction 208Pb -> 238U, measured at backward angles, the slope of the differential cross section at 5.4 MeV/u is in qualitative agreement with the theoretical expectation for Coulomb-fission. The angular distribution of the fission fragments, measured with respect to the semisector axis (apex line towards the projectile), is close to 1/sinTHETA and does not show any of the significant structures predicted by several theories. The anisotropy is smaller in all other coordinate systems investigated. The fission probability in the reaction 238U -> 238U, measured down to 5x10-4 at THETAsub(cm)=540 (corresponding to 75% Esub(cb) at the distance of closest approach) as well as the low excitation energy 0 as expected for Coulomb-fission. The absence of a detectable final state Coulomb interaction yields a lower limit of 1-2x10-20s for the lifetime of the fissioning nucleus. (orig./HSI)
Multimodal nuclear fission model and its application
International Nuclear Information System (INIS)
As the nuclear fission models, the following are explained: random-neck rupture model; nuclear fission channel theory; breakpoint model, especially breakpoint model by Wilkins et al.; and multimodal random-neck rupture model. In addition, the prompt neutron spectrum analysis of multimodal model, and the application to the energy-dependent analysis of delayed neutron yield are also described. In the random-neck fracture model proposed by S. L. Whetstone, a nucleus has a form like 'elongated gourd' just before the rupture, and the mass distribution is determined by the part of the neck where cleavage occurs. The division of mass and charge in nuclear fission, according to the nuclear fission channel theory, is considered to be determined by which transition state the saddle point of fission barrier is passed through. On the other hand, the model, where the deformation of nucleus further proceeds and the division is determined by the breakpoint just before the division to two fissure pieces, is called the breakpoint model. The multimodal nuclear fission model is the concept to consider that there are several deformation channels for nucleus, and that each of them leads to a different rupture state. The model that combines the random-neck rapture model and multimodal fission model is the multimodal random-neck rupture model. (J.P.N.)
Spontaneous Muon Emission during Fission, a New Nuclear Radioactivity
Ion, D. B.; Ion, M. L. D.; Ion-Mihai, Reveica
2011-01-01
In this paper the essential theoretical predictions for the nuclear muonic radioactivity are presented by using a special fission-like model similar with that used in description of the pionic emission during fission. Hence, a fission-like model for the muonic radioactivity takes into account the essential degree of freedom of the system: muon-fissility, muon-fission barrier height, etc. Using this model it was shown that most of the SHE-nuclei lie in the region where the muonic fissility par...
Metal cluster fission: jellium model and Molecular dynamics simulations
DEFF Research Database (Denmark)
Lyalin, Andrey G.; Obolensky, Oleg I.; Solov'yov, Ilia;
2004-01-01
^2+ --> 2 Na_9^+ are presented. Dependence of the fission barriers on isomer structure of the parent cluster is analyzed. Importance of rearrangement of the cluster structure during the fission process is elucidated. This rearrangement may include transition to another isomer state of the parent cluster......Fission of doubly charged sodium clusters is studied using the open-shell two-center deformed jellium model approximation and it ab initio molecular dynamic approach accounting for all electrons in the system. Results of calculations of fission reactions Na_10^2+ --> Na_7^+ + Na_3^+ and Na_18...
Modelling the widths of fission observables in GEF
Directory of Open Access Journals (Sweden)
Schmidt K.-H.
2013-03-01
Full Text Available The widths of the mass distributions of the different fission channels are traced back to the probability distributions of the corresponding quantum oscillators that are coupled to the heat bath, which is formed by the intrinsic degrees of freedom of the fissioning system under the influence of pairing correlations and shell effects. Following conclusion from stochastic calculations of Adeev and Pashkevich, an early freezing due to dynamical effects is assumed. It is shown that the mass width of the fission channels in low-energy fission is strongly influenced by the zero-point motion of the corresponding quantum oscillator. The observed variation of the mass widths of the asymmetric fission channels with excitation energy is attributed to the energy-dependent properties of the heat bath and not to the population of excited states of the corresponding quantum oscillator.
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...
Neutron-induced fission cross sections of short-lived actinides via the surrogate reaction method
International Nuclear Information System (INIS)
A brief discussion of surrogate reaction methods has been made and some of the recent results on neutron induced fission cross section measurements have been presented. The validation of the EMPIRE-3.1. predictions on neutron induced cross sections corresponding to fission barriers used from Barrier Formula (BF) and RIPL-1 libraries have been discussed
Influence of entrance-channel magicity and isospin on quasi-fission
Simenel, Cédric; Hinde, D. J.; Du Rietz, R.; Dasgupta, M.; Evers, M.; C. J. Lin; Luong, D. H.; Wakhle, A.
2011-01-01
The role of spherical quantum shells in the competition between fusion and quasi-fission is studied for reactions forming heavy elements. Measurements of fission fragment mass distributions for different reactions leading to similar compound nuclei have been made near the fusion barrier. In general, more quasi-fission is observed for reactions with non-magic nuclei. However, the $^{40}$Ca+$^{208}$Pb reaction is an exception, showing strong evidence for quasi-fission, though both nuclei are do...
International Nuclear Information System (INIS)
Mass yields from fission induced by a span of neutron energies up to 18 MeV have been measured for Th232, U235 and U238 target nuclei. Particular attention has been given to the dependence of symmetric fission yields on energy. To study the effect of angular momentum, fission yields from the U236 compound nucleus formed by alpha-particle irradiations of Th232 were also studied over the same span of excitation energies. A standard set of Pd109, Ag111, Pd112 and Ag113 symmetric fission yields was generally measured for all irradiations. In addition, yields of Eu156, Cs136 and 2.3-d Cd115 were measured for some selected combinations of projectile, energy and target nucleus. Assays for Zr97 and sometimes also Ba139 served as fission monitors. Altogether 150 fission yields were measured for these combinations of target nucleus, projectile and incident energy. About one-third of these were checked by replicated irradiations. At highest energies for the U236 compound nucleus the symmetric fission yield from alpha-particle-induced fission is about 13% higher than for neutron-induced fission. Dips in symmetric fission yield were observed at the energy onset of third-chance fission for each target and projectile. Some indication of a small central peak in the mass distribution was observed in the yields from U236 compound nucleus fission, but not from the Th233 compound nucleus fission. Detailed mathematical methods have been developed to separate the effects of fissions preceding and following neutron emission. These methods were used to remove the effects of second- and third-chance fissions from the measured symmetric fission yields. These calculated yields for first-chance fission show no dips with energy. The calculations also show that perhaps half the difference between symmetric yields for alpha- particle-induced fission of Th232 and neutron-induced fission of U235 is attributable to angular momentum effects. Both calculated first-chance yields and measured yields
2006-11-01
that oscillate in certain directions. Reflection or scattering of light favours certain orientations of the electric and magnetic fields over others. This is why polarising sunglasses can filter out the glint of sunlight reflected off a pond. When light scatters through the expanding debris of a supernova, it retains information about the orientation of the scattering layers. If the supernova is spherically symmetric, all orientations will be present equally and will average out, so there will be no net polarisation. If, however, the gas shell is not round, a slight net polarisation will be imprinted on the light. This is what broad-band polarimetry can accomplish. If additional spectral information is available ('spectro-polarimetry'), one can determine whether the asymmetry is in the continuum light or in some spectral lines. In the case of the Type Ia supernovae, the astronomers found that the continuum polarisation is very small so that the overall shape of the explosion is crudely spherical. But the much larger polarization in strongly blue-shifted spectral lines evidences the presence, in the outer regions, of fast moving clumps with peculiar chemical composition. "Our study reveals that explosions of Type Ia supernovae are really three-dimensional phenomena," says Dietrich Baade. "The outer regions of the blast cloud is asymmetric, with different materials found in 'clumps', while the inner regions are smooth." "This study was possible because polarimetry could unfold its full strength thanks to the light-collecting power of the Very Large Telescope and the very precise calibration of the FORS instrument," he adds. The research team first spotted this asymmetry in 2003, as part of the same observational campaign (ESO PR 23/03 and ESO PR Photo 26/05). The new, more extensive results show that the degree of polarisation and, hence, the asphericity, correlates with the intrinsic brightness of the explosion. The brighter the supernova, the smoother, or less clumpy
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.
Pomorski, Krzysztof; Ivanyuk, Fedir A
2016-01-01
The fission-fragments mass-yield of 236U 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 the mass-asymmetry mode. 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 the 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 the 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 that final fragment mass distribution.
Tunneling process in heavy-ion fusion and fission
Energy Technology Data Exchange (ETDEWEB)
Iwamoto, Akira [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Kondratyev, V.; Bonasera, A.
1998-10-01
We present a model towards the many-body description of sub-barrier fusion and spontaneous fission based on the semiclassical Vlasov equation and the Feynman path integral method. We define suitable collective variables from the Vlasov solution and use the imaginary time technique for the dynamics below the Coulomb barrier. (author)
Dynamics in heavy ion fusion and fission
International Nuclear Information System (INIS)
Dynamical aspects of heavy ion fussion and fission, mainly the aspect of damping which is meant as the dissipation of kinetic energy and the aspect of the effective mass of the fission motion, are discussed. Two categories of evidence of damping effects are given. One relates to the damping of the fission motion for the ground state shape and for the isomeric more elongated shape. The other relates to the damping of the fission motion from the last barrier to the scission point. The dependence of the effective mass associated with the fission motion on the deormation of nucleus is shown. As the elongation of the nucleus increases the effective mass of the fission motion varies strongly from being about forty times greater than the reduced mass in the beta-vibrational state of the ground state shape to being equal to the reduced mass in the moment of scission. Damping effects are expected to be propartional to the difference between the effective mass and the reduced mass. It is concluded that the damping in fussion reactions is relatively weak for lighter products and quite strong for superheavy products like 236U or 252Cf. (S.B.)
Influence of spin on fission fragments anisotropy
Directory of Open Access Journals (Sweden)
Ghodsi Omid N.
2005-01-01
Full Text Available An analysis of selected fission fragment angular distribution when at least one of the spins of the projectile or target is appreciable in induced fission was made by using the statistical scission model. The results of this model predicate that the spins of the projectile or target are affected on the nuclear level density of the compound nucleus. The experimental data was analyzed by means of the couple channel spin effect formalism. This formalism suggests that the projectile spin is more effective on angular anisotropies within the limits of energy near the fusion barrier.
Dynamic properties of the Coulomb fission
International Nuclear Information System (INIS)
The heavy ion induced fission after quasi-elastic scattering was studied in the systems 208Pb -> 238U for central collision at energies below the Coulomb barrier and 238U -> 238U for peripheral collisions at scattering angles smaller than the grazing angle. The dynamical properties and the phase-space distributions of the reactions could be determined by the method of the kinematical coincidences where positions and time-of-flight of two fission fragments and a scattered projectile-like nucleus were measured at the same time in large-area gas-filled parallel plate counters. (orig./HSI)
Fission neutron statistical emission
International Nuclear Information System (INIS)
The statistical model approach FINESSE (FIssion NEutronS' Statistical Emission) for the description of fission neutron multiplicities, energy spectra and angular distributions is described. Based on an extended Weisskopf ansatz and on a realistic temperature distribution it provides a fragment mass number dependent description of fission neutron data. Model parameters (optical potential, n/γ competition) were fixed on the basis of the 252Cf(sf) (nuclear data standard). Combined with a phenomenological fission model for predicting relevant fragment data as function of asymmetry. FINESSE can be applied to any fission reaction of actinides in the Th-Cf region without further parameter adjustment. Results are presented for 252Cf(sf) and neutron induced fission of 235U, 239Pu, 232Th. Effects of multiple-chance fission are discussed for 232Th(n,xnf) reacation. (author). 46 refs, 11 figs
International Nuclear Information System (INIS)
In several cases of heavy ion induced fusion-fission reactions, the fission fragment angular distributions exhibit much larger anisotropies than predicted by the standard Halpern-Strutinsky theory. Several explanations have been put forward to interpret these anomalous angular distributions. One of them is that a characteristic signature of fission before full K-equilibration will be an entrance channel dependence of the fragment anisotropies for target-projectile combinations across the Businaro-Gallone ridge in the mass/charge asymmetry degree of freedom. To look for any such entrance channel dependence of fragment anisotropies, we have carried out measurements of fragment angular distributions in fission induced by boron, carbon, oxygen ions on thorium and neptunium targets and by fluorine ions on neptunium target at above barrier energies. (author). 7 refs., 1 fig
Fission decay properties of ultra neutron-rich uranium isotopes
Indian Academy of Sciences (India)
L Satpathy; S K Patra; R K Choudhury
2008-01-01
The fission decay of highly neutron-rich uranium isotopes is investigated which shows interesting new features in the barrier properties and neutron emission characteristics in the fission process. 233U and 235U are the nuclei in the actinide region in the beta stability valley which are thermally fissile and have been mainly used in reactors for power generation. The possibility of occurrence of thermally fissile members in the chain of neutron-rich uranium isotopes is examined here. The neutron number = 162 or 164 has been predicted to be magic in numerous theoretical studies carried out over the years. 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 the highly neutron-rich region. Semiempirical study of fission barrier height and width shows that 250U nucleus is stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. On the basis of the calculation of the probability of fragment mass yields and the microscopic study in relativistic mean field theory, this nucleus is shown to undergo exotic decay mode of thermal neutron fission (multi-fragmentation fission) whereby a number of prompt scission neutrons are expected to be simultaneously released along with the two heavy fission fragments. Such properties will have important implications in stellar evolution involving -process nucleosynthesis.
International Nuclear Information System (INIS)
This paper is an account of the work performed at the Oak Ridge Electron Linear Accelerator (ORELA), pertaining to the fission phenomena taking place at energies of the fissioning nucleus which are comparable to the fission barrier potential energy. In this energy region, fission cross-section measurements yield information on the physical properties of the barrier and on the nuclear states at high nuclear deformations. The ORELA facility intense pulsed neutron source and good energy resolution capabilities afford a convenient tool to carry out a program of measurements in the subthreshold and near-subthreshold regions. Extensive and precise measurements in the actinide region were performed at the ORELA facility by an international group of researchers. These measurements were unique in many respects: fission widths and areas were determined for many previously unreported resonances in the subthreshold region and a most detailed study was performed on the physical properties of the fission barrier at high nuclear deformations
Exciton Correlations in Intramolecular Singlet Fission.
Sanders, Samuel N; Kumarasamy, Elango; Pun, Andrew B; Appavoo, Kannatassen; Steigerwald, Michael L; Campos, Luis M; Sfeir, Matthew Y
2016-06-15
We have synthesized a series of asymmetric pentacene-tetracene heterodimers with a variable-length conjugated bridge that undergo fast and efficient intramolecular singlet fission (iSF). These compounds have distinct singlet and triplet energies, which allow us to study the spatial dynamics of excitons during the iSF process, including the significant role of exciton correlations in promoting triplet pair generation and recombination. We demonstrate that the primary photoexcitations in conjugated dimers are delocalized singlets that enable fast and efficient iSF. However, in these asymmetric dimers, the singlet becomes more localized on the lower energy unit as the length of the bridge is increased, slowing down iSF relative to analogous symmetric dimers. We resolve the recombination kinetics of the inequivalent triplets produced via iSF, and find that they primarily decay via concerted processes. By identifying different decay channels, including delayed fluorescence via triplet-triplet annihilation, we can separate transient species corresponding to both correlated triplet pairs and uncorrelated triplets. Recombination of the triplet pair proceeds rapidly despite our experimental and theoretical demonstration that individual triplets are highly localized and unable to be transported across the conjugated linker. In this class of compounds, the rate of formation and yield of uncorrelated triplets increases with bridge length. Overall, these constrained, asymmetric systems provide a unique platform to isolate and study transient species essential for singlet fission, which are otherwise difficult to observe in symmetric dimers or condensed phases. PMID:27183040
Nuclear fission viewed as a diffusion process: Case of very large friction
International Nuclear Information System (INIS)
Using a Fokker-Planck equation, we consider induced nuclear fission for large values of the friction constant. Then, the equation simplifies to the Smoluchowski equation which we solve using a method of van Kampen. We find that the fission rate obeys a scaling law. From our numerical results and those obtained previously, we estimate the transient time tau for fission. For small nuclear temperature, tau is defined as the time delay between the onset of a nuclear reaction and the attainment of the quasistationary probability flow over the fission barrier. For nuclear temperatures large compared to the fission barrier, the entire fission process is governed by transients, and tau essentially yields the fission lifetime. We speculate on the significance of our results for recent experimental observations
Evolution of fission-fragment mass distributions in the neutron-deficient lead region
Ghys, Lars; Andreyev, A.N.; Huyse, Mark; Van Duppen, Piet; Sels, Simon; Andel, B.; Antalic, S; Barzakh, A; Capponi, L.; Cocolios, Thomas Elias; Derkx, X.; De Witte, Hilde; J. Elseviers; Fedorov, D. V.; Fedosseev, V. N.
2014-01-01
Low-energy β-delayed fission of 194,196At and 200,202Fr was studied in detail at the mass separator ISOLDE at CERN. The fission-fragment mass distributions of daughter nuclei 194,196Po and 202Rn indicate a triple-humped structure, marking the transition between asymmetric fission of 178,180Hg and symmetric fission in the light Ra-Rn nuclei. Comparison with the macroscopic-microscopic finite-range liquid-drop model and the self-consistent approach employing the Gogny D1S energy den...
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Experimental studies of fast fission phenomena are presented. The paper is divided into three parts. In the first part, problems associated with fast fission processes are examined in terms of interaction potentials and a dynamic model is presented in which highly elastic collisions, the formation of compound nuclei and fast fission appear naturally. In the second part, a description is given of the experimental methods employed, the observations made and the preliminary interpretation of measurements suggesting the occurence of fast fission processes. In the third part, our dynamic model is incorporated in a general theory of the dissipative processes studied. This theory enables fluctuations associated with collective variables to be calculated. It is applied to highly inelastic collisions, to fast fission and to the fission dynamics of compound nuclei (for which a schematic representation is given). It is with these calculations that the main results of the second part can be interpreted
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Data are summed up necessary for determining the yields of individual fission products from different fissionable nuclides. Fractional independent yields, cumulative and isobaric yields are presented here for the thermal fission of 235U, 239Pu, 241Pu and for fast fission (approximately 1 MeV) of 235U, 238U, 239Pu, 241Pu; these values are included into the 5th version of the YIELDS library, supplementing the BIBFP library. A comparison is made of experimental data and possible improvements of calculational methods are suggested. (author)
3He- and 4He-induced nuclear fission -- A test of the transition state method
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Fission in 3H and 4He induced reactions at excitation energies between the fission barrier and 140 MeV has been investigated. Twenty-three fission excitation functions of various compound nuclei in different mass regions are shown to scale exactly according to the transition state prediction once the shell effects are accounted for. New precise measurements of excitation functions in a mass region where shell effects are very strong, allow one to test the predictions with an even higher accuracy. The fact that no deviations from the transition state method have been observed within the experimentally investigated excitation energy regime allows one to assign limits for the fission transient time. The precise measurement of fission excitation functions of neighboring isotopes enables one to experimentally estimate the first chance fission probability. Even if only first chance fission is investigated, no evidence for fission transient times larger than 30 zs can be found
Fission fragment angular distributions in proton-induced fission of 209 Bi(p,t) and 197 Au(p,f)
De, S S; N H; M. L.
2001-01-01
The fission fragment angular distributions have been measured for proton-induced fission of 209Bi and 197Au nuclei using surface barrier detectors at several energies between 25 MeV and 30 MeV. The experimental anisotropies are found to be in agreement with the predictions of the Standard Saddle-Point Statistical Model (SSPSM). The fission cross sections of 209Bi 197Au nuclei were also measured and compared with the previous works.
Fission fragment angular distributions in proton-induced fission of 209 Bi(p,t and 197 Au(p,f
Directory of Open Access Journals (Sweden)
S. S.
2001-12-01
Full Text Available The fission fragment angular distributions have been measured for proton-induced fission of 209Bi and 197Au nuclei using surface barrier detectors at several energies between 25 MeV and 30 MeV. The experimental anisotropies are found to be in agreement with the predictions of the Standard Saddle-Point Statistical Model (SSPSM. The fission cross sections of 209Bi 197Au nuclei were also measured and compared with the previous works.
The even-odd effect in fission-fragment Z yields – a new kind of nuclear clock
Jurado Beatriz; Schmidt Karl-Heinz
2013-01-01
A model for the even-odd effect in fission based on statistical mechanics is presented. It reveals that the variation of the even-odd effect with the mass of the fissioning nucleus and the increase towards asymmetric splits is due to the important statistical weight of configurations where the light fission fragment populates the ground state of an even-even nucleus. This implies that excitation energy and unpaired nucleons are predominantly transferred to the heavy fragment. Our results indi...
Schmidt, Karl-Heinz; Jurado, Beatriz
2010-01-01
The even-odd effect in fission is explained by a model based on statistical mechanics. It reveals that the variation of the even-odd effect with the mass of the fissioning nucleus and the increase towards asymmetric splits is due to the important statistical weight of configurations where the light fission fragment populates the ground state of an even-even nucleus. This implies that entropy drives excitation energy and unpaired nucleons predominantly to the heavy fragment. Therefore, the eve...
Nuclear fission induced by heavy ions
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Because the accelerators of the 50's and 60's mostly provided beams of light ions, well suited for studying individual quantum states of low angular momentum or reactions involving the transfer of one or two nucleons, the study of fission, being an example of large-scale collective motion, has until recently been outside of the mainstream of nuclear research. This situation has changed in recent years, due to the new generation of accelerators capable of producing beams of heavy ions with energies high enough to overcome the Coulomb barriers of all stable nuclei. These have made possible the study of new examples of large-scale collective motions, involving major rearrangements of nuclear matter, such as deep-inelastic collisions and heavy-ion fusion. Perhaps the most exciting development in the past few years is the discovery that dissipative effects (nuclear viscosity) play an important role in fission induced by heavy ions, contrary to earlier assumptions that the viscosity involved in fission was very weak and played only a minor role. This review will be mainly concerned with developments in heavy-ion induced fission during the last few years and have an emphasis on the very recent results on dissipative effects. Since heavy-ion bombardment usually results in compound systems with high excitation energies and angular momenta, shell effects might be expected to be small, and the subject of low energy fission, where they are important, will not be addressed. 285 refs., 58 figs
New fission valley for 258Fm and nuclei beyond
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Experimental results on the fission properties of nuclei close to 264Fm show sudden and large changes with a change of only one or two neutrons or protons. The nucleus 258Fm, for instance, undergoes symmetric fission with a half-life of about 0.4 ms and a kinetic energy peaked at about 235 MeV whereas 256Fm undergoes asymmetric fission with a half-life of about 3 h and a kinetic energy peaked at about 200 MeV. Qualitatively, these sudden changes hve been postulated to be due to the emergence of fragment shells in symmetric fission products close to 132Sn. A quantitative calculation that shows where high-kinetic-energy symmetric fission occurs and why it is associated with a sudden and large decrease in fission half-lives. The study is based on calculations of potential-energy surfaces in the macroscopic-microscopic model and a semi-empirical model for the nuclear inertia. The implications of the new fission valley on the stability of the heaviest elements is discussed. 33 refs., 12 figs
Calculation of fission reactions within the MM-RNR model
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In the past fission-fragment properties and cross-sections for 235,238U(n, f), 237Np(n, f), 239Pu(n, f) and 252Cf(SF) have been investigated. The interpretation of the experimental data in the frame of the multi-modal random neck-rupture (MM-RNR) model has been incorporated into the most recent evaluation exercise on neutron-induced fission cross-section and prompt-neutron emission data in the actinide region of the chart of nuclides. The three most dominant fission modes were considered, the two asymmetric standard I (S1) and standard II (S2) modes and the symmetric superlong (SL) mode, namely. Except for 252Cf, de-convoluted modal fission cross-sections as well as prompt neutron multiplicity and spectra have been calculated in the energy range from 0.01 MeV to 5.5 MeV in excellent agreement with experimental data. In addition, the obtained fission-mode branching ratios allow the calculation of fission-fragment yield and energy distributions where no experimental data exist. Most recently the first ever-direct measurement of the neutron-induced fission cross-section of 233Pa has been performed at IRMM. The subsequent evaluation suggests a radical revision of today's evaluated data files. (author)
Nuclear fission: What have we learned in 50 years?
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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
Fission decay of $^{282}$Cn studied using cranking inertia
Poenaru, D N
2014-01-01
Superheavy nuclei produced until now are decaying mainly by $\\alpha$~emission and spontaneous fission. Calculated $\\alpha$~decay half-lives are in agreement with experimental data within one order of magnitude. The discrepancy between theory and experiment can be as high as ten orders of magnitude for spontaneous fission. We analyze a way to improve the accuracy by using the action integral based on cranking inertia and a potential barrier computed by the macroscopic-microscopic method with a two-center shell model. Illustrations are given for $^{282}$Cn which has a measured fission half-life.
