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.)
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.
International Nuclear Information System (INIS)
Certain preliminary findings on the workings of the biosphere code BIOMOD are presented. These are intended as the basis for technical discussions relating to the development of BIOMOD1. Discussion is restricted to observations on the relationships between user-defined input and i) relative significance of different pathways for activity transfer to man, ii) total activity consumption by man, and iii) activity released to dose conversion factors to be used in SYVAC. (author)
How spontaneous fission was discovered
International Nuclear Information System (INIS)
The 70th anniversary of the discovery of spontaneous fission by the young Russian physicists Konstantin A. Petrzhak and Georgii N. Flerov is commemorated. The situation in the 1940s is described and the activities of the 2 scientists, including their involvement in the development of the A-bomb, is outlined. (P.A.)
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.
Absolute calibration technique for spontaneous fission sources
International Nuclear Information System (INIS)
An absolute calibration technique for a spontaneously fissioning nuclide (which involves no arbitrary parameters) allows unique determination of the detector efficiency for that nuclide, hence of the fission source strength
Spontaneous fission properties and lifetime systematics
International Nuclear Information System (INIS)
Half-lives for spontaneous fission of nuclides with even and odd numbers of particles are compared with recent theoretical calculations. A summary of odd particle hindrance factors is given. The most recent measurements of kinetic-energy and mass distributions and neutron emission for spontaneous fission of the heaviest nuclides are summarized and discussed. 51 refs., 9 figs
Spontaneous fission of 256Rf, new data
Svirikhin, A. I.; Yeremin, A. V.; Izosimov, I. N.; Isaev, A. V.; Kuznetsov, A. N.; Malyshev, O. N.; Popeko, A. G.; Popov, Yu. A.; Sokol, E. A.; Chelnokov, M. L.; Chepigin, V. I.; Andel, B.; Asfari, M. Z.; Gall, B.; Yoshihiro, N.; Kalaninova, Z.; Mullins, S.; Piot, J.; Stefanova, E.; Tonev, D.
2016-07-01
Spontaneous fission properties of the short-lived neutron-deficient 256Rf nucleus produced in the complete fusion reaction with a beam of multiply charged heavy 50Ti ions from the U-400 cyclotron (FLNR, JINR) are experimentally investigated. Its half-life and decay branching ratio are measured. The average number of neutrons per spontaneous fission of 256Rf (bar v = 4.47 ± 0.09) is determined for the first time.
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
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...
Binary and ternary spontaneous fission of 252 Cf
International Nuclear Information System (INIS)
The high selectivity and sensitivity offered by large detector arrays such as GAMMASPHERE and EUROGAM enable one to identify several gamma-rays related to the binary and ternary spontaneous fission. The yields for Mo-Ba binary spontaneous fission were extracted again from the data with better statistics. A new experiment with the 252 Cf source has been done by using a Delta telescope and GAMMASPHERE arrays at Argonne National Laboratory. From these data and our older data, new relative alpha ternary spontaneous fission yields were extracted. These results and the emission of 10 Be in spontaneous fission and the existence of long lived nuclear molecule also will be discussed. (author)
Spontaneous fission half-lives and their systematics
International Nuclear Information System (INIS)
Spontaneous fission is a phenomenon exhibited by heavy nuclei, which can be a major mode of decay of nuclei of elements heavier than thorium and can be a determining factor in their stability. For purposes of this paper, spontaneous fission will be considered a process in which a nucleus breaks up into two approximately equal parts. The emission of light nuclei or heavy ions such as 12C, 16O, or 32S will not be considered. This radioactive decay mode is often much smaller than the spontaneous fission decay mode, although this is not true in all cases. Barwick noted that this might indicate that the assumed half-life for spontaneous fission of some older experiments might be partially due to heavy fragment radioactivity. Other than taking note of this potential correction to spontaneous fission half-lives, this decay mode of heavy fragment radioactivity will be ignored. Excited states of some heavy nuclei may decay via spontaneous fission. These so-called fission isomers will not be discussed here. Electron capture (EC) or beta-delayed fission is a process in which prompt fission of a sufficiently excited daughter state occurs following population by EC or beta decay. The fission activity will appear to decay with the half-life of the parent and was earlier confused in some cases with SF. This process has been discussed in detail in a review and will not be considered in this paper
Competition between cluster decay and spontaneous fission in superheavy nuclei
International Nuclear Information System (INIS)
Within the new concept of cluster radioactivity (CR) to allow emitted particles with ζ ≥28 we systematically investigate the CR and spontaneous fission for super-heavy elements whit atomic number ζ ≥118. The CR hal-lives are obtained taking Coulomb and proximity potential to the overlap zone and exponential law for the effective inertia. The spontaneous fission half-lives are calculated with a phenomenological formula. The competition between CR and spontaneous fission is analyzed in detail and the branching ratios of these two decays modes are predicted. (Author)
Description of peculiarities of prompt fission neutron spectrum in spontaneous fission of 252Cr
International Nuclear Information System (INIS)
Full text : 252Cf is the model object in theoretical and experimental studying of prompt fission neutron spectrum in the both spontaneous and induced fission of heavy nuclei. However, the form of spectrum observed has not been clearly understood especially in the region of lower and higher energies. The last compiled data are frequently used as a standart for the test of theoretical prescriptions of the neutron spectrum in spontaneous fission of 252Cf
User's guide to the biosphere code BIOMOD
International Nuclear Information System (INIS)
BIOMOD has been designed to interface with SYVAC, the function of which is to perform generic risk assessments on hypothetical repository-geosphere-biosphere combinations. The user's guide contains the detailed specifications for the models used, a description of the interim user-interface, a specification for required input and definition of output. Sources of error are indicated and reference is made to the database description and other documents issued relating to BIOMOD. (author)
Spontaneous fission. A many-body approach
Energy Technology Data Exchange (ETDEWEB)
Iwamoto, Akira; Bonasera, A. [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
1997-03-01
We propose new model to calculate the fission phenomena in tunnel region. By the Vlasov equation and the imaginary time method, we could calculate actinides nuclear fission. This method makes possible to describe unified the motion of fission inside and outside of potential wall. The potential energy and mass parameters can be calculated by no means of the special model. The freedom of internal motion are calculated automatically both collective and a particle motion. Accordingly, particle released during fission process can be calculated. The kinetic energy of fragment after fission was very agreeable with the calculation results. (S.Y.)
Spontaneous 238U fission half-life measurements based on fission-track techniques
International Nuclear Information System (INIS)
In the last recommendation of the International Union of Pure and Applied Chemistry (I.U.P.A.C.) on spontaneous fission half-lives for ground-state nuclides, a number of measurements of 238U based on fission-track techniques were discarded. The arguments given by the authors are not clear. A more detailed discussion of these determinations is given, considering the possible systematical errors inherent in fission-track approaches. (author)
Pairing-induced speedup of nuclear spontaneous fission
Sadhukhan, Jhilam; Nazarewicz, W; Sheikh, J A; Baran, A
2014-01-01
Collective inertia is strongly influenced at the level crossing at which quantum system changes diabatically its microscopic configuration. Pairing correlations tend to make the large-amplitude nuclear collective motion more adiabatic by reducing the effect of those configuration changes. Competition between pairing and level crossing is thus expected to have a profound impact on spontaneous fission lifetimes. To elucidate the role of nucleonic pairing on spontaneous fission, we study the dynamic fission trajectories of $^{264}$Fm and $^{240}$Pu using the state-of-the-art self-consistent framework. We employ the superfluid nuclear density functional theory with the Skyrme energy density functional SkM$^*$ and a density-dependent pairing interaction. Along with shape variables, proton and neutron pairing correlations are taken as collective coordinates. The collective inertia tensor is calculated within the nonperturbative cranking approximation. The fission paths are obtained by using the least action princip...
Search for spontaneous fission emitters in Atlantis II. Pt. 2
International Nuclear Information System (INIS)
In this paper we describe an attempt to isolate superheavy elements from Atlantis II hot brine deposits. Volatile, sulfidic elements (Cd,Pb) were isolated and investigated for spontaneous fission events with a mica-plastic solid state track detector sandwich. During nearly two years exposure time no spontaneous fission activity was observed. The upper limit for the concentration of superheavy elements (following this chemistry) in the Atlantis II-material is found to be 1.4 x 10-14 g/g. This limit is more than one order of magnitude lower than the concentration of a spontaneous fission activity in material from the Cheleken hot brine, as observed by Flerov and coworkers. (orig.)
Database description for the biosphere code BIOMOD
International Nuclear Information System (INIS)
The development of a biosphere model for use in comparative radiological assessments of UK low and intermediate level waste repositories is discussed. The nature, content and sources of data contained in the four files that comprise the database for the biosphere code BIOMOD are described. (author)
Study of spontaneous fission lifetimes using nuclear density functional theory
Directory of Open Access Journals (Sweden)
Sadhukhan Jhilam
2013-12-01
Full Text Available The spontaneous fission lifetimes have been studied microscopically by minimizing the collective action integral in a two-dimensional collective space of quadrupole moments (Q20, Q22 representing elongation and triaxiality. The microscopic collective potential and inertia tensor are obtained by solving the self-consistent Hartree-Fock-Bogoliubov (HFB equations with the Skyrme energy density functional and mixed pairing interaction. The mass tensor is computed within the perturbative Adiabatic Time-Dependent HFB (ATDHFB approach in the cranking approximation. The dynamic fission trajectories have been obtained by minimizing the collective action using two different numerical techniques. The values of spontaneous fission lifetimes obtained in this way are compared with the static results.
Study of spontaneous fission lifetimes using nuclear density functional theory
International Nuclear Information System (INIS)
The spontaneous fission lifetimes have been studied microscopically by minimizing the collective action integral in a two-dimensional collective space of quadrupole moments (Q20, Q22) representing elongation and triaxiality. The microscopic collective potential and inertia tensor are obtained by solving the self-consistent Hartree-Fock-Bogoliubov (HFB) equations with the Skyrme energy density functional and mixed pairing interaction. The mass tensor is computed within the perturbative Adiabatic Time-Dependent HFB (ATDHFB) approach in the cranking approximation. The dynamic fission trajectories have been obtained by minimizing the collective action using two different numerical techniques. The values of spontaneous fission lifetimes obtained in this way are compared with the static results. (authors)
Event-by-event study of neutron observables in spontaneous and thermal fission
R. Vogt; Randrup, J.
2011-01-01
The event-by-event fission model FREYA is extended to spontaneous fission of actinides and a variety of neutron observables are studied for spontaneous fission and fission induced by thermal neutrons with a view towards possible applications for detection of special nuclear materials.
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.
Development of the biosphere code BIOMOD: final report
International Nuclear Information System (INIS)
Final report to DoE on the development of the biosphere code BIOMOD. The work carried out under the contract is itemised. Reference is made to the six documents issued along with the final report. These consist of two technical notes issued as interim consultative documents, a user's guide and a programmer's guide to BIOMOD, a database description, program test document and a technical note entitled ''BIOMOD - preliminary findings''. (author)
Neutron multiplicities in spontaneous fission and nuclear structure studies
International Nuclear Information System (INIS)
New insights into the fission process can be gained by better quantitative knowledge of how the energy released in fission is distributed between the kinetic energy of the two fragments, the excitation energy of the two fragments and the number of neutrons emitted. Studies of prompt gamma-rays emitted in spontaneous fission (SF) with large arrays of Compton suppressed Ge detector arrays are providing new quantitative answers to longstanding questions concerning fission as well as new insights into the structure of neutron-rich nuclei. For the first time the triple gamma coincidence technique was employed in spontaneous fission studies. Studies of SF of 252Cf and 242Pu have been carried out. These γ-γ-γ data provide powerful ways to identify uniquely gamma rays from a particular nucleus in the very complex gamma-ray spectra given off by the over 100 different nuclei produced. The emphasis of this paper is on the first quantitative measurements of the multiplicities of the neutrons emitted in SF and the energy levels populated in the fragments. Indeed, in the break up into Mo-Ba pairs, we have identified for the first time fragments associated with from zero up to ten neutrons emitted and observed the excited energy states populated in these nuclei. The zero neutron emission pairs like 104Mo- 148Ba, 106Mo- 146Ba and 104Zr- 148Ce observed in this work are particularly interesting because they represent a type of cold fission or a new mode of cluster radioactivity as proposed by Greiner, Sandulescu and co-workers. These data provide new insights into the processes of cluster radioactivity and cold fission
Evaluation of mass distribution data from 252Cf spontaneous fission
International Nuclear Information System (INIS)
The mass distribution data of 252Cf spontaneous fission were evaluated based on 7 sets of available experimental data. The measured data were corrected for the standards and γ intensity used by using the new evaluated ones. The errors were made necessary adjusting. The evaluated experimental data were fitted with spline function without any restriction and with symmetric restriction. These two sets of fit data were recommended as reference data of the mass distribution of 252Cf spontaneous fission. The errors of the recommended data were considerably reduced comparing with the measured ones. The light and heavy peaks are not completely symmetric. Also there are fine structures on the right side of the light peak at A=109-111 and left side of the heavy peak at A=137-139. These should be paid attention and studied further. (author)
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.
Improved calculation of the prompt fission neutron spectrum from the spontaneous fission of 252Cf
International Nuclear Information System (INIS)
An improved calculation is presented for the prompt fission neutron spectrum N(E) from the spontaneous fission of 252Cf. In this calculation the fission-spectrum model of Madland and Nix is used, but with several improvements leading to a physically more accurate representation of the spectrum. Specifically, the contributions to N(E) from the entire fission-fragment mass and charge distributions will be calculated instead of calculating on the basis of a seven-point approximation to the peaks of these distributions as has been done in the past. Therefore, values of the energy release in fission, fission-fragment kinetic energy, nuclear level density, and compound nucleus cross section for the inverse process will be considered on a point-by-point basis over the fragment yield distributions instead of considering averages of these quantities over the peaks of the distributions. Particular attention will be given to the energy-dependent compound nucleus cross sections and to the nuclear level density model. Other refinements to the calculation of N(E) will also be discussed. Results will be presented and compared with earlier calculations of the spectrum and with recent experimental measurements of the spectrum. 9 figs
Prompt Neutron Emission in 252CF Spontaneous Fission
Hambsch, F.-J.; Oberstedt, S.; Zeynalov, Sh.
2011-10-01
The prompt neutron emission in spontaneous fission of 252Cf has been investigated applying digital signal electronics. The goal was to compare the results from digital data acquisition and digital signal processing analysis with results of the pioneering work of Budtz-Jørgensen and Knitter. Using a twin Frisch-grid ionization chamber for fission fragment (FF) detection and a NE213-equivalent neutron detector in total about 107 fission fragment-neutron coincidences have been registered. Fission fragment kinetic energy, mass and angular distribution, neutron time-of-flight and pulse shape have been investigated using a 12 bit waveform digitizer. The signal waveforms have been analyzed using digital signal processing algorithms. The results are in very good agreement with literature. For the first time the dependence of the number of emitted neutrons as a function of total kinetic energy (TKE) of the fragments is in very good agreement with theoretical calculations in the range of TKE from 140-220 MeV.
Prompt neutron spectrum of the spontaneous fission of californium-252
International Nuclear Information System (INIS)
The californium-252 spontaneous fission neutron spectrum was measured in the energy range of 0.01 to 10 MeV by the time-of-flight technique using various neutron detectors. The measurements of 252Cf neutron spectrum at energies of 0.01 to 5 MeV were performed as a function of fission fragment kinetic energy. The mean neutron spectrum energy in the range of 0.7 to 10 MeV was found from the results of measurements. The irregularity in the 252Cf neutron spectrum in the neutron energy range of less than 0.7 MeV compared to theoretical values is discussed. The mechanism of 252Cf neutron emission is also discussed on the basis of neutron yield angle measurements. 12 references
International Nuclear Information System (INIS)
The detection system MONA (Modular Neutron Array) consisting of eight large BC-501A liquid scintillators, was applied to determine the temperature of fission fragments emitted in spontaneous fission of 252Cf. The determination of the temperature was based on the measurement of the neutron spectra
Salvador-Castiñeira P.; Bryś T.; Eykens R.; Hambsch F.-J.; Moens A.; Oberstedt S.; Pretel C.; Sibbens G.; Vanleeuw D.; Vidali M.;
2013-01-01
Fast spectrum neutron-induced fission cross sections of transuranic isotopes are being of special demand in order to provide accurate data for the new GEN-IV nuclear power plants. To minimize the uncertainties on these measurements accurate data on spontaneous fission half-lives and detector efficiencies are a key point. High α-active actinides need special attention since the misinterpretation of detector signals can lead to low efficiency values or underestimation in fission fragment detect...
Microscopic modeling of mass and charge distributions in the spontaneous fission of 240Pu
Sadhukhan, Jhilam; Nazarewicz, Witold; Schunck, Nicolas
2016-01-01
We propose a methodology to calculate microscopically the mass and charge distributions of spontaneous fission yields. We combine the multidimensional minimization of collective action for fission with stochastic Langevin dynamics to track the relevant fission paths from the ground-state configuration up to scission. The nuclear potential energy and collective inertia governing the tunneling motion are obtained with nuclear density functional theory in the collective space of shape deformations and pairing. We obtain a quantitative agreement with experimental data and find that both the charge and mass distributions in the spontaneous fission of 240Pu are sensitive both to the dissipation in collective motion and to adiabatic fission characteristics.
On the potential of active coincidence counting using a spontaneous fission source to induce fission
International Nuclear Information System (INIS)
Using the one-group point-model equations as a guide, we compare the active neutron Doubles rate from a multiplying item interrogated with a spontaneous fission neutron source with that of a random neutron source of equal emission rate. We find that, especially for highly multiplying items, 252Cf is likely to provide a viable alternative to the commonly used Am/Li interrogation source. We conclude that detailed design studies and experiments are warranted to develop this concept into practical assay tools. Keywords: coincidence counting; active interrogation; 252Cf active driver; point-model; collar detector
Prompt neutron multiplicity in correlation with fragments from spontaneous fission of 252Cf
GÖÖK Alf; Hambsch, Franz-Josef; Vidali, Marzio
2014-01-01
The spontaneous fission of 252Cf serves as an excellent benchmark of prompt emission in fission since experimental data can be obtained without the need of an incident beam. With the purpose of providing experimental data on the prompt fission neutron properties in correlation with fission fragment characteristics an experiment on 252Cf(SF) has been performed. In addition, the experiment serves as benchmark of setup and analysis procedures for measurements of fluctuations in the prompt neutro...
Salvador-Castiñeira, P.; Bryś, T.; Eykens, R.; Hambsch, F.-J.; Moens, A.; Oberstedt, S.; Pretel, C.; Sibbens, G.; Vanleeuw, D.; Vidali, M.
2013-12-01
Fast spectrum neutron-induced fission cross sections of transuranic isotopes are being of special demand in order to provide accurate data for the new GEN-IV nuclear power plants. To minimize the uncertainties on these measurements accurate data on spontaneous fission half-lives and detector efficiencies are a key point. High α-active actinides need special attention since the misinterpretation of detector signals can lead to low efficiency values or underestimation in fission fragment detection. In that context, 240,242Pu isotopes have been studied by means of a Twin Frisch-Grid Ionization Chamber (TFGIC) for measurements of their neutron-induced fission cross section. Gases with different drift velocities have been used, namely P10 and CH4. The detector efficiencies for both samples have been determined and improved spontaneous fission half-life values were obtained.
Directory of Open Access Journals (Sweden)
Salvador-Castiñeira P.
2013-12-01
Full Text Available Fast spectrum neutron-induced fission cross sections of transuranic isotopes are being of special demand in order to provide accurate data for the new GEN-IV nuclear power plants. To minimize the uncertainties on these measurements accurate data on spontaneous fission half-lives and detector efficiencies are a key point. High α-active actinides need special attention since the misinterpretation of detector signals can lead to low efficiency values or underestimation in fission fragment detection. In that context, 240,242Pu isotopes have been studied by means of a Twin Frisch-Grid Ionization Chamber (TFGIC for measurements of their neutron-induced fission cross section. Gases with different drift velocities have been used, namely P10 and CH4. The detector efficiencies for both samples have been determined and improved spontaneous fission half-life values were obtained.
Nuclear isomerism in fission fragments produced by the spontaneous fission of 252Cf
International Nuclear Information System (INIS)
This thesis is devoted to the study of the nuclear structure of neutron-rich nuclei, via the search of isomeric nuclear states. Neutron-rich nuclei were produced in the spontaneous fission of 252Cf. The experimental study of isomeric states in these nuclei was performed with the γ-array EUROGAM II, coupled to an additional and original fission fragment detector composed by photovoltaic cells, SAPhIR. The photovoltaic cells are well adapted to detect low energy heavy ions and have good energy and time resolutions to obtain a good fission fragment detection. This experiment led to the discovery of new isomeric states in 135Xe, 104Mo, 146,147,148Ce and 152,154,156Nd, with lifetimes between 60 ns and 2 μs. Level schemes of these nuclei have been completed. An interpretation of the isomeric states in the nuclei 154,156Nd and 156,158Sm was performed by Hartree-Fock-Bogolyubov calculations using the DIS Gogny force with two quasi-particles excitations. The confrontation with the experimental results led to an interpretation of these isomeric states as K-isomers. (author)
Microscopic modeling of mass and charge distributions in the spontaneous fission of 240Pu
Sadhukhan, Jhilam; Schunck, Nicolas
2016-01-01
In this letter, we outline a methodology to calculate microscopically mass and charge distributions of spontaneous fission yields. We combine the multi-dimensional minimization of collective action for fission with stochastic Langevin dynamics to track the relevant fission paths from the ground-state configuration up to scission. The nuclear potential energy and collective inertia governing the tunneling motion are obtained with nuclear density functional theory in the collective space of shape deformations and pairing. We obtain a quantitative agreement with experimental data and find that both the charge and mass distributions in the spontaneous fission of 240Pu are sensitive both to the dissipation in collective motion and to adiabatic characteristics.
Measurement of Neutron Induced and Spontaneous Fission in Pu-242 at DANCE
Chyzh, Andrii; Wu, C. Y.; Henderson, R.; Couture, A.; Lee, H. Y.; Ullmann, J.; O'Donnell, J. M.; Jandel, M.; Haight, R. C.; Bredeweg, T. A.; Dance Collaboration
2013-10-01
Neutron capture and fission reactions are important in nuclear engineering and physics. DANCE (Detector for Advanced Neutron Capture Measurement, LANL) combined with PPAC (avalanche technique based fission tagging detector, LLNL) were used to study neutron induced and spontaneous fission in 242Pu. 2 measurements were performed in 2013. The first experiment was done without the incident neutron beam with the fission tagging ability to study γ-rays emitted in the spontaneous fission of 242Pu. The second one - with the neutron beam to measure both the neutron capture and fission reactions. This is the first direct measurement of prompt fission γ-rays in 242Pu. The γ-ray multiplicity, γ-ray energy, and total energy of γ-rays per fission in 242Pu will be presented. These distributions of the 242Pu spontaneous fission will be compared to those in the 241Pu neutron induced fission. This work was performed under the auspices of the US Department of Energy by Los Alamos National Laboratory under Contract DE-AC52-06NA25396 and Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Alpha decay favoured isotopes of some superheavy nuclei: Spontaneous fission versus alpha decay
Kiren, O V; Bubbly, S G
2013-01-01
Spontaneous fission and alpha decay are the main decay modes for superheavy nuclei. The superheavy nuclei which have small alpha decay half-life compared to spontaneous fission half-life will survive fission and can be detected in the laboratory through alpha decay. We have studied the alpha decay half-life and spontaneous half-life of some superheavy elements in the atomic range Z = 100-130. Spontaneous fission half-lives of superheavy nuclei have been calculated using the phenomenological formula and the alpha decay half-lives using Viola-Seaborg-Sobiczewski formula (Sobiczewski et al. 1989), semi empirical relation of Brown (1992) and formula based on generalized liquid drop model proposed by Dasgupta-Schubert and Reyes (2007). The results are reported here.
International Nuclear Information System (INIS)
A chain reaction could result in case of the exceedance of the critical concentration of spontaneously fissionable compounds. It is therefore suggested that C2B10H12 or neutral Ni(C2B9H11)2 i.e., substances effectively absorbing neutrons, be added to the organic phase during extraction. The organic phase may repeatedly be used for the extraction of other fractions of fissionable substances. (M.D.)
LARGE GAMMA ANISOTROPY OBSERVED IN THE CF-252 SPONTANEOUS-FISSION PROCESS
VANDERPLOEG, H; BACELAR, JC; VANDENBERG, T; IACOB, VE; JONGMAN, [No Value; VANDERWOUDE, A
1992-01-01
The energy spectrum and the angular dependence relative to the fission direction of photons in the energy region between 2 and 40 MeV have been measured for the spontaneous fission of Cf-252. A large anisotropy was found in the energy region 8 to 12 MeV implying that photons in this region are emitt
STUDY OF THE GAMMA EMISSION PROBABILITY ACCOMPANYING THE SPONTANEOUS FISSION OF CF-252
VANDERPLOEG, H; LAURENS, CR; BACELAR, JCS; BUDA, A; GAARDHOJE, JJ; VANTHOF, G; KALANTARNAYESTANAKI, N; VANDERWOUDE, A; ZELAZNY, Z
1994-01-01
A study of the gamma emission accompanying the spontaneous fission process of Cf-252 has been performed. The photon emission probability between 3 and 70 MeV and its angular dependence with respect to the fission direction were measured. These measurements were performed as a function of the mass as
International Nuclear Information System (INIS)
Aimed at the problem of the energy spectrum of spontaneous fission source, which was used in neutron albedo experiments, we selected two sets of 252Cf fission spectra, which were fitted by formulae and were universally accepted. And they were applied in neutron albedo experiments independently. Neutron fluence and fission rate on each detecting point were compared and analyzed. The results show that Watt spectrum agrees the experiment data better than that of Maxwell spectrum. (authors)
Disintegration constant of uranium-238 by spontaneous fission redetermined by glass track method
International Nuclear Information System (INIS)
The disintegration constant of U238 by spontaneous fission using glass as fission fragment detector was redetermined. A film of natural uranium (UO3) prepared by chemical methods on the glass lamina was used in a long time experience of exposure (about 16 years). The good conditions of sample preparation and storage allow to observe, after chemical etching, fission fragment tracks. (M.C.K.)
The measurement of prompt neutron spectrum in spontaneous fission of {sup 244}Cm
Energy Technology Data Exchange (ETDEWEB)
Batenkov, O.I.; Boykov, G.S.; Drapchinsky, L.V.; Majorov, M.Ju.; Trenkin, V.A. [V.G. Khlopin Radium Inst., Saint Petersburg (Russian Federation)
1997-03-01
Under the Program of Measurements of Prompt Fission Neutron Spectra of Minor Actinides for Transmutation Purposes the integral neutron spectrum in spontaneous fission of {sup 244}Cm has been measured by the time-of-flight method in the energy range of 0.1-15 MeV relative to the standard neutron spectrum in {sup 252}Cf spontaneous fission. Essential attention was paid to revealing of possible systematic errors. It is shown, that the {sup 244}Cm spectrum shape may be well described by using Mannhart evaluation with appropriate parameter of Maxwell temperature T{sub M} = 1.37 MeV. (author)
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...
Search for scission neutrons in the spontaneous fission of 252Cf
International Nuclear Information System (INIS)
In the spontaneous fission of 252Cf, we observed that the population of spin 2+ in 136Te is closely correlated with the population of spin 4+ of its partner 114Pd. We attribute our results to the emission of two neutrons at scission carrying away two units of angular momentum and the yield is 0.06(2) per 100 spontaneous fission (SF) events whereas the two neutron normal fission yield is 0.12(3) per 100 SF for the 136Te and 114Pd pair. The yield for fission with four scission neutrons for 136Te and 112Pd is observed to be ∼0 whereas the four neutron hot fission yield is 0.28(4) per 100 SF events. copyright 1999 The American Physical Society
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An improved calculation is presented for the prompt fission neutron spectrum N(E) from the spontaneous fission of /sup 252/Cf. In this calculation the fission-spectrum model of Madland and Nix is used, but with several improvements leading to a physically more accurate representation of the spectrum. Specifically, the contributions to N(E) from the entire fission-fragment mass and charge distributions will be calculated instead of calculating on the basis of a seven- point approximation to the peaks of these distributions as has been done in the past. Therefore, values of the energy release in fission, fission-fragment kinetic energy, and compound nucleus cross section for the inverse process will be considered on a point-by-point basis over the fragment yield distributions instead of considering averages of these quantities over the peaks of the distributions. Preliminary results will be presented and compared with a measurement, an earlier calculation, and a recent evaluation of the spectrum. 14 refs., 4 figs
Highly accurate measurements of the spontaneous fission half-life of 240,242Pu
SALVADOR CASTINEIRA PAULA; BRYS TOMASZ; EYKENS ROGER; Hambsch, Franz-Josef; MOENS Andre; Oberstedt, Stephan; SIBBENS Goedele; VANLEEUW DAVID; Vidali, Marzio; Pretel, C.
2013-01-01
Fast spectrum neutron-induced fission cross-section data for transuranic isotopes are of special demand from the nuclear data community. In particular highly accurate data are needed for the new generation IV nuclear applications. The aim is to obtain precise neutron-induced fission cross sections for 240Pu and 242Pu. To do so, accurate data on spontaneous fission half-lives must be available. Also, minimizing uncertainties in the detector efficiency is a key point. We studied both isotopes b...
Neutron emission as a function of fragment energy in the spontaneous fission of 260Md
International Nuclear Information System (INIS)
The authors have made the first measurement of the number of neutrons emitted in the spontaneous fission of a nuclide in which very high fragment energies dominate the fission process. In bombardments of 254Es, they produced 28-d 260Md, which was neutron-counted in a 1-m-diam spherical tank containing a Gd-doped scintillator solution. The average number of neutrons emitted per fission is only 2.58 ± 0.11, substantially less than for other actinides. A direct correlation of neutron multiplicity with fragment excitation energy is clearly demonstrated
The Bohr-Wheeler spontaneous fission limit: an undergraduate-level derivation
International Nuclear Information System (INIS)
An upper-undergraduate level derivation of the Z2/A ∼ 50 limit against spontaneous fission first published by Bohr and Wheeler (1939 Phys. Rev. 56 426) is provided. The purpose in offering this derivation is that most textbooks give no details of it and sometimes fail to make clear key assumptions and mathematical manipulations underlying the Bohr and Wheeler model
Study of the shielding for spontaneous fission sources of Californium-252
International Nuclear Information System (INIS)
A shielding study is made to attenuate, until maximum permissible levels, the neutrons radiation and photons emitted by spontaneous fission coming from a source of Californium-252. The compound package by a database (Library DLC-23) and the ANISNW code is used, in it version for personal computer. (Author)
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.
Microscopic phase-space exploration modeling of $^{258}$Fm spontaneous fission
Tanimura, Yusuke; Ayik, Sakir
2016-01-01
We show that the total kinetic energy (TKE) of nuclei after the spontaneous fission of $^{258}$Fm can be well reproduced using simple assumptions on the quantum collective phase-space explored by the nucleus after passing the fission barrier. Assuming energy conservation and phase-space exploration according to the stochastic mean-field approach, a set of initial densities is generated. Each density is then evolved in time using the nuclear time-dependent density-functional theory. This approach goes beyond mean-field by allowing spontaneous symmetry breaking as well as a wider dynamical phase-space exploration leading to larger fluctuations in collective space. The total kinetic energy and mass distributions are calculated. New information on the fission process: fluctuations in scission time, strong correlation between TKE and collective deformation of daughter nuclei as well as pre- and post-scission particle emission, are obtained.
Multidimensionally-constrained relativistic Hartree-Bogoliubov study of nuclear spontaneous fission
Zhao, Jie; Niksic, Tamara; Vretenar, Dario
2015-01-01
Recent microscopic studies, based on the theoretical framework of nuclear energy density functionals, have analyzed dynamic (least action) and static (minimum energy) fission paths, and it has been shown that in addition to the important role played by nonaxial and/or octupole collective degrees of freedom, fission paths crucially depend on the approximations adopted in calculating the collective inertia. The dynamics of spontaneous fission of $^{264}$Fm and $^{250}$Fm is explored. The fission paths, action integrals and the corresponding half-lives predicted by the functionals PC-PK1 and DD-PC1 are compared and, in the case of $^{264}$Fm, discussed in relation with recent results obtained using the HFB model based on the Skyrme functional SkM$^*$ and a density dependent mixed pairing interaction. Deformation energy surfaces, collective potentials, and perturbative and nonperturbative cranking collective inertia tensors are calculated using the multidimensionally-constrained relativistic Hartree-Bogoliubov (M...