Fission decay of 282Cn studied using cranking inertia
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Superheavy nuclei produced until now are decaying mainly by α emission and spontaneous fission. Calculated α decay half-lives are in agreement with experimental data to within one order of magnitude. The discrepancy between theory and experiment can be as high as ten orders of magnitude for spontaneous fission. We analyze a way to improve the accuracy by using the action integral based on cranking inertia and a potential barrier computed by the macroscopic-microscopic method with a two-center shell model. Illustrations are given for 282Cn which has a measured fission half-life. (paper)
Analytic description of the fusion and fission processes through compact quasi-molecular shapes
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Recent studies have shown that the characteristics of the entrance and exit channels through compact quasi-molecular shapes are compatible with the experimental data on fusion, fission and cluster radioactivity when the deformation energy is determined within a generalized liquid drop model. Analytic expressions allowing to calculate rapidly the main characteristics of this deformation path through necked shapes with quasi-spherical ends are presented now; namely formulas for the fusion and fission barrier heights, the fusion barrier radius, the symmetric fission barriers and the proximity energy. (author)
Fission Distribution in Neutron-Induced Fission of Th230, Pu238 and Am241
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The angular distribution of fragments in the neutron-induced fission of Th230, Pu238 and Am241 was measured in-the neutron energy range 100 - 1200 keV. Measurements were also made for Am241 at neutron energies of 4 and 5 MeV, and the dependence of the fission cross-section of Pu238 on neutron energy in the 50 -1400 keV range was likewise determined. The partial fission cross-sections for the different K-bands were derived for Th230 on the basis of the angular distributions obtained, using fission cross-sections taken from another paper, and also the neutron capture cross-sections of the neutron permeabilities calculated by the optical coefficients of adhesion. The following band sequence was established: 1/2-, 3/2-, 3/2+ the energy interval between the bands is ∼ 100 keV. The pattern of the cross-section for band shows in the sub-barrier region (at a neutron energy of 860keV) the same dip as the total fission cross-section. This pattern in the sub-barrier region cannot be explained by the normal change in neutron width, as it can be in the case of fission above the barrier, and gives grounds for assuming the presence of some other mechanism powerfully affecting the fission cross-section. The angular distributions of the fragments can be explained satisfactorily only on the assumption that there is an energy shift between the individual states within the bands. This indicates that the widths of the levels at the saddle are probably less than the distances between the levels themselves. Assuming that the levels are rotatory, a value of about 4 keV is obtained for h2/2J. From analysing the anisotropy of Pu238 fission, we may assume the band sequence 1/2+, 3/2-, 1/2-. In the case of Am241 fission, the angular distributions show a weak energy dependence and little anisotropy; this is explained by the large number of participating states. The measurements at 4 and 5 MeV made it possible to determine the value of K20, and to compare it with the data for Np237. This
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A review of recent experimental results on negative-muon-induced fission, both of 238U and 232Th, is given. Some conclusions drawn by the author are concerned with muonic atoms of fission fragments and muonic atoms of the shape isomer of 238U. (author)
Colburn, Richard P.
1985-01-01
A device for collecting fission gas released by a failed fuel rod which device uses a filter to pass coolant but which filter blocks fission gas bubbles which cannot pass through the filter due to the surface tension of the bubble.
Mathew, K. J.; Marti, K.; Marty, B.
2002-01-01
Fission Xe components due to Pu-244 decay in the early history of Mars have been identified in nakhlites; as in the case of ALH84001 and Chassigny the fission gas was assimilated into indigenous solar-type Xe. Additional information is contained in the original extended abstract.
β-delayed fission and α decay of 178Tl
Liberati, V.; Andreyev, A.N.; Antalic, S; Barzakh, A; Cocolios, Thomas Elias; J. Elseviers; Fedorov, D.; Fedoseeev, V. N.; Huyse, Mark; Joss, D. T.; Kalaninova, Z.; Koster, U; Lane, J. F. W.; Marsh, B; Mengoni, D.
2013-01-01
A detailed nuclear-decay spectroscopy study of the neutron-deficient isotope 178Tl has been performed using the highly selective Resonance Ionization Laser Ion Source and ISOLDE mass separator (CERN), which allowed a unique isobarically pure beam of 178Tl to be produced. The first identification of the β-delayed fission of this isotope was made and its probability PβDF(178Tl) = 0.15(6)% was determined. An asymmetric fission fragment mass distribution of the daughter isotope 178Hg (populated b...
Fission properties of the BCPM energy-density functional
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Fission dynamics properties of the Barcelona-Catania-Paris-Madrid energy density functional are explored with mean-field techniques. Potential energy surfaces as well as collective inertia relevant in the fission process are computed for several nuclei where experimental data exist. Inner and outer barrier heights as well as fission isomer excitation energies are reproduced quite well in all the cases. The spontaneous fission half-lives tsf are also computed using the standard semiclassical approach and the results are compared with the experimental data. The experimental trend with mass number is reasonably well reproduced over a range of 27 orders of magnitude. However, the theoretical predictions suffer from large uncertainties when the quantities that enter the spontaneous fission half-life formula are varied. Modifications of only a few per cent in the pairing correlation strengths strongly modify the collective inertia with a large impact on the spontaneous fission lifetimes in all the nuclei considered. Encouraged by the quite satisfactory description of the trend of fission properties with mass number, we explore the fission properties of the even-even uranium isotope chain from 226U to 282U. Very large lifetimes are found beyond A = 256 with a peak at neutron number N = 184.
Shell Effects in Nuclear Fission
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the same deformation) are greater for magic than for non-magic nuclei. In fact, since the energy gain for magic spherical fragments is greater than the loss resulting from the increase in elasticity, the formation of magic and near-magic fragments, i.e. asymmetrical fission, is energetically advantageous. This energy gain is essentially connected with the fact that because of the high elasticity value at low deformations the magic fragments are so little deformed that the deformation energy does not compensate for the difference in mass of magic and non-magic fragments. Apart from the deformation energy, the kinetic energy of the separating degrees of freedom at the moment of scission should be taken into account when calculating the excitation energy of fragments. For the shell effects of the fragments to play an important part in fission, the process of deformation of the nucleus on descending from the saddle point (in the case of threshold fission) must be, as in fact it is, fairly slow with respect to the nucleonic degrees of freedom, i.e. τdef >> τnucleon (τdef is the descent time, τnucleon ∼ n/ΔEnucleon, and ΔEnucleon is the distance between the nucleon levels). In this case nucleonic shells are formed before scission. At the same time τdef rot, i.e. the process of descent is fast with respect to the rotational degrees of freedom (τrot h/ΔErot) - In the case of fission of an excited nucleus with fairly high excitation energy at the saddle point, ΔEnucleon may be so low that not only τdef rot but also τdef nucleon, i.e. the process of descent is accelerated with respect to all the degrees of freedom. In this case the density matrix of the nucleus does not change on moving from the saddle point. This would seem to explain the fact that the theoretical angular distribution of fragments at fission of an excited nucleus agrees with the experimental value only when the parameters determining the rotational state of the nucleus (moment of inertia) at the
Fission Fragments Discriminator
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Nuclear fission reaction between Uranium-235 nucleus and thermal neutron caused the high energy fission fragments with uncertainly direction. The particle direction discrimination was determined. The 2.5 x 3.0 mm2 polyethylene gratings with 1-6 mm thickness were used. The grating was placed between uranium screen that fabricated from ammonium-diurinate compound and polycarbonate nuclear track film recorder irradiated by neutron from Thai Research Reactor (TRR-1/M1) facility. The nuclear track density was inversely with grating thickness. It's only fission fragments normal to uranium screen pass through film recorder when grating thickness was 4-6 mm
Thermal quenching of electronic shells and channel competition in cluster fission
Yannouleas, Constantine; Landman, Uzi; Brechignac, C.; Cahuzac, Ph.; Concina, B.; Leygnier, J.
2002-01-01
Experimental and theoretical studies of fission of doubly-charged Li, Na, and K clusters in the low fissility regime reveal the strong influence of electronic shell effects on the fission products. The electronic entropy controls the quenching of the shell effects and the competition between magic-fragment channels, leading to a transition from favored channels of higher mass symmetry to the asymmetric channel involving the trimer cation at elevated temperatures.
Fission fragment rocket concept
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A new propulsion scheme is outlined which may permit interstellar missions for spacecraft. This scheme is based on the idea of allowing fission fragments to escape from the core of a nuclear reactor. (orig.)
Proton-induced fission of heavy nuclei at intermediate energies
Deppman, A; Guimaraes, V; Karapetyan, G S; Balabekyan, A R; Demekhina, N A
2013-01-01
The intermediate energy proton-induced fission of 241Am, 238$U and 237$Np is studied. The inelastic interactions of protons and heavy nuclei are described by a CRISP model, in which the reaction proceeds in two steps. The first one corresponds fast cascade, where a series of individual particle-particle collisions occurs within the nucleus. It leaves a highly excited cascade residual nucleus, assumed to be in thermal equilibrium. Subsequently, in the second step the excited nucleus releases its energy by evaporation of neutrons and light charged particles as well. Both the symmetric and asymmetric fission are regarded, and the fission probabilities are obtained from CRISP code calculations, by means of statistical weighting factors. The fission cross sections, the fissility of the fissioning nuclei, and the number of nucleons lost by the target - before and after fission - are calculated and compared to experiments for 660 MeV protons incident on 241Am, 238$U and 237$Np. Some of the model predictions are in f...
Electron-capture delayed fission properties of 242Es
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Electron-capture delayed fission of 242Es produced via the 233U(14N,5n)242Es reaction at 87 MeV (on target) was observed to decay with a half-life of 11±3 s, consistent with the reported α-decay half-life of 242Es of 16-4+6 s. The mass-yield distribution of the fission fragments is highly asymmetric. The average pre-neutron emission total kinetic energy of the fragments was measured to be 183±18 MeV. Based on the ratio of the measured number of fission events to the measured number of α decays from the electron-capture daughter 242Cf (100% α branch), the probability of delayed fission was determined to be 0.006±0.002. This value for the delayed fission probability fits the experimental trend of increasing delayed fission probability with increasing Q value for electron capture. (c) 2000 The American Physical Society
Fission Systems for Mars Exploration
Houts, Michael G.; Kim, T.; Dorney, D. J.; Swint, Marion Shayne
2012-01-01
Fission systems are used extensively on earth, and 34 such systems have flown in space. The energy density of fission is over 10 million times that of chemical reactions, giving fission the potential to eliminate energy density constraints for many space missions. Potential safety and operational concerns with fission systems are well understood, and strategies exist for affordably developing such systems. By enabling a power-rich environment and highly efficient propulsion, fission systems could enable affordable, sustainable exploration of Mars.
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A survey of the present state of fission theory is attempted. The basic requirements of a theory of a physical process are outlined and against this background the state of fission theory is summarized, with special emphasis on developments in the past few years. An attempt is made to bring out the most important outstanding problems to be settled by future experiments and theory. (author)
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The response of photovoltaic cells to heavy ions and fission products have been tested on beam. Their main advantages are their extremely low price, their low sensitivity to energetic light ions with respect to fission products, and the possibility to cut and fit them together to any shape without dead zone. The time output signals of a charge sensitive preamplifier connected to these cells allows fast coincidences. A resolution of 12ns (F.W.H.M.) have been measured between two cells
The Asymmetric Leximin Solution
Driesen, Bram W.
2012-01-01
In this article we define and characterize a class of asymmetric leximin solutions, that contains both the symmetric leximin solution of Imai[5] and the two-person asymmetric Kalai-Smorodinsky solution of Dubra [3] as special cases. Solutions in this class combine three attractive features: they are defined on the entire domain of convex n-person bargaining problems, they generally yield Pareto efficient solution outcomes, and asymmetries among bargainers are captured by a single parameter ve...
Graesser, Michael L.; Shoemaker, Ian M.; Vecchi, Luca
2011-01-01
In existing dark matter models with global symmetries the relic abundance of dark matter is either equal to that of anti-dark matter (thermal WIMP), or vastly larger, with essentially no remaining anti-dark matter (asymmetric dark matter). By exploring the consequences of a primordial asymmetry on the coupled dark matter and anti-dark matter Boltzmann equations we find large regions of parameter space that interpolate between these two extremes. Interestingly, this new asymmetric WIMP framewo...
The Impact of Fission on R-Process Calculations
Eichler, M.; Arcones, A.; Käppeli, R.; Korobkin, O.; Liebendörfer, M.; Martinez-Pinedo, G.; Panov, I. V.; Rauscher, T.; Rosswog, S.; Thielemann, F.-K.; Winteler, C.
2016-01-01
We have performed r-process calculations in neutron star mergers (NSM) and jets of magnetohydrodynamically driven (MHD) supernovae. In these very neutron-rich environments the fission model of heavy nuclei has an impact on the shape of the final abundance distribution and the second r-process peak in particular. We have studied the effect of different fission fragment mass distribution models in calculations of low-Ye ejecta, ranging from a simple parametrization to extensive statistical treatments (ABLA07). The r-process path ends when it reaches an area in the nuclear chart where fission dominates over further neutron captures. The position of this point is determined by the fission barriers and the neutron separation energies of the nuclei involved. As these values both depend on the choice of the nuclear mass model, so does the r-process path. Here we present calculations using the FRDM (Finite Range Droplet Model) and the ETFSI (Extended Thomas Fermi with Strutinsky Integral) mass model with the related TF and ETFSI fission barrier predictions. Utilizing sophisticated fission fragment distribution leads to a highly improved abundance distribution.
Fission of Oriented Nuclei by Low Energy Neutrons. RCN Report
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This report describes the study of the angular distribution of α-particles and of fission fragments originating from neutron capture in heavy nuclei, which are aligned at low temperatures by the method of hyperfine interaction. The results of the measurements with the target nucleus 233U with neutrons in the energy range from 0 to 2000 eV can be interpreted with the Bohr-theory of transition states at the deformation barrier for nuclear fission. The relatively invariant behaviour of the anisotropy in the angular distribution of fission fragments as a function of neutron energy indicates that the available fission channels are strongly mixed. For neutron resonances with spin and parity 2+ 2 to 3 channels are open and for 3+ resonances 1 to 2. The group structure in the subthreshold fission cross section of 237Np has been explained by the double-humped deformation barrier proposed by Strutinsky. The implication of this interpretation is that all the resonances in one group have the same spin. The resonances in the first group at 40 eV agree consistently with the fission channel (2+,2). The groups at higher neutron energies up to 2000 eV correspond mainly with the channels (2+,2) and (3+,2). (author)
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During irradiation of water reactor fuel rods, gaseous fission products are produced in the fuel and are slowly released to various voipd volumes in the fuel rods. The released fission gases degrade the initial fill gas thermal conductivity and thus change the thermal response of the fuel rods. Moreover, fuel rod internal pressure is increased so that the cladding mechanical response is affected. The fission gas release subcode FGASRL is intended for use in analytical codes which predict water reactor fuel pin behavior. The development effort was directed primarily at improving code predictions of the gas release model used in FRAP-S3 which overpredicts release of fuels irradiated at relatively low operating temperatures and therefore small gas release fractions. The fission gas release subcode (FGASRL) presented in the report describes a two-step gas release process: (a) fission gas release from fuel grains to the grain boundaries, and (b) fission gas release from the grain boundaries to internal free volume of the fuel pin
Mass and Inertia Parameters for Nuclear Fission
International Nuclear Information System (INIS)
The effective mass parameter and the moments of inertia for a deformed nucleus are evaluated using the cranking-model formalism. Special attention is paid to the dependence of these quantities on the intrinsic structure, which may arise due to shells in deformed nuclei. It is found that these inertial parameters are very much influenced by the shells present. The effective-mass parameter, which appears in an important way in the theory of spontaneous fission, fluctuates in the same manner as the shell-energy corrections. Its values at the fission barrier are up to two or three times larger than those at the equilibrium minima. This correlation comes about because for the effective mass the change in the local density of single-particle states is very important, much more so than the change in the pairing correlation. The moments of inertia which enter in the theory of angular anisotropy of fission fragments, also fluctuate as a function of the deformation. At low temperatures, the fluctuation is large and shows a distinct but more complicated correlation with the shells. At high temperatures, the moments of inertia fluctuate with a smaller amplitude about the rigid-body value in correlation with the energy-shell corrections. For the first-and second barriers, the rigid-body values are essentially reached at a nuclear temperature of 0.8 to 1.0 MeV. (author)
Mass and inertia parameters for nuclear fission
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The effective mass parameter and the moments of inertia for a deformed nucleus are evaluated using the cranking-model formalism. Special attention is paid to the dependence of these quantities on the intrinsic structure, which may arise due to shells in deformed nuclei. It is found that these inertial parameters are very much influenced by the shells present. The effective-mass parameter, which appears in an important way in the theory of spontaneous fission, fluctuates in the same manner as the shell-energy corrections. Its values at the fission barrier are up to two or three times larger than those at the equilibrium minima. This correlation comes about because for the effective mass the change in the local density of single-particle states is very important, much more so than the change in the pairing correlation. The moments of inertia which enter in the theory of angular anisotropy of fission fragments, also fluctuate as a function of the deformation. At low temperatures, the fluctuation is large and shows a distinct but more complicated correlation with the shells. At high temperatures, the moments of inertia fluctuate with a smaller amplitude about the rigid-body value in correlation with the energy-shell corrections. For the first-and second barriers, the rigid-body values are essentially reached at a nuclear temperature of 0.8 to 1.0 MeV. (author)
The contrasting fission potential-energy structure of actinides and mercury isotopes
Ichikawa, Takatoshi; Möller, Peter; Sierk, Arnold J
2012-01-01
Fission-fragment mass distributions are asymmetric in fission of typical actinide nuclei for nucleon number $A$ in the range $228 \\lnsim A \\lnsim 258$ and proton number $Z$ in the range $90\\lnsim Z \\lnsim 100$. For somewhat lighter systems it has been observed that fission mass distributions are usually symmetric. However, a recent experiment showed that fission of $^{180}$Hg following electron capture on $^{180}$Tl is asymmetric. An earlier experiment has shown fission of $^{198}$Hg and nearby nuclei is symmetric, but with hints of asymmetric yield distributions up to about 10 MeV above the saddle-point energy. We calculate potential-energy surfaces for a typical actinide nucleus and for 12 even isotopes in the range $^{178}$Hg--$^{200}$Hg, demonstrating the radical differences between actinide and mercury potential surfaces. We discuss these differences and how the changing potential-energy structure along the mercury isotope chain affects the observed (a)symmetry of the fission fragments. We show that the ...
International Nuclear Information System (INIS)
A survey is given of the present state of knowledge of the spectrum, angular distribution and number of prompt fission neutrons, as functions of incident neutron energy and individual fragment mass, for low-energy fission. The energy spectrum of prompt neutrons has been found to be of the same form (nearly Maxwellian) for many different types of fission. It has been shown that this type of spectrum is to be expected on the basis of evaporation from moving fragments, and theoretical predictions of the spectrum agree very accurately with experimental data. Some data are now available on the variation of the neutron spectrum with fragment mass and angle of emission. Only recently has it become possible to take accurate data on the angular distribution of the neutrons. It appears that the neutrons have the angular distribution to be expected if emitted almost isotropically from the moving fragments, with a possibility that some small fraction are not emitted in this way, but directly from the fissioning nuclide. Much work has been done on the variation of fission neutron number v with incident neutron energy for neutron-induced fission. The neutron number increases roughly linearly with energy, with a slope of about 0.15 n/MeV. There is now evidence that this slope changes somewhat with energy. This change must be associated with other changes in the-fission process. The most interesting recent discovery concerning fission neutrons is the strong dependence of neutron number on individual fragment mass. The data are being rapidly improved by means of the newer techniques of determining fragment mass yields from velocity and pulse-height data, and of determining neutron yields from cumulative mass yields. There is evidence of similar dependence of neutron yield on fragment mass in a number of cases. It has been suggested that this property is directly connected with the deformability of the fragments, and in particular with the near-spherical shapes of magic
Excitation energy dependence of fission in the mercury region
McDonnell, J D; Sheikh, J A; Staszczak, A; Warda, M
2014-01-01
Background: Recent experiments on beta-delayed fission reported an asymmetric mass yield in the neutron-deficient nucleus 180Hg. Earlier experiments in the mass region A=190-200 close to the beta-stability line, using the (p,f) and (\\alpha,f) reactions, observed a more symmetric distribution of fission fragments. While the beta-delayed fission of 180Hg can be associated with relatively low excitation energy, this is not the case for light-ion reactions, which result in warm compound nuclei. Purpose: To elucidate the roles of proton and neutron numbers and excitation energy in determining symmetric and asymmetric fission yields, we compute and analyze the isentropic potential energy surfaces of 174,180,198Hg and 196,210Po. Methods: We use the finite-temperature superfluid nuclear density functional theory, for excitation energies up to E*=30MeV and zero angular momentum. For our theoretical framework, we consider the Skyrme energy density functional SkM* and a density-dependent pairing interaction. Results: Fo...
Resonance structure in the fission of (235U+n)
International Nuclear Information System (INIS)
A new multilevel reduced R-matrix analysis of the neutron-induced resonance cross sections of 235U has been carried out. We used as a constraint in the analysis the angular anisotropy measurements of Pattenden and Postma, obtaining a Bohr-channel (or J, K channel) representation of the resonances in a two-fission vector space for each spin state. Hambsch et al., have reported definitive measurements of the mass- and kinetic-energy distributions of fission fragments of (235U+n) in the resonance region and analyzed their results according to the fission-channel representation of Brosa et al., extracting relative contributions of the two asymmetric and one symmetric Brosa fission channels. We have explored the connection between Bohr-channel and asymmetric Brosa-channel representations. The results suggest that a simple rotation of coordinates in channel space may be the only transformation required; the multilevel fit to the total and partial cross sections is invariant to such a transformation. (orig.)
International Nuclear Information System (INIS)
Analyses of the prismatic VHTR with Monte Carlo method suffer from slow fission source convergence. MHTGR-350 is a prismatic VHTR, which has an asymmetric reflector thickness along the axial direction. In this case, fission source distribution also becomes strong asymmetrical distribution according to the asymmetric reactor reflector thickness. Therefore, the converged fission source must be verified to pursue the Monte Carlo simulation of the reactor type. In this study, how the axial reflector thickness affects the fission source convergence was evaluated with changing the prismatic VHTR reflector thickness. In this study, how the axial reflector thickness affects the fission source convergence was evaluated. For the symmetric reflector cases, the results show the fission source distribution was converged within 60th cycle. However, in the cases of the asymmetric reflector thickness, it is notified that the convergence cycle of the fission source distribution exceeded 200th cycle. Analysis shows that the inactive cycle for the Monte Carlo eigenvalue calculation should be considerably decided when the reactor has asymmetric reflector thicknesses such as the MHTGR-350. It is expected that these results can be directly used for evaluating and analyzing the prismatic VHTR with Monte Carlo method
Energy dissipation in the cold fission of 252Cf
International Nuclear Information System (INIS)
The conversion of energy of collective nuclear motion into internal single particle excitation energy is one of the modes of nuclear energy dissipation. Dissipation and its relation to pair breaking is one of the challenges in nuclear field. A characteristic of low energy fission is odd-even effect. Odd-even staggering in the mass or charge yields and in the total kinetic energies will be of useful to analyze dissipation energy. The odd even effects in the charge distribution of cold fission fragments can be analysed to extract information on the energy dissipation during the passage from the first potential well towards the scission point through the fission barrier. The Q value during a fission process is decomposed into the total kinetic and excitation energies (TKE and TXE)
Directory of Open Access Journals (Sweden)
Schmidt K.-H.
2010-10-01
Full Text Available A new model description of fission-fragment yields and prompt neutron emission is developed. The yields of the different fission channels and their properties are attributed to the number of relevant states above the potential-energy landscape on the fission path at the moment of dynamical freeze-out, which is specific to the collective coordinate considered. The model combines well established ideas with novel concepts. The separability principle of macroscopic properties of the compound nucleus and microscopic properties of the fragments strongly reduces the number of model parameters and assures a high predictive power. The recently discovered energy-sorting mechanism in superfluid nuclear dynamics determines the sharing of intrinsic excitation energy at scission and the enhancement of even-odd structure in asymmetric splits.
Fission life-time calculation using a complex absorbing potential
Directory of Open Access Journals (Sweden)
Scamps Guillaume
2016-01-01
Full Text Available A comparison between the semi-classical approximation and the full quantum calculation with a complex absorbing potential is made with a model of the fission of 258Fm. The potential barrier is obtained with the constrained Skyrme HF+BCS theory. The life-time obtained by the two calculations agree with each other the difference being only by 25%.
Fission life-time calculation using a complex absorbing potential
Scamps, Guillaume
2015-01-01
A comparison between the semi-classical approximation and the full quantum calculation with a complex absorbing potential is made with a model of the fission of 258Fm. The potential barrier is obtained with the constrained Skyrme HF+BCS theory. The life-time obtained by the two calculations agree with each other the difference being only by 25%.
What can we learn from the fission time of the super-heavy elements?
International Nuclear Information System (INIS)
Recent experiments performed at GANIL with a crystal blocking technique have shown direct evidences of long fission times in the Super-Heavy Elements (SHE) region. Aimed to localize the SHE island of stability, can these experiments give access to the fission barrier and then to the shell-correction energy? In this paper, we calculate the fission time of heavy elements by using a new code, KEWPIE2, devoted to the study of the SHE. We also investigate the effect of potential structure beyond the saddle on the fission time. (authors)
Induced Fission of 240Plutonium within a Real-Time Microscopic Framework
Energy Technology Data Exchange (ETDEWEB)
Bulgac, Aurel; Magierski, Piotr; Roche, Kenneth J.; Stetcu, Ionel
2016-03-25
We describe the fissioning dynamics of 240Pu from a configuration in the proximity of the outer fission barrier to full scission and the formation of the fragments within an implementation of the Density Functional theory extended to superfluid systems and real-time dynamics. While the fission products emerge with properties very similar to those determined experimentally, the fission dynamics appears to be quite complex, with various shape and pairing modes being excited during the evolution. Consequently the time scale of the evolution turned out to be much slower than previously expected.
Osborne, Andrew G
2016-01-01
Under the right conditions, self sustaining fission waves can form in fertile nuclear materials. These waves result from the transport and absorption of neutrons and the resulting production of fissile isotopes. When these fission, additional neutrons are produced and the chain reaction propagates until it is poisoned by the buildup of fission products. It is typically assumed that fission waves are soliton-like and self stabilizing. However, we show that in uranium, coupling of the neutron field to the 239U->239Np->239Pu decay chain can lead to a Hopf bifurcation. The fission reaction then ramps up and down, along with the wave velocity. The critical driver for the instability is a delay, caused by the half-life of 239U, between the time evolution of the neutron field and the production of 239Pu. This allows the 239Pu to accumulate and burn out in a self limiting oscillation that is characteristic of a Hopf bifurcation. Time dependent results are obtained using a numerical implementation of a reduced order r...
Photon and proton induced fission on heavy nuclei at intermediate energies
Energy Technology Data Exchange (ETDEWEB)
Andrade-II, E.; Karapetyan, G.S.; Deppman, A.; Guimaraes, V. [Universidade de Sao Paulo (USP), Sao Paulo, SP (Brazil). Instituto de Fisica; Balabekyan, A.R. [Yerevan State University, Alex Manoogian 1, Yerevan (Armenia); Demekhina, N.A. [Yerevan Physics Institute, Alikhanyan Brothers 2, Yerevan (Armenia); Joint Institute for Nuclear Research (JINR), Flerov Laboratory of Nuclear Reactions (LNR), Moscow (Russian Federation)
2014-07-01
We present an analysis of fission induced by intermediate energy protons or photons on actinides. The 660 MeV proton induced reactions are on {sup 241}Am, {sup 238}U, and {sup 237}Np targets and the Bremsstrahlung-photons with end-point energies at 50 MeV and 3500 MeV are on {sup 232}Th and {sup 238}U targets. The study was performed by means of the Monte Carlo simulation code CRISP. A multimodal fission extension was added to the code within an approach which accounts for the contribution of symmetric and asymmetric fission. This procedure allowed the investigation of fission cross sections, fissility, number of evaporated nucleons and fission-fragment charge distributions. The comparison with experimental data show a good agreement between calculations and experiments. (author)
Photon and proton induced fission on heavy nuclei at intermediate energies
Directory of Open Access Journals (Sweden)
Andrade-II E.
2014-04-01
Full Text Available We present an analysis of fission induced by intermediate energy protons or photons on actinides. The 660 MeV proton induced reactions are on 241Am, 238U, and 237Np targets and the Bremmstrahlung-photons with end-point energies at 50 MeV and 3500 MeV are on 232Th and 238U targets. The study was performed by means of the Monte Carlo simulation code CRISP. A multimodal fission extension was added to the code within an approach which accounts for the contribution of symmetric and asymmetric fission. This procedure allowed the investigation of fission cross sections, fissility, number of evaporated nucleons and fission-fragment charge distributions. The comparison with experimental data show a good agreement between calculations and experiments.
Comparison of Yields of neutron rich nuclei in Proton and Photon induced $^{238}$U fission
Khan, F A; Basu, D N; Farooq, M; Chakrabarti, Alok
2016-01-01
A comparative study of fission of actinides specially $^{238}$U, by proton and bremsstrahlung photon is performed. Relative mass distribution of $^{238}$U fission fragments have been explored theoretically for both proton and photon induced fission. The integrated yield along with charge distribution of the products are calculated to find out the neutron richness in comparison to the nuclei produced by r-process in nucleosynthesis. Some r-process nuclei in intermediate mass range for symmetric fission mode are found to be produced almost two order of magnitude more for proton induced fission than photofission, although rest of the neutron rich nuclei in the asymmetric mode are produced in comparable proportion for both the processes.
Neutron-Induced Fission of Actinium-227, Protactinium-231 and Neptunium-237: Mass Distribution
International Nuclear Information System (INIS)
Results of radiochemical studies on the mass distribution in the neutron-induced fission of actinium-227, protactinium-231 and neptunium-237 have been presented. This work has been carried out as part of a programme to determine the mass distribution in the fission of heavy elements as a function of Z and A. All irradiations have been carried out in the core of the swimming-pool type reactor APSARA with cadmium shielding wherever necessary. Relative yields of several fission product nuclides have been obtained by a method involving a comparison of the fission product activities from the respective targets with those formed from uranium-235 simultaneously irradiated. Thermal-neutron fission yields of uranium-235 have been assumed. These results indicate a predominantly asymmetric mass distribution in all the three cases, and also a distinct though small symmetric peak in the case of actinium-227. (author)
Photon and proton induced fission on heavy nuclei at intermediate energies
International Nuclear Information System (INIS)
We present an analysis of fission induced by intermediate energy protons or photons on actinides. The 660 MeV proton induced reactions are on 241Am, 238U, and 237Np targets and the Bremsstrahlung-photons with end-point energies at 50 MeV and 3500 MeV are on 232Th and 238U targets. The study was performed by means of the Monte Carlo simulation code CRISP. A multimodal fission extension was added to the code within an approach which accounts for the contribution of symmetric and asymmetric fission. This procedure allowed the investigation of fission cross sections, fissility, number of evaporated nucleons and fission-fragment charge distributions. The comparison with experimental data show a good agreement between calculations and experiments. (author)
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
Current position on fission product behavior
International Nuclear Information System (INIS)
The following phenomena are treated and modeled: fission product release from fuel, both in-vessel and ex-vessel; fission product deposition in the primary system, fission product deposition in the containment, and fission product revolatization
International Nuclear Information System (INIS)
An ion trap having two end cap electrodes disposed asymmetrically about a center of a ring electrode is disclosed. The inner surface of the end cap electrodes are conformed to an asymmetric pair of equipotential lines of the harmonic formed by the application of voltages to the electrodes. The asymmetry of the end cap electrodes allows ejection of charged species through the closer of the two electrodes which in turn allows for simultaneously detecting anions and cations expelled from the ion trap through the use of two detectors charged with opposite polarity. 4 figs
Fission modelling with FIFRELIN
Litaize, Olivier; Serot, Olivier; Berge, Léonie
2015-12-01
The nuclear fission process gives rise to the formation of fission fragments and emission of particles (n,γ , e-) . 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 the
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
Fission modelling with FIFRELIN
International Nuclear Information System (INIS)
The nuclear fission process gives rise to the formation of fission fragments and emission of particles (n,γ, e-). 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 the
Characteristics of Coulomb fission
Oberacker, Volker; Greiner, Walter; Kruse, Hans; Pinkston, William T.
2006-01-01
Within an extended semiquantal theory we perform large-sized coupled-channel calculations involving 260 collective levels for Coulomb fission of 238U. Differential Coulomb fission cross sections are studied as a function of bombarding energy and impact parameter for several projectiles. In the Xe + U case, total cross sections are also given. We find a strong dependence on projectile charge number, PCF(180°)∼(Zp)6 in the region 50≤Zp≤92 for a fixed ratio E/ECoul, which might...
Influence of the angular momentum on nuclear fission
Energy Technology Data Exchange (ETDEWEB)
Tanikawa, Masashi [Tokyo Univ. (Japan). Faculty of Science
1996-03-01
The effects of the angular momentum on the mechanism of nuclear fission are studied about the reaction systems of compound nucleus of {sup 210}P and {sup 239}Np by the time-of-flight (TOF) method. The reaction systems in this work are {sup 209}Bi+P, {sup 206}Pb+{alpha}, {sup 206}Po+{alpha}, {sup 198}Pt+{sup 12}C, {sup 238}U+P and {sup 232}Th+{sup 7}Li. Target was prepared by vacuum evaporating of each about 100 {mu}g/cm{sup 2} of {sup 209}Bi, {sup 206}Pb and {sup 198}Pt on 10 {mu}g/cm{sup 2} of carbon film. On compound nucleus {sup 210}Po, {sup 210}Po fissions at Ex=45McV but it fissions after 1 or 2 neutrons emission at higher excited energy (Ex=57 MeV). TKE shows almost the same values except higher value of {sup 209}Bi+P. The decreasing tendency of width of TKE distribution with increasing the angular momentum is found at the first time in this work. The effect of the angular momentum on the fission is small in the case of low angular momentum. On the compound nucleus {sup 239}Np, the effects are shown at the asymmetric fission part of the mass distribution. (S.Y.)
International Nuclear Information System (INIS)
The fission cross section of 233U has been calculated using a new version of the statistical model and recent data for inelastic scattering levels and fission barrier parameters. The calculation accurately reproduces the experimental fission cross section. The calculated partial cross section for fission through different saddle point states (JKπ) has been used in the explanation of structure in average number of fission prompt neutrons anti νsub(p) and average total fission fragment kinetic energy anti Esub(k) and the energy dependence of the fission fragment anisotropy
Fission dynamics of hot nuclei
Indian Academy of Sciences (India)
Santanu Pal; Jhilam Sadhukhan
2014-04-01
Experimental evidence accumulated during the last two decades indicates that the fission of excited heavy nuclei involves a dissipative dynamical process. We shall briefly review the relevant dynamical model, namely the Langevin equations for fission. Statistical model predictions using the Kramers’ fission width will also be discussed.
Discoveries of isotopes by fission
Indian Academy of Sciences (India)
M Thoennessen
2015-09-01
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.
Status of fission yield measurements
International Nuclear Information System (INIS)
Fission yield measurement and yield compilation activities in the major laboratories of the world are reviewed. In addition to a general review of the effort of each laboratory, a brief summary of yield measurement activities by fissioning nuclide is presented. A new fast reactor fission yield measurement program being conducted in the US is described
Asymmetric reactions in continuous flow
Directory of Open Access Journals (Sweden)
Xiao Yin Mak
2009-04-01
Full Text Available An overview of asymmetric synthesis in continuous flow and microreactors is presented in this review. Applications of homogeneous and heterogeneous asymmetric catalysis as well as biocatalysis in flow are discussed.
International Nuclear Information System (INIS)
A library is described of data for 584 isotopes of fission products, including decay constants, branching ratios (both burn-up and decay), the type of emitted radiation, relative and absolute yields, capture cross sections for thermal neutrons, and resonance integrals. When a detailed decay scheme is not known, the mean energies of beta particles and neutrino and gamma radiations are given. In the ZVJE SKODA system the library is named BIBFP and is stored on film No 49 of the NE 803 B computer. It is used in calculating the inventory of fission products in fuel elements (and also determining absorption cross sections for burn-up calculations, gamma ray sources, heat generation) and in solving radioactivity transport problems in the primary circuit. It may also be used in the spectrometric method for burn-up determination of fuel elements. The library comprises the latest literary data available. It serves as the basis for library BIBGRFP storing group constants of fission products with independent yields of isotopes from fission. This, in turn, forms the basis for the BIBDN library collecting data on the precursors of delayed neutron emitters. (author)
Fission yields in the thermal neutron fission of plutonium-239
International Nuclear Information System (INIS)
Fission yields for 27 mass numbers were determined in the thermal neutron fission of 239Pu using high resolution gamma ray spectrometry and radiochemical method. The results obtained using gamma ray spectrometry and from the investigations on the fission yield of 99Mo using radiochemical method were reported earlier. These data along with fission yields for 19 mass numbers determined using radiochemical method formed a part of Ph.D. thesis. The data given here are a compilation of all the results and are presented considering the neutron temperature correction to 239Pu fission cross-section which is used for calculating the total number of fissions in these studies. A comparison is made of the resulting fission yield values with the latest experimentally determined values and those given in two recent compilations. (author)
Simultaneous Measurements of Flight Times and Energies of Fission Fragments
International Nuclear Information System (INIS)
In a companion paper the results of measuring the prompt neutron emission from individual fission fragments arising in thermal fission are reported. In that experiment a large volume liquid scintillation counter was .used to. record the fission neutrons, and fragment mass was identified by a gold silicon surface barrier counter.- arrangement. An alternative Way of measuring the prompt neutron emission is described here. Fragment time-of- flight apparatus is mounted in an evacuated tube that passes laterally through the thermal column of the 5-MW research reactor HERALD. A centrally positioned thin source produces 3 x 105 fissions s-1. Fragments travel distances of 180 cm and 300 cm respectively to the terminal detectors, and in passing through a VYNS film, positioned 180 cm from the source along the longer flight path, eject electrons that are used to form a reference time-signal. Essentially the times of flight of both fission fragments are measured simultaneously with the kinetic energy of one of the pair. This is achieved by using a surface barrier counter for the 300-cm detector. The difficulty of maintaining good timing and energy resolutions simultaneously is overcome by routing the pulse to the charge sensitive preamplifier through a delay line amplifier from which a fast timing pulse is derived. The collected data enables the fragment mass to be determined both before and after prompt neutrons have been emitted. Hence the experiment provides a means for studying the behaviour of neutron emission from individual fragments. The experimental uncertainties are those associated with the measurement of small differences, and an appraisal is made of the errors and calibrations that enter into the measurements. Of particular importance, the response of the surface barrier counter to fission fragments is obtained directly, from the collected data from events in which the neutron emission is low. These calibrations are used in the measurements of postneutron mass
Microscopic structure inputs for reaction models of fission
Energy Technology Data Exchange (ETDEWEB)
Goutte, H.; Dobrowolski, A.; Girod, M.; Delaroche, J.P. [CEA Bruyeres-le-Chatel (DPTA/SPN), 91 (France). Dept. de Physique Theorique et Appliquee
2008-07-01
Reliable nuclear structure predictions are needed for reaction data evaluations, whenever experimental information is missing. Even if full parameter-free evaluations are not possible nowadays, some noteworthy progress in both structure and reaction fields has been accomplished recently. We present here some results on fission barriers and shape isomers partial {gamma}-back decay and fission lifetimes. Calculations have been performed using the effective D1S Gogny force and the Generator Coordinate Method with the Gaussian Overlap Approximation based on Hartree- Fock-Bogoliubov results. (authors)
Microscopic structure inputs for reaction models of fission
International Nuclear Information System (INIS)
Reliable nuclear structure predictions are needed for reaction data evaluations, whenever experimental information is missing. Even if full parameter-free evaluations are not possible nowadays, some noteworthy progress in both structure and reaction fields has been accomplished recently. We present here some results on fission barriers and shape isomers partial γ-back decay and fission lifetimes. Calculations have been performed using the effective D1S Gogny force and the Generator Coordinate Method with the Gaussian Overlap Approximation based on Hartree- Fock-Bogoliubov results. (authors)
A new prompt heavy-ion-induced fission mode
Indian Academy of Sciences (India)
W Udo Schröder
2015-08-01
Fission instabilities induced by mechanical and thermal stresses on intermediate nuclear systems in heavy-ion reactions are poorly understood but should reveal independent evidence for the nuclear equation of state (EoS), notably the tensile strength of finite nuclei. 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 process recalls the ‘L-window for fusion’ phenomenon, which was predicted by the early reaction theory and reappears in modern DFT model calculations.
International Nuclear Information System (INIS)
This paper presents measurements of the concentrations of 42 of the long-lived U-235 fission products in a high-level radioactive waste sludge stored at Savannah River Site. The 42 fision products make up 98% of the waste sludge. We used inductively coupled plasma-mass spectroscopy for the analysis. The relative yields for most of the fission products are in complete agreement with the known relative yields for the beta decay chains of the two asymmetric branches of the slow neutron fission of U-235. Disagreements can be reconciled based on the chemistry of the fission products in the caustic waste sludges, the neutron fluences in SRS reactors, or interferences in the ICP-MS analyses. This paper presents measurements of the concentrations of 42 (98%) of the long-lived U-235 fission products in a high-level radioactive waste sludge stored at the Savannah River Site. We analyzed the sludge with inductively coupled plasma-mass spectroscopy. The relative yields for most of the fission products agree completely with the known relative vields for the beta decay chains of the two asymmetric: branches of the slow neutron fission of U-235. The chemistry of the fission products in the caustic waste sludges, the neutron fluences in SRS reactors, or interferences in the ICP-MS analyses explain the differences in the measured and calculated results
Dynamical features of nuclear fission
Indian Academy of Sciences (India)
Santanu Pal
2015-08-01
It is now established that the transition-state theory of nuclear fission due to Bohr and Wheeler underestimates several observables in heavy-ion-induced fusion–fission reactions. Dissipative dynamical models employing either the Langevin equation or equivalently the Fokker–Planck equation have been developed for fission of heavy nuclei at high excitations (T ∼1 MeV or higher). Here, we first present the physical picture underlying the dissipative fission dynamics. We mainly concentrate upon the Kramers’ prescription for including dissipation in fission dynamics. We discuss, in some detail, the results of a statistical model analysis of the pre-scission neutron multiplicity data from the reactions 19F+194,196,198Pt using Kramers’ fission width. We also discuss the multi-dimensional Langevin equation in the context of kinetic energy and mass distribution of the fission fragments.
International Nuclear Information System (INIS)
In the late 1960s, Strutinsky's theoretical work on the structure of the fission barrier, together with some new neutron cross-section measurements performed at Saclay and Gel, was called to Gerard de Saussure's attention, and he immediately recognized the importance of those developments. Indeed, de Saussure was quick to note that for neutron energies in the range of the fission barrier potential energy, fission cross-section measurements would yield direct information about the physical properties of the fission barrier. Under his leadership, a set of extensive and precise measurements was performed at the Oak Ridge Electron Linear Accelerator (ORELA) by an international group of researchers, lasting over two decades. Those measurements were unique in many respects: Fission widths were determined for many previously unreported resonances in the subthreshold region, and a detailed study was performed on the physical properties of the fission barrier at high nuclear deformations. In this paper, we report a specific part of the de Saussure's extensive involvement in the area of subthreshold fission physics: the 1979 measurement of the 238U(n,f) cross ection in the subthreshold and near-subthreshold regions. This cross section was measured in the energy region between 5 eV and 3.5 MeV using a large fission chamber loaded with high-purity 238U, which had 235U
A Study of Fission Following (d, p) and (t, p) Reactions in Uranium Isotopes
International Nuclear Information System (INIS)
The fission of U233, U234, U235, U236 and U238 induced by (d, p) and (t, p) reactions has been studied, at a bombarding energy of 13 MeV. The protons were detected in an annular counter system situated at about 170° to the beam, and the proton spectrum in coincidence with fission fragments was recorded. The annular counter system consisted of an E- ΔE telescope with a thin (0.002-in) surface barrier semiconductor counter in front of a thick surface barrier counter in which the protons were stopped. The particles were identified using a conventional pulse multiplier. The fission fragments were detected in other surface barrier counters at 90°, 135° and 170°. For this latter angle the annular ΔE counter was used to detect the fission fragments, since it was found that of the various particles emerging from the target only the protons were in coincidence with fission fragments. Differences in the fission thresholds deduced from the U234 (t, pf) and U235 (d, pf) reactions were observed, indicating that the (t,p) reaction feeds fissioning states of lower excitation in the compound nucleus. A difference in the behaviour of the fission- fragment angular distributions for these two reactions was also observed at energies close to the fission threshold. Both effects provide evidence for a detailed structure consistent with the existence of the low-lying collective excitations at the saddle point of fission, analogous to those observed at the stable shape, which has been described by A. Bohr. (author)
Asymmetric information and economics
Frieden, B. Roy; Hawkins, Raymond J.
2010-01-01
We present an expression of the economic concept of asymmetric information with which it is possible to derive the dynamical laws of an economy. To illustrate the utility of this approach we show how the assumption of optimal information flow leads to a general class of investment strategies including the well-known Q theory of Tobin. Novel consequences of this formalism include a natural definition of market efficiency and an uncertainty principle relating capital stock and investment flow.
Asymmetric Organocatalytic Cycloadditions
DEFF Research Database (Denmark)
Mose, Rasmus
2016-01-01
were pioneered by Otto Paul Hermann Diels and Kurt Alder who discovered what later became known as the Diels Alder reaction. The Diels Alder reaction is a [4+2] cycloaddition in which a π4 component reacts with a π2 component via a cyclic transition state to generate a 6 membered ring. This reaction...... reactions constitute the first organocatalytic asymmetric higher order cycloadditions and a rational for the periselectivity and stereoselectivity is provided based on experimental and computational investigations....
Asymmetric extractions in orthodontics
Directory of Open Access Journals (Sweden)
Camilo Aquino Melgaço
2012-04-01
Full Text Available INTRODUCTION: Extraction decisions are extremely important in during treatment planning. In addition to the extraction decision orthodontists have to choose what tooth should be extracted for the best solution of the problem and the esthetic/functional benefit of the patient. OBJECTIVE: This article aims at reviewing the literature relating the advantages, disadvantages and clinical implications of asymmetric extractions to orthodontics. METHODS: Keywords were selected in English and Portuguese and the EndNote 9 program was used for data base search in PubMed, Web of Science (WSc and LILACS. The selected articles were case reports, original articles and prospective or retrospective case-control studies concerning asymmetrical extractions of permanent teeth for the treatment of malocclusions. CONCLUSION: According to the literature reviewed asymmetric extractions can make some specific treatment mechanics easier. Cases finished with first permanent molars in Class II or III relationship in one or both sides seem not to cause esthetic or functional problems. However, diagnosis knowledge and mechanics control are essential for treatment success.
Asymmetric Evolutionary Games.
McAvoy, Alex; Hauert, Christoph
2015-08-01
Evolutionary game theory is a powerful framework for studying evolution in populations of interacting individuals. A common assumption in evolutionary game theory is that interactions are symmetric, which means that the players are distinguished by only their strategies. In nature, however, the microscopic interactions between players are nearly always asymmetric due to environmental effects, differing baseline characteristics, and other possible sources of heterogeneity. To model these phenomena, we introduce into evolutionary game theory two broad classes of asymmetric interactions: ecological and genotypic. Ecological asymmetry results from variation in the environments of the players, while genotypic asymmetry is a consequence of the players having differing baseline genotypes. We develop a theory of these forms of asymmetry for games in structured populations and use the classical social dilemmas, the Prisoner's Dilemma and the Snowdrift Game, for illustrations. Interestingly, asymmetric games reveal essential differences between models of genetic evolution based on reproduction and models of cultural evolution based on imitation that are not apparent in symmetric games. PMID:26308326
Fission product revaporization
International Nuclear Information System (INIS)
One of the major developmental advances in severe accident analysis since the Reactor Safety Study relates to the accounting for radionuclide retention in the reactor coolant system (RCS). The retention is predicted to occur as materials released during core heatup and degradation are transported through the RCS to the break (broken pipe, relief valve, etc.). For accidents involving relatively long RCS-transit times (e.g., station blackout in PWRs), the fraction of released material predicted to remain in the RCS can be large. For example, calculations for the Surry station blackout sequence showed retention of approximately 80% of the cesium and iodine species. Factors affecting fission product revaporization are post-vessel-failure thermal hydraulics, heat loss through vessel and pipe walls, and revaporization chemistry. The accident conditions relevant to this issue range from those present immediately after vessel failure to those present after containment failure. The factors that affect fission product revaporization are discussed
Heavy ion reactions around the Coulomb barrier
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
The angular distributions of fission fragments for the 32S+184W reaction near Coulomb barrier energies are measured. The ex perimental fission excitation function is obtained. The measured fission cross sections are decomposed into fusion-fission, quasi-fission and fast fission contributions by the dinuclear system (DNS) model. The hindrance to completing fusion both at small and large collision energies is explained. The fusion excitation functions of 32S+90,96Zr in an energy range from above to below the Coulomb barrier are measured and analyzed within a semi-classical model. The obvious effect of positive Q-value multi-neutron transfers on the sub-barrier fusion enhancement is observed in the 32S+96Zr system. In addition, the excitation functions of quasi-elastic scattering at a backward angle have been measured with high precision for the systems of 16O+208Pb, 196Pt, 184W, and 154,152Sm at energies well below the Coulomb barrier. Considering the deformed coupling effects, the extracted diffuseness parameters are close to the values extracted from the systematic analysis of elastic and inelastic scattering data. The elastic scattering angular distribution of 17F+12C at 60 MeV is measured and calculated by using the continuum-discretized coupled-channels (CDCC) approach. It is found that the diffuseness parameter of the real part of core-target potential has to be increased by 20% to reproduce the experimental result, which corresponds to an increment of potential depth at the surface re gion. The breakup cross section and the coupling between breakup and elastic scattering are small.