TYPE A PACKAGE LIMITS OF SPONTANEOUS FISSION RADIONUCLIDES
International Nuclear Information System (INIS)
The maxima value of the depth dose coefficient for fission neutrons in ICRP Publication 21 was a reasonable estimator of the effective dose coefficient recently tabulated in ICRP Publication 74. Thus the inflation of the coefficient in the 1996 Q-System analysis (IAEA 2000b) for the purpose of being consistent with respect to ICRP guidance on the neutron weighting factor was unnecessary from the standpoint of the effective dose. The consequence resulted in an unnecessarily restrictive value of A1 for 248Cm, 252Cf, and 254Cf. The calculations presented here support a relaxation of the A1 limits for these radionuclides
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
New data on the fragment angular momentum in spontaneous fission of 252 Cf
International Nuclear Information System (INIS)
Though a considerable progress has been made in understanding the process of low-energy fission still only a little is known about the energy balance occurring at the scission point. Regarding the value of the energy that is released at the descent of the nucleus from saddle to scission only theory estimates exist. For the case of 252 Cf spontaneous fission a value of 30 MeV could be assumed for this energy release. However, the partition of this free energy remains so far the least-understood aspect of nuclear fission. Evidently, the fragment pre-scission collective motion and internal excitation degrees of freedom share a part of this energy release resulting in the pre-scission kinetic energy and pre-scission excitation of fragments. It is generally recognized that the angular momentum that fission fragments acquire in the low-energy fission is a probe for the states of excitation for some of the orthogonal angular-momentum bearing modes at the scission point. In this work the average angular momentum for primary fission fragments as a function of neutron multiplicity and neutron-to-proton ratio of the primary fission fragments was extracted for the first time for the Mo-Ba and Zr-Ce charge splits of 252 Cf. The data are discussed in terms of the energy balance occurring at the scission point. (authors)
238U spontaneous fission half-life and a new probable radioactivity mode
International Nuclear Information System (INIS)
The 238U spontaneous fission half-life is reinvestigated using a special nuclear emulsion technique previously developed in our laboratory. A perfect visualisation of the fission fragments tracks in the absence of alpha particle tracks was obtained with the present method that also avoids the fading of the latent image. Under these conditions, two well defined peaks are observed experimentaly: one corresponding to the well-known range (approx 24 μm) of the 238U fission fragments tracks and the other showing evidence of short range tracks (approx 10 μm). For the 238U spontaneous fission half-life our result is (6.0+-0.4) x1015 y, in good agreement with the values obtained by some other workers using different experimental methods. A systematic theoretical analysis shows that the 238U spontaneous emission of nuclides with mass number between approx 20 e 70 is possible. The Kinetic energies calculated for these nuclides are found to fit the short range tracks observed in our experiment. From the experimental data, we attribute a (2 +- 1) x 1015 y half-life for all modes of emission involved in this process. (Author)
Highly accurate measurements of the spontaneous fission half-life of 240,242Pu
Salvador-Castiñeira, P.; Bryś, T.; Eykens, R.; Hambsch, F.-J.; Moens, A.; Oberstedt, S.; Sibbens, G.; Vanleeuw, D.; Vidali, M.; Pretel, C.
2013-12-01
Fast spectrum neutron-induced fission cross-section data for transuranic isotopes are of special demand from the nuclear data community. In particular highly accurate data are needed for the new generation IV nuclear applications. The aim is to obtain precise neutron-induced fission cross sections for 240Pu and 242Pu. To do so, accurate data on spontaneous fission half-lives must be available. Also, minimizing uncertainties in the detector efficiency is a key point. We studied both isotopes by means of a twin Frisch-grid ionization chamber with the goal of improving the present data on the neutron-induced fission cross section. For the two plutonium isotopes the high α-particle decay rates pose a particular problem to experiments due to piling-up events in the counting gas. Argon methane and methane were employed as counting gases, the latter showed considerable improvement in signal generation due to its higher drift velocity. The detection efficiency for both samples was determined, and improved spontaneous fission half-lives were obtained with very low statistical uncertainty (0.13% for 240Pu and 0.04% for 242Pu): for 240Pu, T1/2,SF=1.165×1011 yr (1.1%), and for 242Pu, T1/2,SF=6.74×1010 yr (1.3%). Systematic uncertainties are due to sample mass (0.4% for 240Pu and 0.9% for 242Pu) and efficiency (1%).
M-C simulation of 252Cf spontaneous fission n/γ TOF and TCC spectra
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Time correlation coincidence (TCC) is an effective method to measure characteristics of fission materials. In this paper, MCNP code is used to simulate n/γ time-of-flight spectra (TOF) of a 252Cf spontaneous fission source detected by a BC-501A liquid scintillator. The results are in good agreement with the measured spectra. Therefore, n/γ TCC spectra of the 252Cf source are simulated. The results indicate that the n/γ TCC spectra are composed of the n-n, γ-γ, n-γ and γ-n coincidence. (authors)
Nuclear charge distribution in the spontaneous fission of 252Cf
Wang, Taofeng; Wang, Liming; Men, Qinghua; Han, Hongyin; Xia, Haihong
2015-01-01
The measurement for charge distributions of fragments in 252Cf has been performed by using a unique style of detector setup consisting of a typical grid ionization chamber and a dE-E particle telescope. We found that the fragment mass dependency of the average width of the charge distribution shows a systematic decreased trend with the obvious odd-even effect. The variation of widths of charge distribution with kinetic energies shows an approximate V-shape curve due to the large number of neutron emission for the high excitation energies and cold fragmentation with low excitation energies. As for the behavior of the average nuclear charge with respect to its deviation {\\Delta}Z from the unchanged charge distribution (UCD) as a function of the mass number of primary fragments A*, for asymmetric fission products {\\Delta}Z is negative value, while upon approaching mass symmetry {\\Delta}Z turns positive. Concerning the energy dependence of the most probable charge for given primary mass number A*, the obvious inc...
Observed mass distribution of spontaneous fission fragments from samples of lime - an SSNTD study
International Nuclear Information System (INIS)
SSNTD is one of the most commonly used detectors in the studies involving nuclear phenomena. The ease of registration of the presence of alpha particles and fission fragments has made it particularly suitable in studies where stable long exposures are needed to extract reliable information. Studies on the presence of alpha emitting nuclides in the environment assume importance since they are found to be carcinogenic. Lime samples from Silchar in Assam of Eastern India have shown the presence of spontaneous fission fragments besides alphas. In the present study we look at the ratio of the average mass distribution of these fission fragments, that gives us an indication of the presence of the traces of transuranic elements
The chemical states of tellurium produced by spontaneous fission of 252Cf
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The distribution of the chemical states of tellurium isotopes produced by 252Cf spontaneous fission, collected separately in the matrixes of NaCl, Kl, NaF, CH3COONa x 3H2O, Na2SO4 and NaNO3 crystals was investigated. Two chemical states of tellurium isotopes maintained in these matrixes are Te(IV) and Te(VI). The relationships between the distribution of the chemical states of tellurium isotopes and the produced mode of tellurium, the chemical properties of collection matrixes, the time for collecting fission fragments are studied and the possible mechanism of the interactions of the fission products and the matrixes is discussed. The results show that the distribution of chemical states of tellurium isotopes depends primarily on the chemical properties of the collection matrixes. (author) 18 refs.; 2 figs.; 10 tabs
Gamma-ray studies of the spontaneous fission of 242Pu and 252Cr using gammasphere
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The authors report on the new results on 242Pu and 252Cf spontaneous fission gamma-rays with emphasis on the dependence of spin distributions on numbers of neutrons emitted. The analysis has concentrated first on extracting relative intensities of ground rotational transitions as a function of number of neutrons emitted. open-quotes Cold fissionclose quotes, or zero-neutron fission, is observed in a number of fissioning systems. Some isotopic series show a trend of decreasing fragment average spin with increasing numbers of neutrons emitted, contrary to the initial expectations of a simple quantal model based on neck thickness expected at scission. A simple open-quotes atomic orbitalclose quotes model plus Coulomb excitation is compared with the data. Preliminary results from an April 1994 run using 36 Ge detectors in Early Implementation of Gammasphere coupled with 4 neutron detectors and 1 X-ray detector are shown
Total and spontaneous fission half-lives of the uranium and plutonium nuclides
International Nuclear Information System (INIS)
The total half-life and the half-life for spontaneous fission are evaluated for the various long-lived nuclides of interest. Recommended values are presented for 232U, 233U, 234U, 235U, 236U, 238U, 236Pu, 238Pu, 239Pu, 240Pu, 241Pu, 242Pu, and 244Pu. The uncertainties are provided at the 95% confidence limit for each of the recommended values
Prompt neutron multiplicity in correlation with fragments from spontaneous fission of 252Cf
Göök, A.; Hambsch, F.-J.; Vidali, M.
2014-12-01
The spontaneous fission of 252Cf serves as an excellent benchmark of prompt emission in fission since experimental data can be obtained without the need of an incident beam. With the purpose of providing experimental data on the prompt fission neutron properties in correlation with fission-fragment characteristics, an experiment on 252Cf(SF) has been performed. In addition, the experiment serves as a benchmark of setup and analysis procedures for measurements of fluctuations in the prompt-neutron properties as a function of incident neutron energy in fission of the major actinides 235U and 239Pu. The experiment employs a twin Frisch grid ionization chamber as fission-fragment detector while neutrons were counted by using a liquid scintillator placed along the symmetry axis of the ionization chamber. Average neutron multiplicity has been obtained as a function of fission-fragment mass and total kinetic energy (TKE). The average multiplicity as a function of mass agrees well with available data in the literature in the mass range from 80 to 170 u. The existence of additional sawtooth structures in the far asymmetric mass region could not be confirmed, although the statistical accuracy of the present experiment is as good as the previous study where such structures have been reported [Nucl. Phys. A 490, 307 (1988)., 10.1016/0375-9474(88)90508-8]. The available data in the literature on the TKE dependence of the multiplicity show strong deviations. Therefore, effort was focused on investigating experimental factors in low-efficiency neutron-counting experiments that may lead to faulty determination of this dependence. Taking these factors into account, a result that agrees well with data from high-efficiency neutron-counting experiments is obtained. The experimental arrangement allows determination of the angle between the detected neutron and the fission axis, which permits the neutron properties to be transformed into the fission-fragment rest frame. Fission neutron
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The 252Cf spontaneous prompt fission neutron spectrum at 0 degree and 180 degree relative to the motion direction of corresponding fission fragments was measured. High angular resolution for fragment measurements and high energy resolution for neutron measurements were obtained using multi-parameter TOF spectrometer. The results showed that there is a symmetric distribution of 'forward' and 'backward' for low energy in C.M.S. neutrons, which was an evidence of nonequilibrium neutrons existed in fission process
Uranium and plutonium total half-lives and for the spontaneous fission branch
Energy Technology Data Exchange (ETDEWEB)
Holden, N.E.
1985-01-01
The long-lived nuclides of the uranium and plutonium elements are of interest for their use in nuclear reactors, as well as in certain safeguard applications, e.g., alpha counting is often used to determine the amount of material present. The total half-life and the half-life for spontaneous fission are evaluated for these various long-lived nuclides of interest. The various experiments have been reanalyzed and recommended values are presented for /sup 232,233,234/U, /sup 235,236,238/U, and for /sup 236,238,239,240,241,242,244/Pu. These values improve upon preliminary estimates previously presented, in particular with respect to the uncertainties reported. The /sup 234/U half-life of 2.456 +- 0.005 x 10/sup 5/ years impacts directly on the 2200 meters/second fission cross section of /sup 235/U, since earlier measurements used values of 2.47 to 2.5 x 10/sup 5/ years and obtained correspondingly lower cross sections. In a similar manner, the /sup 239/Pu half-life is 1.25% lower than earlier estimates, which results in a 1.25% increase in the 2200 m/s fission cross section for /sup 239/Pu in some earlier cross section measurements. The total half-lives for the uranium nuclides were reviewed some time ago. At that time, the only spontaneous fission value which was evaluated was /sup 238/U. Recently, the uranium and plutonium nuclides were reviewed for both total and fission half-lives. The general procedure followed in this paper has been to review each of the experiments and revise the published values for the latest estimates of the various parameters used by the original authors. For the case of the total half-lives of uranium, only differences from the original work have been discussed. 120 refs., 23 tabs.
Uranium and plutonium total half-lives and for the spontaneous fission branch
International Nuclear Information System (INIS)
The long-lived nuclides of the uranium and plutonium elements are of interest for their use in nuclear reactors, as well as in certain safeguard applications, e.g., alpha counting is often used to determine the amount of material present. The total half-life and the half-life for spontaneous fission are evaluated for these various long-lived nuclides of interest. The various experiments have been reanalyzed and recommended values are presented for /sup 232,233,234/U, /sup 235,236,238/U, and for /sup 236,238,239,240,241,242,244/Pu. These values improve upon preliminary estimates previously presented, in particular with respect to the uncertainties reported. The 234U half-life of 2.456 +- 0.005 x 105 years impacts directly on the 2200 meters/second fission cross section of 235U, since earlier measurements used values of 2.47 to 2.5 x 105 years and obtained correspondingly lower cross sections. In a similar manner, the 239Pu half-life is 1.25% lower than earlier estimates, which results in a 1.25% increase in the 2200 m/s fission cross section for 239Pu in some earlier cross section measurements. The total half-lives for the uranium nuclides were reviewed some time ago. At that time, the only spontaneous fission value which was evaluated was 238U. Recently, the uranium and plutonium nuclides were reviewed for both total and fission half-lives. The general procedure followed in this paper has been to review each of the experiments and revise the published values for the latest estimates of the various parameters used by the original authors. For the case of the total half-lives of uranium, only differences from the original work have been discussed. 120 refs., 23 tabs
Zhao, Jie; Niksic, Tamara; Vretenar, Dario; Zhou, Shan-Gui
2016-01-01
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. 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. The dynamics of spontaneous fission of $^{264}$Fm and $^{250}$Fm are explored. Fission paths, action integrals and corresponding half-lives computed in the three-dimensional collective space of shape and pa...
Relative Yields of 149-153Pr in Spontaneous Fission of 252Cf
Eldridge, Jonathan; Wang, Enhong; Hwang, J. K.; Hamilton, Joe; Ramayya, A. V.; Luo, Y. X.; Rasmussen, J. O.; Zhu, S. J.; Liu, S. H.; Ter-Akopian, G. M.; Oganessian, Yu. Ts.
2013-10-01
The relative yields of the fission partners of 149-153Pr, resulting from the spontaneous fission of 252Cf, were studied. This study was done by means of γ - γ - γ , and γ - γ - γ - γ coincidence data taken in 2000 by the multi-HPGe, Compton-suppressed, gamma detector array, Gammasphere, at Lawrence Berkeley National Lab. The coincidence data were analyzed by double- and triple-gating on transitions in 149-153Pr and obtaining the intensities of the 93-101Y transitions. For 150 , 151 , 152 , 153Pr the 3n channel was found to be the strongest. The 149Pr, however, was found to peak at the 4n channel. These results were used to verify the assignments of the level schemes of 151 , 152 , 153Pr. The data are found to be in agreement with Wahl's independent yield tables.
International Nuclear Information System (INIS)
Absolute absorption cross sections have been measured for 232Th and 197Au for 252Cf spontaneous fission neutrons. Irradiations were performed in an exceptionally low mass source-foil arrangement, providing a ''pure'' spectrum with few corrections. Calibration of the activation detector was achieved by irradiating identical foils in the National Bureau of Standards (NBS) Standard Thermal Flux. A simple ratio technique was also used to obtain an independent estimate of the relative 232Th to 197Au integral cross sections, yielding a value in good agreement with that above. This technique was extended to 181Ta, 98Mo, and 63Cu. (5 tables, 3 figures) (U.S.)
Staszczak, A; Nazarewicz, W
2012-01-01
Lifetimes of super-heavy (SH) nuclei are primarily governed by alpha decay and spontaneous fission (SF). Here we study the competing decay modes of even-even SH isotopes with 108 <= Z <= 126 and 148 <= N <= 188 using the state-of-the-art self-consistent nuclear density functional theory framework capable of describing the competition between nuclear attraction and electrostatic repulsion. The collective mass tensor of the fissioning superfluid nucleus is computed by means of the cranking approximation to the adiabatic time-dependent Hartree-Fock-Bogoliubov approach. Along the path to fission, our calculations allow for the simultaneous breaking of axial and space inversion symmetries; this may result in lowering SF lifetimes by more than seven orders of magnitude in some cases. We predict two competing SF modes: reflection-symmetric and reflection-asymmetric.The shortest-lived SH isotopes decay by SF; they are expected to lie in a narrow corridor formed by $^{280}$Hs, $^{284}$Fl, and $^{284}_{118}...
High energy γ emission in the spontaneous fission of 252Cf
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The prompt γ emission in the spontaneous fission of 252Cf is characterized by an energy spectrum which extends up to 20 MeV. It was established that the spectrum presents in the neighbourhood of symmetric fission an intensity bump in the 3-8 MeV γ energy interval. The origin of this phenomenon is still not well understood, so that it was found interesting to carry out new measurements. The spectrum of the γ rays emitted in spontaneous fission of 252Cf has been measurement in the EUROGAM II multidetector using photovoltaic cells to detect fragments. The aim of the experiment was to investigate the γ yield enhancement which appears for mass fragment ratio near 132/120. This enhancement was found to be composed of two peaks located at 4 MeV and 5.5 MeV respectively. The results obtained confirm the intensity bound in the 3-8 MeV region but this augmentation reaches the maximum when the heavy fragment is near the mass 132. Beyond mass 140 the phenomenon diminish and the γ spectrum regains the behaviour expected for a statistic emission. The additional structure at 5.5 MeV does not vary with excitation energy while the excitation function of the 4 MeV structure is more structured and presents a maximum when the excitation energy is near 8 MeV. It is likely that all or part of this observed phenomenon is due to a particular excitation mode of this isotope associated for instance with a low energy dipole resonance. A theoretical study of this collective effect is under way
Energy Technology Data Exchange (ETDEWEB)
Anghel, Claudia Ioana, E-mail: claudia.anghel@theory.nipne.ro [Department of Theoretical Physics, Horia Hulubei National Institute for Physics and Nuclear Engineering, Magurele, P.O.Box MG-6, RO-077125 (Romania); University of Bucharest, Faculty of Physics, RO-077125 Bucharest - Magurele (Romania); Silisteanu, Andrei Octavian [Radiopharmaceutical Research Center, Horia Hulubei National Institute for Physics and Nuclear Engineering, Magurele, P.O.Box MG-6, RO-077125 (Romania)
2015-12-07
The most important decay modes for heavy and superheavy nuclei are their α-decay and spontaneous fission. This work investigates the evolution and the competition of these decay modes in long isotopic sequences. The partial half-lives are given by minimal sets of parameters extracted from the fit of experimental data and theoretical results. A summary of the experimental and calculated α-decay and spontaneous fission half-lives of the isotopes of elements Rf, Db, and Sg is presented. Some half-life extrapolations for nuclides not yet known are also obtained.
International Nuclear Information System (INIS)
The most important decay modes for heavy and superheavy nuclei are their α-decay and spontaneous fission. This work investigates the evolution and the competition of these decay modes in long isotopic sequences. The partial half-lives are given by minimal sets of parameters extracted from the fit of experimental data and theoretical results. A summary of the experimental and calculated α-decay and spontaneous fission half-lives of the isotopes of elements Rf, Db, and Sg is presented. Some half-life extrapolations for nuclides not yet known are also obtained
Pre-scission configuration of the tri-nuclear system at spontaneous ternary fission of 252Cf
Nasirov, A. K.; Tashkhodjaev, R. B.; von Oertzen, W.
2016-05-01
The potential energy surface for the pre-scission configurations of tri-nuclear systems formed in the spontaneous ternary fission of 252Cf is calculated. The fission channel 70Ni + 50Ca + 132Sn is chosen as one of the more probable channels of true ternary fission of 252Cf . A study of the collinear arrangement of the reaction products for true ternary fission is the aim of this work. The results are presented as a function of the relative distance R12 between the centres of mass of 70Ni and 132Sn and the distance from the centre of mass of 50Ca , which is perpendicular to R12. The results show that only for a particular range of the R12 values the collinear tripartion of the fissioning nucleus occurs.
Vorobyev, A. S.; Dushin, V. N.; Hambsch, F.-J.; Jakovlev, V. A.; Kalinin, V. A.; Laptev, A. B.; Petrov, B. F.; Shcherbakov, O. A.
2005-05-01
Neutrons emitted in fission events were measured separately for each complementary fragment in correlation with fission fragment energies. Two high-efficiency Gd-loaded liquid scintillator tanks were used for neutron registration. Fission fragment energies were measured using a twin Frisch gridded ionization chamber with a pinhole collimator. The neutron multiplicity distributions were obtained for each value of the fission fragment mass and energy and corrected for neutron registration efficiency, background, and pile-up. The dependency of these distributions on fragment mass and energy for different energy and mass bins as well as mass and energy distribution of fission fragments are presented and discussed.
International Nuclear Information System (INIS)
The distribution of nuclear charge in the spontaneous fission of Cf252 has been determined directly by simultaneous measurement of the masses and characteristic K-X-ray energies associated with the primary fission products. The X-rays were detected by a thin Nal (Tl) crystal (or by an argon-filled proportional counter) in coincidence with a pair of solid-state detectors for the complementary fission fragments. Preliminary to the three-parameter study of the charge-mass distribution the gross characteristics of the K-X-rays were examined in some detail. The average yield of K-X-rays is 0.55 ± 0.1 pet fission (the heavy group accounting fot 70% of the total). From delayed-coincidence and fragment time-of-flight experiments it was.found that about 30% of the X-rays are emitted within 0.1 ns after fission, another 30% between 0.1 and 1 ns, 25% between 1 and 10 ns, the remainder appearing as two delayed components of equal intensity with half-lives of ∼30 ns and ∼100 ns. These characteristics indicate that the X-rays arise from internal conversion during de-excitation of the primary fission fragments, an interpretation supported by the observed yield 1 per fission) of 50 - 300 - keV electrons emitted within 2 ps of fission. In the three-parameter experiments the yield and energy of K-X-rays emitted in the first centimeter (ns) of fragment flight were determined as a function of fragment mass. The yield of K-X-rays per fragment is a pronounced saw-tooth function of mass, rising from p) function in better agreement with the empirical rule of equal charge displacement (ECD) than with other postulates for charge division in nuclear fission. (author)
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.
International Nuclear Information System (INIS)
The number of prompt neutrons emitted in the fission event have been measured separately for each complementary fragment in coincidence with fragment mass and kinetic energies in spontaneous fission of 252Cf, 244Cm and 248Cm. Two high efficient Gd-loaded liquid scintillator tanks were used for the neutron registration. Approximately 3x106 fission events coincident with prompt neutron emission have been accumulated for each isotope. The mean neutron multiplicity, the dispersion and the covariance of the multiplicity distributions have been obtained as a function of fission fragment mass and kinetic energy. The neutron multiplicity data have been corrected for neutron registration efficiency, background and pile-up. Dependencies of the moments of the multiplicity distributions on the fragment mass and total kinetic energy for different mass bins, as well as mass and total kinetic energy distributions of the fission fragments are presented, discussed and compared for the different isotopes investigated. The results showed a different behavior of the moments of the multiplicity distribution depending on the fragment mass asymmetry that reflects changes in the dynamical effects for different fission modes. (author)
International Nuclear Information System (INIS)
In order to concentrate a new not yet identified spontaneously fissioning nuclide (NSFN) discovered in geothermal brines of Cheleken Peninsula various heterogenic processes were used in the brine-solid phase systems (ionites, inorganic sorbents, metals, etc.). Besides, natural inorganic collectors selected on the borehole mouths were analysed. Concentrates with approx. 105 enrichment coefficient have been obtained. It is shown that NSFN has a low degree of coprecipitation with sulfides and metal hydroxydes. It is not reduced by neither iron, nor by aluminium, is sorbed on cationites and anionites. The results obtained allow one to draw a conclusion that NSFN is not an isotope of transuranium elements. NSFN is near by its chemical properties to gold and mercury. According to the experimental data, its standard electrode potential equals (1.3+-0.2) B
Unified description of the proton, alpha, cluster decays and spontaneously fissions half- life
Mavrodiev, Strachimir Cht
2016-01-01
Some time ago the possibility of classical (without Gamow tunneling) universal description of radioactive nuclei decay was demonstrated. Such possibility is basis on the classical interpretation of Bohmian Psi-field reality in Bohmian-Chetaev mechanics and the hypothesis for the presence of dissipative forces, generated from the Gryzinski translational precession of the charged particles spin, in Langevin- Kramers diffusion mechanism. In this paper is present an unified model of proton, alpha decay, cluster radioactivity and spontaneous fission half-life as explicit function which depends on the total decay energy and kinetic energy, the number of protons and neutrons of daughter product, the number of protons and neutrons of mother nuclei and from a set) unknown digital parameters. The Half- lifes of the 573 nuclei taken from NuDat database together with the recent experimental data from Oganessian provide a basis for discovering the explicit form of the Kramers solution of Langevin type equation in a framew...
A new spontaneous fission mode for 252Cf: Hyperdeformation, cluster radioactivity, new levels
International Nuclear Information System (INIS)
Direct measurements of yields and neutron multiplicities were made for Sr-Nd, Zr-Ce, Mo-Ba, Ru-Xe, and Pd-Te from γ-ray coincidence studies in spontaneous fission of 252Cf. Strong enhancement of the 7-10 ν emission channels is seen in the Mo-Ba data. Unfolding the Mo-Ba data revealed a new fission mode associated with the enhanced ν yields with much lower total kinetic energy going by 108Mo-144Ba, 107Mo- 145Ba, and/or 106Mo-146Ba. Analysis indicates one or more of 144,145,146Ba are hyperdeformed with 3:1 axis ratio. Theoretical calculations predict a third minimum in the PES for 252Cf with β2 ∼ 0.9 and β3 ∼ 0.7. Zero neutron emission channels, a new form of cluster radioactivity, are seen in 8 and 7 correlated pairs in SF of 252Cf and 242Pu, respectively, with the odd-odd zero neutron channel yields strongly enhanced as predicted for cluster radioactivity. New level structures and isotopes include new octupole deformations, identical bands and other structures
Applicability of parallel plate avalanche counters to spontaneous fission from 252Cf
International Nuclear Information System (INIS)
The construction and performance of the parallel plate avalanche counters (PPACs) using a spontaneous fission source 252Cf is described in this paper. The parallel plate circular electrodes are made of aluminum foils having a thickness less than ten microns. After fabrication, the detectors and the source are mounted inside a reaction chamber, the source between the two detectors. A low pressure is created inside the chamber using isobutane (C4H10) and a high voltage is applied to the electrodes. The detectors are first operated at different pressures and voltages to find the optimum values of the pressure and the voltage. This is necessary to avoid the sparking threshold, to achieve a good time resolution and to keep the gain of the detectors high and constant. The PPACs are operated in 2π- and 4π-geometries. In 4π-geometry the detectors are allowed to function in coincidence and noncoincidence mode. The resulting pulse height and the time spectra are studied using the computer code ROOT and some conclusions are drawn from these analyses. The pulse height spectrum shows a clear separation between the fission fragments and the alpha particles and the time spectrum indicates a good intrinsic time resolution, 0.76 ns. (author)
Study of the isomer nuclei produced in the spontaneous fission of 252Cf
International Nuclear Information System (INIS)
Isomeric states have been studied in fission fragments produced by spontaneous fission of 252Cf. 34 isomeric nuclei have been identified by using coincidences between γ-rays detected in EUROGAM II and fission fragments detected in photovoltaic cells. Lifetimes from 20 ns up to 2 μs have been measured. Microscopic interpretation of the isomeric levels discovered has been tried by means of the Hartree-Fock-Bogolyubov procedure using Gogny force. It was found that the 152,154,156Nd nuclei have prolate deformation in their ground state; the rotational band built on this ground state is well reproduced by the calculation. For these nuclei the 2 quasi-particle excited states energies are above 1 MeV in agreement with the experiment. The computation confirms the similitude of the 156Nd and 158Sm isomeric states associated to neutron 2 quasi-particles of Jπ Kπ = 5- (ν 5/2 (642) x ν 5/2 (523)) while such similitude does not occur for the isotone nuclei 154Nd and 156Sm. The computation predicts a proton 2 quasi-particle excited states of Jπ = 5-, near the isomeric level measured in 156Sm but not for that of 154Nd. Concerning the 152Nd the calculated level density is very near that of the states measured in the 1.6 to 2.3 MeV interval. However, the lack of precise information on spins and parities of the measured levels does make not possible a confrontation with the calculations. An up-graded equipment implying 32 photovoltaic cells instead of 2 cells is to be developed and installed by the EUROGAM
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A method was developed for measuring the absolute neutron activity of a large 252Cf source. The neutron counting assembly is composed of eight BF3 counters mounted in a large tank filled with water which is used as a moderator. The detection efficiency is determined using a low activity 252Cf source. The method is based on the identification of every fission event, followed by the counting of the fission neutrons detected by the BF3 counters during a time interval equal to the maximum neutron lifetime in the moderator. The efficiency is thus obtained relative to the average number of prompt neutrons emitted per 252Cf spontaneous fission which is commonly used as a standard. The measurement accuracy is estimated to be of the order of 1%
Energy Technology Data Exchange (ETDEWEB)
Gautherin, C
1997-09-01
This thesis is devoted to the study of the nuclear structure of neutron-rich nuclei, via the search of isomeric nuclear states. Neutron-rich nuclei were produced in the spontaneous fission of {sup 252}Cf. The experimental study of isomeric states in these nuclei was performed with the {gamma}-array EUROGAM II, coupled to an additional and original fission fragment detector composed by photovoltaic cells, SAPhIR. The photovoltaic cells are well adapted to detect low energy heavy ions and have good energy and time resolutions to obtain a good fission fragment detection. This experiment led to the discovery of new isomeric states in {sup 135}Xe, {sup 104}Mo, {sup 146,147,148}Ce and {sup 152,154,156}Nd, with lifetimes between 60 ns and 2 {mu}s. Level schemes of these nuclei have been completed. An interpretation of the isomeric states in the nuclei {sup 154,156}Nd and {sup 156,158}Sm was performed by Hartree-Fock-Bogolyubov calculations using the DIS Gogny force with two quasi-particles excitations. The confrontation with the experimental results led to an interpretation of these isomeric states as K-isomers. (author)
Nuclear Structure Studies of Some Neutron Rich Nuclei Produced in 252Cf Spontaneous Fission
International Nuclear Information System (INIS)
High spin states of neutron-rich nuclei such as 133,134Te, 93Sr, 105Nb have been studied by measuring γ- γ- γ coincidences (cube), γ- γ- γ- γ coincidences (hypercube) and angular correlations from the spontaneous fission of 252Cf with the LBNL Gammasphere detector array. Four types of particle-hole bands built on the known 334.3 keV isomer in 133Te were identified. The level structure of 93Sr is interpreted, in part, as arising from the weak coupling of the 1d5/2 neutron hole to the yrast states of the 94Sr core. The g-factor of the 4+ state in 134Te was measured, for the first time, by using a new technique developed for measuring angular correlations with Gammasphere. A new level scheme of 105Nb was established. Three new collective bands were identified with a total of 14 new levels and 36 new γ transitions. In 117-122Cd, a shift to more slightly deformed structures was found where the excited levels do not fit the long held picture of one, two and three phonon bands
Searches for superheavy elements in nature: Cosmic-ray nuclei; spontaneous fission
Ter-Akopian, G. M.; Dmitriev, S. N.
2015-12-01
There is little chance that superheavy nuclei with lifetimes of no less than 100 million years are present on the stability island discovered at present. Also, pessimistic are the results of estimates made about their nucleosynthesis in r-process. Nevertheless, the search for these nuclei in nature is justified in view of the fundamental importance of this topic. The first statistically significant data set was obtained by the LDEF Ultra-Heavy Cosmic-Ray Experiment, consisting of 35 tracks of actinide nuclei in galactic cosmic rays. Because of their exceptionally long exposure time in Galaxy, olivine crystals extracted from meteorites generate interest as detectors providing unique data regarding the nuclear composition of ancient cosmic rays. The contemporary searches for superheavy elements in the earth matter rely on knowledge obtained from chemical studies of artificially synthesized superheavy nuclei. New results finding out the chemical behavior of superheavy elements should be employed to obtain samples enriched in their homologues. The detection of rare spontaneous fission events and the technique of accelerator mass spectrometry are employed in these experiments.
Prompt Neutron Emission from Fragments in Spontaneous Fission of 244, 248Cm and 252Cf
Vorobyev, A. S.; Dushin, V. N.; Hambsch, F.-J.; Jakovlev, V. A.; Kalinin, V. A.; Laptev, A. B.; Petrov, B. F.; Shcherbakov, O. A.
2005-11-01
Neutrons emitted in fission were measured separately for each complementary fragment in correlation with fission fragment energies. Two high efficient Gd-loaded liquid scintillator tanks were used for neutron registration. Fission fragment energies were measured using a twin Frisch gridded ionization chamber with a pin-hole collimator. The neutron multiplicity distributions were obtained for each value of the fission fragment mass and energy and corrected for neutron registration efficiency, background and pile-up. The dependencies of these distributions on fragment mass and energy for different energy and mass bins, as well as the mass and energy distribution of the fission fragments are presented and discussed.
Observation of new spontaneous fission activities from elements 100 to 105
Energy Technology Data Exchange (ETDEWEB)
Somerville, L.P.
1982-03-01
Several new Spontaneous Fission (SF) activities have been found. No definite identification could be made for any of the new SF activities; however, half-lives and possible assignments to element-104 isotopes consistent with several cross bombardments include /sup 257/Rf(3.8 s, 14% SF), /sup 258/Rf(13 ms), /sup 259/Rf(approx. 3 s, 8% SF), /sup 260/Rf(approx. 20 ms), and /sup 262/Rf(approx. 50 ms). The 80-ms SF activity claimed by the Dubna group for the discovery of element 104 (/sup 260/104) was not observed. A difficulty exists in the interpretation that /sup 260/Rf is a approx. 20-ms SF activity: in order to be correct, for example, the SF activities with half-lives between 14 and 24 ms produced in the reactions 109- to 119-MeV /sup 18/O + /sup 248/Cm, 88- to 100-MeV /sup 15/N + /sup 249/Bk, and 96-MeV /sup 18/O + /sup 249/Cf must be other nuclides due to their large production cross sections, or the cross sections for production of /sup 260/Rf must be enhanced by unknown mechanisms. Based on calculated total production cross sections a possible approx. 1% electron-capture branch in /sup 258/Lr(4.5 s) to the SF emitter /sup 258/No(1.2 ms) and an upper limit of 0.05% for SF branching in /sup 254/No(55 s) were determined. Other measured half-lives from unknown nuclides produced in respective reactions include approx. 1.6 s (/sup 18/O + /sup 248/CM), indications of a approx. 47-s SF activity (75-MeV /sup 12/C + /sup 249/Cf), and two or more SF activities with 3 s less than or equal to T/sub 1/2/ less than or equal to 60 s (/sup 18/O + /sup 249/Bk). The most exciting conclusion of this work is that if the tentative assignments to even-even element 104 isotopes are correct, there would be a sudden change in the SF half-life systematics at element 104 which has been predicted theoretically and attributed to the disappearance of the second hump of the double-humped fission barrier.
Energy Technology Data Exchange (ETDEWEB)
Badimon, C.; Barreau, G.; Doan, T.P.; Pedemay, G. [Centre d`Etudes Nucleaires, Bordeaux-1 Univ., 33 Gradignan (France); Gautherin, C.; Houry, M.; Korten, W.; Le Coz, Y.; Lucas, R.; Thiesen, Ch. [Dept. d`Astrophysique, de la Physique des Particules, de la Physique Nucleaire et de l`Instrumentation Associee, CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France); Belier, G.; Meot, M.V. [CEA Centre d`Etudes de Bruyeres-le-Chatel, 91 (France); Astier, A.; Ducroux, L.; Meyer, M.; Redon, N. [Inst.de Physique Nucleaire, Lyon-1 Univ., 69 - Villeurbanne (France)
1997-06-01
The prompt {gamma} emission in the spontaneous fission of {sup 252}Cf is characterized by an energy spectrum which extends up to 20 MeV. It was established that the spectrum presents in the neighbourhood of symmetric fission an intensity bump in the 3-8 MeV {gamma} energy interval. The origin of this phenomenon is still not well understood, so that it was found interesting to carry out new measurements. The spectrum of the {gamma} rays emitted in spontaneous fission of {sup 252}Cf has been measurement in the EUROGAM II multidetector using photovoltaic cells to detect fragments. The aim of the experiment was to investigate the {gamma} yield enhancement which appears for mass fragment ratio near 132/120. This enhancement was found to be composed of two peaks located at 4 MeV and 5.5 MeV respectively. The results obtained confirm the intensity bound in the 3-8 MeV region but this augmentation reaches the maximum when the heavy fragment is near the mass 132. Beyond mass 140 the phenomenon diminish and the {gamma} spectrum regains the behaviour expected for a statistic emission. The additional structure at 5.5 MeV does not vary with excitation energy while the excitation function of the 4 MeV structure is more structured and presents a maximum when the excitation energy is near 8 MeV. It is likely that all or part of this observed phenomenon is due to a particular excitation mode of this isotope associated for instance with a low energy dipole resonance. A theoretical study of this collective effect is under way 3 refs.
International Nuclear Information System (INIS)
In this paper, a mathematical model is derived for the factorial moments of the probability distribution of neutron signal multiplets within signal-triggered inspection intervals, detected with a paralyzing neutron dead-time counter. These moments are a function of the spontaneous fission rate, the (α,n) reaction rate, the probability that a neutron generates an induced fission, the neutron detection probability, the dead time, and the nuclear physics data. Monte Carlo calculations are used to check the derived algorithms and the iterative procedure. This procedure is then applied to real measurement data of a PuO2 sample to obtain the correlated multiplets from the numerical values of the factorial moments
Energy Technology Data Exchange (ETDEWEB)
Gerasimenko, B.F. [V.G. Khlopin Radium Inst., Saint Peterburg (Russian Federation)
1997-03-01
The calculations of integral spectra of prompt neutrons of spontaneous fission of {sup 244}Cm and {sup 246}Cm were carried out. The calculations were done by the Statistical Computer Code Complex SCOFIN applying the Hauser-Feschbach method as applied to the description of the de-excitation of excited fission fragments by means of neutron emission. The emission of dipole gamma-quanta from these fragments was considered as a competing process. The average excitation energy of a fragment was calculated by two-spheroidal model of tangent fragments. The density of levels in an excited fragment was calculated by the Fermi-gas model. The quite satisfactory agreement was reached between theoretical and experimental results obtained in frames of Project measurements. The calculated values of average multiplicities of neutron number were 2,746 for {sup 244}Cm and 2,927 for {sup 246}Cm that was in a good accordance with published experimental figures. (author)
International Nuclear Information System (INIS)
SOURCES 4A is a computer code that determines neutron production rates and spectra from (α,n) reactions, spontaneous fission, and delayed neutron emission due to the decay of radionuclides. The code is capable of calculating (α,n) source rates and spectra in four types of problems: homogeneous media (i.e., a mixture of α-emitting source material and low-Z target material), two-region interface problems (i.e., a slab of α-emitting source material in contact with a slab of low-Z target material), three-region interface problems (i.e., a thin slab of low-Z target material sandwiched between α-emitting source material and low-Z target material), and (α,n) reactions induced by a monoenergetic beam of α-particles incident on a slab of target material. Spontaneous fission spectra are calculated with evaluated half-life, spontaneous fission branching, and Watt spectrum parameters for 43 actinides. The (α,n) spectra are calculated using an assumed isotropic angular distribution in the center-of-mass system with a library of 89 nuclide decay α-particle spectra, 24 sets of measured and/or evaluated (α,n) cross sections and product nuclide level branching fractions, and functional α-particle stopping cross sections for Z < 106. The delayed neutron spectra are taken from an evaluated library of 105 precursors. The code outputs the magnitude and spectra of the resultant neutron source. It also provides an analysis of the contributions to that source by each nuclide in the problem
Energy Technology Data Exchange (ETDEWEB)
Wilson, W. B. (William B.); Perry, R. T. (Robert T.); Shores, E. F. (Erik F.); Charlton, W. S. (William S.); Parish, Theodore A.; Estes, G. P. (Guy P.); Brown, T. H. (Thomas H.); Arthur, Edward D. (Edward Dana),; Bozoian, Michael; England, T. R.; Madland, D. G.; Stewart, J. E. (James E.)
2002-01-01
SOURCES 4C is a computer code that determines neutron production rates and spectra from ({alpha},n) reactions, spontaneous fission, and delayed neutron emission due to radionuclide decay. The code is capable of calculating ({alpha},n) source rates and spectra in four types of problems: homogeneous media (i.e., an intimate mixture of a-emitting source material and low-Z target material), two-region interface problems (i.e., a slab of {alpha}-emitting source material in contact with a slab of low-Z target material), three-region interface problems (i.e., a thin slab of low-Z target material sandwiched between {alpha}-emitting source material and low-Z target material), and ({alpha},n) reactions induced by a monoenergetic beam of {alpha}-particles incident on a slab of target material. Spontaneous fission spectra are calculated with evaluated half-life, spontaneous fission branching, and Watt spectrum parameters for 44 actinides. The ({alpha},n) spectra are calculated using an assumed isotropic angular distribution in the center-of-mass system with a library of 107 nuclide decay {alpha}-particle spectra, 24 sets of measured and/or evaluated ({alpha},n) cross sections and product nuclide level branching fractions, and functional {alpha}-particle stopping cross sections for Z < 106. The delayed neutron spectra are taken from an evaluated library of 105 precursors. The code provides the magnitude and spectra, if desired, of the resultant neutron source in addition to an analysis of the'contributions by each nuclide in the problem. LASTCALL, a graphical user interface, is included in the code package.
Energy Technology Data Exchange (ETDEWEB)
Gautherin, C.; Houry, M.; Korten, W.; Le Coz, Y.; Lucas, R.; Thiesen, Ch. [Dept. d`Astrophysique, de la Physique des Particules, de la Physique Nucleaire et de l`Instrumentation Associee, CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France); Badimon, C.; Barreau, G.; Doan, T.P.; Pedemay, G. [Centre d`Etudes Nucleaires, Bordeaux-1 Univ., 33 Gradignan (France); Belier, G.; Girod, M.; Meot, M.V. [CEA Centre d`Etudes de Bruyeres-le-Chatel, 91 (France); Astier, G.; Meot, V.; Peru, S. [CEA Centre d`Etudes de Bruyeres-le-Chatel, 91 (France); Astier, A.; Ducroux, L.; Meyer, M.; Redon, N. [Inst.de Physique Nucleaire, Lyon-1 Univ., 69 - Villeurbanne (France)
1997-06-01
Isomeric states have been studied in fission fragments produced by spontaneous fission of {sup 252}Cf. 34 isomeric nuclei have been identified by using coincidences between {gamma}-rays detected in EUROGAM II and fission fragments detected in photovoltaic cells. Lifetimes from 20 ns up to 2 {mu}s have been measured. Microscopic interpretation of the isomeric levels discovered has been tried by means of the Hartree-Fock-Bogolyubov procedure using Gogny force. It was found that the {sup 152,154,156}Nd nuclei have prolate deformation in their ground state; the rotational band built on this ground state is well reproduced by the calculation. For these nuclei the 2 quasi-particle excited states energies are above 1 MeV in agreement with the experiment. The computation confirms the similitude of the {sup 156}Nd and {sup 158}Sm isomeric states associated to neutron 2 quasi-particles of J{sup {pi}} K{sup {pi}} = 5{sup -} ({nu} 5/2 (642) x {nu} 5/2 (523)) while such similitude does not occur for the isotone nuclei {sup 154}Nd and {sup 156}Sm. The computation predicts a proton 2 quasi-particle excited states of J{sup {pi}} = 5{sup -}, near the isomeric level measured in {sup 156}Sm but not for that of {sup 154}Nd. Concerning the {sup 152}Nd the calculated level density is very near that of the states measured in the 1.6 to 2.3 MeV interval. However, the lack of precise information on spins and parities of the measured levels does make not possible a confrontation with the calculations. An up-graded equipment implying 32 photovoltaic cells instead of 2 cells is to be developed and installed by the EUROGAM 3 refs.
International Nuclear Information System (INIS)
In the framework of Bohmian quantum mechanics supplemented with the Chetaev theorem on stable trajectories in dynamics in the presence of dissipative forces we have shown the possibility of the classical (without tunneling) universal description of radioactive decay of heavy nuclei, in which under certain conditions the so-called noise-induced transition is generated or, in other words, the stochastic channel of alpha decay, cluster radioactivity and spontaneous fission conditioned by the Kramers diffusion mechanism. Based on the ENSDF database we have found the parametrized solutions of the Kramers equation of Langevin type by Alexandrov dynamic auto--regularization method (FORTRAN code REGN-Dubna). These solutions describe with high accuracy the dependence of the half-life (decay probability) of heavy radioactive nuclei on total kinetic energy of daughter decay products. The verification of inverse problem solution in the framework of the universal Kramers description of the alpha decay, cluster radioactivity and spontaneous fission, which was based on the newest experimental data for alpha decay of even-even superheavy nuclei (Z = 114, 116, 118), has shown good coincidence of the experimental and theoretical half-life dependence on alpha-decay energy
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.
He and Be ternary spontaneous fission of sup 2 sup 5 sup 2 Cf
Hwang, J K; Ramayya, A V; Hamilton, J H
2002-01-01
Ternary and binary fission studies of sup 2 sup 5 sup 2 Cf have been carried out by using the Gammasphere detector array with light charged particle (LCD) detectors. The relative sup 4 He and sup 5 He ternary fission yields were determined. The kinetic energies of the sup 5 He and sup 4 He ternary particles were found to be approximately 11 and 16 MeV, respectively. The sup 5 He particles contribute 10-20 % to the total observed alpha ternary yield. The data indicate that in nuclei with octupole deformations the population for the negative parity bands might be enhanced in the alpha ternary fission. >From LCP-gamma double gated spectra, neutron multiplicity distributions for alpha ternary fission pairs were measured. The average neutron multiplicity decreases about 0.7 AMU in going from the binary to alpha ternary fission in the approximately same mass splittings (104-146). From the analysis of the gamma-gamma matrix gated on the sup 1 sup 0 Be particles, the two fragment pairs of sup 1 sup 3 sup 8 Xe - sup 1...
International Nuclear Information System (INIS)
A rapid radiochemical procedure for Pd separation was developed. It was the first time to use radiochemical techniques to determine 114Pd cumulative yield (2.50 ± 0.14)% in 252Cf spontaneous fission. The cumulative yields of (3.50 ± 0.13)% and (3.70 ± 0.11)% for 112Pd and 113gAg were also obtained. These are in agreement with Skovorodkin's results. The cumulative yields determined show that there is a fine-structure at light peak of mass number A = 113 in the mass distribution of 252Cf spontaneous fission
Investigation of the prompt-neutron spectrum for spontaneously-fissioning 252Cf
International Nuclear Information System (INIS)
The prompt-fission-neutron spectrum of 252Cf was investigated. The spectrum was measured with Black Neutron Detectors which have a well known efficiency. Considerations of various issues in such measurements lead to an experiment in which a time-calibration pulser, a random pulser, the neutron detector time-of-flight spectrum, the pulse-shape-discriminator gamma time-of-flight spectrum, and the detector-response spectra were simultaneously recorded for the prompt-fission neutrons, transmission through carbon, and shadowbars in a total-cross-section-type measurement. Corrections and associated uncertainties were applied for a large variety of effects which may have been overlooked in many of the previously reported measurements. Preliminary results indicate deviations from a Maxwellian shape toward a Watt-spectrum shape. Agreement is good with the shape differences relative to a Maxwellian from the recent theoretical calculation by Madland and Nix, however, a lower average energy was found
Investigation of the prompt-neutron spectrum for spontaneously-fissioning /sup 252/Cf
Energy Technology Data Exchange (ETDEWEB)
Poenitz, W.P.; Tamura, T.
1982-01-01
The prompt-fission-neutron spectrum of /sup 252/Cf was investigated. The spectrum was measured with Black Neutron Detectors which have a well known efficiency. Considerations of various issues in such measurements lead to an experiment in which a time-calibration pulser, a random pulser, the neutron detector time-of-flight spectrum, the pulse-shape-discriminator gamma time-of-flight spectrum, and the detector-response spectra were simultaneously recorded for the prompt-fission neutrons, transmission through carbon, and shadowbars in a total-cross-section-type measurement. Corrections and associated uncertainties were applied for a large variety of effects which may have been overlooked in many of the previously reported measurements. Preliminary results indicate deviations from a Maxwellian shape toward a Watt-spectrum shape. Agreement is good with the shape differences relative to a Maxwellian from the recent theoretical calculation by Madland and Nix, however, a lower average energy was found.
Shell and pairing effects in spontaneous fission for a wide range of mass asymmetries
International Nuclear Information System (INIS)
The following main contributions are emphasized. Calculations of symmetrical cold fission barriers by using the macroscopic Yukawa-plus-Exponential Model and parametrization of the nuclear shapes of two intersected spheres. A second (shallow) minimum occurs in a certain region of heavy nuclei. The introduction of a correction term takes into account the shell and pairing effects in the calculation of half lives against cluster emission within the analytical superasymmetric fission model. In this way we gave more realistic predictions. The resulting tables, referring to emission of heavy ions, alpha decay and cold fission, served as a guide for experimenters. The emission of 14 C, 20 O, 23 F, 24-26 Ne, 28,30 Mg, 32,34 Si from some Fr, Ra, Ac, Th, Pa, U, Pu, Cm isotopes covering a half live range of 15 orders of magnitude (1011-1026 s) have been already confirmed and are in good agreement with our predictions. By considering that the cold fission process is a cluster emission phenomenon, we have been able to reproduce numerically the most probable fragments experimentally determined in two regions of parent nuclei: U, Np, Pu, Cm, and Fm, Md, No. The transition from asymmetry to symmetry for the heavy Fm isotopes has also been fairly well reproduced. It was shown that even some 'stable' nuclei and neutron-rich non alpha-emitters are metastable against cluster emission. A new island of proton-rich cluster emission leading to daughter nuclei in the neighbourhood of 100 Sn has been predicted. Preliminary measurements recently performed in JINR-Dubna and GSI-Darmstadt have confirmed the 12 C radioactivity of 114 Ba. (Author) 38 Figs., 4 Tabs., 123 Refs
Identification of new neutron-rich rare-earth nuclei produced in /sup 252/Cf spontaneous fission
Greenwood, R C; Gehrke, R J; Meikrantz, D H
1981-01-01
A program of systematic study of the decay properties of neutron-rich rare-earth nuclei with 30 s
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)
Fragment angular momenta and descent dynamics in sup 2 sup 5 sup 2 Cf spontaneous fission
Popeko, J S; Ter-Akopian, G M
2002-01-01
Average angular momentum values of primary fission fragments as a function of neutron multiplicity and neutron-to-proton ratio were extracted for the first time for the Mo-Ba and Zr-Ce charge splittings of sup 2 sup 5 sup 2 Cf. The results are discussed in terms of the energy balance occurring at the scission point. For the first time we show that for large fragment elongation associated with larger numbers of evaporated neutrons (v sub t sub o sub t >=6), essentially only zero point bending oscillation takes places, i.e. T = 0 for this degree of freedom. For the major part of the fission events, with v sub t sub o sub t = 2-5, the banding oscillation is excited to a temperature of 2-3 MeV. Such a high bending temperature implies that the coupling between the collective and internal degrees of freedom is weak at the descent of the even-even nucleus of sup 2 sup 5 sup 2 Cf to the scission point. The dipole oscillations occurring at the descent take away some 2.5 - 3.0 MeV from the release energy. A correlation...
Fragment angular momenta and descent dynamics in 252 Cf spontaneous fission
International Nuclear Information System (INIS)
Average angular momentum values of primary fission fragments as a function of neutron multiplicity and neutron-to-proton ratio were extracted for the first time for the Mo-Ba and Zr-Ce charge splittings of 252 Cf. The results are discussed in terms of the energy balance occurring at the scission point. For the first time we show that for large fragment elongation associated with larger numbers of evaporated neutrons (vtot ≥6), essentially only zero point bending oscillation takes places, i.e. T = 0 for this degree of freedom. For the major part of the fission events, with vtot = 2-5, the banding oscillation is excited to a temperature of 2-3 MeV. Such a high bending temperature implies that the coupling between the collective and internal degrees of freedom is weak at the descent of the even-even nucleus of 252 Cf to the scission point. The dipole oscillations occurring at the descent take away some 2.5 - 3.0 MeV from the release energy. A correlation between the fragment angular momentum and the mass asymmetry dependent yields of primary fragment pairs is reported. This correlation shows that the subtraction of 2.5 - 3.0 MeV from the total energy balance results in a remarkable reduction of the bending temperature. (authors)
International Nuclear Information System (INIS)
Idaho National Laboratory (INL) produces 135Xe, 133mXe, 133Xe, and 131mXe standards for the calibration and testing of the collection equipment and analytical techniques used to monitor radioactive xenon emissions. At INL, xenon is produced and collected as one of several spontaneous fission products from a 252Cf source in a stagnant volume of pressurized helium. Solids are separated from gases by sintered steel filtration. Further chromatographic purification of the fission gases separates the xenon fraction for selective collection. An explanation of gas system, separation, and purification is presented. 135Xe and 133Xe activity ratio adjustments are explained. (author)
Vermote, Sofie
2009-01-01
Talking about fission, people think almost automatically about a nucleus that splits into two heavy pieces. However, in 1946 the phenomenon of ternary fission has been discovered, in which the two fission fragments are accompanied by a light charged particle. Ternary fission data are of interest for nuclear physics, however also the nuclear industry requests accurate data for ternary fission yields, especially 3H and 4He, since they are at the origin of the production of He gas and the radioa...
International Nuclear Information System (INIS)
Plutonium-containing compounds vary widely in isotopic content, and as a result, the dose as function of isotopic content also varies considerably. Determination of the dose from neutrons, decay and capture gammas from plutonium in the form of compounds thus requires that the spontaneous fission and (α,n) source and spectra from each individual isotope be known. To facilitate dose calculations from plutonium-containing compounds, we have calculated the spontaneous fission and (α,n) sources and spectra for 1 g of each of the plutonium isotopes in the form of either PuF4 or PuO2. As 241Am is often a component in a mixture of plutonium isotopic compounds, the source and spectra from 1 g of 241Am mixed with PuF4 or PuO2 has also been determined. Using these results, the neutron source and spectra may be determined for any sample composition. 2 refs., 3 tabs
Even–odd effects in prompt emission of spontaneously fissioning even–even Pu isotopes
Energy Technology Data Exchange (ETDEWEB)
Tudora, A., E-mail: anabellatudora@hotmail.com [University of Bucharest, Faculty of Physics, Bucharest Magurele, POB MG-11, R-76900 (Romania); Hambsch, F.-J. [EC-JRC Institute for Reference Materials and Measurements (IRMM), Retieseweg 111, B-2440, Geel (Belgium); Giubega, G.; Visan, I. [University of Bucharest, Faculty of Physics, Bucharest Magurele, POB MG-11, R-76900 (Romania)
2015-01-15
The available experimental Y(A,TKE) data for {sup 236,238,240,242,244}Pu(SF) together with the Zp model prescription with appropriate parameters allows the investigation of even–odd effects in fragment distributions. The size of the global even–odd effect in Y(Z) is decreasing from {sup 244}Pu(SF) to {sup 236}Pu(SF) confirming the general observation of a decrease of the even–odd effect with the fissility parameter. Charge polarizations (ΔZ) and root-mean squares (rms) as a function of A of {sup 236–244}Pu(SF) were obtained for the first time. In the asymmetric fission region both ΔZ(A) and rms(A) exhibit oscillations with a periodicity of about 5 mass units due to the even–odd effects. The total average charge deviations 〈ΔZ〉 (obtained by averaging ΔZ(A) over the experimental Y(A) distribution) are of about |0.5| for all studied Pu(SF) systems. The comparison of the calculated ΔZ(A) and rms(A) of {sup 240}Pu(SF) with those of {sup 239}Pu(n{sub th},f) reported by Wahl shows an in-phase oscillation with a higher amplitude in the case of {sup 240}Pu(SF), confirming the higher even–odd effect in the case of SF. As in the previously studied cases ({sup 233,235}U(n{sub th},f), {sup 239}Pu(n{sub th},f), {sup 252}Cf(SF)) the even–odd effects in the prompt emission of {sup 236–244}Pu(SF) are mainly due to the Z even–odd effects in fragment distributions and charge polarizations and the N even–odd effects in the average neutron separation energies from fragments 〈Sn〉. The size of the global N even–odd effect in 〈Sn〉 is decreasing with the fissility parameter, being higher for the Pu(SF) systems compared to the previously studied systems. The prompt neutron multiplicities as a function of Z, ν(Z), exhibit sawtooth shapes with a visible staggering for asymmetric fragmentations. The size of the global Z even–odd effect in ν(Z) exhibits a decreasing trend with increasing fissility. The average prompt neutron multiplicities as a
International Nuclear Information System (INIS)
The disposal of high-level defense waste in a geologic repository necessitates conversion of the waste to a stable form. For this purpose, the Hanford Waste Vitrification Plant (HWVP) will be constructed. In this facility the waste will be converted into 6.3 x 105 cm3 glassified cylinders, 59 cm in diameter and 230 cm in height, which will be placed in steel containers and buried. The waste packages must be adequately shielded to ensure the safety of personnel handling them. To calculate the shielding necessary, the radiation source term must be determined. Although the γ-ray source term does not present a problem, the neutron source term is a concern. Because the glass matrix is composed of light elements, the presence of any α-particle emitting radionuclides in the waste will contribute to the neutron flux. This paper attempts to ascertain the neutron flux and spectrum from (α,n) reactions and add it to the flux resulting from spontaneous fission
International Nuclear Information System (INIS)
Highlights: • The neutron flux due to the metal fuel alloy is modeled. • This is part of a series of studies into major system components. • The strength of the neutron flux will affect hot cell shielding and design. • A residual mass in the injection casting system was determined. • This residual mass could be used in materials accounting. -- Abstract: Advanced nuclear reactor systems (NESs) will utilize remotely-handled facilities in which batch-type processing will occur in hot cells. There are no current formalized criteria for International Atomic Energy Agency (IAEA) safeguards for these systems. This creates new challenges to develop methodologies for demonstrating the safeguardability of these facilities. A High Reliability Safeguards (HRS) approach therefore has been proposed to enhance intrinsic proliferation resistance by establishing an envelope of adaptable functional components as part of a facility design strategy. Additionally, system assessment can be modeled concurrently with safety and physical security by a risk-informed approach. The HRS approach is currently applied to a commercial pyroprocessing facility as an example system. A scoping study is presented as the first in a series of quantitative modeling efforts to extend the HRS approach. These efforts currently focus on investigating the magnitude of neutron fluxes due to spontaneous fission of curium for commercial batch sizes and held up materials for important processes in the system. Here, the fuel fabrication process is studied. The intent of these initial studies is to learn how the intrinsic properties of materials in the pyroprocessing system will affect facility design and safeguards. The model presented in this paper is intended to be adaptable to more practical and complex scenarios in order to evaluate the safeguardability of remotely-handled nuclear facilities
Energy Technology Data Exchange (ETDEWEB)
Bowyer, Ted W. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Gesh, Christopher J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Haas, Derek A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Hayes, James C. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Mahoney, Lenna A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Meacham, Joseph E. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Mendoza, Donaldo P. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Olsen, Khris B. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Prinke, Amanda M. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Reid, Bruce D. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Woods, Vincent T. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2014-12-01
We report on a technique to detect and quantify the amount of ^{240}Pu in a large tank used to store nuclear waste from plutonium production at the Hanford nuclear site. While the contents of this waste tank are known from previous grab sample measurements, our technique could allow for determination of the amount of ^{240}Pu in the tank without costly sample retrieval and analysis of this highly radioactive material. This technique makes an assumption, which was confirmed, that ^{240}Pu dominates the spontaneous fissions occurring in the tank.
International Nuclear Information System (INIS)
We report on a technique to detect and quantify the amount of 240Pu in a large tank used to store nuclear waste from plutonium production at the Hanford nuclear site. While the contents of this waste tank are known from previous grab sample measurements, our technique could allow for determination of the amount of 240Pu in the tank without costly sample retrieval and analysis of this highly radioactive material. This technique makes an assumption, which was confirmed, that 240Pu dominates the spontaneous fissions occurring in the tank.
International Nuclear Information System (INIS)
To obtain information on the energy of deformation of fission fragments of tpansfermium isotopes in the correlation with prompt neutrons, a binary ionization chamber for the measurement of emission angle of fission fragments relatively to cathode plane, is developed. A range chamber is placed into the ionization chamber having lavsan windows in the 5 mm cathode plane. Two identical chambers with that parallel electrodes have a common cathode, screen grids in front of anode and signal grids in front of screen grids which serve to determine the emission angle of fission fragments. The cathode-signal (first) grid-screen (second) grid-collecting electrode distances are 32.7 and 10 mm, respectively. The grids are made of nichromium wire 100 μm thick, which is wired with the spacing of 1.5 and 1.0 mm for the first and for the second grid respectively. Chamber characteristics are: angle resolution 3-8 deg, energy resolution 1.5%, mass resolution 2-3 a m.u. Results of model experiments are presented. Spectra f 235U, fission fragments, those of distribution of fission fragments in mass and total kinetic energy are measured
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 ...
International Nuclear Information System (INIS)
Absorbed doses, linear energy transfers (LETs) and quality factors of secondary charged particles in organs and tissues, generated via the interactions of the spontaneous fission neutrons from. 252Cf and. 244Pu within the human body, were studied using the Particle and Heavy Ion Transport Code System (PHITS) coupled with the ICRP Reference Phantom. Both the absorbed doses and the quality factors in target organs generally decrease with increasing distance from the source organ. The analysis of LET distributions of secondary charged particles led to the identification of the relationship between LET spectra and target-source organ locations. A comparison between human body-averaged mean quality factors and fluence-averaged radiation weighting factors showed that the current numerical conventions for the radiation weighting factors of neutrons, updated in ICRP103, and the quality factors for internal exposure are valid. (authors)
Energy Technology Data Exchange (ETDEWEB)
HOLDEN, H.E.
2003-08-08
In his review of radionuclides for dating purposes, Roth noted that there were a large number of nuclides, normally considered ''stable'' but which are radioactive with a very long half-life. Roth suggested that I review the data on the half-life values of these long-lived nuclides for the 2001 Atomic Weights Commission meeting in Brisbane. I provided a report, BNL-NCS-68377, to fulfill Roth's request. Peiser has now made a similar suggestion that I review these data for our next Commission meeting in Ottawa for their possible inclusion in our Tables. These half-life values for long-lived nuclides include those due to various decay modes, {alpha}-decay, {beta}-decay, electron capture decay, {beta}{beta}-decay, proton decay and spontaneous fission decay. This data review (post Brisbane) provides an update to the recommendation of the 2001 review.
Neutron production from (α,n) reactions and spontaneous fission in ThO2, UO2, and (U,Pu)O2 fuels
International Nuclear Information System (INIS)
Available alpha-particle stopping cross-section and 1718O(α,n) cross-section data were adjusted, fitted, and used in calculating the thick-target neutron production function for alpha particles below 10 MeV in oxide fuels. The spent UO2 function produced was folded with actinide decay spectra to determine (α,n) neutron production by each of 89 actinides. Spontaneous-fission (SF) neutron production for 40 actinides was calculated as the product of anti ν(SF) and SF branching-fraction values accumulated or estimated from available data. These contributions and total neutron production in spent UO2 fuel are tabulated and, when combined with any calculated inventory, describe the spent UO2 neutron source. All data are tabulated and methodology is described to permit easy extension to specialized problems
Study of the spontaneous fission of 252Cf at the Darmstadt-Heidelberg Crystal-Ball Spectrometer
International Nuclear Information System (INIS)
This work was performed at the Darmstadt-Heidelberg Crystal-Ball Spectrometer, a 4π detector with good efficiency for gamma quanta and neutrons consisting of 162 NaI single counters. By means of a semiconductor counter and a 2π parallel-plate heavy-ion detector the mass of the fission fragments could be determined with a mean mass resolution of 3 mass units. It was the aim of the thesis to contribute by a large number of single quantities and correlations between these parameters to a better understanding of the fission process. A comparison of the results with reliable literature data resulted a very sufficient agreement. Interesting results were shown above all in the correlations between the gamma respectively neutron emission and the fragment mass respectively the total kinetic energy (TKE): The saw-tooth shaped slope of the gamma multiplicity with the mass known from literature was disproved by means of the Doppler-shift method. The single energy spectrum of the gamma quanta shows for different energy ranges a very different mass dependence. In the region of symmetric fragmentation a new high-energetic gamma component was found. The dependence of the neutron multiplicity on the TKE is for fixed mass partition within the error limits linear. The changes of the gradiation of this straight line with the mass allows far reaching predictions about the shape of the nucleus immediately before the fission. The neutron saw-tooth exists also for high internal excitation energies. (orig.)