Fission fragment angular distributions
International Nuclear Information System (INIS)
Recently a Letter appeared (Phys. Rev. Lett., 522, 414(1984)) claiming that the usual expression for describing the angula distribution of fission fragments from compound nuclear decay is not a necessarily valid limit of a more general expression. In this comment we wish to point out that the two expressions arise from distinctly different models, and that the new expression as used in the cited reference is internally inconsistent
Molecular dynamics simulations of cluster fission and fusion processes
DEFF Research Database (Denmark)
Lyalin, Andrey G.; Obolensky, Oleg I.; Solov'yov, Ilia;
2004-01-01
groups of atoms from the parent cluster is largely independent of the isomer form of the parent cluster. The importance of rearrangement of the cluster structure during the fission process is elucidated. This rearrangement may include transition to another isomer state of the parent cluster before actual......Results of molecular dynamics simulations of fission reactions Na_10^2+ --> Na_7^+ +Na_3^+ and Na_18^2+ --> 2Na_9^+ are presented. The dependence of the fission barriers on the isomer structure of the parent cluster is analyzed. It is demonstrated that the energy necessary for removing homothetic...... separation of the daughter fragments begins and/or forming a "neck" between the separating fragments. A novel algorithm for modeling the cluster growth process is described. This approach is based on dynamic search for the most stable cluster isomers and allows one to find the optimized cluster geometries...
Cold fission description with constant and varying mass asymmetries
International Nuclear Information System (INIS)
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)
Nuclear fission dynamics within a generalized Langevin approach
International Nuclear Information System (INIS)
Within the generalized (non-Markovian) multidimensional Langevin approach, the time and energy characteristics of symmetric fission of highly excited heavy nuclei are studied. In two-dimensional space of the collective deformation parameters, it is considered a nuclear descent from the top of the fission barrier to the scission point. The distributions of descent times and total kinetic energy of fission fragments are calculated as functions of memory time, measuring the relative size of memory effects in the collective dynamics. We found that the peculiarities of the non-Markovian dynamics at fairly large values of the memory time are reflected in the saturation of the mean time of motion from the saddle to scission with the growth of the strength of memory effects in the system.
Cold fission description with constant and varying mass asymmetries
Energy Technology Data Exchange (ETDEWEB)
Duarte, S.B.; Rodriguez, O.; Tavares, O.A.P. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); Goncalves, M. [Instituto de Radioprotecao e Dosimetria (IRD), Rio de Janeiro, RJ (Brazil); Garcia, F.; Guzman, F. [Sao Paulo Univ., SP (Brazil). Inst. de Fisica
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 {sup 234} U cold fission are satisfactorily reproduced. (author) 39 refs., 6 figs., 2 tabs.; e-mail: telo at ird.gov.br
Revisiting the even-odd staggering in fission-fragment yields
International Nuclear Information System (INIS)
The even-odd staggering observed in the experimental fission-fragment nuclear-charge yields is investigated over a wide systematics of fission fragments measured at Lohengrin in direct kinematics and at GSI in inverse kinematics. The general increase of the even-odd staggering in the fission-fragment charge yields towards asymmetric charge splits is explained by the absorption of the unpaired nucleons by the heavy fragment. As a consequence, the well established trend of even-odd staggering in the fission fragment charge yields to decrease with the fissility is attributed in part to the asymmetry evolution of the charge distribution. This interpretation is strongly supported by the data measured at GSI, which cover the complete charge distribution and include precise yields at symmetry. They reveal that the even-odd effect around symmetry remains constant over a large range of fissility. (authors)
Development of gridded ionization chamber for measuring atomic number of fission fragments
International Nuclear Information System (INIS)
In order to investigate the mechanism of asymmetric mass division in low energy fission of actinides, the detector for measuring an atomic number (Z) for fission fragments has been developed. Because the atomic number is closely related to energy losses of fragments, the gridded ionization chamber with divided anode is useful for this purpose. The detector was designed and optical conditions such as the distance and electric potential between electrodes were searched using alpha particles from 252Cf. The total energy and energy losses of fission fragments from 252Cf were measured under the obtained conditions. It was found that fission fragments lost most of the kinetic energy in the beginning of their range. This behavior agrees qualitatively with results of simulation by TRIM code. In the presentation, the results of energy measurements under various conditions will be shown and discussed. (author)
Super-heavy nuclei with Z = 118 and their mass and charge spectrum of fission fragments
Maslyuk, V. T.; Smolyanyuk, A. V.
2015-12-01
The first results of the calculation of the mass and charge yields of fission fragments for over 60 isotopes which have Z = 118 are presented. The results were obtained from the condition of thermodynamic ordering of the ensemble of fission fragments. The role of neutrons shells with N = 82 or N = 126 and protons shells with Z = 50 in the realization of symmetric (or one-humped) and asymmetric (2- or 3-humped) shapes of the fission-fragment yields with the transition from neutron-proficient to neutron-deficient isotopes was investigated. The data of fragments yields had been analyzed under the conditions of a “cold” and “hot” fission. The calculations show the possibility to identify super-heavy nuclei with Z ≥ 118 produced synthetically by heavy-ion reaction on their mass/charge spectrum division.
Fission fragment mass distribution in the 13C+182W and 176Yb reactions
International Nuclear Information System (INIS)
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 13C beams on 182W and 176Yb targets
Charge and mass distribution in 7Li induced fission of 232Th
International Nuclear Information System (INIS)
Formation cross sections of about forty fission products have been determined using recoil catcher technique followed by off line gamma-ray spectrometry in 7Li induced fission of 232Th at Elab=41.9, 36.6 and 31.4 MeV. The measured data have been used to deduce charge and mass distributions. Mass distribution is found to be asymmetric at all the three energies. Cross sections of evaporation residues formed in both transfer reactions (232,233,234Pa) as well as in complete fusion (234Np), have also been measured. The measured evaporation residue cross sections and the decay probabilities of target like nuclei (233,234,235Pa) formed in the various transfer reactions, as calculated by PACE2, have been used to estimate the transfer induced fission cross sections. The data indicated that the magnitude of transfer induced fission is very small
International Nuclear Information System (INIS)
With the detector system DIOGENES thermal neutron induced and spontaneous α particle associated fission and spontaneous nuclear tripartition into three fragments of similar masses has been investigated. DIOGENES is a concentric arrangement of toroidal angular position sensitive ionization chambers and proportional counters to measure the kinetic energies and relative angular distributions of the three reaction products of ternary fission. For α-particle accompanied fission some of the many possible α particle fission-fragment parameter correlations will be discussed. For nearly symmetric low-energy nuclear tripartition new upper limits are presented. Former experimental results which pretended evidence for so called true ternary fission could be explained by charged-particle associated fission with a light particle in the mass range of 13 < A < 23
Prompt Gamma Radiation from Fragments in the Thermal Fission of 235U
International Nuclear Information System (INIS)
Measurements were made on the gamma radiation emitted from fission fragments in slow neutron induced fission of 235U. The fragments were detected with solid state detectors of the surface barrier type and the gamma radiation with a Nal(Tl) scintillator. Mass selection was used so that the gamma radiation could be measured as a function of fragment mass. Time discrimination between the fission gammas and the prompt neutrons released in the fission process was employed to reduce the background. The gamma radiation emitted during different time intervals after the fission event was studied with the help of a collimator, the position of which was changed along the path of the fission fragments. In this way a decay curve was obtained from which the life-time of one of the gamma-emitting states could be estimated. The relative yield of the gamma-rays was determined as a function of mass for different gamma-ray energy portions and two specific time intervals after the fission events. Comparisons were made with data obtained from 252 Cf-fission. Attention is drawn to some features which seem to be the same in 235U and 252 Cf-fission
Role of shell structure in the fusion-fission processes
International Nuclear Information System (INIS)
A comparison of the theoretical and experimental excitation functions of evaporation residues allows one the reveal an effect of the entrance channel and shell structure of reacting nuclei on the fusion-fission mechanism in heavy ion collisions at the near barrier energies. The same aim is purposed by study of dependence of the evaporation residues cross section on the isotope number of projectile or target. It is shown that competition between quasi-fission process and complete fusion may be drastic in case of collision of two massive nuclei and increases by increasing of the projectile energy even in collisions of the intermediate mass nuclei. The excitation functions for evaporation residues produced in the reaction leading to same compound nucleus were analyzed in the framework of the combined model based on the dinuclear system concept and advanced statistical model. It is shown that the competition of complete fusion with quasi fission process is strongly related to peculiarities of the entrance channel, i. e. to the intrinsic fusion barrier and the quasi fission barrier. The results of calculations are in good agreement with the experimental data on synthesis new superheavy elements is discussed. The effect of multi nucleons transfer and surface vibration of nuclei on the dynamics of capture and fusion process is considered. It is demonstrated that the peculiarities of the potential energy surface of interaction of two nuclei determine the spin distribution of compound nuclei and yield of fusion-fission reaction fragments. It is calculated as a function of their atomic and charge number, deformation parameters and binding energies. The decisive role of shell structure of initial nuclei and reaction products is shown by comparison of the calculated results with the experimental data
The even-odd effect in fission-fragment Z yields – a new kind of nuclear clock
Directory of Open Access Journals (Sweden)
Jurado Beatriz
2013-12-01
Full Text Available A model for the even-odd effect in fission based on statistical mechanics is presented. It reveals that the variation of the even-odd effect with the mass of the fissioning nucleus and the increase towards asymmetric splits is due to the important statistical weight of configurations where the light fission fragment populates the ground state of an even-even nucleus. This implies that excitation energy and unpaired nucleons are predominantly transferred to the heavy fragment. Our results indicate that the time for transfer of excitation energy and nucleons is shorter than the saddle-to-scission time.
The even-odd effect in fission-fragment Z yields - A new kind of nuclear clock
International Nuclear Information System (INIS)
A model for the even-odd effect in fission based on statistical mechanics is presented. It reveals that the variation of the even-odd effect with the mass of the fissioning nucleus and the increase towards asymmetric splits is due to the important statistical weight of configurations where the light fission fragment populates the ground state of an even-even nucleus. This implies that excitation energy and unpaired nucleons are predominantly transferred to the heavy fragment. Our results indicate that the time for transfer of excitation energy and nucleons is shorter than the saddle-to-scission time. (authors)
Fission yield measurements at IGISOL
Directory of Open Access Journals (Sweden)
Lantz M.
2016-01-01
Full Text Available The fission product yields are an important characteristic of the fission process. In fundamental physics, knowledge of the yield distributions is needed to better understand the fission process. For nuclear energy applications good knowledge of neutroninduced fission-product yields is important for the safe and efficient operation of nuclear power plants. With the Ion Guide Isotope Separator On-Line (IGISOL technique, products of nuclear reactions are stopped in a buffer gas and then extracted and separated by mass. Thanks to the high resolving power of the JYFLTRAP Penning trap, at University of Jyväskylä, fission products can be isobarically separated, making it possible to measure relative independent fission yields. In some cases it is even possible to resolve isomeric states from the ground state, permitting measurements of isomeric yield ratios. So far the reactions U(p,f and Th(p,f have been studied using the IGISOL-JYFLTRAP facility. Recently, a neutron converter target has been developed utilizing the Be(p,xn reaction. We here present the IGISOL-technique for fission yield measurements and some of the results from the measurements on proton induced fission. We also present the development of the neutron converter target, the characterization of the neutron field and the first tests with neutron-induced fission.
Fission yield measurements at IGISOL
Lantz, M.; Al-Adili, A.; Gorelov, D.; Jokinen, A.; Kolhinen, V. S.; Mattera, A.; Moore, I.; Penttilä, H.; Pomp, S.; Prokofiev, A. V.; Rakopoulos, V.; Rinta-Antila, S.; Simutkin, V.; Solders, A.
2016-06-01
The fission product yields are an important characteristic of the fission process. In fundamental physics, knowledge of the yield distributions is needed to better understand the fission process. For nuclear energy applications good knowledge of neutroninduced fission-product yields is important for the safe and efficient operation of nuclear power plants. With the Ion Guide Isotope Separator On-Line (IGISOL) technique, products of nuclear reactions are stopped in a buffer gas and then extracted and separated by mass. Thanks to the high resolving power of the JYFLTRAP Penning trap, at University of Jyväskylä, fission products can be isobarically separated, making it possible to measure relative independent fission yields. In some cases it is even possible to resolve isomeric states from the ground state, permitting measurements of isomeric yield ratios. So far the reactions U(p,f) and Th(p,f) have been studied using the IGISOL-JYFLTRAP facility. Recently, a neutron converter target has been developed utilizing the Be(p,xn) reaction. We here present the IGISOL-technique for fission yield measurements and some of the results from the measurements on proton induced fission. We also present the development of the neutron converter target, the characterization of the neutron field and the first tests with neutron-induced fission.
Fission approach to cluster radioactivity
Indian Academy of Sciences (India)
D N Poenaru; R A Gherghescu
2015-09-01
Fission theory is used to explain decay. Also, the analytical superasymmetric fission (ASAF) model is successfully employed to make a systematic search and to predict, with other models, cluster radioactivity. The macroscopic–microscopic method is illustrated for the superheavy nucleus 286Fl. Then a few results of the theoretical approach of decay (ASAF, UNIV and semFIS models), cluster decay (ASAF and UNIV) and spontaneous fission dynamics are described with Werner–Wheeler and cranking inertia. UNIV denotes universal curve and semFIS the fission-based semiempirical formula.
International Nuclear Information System (INIS)
The absolute fission rates was measured by the depleted uranium fission chamber. The efficiency of the fission fragments recorded in the fission chamber was analyzed. The factor influencing absolute fission rates was studied in the experiment, including the disturbing effect between detectors and the effect of the structural material of the fission chamber, etc
Facilitated Asymmetric Exclusion
Gabel, Alan; Krapivsky, P. L.; Redner, S.
2010-01-01
We introduce a class of facilitated asymmetric exclusion processes in which particles are pushed by neighbors from behind. For the simplest version in which a particle can hop to its vacant right neighbor only if its left neighbor is occupied, we determine the steady state current and the distribution of cluster sizes on a ring. We show that an initial density downstep develops into a rarefaction wave that can have a jump discontinuity at the leading edge, while an upstep results in a shock w...
Morrison, James
1984-01-01
Asymmetric Synthesis, Volume 4: The Chiral Carbon Pool and Chiral Sulfur, Nitrogen, Phosphorus, and Silicon Centers describes the practical methods of obtaining chiral fragments. Divided into five chapters, this book specifically examines initial chiral transmission and extension. The opening chapter describes the so-called chiral carbon pool, the readily available chiral carbon fragments used as building blocks in synthesis. This chapter also provides a list of 375 chiral building blocks, along with their commercial sources, approximate prices, and methods of synthesis. Schemes involving
Fission fragment mass distribution in the 13C+182W and 176Yb reactions
Directory of Open Access Journals (Sweden)
Ramachandran K.
2013-12-01
Full Text Available 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 180Hg following electron capture of 180Tl 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 13C+182W,176Yb reactions forming the compound nuclei 195Hg and 189Os 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 195Hg, whereas for 189Os, the mass distribution is well fitted with a single Gaussian distribution.
Fission fragment mass distribution in the 13C+182W and 176Yb reactions
International Nuclear Information System (INIS)
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 180Hg following electron capture of 180Tl 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 13C+182W, 176Yb reactions forming the compound nuclei 195Hg and 189Os 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 195Hg, whereas for 189Os, the mass distribution is well fitted with a single Gaussian distribution. (authors)
Fragment properties from fission of 234,238U induced by 6 -10 MeV bremsstrahlung
International Nuclear Information System (INIS)
Experiments to investigate the photon-induced fission of actinide nuclei at excitation energies in the vicinity of the fission barrier are carried out at the super conducting Darmstadt linear electron accelerator S-DALINAC. A twin Frisch grid ionization chamber is used to deduce mass, total kinetic energy, and angular distributions of the fission fragments. In this contribution results on fission fragment mass and total kinetic energy distributions from 234,238U are presented along with the currently on-going investigation of 234U and 232Th fragment angular distributions.
Measurement of fission products yields in the quasi-mono-energetic neutron-induced fission of 232Th
Naik, H.; Mukherji, Sadhana; Suryanarayana, S. V.; Jagadeesan, K. C.; Thakare, S. V.; Sharma, S. C.
2016-08-01
The cumulative yields of various fission products in the 232Th(n, f) reaction at average neutron energies of 5.42, 7.75, 9.35 and 12.53 MeV have been determined by using an off-line γ-ray spectrometric technique. The neutron beam was produced from the 7Li(p, n) reaction by using the proton energies of 7.8, 12, 16 and 20 MeV. The mass chain yields were obtained from the cumulative fission yields by using the charge distribution correction of medium energy fission. The fine structure in the mass yield distribution was interpreted from the point of nuclear structure effect. On the other hand, the higher yield around mass number 133-134 and 143-144 as well as their complementary products were explained based on the standard I and standard II asymmetric mode of fission. From the mass yield data, the average value of light mass (), heavy mass (), the average number of neutrons () and the peak-to-valley (P / V) ratios at different neutron energies of present work and literature data were obtained in the 232Th(n, f) reaction. The different parameters of the mass yield distribution in the 232Th(n, f) reaction were compared with the similar data in the 232Th(γ, f) reaction at comparable excitation energy and a surprising difference was observed.
Study of the fission process of deformed Na clusters in liquid-drop stabilized jellium model
Directory of Open Access Journals (Sweden)
M Payami
2008-07-01
Full Text Available In this work, using the liquid drop model in the context of the stabilized jellium model, we have studied the fission of charged Na clusters. In this study we have assumed a deformed non-spherical shape for the cluster. The ground state energies, critical sizes, fission barrier height, and the evaporation energies have been calculated. The results show a better agreement to the experimental results compared to our earlier work.
Excitation effect on a fission process of nuclei of the heaviest elements
International Nuclear Information System (INIS)
Calculations have been carried out of the fission barriers of excited nuclei for elements with Z=102-108. The effect of nuclear heating is taken into account according to the conventional quantum-statistical formulae. The realistic Woods-Saxon potential is employed to calculate single-particle states. The degree of deviation of the fissioning nucleus shape from axial symmetry and changes in the depth of the intermediate minimum are discussed
Induced Fission of $^{240}$Plutonium within a Real-Time Microscopic Framework}
Bulgac, Aurel; Roche, Kenneth J; Stetcu, Ionel
2015-01-01
We describe the fissioning dynamics of $^{240}$Pu from a configuration in the proximity of the outer fission barrier to full scission and the formation of the fragments within an implementation of the Density Functional Theory (DFT) extended to superfluid systems and real-time dynamics. We predict the total kinetic energy released, the average proton and neutron numbers, and the excitation energies of the fission fragments. The fission fragments emerge with properties similar to those determined experimentally, while the fission dynamics appears to be quite complex, with various shape and pairing modes being excited during the evolution. The time scales of the evolution are found to be much slower than previously expected and the role of the collective inertia in the dynamics is found to be negligible.
In these lectures we have described two different phenomena occuring in dissipative heavy ion collisions : neutron-proton asymmetry and fast fission. Neutron-proton asymmetry has provided us with an example of a fast collective motion. As a consequence quantum fluctuations can be observed. The observation of quantum or statistical fluctuations is directly connected to the comparison between the phonon energy and the temperature of the intrinsic system. This means that this mode might also provide a good example for the investigation of the transition between quantum and statistical fluctuations which might occur when the bombarding energy is raised above 10 MeV/A. However it is by no means sure that in this energy domain enough excitation energy can be put into the system in order to reach such high temperatures over the all system. The other interest in investigating neutron-proton asymmetry above 10 MeV/A is that the interaction time between the two incident nuclei will decrease. Consequently, if some collective motion should still be observed, it will be one of the last which can be seen. Fast fission corresponds on the contrary to long interaction times. The experimental indications are still rather weak and mainly consist of experimental data which cannot be understood in the framework of standard dissipative models. We have seen that a model which can describe both the entrance and the exit configuration gives this mechanism in a natural way and that the experimental data can, to a good extend, be explained. The nicest thing is probably that our old understanding of dissipative heavy ion collisions is not changed at all except for the problems that can now be understood in terms of fast fission. Nevertheless this area desserve further studies, especially on the experimental side to be sure that the consistent picture which we have on dissipative heavy ion collisions still remain coherent in the future.
The SPIDER fission fragment spectrometer for fission product yield measurements
International Nuclear Information System (INIS)
The SPectrometer for Ion DEtermination in fission Research (SPIDER) has been developed for measuring mass yield distributions of fission products from spontaneous and neutron-induced fission. The 2E–2v method of measuring the kinetic energy (E) and velocity (v) of both outgoing fission products has been utilized, with the goal of measuring the mass of the fission products with an average resolution of 1 atomic mass unit (amu). The SPIDER instrument, consisting of detector components for time-of-flight, trajectory, and energy measurements, has been assembled and tested using 229Th and 252Cf radioactive decay sources. For commissioning, the fully assembled system measured fission products from spontaneous fission of 252Cf. Individual measurement resolutions were met for time-of-flight (250 ps FWHM), spacial resolution (2 mm FHWM), and energy (92 keV FWHM for 8.376 MeV). Mass yield results measured from 252Cf spontaneous fission products are reported from an E–v measurement
The SPIDER fission fragment spectrometer for fission product yield measurements
Energy Technology Data Exchange (ETDEWEB)
Meierbachtol, K.; Tovesson, F. [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); Arnold, C. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Blakeley, R. [University of New Mexico, Albuquerque, NM 87131 (United States); Bredeweg, T.; Devlin, M. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Hecht, A.A.; Heffern, L.E. [University of New Mexico, Albuquerque, NM 87131 (United States); Jorgenson, J.; Laptev, A. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Mader, D. [University of New Mexico, Albuquerque, NM 87131 (United States); O' Donnell, J.M.; Sierk, A.; White, M. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
2015-07-11
The SPectrometer for Ion DEtermination in fission Research (SPIDER) has been developed for measuring mass yield distributions of fission products from spontaneous and neutron-induced fission. The 2E–2v method of measuring the kinetic energy (E) and velocity (v) of both outgoing fission products has been utilized, with the goal of measuring the mass of the fission products with an average resolution of 1 atomic mass unit (amu). The SPIDER instrument, consisting of detector components for time-of-flight, trajectory, and energy measurements, has been assembled and tested using {sup 229}Th and {sup 252}Cf radioactive decay sources. For commissioning, the fully assembled system measured fission products from spontaneous fission of {sup 252}Cf. Individual measurement resolutions were met for time-of-flight (250 ps FWHM), spacial resolution (2 mm FHWM), and energy (92 keV FWHM for 8.376 MeV). Mass yield results measured from {sup 252}Cf spontaneous fission products are reported from an E–v measurement.
Directory of Open Access Journals (Sweden)
Ripani M.
2015-01-01
Full Text Available The main features of nuclear fission as physical phenomenon will be revisited, emphasizing its peculiarities with respect to other nuclear reactions. Some basic concepts underlying the operation of nuclear reactors and the main types of reactors will be illustrated, including fast reactors, showing the most important differences among them. The nuclear cycle and radioactive-nuclear-waste production will be also discussed, along with the perspectives offered by next generation nuclear assemblies being proposed. The current situation of nuclear power in the world, its role in reducing carbon emission and the available resources will be briefly illustrated.