Westgate, John A.; Pearce, Nicholas J. G.; Gatti, Emma; Achyuthan, Hema
2014-09-01
Determination of the area density of spontaneous fission tracks (ρs) in glass shards of Toba tephra is a reliable way to distinguish between the Youngest Toba Tuff (YTT) and the Oldest Toba Tuff (OTT). The ρs values for YTT, uncorrected for partial track fading, range from 70 to 181 tracks/cm2 with a weighted mean of 108 ± 5 tracks/cm2, based on 15 samples. Corrected ρs values for YTT are in the range of 77-140 tracks/cm2 with a weighted mean of 113 ± 8 tracks/cm2, within the range of uncorrected ρs values. No significant difference in ρs exists between YTT samples collected from marine and continental depositional settings. The uncorrected ρs for OTT is 1567 tracks/cm2 so that confusion with YTT is unlikely. The ρs values of the Toba tephra at Bori, Morgaon, and Gandhigram in northwestern India indicate a YTT identity, in agreement with geochemical data on their glass shards, the presence of multiple glass populations, and a glass fission-track age determination. Therefore, the view of others that OTT is present at these sites - and thereby indicates a Lower Pleistocene age for the associated Acheulean artifacts - is incorrect.
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 ...
Wang, Taofeng; Li, Guangwu; Zhu, Liping; Meng, Qinghua; Wang, Liming; Han, Hongyin; Zhang, Wenhui; Xia, Haihong; Hou, Long; Vogt, Ramona; Randrup, Jørgen
2016-01-01
The dependence of correlations of neutron multiplicity ν and γ -ray multiplicity Mγ in spontaneous fission of 252Cf on fragment mass A* and total kinetic energy (TKE) have been investigated by employing the ratio of Mγ/ν and the form of Mγ(ν ) . We show for the first time that Mγ and ν have a complex correlation for heavy fragment masses, while there is a positive dependence of Mγ for light fragment masses and for near-symmetric mass splits. The ratio Mγ/ν exhibits strong shell effects for neutron magic number N =50 and near doubly magic number shell closure at Z =50 and N =82 . The γ -ray multiplicity Mγ has a maximum for TKE=165 -170 MeV. Above 170 MeV Mγ(TKE) is approximately linear, while it deviates significantly from a linear dependence at lower TKE. The correlation between the average neutron and γ -ray multiplicities can be partly reproduced by model calculations.
International Nuclear Information System (INIS)
The mean neutron number per isomeric fission event of 242Am is measured. Correlations between the isomeric fission probabilities and the fission widths of neutron resonance of 241Am are investigated. For these experiments neutron time-of-flight spectrometers based on pulsed reactors IBR-30 and IBR-2 at the JINR Dubna are used
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 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
Subroutines to Simulate Fission Neutrons for Monte Carlo Transport Codes
Lestone, J. P.
2014-01-01
Fortran subroutines have been written to simulate the production of fission neutrons from the spontaneous fission of 252Cf and 240Pu, and from the thermal neutron induced fission of 239Pu and 235U. The names of these four subroutines are getnv252, getnv240, getnv239, and getnv235, respectively. These subroutines reproduce measured first, second, and third moments of the neutron multiplicity distributions, measured neutron-fission correlation data for the spontaneous fission of 252Cf, and meas...
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
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.
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)
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
Microscopic description of complex nuclear decay: multimodal fission
Staszczak, A.; Baran, A.; Dobaczewski, J.; Nazarewicz, W.
2009-01-01
Our understanding of nuclear fission, a fundamental nuclear decay, is still incomplete due to the complexity of the process. In this paper, we describe a study of spontaneous fission using the symmetry-unrestricted nuclear density functional theory. Our results show that the observed bimodal fission can be explained in terms of pathways in multidimensional collective space corresponding to different geometries of fission products. We also predict a new phenomenon of trimodal spontaneous fissi...
General Description of Fission Observables: GEF Model Code
Schmidt, Karl-Heinz; Jurado, Beatriz; Amouroux, Charlotte; Schmitt, C.
2015-01-01
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 barrie...
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.)
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
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
Fission - track age of the Marjalahti Pallasite
International Nuclear Information System (INIS)
Full text: Investigation of fossil charged-particle tracks in various mineral phases of extraterrestrial samples is a powerful method for research the early stages of the solar system. Over geological time, meteorites crystals have accumulated a record of tracks produced by heavily charged energetic particles from both internal (spontaneous fission of 238U and some other extinct isotopes) and external sources (galactic cosmic rays with Z>20). The fortunate fact that meteorite grains can accumulate latent and very long-lived tracks since soon after the end of nucleosynthesis in the solar nebula enables one to decode their radiation history and to detect any thermal events in the meteorite cosmic history by revealing these tracks through suitable etching procedures. Only a few minerals in meteorites (mainly phosphates) contain small amount of uranium; the fact that 238U undergoes fission with fission-decay constant λf∼8.2x10-17 yr-1 allows one to use this isotope as a chronometer. By measuring the U concentration in the crystals (by reactor irradiation) and the density of the spontaneous-fission tracks it is relatively easy to calculate the 'fission-track age' if 238U is the main source of fission tracks. However the fission-track dating of extraterrestrial samples compared with the terrestrial ones has some peculiar features due to presence of a number of other potential track sources except the spontaneous fission of 238U, such as the spontaneous fission of presently extinct 244Pu, heavy nuclei of cosmic rays and induced fission by cosmic ray primaries. Only tracks from the spontaneous fission of U and Pu are suitable for fission-track dating. The competing effects of these fissioning elements, whose half-lives differ by a factor of ∼50, form a basis for a fission-track chronology for samples older than ∼ 4.0 Gyr. Over small intervals in time (∼ few x108 yr ) the track density from spontaneous fission of 238U is nearly constant. However, the contribution
Cold fission studies using a double-ionization chamber
International Nuclear Information System (INIS)
An investigation on spontaneous fission of 252Cf is described. Both fission fragments are detected coincidentally with a double ionization chamber as a 4 π detector. Special techniques are demonstrated which allow the determination of nuclear masses and charges for cold fission fragments. Detector properties such as systematic errors and their correction are studied with the help of α particles. (orig.)
Fission fragment orientation and gamma ray emission anisotropy
Barabanov, A. L.
1994-01-01
Experimental data on angular distributions of gamma rays emitted from binary and ternary spontaneous fission of $^{252}{\\rm Cf}$ are analyzed. Their difference indicates that the alignment of fragments is higher in ternary fission than in binary one. The consequences of possible relation between the mechanism of ternary fission and the excitation of collective modes during the saddle-to-scission stage are discussed.
Subroutines to Simulate Fission Neutrons for Monte Carlo Transport Codes
Lestone, J P
2014-01-01
Fortran subroutines have been written to simulate the production of fission neutrons from the spontaneous fission of 252Cf and 240Pu, and from the thermal neutron induced fission of 239Pu and 235U. The names of these four subroutines are getnv252, getnv240, getnv239, and getnv235, respectively. These subroutines reproduce measured first, second, and third moments of the neutron multiplicity distributions, measured neutron-fission correlation data for the spontaneous fission of 252Cf, and measured neutron-neutron correlation data for both the spontaneous fission of 252Cf and the thermal neutron induced fission of 235U. The codes presented here can be used to study the possible uses of neutron-neutron correlations in the area of transparency measurements and the uses of neutron-neutron correlations in coincidence neutron imaging.
Theory of nuclear fission. A textbook
International Nuclear Information System (INIS)
This book brings together various aspects of the nuclear fission phenomenon discovered by Hahn, Strassmann and Meitner almost 70 years ago. Beginning with an historical introduction the authors present various models to describe the fission process of hot nuclei as well as the spontaneous fission of cold nuclei and their isomers. The role of transport coefficients, like inertia and friction in fission dynamics is discussed. The effect of the nuclear shell structure on the fission probability and the mass and kinetic energy distributions of the fission fragments is presented. The fusion-fission process leading to the synthesis of new isotopes including super-heavy elements is described. The book will thus be useful for theoretical and experimental physicists, as well as for graduate and PhD students. (orig.)
Progress in fission product nuclear data
International Nuclear Information System (INIS)
This is the eleventh issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (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 types of activities being included in this report 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 main part of this report consists of unaltered original contributions which the authors have sent to IAEA/NDS
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
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)
Applications of Event-by-Event Fission Modeling with FREYA
Vogt R.; Randrup J.
2012-01-01
The recently developed code FREYA (Fission Reaction Event Yield Algorithm) generates large samples of complete fission events, consisting of two receding product nuclei as well as a number of neutrons and photons, all with complete kinematic information. Thus it is possible to calculate arbitrary correlation observables whose behavior may provide unique insight into the fission process. We first discuss the present status of FREYA, which has now been extended to include spontaneous fission. C...
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
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.
Mass and Charge Distribution in Low-Energy Fission
International Nuclear Information System (INIS)
The mass and charge distributions for thermal-neutron fission of U235 are discussed in considerable detail and compared with the corresponding distributions in other low-energy fission processes. Points discussed in connection with the mass distributions for binary fission include the positions of the peaks, valley and fine structure in a mass yield curve with respect to filled nuclear shells and the changes in the positions that occur with changing fissioning nucleus and excitation energy. The mass distribution from ternary fission is discussed also. For both binary and ternary fission comments are made concerning the mass distributions of primary fragments (before neutron evaporation) and of fission products (after neutron evaporation). Charge distribution is discussed in terms of charge dispersion among fission products with the same mass number and the variation with mass number of Zp, the ''most probable charge'' (non-integral) for a given mass number. Although direct information about charge distribution is limited to fission products, estimates are presented of charge distribution for primary fission fragments. Knowledge and estimates of mass and charge distribution for a fission process allow estimation of primary yields of all fission products or fragments. Although many estimated primary yields are quite uncertain mainly because of lack of knowledge of charge distribution, especially for fission products formed in low yield; some estimates of primary yields are presented to illustrate the need for and possible practicality of further experimentation. Fission processes other than thermal-neutron fission of U235 that are discussed include thermal-neutron fission of U233 and Pu239, spontaneous fission of Pu240 and Cf252, 14-MeV neutron fission of U235 and U238, 11-MeV proton fission of Ra226 and 22-MeV deuteron fission of Bi209. (author)
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.)
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
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
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)
14. International workshop on nuclear fission physics. Proceedings
International Nuclear Information System (INIS)
The meetings on nuclear fission took place 12-15 October 1998 and was organized by Institute of Physics and Power Engineering. The aim of the workshop was to present and discuss main new both theoretical and experimental results obtained in the area of nuclear fission, dynamical feature, properties of fission fragments and complementary radiation. As usual the program of the workshop was designed to cover a wide range of physical phenomena - from low energy and spontaneous fission to fission of hot rotating nuclei and multifragmentation at intermediate and high energies. Reaction induced by slow and fast neutron, light and heavy ions were discussed
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...
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
Model Calculation of Fission Product Yields Data using GEF Code
International Nuclear Information System (INIS)
Fission yields data are classified with spontaneous fission data and neutron induced fission data. The fission product yields data at several energy points for the limited actinides are included in nuclear data libraries such as ENDF/B, JEFF and JENDL because production of those is based mainly on experimental results and it is very difficult to conduct experiments for all actinides and continuous energies. Therefore, in order to obtain fission yields data without experimental data, a theoretical fission model should be introduced to produce the yields data. GEneral Fission model (GEF) is developed to predict the properties for fissioning systems that have not been measured and that are not accessible to experiment. In this study, the fission yields data generated from GEF code are compared with the measured data and the recently available nuclear data libraries. The GEF code is very powerful tool to generate fission yields without measurements. Also, it can produce the distribution of fission product yields for continuous neutron energy while measured data are given only at several energies. The fission yields data of 235U have been tentatively generated with GEF code in this work. Comparing GEF results with measurements and recently released evaluated fission yields data, it is confirmed that GEF code can successfully predict the fission yields data. With its sophisticated model, GEF code is playing a significant role in nuclear industry
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...
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.
Microscopic Theory of Nuclear Fission: A Review
Schunck, N
2015-01-01
This article reviews how nuclear fission is described within nuclear density functional theory. In spontaneous fission, half-lives are the main observables and quantum tunnelling the essential concept, while in induced fission the focus is on fragment properties and explicitly time-dependent approaches are needed. The cornerstone of the current microscopic theory of fission is the energy density functional formalism. Its basic tenets, including tools such as the HFB theory, effective two-body effective nuclear potentials, finite-temperature extensions and beyond mean-field corrections, are presented succinctly. The EDF approach is often combined with the hypothesis that the time-scale of the large amplitude collective motion driving the system to fission is slow compared to typical time-scales of nucleons inside the nucleus. In practice, this hypothesis of adiabaticity is implemented by introducing (a few) collective variables and mapping out the many-body Schr\\"odinger equation into a collective Schr\\"odinge...
Discovery of a new mode of nuclear fission
International Nuclear Information System (INIS)
We measured the mass and kinetic-energy partitioning in the spontaneous fission of 258Fm, 259Md, 260Md, 258No, and 260[104]. Surprisingly, these energy distributions were skewed upward or downward from the peak in each case, except for 260[104], indicating a composite of two energy distributions. We interpret this as a new mode of fission in which there is mixture of liquid-drop-like and fragment-shell-directed symmetric fission
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...
A method to measure prompt fission neutron spectrum using gamma multiplicity tagging
Blain, E.; Daskalakis, A.; Block, R. C.; Barry, D.; Danon, Y.
2016-01-01
In order to improve on current prompt fission neutron spectrum measurements, a gamma multiplicity tagging method was developed at the Rensselaer Polytechnic Institute Gearttner Linear Accelerator Center. This method involves using a coincidence requirement on an array of BaF2 gamma detectors to determine the timing of a fission event. This allows for much larger fission samples to be used due to the higher penetrability of gammas compared to fission fragments. Additionally, since the method relies on gammas as opposed to fission fragments, the effects of the low level discriminator, used in fission chambers to eliminate alpha events, are not seen. A 252Cf fission chamber was constructed in order to determine the viability of this method as well as the efficiency when compared to a fission chamber. The implemented multiple gamma tagging method was found to accurately reproduce the prompt fission neutron spectrum for the spontaneous fission of 252Cf and to detect 30% of fission events.
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.
Progress in fission product nuclear data
International Nuclear Information System (INIS)
This is the seventh issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (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 present issue contains also a section with some recent references relative to fission product nuclear data, which were not covered by the contributions submitted. The types of activities being included in this report 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 sixth issue of this series has been published in June 1980 as INDC(NDS)-113/G+P. The present issue includes contributions which were received by NDS between 1 August 1980 and 25 May 1981
Progress in fission product nuclear data
International Nuclear Information System (INIS)
This is the ninth issue of a report series on Fission Product Nuclear Data (FPND) which is published by the Nuclear Data Section (NDS) of the International Atomic Energy Agency (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 main part of this report consists of unaltered original contributions which the authors have sent to IAEA/NDS. The present issue contains also a section with some recent references relative to fission product nuclear data, which were not covered by the contributions submitted. The types of activities being included in this report 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 eighth issue of this series has been published in July 1982 as INDC(NDS)-130. The present issue includes contributions which were received by NDS between 1 August 1982 and 25 June 1983
Progress in fission product nuclear data. No. 13
International Nuclear Information System (INIS)
This is the 13th issue of a report series published by the Nuclear Data Section of the IAEA. 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 and bumped fission product data (decay heat, absorption, etc.). The first part of the report consists of unaltered original data which the authors have sent to IAEA/NDS. The second part contains some recent references relative to fission product nuclear data, which were not covered by the contributions submitted, and selected papers from conferences. Part 3 contains requirements for further measurements
Progress in fission product nuclear data. No. 14
International Nuclear Information System (INIS)
This is the 14th issue of a report series on Fission Product Nuclear Data published by the Nuclear Data Section of the IAEA. The types of activities included are measurements, compilations and evaluations of fission product yields, neutron reaction cross sections of fission products, data related to the radioactive decay of fission products, delayed neutron data from neutron induced and spontaneous fission, lumped fission product data. The first part of the report consists of unaltered original contributions which the authors have sent to IAEA/NDS. The second part contains some recent references relative to fission product nuclear data, which were not covered by the contributions submitted, and selected papers from conferences. The third part contains requirements for further measurements
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
International Nuclear Information System (INIS)
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)
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
Directory of Open Access Journals (Sweden)
Davari R
1996-07-01
Full Text Available A case with bilateral spontaneous pneumothorax was presented. Etiology, mechanism, and treatment were discussed on the review of literature. Spontaneous Pneumothorax is a clinical entity resulting from a sudden non traumatic rupture of the lung. Biach reported in 1880 that 78% of 916 patients with spontaneous pneumothorax had tuberculosis. Kjergaard emphasized 1932 the primary importance of subpleural bleb disease. Currently the clinical spectrum of spontaneous pneumothorax seems to have entered a third era with the recognition of the interstitial lung disease and AIDS as a significant etiology. Standard treatment is including: observation, thoracocentesis, tube thoracostomy. Chemical pleurodesis, bullectomy or wedge resection of lung with pleural abrasion and occasionally pleurectomy. Little information has been reported regarding the efficacy of such treatment in spontaneous pneumothorax secondary to non bleb disease
Fission properties of the BCPM energy-density functional
International Nuclear Information System (INIS)
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.
Berge, Léonie
2015-01-01
The prompt fission neutron spectrum (PFNS) is very important for various nuclear physics applications. Yet, except for the 252Cf spontaneous fission spectrum which is an international standard and is used for metrology purposes, the PFNS is still poorly known for most of the fissionning nuclides. In particular, few measurements exist for the fast fission spectrum (induced by a neutron whose energy exceeds about 100 keV), and the international evaluations show strong discrepancies. There are a...
A multiple parallel-plate avalanche counter for fission-fragment detection
Energy Technology Data Exchange (ETDEWEB)
Wu, C.Y., E-mail: wu24@llnl.gov [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); Henderson, R.A. [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); Haight, R.C.; Lee, H.Y.; Taddeucci, T.N. [Los Alamos National Laboratory, Los Alamos, MN 87545 (United States); Bucher, B.; Chyzh, A. [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); Devlin, M.; Fotiades, N. [Los Alamos National Laboratory, Los Alamos, MN 87545 (United States); Kwan, E. [Lawrence Livermore National Laboratory, Livermore, CA 9455 (United States); National Superconducting Cyclotron Laboratory, East Lansing, MI 48824 (United States); O’Donnell, J.M.; Perdue, B.A.; Ullmann, J.L. [Los Alamos National Laboratory, Los Alamos, MN 87545 (United States)
2015-09-11
A new low-mass multiple gas-filled parallel-plate avalanche counter for the fission-fragment detection has been developed to mark the fission occurrence in measurements of the prompt fission neutron energy spectrum as a function of incident neutron energy. It was used successfully for the neutron-induced fission of {sup 235}U and {sup 239}Pu with a total mass near 100 mg each and the spontaneous fission of {sup 252}Cf. Both the incident neutron energy and the prompt fission neutron energy are measured by using the time-of-flight method. The design and performance of this avalanche counter are described.
A multiple parallel-plate avalanche counter for fission-fragment detection
International Nuclear Information System (INIS)
A new low-mass multiple gas-filled parallel-plate avalanche counter for the fission-fragment detection has been developed to mark the fission occurrence in measurements of the prompt fission neutron energy spectrum as a function of incident neutron energy. It was used successfully for the neutron-induced fission of 235U and 239Pu with a total mass near 100 mg each and the spontaneous fission of 252Cf. Both the incident neutron energy and the prompt fission neutron energy are measured by using the time-of-flight method. The design and performance of this avalanche counter are described
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.
An improved technique for fission track dating
International Nuclear Information System (INIS)
The necessity of improving the fission track dating (FTD) technique both at home and abroad is illustrated. The ways of making such improvement are also proposed. It is suggested to calibrate the constant b value of the uranium standard glass by using the method of fission products activity. The 3 kinds of uranium standard glass which have been calibrated are NBS SRM962a, UB1 and UB2. An established new method σ·Φ ρd/b, to measure neutron fluence, avoids the influence of the varying neutron spectrum on measuring neutron fluence. The improved etching technique for fission tracks in zircon adopted a two-step method which includes the molten alkali system etching using NaOH + KOH and the mixed acid system etching using HNO3 + HF; this technique results in adequate track etching, increased track clarity and less interference. In this way the intensity of tracks is authentically reflected. Dividing angular zone in accordance with the angular distribution of spontaneous fission track on the crystal surface of minerals to count the tracks and using the improved etching technique to remove the non-uniform angular distribution of spontaneous fission tracks in zircon, ensure the accuracy of tracks count. The improved FTD techniques were used to finish Laboratory Standardized Calibration. The tests using international FTD age standards samples have proved that above mentioned techniques are reliable and practical in obtaining the accurate FTD data. (8 tabs.; 3 figs.)
Nuclear data for neutron emission in the fission process
International Nuclear Information System (INIS)
This document contains the proceedings of the IAEA Consultants' Meeting on Nuclear Data for Neutron Emission in the Fission Process, Vienna, 22 - 24 October 1990. Included are the conclusions and recommendations reached at the meeting and the papers presented by the meeting participants. These papers provide a review of the status of experimental and theoretical data on neutron emission in spontaneous and neutron induced fission with reference to the data needs for reactor applications oriented towards actinide burner studies. The specific topics covered are the following: experimental measurements and theoretical predictions and evaluations of fission neutron energy spectra, average prompt fission neutron multiplicity, correlation in neutron emission from complementary fragments, neutron emission during acceleration of fission fragments, statistical properties of neutron rich nuclei by study of emission spectra of neutrons from the excited fission fragments, integral qualification of nu-bar for the major fissile isotopes, nu-bar total of 239Pu and 235U, and related problems. Refs figs and tabs
Prompt Fission Gamma-ray Studies at DANCE
Jandel, M.; Rusev, G.; Bond, E. M.; Bredeweg, T. A.; Chadwick, M. B.; Couture, A.; Fowler, M. M.; Haight, R. C.; Kawano, T.; Keksis, A. L.; Mosby, S. M.; O'Donnell, J. M.; Rundberg, R. S.; Stetcu, I.; Talou, P.; Ullmann, J. L.; Vieira, D. J.; Wilhelmy, J. B.; Stoyer, M. A.; Haslett, R. J.; Henderson, R. A.; Becker, J. A.; Wu, C. Y.
Measurements of correlated data on prompt-fission γ-rays (PFG) have been carried out for various actinide isotopes in recent years using the Detector for Advanced Neutron Capture Experiments (DANCE) at Los Alamos National Laboratory (LANL). We have developed a model that conveniently parametrizes the correlated data of γ-ray multiplicity and energy. New results on two- dimensional prompt-fission γ-ray multiplicity versus energy distributions from spontaneous fission on 252Cf and neutron-induced fission on 242mAm are presented together with previously obtained results on 233,235U and 239Pu. Correlated PFG data from 252Cf are also compared to results of the detailed theoretical model developed at LANL, for different thresholds of PFG energies. Future plans to measure correlated data on fission fragments, prompt fission neutrons and γ-rays at DANCE are presented.
International Nuclear Information System (INIS)
Formation mechanism of prompt neutrons spectrum during the fission of the 235U, 239Pu nuclei by thermal and fast neutrons and spontaneous fission of 252Cf is investigated. The formation procedure for prompt neutrons spectrum during the fission of nuclei as superposition of three partial evaporation Weisskopf spectra with the mean energy of neutrons 0.4, 2.06 and 2.8 MeV is proposed. Formation mechanism of the spectrum just as during the fission of the 235U, 239Pu nuclei by thermal and fast neutrons, so spontaneous fission of the 252Cf nuclei is identical
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)
Wakai, Abel P
2008-01-01
Spontaneous pneumothorax is defined as air entering the pleural space without any provoking factor, such as trauma, surgery, or diagnostic intervention. Incidence is 24/100,000 a year in men, and 10/100,000 in women in England and Wales, and the major contributing factor is smoking, which increases the likelihood by 22 times in men and by 8 times in women.While death from spontaneous pneumothorax is rare, rates of recurrence are high, with one study of men in the US finding a total recurre...
Wakai, Abel P
2011-01-01
Spontaneous pneumothorax is defined as air entering the pleural space without any provoking factor, such as trauma, surgery, or diagnostic intervention. Incidence is 24/100,000 a year in men, and 10/100,000 a year in women in England and Wales, and the major contributing factor is smoking, which increases the likelihood by 22 times in men and by 8 times in women.While death from spontaneous pneumothorax is rare, rates of recurrence are high, with one study of men in the US finding a total ...
A new approach to prompt fission neutron TOF data treatment
Zeynalov, Sh.; Zeynalova, O. V.; Hambsch, F.-J.; Oberstedt, S.
The prompt neutron emission in spontaneous fission of 252Cf has been investigated applying digital signal electronics along with associated digital signal processing algorithms. A new mathematical approach, applicable to single events, was developed for prompt fission neutron (PFN) time-offlight distribution unfolding. The main goal was to understand the reasons of the long existing discrepancy between theoretical calculations and the measurements of prompt fission neutron (PFN) emission dependence on the total kinetic energy (TKE) of the fission fragments (FF). Since the 252Cf (sf) reaction is one of the main references for nuclear data the understanding of the PFN emission mechanism is very important both for nuclear fission theory and nuclear data. The experimental data were taken with a twin Frisch-grid ionization chamber and a NE213-equivalent neutron detector in an experimental setup similar to the well known work of C. Budtz-Jorgensen and H.-H. Knitter. About 2.5 × 105 coincidences between fission fragment (FF) and neutron detector response to prompt fission neutron detection have been registered (∼ 1.6 × 107 of total recorded fission events). Fission fragment kinetic energy, mass and angular distribution, neutron time-of-flight and pulse shape have been investigated using a 12-bit waveform digitizer. The signal waveforms have been analyzed using digital signal processing algorithms. The main goal of this work was a detailed description of the prompt fission neutron treatment.
Status of fission yield evaluations
International Nuclear Information System (INIS)
Very few yield compilations are also evaluations, and very few contain an extensive global library of measured data and extensive models for unmeasured data. The earlier U.K. evaluations and US evaluations were comparable up to the retirements of the primary evaluators. Only the effort in the US has been continued and expanded. The previous U.K. evaluations have been published. In this paper we summarize the current status of the US evaluation, philosophy, and various integral yield tests for 34 fissioning nuclides at one or more neutron incident energies and/or for spontaneous fission. Currently there are 50 yield 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 the next version of the US Evaluated Nuclear Data File (ENDF/B-VI). The complete set of data, including the basic input of measured yields, will be issued as a sequel to the General Electric evaluation reports (better known by the authors' names: Rider - or earlier - Meek and Rider). 16 references
Coincident measurements of prompt fission γ rays and fission fragments at DANCE
Walker, C. L.; Baramsai, B.; Jandel, M.; Rusev, G.; Couture, A.; Mosby, S.; Ullmann, J.; Kawano, T.; Stetcu, I.; Talou, P.
2015-10-01
Modern statistical approaches to modeling fission involve the calculation of not only average quantities but also fully correlated distributions of all fission products. Applications such as those involving the detection of special nuclear materials also rely on fully correlated data of fission products. Experimental measurements of correlated data are thus critical to the validation of theory and the development of important applications. The goal of this experiment was to measure properties of prompt fission gamma-ray emission as a function of fission fragments' total kinetic energy in the spontaneous fission of 252Cf. The measurement was carried out at the Detector for Advanced Neutron Capture Experiments (DANCE), a 4 π γ-ray calorimeter. A prototype design consisting of two silicon detectors was installed in the center of DANCE, allowing simultaneous measurement of fission fragments and γ rays. Effort has been taken to simulate fragment kinetic energy losses as well as γ-ray attenuation in DANCE using such tools as GEANT4 and SRIM. Theoretical predictions generated by the code CGMF were also incorporated as input for these simulations. Results from the experiment and simulations will be presented, along with plans for future measurements.
Microscopic Calculations of 240Pu Fission
Energy Technology Data Exchange (ETDEWEB)
Younes, W; Gogny, D
2007-09-11
Hartree-Fock-Bogoliubov calculations have been performed with the Gogny finite-range effective interaction for {sup 240}Pu out to scission, using a new code developed at LLNL. A first set of calculations was performed with constrained quadrupole moment along the path of most probable fission, assuming axial symmetry but allowing for the spontaneous breaking of reflection symmetry of the nucleus. At a quadrupole moment of 345 b, the nucleus was found to spontaneously scission into two fragments. A second set of calculations, with all nuclear moments up to hexadecapole constrained, was performed to approach the scission configuration in a controlled manner. Calculated energies, moments, and representative plots of the total nuclear density are shown. The present calculations serve as a proof-of-principle, a blueprint, and starting-point solutions for a planned series of more comprehensive calculations to map out a large set of scission configurations, and the associated fission-fragment properties.
Our 50-year odyssey with fission: Summary
International Nuclear Information System (INIS)
On the occasion of this International Conference on Fifty Years Research in Nuclear Fission, we summarize our present understanding of the fission process and the challenges that lie ahead. The basic properties of fission arise from a delicate competition between disruptive Coulomb forces, cohesive nuclear forces, and fluctuating shell and pairing forces. These static forces are primarily responsible for such experimental phenomena as deformed ground-state nuclear shapes, fission into fragments of unequal size, sawtooth neutron yields, spontaneously fissioning isomers, broad resonances and narrow intermediate structure in fission cross sections, and cluster radioactivity. However, inertial and dissipative forces also play decisive roles in the dynamical evolution of a fissioning nucleus. The energy dissipated between the saddle and scission points is small for low initial excitation energy at the saddle point and increases with increasing excitation energy. At moderate excitation energies, the dissipation of collective energy into internal single-particle excitation energy proceeds largely through the interaction of nucleons with the mean field and with each other in the vicinity of the nuclear surface, as well as through the transfer of nucleons between the two portions of the evolving dumbell-like system. These unique dissipation mechanisms arise from the Pauli exclusion principle for fermions and the details of the nucleon-nucleon interaction, which make the mean free path of a nucleon near the Fermi surface at low excitation energy longer than the nuclear radius. With its inverse process of heavy-ion fusion reactions, fission continues to yield surprises in the study of large-amplitude collective nuclear motion. 87 refs., 12 figs
Development of glass ceramics for the incorporation of fission products
International Nuclear Information System (INIS)
Spontaneous devitrification of fission-product-containing borosilicate glasses can be avoided by controlled crystallization after melting. Glass ceramics have been developed from a vitrified simulated waste and further improvement of product properties was achieved. In particular perovskite, h-celsian, diopside and eucryptite glass ceramics were prepared. These contained leach resistant host phases which exhibited considerable enrichment of long-lived fission products. All products showed increased impact resistance, but the thermal expansion was only slightly improved
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
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.
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.
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.
Advanced model for the prediction of the neutron-rich fission product yields
Rubchenya V.A.; Gorelov D.; Jokinen A.; Penttilä H.; Äystö J.
2013-01-01
The consistent models for the description of the independent fission product formation cross sections in the spontaneous fission and in the neutron and proton induced fission at the energies up to 100 MeV is developed. This model is a combination of new version of the two-component exciton model and a time-dependent statistical model for fusion-fission process with inclusion of dynamical effects for accurate calculations of nucleon composition and excitation energy of the fissioning nucleus a...
Effect of α-damage on fission-track annealing in zircon
Kasuya, Masao; Naeser, Charles W.
1988-01-01
The thermal stability of confined fission-track lengths in four zircon samples having different spontaneous track densities (i.e., different amounts of ??-damage) has been studied by one-hour isochronal annealing experiments. The thermal stability of spontaneous track lengths is independent of initial spontaneous track density. The thermal stability of induced track lengths in pre-annealed zircon, however, is significantly higher than that of spontaneous track lengths. The results indicate that the presence of ??-damage lowers the thermal stability of fission-tracks in zircon.
Predetonation probability of a fission-bomb core
Reed, B. Cameron
2010-08-01
An undergraduate-level derivation of the probability that a uranium or plutonium fission bomb will suffer an uncontrolled predetonation due to neutrons liberated in spontaneous fissions in the fissile material is developed. Consistent with what was learned by Los Alamos bomb designers during World War II, it is shown why uncontrolled predetonation was not a problem for a U-235 bomb of the Little Boy "gun" design but necessitated development of implosion engineering for the Pu-239 Trinity and Fat Man bombs where the cores were contaminated with highly spontaneously fissile Pu-240.
Clusters in true ternary fission in the 252Cf (Sf) reaction
International Nuclear Information System (INIS)
In the paper effect of the formation of clusters on production of the true ternary fission at simultaneous fission of 2'52Cf is investigated. Unlike conventional ternary fission with the emission of the alpha particle and binary fission, in true ternary fission reaction products are observed with the comparable masses and charges. By studying the potential energy surface calculated for the ternary system before splitting, charge and mass distributions of the nascent products at the spontaneous fission of 252Cf are estimated. Probabilities of the true ternary fission products will be greater where the potential energy surface has minima deeper. Results showed that the products of true ternary fission with magical numbers 20, 28, 50 and 82 for protons and neutrons are formed with a high probability. (authors)
Review of measurements of the average number of prompt fission neutrons
International Nuclear Information System (INIS)
The report summarises in tables and graphs data from measurements of the average number of prompt neutrons for spontaneous and neutron-induced fission carried out after 1972 and analyses some material contained in 116 references
Cross correlation method application to prompt fission neutron investigation
Zeynalova, O. V.; Zeynalov, Sh.; Nazarenko, M. A.; Hambsch, F.-J.; Oberstedt, S.