Swi1Timeless Prevents Repeat Instability at Fission Yeast Telomeres
Gadaleta, Mariana C.; Das, Mukund M.; Hideki Tanizawa; Ya-Ting Chang; Ken-ichi Noma; Nakamura, Toru M.; Eishi Noguchi
2016-01-01
Genomic instability associated with DNA replication stress is linked to cancer and genetic pathologies in humans. If not properly regulated, replication stress, such as fork stalling and collapse, can be induced at natural replication impediments present throughout the genome. The fork protection complex (FPC) is thought to play a critical role in stabilizing stalled replication forks at several known replication barriers including eukaryotic rDNA genes and the fission yeast mating-type locus...
Asymmetric quantum cloning machines
International Nuclear Information System (INIS)
A family of asymmetric cloning machines for quantum bits and N-dimensional quantum states is introduced. These machines produce two approximate copies of a single quantum state that emerge from two distinct channels. In particular, an asymmetric Pauli cloning machine is defined that makes two imperfect copies of a quantum bit, while the overall input-to-output operation for each copy is a Pauli channel. A no-cloning inequality is derived, characterizing the impossibility of copying imposed by quantum mechanics. If p and p' are the probabilities of the depolarizing channels associated with the two outputs, the domain in (√p,√p')-space located inside a particular ellipse representing close-to-perfect cloning is forbidden. This ellipse tends to a circle when copying an N-dimensional state with N→∞, which has a simple semi-classical interpretation. The symmetric Pauli cloning machines are then used to provide an upper bound on the quantum capacity of the Pauli channel of probabilities px, py and pz. The capacity is proven to be vanishing if (√px, √py, √pz) lies outside an ellipsoid whose pole coincides with the depolarizing channel that underlies the universal cloning machine. Finally, the tradeoff between the quality of the two copies is shown to result from a complementarity akin to Heisenberg uncertainty principle. (author)
Reuveni, Shlomi; Eliazar, Iddo; Yechiali, Uri
2011-10-01
We introduce and explore the asymmetric inclusion process (ASIP), an exactly solvable bosonic counterpart of the fermionic asymmetric exclusion process (ASEP). In both processes, random events cause particles to propagate unidirectionally along a one-dimensional lattice of n sites. In the ASEP, particles are subject to exclusion interactions, whereas in the ASIP, particles are subject to inclusion interactions that coalesce them into inseparable clusters. We study the dynamics of the ASIP, derive evolution equations for the mean and probability generating function (PGF) of the sites’ occupancy vector, obtain explicit results for the above mean at steady state, and describe an iterative scheme for the computation of the PGF at steady state. We further obtain explicit results for the load distribution in steady state, with the load being the total number of particles present in all lattice sites. Finally, we address the problem of load optimization, and solve it under various criteria. The ASIP model establishes bridges between statistical physics and queueing theory as it represents a tandem array of queueing systems with (unlimited) batch service, and a tandem array of growth-collapse processes.
Observation of cold fission in 242Pu spontaneous fission
International Nuclear Information System (INIS)
Coincidence γ-ray data from the spontaneous fission of 242Pu were collected at the Lawrence Berkeley Laboratory high purity Ge (HPGe) array, GAMMASPHERE. Data from several cold-fission (0 neutron emission) isotopic pairs were observed and are presented. An interesting trend in the fractional population of cold-fission events was observed and is discussed. Relative yields of Zr-Xe, Sr-Ba, and Mo-Te pairs were measured. The Zr-Xe system has the most complete data set. Some speculations on the trend in the number of neutrons emitted as a function of the mass of the Xe isotope populated are presented. Comparisons between the yields from the spontaneous fission of 242Pu and the yields from thermal-neutron-induced fission of 241Pu are also presented. copyright 1996 The American Physical Society
$\\beta$-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...
Fission lifetimes of heavy nuclei as probe of the shell effects
International Nuclear Information System (INIS)
The crystal blocking technique has been used to measure delay times in the fission channel for excited nuclei produced in the 28Si + natPt reaction. Experimental results range from 10-17 to 10-18 s at bombarding energies from 140 to 170 MeV. It is shown that fission barriers keep their double-humped structure in the range of excitation energies here considered (40-70 MeV), and that the lifetimes of excited states in the second potential well contribute essentially to the observed delay times in the fission channel
Static aspects of the fission and fusion of liquid 3He drops
International Nuclear Information System (INIS)
Using an effective 3He-3He interaction, the fission and fusion of 3He drops have been investigated from a static point of view. The calculations show that a fission barrier develops for these neutral systems, and that their saddle configurations are rather elongate. The transition from oblate to prolate shapes as a function of the angular momentum L, as well as critical values for fission and fusion are discussed for some selected cases. A kind of proximity potential can be extracted from the drop-drop interaction potentials. (author) 33 refs.; 9 figs
Entrance-channel dependence of fission transients
Charity, R. J.
2004-01-01
Fission transients describe the fission rate as it evolves towards the quasistationary value given by Kramers' formula. The nature of fission transients is dependent on the assumed initial distribution of the compound nuclei along the fission coordinate. Although the standard initial assumption of a near-spherical object leads to a transient suppression of the fission rate (fission delay), a moderate initial fissionlike deformation can reduce the magnitude of this suppression. For still large...
Resolution of the nature of the coupling in subthreshold fission in 238U+n
International Nuclear Information System (INIS)
The analysis of a recent high-resolution neutron capture measurement at 152 m has provided the first evidence that the strong fission resonance at 721 eV is a class-II resonance. This conclusion is based on the measured capture width of 4.7 +- 0.6 MeV, which is considerably smaller than the average capture width of 23.5 MeV for the neighboring resonances. Furthermore, after analyzing the fission widths for the 721- and 1211-eV clusters, we conclude for the J/sup π/ = 1/2+ fission barrier in 239U that the inner barrier is lower than the outer barrier by approx.1.5 MeV
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.
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.
Even-odd effects in the prompt fission emission of even Z actinides
Tudora, Anabella; Hambsch, Franz-Josef; Giubega, Georgiana; Visan, Iuliana
2016-03-01
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.
Fission throughout the periodic table
International Nuclear Information System (INIS)
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
Fission fragment driven neutron source
Miller, Lowell G.; Young, Robert C.; Brugger, Robert M.
1976-01-01
Fissionable uranium formed into a foil is bombarded with thermal neutrons in the presence of deuterium-tritium gas. The resulting fission fragments impart energy to accelerate deuterium and tritium particles which in turn provide approximately 14 MeV neutrons by the reactions t(d,n).sup.4 He and d(t,n).sup.4 He.
Fission at high angular momenta
International Nuclear Information System (INIS)
By studies on the system 40Ar+165Ho by means of selected measuring methods which made a differential selection of certain angular momentum ranges and by this a discrimination between ''fast fission'' and compound-nucleus fission possible the validity of fundamental predictions of the model of the ''fast fission'' hitherto experimentally no yet confirmed was studied: 1) At the turning point of the trajectory for ''fast fission'' calculated by Gregoire the corresponding shape of which must be responsible for the angular distribution the centers of the two fragments must be separated by about 11 fm. 2) The widths of the mass distributions after ''fast fission'' and compound-nucleus fission must be different by a factor 2. The measurements of the angular dependence showed that both prediction cannot be simultaneously brought into accordance with the experimental results. The results of coincidence measurements between fission fragments and alpha particles confirmed the assumption mentioned under topic 2. The analysis of the angular dependence then yielded for the shape of the nuclear complex leading to ''fast fission'' a more compact shape than that indicated by Gregoire, namely with a distance of the fragments of about 7 fm. (orig.)
Fission throughout the periodic table
Energy Technology Data Exchange (ETDEWEB)
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.
Fission of Halving Edges Graphs
Khovanova, Tanya; Yang, Dai
2013-01-01
In this paper we discuss an operation on halving edges graph that we call fission. Fission replaces each point in a given configuration with a small cluster of k points. The operation interacts nicely with halving edges, so we examine its properties in detail.
Fission Dynamics of Compound Nuclei
Iwata, Yoritaka; Heinz, Sophia
2012-01-01
Collisions between $^{248}$Cm and $^{48}$Ca are systematically investigated by time-dependent density functional calculations with evaporation prescription. Depending on the incident energy and impact parameter, fusion, deep-inelastic and quasi-fission events are expected to appear. In this paper, possible fission dynamics of compound nuclei is presented.
Ternary fission of nuclei into comparable fragments
Energy Technology Data Exchange (ETDEWEB)
Karpeshin, F. F., E-mail: fkarpeshin@gmail.com [D.I. Mendeleev Institute forMetrology (VNIIM) (Russian Federation)
2015-07-15
The problem of nuclear fission into three comparable fragments is considered. A mechanism of true ternary fission is proposed. In contrast to sequential fission, where the three fragments arise upon two sequential events of binary fission, the mechanism in question relies on a scenario that originally involves fission into three fragments. This mechanism is driven by a hexadecapole deformation of the fissioning nucleus, in contrast to binary fission associated with quadrupole vibrations of the nuclear surface. The fragment-mass ratios are estimated. The dynamics of formation of collinear fragments and their subsequent motion in opposite directions is traced. The calculated probability of true ternary fission complies with observed values.
Progress in fission product nuclear data
International Nuclear Information System (INIS)
This is the tenth issue of a report series on Fission Product Data, which informs us about all the activities in this field, which are planned, ongoing, or have recently been completed. The types of activities included are measurements, compilations and evaluations of: fission product yields (neutron induced and spontaneous fission), neutron reaction cross sections of fission products, data related to the radioactive decay of fission products, delayed neutron data of fission products, lumped fission product data (decay heat, absorption, etc.). There is also a section with recent references relative to fission product nuclear data
Ternary fission of nuclei into comparable fragments
International Nuclear Information System (INIS)
The problem of nuclear fission into three comparable fragments is considered. A mechanism of true ternary fission is proposed. In contrast to sequential fission, where the three fragments arise upon two sequential events of binary fission, the mechanism in question relies on a scenario that originally involves fission into three fragments. This mechanism is driven by a hexadecapole deformation of the fissioning nucleus, in contrast to binary fission associated with quadrupole vibrations of the nuclear surface. The fragment-mass ratios are estimated. The dynamics of formation of collinear fragments and their subsequent motion in opposite directions is traced. The calculated probability of true ternary fission complies with observed values
Alternative Asymmetric Stochastic Volatility Models
M. Asai (Manabu); M.J. McAleer (Michael)
2010-01-01
textabstractThe stochastic volatility model usually incorporates asymmetric effects by introducing the negative correlation between the innovations in returns and volatility. In this paper, we propose a new asymmetric stochastic volatility model, based on the leverage and size effects. The model is
Fifty years with nuclear fission
International Nuclear Information System (INIS)
The news of the discovery of nuclear fission, by Otto Hahn and Fritz Strassmann in Germany, was brought to the United States by Niels Bohr in January 1939. Since its discovery, the United States, and the world for that matter, has never been the same. It therefore seemed appropriate to acknowledge the fifieth anniversary of its discovery by holding a topical meeting entitled, ''Fifty Years with Nuclear Fission,'' in the United States during the year 1989. The objective of the meeting was to bring together pioneers of the nuclear industry and other scientists and engineers to report on reminiscences of the past and on the more recent development in fission science and technology. The conference highlighted the early pioneers of the nuclear industry by dedicated a full day (April 26), consisting of two plenary sessions, at the National Academy of Sciences (NAS) in Washington, DC. More recent developments in fission science and technology in addition to historical reflections were topics for two fully days of sessions (April 27 and 28) at the main site of the NIST in Gaithersburg, Maryland. The wide range of topics covered in this Volume 1 by this topical meeting included plenary invited, and contributed sessions entitled: Preclude to the First Chain Reaction -- 1932 to 1942; Early Fission Research -- Nuclear Structure and Spontaneous Fission; 50 Years of Fission, Science, and Technology; Nuclear Reactors, Secure Energy for the Future; Reactors 1; Fission Science 1; Safeguards and Space Applications; Fission Data; Nuclear Fission -- Its Various Aspects; Theory and Experiments in Support of Theory; Reactors and Safeguards; and General Research, Instrumentation, and By-Product. The individual papers have been cataloged separately
Prompt Fission Neutron Emission in Resonance Fission of 239Pu
Hambsch, Franz-Josef; Varapai, Natallia; Zeinalov, Shakir; Oberstedt, Stephan; Serot, Olivier
2005-05-01
The prompt neutron emission probability from neutron-induced fission in the resonance region is being investigated at the time-of-flight facility GELINA of the IRMM. A double Frisch-gridded ionization chamber is used as a fission-fragment detector. For the data acquisition of both the fission-fragment signals as well as the neutron detector signals the fast digitization technique has been applied. For the neutron detection, large-volume liquid scintillation detectors from the DEMON collaboration are used. A specialized data analysis program taking advantage of the digital filtering technique has been developed to treat the acquired data. Neutron multiplicity investigations for actinides, especially in resonance neutron-induced fission, are rather scarce. They are, however, important for reactor control and safety issues as well as for understanding the basic physics of the fission process. Fission yield measurements on both 235U and 239Pu without prompt neutron emission coincidence have shown that fluctuation of the fission-fragment mass distribution exists from resonance to resonance, larger in the case of 235U. To possibly explain these observations, the question now is whether the prompt neutron multiplicity shows similar fluctuations with resonance energy.
Engineered Asymmetric Synthetic Vesicles
Lu, Li; Chiarot, Paul
2013-11-01
Synthetic vesicles are small, fluid-filled spheres that are enclosed by a bilayer of lipid molecules. They can be used as models for investigating membrane biology and as delivery vehicles for pharmaceuticals. In practice, it is difficult to simultaneously control membrane asymmetry, unilamellarity, vesicle size, vesicle-to-vesicle uniformity, and luminal content. Membrane asymmetry, where each leaflet of the bilayer is composed of different lipids, is of particular importance as it is a feature of most natural membranes. In this study, we leverage microfluidic technology to build asymmetric vesicles at high-throughput. We use the precise flow control offered by microfluidic devices to make highly uniform emulsions, with controlled internal content, that serve as templates to build the synthetic vesicles. Flow focusing, dielectrophoretic steering, and interfacial lipid self-assembly are critical procedures performed on-chip to produce the vesicles. Fluorescent and confocal microscopy are used to evaluate the vesicle characteristics.
Directory of Open Access Journals (Sweden)
I. Cabrera-Munguia
2015-04-01
Full Text Available A 6-parametric asymptotically flat exact solution, describing a two-body system of asymmetric black dyons, is studied. The system consists of two unequal counterrotating Kerr–Newman black holes, endowed with electric and magnetic charges which are equal but opposite in sign, separated by a massless strut. The Smarr formula is generalized in order to take into account their contribution to the mass. The expressions for the horizon half-length parameters σ1 and σ2, as functions of the Komar parameters and of the coordinate distance, are displayed, and the thermodynamic properties of the two-body system are studied. Furthermore, the seven physical parameters satisfy a simple algebraic relation which can be understood as a dynamical scenario, in which the physical properties of one body are affected by the ones of the other body.
International Nuclear Information System (INIS)
We study a natural implementation of Asymmetric Dark Matter in Twin Higgs models. The mirroring of the Standard Model strong sector suggests that a twin baryon with mass around 5 GeV is a natural Dark Matter candidate once a twin baryon number asymmetry comparable to the SM asymmetry is generated. We explore twin baryon Dark Matter in two different scenarios, one with minimal content in the twin sector and one with a complete copy of the SM, including a light twin photon. The essential requirements for successful thermal history are presented, and in doing so we address some of the cosmological issues common to many Twin Higgs models. The required interactions we introduce predict signatures at direct detection experiments and at the LHC
Organizing for Asymmetric Collaboration
DEFF Research Database (Denmark)
Nielsen, Jørn Flohr; Sørensen, Henrik B.
meet each other. On the contrary, we assume that asymmetry is both important and normal; moreover, asymmetry should be considered to be more complex than economists indicate with their concept of asymmetric information. Thus, the aim of the paper is to explore how asymmetries related to partners...... The vision of new organizational forms consists of less-organized networks and alliances between organizations, in which collaborative capabilities are assumed to be crucial (Miles et al., 2005). The path to such new forms may go through fragile cooperative efforts. Despite the good will of many......' different motives and different situational factors appear in an interorganizational setting. We classify interfaces according to the symmetry/asymmetry in the respective parent organizations' resources, commitment, and control of representatives and indicate how classification schemes can be used to...
Annihilating Asymmetric Dark Matter
Bell, Nicole F; Shoemaker, Ian M
2014-01-01
The relic abundance of particle and antiparticle dark matter (DM) need not be vastly different in thermal asymmetric dark matter (ADM) models. By considering the effect of a primordial asymmetry on the thermal Boltzmann evolution of coupled DM and anti-DM, we derive the requisite annihilation cross section. This is used in conjunction with CMB and Fermi-LAT gamma-ray data to impose a limit on the number density of anti-DM particles surviving thermal freeze-out. When the extended gamma-ray emission from the Galactic Center is reanalyzed in a thermal ADM framework, we find that annihilation into $\\tau$ leptons prefer anti-DM number densities 1-4$\\%$ that of DM while the $b$-quark channel prefers 50-100$\\%$.
Asymmetric spin absorption across a low-resistance oxide barrier
International Nuclear Information System (INIS)
An unconventional method of nonlocal spin detection is demonstrated in mesoscopic lateral spin valves at room temperature. Clear nonlocal spin signals are detected between the two ends of an extended ferromagnetic spin detector. This is different from the conventional method in which the nonlocal voltage is measured between the spin detector and the nonmagnetic channel. The results can be understood as spatially non-uniform absorption of a pure spin current into the spin detector across a low-resistance oxide interface
Interplay of fission modes in mass distribution of light actinide nuclei 225,227Pa
R Dubey; Sugathan, P; Jhingan, A.; Gurpreet Kaur; Ish Mukul; G. Mohanto; Siwal, D.; Saneesh, N.; T Banerjee; Meenu Thakur; Ruchi Mahajan; Kumar, N; Chatterjee, M. B.
2016-01-01
Fission-fragment mass distributions were measured for 225,227 Pa nuclei formed in fusion reactions of 19 F + 206,208 Pb around fusion barrier energies. Mass-angle correlations do not indicate any quasi-fission like events in this bombarding energy range. Mass distributions were fitted by Gaussian distribution and mass variance extracted. At below-barrier energies, the mass variance was found to increase with decrease in energy for both nuclei. Results from present work were compared with exis...
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...
Prompt fission neutron emission in resonance fission of 239Pu
International Nuclear Information System (INIS)
The prompt fission neutron emission probability was investigated at the time-of-flight facility GELINA at the IRMM. A double Frisch-gridded ionization chamber was used as a fission fragment detector. For the data acquisition of both fission fragment signals as well as the neutron detector signals the fast digitization technique has been applied. For the neutron detection large volume liquid scintillation detectors from the DEMON collaboration were used. A specialized data analysis program taking advantage of the digital filtering technique has been developed to treat the acquired data
The decay and fission of uranium
International Nuclear Information System (INIS)
According to the Bernai liquid drop alpha particle model, the nuclear structure of uranium contains a core of 38 alpha particles comprised of 5 concentric layers. The innermost core of 4 alpha particles corresponding to the oxygen 16 nuclide is enclosed by 4 more alpha particles giving the structure of the sulphur 32 nuclide. The third layer of 6 alpha particles completes the 14 alpha particle model of nickel 56. The fourth and fifth layers each contain 12 alpha particles. It will be shown that the fifth layer forms a barrier to the natural radioactive decay of uranium isotopes. Furthermore, it appears that whist the fourth layer sets a limit on the minimum size of the larger daughter fragment of the thermal neutron induced fission of a uranium isotope, the third layer sets a limit on the minimum size of the smaller fragment
Asymmetric Trade Estimator in Modified Gravity: Corporate Tax Rates and Trade in OECD Countries
Estelle P. Dauchy; Christopher Balding
2013-01-01
To study the potentially distortionary impact of differing corporate income tax rates on international trade flows, we use an augmented empirical specification of the gravity model. Incorporating an asymmetric trade barrier measure into a modified gravity model, we capture the impact of corporate income tax rates via the price mechanism impact on trade. Holding other factors constant in a gravity model, one should theoretically expect asymmetric corporate income tax rates to impact bilateral ...
International Nuclear Information System (INIS)
Full text: The implementation in the reaction code system EMPIRE-2.19 of an advanced formalism for fission cross-section calculation has been completed. The formalism is based on the optical model for fission and can be applied for nuclei exhibiting double- or triple-humped barrier starting from sub-barrier excitation energies. The optical model for fission, initially developed to describe the resonant structure of the fission cross section at sub-barrier excitation energies due to the vibrational states in the second well of a double-humped fission barrier, was extended to light actinides by including the relations for the transmission coefficients through a complex triple-humped fission barrier. The real part of the fission barrier is parameterised as a function of the nucleus deformation by five smoothly joined parabolas. The imaginary potential is introduced only in the deformation range corresponding to the second well because the tertiary well is supposed to be shallow enough to neglect the damping of class III vibrational states. The transition states are assumed to be rotational states built on vibrational or non-collective band-heads. As the excitation energy increases, the shell effect, which causes the splitting of the outer barrier, diminishes and the outer humps lump into a single one. Therefore, in the present formalism, triple-humped barriers are associated only to the discrete transition states; the contribution of continuum to the fission coefficients is calculated considering a double-humped barrier. The parameters of the second single barrier equivalent with the outer humps are being determined from the condition of equal transmission coefficients. The saddle-point transition states in continuum are described by level densities (BCS below the critical energy and a modified version of Fermi Gas above) accounting for collective enhancements specific to the nuclear shape asymmetry at each saddle point . The neutron cross sections of 232Th in the
Fifty years with nuclear fission
International Nuclear Information System (INIS)
The news of the discovery of nucler fission, by Otto Hahn and Fritz Strassmann in Germany, was brought to the United States by Niels Bohr in January 1939. Since its discovery, the United States, and the world for that matter, has never been the same. It therefore seemed appropriate to acknowledge the fiftieth anniversary of its discovery by holding a topical meeting entitled, ''Fifty years with nuclear fission,'' in the United States during the year 1989. The objective of the meeting was to bring together pioneers of the nuclear industry and other scientists and engineers to report on reminiscences of the past and on the more recent developments in fission science and technology. The conference highlighted the early pioneers of the nuclear industry by dedicating a full day (April 26), consisting of two plenary sessions, at the National Academy of Sciences (NAS) in Washington, DC. More recent developments in fission science and technology in addition to historical reflections were topics for two full days of sessions (April 27 and 28) at the main sites of the NIST in Gaithersburg, Maryland. The wide range of topics covered by Volume 2 of this topical meeting included plenary invited, and contributed sessions entitled, Nuclear fission -- a prospective; reactors II; fission science II; medical and industrial applications by by-products; reactors and safeguards; general research, instrumentation, and by-products; and fission data, astrophysics, and space applications. The individual papers have been cataloged separately
Influence of different proton and neutron deformations on fission barriers
Energy Technology Data Exchange (ETDEWEB)
Dobrowolski, Artur; Pomorski, Krzysztof [Univ. Marii Curie-Sklodowskiej, Lublin (Poland). Katedra Fizyki Teoretycznej; Bartel, Johann [ULP-CNRS, Strasbourg (France). Inst. of Subatomic Researches
2006-07-15
The response of the nuclear energy with respect to relative changes of proton versus neutron distributions is investigated. Contrary to most macroscopic-microscopic approaches, different multipole deformations of both distributions are admitted. The average part of the total energy is evaluated using the Yukawa-folded model, while microscopic energy corrections are obtained within the Strutinsky and BCS methods.