2012-10-01
Do The prompt neutron emission in spontaneous fission of 252Cf has been investigated applying cross correlation method and digital signal processing algorithms. A new mathematical approach for neutron/gamma pulse shape separation was developed and implemented for prompt fission neutron (PFN) time-of-flight measurement. The main goal was development of automated data analysis algorithms and procedures for data analysis with minimum human intervention. Experimental data was taken with a twin Frisch-grid ionization chamber and a NE213-equivalent neutron detector in an experimental setup similar to well work of C. Budtz-Jorgensen and H.-H. Knitter [1]. About 2*107 fission events were registered with 2*105 neutron/gamma detection in coincidence with fission fragments. Fission fragment kinetic energy, mass and angular distribution, neutron time-of-flight and pulse shape have been investigated using a 12 bit waveform digitizer.
Applications of Event-by-Event Fission Modeling with FREYA
Directory of Open Access Journals (Sweden)
Vogt R.
2012-02-01
Full Text Available The recently developed code FREYA (Fission Reaction Event Yield Algorithm generates large samples of complete fission events, consisting of two receding product nuclei as well as a number of neutrons and photons, all with complete kinematic information. Thus it is possible to calculate arbitrary correlation observables whose behavior may provide unique insight into the fission process. We first discuss the present status of FREYA, which has now been extended to include spontaneous fission. Concentrating on 239Pu(nth,f, 240Pu(sf and 252Cf(sf, we discuss the neutron multiplicity correlations, the dependence of the neutron energy spectrum on the neutron multiplicity, and the relationship between the fragment kinetic energy and the number of neutrons and their energies. We also suggest novel fission observables that could be measured with modern detectors.
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
Dating by fission track method: study of neutron dosimetry with natural uranium thin films
International Nuclear Information System (INIS)
Fission track dating is described, focalizing the problem of the decay constant for spontaneous fission of 238 U and the use of neutron dosimetry in fission track analysis. Experimental procedures using thin films of natural uranium as neutron dosimeters and its results are presented. The author shows a intercomparison between different thin films and between the dosimetry with thin film and other dosimetries. (M.V.M.). 52 refs, 12 figs, 9 tabs
International Nuclear Information System (INIS)
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
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...
Late Time Emission of Prompt Fission Gamma Rays
Talou, P; Stetcu, I; Lestone, J P; McKigney, E; Chadwick, M B
2016-01-01
The emission of prompt fission $\\gamma$ rays within a few nanoseconds to a few microseconds following the scission point is studied in the Hauser-Feshbach formalism applied to the deexcitation of primary excited fission fragments. Neutron and $\\gamma$-ray evaporations from fully accelerated fission fragments are calculated in competition at each stage of the decay, and the role of isomers in the fission products, before $\\beta$-decay, is analyzed. The time evolution of the average total $\\gamma$-ray energy, average total $\\gamma$-ray multiplicity, and fragment-specific $\\gamma$-ray spectra, is presented in the case of neutron-induced fission reactions of $^{235}$U and $^{239}$Pu, as well as spontaneous fission of $^{252}$Cf. The production of specific isomeric states is calculated and compared to available experimental data. About 7% of all prompt fission $\\gamma$ rays are predicted to be emitted between 10 nsec and 5 $\\mu$sec following fission, in the case of $^{235}$U and $^{239}$Pu $(n_{\\rm th},f)$ reactio...
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)
International Nuclear Information System (INIS)
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)
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)
New insights into neutron rich nuclei from fission
International Nuclear Information System (INIS)
Neutron-rich nuclei populated in spontaneous fission are providing new tests for microscopic models. The neutron-rich 104-108Mo, 108-114Ru and 112-116Pd exhibit a variety of rapidly changing collective band structures to high spins. The first evidence for chiral band doublets in any even-even nucleus are reported
Numbers of prompt neutrons per fission for U233, U235, Pu239, and Cf252
International Nuclear Information System (INIS)
An absolute measurement of #-v#, the average number of prompt neutrons emitted per fission, is being made for the spontaneous fission of Cf262. The relative values of #-v# are being measured for neutron-induced fission of U233, U235, and Pu239, and are being compared with the spontaneous fission #-v# of Cf252. Neutrons with energies between thermal and 15 MeV are used. Particular emphasis is put on studying the dependence of #-v# on the incident neutron energy. A fission counter containing the appropriate isotope is placed in the centre of a large cadmium-loade d liquid scintillator. Through the fissionable isotope is passed a collimated beam of neutrons. Fission events, identified by pulses from the fission counter, open an electronic gate between the large liquid scintillator and a scaler. Scintillator pulses due to capture in the scintillating solution of thermalized fission neutrons are counted during the gate. The fission neutrons are detected almost independently of energy and with very high efficiency. With this technique values of #-v# to an accuracy of 1 % are expected. (author)
International Nuclear Information System (INIS)
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.
Double treeing phenomenon of fission fragment tracks in plastic detectors
International Nuclear Information System (INIS)
Several possible theories that explain the formation of double tree observed while detecting 235U fission fragments in plastic detectors have been presented. Two likely explanations have been given: First, 235U fission and the emission of long range alpha 8Be particles, and the second is the spontaneous emission of 4.4 MeV alpha particles from 235U. The assumption backed with appropriate range calculations in Lexan. three less likely causes of the double tree phenomenon are : the recoil of the detector atoms as a result of the collision with fission fragments, the fission fragments themselves being reflected off the stainless-steel sample holder, and some mechanical and physical defects in the detectors at the production or utilization stage. We have made some suggestions related to experimental design that might prove these theories. (Author)
Spontaneous curvature of phosphatidic acid and lysophosphatidic acid.
Kooijman, Edgar E; Chupin, Vladimir; Fuller, Nola L; Kozlov, Michael M; de Kruijff, Ben; Burger, Koert N J; Rand, Peter R
2005-02-15
The formation of phosphatidic acid (PA) from lysophosphatidic acid (LPA), diacylglycerol, or phosphatidylcholine plays a key role in the regulation of intracellular membrane fission events, but the underlying molecular mechanism has not been resolved. A likely possibility is that PA affects local membrane curvature facilitating membrane bending and fission. To examine this possibility, we determined the spontaneous radius of curvature (R(0p)) of PA and LPA, carrying oleoyl fatty acids, using well-established X-ray diffraction methods. We found that, under physiological conditions of pH and salt concentration (pH 7.0, 150 mM NaCl), the R(0p) values of PA and LPA were -46 A and +20 A, respectively. Thus PA has considerable negative spontaneous curvature while LPA has the most positive spontaneous curvature of any membrane lipid measured to date. The further addition of Ca(2+) did not significantly affect lipid spontaneous curvature; however, omitting NaCl from the hydration buffer greatly reduced the spontaneous curvature of PA, turning it into a cylindrically shaped lipid molecule (R(0p) of -1.3 x 10(2) A). Our quantitative data on the spontaneous radius of curvature of PA and LPA at a physiological pH and salt concentration will be instrumental in developing future models of biomembrane fission. PMID:15697235
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
Thermal annealing effect on fission fragment track recording properties of polycarbonate
International Nuclear Information System (INIS)
Polycarbonate Track Detector is a commonly used Solid State Nuclear Track Detector (SSNTD) to identify the fission fragment. The phenomenon of spontaneous fission was discussed in papers. The most useful polycarbonate track detector Makrofol-N for recording fission tracks was used. This detector is insensitive to detect the light particles background such as alpha particle, proton etc. The present paper deals with the study of thermal annealing and the mass distribution of 252Cf fission fragments using unannealed and annealed Makrofol-N detectors
A New Method of Prompt Fission Neutron Energy Spectrum Unfolding
Zeynalova, O. V.; Zeynalov, Sh.; Hambsch, F.-J.; Oberstedt, S.
2010-11-01
The prompt neutron emission in spontaneous fission of 252Cf has been investigated applying digital signal electronics along with associated digital signal processing algorithms. The goal was to find out the reasons of a long time existing discrepancy between theoretical calculations and the measurements of prompt fission neutron (PFN) emission dependence on the total kinetic energy (TKE) of fission fragments (FF). On the one hand the 252Cf (sf) reaction is one of the main references for nuclear data, on the other hand the understanding of PFN emission mechanism is very important for nuclear fission theory. Using a twin Frisch-grid ionization chamber for fission fragment (FF) detection and a NE213-equivalent neutron detector in total about 107 fission fragment-neutron coincidences have been registered. Fission fragment kinetic energy, mass and angular distribution, neutron time-of-flight and pulse shape have been investigated using a 12 bit waveform digitizer. The signal waveforms have been analyzed using digital signal processing algorithms. For the first time the dependence of the number of emitted neutrons as a function of total kinetic energy (TKE) of the fragments is in very good agreement with theoretical calculations in the range of TKE from 140-220 MeV.
Prompt fission neutron spectra and average prompt neutron multiplicities
International Nuclear Information System (INIS)
We present a new method for calculating the prompt fission neutron spectrum N(E) and average prompt neutron multiplicity anti nu/sub p/ as functions of the fissioning nucleus and its excitation energy. The method is based on standard nuclear evaporation theory and takes into account (1) the motion of the fission fragments, (2) the distribution of fission-fragment residual nuclear temperature, (3) the energy dependence of the cross section sigma/sub c/ for the inverse process of compound-nucleus formation, and (4) the possibility of multiple-chance fission. We use a triangular distribution in residual nuclear temperature based on the Fermi-gas model. This leads to closed expressions for N(E) and anti nu/sub p/ when sigma/sub c/ is assumed constant and readily computed quadratures when the energy dependence of sigma/sub c/ is determined from an optical model. Neutron spectra and average multiplicities calculated with an energy-dependent cross section agree well with experimental data for the neutron-induced fission of 235U and the spontaneous fission of 252Cf. For the latter case, there are some significant inconsistencies between the experimental spectra that need to be resolved. 29 references
Compilation of fission product yields Vallecitos Nuclear Center
International Nuclear Information System (INIS)
This document is the ninth in a series of compilations of fission yield data made at Vallecitos Nuclear Center in which fission yield measurements reported in the open literature and calculated charge distributions have been utilized to produce a recommended set of yields for the known fission products. The original data with reference sources, as well as the recommended yields are presented in tabular form for the fissionable nuclides U-235, Pu-239, Pu-241, and U-233 at thermal neutron energies; for U-235, U-238, Pu-239, and Th-232 at fission spectrum energies; and U-235 and U-238 at 14 MeV. In addition, U-233, U-236, Pu-240, Pu-241, Pu-242, Np-237 at fission spectrum energies; U-233, Pu-239, Th-232 at 14 MeV and Cf-252 spontaneous fission are similarly treated. For 1979 U234F, U237F, Pu249H, U234He, U236He, Pu238F, Am241F, Am243F, Np238F, and Cm242F yields were evaluated. In 1980, Th227T, Th229T, Pa231F, Am241T, Am241H, Am242Mt, Cm245T, Cf249T, Cf251T, and Es254T are also evaluated
Nuclear fission: What have we learned in 50 years?
International Nuclear Information System (INIS)
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 Fragments Discriminator
International Nuclear Information System (INIS)
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
Fission fragment rocket concept
International Nuclear Information System (INIS)
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.)
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
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
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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
Nuclear charge distribution in the spontaneous fission of 252Cf
Wang, Taofeng; Zhu, Liping; WANG, LIMING; Men, Qinghua; Han, Hongyin; Xia, Haihong
2015-01-01
The measurement for charge distributions of fragments in 252Cf has been performed by using a unique style of detector setup consisting of a typical grid ionization chamber and a dE-E particle telescope. We found that the fragment mass dependency of the average width of the charge distribution shows a systematic decreased trend with the obvious odd-even effect. The variation of widths of charge distribution with kinetic energies shows an approximate V-shape curve due to the large number of neu...
Angular momenta of near-spherical fission fragments
International Nuclear Information System (INIS)
Angular momenta of fission fragments are sometimes exceeding 10 ℏ for thermal neutron induced and spontaneous fission. This is surprising since in the latter case the mother nucleus may have zero spin (e.g. 252Cf). In theory fragment spins are explained as a quantum mechanical effect. It is argued that they are due to zero-point oscillations of fragments being deformed at scission. In contrast to current theory it is shown that, for the specific case of near-magic 132Te, a large spin is generated by thermal excitation of single-particle states. (author)
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.
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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
Testing actinide fission yield treatment in CINDER90 for use in MCNP6 burnup calculations
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Most of the development of the MCNPX/6 burnup capability focused on features that were applied to the Boltzman transport or used to prepare coefficients for use in CINDER90, with little change to CINDER90 or the CINDER90 data. Though a scheme exists for best solving the coupled Boltzman and Bateman equations, the most significant approximation is that the employed nuclear data are correct and complete. Thus, the CINDER90 library file contains 60 different actinide fission yields encompassing 36 fissionable actinides (thermal, fast, high energy and spontaneous fission). Fission reaction data exists for more than 60 actinides and as a result, fission yield data must be approximated for actinides that do not possess fission yield information. Several types of approximations are used for estimating fission yields for actinides which do not possess explicit fission yield data. The objective of this study is to test whether or not certain approximations of fission yield selection have any impact on predictability of major actinides and fission products. Further we assess which other fission products, available in MCNP6 Tier 3, result in the largest difference in production. Because the CINDER90 library file is in ASCII format and therefore easily amendable, we assess reasons for choosing, as well as compare actinide and major fission product prediction for the H. B. Robinson benchmark for, three separate fission yield selection methods: (1) the current CINDER90 library file method (Base); (2) the element method (Element); and (3) the isobar method (Isobar). Results show that the three methods tested result in similar prediction of major actinides, Tc-99 and Cs-137; however, certain fission products resulted in significantly different production depending on the method of choice
Fragment-mass distributions in fission of heavy nuclei by intermediate and high-energy probes
Energy Technology Data Exchange (ETDEWEB)
Deppman, Airton; Andrade-II, E. [Universidade de Sao Paulo (IF/USP), SP (Brazil). Inst. de Fisica; Menezes, J.C.M.; Garcia, F. [Universidade Estadual de Santa Cruz (UESC), Ilheus, BA (Brazil); Duarte, S.B.; Tavares, O.A.P. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); Rossi, P.C.R. [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)
2011-07-01
Full text: Recent experiments have shown that the multimode approach for describing the fission process leads to some compatibility with the observed results. A systematic analysis of the parameters obtained by fitting the fission-fragment mass distribution to the spontaneous and low-energy data has shown that the values for those parameters present a smooth dependence upon the nuclear mass number. In the present work it is shown that the same parameter-values obtained for low- energy fission can be used to describe high-energy fission results of fragment-mass distributions if one takes into account the appropriate distribution of the fissioning system. To calculate the fission-fragment mass distributions, Monte Carlo simulations are used. This simulation considers a two-step reaction mechanism, namely, an intranuclear cascade providing the compound nucleus followed by a mechanism of competition between particle evaporation and fission. The fission-fragment masses are obtained according to the multimode approach following the Statistical Scission Model. Simulations for fission induced by 660 MeV protons on 241Am and 237Np, and for fission of 238U induced by photons from Bremsstrahlung with end-point energies of 50 MeV and 3500 MeV have been performed, and the results have been compared with recent experimental data. (author)
Contributions to the theory of fission neutron emission
International Nuclear Information System (INIS)
This report gives a compilation of recent work performed at Technical University, Dresden by D. Seeliger, H. Maerten and A. Ruben on the topic of fission neutron emission. In the first paper calculated fission neutron spectra are presented using the temperature distribution model FINESSE for fissioning actinide nuclei. In the second paper, starting from a general energy balance, Terrell's approach is generalized to describe average fragment energies as a function of incident energy; trends of fragment energy data in the Th-Pu region are well reproduced. In the third contribution, prompt fission neutron spectra and fragment characteristics for spontaneous fission of even Pu-isotopes are presented and discussed in comparison with experimental data using a phenomenological scission point model including temperature dependent shell effects. In the fourth paper, neutron multiplicities and energy spectra as well as average fragment energies for incident energies from threshold to 20 MeV (including multiple-chance fission) for U-238 are compared with traditional data representations. (author). Refs, figs and tabs
Neutron-induced fission: properties of prompt neutron and γ rays as a function of incident energy
Stetcu, I.; Talou, P.; Kawano, T.
2016-06-01
We have applied the Hauser-Feshbach statistical theory, in a Monte-Carlo implementation, to the de-excitation of fission fragments, obtaining a reasonable description of the characteristics of neutrons and gamma rays emitted before beta decays toward stability. Originally implemented for the spontaneous fission of 252Cf and the neutroninduced fission of 235U and 239Pu at thermal neutron energy, in this contribution we discuss the extension of the formalism to incident neutron energies up to 20 MeV. For the emission of pre-fission neutrons, at incident energies beyond second-chance fission, we take into account both the pre-equilibrium and statistical pre-fission components. Phenomenological parameterizations of mass, charge and TKE yields are used to obtain the initial conditions for the fission fragments that subsequently decay via neutron and emissions. We illustrate this approach for 239Pu(n,f).
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
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)
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...
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
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...
Evaluation and compilation of fission product yields 1993
International Nuclear Information System (INIS)
This document is the latest in a series of compilations of fission yield data. Fission yield measurements reported in the open literature and calculated charge distributions have been used to produce a recommended set of yields for the fission products. The original data with reference sources, and the recommended yields axe presented in tabular form. These include many nuclides which fission by neutrons at several energies. These energies include thermal energies (T), fission spectrum energies (F), 14 meV High Energy (H or HE), and spontaneous fission (S), in six sets of ten each. Set A includes U235T, U235F, U235HE, U238F, U238HE, Pu239T, Pu239F, Pu241T, U233T, Th232F. Set B includes U233F, U233HE, U236F, Pu239H, Pu240F, Pu241F, Pu242F, Th232H, Np237F, Cf252S. Set C includes U234F, U237F, Pu240H, U234HE, U236HE, Pu238F, Am241F, Am243F, Np238F, Cm242F. Set D includes Th227T, Th229T, Pa231F, Am241T, Am241H, Am242MT, Cm245T, Cf249T, Cf251T, Es254T. Set E includes Cf250S, Cm244S, Cm248S, Es253S, Fm254S, Fm255T, Fm256S, Np237H, U232T, U238S. Set F includes Cm243T, Cm246S, Cm243F, Cm244F, Cm246F, Cm248F, Pu242H, Np237T, Pu240T, and Pu242T to complete fission product yield evaluations for 60 fissioning systems in all. This report also serves as the primary documentation for the second evaluation of yields in ENDF/B-VI released in 1993
Evaluation and compilation of fission product yields 1993
Energy Technology Data Exchange (ETDEWEB)
England, T.R.; Rider, B.F.
1995-12-31
This document is the latest in a series of compilations of fission yield data. Fission yield measurements reported in the open literature and calculated charge distributions have been used to produce a recommended set of yields for the fission products. The original data with reference sources, and the recommended yields axe presented in tabular form. These include many nuclides which fission by neutrons at several energies. These energies include thermal energies (T), fission spectrum energies (F), 14 meV High Energy (H or HE), and spontaneous fission (S), in six sets of ten each. Set A includes U235T, U235F, U235HE, U238F, U238HE, Pu239T, Pu239F, Pu241T, U233T, Th232F. Set B includes U233F, U233HE, U236F, Pu239H, Pu240F, Pu241F, Pu242F, Th232H, Np237F, Cf252S. Set C includes U234F, U237F, Pu240H, U234HE, U236HE, Pu238F, Am241F, Am243F, Np238F, Cm242F. Set D includes Th227T, Th229T, Pa231F, Am241T, Am241H, Am242MT, Cm245T, Cf249T, Cf251T, Es254T. Set E includes Cf250S, Cm244S, Cm248S, Es253S, Fm254S, Fm255T, Fm256S, Np237H, U232T, U238S. Set F includes Cm243T, Cm246S, Cm243F, Cm244F, Cm246F, Cm248F, Pu242H, Np237T, Pu240T, and Pu242T to complete fission product yield evaluations for 60 fissioning systems in all. This report also serves as the primary documentation for the second evaluation of yields in ENDF/B-VI released in 1993.
A Monte Carlo Simulation of Prompt Gamma Emission from Fission Fragments
Litaize O.; Regnier D.; Serot O.
2013-01-01
The prompt fission gamma spectra and multiplicities are investigated through the Monte Carlo code FIFRELIN which is developed at the Cadarache CEA research center. Knowing the fully accelerated fragment properties, their de-excitation is simulated through a cascade of neutron, gamma and/or electron emissions. This paper presents the recent developments in the FIFRELIN code and the results obtained on the spontaneous fission of 252Cf. Concerning the decay cascades simulation, a fully Hauser-Fe...
Fission prompt γ-ray multiplicity distribution measurements and simulations at DANCE
International Nuclear Information System (INIS)
The nearly energy independence of the DANCE efficiency and multiplicity response to γ rays makes it possible to measure the prompt γ-ray multiplicity distribution in fission. We demonstrate this unique capability of DANCE through the comparison of γ-ray energy and multiplicity distribution between the measurement and numerical simulation for three radioactive sources 22Na, 60Co, and 88Y. The prospect for measuring the γ-ray multiplicity distribution for both spontaneous and neutron-induced fission is discussed.
UF6 as a detector gas for fission studies
International Nuclear Information System (INIS)
A Frisch-grid ionization chamber has been built to test a mixture of argon with gaseous UF6 and to study its properties as a counting gas. We present first results using increasing mass fractions of 238UF6 mixed into argon. The drift velocity of the electrons increases with the content of 238UF6, while a good signal quality and energy resolution of the ionization chamber is preserved. Using uranium hexafluoride in the detector gas may give access to experiments where extremely high luminosity is required in combination with good angular and energy and/or mass resolution. Examples comprise the investigation of spontaneous fission of 238U, the study of parity non-conservation in the fission process, or precision measurements of fission fragments with good resolution using tagged photons in the entrance channel.
Status of measurements of fission neutron spectra of Minor Actinides
Energy Technology Data Exchange (ETDEWEB)
Drapchinsky, L.; Shiryaev, B. [V.G. Khlopin Radium Inst., Saint Petersburg (Russian Federation)
1997-03-01
The report considers experimental and theoretical works on studying the energy spectra of prompt neutrons emitted in spontaneous fission and neutron induced fission of Minor Actinides. It is noted that neutron spectra investigations were done for only a small number of such nuclei, most measurements, except those of Cf-252, having been carried out long ago by obsolete methods and imperfectapparatus. The works have no detailed description of experiments, analysis of errors, detailed numerical information about results of experiments. A conclusion is made that the available data do not come up to modern requirements. It is necessary to make new measurements of fission prompt neutron spectra of transuranium nuclides important for the objectives of working out a conception of minor actinides transmutation by means of special reactors. (author)
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)
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
Neutron Capture and Fission Measurement on ^238Pu at DANCE
Chyzh, Andrii; Wu, Ching-Yen; Kwan, Elaine; Henderson, Roger; Gostic, Jolie; Couture, Aaron; Young, Hye; Ullmann, John; O'Donnell, John; Jandel, Marian; Haight, Robert; Bredeweg, Todd
2012-10-01
Neutron capture and fission reactions on actinides are important in nuclear engineering and physics. DANCE (Detector for Advanced Neutron Capture Measurement, LANL) combined with PPAC (avalanche technique based fission tagging detector, LLNL) were used to study the neutron capture reactions in ^238Pu. Because of extreme spontaneous α-radioactivity in ^238Pu and associated safety issues, 3 separate experiments were performed in 2010-2012. The 1st measurement was done without fission tagging on a 396-μg thick target. The 2nd one was with PPAC on the same target. The 3rd final measurement was done on a thin target with a mass of 40 μg in order to reduce α-background load on PPAC. This was the first such measurement in a laboratory environment. The absolute ^238Pu(n,γ) cross section is presented together with the prompt γ-ray multiplicity in the ^238Pu(n,f) reaction.
Fission approach to heavy particle radioactivities
International Nuclear Information System (INIS)
Since 1980, as reported in our paper published with A. Sandulescu, we employed two kinds of approaches in order to predict new nuclear decay modes by spontaneous emission of heavy ions intermediate between alpha-particle and fission fragments. Either fission theories were extended to the extremely large mass asymmetries, or alpha-like theories were applied to heavier particles. Particularly useful at that moment, and in the next years, was the analytical superasymmetric fission (ASAF) model with which we could produce comprehensive tables to guide the experiments. In this workshop we shall present some important results obtained within fission approach and compare with experimental data. The first confirmation came from Oxford University in 1984, when Rose and Jones reported the successful experiment on 14 C radioactivity of 223 Ra. This experiment was performed by using standard electronics methods to identify with a Si ΔE-E telescope the 14 C particles. Only eleven events were obtained in a run of about 6 months. The main experimental difficulty comes from the strong competition of α-decay. An elegant method was used later by Hourany and Hussonnois in Orsay and by Henning and Kutschera in Argonne in order to get rid of these unwanted alpha particles; they were deviated by the magnetic field of SOLENO and Enge split pole magnetic spectrometers, respectively. In this way a stronger source of 223 Ra could be used and in 5 days the same number of events could be observed. The solid state track detectors (plastic foils or glasses) which are not sensitive to α-particles were employed by experimentalist groups like that of Price at Berkeley, Tretyakova and Ogloblin in Dubna and Moscow, Bonetti and Guglielmetti in Milan, Qiangyan Pan in Beijing, etc. (authors)
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.
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.
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
Spontaneous actin dynamics in contractile rings
Kruse, Karsten; Wollrab, Viktoria; Thiagarajan, Raghavan; Wald, Anne; Riveline, Daniel
Networks of polymerizing actin filaments are known to be capable to self-organize into a variety of structures. For example, spontaneous actin polymerization waves have been observed in living cells in a number of circumstances, notably, in crawling neutrophils and slime molds. During later stages of cell division, they can also spontaneously form a contractile ring that will eventually cleave the cell into two daughter cells. We present a framework for describing networks of polymerizing actin filaments, where assembly is regulated by various proteins. It can also include the effects of molecular motors. We show that the molecular processes driven by these proteins can generate various structures that have been observed in contractile rings of fission yeast and mammalian cells. We discuss a possible functional role of each of these patterns. The work was supported by Agence Nationale de la Recherche, France, (ANR-10-LABX-0030-INRT) and by Deutsche Forschungsgemeinschaft through SFB1027.
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)
Fission fragment properties and the problem of the pulse height defect
International Nuclear Information System (INIS)
The pulse height defect (PHD) has been investigated for three different counting gases commonly used in ionization chambers. The PHD introduces an underestimation of the kinetic energy of a charged particle detected with an ionization chamber. Thus, in some cases it is of crucial importance to correct for this effect, e.g. when studying fission fragment properties. A new method was used, applying a waveform digitizer, to study the PHD. The fission fragment properties from spontaneous fission of 252Cf where determined using different counting gases and different ways of correcting for the PHD were evaluated. (author)
Characteristics of prompt fission gamma-ray emission - Experimental results and predictions
International Nuclear Information System (INIS)
Systematics from 2001, describing prompt fission gamma-ray spectra (PFGS) characteristics as function of mass and atomic number of the fissioning system, has been revisited and parameters have been revised based on recent experimental results. Although originally expressed for spontaneous and thermal neutron-induced fission, validity for fast neutrons was assumed and applied to predict PFGS characteristics for the reaction n + 238U up to incident neutron energies of En = 20 MeV. The results from this work are in good agreement with corresponding results from both model calculations and experiments. (authors)
Empirical description of beta-delayed fission partial half-lives
Ghys, Lars; Andreyev, A.N.; Antalic, S; Huyse, Mark; Van Duppen, Piet
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 de...
Advanced model for the prediction of the neutron-rich fission product yields
Directory of Open Access Journals (Sweden)
Rubchenya V. A.
2013-12-01
Full Text Available The consistent models for the description of the independent fission product formation cross sections in the spontaneous fission and in the neutron and proton induced fission at the energies up to 100 MeV is developed. This model is a combination of new version of the two-component exciton model and a time-dependent statistical model for fusion-fission process with inclusion of dynamical effects for accurate calculations of nucleon composition and excitation energy of the fissioning nucleus at the scission point. For each member of the compound nucleus ensemble at the scission point, the primary fission fragment characteristics: kinetic and excitation energies and their yields are calculated using the scission-point fission model with inclusion of the nuclear shell and pairing effects, and multimodal approach. The charge distribution of the primary fragment isobaric chains was considered as a result of the frozen quantal fluctuations of the isovector nuclear matter density at the scission point with the finite neck radius. Model parameters were obtained from the comparison of the predicted independent product fission yields with the experimental results and with the neutron-rich fission product data measured with a Penning trap at the Accelerator Laboratory of the University of Jyväskylä (JYFLTRAP.
Beta-delayed fission probabilities of transfermium nuclei, involved in the r-process
Panov, I.; Lutostansky, Yu; Thielemann, F.-K.
2016-01-01
For the nucleosynthesis of heavy and superheavy nuclei fission becomes very important when the r-process runs in a very high neutron density environment. In part, fission is responsible for the formation of heavy nuclei due to the inclusion of fission products as new seed nuclei (fission cycling). More than that, beta-delayed fission, along with spontaneous fission, is responsible in the late stages of the r-process for the suppression of superheavy element yields. For beta-delayed fission probability calculations a model description of the beta-strength- functions is required. Extended theoretical predictions for astro-physical applications were provided long ago, and new predictions also for superheavy nuclei with uptodate nuclear input are needed. For the further extension of data to heavier transactinides the models of strength- functions should be modified, taking into account more complicated level schemes. In our present calculations the strength-function model is based on the quasi-particle approximation of Finite Fermi Systems Theory. The probabilities of beta-delayed fission and beta-delayed neutron emission are calculated for some transfermium neutron-rich nuclei, and the influence of beta-delayed fission upon superheavy element formation is discussed.
Library of prompt neutron and γ-emission spectra from fission fragments
International Nuclear Information System (INIS)
The statistical model of nuclear reactions is applied to describe the fission fragment neutron and gamma emission characteristics for spontaneous fission of 252Cf and for fission of 233,235U, 239Pu by thermal neutrons. The calculations of neutron and gamma-spectra are carried out for the fragments with A=70-160, excited up to 100 MeV. After testing of the model and input data library, calculations of neutron and γ-emission spectra for nuclei with A=70-170 excited up to 100 MeV were done to produce the Fission Fragments Emission Spectra Library (FFESL). FFESL contains the data of 1000 nuclei and will be used in calculations of neutron and γ-spectra for fission of heavy nuclei by intermediate energy nucleons. (author)
International Nuclear Information System (INIS)
Nuclear fission allows us to produce and study the properties of the nuclei with a higher neutron to proton ratio. Spectroscopic studies of such neutron-rich fragment nuclei provide direct information on the nuclear excited states. Such studies help to explore the new regions of nuclear deformations, and to extend the theoretical model(s) to regions which have hitherto been inaccessible. A lot of work has already been done on these set of nuclei by means of spontaneous fission of 252Cf and 248Cm sources, heavy-ion induced fusion-fission reactions, and also using deep-inelastic reactions. More recently, spectroscopic studies were performed using thermal neutron induced fission of 235U using CIRUS reactor facility. Here we report the yield distribution of the isotopes, produced in thermal neutron induced fission of 235U, using prompt γ-γ coincidence measurement technique
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.
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.
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
Comparison of {sup 235}U fission cross sections in JENDL-3.3 and ENDF/B-VI
Energy Technology Data Exchange (ETDEWEB)
Kawano, Toshihiko [Kyushu Univ., Fukuoka (Japan); Carlson, Allan D. [National Institute of Standards and Technology (United States); Matsunobu, Hiroyuki [Data Engineering, Inc., Fujisawa, Kanagawa (Japan); Nakagawa, Tsuneo; Shibata, Keiichi [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment; Talou, Patrick; Young, Philip G.; Chadwick, Mark B. [Los Alamos National Laboratory, Los Alamos, NM (United States)
2002-01-01
Comparisons of evaluated fission cross sections for {sup 235}U in JENDL-3.3 and ENDF/B-VI are carried out. The comparisons are made for both the differential and integral data. The fission cross sections as well as the fission ratios are compared with the experimental data in detail. Spectrum averaged cross sections are calculated and compared with the measurements. The employed spectra are the {sup 235}U prompt fission neutron spectrum, the {sup 252}Cf spontaneous fission neutron spectrum, and the neutron spectrum produced by a {sup 9}Be(d, xn) reaction. For {sup 235}U prompt fission neutron spectrum, the ENDF/B-VI evaluation reproduces experimental averaged cross sections. For {sup 252}Cf and {sup 9}Be(d, xn) neutron spectra, the JENDL-3.3 evaluation gives better results than ENDF/B-VI. (author)
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
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.
International Nuclear Information System (INIS)
The SSNTD has come a long way in its application for the study of nuclear phenomena. Spontaneous fission of transuranic elements is one such phenomena wherein use of SSNTD offers easy registration of the signature of the fission fragments. The object of the present study is to explore whether any one of the track parameters such as the diameter can be used to estimate the atomic mass ratios of the spontaneous fission fragments. The spontaneous fission data from 252Cf recorded almost at the end of one and four half-life periods for alpha decay are analysed, taking a plot of the number of tracks versus the track diameter. From these plots it is seen that initially, when significant alpha activity of 252Cf persists, the fission fragments appear to cluster into two predominant groups as indicated by two peaks. The ratio of the diameters at these peak positions appear to be related to the ratio of average mass numbers of the light and heavy groups of fission fragments. However, absence of two peaks for similar plots at the end of about four half-life periods for alpha decay suggests that presumably the presence of alphas influence the mass distribution of the fission fragments
A Fission-Fusion Origin for Life
Norris, V.; Raine, D. J.
1998-10-01
To develop a comprehensive `cells-first' approach to the origin of life, we propose that protocells form spontaneously and that the fission and fusion of these protocells drives the dynamics of their evolution. The fitness criterion for this evolution is taken to be the the stability (conservation) of domains in the protocellular membrane as determined by non-covalent molecular associations between the amphiphiles of the membrane and a subset of the macromolecules in the protocell. In the presence of a source of free energy the macromolecular content of the protocell (co-)evolves as the result of (domain-dependent) membrane-catalysed polymerisation of the prebiotic constituents delivered to the protocell by fusion. The metabolism of the cell therefore (co-)evolves on a rugged fitness landscape. We indicate how domain evolution with the same fitness criterion can potentially give rise to coding. Membrane domains may therefore provide the link between protocells and the RNA/DNA-world.
International Nuclear Information System (INIS)
The study is aimed at concentration of yet nonidentified spontaneous fission nuclide (NSFN), discovered in geothermal brines of the Cheleken peninsula, when coprecipitation with inorganic collectors (metal hydroxides, ZnS, FeS, BaSO4; ionic exchange on organic and inorganic sorbents, as well as reduction by metals (Fe, Al) are used. The NSFN enrichment level turns out to be insufficient to identify its atomic number by physical methods. However, using the obtained data and measurement results of NSFN spontaneous fission activity in different concentrates, some of its chemical properties are studied. A certain analogy in chemical behaviour of NSFN and noble metals like Au and Hg is noted
Spontaneous intracranial hypotension.
LENUS (Irish Health Repository)
Fullam, L
2012-01-31
INTRODUCTION: Spontaneous\\/primary intracranial hypotension is characterised by orthostatic headache and is associated with characteristic magnetic resonance imaging findings. CASE REPORT: We present a case report of a patient with typical symptoms and classical radiological images. DISCUSSION: Spontaneous intracranial hypotension is an under-recognised cause of headache and can be diagnosed by history of typical orthostatic headache and findings on MRI brain.
Prompt neutron emission in nuclear fission
International Nuclear Information System (INIS)
Experimental results obtained in recent fragment-neutron correlation measurements are the basis for a detailed analysis of neutron emission characteristics in conjunction with several statistical-model approaches: (i) temperature distribution model (applied calculations), (ii) standard evaporation theory I (Weisskopf-Ewing approach extended by a rough angular momentum correction term), (iii) standard evaporation theory II (Hauser-Feshbach type calculations including angular momentum effects), (iv) statistical multistep compound theory (closed-form description including equilibrium as well as non-equilibrium emissions). All emission models account for an intricate fragment occurrence probability distribution in nucleon numbers, excitation energy, kinetic energy, and (except models (i) and (iv)) angular momentum. They have been used to predict yields, energy and angular distributions as well as representative c.m.s. spectrum shape parameters in the case of 252-Cf spontaneous fission in order to study the mechanisms of prompt fission neutron emission and several features of statistical emission. Model (iv) describes the development of the fragment compound system as a stochastic process starting at scission point and, hence, considering emission processes during fragment acceleration. The results of all model calculations indicate a clear predominance of the evaporation mechanism. The possible role of secondary mechanisms and difficulties in deducing information about them are discussed. The present paper gives a review on all four models. Results obtained within standard evaporation theory II (full-scale Hauser-Feshbach calculation) are discussed in more detail. (author). 27 refs, 4 figs
Pion-Induced Fission of 209Bi and 119Sn:. Measurements, Calculations, Analyses and Comparison
Rana, Mukhtar Ahmed; Sher, Gul; Manzoor, Shahid; Shehzad, M. I.
Cross-sections for the π--induced fission of 209Bi and 119Sn have been measured using the most sensitive CR-39 solid-state nuclear track detector. In experiments, target-detector stacks were exposed to negative pions of energy 500, 672, 1068, and 1665 MeV at the Brookhaven National Laboratory, USA. An important aspect of the present paper is the comparison of pion-induced fission fragment spectra of above mentioned nuclei with the spontaneous fission fragment spectra of 252Cf. This comparison is made in terms of fission fragment track lengths in the CR-39 detectors. Measurement results are compared with calculations of Monte Carlo and statistical weight functions methods using the computer code CEM95. Agreement between measurements and calculations is fairly good for 209Bi target nuclei whereas it is indigent for the case of 119Sn. The possibilities of the trustworthy calculations, using the computer code CEM95, comparable with measurements of pion-induced fission in intermediate and heavy nuclei are explored by employing various systematics available in the code. Energy dependence of pion-induced fission in 119Sn and 209Bi is analyzed employing a newly defined parameter geometric-size-normalized fission cross-section (χfg). It is found that the collective nuclear excitations, which may lead to fission, become more probable for both 209Bi and 119Sn nuclei with increasing energy of negative pions from 500 to 1665 MeV.
International Nuclear Information System (INIS)
An analysis of basicmechanisms of binary and ternary fission of nuclei led to the conclusion that true ternary and quaternary fission of nuclei has a sequential two-step (three-step) character, where, at the first step, a fissile nucleus emits a third light particle (third and fourth light particles) under shakeup effects associated with a nonadiabatic character of its collective deformation motion, whereupon the residual nucleus undergoes fission to two fission fragments. Owing to this, the formulas derived earlier for the widths with respect to sequential two- and three-step decays of nuclei in constructing the theory of two-step twoproton decays and multistep decays in chains of genetically related nuclei could be used to describe the relative yields and angular and energy distributions of third and fourth light particles emitted in (α, α), (t, t), and (α, t) pairs upon the true quaternary spontaneous fission of 252Cf and thermal-neutron-induced fission of 235U and 233U target nuclei. Mechanisms that explain a sharp decrease in the yield of particles appearing second in time and entering into the composition of light-particle pairs that originate from true quaternary fission of nuclei in relation to the yields of analogous particles in true ternary fission of nuclei are proposed
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.
Hidden systematics of fission channels
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Schmidt Karl-Heinz
2013-12-01
Full Text Available 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 the potential-energy landscape between the outer saddle and the scission configuration in the multi-channel fission model of Brosa. When the relative yields, the widths and the mean mass-asymmetry values of these components are fitted to experimental data, the mass distributions can be very well reproduced. Moreover, these fission channels are characterised by specific values of charge polarisation, total kinetic energy and prompt-neutron yields. The present contribution investigates the systematic variation of the characteristic fission-channel properties as a function of the composition and the excitation energy of the fissioning system. The mean position of the asymmetric fission channels in the heavy fragment is almost constant in atomic number. The deformation of the nascent fragments at scission, which is the main source of excitation energy of the separated fission fragments ending up in prompt-neutron emission, is found to be a unique function of Z for the light and the heavy fragment of the asymmetric fission channels. A variation of the initial excitation energy of the fissioning system above the fission saddle is only seen in the neutron yield of the heavy fragment. The charge polarisation in the two most important asymmetric fission channels is found to be constant and to appreciably exceed the macroscopic value. The variation of the relative yields and of the positions of the fission channels as a function of the composition and excitation energy
Fission yield measurements at IGISOL
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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.
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
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.
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.
International Nuclear Information System (INIS)
The spontaneous fission half-lives for heavy and superheavy nuclei between U and Hs isotopes are calculated in framework of the generalized liquid drop model by applying a new method of numerically solving Schrödinger equation compared with the semi-empirical WKB approximation. The calculated half-lives are in very good agreement with the experimental data, indicating the reliability of the new approach. The second part of this work is to estimate the fission half-lives of 238Np⁎ at excited state of 7.3 MeV and 239U⁎ at excited states of 7.081, 8.078, 8.387 and 8.989 MeV with the numerical method. The estimated results compared with the experimental values and with the results by WKB approximation show the numerical method is applicable to both the spontaneous fission and excited fission
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...
Fission-track dating using object-based image analysis
International Nuclear Information System (INIS)
Full text: Geological dating with the help of fission track analysis is based on a time-consuming counting of the spontaneous and induced tracks in the minerals. Fission tracks are damage trails in minerals caused by fast charged particles, released in nuclear fission. In this study the 950;-method is used for fission-track dating. In order to determine the age, spontaneous tracks in the apatite and induced tracks in the muscovite external detector have to be counted. The automatic extraction and identification would not only improve the speed of track counting and eliminate the personal factor. Pixel values alone are not enough to distinguish between tracks and background. Traditional pixel based approaches are therefore inefficient for fission track counting. Image analysis based on objects, which include shape, texture and contextual information is a more promising method. A procedure for automatic object - based classification is used to extract the track objects. Resolving the individual tracks in a multi-track object is based on morphological operations. The individual track objects are skeletonized and the number of individual tracks in the object is counted by processing the skeletons. To give the right fission track age, there has to be a calibration of every single user manually counting the tracks. We calibrate the automatic approach for counting in the same way. Durango apatite standard samples are used to determine the 950;- and Z-calibration factor. The automatic approach is useful for counting tracks in apatite standards and induced tracks in muscovite external detectors where the quality and quantities of the etched tracks is high. Muscovite detectors irradiated against glasses can also be used to determine the thermal neutron fluence, which is necessary to determine an absolute age. These images are of high quality and free of disturbing background irregularities. Here the automatic approach is a practical alternative. However for natural samples
Spontaneous Resolution of Massive Spontaneous Tubercular Pneumothorax
Surya Kant; Saheer, S.; Hassan, G; Jabeed Parengal
2012-01-01
A 29-year-old female presented with complaints of fever and productive cough of three weeks duration. Pulmonary tuberculosis was diagnosed bacteriologically and she was prescribed antituberculosis drugs. During follow-up she developed massive pneumothorax, for which patient refused surgical management and was managed conservatively. After six months there was complete spontaneous resolution of pneumothorax. The unusual presentation and unexpected outcome prompted us to report this case.
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.
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
Spontaneous pneumomediastinum in adolescents
Institute of Scientific and Technical Information of China (English)
SHEN Gang; CHAI Ying
2007-01-01
@@ Spontaneous pneumomediastinum (SPM),reported firstly by Hamman in 1939,is an uncommon,and usually benign,and self-limiting clinical disorder found in young people often without apparent precipitating factors or diseases.
International Nuclear Information System (INIS)
When the isotopic composition of nuclear materials to control is known, it is possible to determine the amount of plutonium by measuring the rate of spontaneous fissions. The induced fissions alter significantly the measures. Therefore we must evaluate the multiplicative factor. For a not very multiplicative sample, the observed neutron coincidences of multiplicity 0 to n agree with spontaneous emissions given by nuclear tables. This is not true in the opposite case (large amounts). Multiplicities are given by eighteen counting-scales associated with a shift-register coincidence system (SCRD) and compared with theoretical spontaneous emissions of the sample. A calculator leads all equipment and compares theoretical and experimental results about the controlled amount of Pu
Neutron emission in fission of 252Cf(sf)
Zeynalov, Sh.; Hambsch, F.-J.; Oberstedt, S.; Fabry, I.
2009-10-01
The prompt neutron emission in spontaneous fission of 252Cf has been investigated applying digital signal electronics. The goal was to compare the results of this digital data acquisition and digital signal processing analysis to the results of the pioneering work of Budtz-Jo/rgensen and Knitter. Using a twin Frisch-grid ionization chamber for fission fragment (FF) detection and a NE213 equivalent neutron detector in total about 10 neutron coincidences have been registered. Fission fragment kinetic energy, mass and angular distribution have been investigated using a 10 bit waveform digitizer. Neutron time- of- flight and pulse shape have been measured using analogue CAMAC modules, a 1 ns TDC and a pair of 12 bit charge-to-digital-converters. The fission fragment signals have been analyzed using digital signal processing algorithms. The results are in very good agreement with literature. For the first time the dependence of the number of neutrons as a function of total kinetic energy (TKE) of the fragments does not drop at low TKE.
Spontaneous Rupture of Pyometra
Fatemeh Mallah; Tahere Eftekhar; Mohammad Naghavi-Behzad
2013-01-01
Spontaneous perforation is a very rare complication of pyometra. The clinical findings of perforated pyometra are similar to perforation of the gastrointestinal tract and other causes of acute abdomen. In most cases, a correct and definite diagnosis can be made only by laparotomy. We report two cases of diffuse peritonitis caused by spontaneous perforated pyometra. The first case is a 78-year-old woman with abdominal pain for which laparotomy was performed because of suspected incarcerated he...
Measurement of the neutron-induced fission cross-section of 240,242Pu
International Nuclear Information System (INIS)
Fast spectrum neutron-induced fission cross-section data for transuranic isotopes are in high demand in the nuclear data community. In particular, highly accurate data are needed for the new Generation-IV nuclear applications. The aim is to obtain precise neutron-induced fission cross-sections for 240Pu and 242Pu. In this context accurate data on spontaneous fission half-lives have also been measured. To minimise the total uncertainty on the fission cross-sections the detector efficiency has been studied in detail. Both isotopes have been measured using a twin Frisch-grid ionisation chamber (TFGIC) due to its superiority compared to other detector systems in view of radiation hardness, 2 x 2π solid angle coverage and very good energy resolution. (authors)
International Nuclear Information System (INIS)
Certain applications require knowledge of the higher moments of the neutron multiplicity probability. It can be shown that the second factorial moment is proportional to the fission rate in the sample, and that the third factorial moment can be of use in disentangling spontaneous fission from induced fission. Using a source of unpublished work in which neutron multiplicities were derived for the fast neutron induced fission of U-235, U-238, and Pu-239, the multiplicity probability has been calculated as a function of neutron energy for the energy range 0 to 10 MeV
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.
V-bar in Neutron-Induced Fission of U235 and Th232, and in Photofission of U238
International Nuclear Information System (INIS)
The average number of prompt neutrons (v) emitted in the neutron-induced fission of U235 and Th232 and in the photofission of U238 has been measured with a large liquid scintillator as the fission neutron detector. The measurements were made relative to v for the spontaneous fission of Cf252. The v-values of U235 were measured at some different incident energies between 30 keV and 15 MeV, and the results are in agreement with measurements by Moat et al., and Hopkins and Diven. The measurements of Th232 were made for several incident neutron energies from the fission threshold at about 1.4 MeV to 15 MeV. Special interest was concentrated on the energy region near the fission threshold where the fission cross-section and the fragment angular distribution show strong variations with neutron energy. The measurements indicate that the energy dependence of b in this region may be non-linear. A measurement of v in the photofission of U238 at a gamma-ray energy of 7 MeV has been made. The result is not in agreement with measurements by Prokohorova et al. arid Lazareva et al. The spontaneous fission of Pu245 and the thermal-neutron-induced fission of Pu239 give a difference in v corresponding to 0.10 n/MeV. The result of the present investigation combined with the D-value for the spontaneous fission of U238 gives 0.10 ± 0.02 in agreement with the data obtained for the compound nucleus of Pu240. (author)
RAPID QUANTITATION OF URANIUM FROM MIXED FISSION PRODUCT SAMPLES
Energy Technology Data Exchange (ETDEWEB)
Haney, Morgan M.; Seiner, Brienne N.; Finn, Erin C.; Friese, Judah I.
2016-03-09
Chemical similarities between U(VI) and Mo(VI) create challenges for separation and quantification of uranium from a mixed fission product sample. The purpose of this work was to demonstrate the feasibility of using Eichrom’s® UTEVA resin in addition to a tellurium spontaneous deposition to improve the quantitation of 235U using gamma spectroscopy. The optimized method demonstrated a consistent chemical yield of 74 ± 3 % for uranium. This procedure was evaluated using 1.41x1012 fissions produced from an irradiated HEU sample. The uranium was isotopically yielded by HPGe, and the minimum detectable activity (MDA) determined from the gamma spectra. The MDA for 235U, 237U, and 238U was reduced by a factor of two. The chemical isolation of uranium was successfully achieved in less than four hours, with a separation factor of 1.41x105 from molybdenum.
Fission-neutrons source with fast neutron-emission timing
Rusev, G.; Baramsai, B.; Bond, E. M.; Jandel, M.
2016-05-01
A neutron source with fast timing has been built to help with detector-response measurements. The source is based on the neutron emission from the spontaneous fission of 252Cf. The time is provided by registering the fission fragments in a layer of a thin scintillation film with a signal rise time of 1 ns. The scintillation light output is measured by two silicon photomultipliers with rise time of 0.5 ns. Overall time resolution of the source is 0.3 ns. Design of the source and test measurements using it are described. An example application of the source for determining the neutron/gamma pulse-shape discrimination by a stilbene crystal is given.
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
Spontaneous pneumomediastinum in adult dermatomyositis.
Bradley, J D
1986-01-01
Spontaneous pneumomediastinum has not been reported in adult polymyositis or dermatomyositis, either in conjunction with spontaneous pneumothorax or in isolation. Spontaneous pneumothorax has been rarely reported as a complication of rheumatoid arthritis, systemic lupus erythematosus, scleroderma, and childhood dermatomyositis. It is associated with active, progressive pulmonary involvement and a poor prognosis. We describe an adult with dermatomyositis and spontaneous pneumomediastinum with ...
Directory of Open Access Journals (Sweden)
Blanc A.
2013-12-01
Full Text Available One way to explore exotic nuclei is to study their structure by performing γ-ray spectroscopy. At the ILL, we exploit a high neutron flux reactor to induce the cold fission of actinide targets. In this process, fission products that cannot be accessed using standard spontaneous fission sources are produced with a yield allowing their detailed study using high resolution γ-ray spectroscopy. This is what was pursued at the ILL with the EXILL (for EXOGAM at the ILL campaign. In the present work, the EXILL setup and performance will be presented.
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.
Fission-Neutron Spectra of U235, Pu239 And Cf252
International Nuclear Information System (INIS)
Measurements of the fission neutron spectra from the neutron-induced fission of U235 and Pu239, and the spontaneous fission of Cf252, have been made. The spectra were measured with a time-of-flight technique using a plastic scintillator as the fission-neutron detector. The low energy part of the Cf252 fission-neutron spectrum (below 0.3 MeV) was also measured with a Li6 -glass detector replacing the plastic scintillator. The fissile materials were mounted in xenon-gas scintillation cham-bers. The primary neutrons were produced by a 2.5-MeV Van de Graaff accelerator with top terminal pulsing. The resolving time of the time-of-flight equipment was better than 3 ns. Results fitted to Maxwellian distributions, √Ee-E/T, are presented for neutron-induced fissions of U235 at 40 keV and 1.5 MeV of incident neutron energy and for Pu239 at 40 keV. Results are also given for the fission-neutron energy spectrum of Cf252. (author)
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.)
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
The Emission of Long-Range Alpha Particles in Fission
International Nuclear Information System (INIS)
Fraenkel and Thompson (1964) have shown that the most probable direction of emission of the long-range alpha particles in the spontaneous fission of californium-252 varies with the ratio of the masses of the residual fission fragments. The angle of emission relative to the direction of motion of the lighter fragment increases significantly as the mass of the lighter fragment decreases. Assuming that the alpha particle is emitted at the scission point, these authors conclude that the scission point, in ternary fission, occurs progressively nearer to the lighter fragment as the fragment mass ratio is greater. They point out that this is one of the assumptions underlying the ''geometrical'' model of mass division of Whetstone (1959) and Vladimirski (1957), and is the feature of that model in terms of which the variation of the average number of neutrons with fragment mass in binary fission is successfully explained. They suggest that these various considerations together indicate that the configuration of the scissioning nucleus at (and before) scission in ternary fission closely resembles the corresponding configuration in binary fission. Adopting this last hypothesis in relation to the thermal-neutron-induced fission of uranium-235, the writer (1964) has shown that if the liberation cf the alpha particle occurs at or just after the moment of scission, so that it may be regarded as emitted from a newly formed, but still deformed, fragment then the probability of emission can be deduced from the experiments of Schmitt et al. (1962), if certain further assumptions are made. On the assumption that the alpha particle is derived from the heavy fragment exclusively, it appears that the prob-ability of release from that fragment correlates directly with the average number of secondary neutrons emitted in in binary fission, and also with the energy available for alpha-particle emission from the undeformed (ground state) fragment. There would be no correlation with the energy
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.
Multi-dimensional fission model with a complex absorbing potential
Scamps, Guillaume
2015-01-01
We study the dynamics of multi-dimensional quantum tunneling by introducing a complex absorbing potential to a two-dimensional model for spontaneous fission. We fist diagonalize the Hamiltonian with the complex potential to determine a resonance state as well as its life-time. We then solve the time-dependent Schr\\"odinger equation with such basis in order to investigate the tunneling path. We compare this method with the semi-classical method for multi-dimensional tunneling with imaginary time. A good agreement is found both for the life-time and for the tunneling path.
Obsidian ages from Ecuador by the fission track dating
International Nuclear Information System (INIS)
Fission track dating was applied in order to study obsidian samples originated from Mullumica and Callejones flows, Oyacachi, Ecuador. Preliminary data show that the ratio between the mean diameter os spontaneous and induced tracks is about 0.9, an indication that the analysed samples were submitted to small fading during their geological histories. Ages were obtained around 0.2 x 106a, in agreement with Miller and Wagners's results. Ages ranging from 0.17 x 106a up to 0.23 x 106a were obtained correcting the apparent ages by means of the plateau method. (author)
Case of spontaneous ventriculocisternostomy
Energy Technology Data Exchange (ETDEWEB)
Yamane, Kanji; Yoshimoto, Hisanori; Harada, Kiyoshi; Uozumi, Tohru (Hiroshima Univ. (Japan). School of Medicine); Kuwabara, Satoshi
1983-05-01
The authors experienced a case of spontaneous ventriculocisternostomy diagnosed by CT scan with metrizamide and Conray. Patient was 23-year-old male who had been in good health until one month before admission, when he began to have headache and tinnitus. He noticed bilateral visual acuity was decreased about one week before admission and vomiting appeared two days before admission. He was admitted to our hospital because of bilateral papilledema and remarkable hydrocephalus diagnosed by CT scan. On admission, no abnormal neurological signs except for bilateral papilledema were noted. Immediately, right ventricular drainage was performed. Pressure of the ventricle was over 300mmH/sub 2/O and CSF was clear. PVG and PEG disclosed an another cavity behind the third ventricle, which was communicated with the third ventricle, and occlusion of aqueduct of Sylvius. Metrizamide CT scan and Conray CT scan showed a communication between this cavity and quadrigeminal and supracerebellar cisterns. On these neuroradiological findings, the diagnosis of obstructive hydrocephalus due to benign aqueduct stenosis accompanied with spontaneous ventriculocisternostomy was obtained. Spontaneous ventriculocisternostomy was noticed to produce arrest of hydrocephalus, but with our case, spontaneous regression of such symptoms did not appeared. By surgical ventriculocisternostomy (method by Torkildsen, Dandy, or Scarff), arrest of hydrocephalus was seen in about 50 to 70 per cent, which was the same results as those of spontaneous ventriculocisternostomy. It is concluded that VP shunt or VA shunt is thought to be better treatment of obstructive hydrocephalus than the various kinds of surgical ventriculocisternostomy.
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...
Fissioning universe: Topological inflation and Kaluza-Klein cosmologies
Energy Technology Data Exchange (ETDEWEB)
Kaku, Michio; Lykken, J.
1986-05-05
We propose a Kaluza-Klein cosmology by reversing the usual scenario: instead of starting with a flat 4+N dimensional universe in which N of the dimensions curl up into a compact manifold, we start with a compact 3+N dimensional manifold in which 3 of the dimensions are allowed to peel off and expand into the known universe. We reverse the usual ''spontaneous compactification'' scenario begin with a closed manifold Msup(3+N) which undergoes ''spontaneous fissioning'' into a product manifold M/sup 3/xMsup(N). Remarkably, the 3-dimensional universe M/sup 3/ can undergo a rapid de Sitter expansion large enough to solve the horizon and flatness problem. We call this ''topological inflation'', which we propose as an alternative to the usual GUT inflation. The inflationary phase automatically terminates into a big bang phase. (orig.).
Spontaneous Perforation of Pyometra
Directory of Open Access Journals (Sweden)
Begüm Yildizhan
2006-01-01
Full Text Available Pyometra is the accumulation of purulent material in the uterine cavity. Its reported incidence is 0.01–0.5% in gynecologic patients; however, as far as elderly patients are concerned, its incidence is 13.6% [3]. The most common cause of pyometra is malignant diseases of genital tract and the consequences of their treatment (radiotherapy. Other causes are benign tumors like leiomyoma, endometrial polyps, senile cervicitis, cervical occlusion after surgery, puerperal infections, and congenital cervical anomalies. Spontaneous rupture of the uterus is an extremely rare complication of pyometra. To our knowledge, only 21 cases of spontaneous perforation of pyometra have been reported in English literature since 1980. This paper reports an additional case of spontaneous uterine rupture.
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)
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
Spontaneous regression of osteochondromas
Energy Technology Data Exchange (ETDEWEB)
Hoshi, Manabu; Takami, Masatsugu; Hashimoto, Ryouji; Okamoto, Takashi; Yanagida, Ikuhisa; Matsumura, Akira; Noguchi, Kazuko [Yodogawa Christian Hospital, Department of Orthopaedic Surgery, Osaka (Japan)
2007-06-15
Spontaneous regression of an osteochondroma is an infrequent event. In this report, two cases with spontaneous regression of osteochondromas are presented. The first case was a solitary osteochondroma of the pedunculated type involving the right proximal humerus in a 7-year-old boy. This lesion resolved over 15 months of observation. The second case was a 3-year-old girl with multiple osteochondromatosis, in whom sessile osteochondromas of the right tibia and left fibula regressed over 33 months.The mechanism of this phenomenon is discussed with a review of previous reports. Regarding treatment, careful observation may be acceptable for typical osteochondromas, especially in young children. (orig.)
[Spontaneous mediastinal emphysema].
Svedbrand, Charlotte; Lange, Peter; Nielsen, Klaus
2016-01-01
Spontaneous mediastinal emphysema, also known as spontaneous pneumomediastinum, is defined as radiologically detected free air in the mediastinum, without preceding trauma. It is a rare condition, mainly affecting young adults. It can be caused by coughing, strenuous sports or cocaine inhalation, however, 40% are idiopatic. Common symptoms are chest pain and dyspnoea. 75-90% can be diagnosed with a chest X-ray, and 100% with a computed tomography. Treatment is symptomatic and complications are rare, however, pneumothorax and pneumorrachis have been reported. PMID:26750190
Controlling spontaneous emission
DEFF Research Database (Denmark)
Lodahl, Peter
Control over spontaneous emission of light is of great importance in quantum optics. It is essential for diverse applications such as miniature lasers, light-emitting diodes, and single-photon sources for quantum information. We present experimental studies on spontaneous emission of CdSe quantum...... dots (QDs) embedded in 3D photonic crystals consisting of air spheres in titanium dioxide. Performing time-resolved experiments, we show that the photonic crystals control the emission decay rate of excitons confined in the QDs1,2. By varying the lattice parameter of the photonic crystals, we...
Spontaneous tension haemopneumothorax
Directory of Open Access Journals (Sweden)
Itam Sarah
2008-10-01
Full Text Available Abstract We present a patient with sudden onset progressive shortness of breath and no history of trauma, who rapidly became haemodynamically compromised with a pneumothorax and pleural effusion seen on chest radiograph. He was treated for spontaneous tension pneumothorax but this was soon revealed to be a tension haemopneumothorax. He underwent urgent thoracotomy after persistent bleeding to explore an apical vascular abnormality seen on CT scanning. To our knowledge this is the first such case reported. Aetiology and current approach to spontaneous haemothorax are discussed briefly.
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...
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...
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...
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.
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.
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...
Fusion and fission of fluid amphiphilic bilayers.
Gotter, Martin; Strey, Reinhard; Olsson, Ulf; Wennerström, Håkan
2005-01-01
The system water-oil (n-decane)-nonionic surfactant (C12E5) forms bilayer phases in a large concentration region, but, for a given oil-to-surfactant ratio, only in a narrow temperature range. In addition to the anisotropic lamellar phase (Lalpha) there is also, at slightly higher temperature, a sponge or L3-phase where the bilayers build up an isotropic structure extending macroscopically in three dimensions. In this phase the bilayer mid-surface has a mean curvature close to zero and a negative Euler characteristic. In this paper we study how the bilayers in the lamellar and the sponge phase respond dynamically to sudden temperature changes. The monolayer spontaneous curvature depends sensitively on temperature and a change of temperature thus provides a driving force for a change in bilayer topology. The equilibration therefore involves kinetic steps of fusion/fission of bilayers. Such dynamic processes have previously been monitored by temperature jump experiments using light scattering in the sponge phase. These experiments revealed an extraordinarily strong dependence of the relaxation time on the bilayer volume fraction phi. At phi magnetic resonance (2H-NMR) appear feasible. We here report on the first experiments concerned with the dynamics of the macroscopic phase transition sponge-lamellae by 2H-NMR. We find that the sponge-to-lamellae transition occurs through a nucleation process followed by domain growth involving bilayer fission at domain boundaries. In contrast, the lamellae-to-sponge transformation apparently occurs through a succession of uncorrelated bilayer fusion events. PMID:15715316
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)
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
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
Observed branching ratios of alpha to fission fragments of Cf252 using CR-39
International Nuclear Information System (INIS)
There has been a rapid growth in the application of SSNTD to the study of nuclear phenomena in the recent past. The considerable ease introduced in recording the signature of heavy ions in the presence of alpha particles has made them particularly suitable for the study of spontaneous fission of transuranic elements. It is the object of the present study to explore the response of CR-39 for the determination of the branching ratios of alpha to fission fragments of Cf252 at the end of almost one and four half-life periods for alpha decay. The results more or less confirm the expected values
Fission prompt gamma-ray multiplicity distribution measurements and simulations at DANCE
Energy Technology Data Exchange (ETDEWEB)
Chyzh, A; Wu, C Y; Ullmann, J; Jandel, M; Bredeweg, T; Couture, A; Norman, E
2010-08-24
The nearly energy independence of the DANCE efficiency and multiplicity response to {gamma} rays makes it possible to measure the prompt {gamma}-ray multiplicity distribution in fission. We demonstrate this unique capability of DANCE through the comparison of {gamma}-ray energy and multiplicity distribution between the measurement and numerical simulation for three radioactive sources {sup 22}Na, {sup 60}Co, and {sup 88}Y. The prospect for measuring the {gamma}-ray multiplicity distribution for both spontaneous and neutron-induced fission is discussed.
Spontaneous otogenic pneumocephalus.
Mohammed, El Romyssa; Profant, Milan
2011-06-01
The diagnosis and management of spontaneous otogenic pneumocephalus with literature review is described. A young sportsman experienced headache and fluctuating mass in his occiput during increased physical activity. A large extradural intracranial pneumocephalus with corresponding emphysema was imaged on a CT scan. Transmastoid identification and plugging of temporal bone defect solved the problem with complete pneumocephalus and emphysema resorption. PMID:21254960
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.)
Cosmic history of the Bragin pallasite: evidence from the fission-track analysis
International Nuclear Information System (INIS)
Chronology is rather a weak point in the investigation of pallasites, the stony-iron meteorites. No chronological data are known for the Bragin pallasite. Our attempt to reconstruct its cosmic history was based on the interpretation of fission-track analysis data. To apply this method only uranium-rich phosphates can be used. Extremely rare grains of stanfieldite were extracted from the silicate sawing residue and from the pallasite sample directly. The researches pursued by us made it possible to find two populations of fossil tracks in stanfieldite grains. The tracks of these populations strongly differed both in size, shape and character of distribution. The first population, consisting of short (L∼2-6 μm instead of L∼8-12 μm for induced fission tracks), round-shaped tracks irregularly distributed, as we suppose, suffered an intense heating process, which caused a significant amount of partial annealing. The second population, consisting of longer (L∼8-12 μm), rhombic-shaped tracks homogeneously distributed, occurred after this thermal event. Only the second population track density was used for the fission-track age calculation. After correction of the fossil track density, consisting of the second population tracks, for other possible track sources, the revealed tracks were unequivocally identified as those due to the spontaneous fission of 244Pu and 238U. The largest part of them was attributed to the spontaneous fission of 244Pu; ρPu/ρU∼3. The model fission-track age of the studied pallasite turned out to be 4.20 Gyr. This value fix the time of the last shock/thermal event in the cosmic history of the Bragin pallasite, which had caused the partial annealing of tracks presented to that time and 'fission-track clock' reset
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)
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)
Spontaneous pneumothorax complicating Legionnaires' disease
Bali, A; Pierry, A. A.; Bernstein, A.