Multi-Parameter Investigations of Fast Fission Fragments
International Nuclear Information System (INIS)
A number of investigators have noted the peculiar dependence of kinetic energy on the mass of the fragments. This dependence differs considerably for the fission of nuclei by thermal neutrons, neutrons with an energy of 14 MeV and a-particles. It may be that this is a result of the difference not only in excitation energy, but also in the moment introduced by the particle causing fission. It is obviously difficult to deny the part played by nuclear shells in the formation of fragments according to mass, and in this connection the study of the kinetic energy of fragments as a function of their mass is of great interest, as are the corresponding investigations of the widths of distribution of the kinetic energy. Particular attention is given to the characteristics of symmetrical fission of U235 , and it is found that when tails appear in the apparatus spectra of the fission fragments, there occur in the symmetrical mass-region pulses with a most probable total energy of ∼ 120 MeV. Actual symmetrical fission events correspond to a total mean energy of ∼ 155 MeV. The kinetic energy of paired fragments was measured using two surface-barrier silicon counters. The impulses are analysed for amplitude by a two-dimensional 128 x 128 channel ánalyser with a memory on ferrite. The neutron source used was the BR-5 fast neutron reactor, the mean energy of the fast neutron spectrum being ∼250 keV. Layers ofjfissile isotopes with a thickness of 20-30 μg/cm2 were used. The fission of Ù235 by thermal neutrons gave an experimental curve for the mass yield with a 250:1 ratio between peak and vailey. Comparison of the characteristics of the fragments (kinetic energy and mass distribution) showed no noticeable difference in the fission of U235 by thermal and fast neutrons. The total kinetic energy of the fragments in the symmetrical fission of U235 by thermal and fast neutrons proved to be identical, equalling ∼155 MeV, which agrees, within the limits of experimental error
Experiments With Mass-Spectroscopically Separated Fission Product Ions
International Nuclear Information System (INIS)
After a short description of the fission product mass spectrograph installed at the reactor at Garching (Munich) a survey is given of the experiments done with it. Some of these concern the interaction of the swift separated fission product ions with matter. Exact distributions of ion charge numbers were obtained for particles having almost their initial kinetic energies and for those slowed down more or less in thin foils. Their multiple scattering in such foils was also measured. It is hoped that in addition their single scattering on gas atoms can be examined. The energy losses in foils will be studied exactly. The pulse-height defects observed in counting fission particles with surface barrier counters were measured extensively. Other experiments are concerned with features of the fission process and decays of the fission products. In nuclear emulsions the number of β-particle tracks emerging from the ends of the tracks of fission particles of definite mass numbers were counted. From the distributions of these numbers conclusions can be drawn on the distributions of the initial nuclear charges in the decay chains. In addition to this the β- decays of the particles of definite mass numbers are examined directly with a 4π counter. The distributions of the initial kinetic energies of the particles of different mass numbers are also studied. The possibility is discussed of measuring in coincidence with the help of two such spectrographs, both particles of the fission processes travelling in opposite directions. It might also be of advantage to use a mass spectrograph in connection with a large accelerator to study the products of spallation and fragmentation processes. For experiments on the interaction of fission particles with matter the intensity of our spectrograph is sufficient in most cases. In studies of the fission process and the β decays often a-much higher rate of separated particles would be desired. Therefore plans have been made for a new
The spectroscopy of fission fragments
International Nuclear Information System (INIS)
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)
Fission track studies of tektites
International Nuclear Information System (INIS)
The fission track analysis method was used for the age determination of tektites. The tektite samples were obtained from Hainan Island and Leizhou Peninsula. The method consists in cutting and polishing two sections of a sample, irradiating one of these with a known thermal neutron flux (5.90 x 1015/cm2), etching each section identically with hydrofluoric acid, and then comparing the fission track densities in two cases with a microscope. Their fission track age is found to be around 0.7 Ma
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.
Prompt-Neutron Emission from U235 Fission Fragments
International Nuclear Information System (INIS)
A gadolinium-loaded large liquid scintillation counter is being used in conjunction with a neutron beam from the HERALD reactor at the Atomic Weapons Research Establishment, Aldermaston, to study neutron emission in the fission process. In particular, the neutron emission from individual fission fragments is observed. A fission-fragment detector comprising two gold-silicon suríace barrier counters operating in coincidence is situated at the edge of a 1-m-diam. spherical scintillation tank. The solid-state counters are placed on opposite sides of an evaporated fissile deposit on a thin nickel backing. A system of collimators selects for measurement only those fission events that have fragments travelling in the direction along the incident neutron beam and along the axis of the scintillator. Numbers of neutrons detected within 10 ps of a fission event are recorded. The angular correlation of neutron emission with fragment direction is used to associate the neutrons with the particular fission fragment that emitted them. Energies of both fragments are available from the solid-state counters, and identification of fragment mass and of the total kinetic energy of the fragment pair is made. The number of neutrons emitted by each fragment of the pair has been measured as a function of both the fragment mass and the total kinetic energy of the pair for thermal neutrons incident on U2'35. The usual asymmetry in the distribution of excitation energy between the heavy and light fragments is observed. The variation of the number of neutrons from the pair as a function of mass ratio is also determined. (author)
Metal rolling - Asymmetrical rolling process
Alexa, V.; Raţiu, S.; Kiss, I.
2016-02-01
The development of theory and practice related to the asymmetric longitudinal rolling process is based on the general theory of metalworking by pressure and symmetric rolling theory, to which a large number of scientists brought their contribution. The rolling of metal materials was a serious problem throughout history, either economically or technically, because the plating technologies enabled the consumption of raw materials (scarce and expensive) to be reduced, while improving the mechanical properties. Knowing the force parameters related to asymmetric rolling leads to the optimization of energy and raw material consumption. This paper presents data on symmetric rolling process, in order to comparatively highlight the particularities of the asymmetric process.
International Nuclear Information System (INIS)
Fission gamma radiation yields as functions of the total fragment kinetic energy were obtained for 235U thermal-neutron induced fission. The fragments were detected with silicon surface-barrier detectors and the gamma radiation with a Nal(Tl) scintillator. In some of the measurements mass selection was used so that the gamma radiation could also be measured as a function of fragment mass. Time discrimination between the fission gammas and the prompt neutrons released in the fission process was employed to reduce the background. The gamma radiation emitted during different time intervals after the fission event was studied with the help of a collimator, the position of which was changed along the path of the fission fragments. Fission-neutron and gamma-ray data of previous experiments were used for comparisons of the yields, and estimates were made of the variation of the prompt gamma-ray energy with the total fragment kinetic energy
Fusion-fission dynamics and synthesis of the superheavy elements
International Nuclear Information System (INIS)
Experiments of fusion-fission reactions clarify that the life time of nuclear fission is much longer than that expected from Bohr-Wheeler formula from the measurements of multiplicities of neutrons, gamma rays etc. emitted prior scission, and thereby appear to require a dynamical treatment of the process. Following the pioneering work by Kramers with the dissipation- fluctuation dynamics, the fissioning degree of freedom is described with the viewpoint of Brownian motion under incessant interactions with the heat bath particles, i.e., with nucleons in thermal equilibrium, in the present case. In the dynamical description the fission width is no more constant in time, but has a transient feature, as well as the reduction factor, the so-called Kramers factor. Both result in a longer life time, consistent with anomalous multiplicities measured. In the fusion process, Coulomb barriers play a crucial role in lighter heavy ion systems, but in very heavy systems it is known that there exists a hindrance in fusion. That is, the Coulomb barrier is not enough for determination of fusion probability, but an extra-energy above the barrier height is required for the system to fuse. This is understood by the properties of the Liquid Drop Model. After overcoming the Coulomb barrier, the ions touch with each other. But the united system, i.e., the pear-shaped configuration is located outside of the conditional saddle point or of the ridgeline. Therefore, in order to form the spherical compound nucleus, the system has to overcome one more barrier. Naturally, in such a situation, the kinetic energy carried in by the incident projectile has been more or less dissipated, i.e., the composite system is heated up. Thus, the shape evolution toward the spherical shape or toward the re-separation can be considered as a Brownian motion with the heat bath inside. The present author et al. have proposed the two-step model for fusion of massive heavy-ion systems where the fusion probability is
Asymmetric Gepner Models (Revisited)
Gato-Rivera, B
2010-01-01
We reconsider a class of heterotic string theories studied in 1989, based on tensor products of N=2 minimal models with asymmetric simple current invariants. We extend this analysis from (2,2) and (1,2) spectra to (0,2) spectra with SO(10) broken to the Standard Model. In the latter case the spectrum must contain fractionally charged particles. We find that in nearly all cases at least some of them are massless. However, we identify a large subclass where the fractional charges are at worst half-integer, and often vector-like. The number of families is very often reduced in comparison to the 1989 results, but there are no new tensor combinations yielding three families. All tensor combinations turn out to fall into two classes: those where the number of families is always divisible by three, and those where it is never divisible by three. We find an empirical rule to determine the class, which appears to extend beyond minimal N=2 tensor products. We observe that distributions of physical quantities such as th...
Chemical Production using Fission Fragments
International Nuclear Information System (INIS)
Some reactor design considerations of the use of fission recoil fragment energy for the production of chemicals of industrial importance have been discussed previously in a paper given at the Second United Nations International Conference on the Peaceful Uses of Atomic Energy [A/Conf. 15/P.76]. The present paper summarizes more recent progress made on this topic at AERE, Harwell. The range-energy relationship for fission fragments is discussed in the context of the choice of fuel system for a chemical production reactor, and the experimental observation of a variation of chemical effect along the length of a fission fragment track is described for the irradiation of nitrogen-oxygen mixtures. Recent results are given on the effect of fission fragments on carbon monoxide-hydrogen gas mixtures and on water vapour. No system investigated to date shows any outstanding promise for large-scale chemical production. (author)
Background radiation from fission pulses
Energy Technology Data Exchange (ETDEWEB)
England, T.R.; Arthur, E.D.; Brady, M.C.; LaBauve, R.J.
1988-05-01
Extensive source terms for beta, gamma, and neutrons following fission pulses are presented in various tabular and graphical forms. Neutron results from a wide range of fissioning nuclides (42) are examined and detailed information is provided for four fuels: /sup 235/U, /sup 238/U, /sup 232/Th, and /sup 239/Pu; these bracket the range of the delayed spectra. Results at several cooling (decay) times are presented. For ..beta../sup -/ and ..gamma.. spectra, only /sup 235/U and /sup 239/Pu results are given; fission-product data are currently inadequate for other fuels. The data base consists of all known measured data for individual fission products extensively supplemented with nuclear model results. The process is evolutionary, and therefore, the current base is summarized in sufficient detail for users to judge its quality. Comparisons with recent delayed neutron experiments and total ..beta../sup -/ and ..gamma.. decay energies are included. 27 refs., 47 figs., 9 tabs.
Measurement of fission cross sections
International Nuclear Information System (INIS)
A review is presented on the recent progress in the experiment of fission cross section measurement, including recent activity in Japan being carried out under the project of nuclear data measurement. (author)
Lsd1 and Lsd2 Control Programmed Replication Fork Pauses and Imprinting in Fission Yeast
Allyson Holmes; Laura Roseaulin; Catherine Schurra; Herve Waxin; Sarah Lambert; Mikel Zaratiegui; Robert A. Martienssen; Benoit Arcangioli
2012-01-01
In the fission yeast Schizosaccharomyces pombe a chromosomal imprinting event controls the asymmetric pattern of mating-type switching. The orientation of DNA replication at the mating-type locus is instrumental in this process. However, the factors leading to imprinting are not fully identified and the mechanism is poorly understood. Here we show that the replication fork pause at the mat1 locus (MPS1), essential for imprint formation, depends on the lysine specific demethylase, Lsd1. We dem...
Microscopic Description of Nuclear Fission Dynamics
Umar, A. S.; Oberacker, V. E.; Maruhn, J. A.; Reinhard, P.-G.
2010-01-01
We discuss possible avenues to study fission dynamics starting from a time-dependent mean-field approach. Previous attempts to study fission dynamics using the time-dependent Hartree-Fock (TDHF) theory are analyzed. We argue that different initial conditions may be needed to describe fission dynamics depending on the specifics of the fission phenomenon and propose various approaches towards this goal. In particular, we provide preliminary calculations for studying fission following a heavy-io...
Advanced Space Fission Propulsion Systems
Houts, Michael G.; Borowski, Stanley K.
2010-01-01
Fission has been considered for in-space propulsion since the 1940s. Nuclear Thermal Propulsion (NTP) systems underwent extensive development from 1955-1973, completing 20 full power ground tests and achieving specific impulses nearly twice that of the best chemical propulsion systems. Space fission power systems (which may eventually enable Nuclear Electric Propulsion) have been flown in space by both the United States and the Former Soviet Union. Fission is the most developed and understood of the nuclear propulsion options (e.g. fission, fusion, antimatter, etc.), and fission has enjoyed tremendous terrestrial success for nearly 7 decades. Current space nuclear research and technology efforts are focused on devising and developing first generation systems that are safe, reliable and affordable. For propulsion, the focus is on nuclear thermal rockets that build on technologies and systems developed and tested under the Rover/NERVA and related programs from the Apollo era. NTP Affordability is achieved through use of previously developed fuels and materials, modern analytical techniques and test strategies, and development of a small engine for ground and flight technology demonstration. Initial NTP systems will be capable of achieving an Isp of 900 s at a relatively high thrust-to-weight ratio. The development and use of first generation space fission power and propulsion systems will provide new, game changing capabilities for NASA. In addition, development and use of these systems will provide the foundation for developing extremely advanced power and propulsion systems capable of routinely and affordably accessing any point in the solar system. The energy density of fissile fuel (8 x 10(exp 13) Joules/kg) is more than adequate for enabling extensive exploration and utilization of the solar system. For space fission propulsion systems, the key is converting the virtually unlimited energy of fission into thrust at the desired specific impulse and thrust
International Nuclear Information System (INIS)
An information barrier (IB) consists of procedures and technology that prevent the release of sensitive information during a joint inspection of a sensitive nuclear item, and provides confidence that the measurement system into which it has been integrated functions exactly as designed and constructed. Work in the U.S. on radiation detection system information barriers dates back at least to 1990, even though the term is more recent. In January 1999, an Information Barrier Working Group (IBWG) was formed in the United States to help coordinate technical efforts related to information barrier research and development (R and D). This paper presents an overview of the efforts of this group, by its present and former Chairs, as well as recommendations for further information barrier R and D. Progress on the demonstration of monitoring systems containing IBs is also provided. From the U.S. IBWG perspective, the top-level functional requirements for the information barrier portion of an integrated radiation signature-information barrier inspection system are twofold: The host must be assured that its classified information is protected from disclosure to the inspecting party; and The inspecting party must be confident that the integrated inspection system measures, processes, and presents the radiation-signature-based measurement conclusion in an accurate and reproducible manner. It is the position in the United States that in the absence of any agreement to share classified nuclear weapons design information while implementing an inspection regime, the need to protect host country classified warhead design information is paramount and overrules the need to provide confidence to the inspecting party regarding the accuracy and reproducibility of the measurements. The U.S. IBWG has reached a consensus on several critical design elements that define a general standard for radiation signature information barrier design. Technical specialists from cooperating parties must be
Laser spectroscopy of fission fragments
International Nuclear Information System (INIS)
The study of the nuclear structure of fission fragments is discussed. They are neutron-rich nuclei the structure of which possesses some peculiarities. Two regions of fission fragments are discussed: near the shell closures N = 50 and N = 82 and at the boundary of the deformation. A view on the optical properties of these elements is presented and different laser spectroscopic methods for their investigation are proposed. (author)
The microscopic theory of fission
Younes, W.; Gogny, D.
2009-01-01
Fission-fragment properties have been calculated for thermal neutron-induced fission on a $^{239}\\textrm{Pu}$ target, using constrained Hartree-Fock-Bogoliubov calculations with a finite-range effective interaction. A quantitative criterion based on the interaction energy between the nascent fragments is introduced to define the scission configurations. The validity of this criterion is benchmarked against experimental measurements of the kinetic energies and of multiplicities of neutrons emi...
Energy dependence of fission observables
Paşca, Horia
2016-01-01
The mass, charge and isotopic distributions of fission fragments are studied within an improved scission-point statistical model in the reaction 235U+n at different energies of the incident neutron. The available experimental data are well reproduced and the energy-dependencies of the observable characteristics of fission are predicted for future experiments. The calculated mass distribution of 238U+n is also compared with experimental data.
Fission hindrance and nuclear viscosity
Indian Academy of Sciences (India)
Indranil Mazumdar
2015-08-01
We discuss the role of nuclear viscosity in hindering the fission of heavy nuclei as observed in the experimental measurements of GDR -ray spectra from the fissioning nuclei. We review a set of experiments carried out and reported by us previously [see Dioszegi et al, Phys. Rev. C 61, 024613 (2000); Shaw et al, Phys. Rev. C 61, 044612 (2000)] and argue that the nuclear viscosity parameter has no apparent dependence on temperature. However, it may depend upon the deformation of the nucleus.
Dynamin-mediated membrane fission
Morlot, Sandrine
2012-01-01
Membrane fission is required for vesicular traffic between intracellular compartments. Dynamin is a GTPase implicated in vesicle scission during Clathrin-mediated endocytosis. It polymerizes into a helix at the neck of endocytic buds. Upon GTP hydrolysis, conformational changes reduce the helical radius and pitch showing that fission proceeds through a constriction mechanism. We show that the deformation of Dynamin helices is highly concerted and damped by the friction between membrane and Dy...
Magnetically Modified Asymmetric Supercapacitors Project
National Aeronautics and Space Administration — This Small Business Innovation Research Phase I project is for the development of an asymmetric supercapacitor that will have improved energy density and cycle...
Empirical description of beta-delayed fission partial half-lives
Ghys, L; Antalic, S; Huyse, M; Van Duppen, P
2015-01-01
Background: The process of beta-delayed fission (bDF) provides a versatile tool to study low-energy fission in nuclei far away from the beta-stability line, especially for nuclei which do not fission spontaneously. Purpose: The aim of this paper is to investigate systematic trends in bDF partial half-lives. Method: A semi-phenomenological framework was developed to systematically account for the behavior of bDF partial half-lives. Results: The bDF partial half-life appears to exponentially depend on the difference between the Q value for beta decay of the parent nucleus and the fission-barrier energy of the daughter (after beta decay) product. Such dependence was found to arise naturally from some simple theoretical considerations. Conclusions: This systematic trend was confirmed for experimental bDF partial half-lives spanning over 7 orders of magnitudes when using fission barriers calculated from either the Thomas-Fermi or the liquid-drop fission model. The same dependence was also observed, although less p...
Pauwels, D B; Lane, J
2008-01-01
In our recent experiment (March 2007) at the velocity filter SHIP(GSI) we observed the electron-capture delayed fission of the odd-odd isotope $^{194}$At. This is the first unambiguous identification of this phenomenon in the very neutron-deficient nuclei in the vicinity of the proton shell closure at Z=82. In addition, the total kinetic energy (TKE) for the daughter nuclide $^{194}$Po was measured, despite the fact that this isotope does not decay via spontaneous fission. Semi-empirical analysis of the electron-capture Q$_{EC}$ values and fission barriers B$_{f}$ shows that a relatively broad island of ECDF must exist in this region of the Nuclide Chart, with some of the nuclei having unusually high ECDF probabilities. Therefore, this Proposal is intended to initiate the systematic identification and study of $\\beta$-delayed fission at ISOLDE in the very neutron-deficient lead region. Our aim is to provide unique low-energy fission data (e.g. probabilities, TKE release, fission barriers and their isospin dep...
Alpha Particle Emission in Fission
International Nuclear Information System (INIS)
Soon after it was discovered that alpha particles are occasionally emitted in fission, it was concluded, on the basis of the energy and angular distributions of these particles, that they are emitted from the space between the fragments at times close to that of the snapping of the neck that connects them. It is shown that, independent of any (still unknown) dynamic features of the alpha-particle ejection process, the energy required to emit alpha particles from between the fragments at the indicated time is barely available. Presumably the rareness of alpha particles in fission, and the apparent absence of still heavier ''third'' particles, is associated with the marginal energy supply at the time of actual fragment division. The fact that the total kinetic energy release in so-called ternary fission is roughly equal to that in normal binary fission instead of being about 20 MeV larger is shown to imply that the mean fragment separation at the division time is larger in ternary fission. This is interpreted to indicate that alpha particles are emitted with greatest probability n those fissions where ample energy happens to be provided through the stretching of an abnormally long neck between the fragments before they actually divide. It is suggested that the release of the alpha particles is a sudden rather than adiabatic process. (author)
Revealing hidden regularities with a general approach to fission
Energy Technology Data Exchange (ETDEWEB)
Schmidt, Karl-Heinz; Jurado, Beatriz [Chemin du Solarium, CENBG, CNRS/IN2P3, B. P. 120, Gradignan (France)
2015-12-15
Selected aspects of a general approach to nuclear fission are described with the focus on the possible benefit of meeting the increasing need of nuclear data for the existing and future emerging nuclear applications. The most prominent features of this approach are the evolution of quantum-mechanical wave functions in systems with complex shape, memory effects in the dynamics of stochastic processes, the influence of the Second Law of thermodynamics on the evolution of open systems in terms of statistical mechanics, and the topological properties of a continuous function in multi-dimensional space. It is demonstrated that this approach allows reproducing the measured fission barriers and the observed properties of the fission fragments and prompt neutrons. Our approach is based on sound physical concepts, as demonstrated by the fact that practically all the parameters have a physical meaning, and reveals a high degree of regularity in the fission observables. Therefore, we expect a good predictive power within the region extending from Po isotopes to Sg isotopes where the model parameters have been adjusted. Our approach can be extended to other regions provided that there is enough empirical information available that allows determining appropriate values of the model parameters. Possibilities for combining this general approach with microscopic models are suggested. These are supposed to enhance the predictive power of the general approach and to help improving or adjusting the microscopic models. This could be a way to overcome the present difficulties for producing evaluations with the required accuracy. (orig.)
Isotopic yield in alpha accompanied ternary fission of 252Cf
International Nuclear Information System (INIS)
The cold ternary fission of 252Cf with 4He as light charged particle (LCP) is studied with fragments in the equatorial and collinear configuration, taking the interacting barrier as the sum of the Coulomb and proximity potential. The favorable fragment combinations are obtained from the cold valley plot and by calculating the yield for charge-minimized fragments. In both equatorial and collinear configurations, the highest yield is obtained for the fragment combination 116Pd + 4He + 132Sn, which possess doubly magic nuclei 132Sn(N = 82, Z = 50). The presence of doubly or near doubly magic nuclei (132Sn, 130Sn etc.) and higher Q value plays an important role in the alpha accompanied cold ternary fission of 252Cf. The comparison of the relative yield for equatorial configuration with that of collinear configuration, points to the fact that equatorial configuration is the preferred configuration for the LCP (4He) accompanied ternary fission in 252Cf isotope. The yields obtained for the alpha accompanied cold ternary fission of 252Cf in equatorial and collinear configuration are compared with the experimental data. The emission probability of long range alpha (LRA) particle from 252Cf isotope is predicted using our formalism and is found to be in agreement with experimental value. (author)
Revealing hidden regularities with a general approach to fission
International Nuclear Information System (INIS)
Selected aspects of a general approach to nuclear fission are described with the focus on the possible benefit of meeting the increasing need of nuclear data for the existing and future emerging nuclear applications. The most prominent features of this approach are the evolution of quantum-mechanical wave functions in systems with complex shape, memory effects in the dynamics of stochastic processes, the influence of the Second Law of thermodynamics on the evolution of open systems in terms of statistical mechanics, and the topological properties of a continuous function in multi-dimensional space. It is demonstrated that this approach allows reproducing the measured fission barriers and the observed properties of the fission fragments and prompt neutrons. Our approach is based on sound physical concepts, as demonstrated by the fact that practically all the parameters have a physical meaning, and reveals a high degree of regularity in the fission observables. Therefore, we expect a good predictive power within the region extending from Po isotopes to Sg isotopes where the model parameters have been adjusted. Our approach can be extended to other regions provided that there is enough empirical information available that allows determining appropriate values of the model parameters. Possibilities for combining this general approach with microscopic models are suggested. These are supposed to enhance the predictive power of the general approach and to help improving or adjusting the microscopic models. This could be a way to overcome the present difficulties for producing evaluations with the required accuracy. (orig.)
Revealing hidden regularities with a general approach to fission
Schmidt, Karl-Heinz; Jurado, Beatriz
2015-12-01
Selected aspects of a general approach to nuclear fission are described with the focus on the possible benefit of meeting the increasing need of nuclear data for the existing and future emerging nuclear applications. The most prominent features of this approach are the evolution of quantum-mechanical wave functions in systems with complex shape, memory effects in the dynamics of stochastic processes, the influence of the Second Law of thermodynamics on the evolution of open systems in terms of statistical mechanics, and the topological properties of a continuous function in multi-dimensional space. It is demonstrated that this approach allows reproducing the measured fission barriers and the observed properties of the fission fragments and prompt neutrons. Our approach is based on sound physical concepts, as demonstrated by the fact that practically all the parameters have a physical meaning, and reveals a high degree of regularity in the fission observables. Therefore, we expect a good predictive power within the region extending from Po isotopes to Sg isotopes where the model parameters have been adjusted. Our approach can be extended to other regions provided that there is enough empirical information available that allows determining appropriate values of the model parameters. Possibilities for combining this general approach with microscopic models are suggested. These are supposed to enhance the predictive power of the general approach and to help improving or adjusting the microscopic models. This could be a way to overcome the present difficulties for producing evaluations with the required accuracy.
Coriolis interaction and variable reflection asymmetry in fission vibrational resonances
International Nuclear Information System (INIS)
A new analysis of the 720 keV gross resonance in the neutron-induced fission cross section of /sup 230/Th has been made. While confirming some of the main conclusions of earlier analyses (such as presence of a double-parity rotational band, suggesting an underlying vibrational mode in a tertiary well of the fission barrier), the new analysis explores additional features of the vibrational model, as well as employing new fission product angular distribution data and treating already available data in a different way. The new model and least squares analysis indicate strong evidence for Coriolis coupling of the K = 1/2 single-particle state and its coupled rotational motion with a K = (3/2 single-particle state and rotational band, probably lying at 930 keV neutron energy. There is also strong evidence that the opposite parity band in the 720 keV gross resonance, which is brought down by the reflection asymmetry in the tertiary potential energy well, is attenuated by a factor of about 3--5 by the fact that reflection asymmetry is not a property expected of the potential energy surface at the inner barrier containing the well
Active Matter on Asymmetric Substrates
Reichhardt, C. J. Olson; Drocco, J.; Mai, T.; Wan, M. B.; Reichhardt, C.
2011-01-01
For collections of particles in a thermal bath interacting with an asymmetric substrate, it is possible for a ratchet effect to occur where the particles undergo a net dc motion in response to an ac forcing. Ratchet effects have been demonstrated in a variety of systems including colloids as well as magnetic vortices in type-II superconductors. Here we examine the case of active matter or self-driven particles interacting with asymmetric substrates. Active matter systems include self-motile c...
Mobile Termination with Asymmetric Networks
Dewenter, Ralf; Haucap, Justus
2003-01-01
This paper examines mobile termination fees and their regulation when networks are asymmetric in size. It is demonstrated that with consumer ignorance about the exact termination rates (a) a mobile network?s termination rate is the higher the smaller the network?s size (as measured through its subscriber base) and (b) asymmetric regulation of only the larger operators in a market will, ce-teris paribus, induce the smaller operators to increase their termination rates. The results are supporte...
Multicatalyst system in asymmetric catalysis
Zhou, Jian
2014-01-01
This book introduces multi-catalyst systems by describing their mechanism and advantages in asymmetric catalysis. Helps organic chemists perform more efficient catalysis with step-by-step methods Overviews new concepts and progress for greener and economic catalytic reactions Covers topics of interest in asymmetric catalysis including bifunctional catalysis, cooperative catalysis, multimetallic catalysis, and novel tandem reactions Has applications for pharmaceuticals, agrochemicals, materials, and flavour and fragrance
Asymmetric Dark Matter from Leptogenesis
Falkowski, Adam; Ruderman, Joshua T.; Volansky, Tomer
2011-01-01
We present a new realization of asymmetric dark matter in which the dark matter and lepton asymmetries are generated simultaneously through two-sector leptogenesis. The right-handed neutrinos couple both to the Standard Model and to a hidden sector where the dark matter resides. This framework explains the lepton asymmetry, dark matter abundance and neutrino masses all at once. In contrast to previous realizations of asymmetric dark matter, the model allows for a wide range of dark matter mas...
Fission fragment angular distributions and fission cross section validation
International Nuclear Information System (INIS)
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 238U and 232Th have been investigated up to 100 MeV in a single experiment. The n-TOF Collaboration performed the fission cross section measurement of several actinides (232Th, 235U, 238U, 234U, 237Np) 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 232Th, 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 232Th 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 237Np 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 237Np. This sphere was
Report on simulation of fission gas and fission product diffusion in UO_{2}
Energy Technology Data Exchange (ETDEWEB)
Andersson, Anders David [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Perriot, Romain Thibault [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Pastore, Giovanni [Idaho National Lab. (INL), Idaho Falls, ID (United States). Fuel Modeling and Simulation Dept.; Tonks, Michael R. [Idaho National Lab. (INL), Idaho Falls, ID (United States). Fuel Modeling and Simulation Dept.; Cooper, Michael William [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Liu, Xiang-Yang [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Goyal, Anuj [Univ. of Florida, Gainesville, FL (United States). Dept. of Materials Science and Engineering; Uberuaga, Blas P. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Stanek, Christopher Richard [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division
2016-07-22
concentration of the Xe_{U3O} cluster for intrinsic conditions than under irradiation. We speculate that differences in the irradiation conditions and their impact on the Xe_{U3O} cluster can explain the wide range of diffusivities reported in experimental studies. However, all vacancy-mediated mechanisms underestimate the Xe diffusivity compared to the empirical radiation-enhanced rate used in most fission gas release models. We investigate the possibility that diffusion of small fission gas bubbles or extended Xe-vacancy clusters may give rise to the observed radiation-enhanced diffusion coefficient. These studies highlight the importance of U divacancies and an octahedron coordination of uranium vacancies encompassing a Xe fission gas atom. The latter cluster can migrate via a multistep mechanism with a rather low effective barrier, which together with irradiation-induced clusters of uranium vacancies, gives rise to the irradiation-enhanced diffusion coefficient observed in experiments.
International Nuclear Information System (INIS)
Fission energy is reviewed from the viewpoints of technology, economics, politics, manufacturers, consumers, and foreign countries. Technically, the reactor program is operating and the light water reactor industry shows signs of maturing, although recent business has been disappointing. Marketing of gas-cooled reactors depends, not on technical, but economic and political issues. Liquid metal fast breeder reactors have been demonstrated worldwide, while the gas-cooled fast breeder remains an undemonstrated option. Nuclear plants, currently costing the same as coal plants with scrubbers, are the cheapest option for utilities because most of the cost is imbedded. The defeat of nuclear initiatives in seven states indicates that public feeling is not as anti-nuclear as opponents to nuclear power claim. The harshness of last winter demonstrated the advantages of a power source that is not so sensitive to the weather for reliable operation and transport, as well as low cost energy. Other nations are proceeding to build a nuclear capability, which the U.S. may jeopardize because of concerns about the fuel cycle, nuclear waste disposal, uranium reserves, and nuclear proliferation
Neutrons and Kinetic Energy of Fragments in Fission of Heavy Nuclei
International Nuclear Information System (INIS)
The distribution of excitation energy and kinetic energy depending on the mass of the fragment formed in heavy- isotope fission by thermal neutrons is experimentally investigated. The excitation energy is shown to have a low minimum in the region of the double-magic fragment (M ∼132), to increase in the symmetrical fission area and to be at its maximum for fragments complementary to magic. The kinetic energy of the fragments measured for U235 correlates with the excitation energy. The total energy release according to the experimental data is in good agreement with calculations according to Milton's mass tables in every case except that of strongly asymmetric fission. In the measurements conducted, the ratio of the maximum of the fragment yield curve to the minimum (after neutron escape) was 500 : 1. (author)
Asymmetric Gepner models (revisited)
Energy Technology Data Exchange (ETDEWEB)
Gato-Rivera, B. [NIKHEF Theory Group, Kruislaan 409, 1098 SJ Amsterdam (Netherlands)] [Instituto de Fisica Fundamental, CSIC, Serrano 123, Madrid 28006 (Spain); Schellekens, A.N., E-mail: t58@nikhef.n [NIKHEF Theory Group, Kruislaan 409, 1098 SJ Amsterdam (Netherlands)] [Instituto de Fisica Fundamental, CSIC, Serrano 123, Madrid 28006 (Spain)] [IMAPP, Radboud Universiteit, Nijmegen (Netherlands)
2010-12-11
We reconsider a class of heterotic string theories studied in 1989, based on tensor products of N=2 minimal models with asymmetric simple current invariants. We extend this analysis from (2,2) and (1,2) spectra to (0,2) spectra with SO(10) broken to the Standard Model. In the latter case the spectrum must contain fractionally charged particles. We find that in nearly all cases at least some of them are massless. However, we identify a large subclass where the fractional charges are at worst half-integer, and often vector-like. The number of families is very often reduced in comparison to the 1989 results, but there are no new tensor combinations yielding three families. All tensor combinations turn out to fall into two classes: those where the number of families is always divisible by three, and those where it is never divisible by three. We find an empirical rule to determine the class, which appears to extend beyond minimal N=2 tensor products. We observe that distributions of physical quantities such as the number of families, singlets and mirrors have an interesting tendency towards smaller values as the gauge groups approaches the Standard Model. We compare our results with an analogous class of free fermionic models. This displays similar features, but with less resolution. Finally we present a complete scan of the three family models based on the triply-exceptional combination (1,16{sup *},16{sup *},16{sup *}) identified originally by Gepner. We find 1220 distinct three family spectra in this case, forming 610 mirror pairs. About half of them have the gauge group SU(3)xSU(2){sub L}xSU(2){sub R}xU(1){sup 5}, the theoretical minimum, and many others are trinification models.
International Nuclear Information System (INIS)
The different types of ionizing radiation accompanying fission and mixtures of fission products, their activity, the determination of the age of fission products and the biological hazard of radiation caused by instantaneous fission are described. The possibility is described of detection, and of the dosimetry of ionizing radiation resulting from instantaneous fission and emitted by a mixture of fission products, the determination of the dose of neutron radiation, surface contamination, internal contamination and the contamination of water and foods. (J.P.)
Fusion-Fission like studies from medium heavy to light compound systems
International Nuclear Information System (INIS)
It has been shown that for systems as light as ACN = 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 ACN 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
Fission fragment mass distribution studies for 28Si + 197Au, 209Bi, 235U reactions
International Nuclear Information System (INIS)
In reactions with heavy ions, complete fusion and quasi-fission are the competing processes at energies above the Coulomb barrier. The quasi-fission process, in which the system reseparates before reaching a compact compound nucleus, is a major hurdle in forming heavy and superheavy evaporation residues (ER) in heavy-ion reactions. Fission fragment mass distribution for the fully equilibrated compound nucleus is decided at the scission point due to a long descent from saddle to scission. At higher excitation energies, the shell effects are washed out and the mass distribution is expected to be symmetric. The width of the distribution strongly depends on the entrance channel properties, such as mass asymmetry, deformation of interacting nuclei, collision energy, and the Coulomb factor Z1 Z2. Any sudden change in the width of the mass distribution would indicate departure from full equilibration, while onset of mass asymmetry or a sudden increase in width would be a strong signal of quasi fission
Fission characteristics of 216Ra formed in heavy-ion induced reactions
Indian Academy of Sciences (India)
Hadi Eslamizadeh
2013-11-01
A Kramers-modified statistical model is used to calculate the cross-section of the evaporation residue, fission cross-section, average pre-fission multiplicities of protons and -particles for 216Ra formed in 19F + 197Au reactions and results are compared with the experimental data. To calculate these quantities, the effects of temperature and spin K about the symmetry axis have been considered in the calculations of the potential energy surfaces and the fission widths. It is shown that the results of the calculations using values of the temperature coefficient of the effective potential = 0.008 ± 0.003 MeV−2 and scaling factor of the fission-barrier height $r_{s} = 1.004 ± 0.002$ are in good agreement with the experimental data.
Induced Fission of 240Pu within a Real-Time Microscopic Framework
Bulgac, Aurel; Magierski, Piotr; Roche, Kenneth J.; Stetcu, Ionel
2016-03-01
We describe the fissioning dynamics of 240Pu from a configuration in the proximity of the outer fission barrier to full scission and the formation of the fragments within an implementation of density functional theory extended to superfluid systems and real-time dynamics. The fission fragments emerge with properties similar to those determined experimentally, while the fission dynamics appears to be quite complex, with many excited shape and pairing modes. The evolution is found to be much slower than previously expected, and the ultimate role of the collective inertia is found to be negligible in this fully nonadiabatic treatment of nuclear dynamics, where all collective degrees of freedom (CDOF) are included (unlike adiabatic treatments with a small number of CDOF).
Fission time for the {sup 235}U + {alpha} reaction measured by the crystal blocking technique
Energy Technology Data Exchange (ETDEWEB)
Yuminov, O.A. [D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Vorobyevy Gory, Moscow 119991 (Russian Federation)], E-mail: yuminov@p5-lnr.sinp.msu.ru; Borisov, A.M.; Drozdov, V.A.; Eremenko, D.O.; Fotina, O.V. [D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Vorobyevy Gory, Moscow 119991 (Russian Federation); Malaguti, F. [Istituto Nazionale di Fisica Nucleare - Sezione di Bologna, Dipartimento di Fisica dell' Universita, Via Irnerio 46, Bologna (Italy); Olivo, P. [Dipartimento Matemates, Universita' di Bologna, Via Irnerio 46, Bologna (Italy); Platonov, S.Yu. [D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Vorobyevy Gory, Moscow 119991 (Russian Federation); Togo, V. [Istituto Nazionale di Fisica Nucleare - Sezione di Bologna, Dipartimento di Fisica dell' Universita, Via Irnerio 46, Bologna (Italy); Tulinov, A.F. [D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Vorobyevy Gory, Moscow 119991 (Russian Federation)
2009-08-15
The crystal blocking technique has been used to measure the total time of the induced fission process for the {sup 235}U + {alpha} reaction in the energy range of bombarding {alpha}-particles from 25.9 to 31.2 MeV. Experimental fission times observed in this reaction vary from 10{sup -17} to 10{sup -16} s, depending on the projectile energy. Together with the corresponding experimental data on angular anisotropy in the same reaction they were analyzed within the dynamic-statistical approach with allowance for the nuclear dissipation phenomenon and the double-humped fission barrier model. It was demonstrated that the time of induced fission at low excitation energies is sensitive to the nuclear dissipation magnitude.
Fission time for the 235U + α reaction measured by the crystal blocking technique
International Nuclear Information System (INIS)
The crystal blocking technique has been used to measure the total time of the induced fission process for the 235U + α reaction in the energy range of bombarding α-particles from 25.9 to 31.2 MeV. Experimental fission times observed in this reaction vary from 10-17 to 10-16 s, depending on the projectile energy. Together with the corresponding experimental data on angular anisotropy in the same reaction they were analyzed within the dynamic-statistical approach with allowance for the nuclear dissipation phenomenon and the double-humped fission barrier model. It was demonstrated that the time of induced fission at low excitation energies is sensitive to the nuclear dissipation magnitude.
The importance of the giant resonances in hadron and muon induced fission
International Nuclear Information System (INIS)
In the first part of the thesis the fission probability of 238U by means of the reaction 238U(α,α'f) is studied at an incident energy of 480 MeV and a scattering angle of 3.40. In the measured spectrum of the inelastically scattered α particles a strong resonance is found in the excitation energy range from 8 to 13 MeV. The center of mass of the resonance lies at 11 MeV. Its width extends to 4.5 MeV. In the second part of the thesis the muon induced fission of 235U, 238U, 237Np, 242Pu, and 244Pu is studied. Thereby both fission fragments are detected in coincidence by two surface barrier detectors. By this it is possible for the first time to measure the mass and kinetic energy distribution of the fission fragments. (orig./HSI)
Relative quantifying technique to measure mass of fission plate in a fission chamber
International Nuclear Information System (INIS)
Under the same neutron radiation conditions, fission counts are proportional to the number of fission nuclei. Based on this concept, a relative quantifying method has been developed to measure the mass of fission plate in fission chamber on a 14 MeV accelerator neutron source at the Neutron Physics Laboratory, INPC, CAEP. The experimental assembly was introduced and mass of the fission material in several fission chambers was measured. The results by this method agree well (within 1%) with the α-quantifying method. Therefore, it is absolutely feasible to quantify the fission plate mass in fission chambers. The measurement uncertainty is 2%-4%. (authors)
Rodrıguez-Guzmán, R.; Robledo, L. M.
2016-01-01
Mean-field calculations, based on the D1S, D1N and D1M parametrizations of the Gogny energy density functional, have been carried out to obtain the potential energy surfaces relevant to fission in several Ra isotopes with the neutron number 144≤ N≤ 176. Inner and outer barrier heights as well as first and second isomer excitation energies are given. The existence of a well-developed third minimum along the fission paths of Ra nuclei is analyzed in terms of the energetics of the "fragments" defining such elongated configuration. The masses and charges of the fission fragments are studied as functions of the neutron number in the parent Ra isotope. The comparison between fission and α -decay half-lives, reveals that the former becomes faster for increasing neutron numbers. Though there exists a strong variance of the results with respect to the parameters used in the computation of the spontaneous fission rate, a change in tendency is observed at N=164 with a steady increase that makes heavier neutron-rich Ra isotopes stable against fission, diminishing the importance of fission recycling in the r-process.
Energy Technology Data Exchange (ETDEWEB)
Rodriguez-Guzman, R. [Kuwait University, Physics Department, Kuwait (Kuwait); Robledo, L.M. [Universidad Autonoma de Madrid, Departamento de Fisica Teorica, Madrid (Spain)
2016-01-15
Mean-field calculations, based on the D1S, D1N and D1M parametrizations of the Gogny energy density functional, have been carried out to obtain the potential energy surfaces relevant to fission in several Ra isotopes with the neutron number 144 ≤ N ≤ 176. Inner and outer barrier heights as well as first and second isomer excitation energies are given. The existence of a well-developed third minimum along the fission paths of Ra nuclei is analyzed in terms of the energetics of the ''fragments'' defining such elongated configuration. The masses and charges of the fission fragments are studied as functions of the neutron number in the parent Ra isotope. The comparison between fission and α-decay half-lives, reveals that the former becomes faster for increasing neutron numbers. Though there exists a strong variance of the results with respect to the parameters used in the computation of the spontaneous fission rate, a change in tendency is observed at N = 164 with a steady increase that makes heavier neutron-rich Ra isotopes stable against fission, diminishing the importance of fission recycling in the r-process. (orig.)
International Nuclear Information System (INIS)
Mean-field calculations, based on the D1S, D1N and D1M parametrizations of the Gogny energy density functional, have been carried out to obtain the potential energy surfaces relevant to fission in several Ra isotopes with the neutron number 144 ≤ N ≤ 176. Inner and outer barrier heights as well as first and second isomer excitation energies are given. The existence of a well-developed third minimum along the fission paths of Ra nuclei is analyzed in terms of the energetics of the ''fragments'' defining such elongated configuration. The masses and charges of the fission fragments are studied as functions of the neutron number in the parent Ra isotope. The comparison between fission and α-decay half-lives, reveals that the former becomes faster for increasing neutron numbers. Though there exists a strong variance of the results with respect to the parameters used in the computation of the spontaneous fission rate, a change in tendency is observed at N = 164 with a steady increase that makes heavier neutron-rich Ra isotopes stable against fission, diminishing the importance of fission recycling in the r-process. (orig.)
Heavy neutron-deficient radioactive beams: fission studies and fragment distributions
International Nuclear Information System (INIS)
The secondary-beam facility of GSI Darmstadt was used to study the fission process of short-lived radioactive nuclei. Relativistic secondary projectiles were produced by fragmentation of a 1 A GeV 238U primary beam and identified in nuclear charge and mass number. Their production cross sections were determined, and the fission competition in the statistical deexcitation was deduced for long isotopical chains. New results on the enhancement of the nuclear level density in spherical and deformed nuclei due to collective rotational and vibrational excitations were obtained. Using these reaction products as secondary beams, the dipole giant resonance was excited by electromagnetic interactions in a secondary lead target, and fission from excitation energies around 11 MeV was induced. The fission fragments were identified in nuclear charge, and their velocity vectors were determined. Elemental yields and total kinetic energies have been determined for a number of neutron-deficient actinides and preactinides which were not accessible with conventional techniques. The characteristics of multimodal fission of nuclei around 226Th were systematically investigated and related to the influence of shell effects on the potential energy and on the level density between fission barrier and scission. A systematic view on the large number of elemental yields measured gave rise to a new interpretation of the enhanced production of even elements in nuclear fission and allowed for a new understanding of pair breaking in large-scale collective motion. (orig.)
International Nuclear Information System (INIS)
Starting from the first law of thermodynamics, the theoretical principles for the description of interactions between fission products and other materials are derived step by step, using fundamental terms such as phase equilibria, mixtures and solutions. Thereafter, the concepts of Onsager's theory of irreversible thermodynamics are introduced. They serve as an example of modelling fission product transport with special respect to thermochemical properties. In the last chapter real technical concepts for fission product retention are evaluated using thermodynamic criteria. A fine distinction is performed between barrier-, filter- and sinkmechanisms for retention-purposes. One important result is, that a barrier-concept alone doesn't meet the challenge of nuclear power operation without the probability of hazardous accidents. The work is finished by a proposal to improve the fission product retention capabilities of HTR fuel-elements in combination with a coating of the fuel-pebbles. (orig./DG)
A twin grid ion chamber suitable for fission correlation experiment
International Nuclear Information System (INIS)
A twin grid ion chamber suitable for fission multi-parameter correlation experiment is designed and developed. Its behaviour is studied using a 252Cf transfer fissile source on a stainless steel backing in the case when Ar(90%)+CH4(10%) mixture gas and pure CH4 gas are selected as working gases. The ratio of the number of counts per channel at the peak of light fragment group to that at the minimum in the valley is about 2.8, this means that the energy resolution of detecting fission fragments is not worse than that of the barrier type detector. The cosθ of the fragment emission angle can be determined with a resolution in cosθ of 0.03. Because of the constant fast rising leading edge, the cathode signals can be used as timing mark in the multi-parameter correlation experiments
Multi-Nucleon Exchange in Quasi-Fission Reactions
Ayik, S; Yilmaz, O
2015-01-01
Nucleon exchange mechanism is investigated in the central collisions of ${}^{40}$Ca + ${}^{238}$U and ${}^{48}$Ca + ${}^{238}$U systems near the quasi-fission regime in the framework of the Stochastic Mean-Field (SMF) approach. Sufficiently below the fusion barrier, di-nuclear structure in the collisions is maintained to a large extend. Consequently, it is possible to describe nucleon exchange as a diffusion process familiar from deep-inelastic collisions. Diffusion coefficients for proton and neutron exchange are determined from the microscopic basis of the SMF approach in the semi-classical framework. Calculations show that after a fast charge equilibration the system drifts toward symmetry over a very long interaction time. Large dispersions of proton and neutron distributions of the produced fragments indicate that diffusion mechanism may help to populate heavy trans-uranium elements near the quasi-fission regime in these collisions.
Seventy five years of nuclear fission - an overview
International Nuclear Information System (INIS)
The epoch-making discovery of nuclear fission in 1939 by Otto Hahn and Fritz Strassmann heralded the onset of a new era in the history of human civilization. Soon after the discovery of neutron in 1932 by Chadwick, Fermi recognized that due to the absence of Coulomb barrier, neutron was the ideal projectile to induce successive transformations in all nuclei up to uranium. Thus, Fermi and coworkers started experiments with the goal of extending the periodic table by bombarding thorium and uranium with neutrons with the expectation that the neutron capture in the uranium nucleus followed by beta decay will lead to the formation of an element of the next higher atomic number, thus producing a transuranic element. But the observed decay curves of the induced radioactivity did not conform to such a simple picture and intense research activities of those years in Europe in trying to resolve the transuranic puzzle ultimately led to the discovery of nuclear fission
Eremenko, D. O.; Drozdov, V. A.; Fotina, O. V.; Platonov, S. Yu.; Yuminov, O. A.