1981-01-01
Spontaneous pneumothorax is a known but rare complication of pneumonia in adults. A case is described of Legionnaires' disease complicated by spontaneous hydropneumothorax. So far as is known such an association has not been reported previously.
Neutron Capture and Fission Measurements on Actinides at Dance
Chyzh, A.; Wu, C. Y.; Kwan, E.; Henderson, R. A.; Gostic, J. M.; Ullmann, J. L.; Bredeweg, T. A.; Jandel, M.; Couture, A. J.; O'Donnell, J. M.; Haight, R. C.; Lee, H. Y.
2013-03-01
The prompt γ-ray energy and multiplicity distributions in the spontaneous fission of 252Cf have been measured using a highly granular 4π γ-ray calorimeter. Corrections were made for both energy and multiplicity distributions according to the detector response, which is simulated numerically using a model validated with the γ-ray calibration sources. A comparison of the total γray energy distribution was made between the measurement and a simulation by random sampling of the corrected γ-ray energy and multiplicity distributions through the detector response. A reasonable agreement is achieved between the measurement and simulation, indicating weak correlations between γ-ray energy and multiplicity. Moreover, the increasing agreement with increasing multiplicity manifests the stochastic aspect of the prompt γ decay in spontaneous fission. This calorimeter was designed for the study of neutron capture reactions and an example is given, where the238Pu(n, γ) measurement was carried out in the laboratory environment for the first time.
International Nuclear Information System (INIS)
A method for determining the semiconductor detector absolute efficiency, based on the application radioactive nuclide γ radiation in the decay chains of spontaneous fissionable 252Cf fragments is proposed. Proceeding from the values of half-lives of the nuclides used and choosing the irradiation regimes according to gamma spectrum measurement data, the absolute efficiency is calculated. 8 refs.; 1 fig.; 1 tab
Contribution to the study of prompt gamma-rays from fission
International Nuclear Information System (INIS)
This PhD thesis has essentially been motivated by the nuclear heating problematic in reactors. The main goal of this work was the production of methods capable of simulating the prompt gamma emission from fission. First of all, several algorithms for the treatment of the nucleus deexcitation were implemented. They have been successfully tested through various calculations (isomeric branching ratio, total radiative width, etc). These methods were then incorporated in the frame of the fission code FIFRELIN. The tool which results from this work, enables the determination of numerous fission observables in the frame of a single consistent model. A sensitivity study of the results to several numerical and nuclear models has been realized. At last, calculation have been lead for the 252Cf spontaneous fission and the thermal neutron induced fission of 235U and 239Pu. The prompt gamma spectra obtained for those three fissioning systems have been determined. The results are in good agreement with available experimental data, including recent measurements published in 2012 and 2013. (author)
Development of a thin scintillation films fission-fragment detector and a novel neutron source
Rusev, G.; Jandel, M.; Baramsai, B.; Bond, E. M.; Bredeweg, T. A.; Couture, A.; Daum, J. K.; Favalli, A.; Ianakiev, K. D.; Iliev, M. L.; Mosby, S.; Roman, A. R.; Springs, R. K.; Ullmann, J. L.; Walker, C. L.
2015-08-01
Investigation of prompt fission and neutron-capture Υ rays from fissile actinide samples at the Detector for Advanced Neutron Capture Experiments (DANCE) requires use of a fission-fragment detector to provide a trigger or a veto signal. A fission-fragment detector based on thin scintillating films and silicon photomultipliers has been built to serve as a trigger/veto detector in neutron-induced fission measurements at DANCE. The fissile material is surrounded by scintillating films providing a 4π detection of the fission fragments. The scintillations were registered with silicon photomultipliers. A measurement of the 235U(n,f) reaction with this detector at DANCE revealed a correct time-of-flight spectrum and provided an estimate for the efficiency of the prototype detector of 11.6(7)%. Design and test measurements with the detector are described. A neutron source with fast timing has been built to help with detector-response measurements. The source is based on the neutron emission from the spontaneous fission of 252Cf and the same type of scintillating films and silicon photomultipliers. Overall time resolution of the source is 0.3 ns. Design of the source and test measurements with it are described. An example application of the source for determining the neutron/gamma pulse-shape discrimination by a stilbene crystal is given.
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...
Optimal version of a detector for relative measuring of fission neutron yield
International Nuclear Information System (INIS)
A fission neutron detector ( anti ν-detector), registration efficiency E of which does not depend on neutron energy is discussed. The detector represents a cylindrical moderator (polyethylene) along the axis of which a channel for the fission detector is located. Coaxially with the central channel 3He or BF3 cylindrical counters are located in several raws. The account of neutron energy effect on E is carried out by simultaneous measurement of anti ν and THETA, where anti ν - fission neutron yield, THETA-neutron ''temperature'', connected with the mean energy by the relation anti E=3/2 THETA. The method of simultaneous measurements of anti ν and THETA suggests the pulse coincidence registration from the BF3 or 3H counters with pulses from the fission detector. Ratio of the coincidence numbers is used for determining THETA and the sum for anti ν. As an example presented are the results of measuring the 244Cm fission neutron yield with respect to anti νsub(o) in the case of 252Cf spontaneous fission by means of the detector, containing four raws of counters. The data obtained satisfactorily agree with the data published earlier
Averaged U238 fission cross section measurement in Cf-252 neutron spectrum
International Nuclear Information System (INIS)
With regard to the standardization of Cf-252 neutron spectrum, the averaged U-238 fission cross section was measured over the Cf-252 neutron spectrum using foil activation technique. The gamma spectra of the fission products were obtained on a pure germanium detector at different decay times in order to identify the gamma rays of short, medium and long half-life radioisotopes. Analyzing the gamma spectra of the irradiated uranium foils several distinct photopeaks of several fission products were identified. The pure activity of Te-132 was determined from the net area under 228.2 kev photopeak after correcting it for neighbouring photopeaks of Np-239 and Pa-234. The averaged U238 fission cross section was calculated from the corrected counts of Te-132 photopeak to be 329±10 mb. The main sources of errors in the measurements are mainly due to inaccuracy of location of foils, neutron flux, counting statistics, weight of foils, impurity of foils and interference from neighbouring photopeaks. The contribution of fission neutrons from spontaneous fission of Cm-248, daughter of Cf-252, to the total flux density was estimated at 0.13%. (orig.)
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
Total prompt γ-ray emission in fission
Wu, C. Y.; Chyzh, A.; Kwan, E.; Henserson, R. A.; Bredeweg, T. A.; Haight, R. C.; Hayes-Sterbenz, A. C.; Lee, H. Y.; O'Donnell, J. M.; Ullmann, J. L.
2016-06-01
The total prompt γ-ray energy distributions for the neutron-induced fission of 235U, 239,241Pu at incident neutron energy of 0.025 eV ‒ 100 keV, and the spontaneous fission of 252Cf were measured using the Detector for Advanced Neutron Capture Experiments (DANCE) array in coincidence with the detection of fission fragments by a parallel-plate avalanche counter. DANCE is a highly segmented, highly efficient 4π γ-ray calorimeter. Corrections were made to the measured distribution by unfolding the two-dimension spectrum of total γ-ray energy vs multiplicity using a simulated DANCE response matrix. The mean values of the total prompt γ-ray energy, determined from the unfolded distributions, are ~ 20% higher than those derived from measurements using single γ-ray detector for all the fissile nuclei studied. This raises serious concern on the validity of the mean total prompt γ-ray energy obtained from the product of mean values for both prompt γ-ray energy and multiplicity.
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.
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)
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.
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
Evaluating fission neutron-multiplicity data
International Nuclear Information System (INIS)
The present work had its origins in the practical need to obtain Pν for the purpose of calculating the theoretical response of instrumentation that used a correlation technique to assay spontaneously fissioning nuclides. The assay results are proportional to the factorial moments calculated with the Pν distribution. Obtaining experimentally derived sets of Pν from many sources reported over several decades led immediately to the problem of evaluating the data: Aside from the trivial problem of sometimes not being properly normalized, the first moments (ν) = (ν) = ΣνPν were typically not in accord with the best recent evaluations, or the calibration of detector efficiency was based on obsolete values for (ν) for supposedly well-characterized ''standard'' nuclides such as 252Cf. The problem of evaluating Pν is unusual in that, compared to the usual situation where the quantities being evaluated are single numbers, the Pν are sets of numbers, that moreover, are constrained so that ΣPν triple-bond 1 and Σν Pν = (ν), where (ν) is usually determined more accurately from a separate experiment than it can be calculated from the experimentally derived Pν distribution
Spontaneous Quantum Hall Liquids
Zhang, Fan
2012-02-01
Driven by electron-electron interactions, bilayer graphene and its thicker cousins, chirally (ABC) stacked multilayers, exhibit a variety of distinct broken symmetry states in which each spin-valley flavor spontaneously transfers charge between layers, because of their flat touching bands and large pseudospin chiralities. These gapped states are accompanied by large momentum space Berry curvatures and different types of topological orders. These competing ground states are distinguished by their flavor Hall conductivities, orbital magnetizations, edge state properties, and response to external fields. These spontaneous quantum Hall (SQH) states at zero field smoothly evolve into quantum Hall ferromagnet states at finite field. Various phase transitions occur by tuning carrier densities, temperature, and external fields. Recently, SQH states have started to be observed and explored in transport and Hall experiments on suspended devices with dual gates.
Spontaneous Perforation of Pyometra.
Sharma, Nalini; Singh, Ahanthem Santa; Bhaphiralyne, Wankhar
2016-04-01
Pyometra is collection of purulent material which occurs when there is interference with its normal drainage. It is an uncommon condition with incidence of 0.1 to 0.5% of all gynecological patients. Spontaneous rupture of uterus is an extremely rare complication of pyometra. A 65-year-old lady presented with pain abdomen and purulent vaginal discharge. Preoperative diagnosis of pyometra was made by magnetic resonance imaging (MRI). Laparotomy followed by peritoneal lavage and repair of perforation was performed. Although spontaneously perforated pyometra is rare, the condition must be borne in mind with regard to elderly women with acute abdominal pain. Preoperative diagnosis of perforated pyometra is absolutely essential. Computed tomography (CT) and MRI are diagnostic tools. In selected cases conservative approach at surgery can be opted. PMID:27152313
Spontaneous Rupture of Pyometra
Directory of Open Access Journals (Sweden)
Fatemeh Mallah
2013-01-01
Full Text Available Spontaneous perforation is a very rare complication of pyometra. The clinical findings of perforated pyometra are similar to perforation of the gastrointestinal tract and other causes of acute abdomen. In most cases, a correct and definite diagnosis can be made only by laparotomy. We report two cases of diffuse peritonitis caused by spontaneous perforated pyometra. The first case is a 78-year-old woman with abdominal pain for which laparotomy was performed because of suspected incarcerated hernia. The second case is a 61-year-old woman with abdominal pain for which laparotomy was performed because of symptoms of peritonitis. At laparotomy of both cases, 1 liter of pus with the source of uterine was found in the abdominal cavity. The ruptured uterine is also detected. More investigations revealed no malignancy as the reason of the pyometra.
Spontaneous ovarian hyperstimulation syndrome.
Kasum, Miro; Orešković, Slavko; Ježek, Davor
2013-01-01
Spontaneous forms of the ovarian hyperstimulation syndrome (sOHSS) are nearly always reported between 8 and 14 weeks of pregnancy and also with follicle-stimulating hormone (FSH) producing pituitary adenoma. The syndrome has been previously reported in rare instances of increased production of human chorionic gonadotrophin (hCG) such as multiple pregnancies, hydatiforme mole, polycystic ovary disease and elevated concentrations of thyroid-stimulating hormone (TSH) in hypothyreoidism. High lev...
Spontaneous Perforation of Pyometra
Sharma, Nalini; Singh, Ahanthem Santa; Bhaphiralyne, Wankhar
2016-01-01
Pyometra is collection of purulent material which occurs when there is interference with its normal drainage. It is an uncommon condition with incidence of 0.1 to 0.5% of all gynecological patients. Spontaneous rupture of uterus is an extremely rare complication of pyometra. A 65-year-old lady presented with pain abdomen and purulent vaginal discharge. Preoperative diagnosis of pyometra was made by magnetic resonance imaging (MRI). Laparotomy followed by peritoneal lavage and repair of perfor...
Spontaneous spinal epidural abscess.
LENUS (Irish Health Repository)
Ellanti, P
2011-10-01
Spinal epidural abscess is an uncommon entity, the frequency of which is increasing. They occur spontaneously or as a complication of intervention. The classical triad of fever, back pain and neurological symptoms are not always present. High index of suspicion is key to diagnosis. Any delay in diagnosis and treatment can have significant neurological consequences. We present the case of a previously well man with a one month history of back pain resulting from an epidural abscess.
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.
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.)
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...
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.
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.)
[Spontaneous abortion. Etiologic survey. Results].
Baaklini, N; Anguenot, J L; Boulanger, J C; Vitse, M
1990-12-01
The definition of repeated spontaneous abortions is subject to caution. For some, it corresponds to at least three repeated spontaneous abortions with no normal previous pregnancy; for others, it comprises the repeated spontaneous abortions occurring after a normal pregnancy. It is a frequent problem, especially if one tries to give a wider definition. The authors studied the frequency of repeated spontaneous abortions in a continuous series of 14,857 pregnancies which took place between January 1982 and December 1988. In the study of the aetiology of the repeated spontaneous abortions in the various groups of women defined according to the number of previous pregnancies and abortions, they find the classical causes of repeated spontaneous abortions in all the categories: therefore, it seems legitimate to them that a wider definition be given for repeated spontaneous abortions. PMID:2291048
Time-zero fission-fragment detector based on low-pressure multiwire proportional chambers
International Nuclear Information System (INIS)
A time-zero fission fragment (FF) detector, based on the technique of low-pressure multiwire proportional chambers (LPMWPC), has been designed and constructed for the heavy hypernuclear lifetime experiment (E95-002) at Thomas Jefferson National Accelerator Facility. Its characteristics and the method of time-zero reconstruction were investigated using fission fragments from a 252Cf spontaneous fission source. The influence of the ionization energy loss was also studied. It is shown that Heptane, Hexane, and Isobutane gases at a pressure of 1-2 Torr are all suitable for such a FF detector. As desired by experiment, a timing resolution of about 200 ps (FWHM) for a chamber size of 21x21 cm2 was achieved
UF{sub 6} as a detector gas for fission studies
Energy Technology Data Exchange (ETDEWEB)
Eckardt, Christian; Enders, Joachim; Freudenberger, Martin; Neumann-Cosel, Peter von [Technische Univ. Darmstadt (Germany). Inst. fuer Kernphysik; Goeoek, Alf; Oberstedt, Stephan [Commission of the European Communities, Geel (Belgium). Inst. for Reference Materials and Measurements (IRMM); Oberstedt, Andreas [Akademin foer Naturvetenskap och Teknik, Oerebro Univ. (Sweden); Chalmers Tekniska Hoegskola, Goeteborg (Sweden). Fundamental Fysik
2013-07-01
A Frisch-grid ionization chamber has been built to test a mixture of argon with gaseous UF{sub 6} and to study its properties as a counting gas. We present first results using increasing mass fractions of {sup 238}UF{sub 6} mixed into argon. The drift velocity of the electrons increases with the content of {sup 238}UF{sub 6}, while a good signal quality and energy resolution of the ionization chamber is preserved. Using uranium hexafluoride in the detector gas may give access to experiments where extremely high luminosity is required in combination with good angular and energy and/or mass resolution. Examples comprise the investigation of spontaneous fission of {sup 238}U, the study of parity non-conservation in the fission process, or precision measurements of fission fragments with good resolution using tagged photons in the entrance channel.
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)
Time-zero fission-fragment detector based on low-pressure multiwire proportional chambers
Assamagan, Ketevi A; Bayatyan, G L; Carlini, R; Danagulyan, S; Eden, T; Egiyan, K; Ent, R; Fenker, H; Gan, L; Gasparian, A; Grigoryan, N K; Greenwood, Z; Gueye, P; Hashimoto, O; Johnston, K; Keppel, C; Knyazyan, S; Majewski, S; Margaryan, A; Margaryan, Yu L; Marikian, G G; Martoff, J; Mkrtchyan, H G; Parlakyan, L; Sato, Y; Sawafta, R; Simicevic, N; Tadevosyan, V; Takahashi, T; Tang, L; Vartanian, G S; Vulcan, W; Wells, S; Wood, S
1999-01-01
A time-zero fission fragment (FF) detector, based on the technique of low-pressure multiwire proportional chambers (LPMWPC), has been designed and constructed for the heavy hypernuclear lifetime experiment (E95-002) at Thomas Jefferson National Accelerator Facility. Its characteristics and the method of time-zero reconstruction were investigated using fission fragments from a sup 2 sup 5 sup 2 Cf spontaneous fission source. The influence of the ionization energy loss was also studied. It is shown that Heptane, Hexane, and Isobutane gases at a pressure of 1-2 Torr are all suitable for such a FF detector. As desired by experiment, a timing resolution of about 200 ps (FWHM) for a chamber size of 21x21 cm sup 2 was achieved.
Correlation measurements of fission-fragment properties
Oberstedt A.; Martinez T.; Kis Z.; Karlsson J.; Hambsch F.-J.; Cano-Ott D.; Göök A.; Borcea R.; Billnert R.; Belgya T.; Oberstedt S.; Szentmiklosi L.; Takác K.
2010-01-01
For the development of future nuclear fission applications and for a responsible handling of nuclear waste the a-priori assessment of the fission-fragments’ heat production and toxicity is a fundamental necessity. The success of an indispensable modelling of the fission process strongly depends on a good understanding of the particular mechanism of scission, the mass fragmentation and partition of excitation energy. Experimental observables are fission-fragment properties like mass- and energ...
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
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)
Superfluid fission dynamics with microscopic approaches
Simenel, C; Lacroix, D; Umar, A S
2016-01-01
Recent progresses in the description of the latter stage of nuclear fission are reported. Dynamical effects during the descent of the potential towards scission and in the formation of the fission fragments are studied with the time-dependent Hartree-Fock approach with dynamical pairing correlations at the BCS level. In particular, this approach is used to compute the final kinetic energy of the fission fragments. Comparison with experimental data on the fission of 258Fm are made.
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.
Is the Double Giant Dipole Resonance Process Responsible for Alpha Emission in Ternary Fission?
Institute of Scientific and Technical Information of China (English)
HAN Hong-Yin(韩洪银); WAND Yi-Hua(王屹华); G.Mouze
2001-01-01
The Monte Carlo program built on the double giant dipole resonance model proposed by Mouze et al. [Nuovo Cimento A 110(1997)1097] was employed to calculate the energy spectrum of alpha particles emitted in the spontaneous ternary fission of 252Cf. It has been found that in the case of the zero orbital angular momentum of alpha particles in the alpha decay of the fragments, the measured alpha spectrum can be reproduced approximately by the model without any adjustable parameter.
International Nuclear Information System (INIS)
When the isotopic composition of nuclear materials to control is know, it is possible to determine the amount of plutonium by measuring the rate of spontaneous fissions. The induced fissions alter significantly the measures. Therefore we must evaluate the multiplicative factor. For a not very multiplicative sample, the observed real neutron coincidences of multiplicity 0 to n agree with spontaneous emissions given by nuclear tables. This is not true in the opposite case (large amounts). Multiplicities are given by eighteen counting-scales associated with a shift-register coincidence system (SCRD) and compared with theoretical spontaneous emissions of the sample. A calculator leads all the equipment and gives automatically the real amount of Pu
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...
Nuclear-fission studies with relativistic secondary beams: analysis of fission channels
Boeckstiegel, C.; Steinhaeuser, S.; Schmidt, K.-H.; Clerc, H. -G.; Grewe, A.; Heinz, A.; de Jong, M; JUNGHANS A. R.; Mueller, J.; Voss, B.
2007-01-01
Nuclear fission of several neutron-deficient actinides and pre-actinides from excitation energies around 11 MeV was studied at GSI Darmstadt by use of relativistic secondary beams. The characteristics of multimodal fission of nuclei around 226Th are systematically investigated and interpreted as the superposition of three fission channels. Properties of these fission channels have been determined for 15 systems. A global view on the properties of fission channels including previous results is...
Brownian shape dynamics in fission
Randrup Jørgen; Möller Peter
2013-01-01
It was recently shown that remarkably accurate fission-fragment mass distributions are obtained by treating the nuclear shape evolution as a Brownian walk on previously calculated five-dimensional potentialenergy surfaces; the current status of this novel method is described here.
Brownian shape dynamics in fission
Directory of Open Access Journals (Sweden)
Randrup Jørgen
2013-12-01
Full Text Available It was recently shown that remarkably accurate fission-fragment mass distributions are obtained by treating the nuclear shape evolution as a Brownian walk on previously calculated five-dimensional potentialenergy surfaces; the current status of this novel method is described here.
Search for singlet fission chromophores
Czech Academy of Sciences Publication Activity Database
Havlas, Zdeněk; Akdag, Akin; Smith, M. B.; Dron, P.; Johnson, J. C.; Nozik, A. J.; Michl, Josef
Philadelphia: American Chemical Society, 2012. 31PHYS. ISSN 0065-7727. [National Fall Meeting of the American Chemical Society /244./. 19.08.2012-23.08.2012, Philadelphia] Institutional support: RVO:61388963 Keywords : singlet fission * chromophores Subject RIV: CF - Physical ; Theoretical Chemistry
Spontaneous Collapse of Supersymmetry
Buchholz, D A; Buchholz, Detlev; Ojima, Izumi
1997-01-01
It is shown that, if generators of supersymmetry transformations (supercharges) can be defined in a spatially homogeneous physical state, then this state describes the vacuum. Thus, supersymmetry is broken in any thermal state and it is impossible to proceed from it by ``symmetrization'' to states on which an action of supercharges can be defined. So, unlike the familiar spontaneous breakdown of bosonic symmetries, there is a complete collapse of supersymmetry in thermal states. It is also shown that spatially homogeneous superthermal ensembles are never supersymmetric.
Joseph Isaac Lifshitz
2009-01-01
One description of the people of Israel is Kahal, a category that the Talmud is also concerned with. This category was further employed later in the middle ages, and was given to the Jewish community, although some times with a little twist, the Kehila. This paper will focus mainly on the question of the formation of the Kahal as a large political body in the Bible and in the Talmud, and explore the political implications that can be derived from it. The Kahal as a spontaneously-defined, non-...
Endlich, Solomon; Penco, Riccardo
2013-01-01
The Galilei group involves mass as a central charge. We show that the associated superselection rule is incompatible with the observed phenomenology of superfluid helium 4: this is recovered only under the assumption that mass is spontaneously broken. This remark is somewhat immaterial for the real world, where the correct space-time symmetries are encoded by the Poincar\\'e group, which has no central charge. Yet it provides an explicit example of how superselection rules can be experimentally tested. We elaborate on what conditions must be met for our ideas to be generalizable to the relativistic case of the integer/half-integer angular momentum superselection rule.
International Nuclear Information System (INIS)
The method of Fission-Track dating is based upon the detection of the damage caused by fission fragments from the Uranium contained in geological samples.In order to determine the age of a sample, both the amount of spontaneous fissions occurred and the Uranium concentration must be known.The latter requires the irradiation of the samples inside a reactor with a well-thermalized flux, so that fissions are induced over 235U targets only. Therefore, the Uranium concentration may be determined.The main inconvenient presented by the irradiation sites at the RA-6 MTR-type reactor is that neutron flux is not completely thermal there, which means that fissions due to epithermal and fast neutrons will not be negligible.In the same way, tracks due to fissions of 238U and 232Th will be detected. In order to know the corrections that must be applied to those measurements performed in this reactor, it is necessary to characterize fast flux.Because of it, this laboratory's gamma spectrometry equipment had to be calibrated. After that, several activation detectors were irradiated and results were analyzed. Finally, it was determined that it is feasible to Fission-Track date at the I6 position. However, limitations associated to this method were analyzed for the values of flux measured in the different sites
International Nuclear Information System (INIS)
The fission-track method allows geologists to date rocks and to get information on the thermal history of rocks. Fission tracks in minerals are essentially due to the spontaneous fission of uranium 238. The knowledge of the density of tracks and the concentration of uranium 238 lead to the determination of the age of the rock. The irradiation in a neutron flux of a sample of the rock allows the determination of the concentration of uranium. The age obtained is in fact an apparent age that does not take into account possible geological annealing process that may erase fission tracks, some corrections are then necessary. The first part of this work details the fission-track method, its scope and limitations. It is shown that fission-track method on apatites can reveal the thermal evolution of the rock and that the same method used on zircons can give information of the setting of volcanic rocks. The second part is dedicated to the contribution of the fission-track method to a both dating and thermal evolution study of a french-italian part of the Alpine chain
Fission and Properties of Neutron-Rich Nuclei
Hamilton, Joseph H.; Ramayya, A. V.; Carter, H. K.
2008-08-01
. Fission-fragment spectroscopy with STEFF / A. G. Smith ... [et al.]. Gamma ray multiplicity of [symbol]Cf spontaneous fission using LiBerACE / D. L. Bleuel ... [et al.]. Excitation energy dependence of fragment mass and total kinetic energy distributions in proton-induced fission of light actinides / I. Nishinaka ... [et al.]. A dynamical calculation of multi-modal nuclear fission / T. Wada and T. Asano. Structure of fission potential energy surfaces in ten-dimensional spaces / V. V. Pashkevich, Y. K Pyatkov and A. V. Unzhakova. A possible enhancement of nuclear fission in scattering with low energy charged particles / V. Gudkov. Dynamical multi-break processes in the [symbol]Sn + [symbol]Ni system at 35 MeV/Nucleon / M. Papa and ISOSPIN-RE VERSE collaboration -- New experimental techniques. MTOF - a high resolution isobar separator for studies of exotic decays / A. Piechaczek ... [et al.]. Development of ORRUBA: a silicon array for the measurement of transfer reactions in inverse kinematics / S. D. Pain ... [et al.]. Indian national gamma array: present & future / R. K. Bhowmik. Absolute intensities of [symbol] rays emitted in the decay of [symbol]U / H. C. Griffin -- Superheavy elements theory and experiments / M. G. Itkis ... [et al.]. Study of superheavy elements at SHIP / S. Hofinann. Heaviest nuclei from [symbol]Ca-induced reactions / Yu. Ts. Oaanessian. Superheavy nuclei and giant nuclear systems / W. Greiner and V. Zagrebaev. Fission approach to alpha-decay of superheavy nuclei / D.N. Poenaru and W. Greiner. Superheavy elements in the Magic Islands / C. Samanta. Relativistic mean field studies of superheavy nuclei / A. V. Afanas jev. Understanding the synthesis of the heaviest nuclei / W. Loveland -- Mass measurements and g-factors. G factor measurements in neutron-rich [symbol]Cf fission fragments, measured using the gammasphere array / R. Orlandi ... [et al.]. Technique for measuring angular correlations and g-factors in neutron rich nuclei produced by the
Incomplete spontaneous ureteral disruption
International Nuclear Information System (INIS)
Background. The aim of the authors was to present the case of spontaneous partial ureteral rupture during a renal colic, caused by an anorganic concrement in the proximal part of the left ureter, at the level of the transverse processus of L3. Case report. On the excretory urography imaging, the dilatation of the canal system, cups, necks and pyelon, was observed. At the level of the pyeloureteric passage, the contrast medium was leaking. The leakage was found to be extending along the psoas muscle to the pelvis. On the transversal CT imaging scans, the contrast medium was seen along the medial and dorsal part of the perirenal space, and in the distal part, along the psoas muscle to the pelvis. The ureter was imaged from the pyeloureterical rupture to the site of the concrement. No signs of the damage of the renal parenchyma or perirenal bleeding were detected. During surgery, the site of the rupture was found and also a lot of the perirenal and periureteral liquid. After the extraction of the concrement, the suture of the rupture was made. Postoperative urography and CT showed a normal ureteral image. Conclusions. At the spontaneous partial disruption of the ureter, the contrast medium is still seen in the ureter, distally from the site of the rupture and as extravasation along the psoas muscle. (author)
Quantum Spontaneous Stochasticity
Eyink, Gregory L
2015-01-01
The quantum wave-function of a massive particle with small initial uncertainties (consistent with the uncertainty relation) is believed to spread very slowly, so that the dynamics is deterministic. This assumes that the classical motions for given initial data are unique. In fluid turbulence non-uniqueness due to "roughness" of the advecting velocity field is known to lead to stochastic motion of classical particles. Vanishingly small random perturbations are magnified by Richardson diffusion in a "nearly rough" velocity field so that motion remains stochastic as the noise disappears, or classical spontaneous stochasticity, . Analogies between stochastic particle motion in turbulence and quantum evolution suggest that there should be quantum spontaneous stochasticity (QSS). We show this for 1D models of a particle in a repulsive potential that is "nearly rough" with $V(x) \\sim C|x|^{1+\\alpha}$ at distances $|x|\\gg \\ell$ , for some UV cut-off $\\ell$, and for initial Gaussian wave-packet centered at 0. We consi...
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)
Fission product behaviour in severe accidents
International Nuclear Information System (INIS)
The understanding of fission product (FP) behaviour in severe accidents is important for source term assessment and accident mitigation measures. For example in accident management the operator needs to know the effect of different actions on the behaviour and release of fission products. At VTT fission product behaviour have been studied in different national and international projects. In this presentation the results of projects in EU funded 4th framework programme Nuclear Fission Safety 1994-1998 are reported. The projects are: fission product vapour/aerosol chemistry in the primary circuit (FI4SCT960020), aerosol physics in containment (FI4SCT950016), revaporisation of test samples from Phebus fission products (FI4SCT960019) and assessment of models for fission product revaporisation (FI4SCT960044). Also results from the national project 'aerosol experiments in the Victoria facility' funded by IVO PE and VTT Energy are reported
Fission dynamics at low excitation energy
Aritomo, Y
2013-01-01
The origin of mass asymmetry in the fission of uranium at a low excitation energy is clarified by a trajectory analysis of the Langevin equation. The positions of the peaks in the mass distribution of fission fragments are mainly determined by fission saddle points originating from the shell correction energy. The widths of the peaks, on the other hand, result from a shape fluctuation around the scission point caused by the random force in the Langevin equation. We found that a random vibration in the oblate direction of fissioning fragments is essential for the fission process. According to this picture, fission does not occur with continuous stretching in the prolate direction, similarly to that observed in starch syrup. This is expected to lead to a new viewpoint of fission dynamics and the splitting mechanism.
The Fission of Thorium with Alpha Particles
Energy Technology Data Exchange (ETDEWEB)
Newton, Amos S.
1948-04-15
The fission distribution of fission of thorium with alpha particle of average energy 37.5 Mev has been measured by the chemical method. The distribution found shows that the characteristic dip in the fission yield mass spectrum has been raised to within a factor of two of the peaks compared to a factor of 600 in slow neutron fission of U{sup 235}. The raise in the deip has caused a corresponding lowering in fission yield of these elements at the peaks. The cross section for fission of thorium with 37.5 Mev alphas was found to be about 0.6 barn, and the threshold for fission was found to be 23 to 24 Mev.
A fission fragment detector for correlated fission output studies
Energy Technology Data Exchange (ETDEWEB)
Mosby, S., E-mail: smosby@lanl.gov [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Tovesson, F.; Couture, A. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Duke, D.L. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Colorado School of Mines, Golden, CO 80401 (United States); Kleinrath, V. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Idaho State University, Pocatello, ID 83201 (United States); Meharchand, R.; Meierbachtol, K.; O' Donnell, J.M.; Perdue, B.; Richman, D. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Shields, D. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Colorado School of Mines, Golden, CO 80401 (United States)
2014-09-01
A digital data acquisition system has been combined with a double Frisch gridded ionization chamber for use at both moderated and unmoderated neutron sources at the Los Alamos Neutron Science (LANSCE) facility. The high efficiency of the instrument combined with intense LANSCE beams and new acquisition system permits fission output measurements across 11 orders of magnitude incident neutron energy. The acquisition and analysis system is presented along with the first in-beam performance tests of the setup.
A fission fragment detector for correlated fission output studies
International Nuclear Information System (INIS)
A digital data acquisition system has been combined with a double Frisch gridded ionization chamber for use at both moderated and unmoderated neutron sources at the Los Alamos Neutron Science (LANSCE) facility. The high efficiency of the instrument combined with intense LANSCE beams and new acquisition system permits fission output measurements across 11 orders of magnitude incident neutron energy. The acquisition and analysis system is presented along with the first in-beam performance tests of the setup
Cluster fission from the standpoint of nuclear fission
Energy Technology Data Exchange (ETDEWEB)
Lee, Sangmoo [Tsukuba Univ., Ibaraki (Japan). Inst. of Physics
1996-03-01
Atomic nucleus belongs to a quantal finite many body system. Nucleus shows great resemblance to cluster, above all metal cluster, although the strength of interaction is different. The works of Brechignac group, Saunder, Martin and P. Froeblich are explained by the critical size Nc as the central term. The differences between cluster and nucleus are investigated and a future view of cluster fission is explained. (S.Y.)