2016-07-01
Background: It is well known that the anomalous behavior of angular anisotropies of fission fragments at sub- and near-barrier energies is associated with a memory of conditions in the entrance channel of the heavy-ion reactions, particularly, deformations and spins of colliding nuclei that determine the initial distributions for the components of the total angular momentum over the symmetry axis of the fissioning system and the beam axis. Purpose: We develop a new dynamic approach, which allows the description of the memory effects in the fission fragment angular distributions and provides new information on fusion and fission dynamics. Methods: The approach is based on the dynamic model of the fission fragment angular distributions which takes into account stochastic aspects of nuclear fission and thermal fluctuations for the tilting mode that is characterized by the projection of the total angular momentum onto the symmetry axis of the fissioning system. Another base of our approach is the quantum mechanical method to calculate the initial distributions over the components of the total angular momentum of the nuclear system immediately following complete fusion. Results: A method is suggested for calculating the initial distributions of the total angular momentum projection onto the symmetry axis for the nuclear systems formed in the reactions of complete fusion of deformed nuclei with spins. The angular distributions of fission fragments for the 16O+232Th,12C+235,236,238, and 13C+235U reactions have been analyzed within the dynamic approach over a range of sub- and above-barrier energies. The analysis allowed us to determine the relaxation time for the tilting mode and the fraction of fission events occurring in times not larger than the relaxation time for the tilting mode. Conclusions: It is shown that the memory effects play an important role in the formation of the angular distributions of fission fragments for the reactions induced by heavy ions. The
Fission product solvent extraction
International Nuclear Information System (INIS)
Two main objectives concerning removal of fission products from high-level tank wastes will be accomplished in this project. The first objective entails the development of an acid-side Cs solvent-extraction (SX) process applicable to remediation of the sodium-bearing waste (SBW) and dissolved calcine waste (DCW) at INEEL. The second objective is to develop alkaline-side SX processes for the combined removal of Tc, Cs, and possibly Sr and for individual separation of Tc (alone or together with Sr) and Cs. These alkaline-side processes apply to tank wastes stored at Hanford, Savannah River, and Oak Ridge. This work exploits the useful properties of crown ethers and calixarenes and has shown that such compounds may be economically adapted to practical processing conditions. Potential benefits for both acid- and alkaline-side processing include order-of-magnitude concentration factors, high rejection of bulk sodium and potassium salts, and stripping with dilute (typically 10 mM) nitric acid. These benefits minimize the subsequent burden on the very expensive vitrification and storage of the high-activity waste. In the case of the SRTALK process for Tc extraction as pertechnetate anion from alkaline waste, such benefits have now been proven at the scale of a 12-stage flowsheet tested in 2-cm centrifugal contactors with a Hanford supernatant waste simulant. SRTALK employs a crown ether in a TBP-modified aliphatic kerosene diluent, is economically competitive with other applicable separation processes being considered, and has been successfully tested in batch extraction of actual Hanford double-shell slurry feed (DSSF)
The latest progress of fission track analysis
International Nuclear Information System (INIS)
Fission track analysis as a new nuclear track technique is based on fission track annealing in mineral and is used for oil and gas exploration successfully. The west part of China is the main exploration for oil and gas. The oil and gas basins there experienced much more complicated thermal history and higher paleotemperature. In order to apply fission track analysis to these basins, following work was be carried out: 1. The decomposition of grain age distribution of zircon fission tracks. 2. Study on thermal history of Ordos basin using zircon fission track analysis. 3. The fission track study on the Qiang Tang basin in tibet
Energy production using fission fragment rockets
Chapline, G.; Matsuda, Y.
1991-08-01
Fission fragment rockets are nuclear reactors with a core consisting of thin fibers in a vacuum, and which use magnetic fields to extract the fission fragments from the reactor core. As an alternative to ordinary nuclear reactors, fission fragment rockets would have the following advantages: approximately twice the efficiency if the fission fragment energy can be directly converted into electricity; reduction of the buildup of a fission fragment inventory in the reactor could avoid a Chernobyl type disaster; and collection of the fission fragments outside the reactor could simplify the waste disposal problem.
Energy production using fission fragment rockets
International Nuclear Information System (INIS)
Fission fragment rockets are nuclear reactors with a core consisting of thin fibers in a vacuum, and which use magnetic fields to extract the fission fragments from the reactor core. As an alternative to ordinary nuclear reactors, fission fragment rockets would have the following advantages: Approximately twice as efficient if one can directly convert the fission fragment energy into electricity; by reducing the buildup of a fission fragment inventory in the reactor one could avoid a Chernobyl type disaster; and collecting the fission fragments outside the reactor could simplify the waste disposal problem. 6 refs., 4 figs., 2 tabs
Contribution to the study of nuclear fission
International Nuclear Information System (INIS)
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)
Compact fission counter for DANCE
International Nuclear Information System (INIS)
The Detector for Advanced Neutron Capture Experiments (DANCE) consists of 160 BF2 crystals with equal solid-angle coverage. DANCE is a 4π γ-ray calorimeter and designed to study the neutron-capture reactions on small quantities of radioactive and rare stable nuclei. These reactions are important for the radiochemistry applications and modeling the element production in stars. The recognition of capture event is made by the summed γ-ray energy which is equivalent of the reaction Q-value and unique for a given capture reaction. For a selective group of actinides, where the neutron-induced fission reaction competes favorably with the neutron capture reaction, additional signature is needed to distinguish between fission and capture γ rays for the DANCE measurement. This can be accomplished by introducing a detector system to tag fission fragments and thus establish a unique signature for the fission event. Once this system is implemented, one has the opportunity to study not only the capture but also fission reactions. A parallel-plate avalanche counter (PPAC) has many advantages for the detection of heavy charged particles such as fission fragments. These include fast timing, resistance to radiation damage, and tolerance of high counting rate. A PPAC also can be tuned to be insensitive to α particles, which is important for experiments with α-emitting actinides. Therefore, a PPAC is an ideal detector for experiments requiring a fast and clean trigger for fission. A PPAC with an ingenious design was fabricated in 2006 by integrating amplifiers into the target assembly. However, this counter was proved to be unsuitable for this application because of issues related to the stability of amplifiers and the ability to separate fission fragments from α's. Therefore, a new design is needed. A LLNL proposal to develop a new PPAC for DANCE was funded by NA22 in FY09. The design goal is to minimize the mass for the proposed counter and still be able to maintain a stable
Compact fission counter for DANCE
Energy Technology Data Exchange (ETDEWEB)
Wu, C Y; Chyzh, A; Kwan, E; Henderson, R; Gostic, J; Carter, D; Bredeweg, T; Couture, A; Jandel, M; Ullmann, J
2010-11-06
The Detector for Advanced Neutron Capture Experiments (DANCE) consists of 160 BF{sub 2} crystals with equal solid-angle coverage. DANCE is a 4{pi} {gamma}-ray calorimeter and designed to study the neutron-capture reactions on small quantities of radioactive and rare stable nuclei. These reactions are important for the radiochemistry applications and modeling the element production in stars. The recognition of capture event is made by the summed {gamma}-ray energy which is equivalent of the reaction Q-value and unique for a given capture reaction. For a selective group of actinides, where the neutron-induced fission reaction competes favorably with the neutron capture reaction, additional signature is needed to distinguish between fission and capture {gamma} rays for the DANCE measurement. This can be accomplished by introducing a detector system to tag fission fragments and thus establish a unique signature for the fission event. Once this system is implemented, one has the opportunity to study not only the capture but also fission reactions. A parallel-plate avalanche counter (PPAC) has many advantages for the detection of heavy charged particles such as fission fragments. These include fast timing, resistance to radiation damage, and tolerance of high counting rate. A PPAC also can be tuned to be insensitive to {alpha} particles, which is important for experiments with {alpha}-emitting actinides. Therefore, a PPAC is an ideal detector for experiments requiring a fast and clean trigger for fission. A PPAC with an ingenious design was fabricated in 2006 by integrating amplifiers into the target assembly. However, this counter was proved to be unsuitable for this application because of issues related to the stability of amplifiers and the ability to separate fission fragments from {alpha}'s. Therefore, a new design is needed. A LLNL proposal to develop a new PPAC for DANCE was funded by NA22 in FY09. The design goal is to minimize the mass for the proposed
Thorium-uranium fission radiography
Haines, E. L.; Weiss, J. R.; Burnett, D. S.; Woolum, D. S.
1976-01-01
Results are described for studies designed to develop routine methods for in-situ measurement of the abundance of Th and U on a microscale in heterogeneous samples, especially rocks, using the secondary high-energy neutron flux developed when the 650 MeV proton beam of an accelerator is stopped in a 42 x 42 cm diam Cu cylinder. Irradiations were performed at three different locations in a rabbit tube in the beam stop area, and thick metal foils of Bi, Th, and natural U as well as polished silicate glasses of known U and Th contents were used as targets and were placed in contact with mica which served as a fission track detector. In many cases both bare and Cd-covered detectors were exposed. The exposed mica samples were etched in 48% HF and the fission tracks counted by conventional transmitted light microscopy. Relative fission cross sections are examined, along with absolute Th track production rates, interaction tracks, and a comparison of measured and calculated fission rates. The practicality of fast neutron radiography revealed by experiments to data is discussed primarily for Th/U measurements, and mixtures of other fissionable nuclei are briefly considered.
International Nuclear Information System (INIS)
Recently, Blyumkina et al. have noted tfte existence ot fission channel ettects in the total kinetic energy of fragments of fission induced by s- and p-wave neutrons. Effects of this nature can also be expected in the variation of the fragment kinetic energies from resonance to resonance in low-energy (s-wave) neutron-induced fission. A fission-fragment detector whose efficiency is dependent on the kinetic energy of the fragments was used in the study of the slow-neutron-induced fission of U235. Comparing the counting-rate of this detector with a conventional fission detector, whose efficiency is independent of the fragment kinetic energy, shows that there exists a variation in the kinetic energy of certain fragments with neutron energy in the neutron energy region from 0.025 to 1 eV. In order to determine the response of the kinetic-energy-sensitive detector, it was necessary to measure the rangè-energy relations of fission fragments in various media, including noble gases and metallic foils. It was estimated from these data that the variation in the fragment kinetic energy release is ∼500 keV, for those fission events that give the lightest and most energetic of the heavy fragments. The variation in fragment kinetic energy is strongly asymmetric about the 0.28-eV resonance in U235, and suggests that the fragment kinetic energy sensitively reflects the presence of interference effects among resonances in fission. A multi-level multi-channel analysis of the data has been made, based on the parameters of Vogt and under the assumption that different fission channels lead to different configurations at scission, such that the kinetic energy release is also different. Previously a major objection to multi-level multi-channel analysis in fission has been that the parameters obtained are not unique. However, the possibility of observing partial fission cross-sections (fission occurring by way of one channel only) removes one of the ambiguities inherent in the multi
Fragment properties from fission of actinide nuclei induced by 6-10 MeV bremsstrahlungI
Gook, A.; Eckardt, C.; Enders, J.; Freudenberger, M.; von Neumann-Cosel, P.; Oberstedt, A.; Oberstedt, S.; Richter, A.
Experiments to investigate the photon-induced fission of actinide nuclei at excitation energies in the vicinity of the fission barrier are carried out at the superconducting Darmstadt linear electron accelerator S-DALINAC. A twin-Frisch-grid ionization chamber is used to deduce mass, total kinetic energy, and angular distributions of the fission fragments. First experiments on 238U and 234U have shown that the experimental setup provides excellent conditions for investigating low-energy bremsstrahlung induced fission. Further experiments on 234U and 232Th are currently in progress. In this contribution results from the first experiment on fission fragment mass and total kinetic energy distributions from 234,238U are presented along with preliminary data from an on-going investigation of angular distributions from 234U(γ, f)
Nuclear fission and neutron-induced fission cross-sections
James, G D; Michaudon, A; Michaudon, A; Cierjacks, S W; Chrien, R E
2013-01-01
Nuclear Fission and Neutron-Induced Fission Cross-Sections is the first volume in a series on Neutron Physics and Nuclear Data in Science and Technology. This volume serves the purpose of providing a thorough description of the many facets of neutron physics in different fields of nuclear applications. This book also attempts to bridge the communication gap between experts involved in the experimental and theoretical studies of nuclear properties and those involved in the technological applications of nuclear data. This publication will be invaluable to those interested in studying nuclear fis
Dynamics of Cold Atoms Crossing a One-Way Barrier
Thorn, Jeremy J.; Schoene, Elizabeth A.; Li, Tao; Steck, Daniel A.
2009-01-01
We implemented an optical one-way potential barrier that allows ultracold $^{87}$Rb atoms to transmit through when incident on one side of the barrier but reflect from the other. This asymmetric barrier is a realization of Maxwell's demon, which can be employed to produce phase-space compression and has implications for cooling atoms and molecules not amenable to standard laser-cooling techniques. The barrier comprises two focused, Gaussian laser beams that intersect the focus of a far-off-re...
International Nuclear Information System (INIS)
Full text: An information barrier (IB) consists of procedures and technology that prevent the release of sensitive information during a joint inspection of a sensitive nuclear item, and provides confidence that the measurement system into which it has been integrated functions exactly as designed and constructed. Work in the U.S. on radiation detection system information barriers dates back at least to 1990, even though the terminology is more recent. In January 1999 the Joint DoD-DOE Information Barrier Working Group was formed in the United States to help coordinate technical efforts related to information barrier R and D. This paper presents an overview of the efforts of this group, by its Chairs, as well as recommendations for further information barrier R and D. Progress on the demonstration of monitoring systems containing IBs is also provided. From the U.S. perspective, the basic, top-level functional requirements for the information barrier portion of an integrated radiation signature-information barrier inspection system are twofold: The host must be assured that his classified information is protected from disclosure to the inspecting party; and The inspecting party must be confident that the integrated inspection system measures, processes, and presents the radiation-signature-based measurement conclusion in an accurate and reproducible manner. It is the position of the United States that in the absence of any agreement to share classified nuclear weapons design information in the conduct of an inspection regime, the requirement to protect host country classified warhead design information is paramount and admits no tradeoff versus the confidence provided to the inspecting party in the accuracy and reproducibility of the measurements. The U.S. has reached an internal consensus on several critical design elements that define a general standard for radiation signature information barrier design. These criteria have stood the test of time under intense
Ternary fission of superheavy elements
Balasubramaniam, M.; Vijayaraghavan, K. R.; Manimaran, K.
2016-01-01
Ternary fission of superheavy nuclei is studied within the three-cluster model potential energy surfaces (PESs). Due to shell effects, the stability of superheavy nuclei has been predicted to be associated with Z =114 , 120, and 126 for protons and N =184 for neutrons. Taking some representative nuclei we have extended the ternary fission studies to superheavy nuclei. We adopted two minimization procedures to minimize the potential and considered different arrangements of the fragments. The PES from one-dimensional minimization reveals a strong cluster region favoring various ternary breakups for an arrangement in which the lightest fragment is kept at the center. The PES obtained from two-dimensional minimization reveals strong preference of ternary fragmentation in the true ternary fission region. Though the dominant decay mode of superheavy nuclei is α decay, the α -accompanied ternary breakup is found to be a nonfavorable one. Further, the prominent ternary combinations are found to be associated with the neutron magic number.
International Nuclear Information System (INIS)
In this paper we summarize the current status of the recent US evaluation for 34 fissioning nuclides at one or more neutron incident energies and for spontaneous fission. Currently there are 50 yields sets, and for each we have independent and cumulative yields and uncertainties for approximately 1100 fission products. When finalized the recommended data will become part of Version VI of the US ENDF/B. Other major evaluations in progress that are included in a recently formed IAEA Coordinated Research Program are also summarized. In a second part we review two empirical models in use to estimate independent yields. Comparison of model estimates with measured data is presented, including a comparison with some recent data obtained from Lohengrin (Cf-249 T). 18 refs., 13 figs., 3 tabs
Report of fission study meeting
International Nuclear Information System (INIS)
This book is the report of fission Study Meeting held from September 19 to 21, 1985 in the Research Center for Nuclear Physics, Osaka University. The objective of this study meeting was to stimulate the research on nuclear physics in Japan, which began to show new development accompanying the advance of the research on heavy ion nuclear reaction, and to make this a new starting point. More than 50 participants from physical, chemical and engineering fields, who have interest in the theory and experiment related to nuclear fission, gathered, and the meeting was a success beyond expectation. The contents covered a wide range including nuclear smashing reaction as well as nuclear fission in a narrow sense. In this book, the gists of 28 papers are collected. (Kako, I.)
High performance of junctionless MOSFET with asymmetric gate
Wang, Ying; Tang, Yan; Sun, Ling-ling; Cao, Fei
2016-09-01
In this work, we propose a junctionless MOSFET with asymmetric gates (AG-JL MOSFET). This device is a double gate structure with a lateral offset between the gate, and this leads to different characteristic than a conventional double gate structure. Specifically, the asymmetric gate modulates the effective channel length depending on whether the device is in the ON or OFF state, which this leads to more ideal device characteristics. A comprehensive device performance comparison including the ION/IOFF ratio, subthreshold slope (SS), and drain-induced barrier lowering (DIBL) between the proposed device and a conventional device is presented. The proposed device exhibits superior performance when compared a conventional device, and results show that it is also less sensitive to process variations.
Santhosh, K P; Krishnan, Sreejith
2016-01-01
Within the Unified ternary fission model (UTFM), the alpha accompanied ternary fission of even-even $^{244-260}$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 244^Cf isotope, the highest yield is obtained for the fragment combination 108^Ru+4^He+132^Te, which contain near doubly magic nuclei 132^Te (N=80, Z=52). In the case of 246^Cf and 248^Cf isotopes, the highest yield is obtained fo...
Fission valleys of double-magic superheavy nuclei
International Nuclear Information System (INIS)
An alternative Z = 120 proton shell closure is analysed for the superheavy region. The proton magic numbers 114 and 120 are obtained for two different sets of the spin-orbit and l2 strength parameters, κ and μ. The possible double-magic superheavy nuclei 304 120 and 298 114 are compared within a four-dimensional space of deformation which includes mass-asymmetry and three geometrical degrees of freedom. The potential energy is calculated with the macroscopic-microscopic method. A well suited single-particle model for such a study is the two-center shell model. This model is used to obtain the energy levels. The shell corrections are computed using the Strutinsky method and are added to the Yukawa-plus-exponential macroscopic energy. One considers axially symmetric shapes. Spherical ground states are assumed for the initial and final fragments. Different pairs of fragments are obtained by changing the mass asymmetry parameter η. Two energy valleys play a major role in this static study: one leading to the double magic light fragment 132 Sn corresponding to almost symmetric splitting, the other belonging to the double magic heavy fragment 208 Pb at larger mass asymmetry.The lead valley explains the cluster radioactivity for the lighter nuclei. Fission-like barriers are obtained by two intersected spheres with zero neck radius in-between. The fission barriers have been calculated by minimization of the energy within the three dimensional deformation space. At least one magic number and another one close to magic is needed within the fragment pair to shape a valley on the potential energy surfaces. The static barriers are more likely to favour the two fission modes leading to the above mentioned double-magic fragments due to the combined effect of two shell closures on the total energy value. (authors)
Hydroxamic acids in asymmetric synthesis.
Li, Zhi; Yamamoto, Hisashi
2013-02-19
Metal-catalyzed stereoselective reactions are a central theme in organic chemistry research. In these reactions, the stereoselection is achieved predominantly by introducing chiral ligands at the metal catalyst's center. For decades, researchers have sought better chiral ligands for asymmetric catalysis and have made great progress. Nevertheless, to achieve optimal stereoselectivity and to catalyze new reactions, new chiral ligands are needed. Because of their high metal affinity, hydroxamic acids play major roles across a broad spectrum of fields from biochemistry to metal extraction. Dr. K. Barry Sharpless first revealed their potential as chiral ligands for asymmetric synthesis in 1977: He published the chiral vanadium-hydroxamic-acid-catalyzed, enantioselective epoxidation of allylic alcohols before his discovery of Sharpless asymmetric epoxidation, which uses the titanium-tartrate complex as the chiral reagent. However, researchers have reported few highly enantioselective reactions using metal-hydroxamic acid as catalysts since then. This Account summarizes our research on metal-catalyzed asymmetric epoxidation using hydroxamic acids as chiral ligands. We designed and synthesized a series of new hydroxamic acids, most notably the C2-symmetric bis-hydroxamic acid (BHA) family. V-BHA-catalyzed epoxidation of allylic and homoallylic alcohols achieved higher activity and stereoselectivity than Sharpless asymmetric epoxidation in many cases. Changing the metal species led to a series of unprecedented asymmetric epoxidation reactions, such as (i) single olefins and sulfides with Mo-BHA, (ii) homoallylic and bishomoallylic alcohols with Zr- and Hf-BHA, and (iii) N-alkenyl sulfonamides and N-sulfonyl imines with Hf-BHA. These reactions produce uniquely functionalized chiral epoxides with good yields and enantioselectivities. PMID:23157425
The VERDI fission fragment spectrometer
Frégeau M.O.; Bryś T.; Gamboni Th.; 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 conf...
Spontaneous fission of superheavy nuclei
Indian Academy of Sciences (India)
R A Gherghescu; D N Poenaru
2015-09-01
The macroscopic–microscopic method is extended to calculate the deformation energy and penetrability for binary 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. The microscopic shell and pairing corrections are obtained using the Strutinsky and BCS approaches and the cranking formulae yield the inertia tensor. Finally, the WKB method is used to calculate penetrabilities and spontaneous fission half-lives. Calculations are performed for the decay of 282,292120 nuclei.
Advanced Fission Reactor Program objectives
International Nuclear Information System (INIS)
The objective of an advanced fission reactor program should be to develop an economically attractive, safe, proliferation-resistant fission reactor. To achieve this objective, an aggressive and broad-based research and development program is needed. Preliminary work at Brookhaven National Laboratory shows that a reasonable goal for a research program would be a reactor combining as many as possible of the following features: (1) initial loading of uranium enriched to less than 15% uranium 235, (2) no handling of fuel for the full 30-year nominal core life, (3) inherent safety ensured by core physics, and (4) utilization of natural uranium at least 5 times as efficiently as light water reactors
Search for Singlet Fission Chromophores
Energy Technology Data Exchange (ETDEWEB)
Havlas, Z.; Akdag, A.; Smith, M. B.; Dron, P.; Johnson, J. C.; Nozik, A. J.; Michl, J.
2012-01-01
Singlet fission, in which a singlet excited chromophore shares its energy with a ground-state neighbor and both end up in their triplet states, is of potential interest for solar cells. Only a handful of compounds, mostly alternant hydrocarbons, are known to perform efficiently. In view of the large number of conditions that a successful candidate for a practical cell has to meet, it appears desirable to extend the present list of high performers to additional classes of compounds. We have (i) identified design rules for new singlet fission chromophores and for their coupling to covalent dimers, (ii) synthesized them, and (iii) evaluated their performance as neat solids or covalent dimers.
Surface fission tracks in diamond
International Nuclear Information System (INIS)
Scanning Probe Microscope (SPM) images reveal important fingerprint features of latent tracks induced in diamond by fission fragments from a californium source. Collimated fission fragments with a binary distribution of the predominant energies of 79.4 and 103.8 MeV, are assumed. Cavities, reticular formations around these cavities, and black spots of graphite were found. A brief discussion on the possible track formation mechanism is given on the basis of the explosion spike theory; an attempt to determine latent track core and halo parameters is included
International Nuclear Information System (INIS)
In this paper the author presents the problems of the radioactive wastes generated by the nuclear fission. The first part devoted to the fission phenomenon explains the incident neutron energy and the target nuclei role. The second part devoted to the nuclear wastes sources presents the production of wastes upstream of the reactors, in the reactors and why these wastes are dangerous. The third part discusses the radioactive wastes management in France (classification, laws). The last part details the associated research programs: the radionuclides separation, the disposal, the underground storage, the transmutation and the thorium cycle. (A.L.B.)
Studies on the reaction mechanism of the muon induced nuclear fission
International Nuclear Information System (INIS)
The mass and energy distribution of the fission fragments after muon induced nuclear fission allows the determination of the mean excitation energy of the fissioning nucleus after muon capture. By the systematic comparison with a mass distribution of a corresponding reaction for the first time for this an accuracy of about 1 MeV could be reached. Theoretical calculations on the excitation probability in the muon capture allow in connection with the fission probability an estimating calculation of this energy. The experimental result represents by this a test criterium for the valuation of the theoretical calculation. The measured probabilities for the occurrence of radiationless transitions in the muonic γ cascade of 237Np permit an indirect experimental determination of the barrier enhancement which causes the muon present during the fission process. The value found for this extends to 0.75+-0.1 MeV. A change of the mass distribution by the muon cannot be detected in the nuclides 235U, 237Np, and 242Pu studied here. Only the mean total kinetic energy of the fission products is reduced in these three nuclides in the prompt μ- induced fission by 1 to 2 MeV. For this result the incomplete screening of the nuclear charge during the fission process is made responsible. A mass dependence of this reduction has not been stated. Because the muon has appearently no influence on the mass splitting it can be valied as nearly ideal particle in order to study the hitherto little studied dynamics of the fission process. (orig.)
Fission properties of the heaviest elements
International Nuclear Information System (INIS)
The authors discuss fission properties of the heaviest elements. In particular they focus on stability with respect to spontaneous fission and on the prospects of extending the region of known nuclei beyond the peninsula of currently known nuclides
Progress in fission product nuclear data
International Nuclear Information System (INIS)
This is the 12th issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the IAEA. The purpose of this series is to inform scientists working on FPND, or using such data, about all activities in this field which are planned, ongoing, or have recently been completed. The type of activities included are: measurements, compilations and evaluations of fission product yields (neutron induced and spontaneous fission), neutron reaction cross sections of fission products, data related to the radioactive decay of fission products, delayed neutron data of fission products and lumped fission product data (decay heat, absorption etc.). The first part of the report consists of unaltered original contributions which the authors have sent to IAEA/NDS. The second part contains recent references relative to fission product nuclear data, which were not covered by the contributions submitted, and selected papers from conferences