DSP Algorithms for Fission Fragment and Prompt Fission Neutron Spectroscopy
Zeynalova, O.; Zeynalov, Sh.; Hambsch, F.-J.; Oberstedt, S.; Fabry, I.
2009-10-01
Digital signal processing (DSP) algorithms are in high demand for modern nuclear fission investigation due to importance of increase the accuracy of fissile nuclear data for new generation of nuclear power stations. DSP algorithms for fission fragment (FF) and prompt fission neutron (PFN) spectroscopy are described in the present work. The twin Frisch-grid ionization chamber (GTIC) is used to measure the kinetic energy-, mass- and angular distributions of the FF in the 252Cf(SF) reaction. Along with the neutron time-of-flight (TOF) measurement the correlation between neutron emission and FF mass and energy is investigated. The TOF is measured between common cathode of the GTIC and the neutron detector (ND) pulses. Waveform digitizers (WFD) having 12 bit amplitude resolution and 100 MHz sampling frequency are used for the detector pulse sampling. DSP algorithms are developed as recursive procedures to perform the signal processing, similar to those available in various nuclear electronics modules, such as constant fraction discriminator (CFD), pulse shape discriminator (PSD), peak-sensitive analogue-to-digital converter (pADC) and pulse shaping amplifier (PSA). To measure the angle between FF and the cathode plane normal to the GTIC a new algorithm is developed having advantage over the traditional analogue pulse processing schemes. Algorithms are tested by comparing the numerical simulation of the data analysis of the 252Cf(SF) reaction with data available from literature.
Development of position-sensitive time-of-flight spectrometer for fission fragment research
International Nuclear Information System (INIS)
A position-sensitive, high-resolution time-of-flight detector for fission fragments has been developed. The SPectrometer for Ion DEtermination in fission Research (SPIDER) is a 2E–2v spectrometer designed to measure the mass of light fission fragments to a single mass unit. The time pick-off detector pairs to be used in SPIDER have been tested with α-particles from 229Th and its decay chain and α-particles and spontaneous fission fragments from 252Cf. Each detector module is comprised of thin electron conversion foil, electrostatic mirror, microchannel plates, and delay-line anodes. Particle trajectories on the order of 700 mm are determined accurately to within 0.7 mm. Flight times were measured with 250 ps resolution FWHM. Computed particle velocities are accurate to within 0.06 mm/ns corresponding to a precision of 0.5%. An ionization chamber capable of 400 keV energy resolution coupled with the velocity measurements described here will pave the way for modestly efficient measurements of light fission fragments with unit mass resolution
Rodriguez-Guzman, R R
2015-01-01
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 $\\le$ N $\\le$ 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 $\\alpha$-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 ...
International Nuclear Information System (INIS)
The most recent parametrization D1M of the Gogny energy density functional is used to describe fission in the isotopes 232-280Pu. We resort to the methodology introduced in our previous studies (Phys. Rev. C 88, 054325 (2013) and Phys. Rev. C 89, 054310 (2014)) to compute the fission paths, collective masses and zero point quantum corrections within the Hartree-Fock-Bogoliubov framework. The systematics of the spontaneous fission half-lives tSF, masses and charges of the fragments in plutonium isotopes is analyzed and compared with available experimental data. We also pay attention to isomeric states, the deformation properties of the fragments as well as to the competition between the spontaneous fission and α-decay modes. The impact of pairing correlations on the predicted tSF values is demonstrated with the help of calculations for 232-280Pu, in which the pairing strengths of the Gogny-D1M energy density functional are modified by 5% and 10%, respectively. We further validate the use of the D1M parametrization through the discussion of the half-lives in 242-262Fm. Our calculations corroborate that, though the uncertainties in the absolute values of physical observables are large, the Gogny-D1M Hartree-Fock-Bogoliubov framework still reproduces the trends with mass and/or neutron numbers and therefore represents a reasonable starting point to describe fission in heavy nuclear systems from a microscopic point of view. (orig.)
Future research program on prompt γ-ray emission in nuclear fission
Energy Technology Data Exchange (ETDEWEB)
Oberstedt, S.; Hambsch, F.J. [Joint Research Centre IRMM, European Commission, Geel (Belgium); Billnert, R. [Joint Research Centre IRMM, European Commission, Geel (Belgium); Chalmers Tekniska Hoegskola, Fundamental Fysik, Goeteborg (Sweden); Lebois, M.; Wilson, J.N. [Institut de Physique Nucleaire Orsay, Orsay (France); Oberstedt, A. [Chalmers Tekniska Hoegskola, Fundamental Fysik, Goeteborg (Sweden); Ossolution Consulting, Oerebro (Sweden)
2015-12-15
In recent years the measurement of prompt fission γ-ray spectra (PFGS) has gained renewed interest, after about forty years since the first comprehensive studies of the reactions {sup 235}U(n{sub th}, f), {sup 239}Pu(n{sub th},f) and {sup 252}Cf(sf). The renaissance was initiated by requests for new values especially for γ-ray multiplicity and average total energy release per fission in neutron-induced fission of {sup 235}U and {sup 239}Pu. Both isotopes are considered the most important ones with respect to the modeling of innovative cores required for the Generation-IV reactors, the majority working with fast neutrons. During the last 5 years we have conducted a systematic study of spectral data for thermal-neutron-induced fission on {sup 235}U and {sup 241}Pu as well as for the spontaneous fission of {sup 252}Cf with unprecedented accuracy. From the new data we conclude that those reactions do not considerably contribute to the observed heat excess and suspect other reactions playing a significant role. Possible contributions may originate from fast-neutron-induced reactions on {sup 238}U, which is largely present in the fuel, or from γ-induced fission from neutron capture in the construction material. A first experiment campaign on prompt γ-ray emission from fast-neutron-induced fission on {sup 235,238}U was successfully performed in order to test our assumptions. In the following we attempt to summarize, what has been done in the field to date, and to motivate future measurement campaigns exploiting dedicated neutron and photon beams as well as upcoming highly efficient detector assemblies. (orig.)
Future research program on prompt γ-ray emission in nuclear fission
International Nuclear Information System (INIS)
In recent years the measurement of prompt fission γ-ray spectra (PFGS) has gained renewed interest, after about forty years since the first comprehensive studies of the reactions 235U(nth, f), 239Pu(nth,f) and 252Cf(sf). The renaissance was initiated by requests for new values especially for γ-ray multiplicity and average total energy release per fission in neutron-induced fission of 235U and 239Pu. Both isotopes are considered the most important ones with respect to the modeling of innovative cores required for the Generation-IV reactors, the majority working with fast neutrons. During the last 5 years we have conducted a systematic study of spectral data for thermal-neutron-induced fission on 235U and 241Pu as well as for the spontaneous fission of 252Cf with unprecedented accuracy. From the new data we conclude that those reactions do not considerably contribute to the observed heat excess and suspect other reactions playing a significant role. Possible contributions may originate from fast-neutron-induced reactions on 238U, which is largely present in the fuel, or from γ-induced fission from neutron capture in the construction material. A first experiment campaign on prompt γ-ray emission from fast-neutron-induced fission on 235,238U was successfully performed in order to test our assumptions. In the following we attempt to summarize, what has been done in the field to date, and to motivate future measurement campaigns exploiting dedicated neutron and photon beams as well as upcoming highly efficient detector assemblies. (orig.)
Spontaneous Coronary Artery Dissection.
Tweet, Marysia S; Gulati, Rajiv; Hayes, Sharonne N
2016-07-01
Spontaneous coronary artery dissection is an important etiology of nonatherosclerotic acute coronary syndrome, myocardial infarction, and sudden death. Innovations in the catheterization laboratory including optical coherence tomography and intravascular ultrasound have enhanced the ability to visualize intimal disruption and intramural hematoma associated with SCAD. Formerly considered "rare," these technological advances and heightened awareness suggest that SCAD is more prevalent than prior estimates. SCAD is associated with female sex, young age, extreme emotional stress, or extreme exertion, pregnancy, and fibromuscular dysplasia. The clinical characteristics and management strategies of SCAD patients are different than for atherosclerotic heart disease and deserve specific consideration. This review will highlight recent discoveries about SCAD as well as describe current efforts to elucidate remaining gaps in knowledge. PMID:27216840
Spontaneous wave packet reduction
International Nuclear Information System (INIS)
There are taken into account the main conceptual difficulties met by standard quantum mechanics in dealing with physical processes involving macroscopic system. It is stressed how J.A.Wheeler's remarks and lucid analysis have been relevant to pinpoint and to bring to its extreme consequences the puzzling aspects of quantum phenomena. It is shown how the recently proposed models of spontaneous dynamical reduction represent a consistent way to overcome the conceptual difficulties of the standard theory. Obviously, many nontrivial problems remain open, the first and more relevant one being that of generalizing the model theories considered to the relativistic case. This is the challenge of the dynamical reduction program. 43 refs, 2 figs
Nuclear Dissipation from Fission Time
Energy Technology Data Exchange (ETDEWEB)
Gontchar, I.; Morjean, M.; Basnary, S. [GANIL DSM/CEA, IN2P3/CNRS, BP 5027, 14076 Caen Cedex 5 (France)
2000-04-21
Fission times, pre-scission neutron multiplicities and GDR pre-scission {gamma}-ray multiplicities measured for uranium or thorium nuclei formed with temperatures T {approx} 1.8 MeV have been compared with calculations performed with CDSM2, a two-dimensional dynamical model combined with a statistical one. Among the three experimental approaches considered, fission times give access to the most precise pieces of information on nuclear dissipation at high excitation energy. For the temperature range under consideration, an agreement between the model and data is achieved if one-body dissipation is used with a strength factor k{sub red} {approx} 0.45 {+-} 0.10 applied to the wall term for the mononuclear configuration. (authors)
Spontaneous ovarian hyperstimulation syndrome.
Kasum, Miro; Oresković, Slavko; Jezek, Davor
2013-06-01
Spontaneous forms of the ovarian hyperstimulation syndrome (sOHSS) are nearly always reported between 8 and 14 weeks of pregnancy and also with follicle-stimulating hormone (FSH) producing pituitary adenoma. The syndrome has been previously reported in rare instances of increased production of human chorionic gonadotrophin (hCG) such as multiple pregnancies, hydatiforme mole, polycystic ovary disease and elevated concentrations of thyroid-stimulating hormone (TSH) in hypothyreoidism. High levels of these hormones are able to stimulate by natural promiscuous activation the wild-type FSHr, resulting in sporadic presentations of the syndrome. Since 2003, only six different activating FSHr gene mutations have been reported in cases of familial or habitual sOHSS. In addition to five mutations which have been found in the transmembrane helices (Asp567Asn, Asp567Gly, Thr449Ile, Thr449Ala, Ile545Thr), the first germline mutation (c.383C > A, p. Ser 128 Tyr) in the extracelullar domain was identified. All five mutants were abnormally activated by TSH and normal levels of hCG while displaying constitutive activity. In contrast to these mutations, the p.Ser128Tyr mutant displayed an increase in sensitivity only toward hCG. Accordingly, the mutated FSHrs, may be hyperstimulated by the pregnancy-derived hCG or TSH, inducing the occurrence of the syndrome. In the differential diagnosis, malignancy, pregnancy luteoma and hyperreactio luteinalis would have to be excluded. In almost all of the cases the disease regresses spontaneously and could be managed expectantly or conservatively, but with termination of pregnancy or surgery in cases of complications. PMID:23941020
Fission product yields from 22 MeV neutron-induced fission of 235U
International Nuclear Information System (INIS)
The chain yields of 28 product nuclides were determined for the fission of 235U induced by 22 MeV neutrons for the first time. Absolute fission rate was monitored with a double-fission chamber. Fission product activities were measured by HPGe γ-ray spectrometry. Time of flight technique was used to measure the neutron spectrum in order to estimate fission events induced by break-up neutrons and scattering neutrons. A mass distribution curve was obtained and the dependence of fission yield on neutron energy is discussed
Fission product yields from 19.1 MeV neutron induced fission of 238U
International Nuclear Information System (INIS)
36 chain yields were determined for the fission of 238U induced by 19.1 MeV neutrons for the first time. Absolute fission rate was monitored with a double-fission chamber. Fission product activities were measured by HPGe γ-ray spectrometry. Threshold detector method was used to measure the neutron spectrum in order to estimate the fission events induced by break-up neutrons and scattering neutrons. A mass distribution curve was obtained and the dependence of fission yield on neutron energy was discussed
Fission Data and Nuclear Technology
International Nuclear Information System (INIS)
Accurate nuclear data for fissile nuclei are required not only by reactor designers, but also by reactor physicists for the interpretation of integral experiments, e.g. studies of the change of reactivity with irradiation. Some of the requests that have been made for such fission data, and the reasons behind them, are discussed, along with the progress that has been made towards their fulfilment. An attempt is made to outline those areas where better data are required. (author)
The VERDI fission fragment spectrometer
International Nuclear Information System (INIS)
The VERDI time-of-flight spectrometer is dedicated to measurements of fission product yields and of prompt neutron emission data. Pre-neutron fission-fragment masses will be determined by the double time-of-flight (TOF) technique. For this purpose an excellent time resolution is required. The time of flight of the fragments will be measured by electrostatic mirrors located near the target and the time signal coming from silicon detectors located at 50 cm on both sides of the target. This configuration, where the stop detector will provide us simultaneously with the kinetic energy of the fragment and timing information, significantly limits energy straggling in comparison to legacy experimental setup where a thin foil was usually used as a stop detector. In order to improve timing resolution, neutron transmutation doped silicon will be used. The high resistivity homogeneity of this material should significantly improve resolution in comparison to standard silicon detectors. Post-neutron fission fragment masses are obtained form the time-of-flight and the energy signal in the silicon detector. As an intermediary step a diamond detector will also be used as start detector located very close to the target. Previous tests have shown that poly-crystalline chemical vapour deposition (pCVD) diamonds provides a coincidence time resolution of 150 ps not allowing complete separation between very low-energy fission fragments, alpha particles and noise. New results from using artificial single-crystal diamonds (sCVD) show similar time resolution as from pCVD diamonds but also sufficiently good energy resolution. (authors)
The VERDI fission fragment spectrometer
Directory of Open Access Journals (Sweden)
Frégeau M.O.
2013-12-01
Full Text Available The VERDI time-of-flight spectrometer is dedicated to measurements of fission product yields and of prompt neutron emission data. Pre-neutron fission-fragment masses will be determined by the double time-of-flight (TOF technique. For this purpose an excellent time resolution is required. The time of flight of the fragments will be measured by electrostatic mirrors located near the target and the time signal coming from silicon detectors located at 50 cm on both sides of the target. This configuration, where the stop detector will provide us simultaneously with the kinetic energy of the fragment and timing information, significantly limits energy straggling in comparison to legacy experimental setup where a thin foil was usually used as a stop detector. In order to improve timing resolution, neutron transmutation doped silicon will be used. The high resistivity homogeneity of this material should significantly improve resolution in comparison to standard silicon detectors. Post-neutron fission fragment masses are obtained form the time-of-flight and the energy signal in the silicon detector. As an intermediary step a diamond detector will also be used as start detector located very close to the target. Previous tests have shown that poly-crystalline chemical vapour deposition (pCVD diamonds provides a coincidence time resolution of 150 ps not allowing complete separation between very low-energy fission fragments, alpha particles and noise. New results from using artificial single-crystal diamonds (sCVD show similar time resolution as from pCVD diamonds but also sufficiently good energy resolution.
Sexual differentiation in fission yeast
DEFF Research Database (Denmark)
Egel, R; Nielsen, O; Weilguny, D;
1990-01-01
The regulation of sexual reproduction in yeast constitutes the highest level of differentiation observed in these unicellular organisms. The various ramifications of this system involve DNA rearrangement, transcriptional control, post-translational modification (such as protein phosphorylation) a......) and receptor/signal processing. A few basic similarities are common to both fission and budding yeasts. The wiring of the regulatory circuitry, however, varies considerably between these divergent yeast groups....
Experimental techniques for fission data measurements
International Nuclear Information System (INIS)
Progresses in the development of experimental techniques or fission data measurements are reviewed briefly. This review comprises techniques for the preparation of special compound nuclei leading to fission (fission entrance) as well as experimental techniques which permit the measurement of the diversified characteristics of the emitted radiations in fission (fission exit). The latter developments are only considered when also other parameters than yield, mass, and energy of fission fragments are determined. Ionization chambers developed at CBNM are described in more detail. A simple ionization chamber with Frisch grid was used to determine fission layer characteristics, e.g. the number of fissile nuclei of a sample with an accuracy of smaller than 0.3 %. A twin ionization chamber is described which has an advantageous 2 x 2π solid angle for fission fragment detection, a timing jitter of less than 0.7 ns, an energy resolution of smaller than 500 keV for fission fragments, and an angular resolution of ΔcosΘ < 0.005. Also the nuclear charge distribution of the fragments can be determined. A pulse pile-up rejection circuit was developed, which reduces pulse pile-up by more than a factor 30. This detector is well suited for correlation measurements between fission fragment parameters, like mass and total kinetic energy, and the characteristics of the different radiations emitted from the fragments. This type of ionization chamber was successfully used in several experiments and some results are shown to demonstrate its capabilities. (author)
Sensitivity of Makrofol fission track detectors
International Nuclear Information System (INIS)
Neutron fluence can be determined by means of fission track detectors consisting of fission foils in contact with suitable dielectrics (Makrofol E plastic was used in this case). Fission fragments emitted from the fissionable material into the plastic sheet generate permanent damage trails which can be made visible by an etching process. These tracks are then counted by means of an optical microscope or other methods and the number of tracks is proportional to the neutron fluence. The efficiency is defined as the ration of the number of tracks counted to the number of fissions in the fissionable layer. It is calculated from the mean range of the fission products in the fissionable material and in the plastic. The loss of very flat tracks with a small penetration angle caused by etching a certain bulk layer from the plastic foil is also taken into account. The formulas for the efficiency are deduced for thin fission layers and for thick fission foils. These calculations are made on the basis of the experimentally confirmed assumption that the ratio V of the track etching rate to the bulk etching rate is at least equal to 200. These high values for this ratio V are valid if an adequate period (several days) of oxygen influence to the damage trails is guaranteed. The calculated values of the efficiency are compared with experimental values and the uncertainty is discussed. (orig./HP)
Technical Application of Nuclear Fission
Denschlag, J. O.
The chapter is devoted to the practical application of the fission process, mainly in nuclear reactors. After a historical discussion covering the natural reactors at Oklo and the first attempts to build artificial reactors, the fundamental principles of chain reactions are discussed. In this context chain reactions with fast and thermal neutrons are covered as well as the process of neutron moderation. Criticality concepts (fission factor η, criticality factor k) are discussed as well as reactor kinetics and the role of delayed neutrons. Examples of specific nuclear reactor types are presented briefly: research reactors (TRIGA and ILL High Flux Reactor), and some reactor types used to drive nuclear power stations (pressurized water reactor [PWR], boiling water reactor [BWR], Reaktor Bolshoi Moshchnosti Kanalny [RBMK], fast breeder reactor [FBR]). The new concept of the accelerator-driven systems (ADS) is presented. The principle of fission weapons is outlined. Finally, the nuclear fuel cycle is briefly covered from mining, chemical isolation of the fuel and preparation of the fuel elements to reprocessing the spent fuel and conditioning for deposit in a final repository.
The discovery of uranium fission
International Nuclear Information System (INIS)
Uranium was discovered 200 years ago. Its radioactive character was first demonstrated in 1896 and two years later radium was extracted from uranium minerals. In 1911 studies with alpha rays from radioactive decay led to the unexpected discovery of the atomic nucleus. Exposure of beryllium to alpha rays yielded neutrons, first detected in 1932. Starting in 1934, neutron irradiation of uranium produced radioactive substances erroneously attributed to transuranium elements but with confusing properties. Painstaking experiments by chemists left no doubt on 17 December 1938 that barium was produced by these irradiations: the neutrons had split some uranium nuclei. The physics of the fission process was understood two weeks later; after a few months, neutron multiplication was found to be probable. This review deals with the eminent scientists involved, their successes, errors and disappointments, and the unexpected insights which occurred on the paths and detours of scientific research. It is, therefore, instructive also to discuss how fission was not discovered. The momentous discovery must be considered inevitable; the great tragedy was that Germany started World War II just at the time when the possibility of nuclear chain reactions and bombs became known. The consequences and anxieties that remain after 50 years of nuclear fission demand that mankind act with reason and conscience to maintain peace. (author)
Fission fusion hybrids- recent progress
Kotschenreuther, M.; Valanju, P.; Mahajan, S.; Covele, B.
2012-03-01
Fission-fusion hybrids enjoy unique advantages for addressing long standing societal acceptability issues of nuclear fission power, and can do this at a much lower level of technical development than a competitive fusion power plant- so it could be a nearer term application. For waste incineration, hybrids can burn intransigent transuranic residues (with the long lived biohazard) from light water reactors (LWRs) with far fewer hybrid reactors than a comparable system within the realm of fission alone. For fuel production, hybrids can produce fuel for ˜4 times as many LWRs with NO fuel reprocessing. For both waste incineration or fuel production, the most severe kind of nuclear accident- runaway criticality- can be excluded, unlike either fast reactors or typical accelerator based reactors. The proliferation risks for hybrid fuel production are, we strongly believe, far less than any other fuel production method, including today's gas centrifuges. US Thorium reserves could supply the entire US electricity supply for centuries. The centerpiece of the fuel cycle is a high power density Compact Fusion Neutron Source (major+minor radius ˜ 2.5-3.5 m), which is made feasible by the super-X divertor.
Pregnancy outcome following spontaneous abortions
Directory of Open Access Journals (Sweden)
Swati Agrawal
2015-12-01
Conclusions: Previous history of spontaneous abortion is associated with adverse pregnancy outcome. There is increased risk of abortion, preterm delivery, need for caesarean sections and fetal loss in cases of previous spontaneous abortions. These complications and fetal loss can be reduced by booking the patients and giving due antenatal care. [Int J Reprod Contracept Obstet Gynecol 2015; 4(6.000: 1891-1893
Montoya, Modesto
2014-01-01
This work is focused on even-odd effects on the minimal total fragment excitation energy in thermal neutron induced fission of 233U and 235U as well as in spontaneous fission of 252Cf. In a scission model, taking into account the fragment deformation properties and Coulomb interaction between fragments, the expression of the difference between Q-values referred to even/even and odd/odd charge splits, respectively, on the corresponding difference between the minimal total fragment excitation e...
Montoya, Modesto
2014-01-01
This work is focused on even-odd effects on the minimal total fragment excitation energy in thermal neutron induced fission of 233U and 235U as well as in spontaneous fission of 252Cf. In a scission model, taking into account the fragment deformation properties and Coulomb interaction between fragments, the expression of the difference between Q-values referred to even/even and odd/odd charge splits, respectively, on the corresponding difference between the minimal total fragment excitation energy is studied.
Emergency Surgery for Spontaneous Hemopneumothorax
International Nuclear Information System (INIS)
Emergency management of spontaneous hemopneumothorax patients was retrospectively analysed in this study. From November 2009 to August 2012, 221 patients with spontaneous pneumothorax were treated in the thoracic surgery clinic. Among them, 9 (4.07%) were diagnosed with spontaneous hemopneumothorax. Chest X-ray and computed tomography were the diagnostic tools. Emergency thoracotomy was performed for 7 of 9 patients because of massive hemothorax and continuous bleeding from the chest tube. Massive hematoma was documented in 2 of 7 patients at tomography. Bridging veins and torn pleural adhesion between parietal and visceral pleura were the source of bleeding determined at thoracotomy. Hematoma evacuation, resection of bullae, ligation of pleural adhesions and apical pleurectomy were performed. Spontaneous hemopneumothorax is an emergency due to massive hemorrhage and hematoma formation. Early surgical treatment is recommended for patients with spontaneous hemopneumothorax. (author)
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.
Radiochemical studies on nuclear fission at Trombay
Indian Academy of Sciences (India)
Asok Goswami
2015-08-01
Since the discovery of nuclear fission in the year 1939, both physical and radiochemical techniques have been adopted for the study of various aspects of the phenomenon. Due to the ability to separate individual elements from a complex reaction mixture with a high degree of sensitivity and selectivity, a chemist plays a significant role in the measurements of mass, charge, kinetic energy, angular momentum and angular distribution of fission products in various fissioning systems. At Trombay, a small group of radiochemists initiated the work on radiochemical studies of mass distribution in the early sixties. Since then, radiochemical investigations on various fission observables have been carried out at Trombay in , , and heavy-ion-induced fissions. An attempt has been made to highlight the important findings of such studies in this paper, with an emphasis on medium energy and heavy-ion-induced fission.
International conference on fifty years research in nuclear fission
International Nuclear Information System (INIS)
These proceedings contain extended abstracts of the papers presented at the named conference. They deal with static properties of fission, instrumentation for fission studies, fission in compound-nucleus reactions, fission dynamics, fission-like heavy ion reactions, and fusion reactions. See hints under the relevant topics. (HSI)
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 ...
Clement, J. D.
1973-01-01
Different types of nuclear fission reactors and fissionable materials are compared. Special emphasis is placed upon the environmental impact of such reactors. Graphs and charts comparing reactor facilities in the U. S. are presented.
Mechanisms of Mitochondrial Fission and Fusion
van der Bliek, Alexander M.; Shen, Qinfang; Kawajiri, Sumihiro
2013-01-01
Mitochondria continually change shape through the combined actions of fission, fusion, and movement along cytoskeletal tracks. The lengths of mitochondria and the degree to which they form closed networks are determined by the balance between fission and fusion rates. These rates are influenced by metabolic and pathogenic conditions inside mitochondria and by their cellular environment. Fission and fusion are important for growth, for mitochondrial redistribution, and for maintenance of a hea...
Measurements of Fission Cross Sections of Actinides
Wiescher, M; Cox, J; Dahlfors, M
2002-01-01
A measurement of the neutron induced fission cross sections of $^{237}$Np, $^{241},{243}$Am and of $^{245}$Cm is proposed for the n_TOF neutron beam. Two sets of fission detectors will be used: one based on PPAC counters and another based on a fast ionization chamber (FIC). A total of 5x10$^{18}$ protons are requested for the entire fission measurement campaign.
Fission product retention in HTGR fuels
International Nuclear Information System (INIS)
Retention data for gaseous and metallic fission products are presented for both Triso-coated and Biso-coated HTGR fuel particles. Performance trends are established that relate fission product retention to operating parameters, such as temperature, burnup, and neutron exposure. It is concluded that Biso-coated particles are not adequately retentive of fission gas or metallic cesium, and Triso-coated particles which retain cesium still lose silver. Design implications related to these performance trends are identified and discussed
Nuclear fission with a Langevin equation
International Nuclear Information System (INIS)
A microscopically derived Langevin equation is applied to thermally induced nuclear fission. An important memory effect is pointed out and discussed. A strong friction coefficient, estimated from microscopic quantities, tends to decrease the stationary limit of the fission rate and to increase the transient time. The calculations are performed with a collective mass depending on the collective variable and with a constant mass. Fission rates calculated at different temperatures are shown and compared with previous available results. (author) 23 refs.; 7 figs
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
Improved Calculation of Thermal Fission Energy
Ma, X. B.; Zhong, W. L.; Wang, L. Z.; Y. X. Chen; Cao, J
2012-01-01
Thermal fission energy is one of the basic parameters needed in the calculation of antineutrino flux for reactor neutrino experiments. It is useful to improve the precision of the thermal fission energy calculation for current and future reactor neutrino experiments, which are aimed at more precise determination of neutrino oscillation parameters. In this article, we give new values for thermal fission energies of some common thermal reactor fuel isotopes, with improvements on three aspects. ...
Fission of nuclei far from stability
International Nuclear Information System (INIS)
The secondary-beam facility of GSI provided the technical equipment for a new kind of fission experiment. Fission properties of short-lived neutron-deficient nuclei have been investigated in inverse kinematics. The measured element distributions reveal new kinds of systematics on shell structure and even-odd effects and lead to an improved understanding of structure effects in nuclear fission. Prospects for further experimental studies are discussed. (orig.)
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...
Fission dynamics at low excitation energy
Aritomo, Y.; Chiba, S.
2013-01-01
The origin of mass asymmetry in the fission of uranium at a low excitation energy is clarified by a trajectory analysis of the Langevin equation. The positions of the peaks in the mass distribution of fission fragments are mainly determined by fission saddle points originating from the shell correction energy. The widths of the peaks, on the other hand, result from a shape fluctuation around the scission point caused by the random force in the Langevin equation. We found that a random vibrati...
Rapid Separation of Fission Product 141La
Institute of Scientific and Technical Information of China (English)
XIA; Wen; YE; Hong-sheng; LIN; Min; CHEN; Ke-sheng; XU; Li-jun; ZHANG; Wei-dong; CHEN; Yi-zhen
2013-01-01
141La was separated and purified from fission products in this work for physical measurements aimed at improving the accuracy of its decay parameters.As the impact of 142La and other fission products,cesium(141Cs,142Cs included)was rapid separated from the fission products,141Cs and 142Ba separation was prepared after a cooling time about 25 s when 142Cs decays to daughter 142Ba,141La purification then
Theoretical description of prompt fission neutron multiplicity and spectra
Manailescu, Cristian
2014-01-01
The present work concerns two successful models used today: Point by Point (PbP) and the Monte Carlo approaches. The description of the PbP model and of the extended Los Alamos model for higher energies that takes into account the secondary chains and ways is given in Chapter II. In this chapter are given also examples of PbP and most probable fragmentation approach calculations for various quantities which characterize prompt emission: multi-parametric matrices, quantities as a function of fragment mass, quantities as a function of the TKE and total average quantities, for different spontaneous and neutron induced fissioning systems. Special care was given to the TXE partition between the fully accelerated fission fragments, two partition methods used in the PbP model being discussed in details. In Chapter III is given the description of the Monte Carlo treatment included in the FIFRELIN code. Only those aspects that differ from the PbP treatment are emphasized. A special attention is given to the latest dev...
Odd-even effects in the nuclear fission
International Nuclear Information System (INIS)
By the adopted way it succeeded without a completely free parameter to reproduce the experimental values for the odd-even effect for all those nuclei for which data were present. These are all even-charged nuclei from thorium to californium. Partly the OE-effect was studied in spontaneous fission, partly in neutron induced fission with thermal, 1.9-, and 3.0- MeV neutrons. It was shown that the calculated values depend very strongly from the one-particle model which is assumed in order to calculate the probabilities for pairing excitations. Thereby not only the steepness plays a role with which the one-particle energies cross the Fermi edge, but also the deformation velocity, and finally the remaining time until the scission point. That means that the whole procedure depends extremely from details of the one-particle model. Different one-particle models can be excluded because they contain simply too many crossings and then the OE effect tends to O. (orig./HSI)
Fission dynamics within time-dependent Hartree-Fock: boost-induced fission
Goddard, P. M.; Stevenson, P. D.; 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. Method...
Fission Product Decay Heat Calculations for Neutron Fission of 232Th
Son, P. N.; Hai, N. X.
2016-06-01
Precise information on the decay heat from fission products following times after a fission reaction is necessary for safety designs and operations of nuclear-power reactors, fuel storage, transport flasks, and for spent fuel management and processing. In this study, the timing distributions of fission products' concentrations and their integrated decay heat as function of time following a fast neutron fission reaction of 232Th were exactly calculated by the numerical method with using the DHP code.
Use of the biomodal theory in reactor crisis
International Nuclear Information System (INIS)
A model is proposed which explains distortions of perception and disruptions of analytical abilities under high stress. This is accomplished through a synthesis of three previously independent sets of observed phenomena: cognitive flexibility, behavioral conditioning, and loss of flexibility under stress. The model, the Bimodal Paradigm, identifies two distinct modes of metal operation (Actualizing and Programmed), with stress as the modifying variable in the switch to rigid (Programmed) operation. Implications are important and numerous, contradicting the interpretation of behavior under crisis as erratic, providing specific indications for operator training and selection, control-panel design, and decisional procedures in crisis
Shell Effects in Nuclear Fission
International Nuclear Information System (INIS)
The important part played by shell effects in nuclear fission has been reliably established experimentally and forms the basis of the theory of asymmetry of fission and other properties of fission fragments. However, from the theoretical point of view there are certain difficulties in understanding these effects, since at the moment of scission the fragments axe considerably deformed. When the shell effects are calculated in succession, the energy of the fissioning nucleus before scission may be presented in the form of the sum of the energies of the spherical fragments taking shell effects into account, the Coulomb interaction energy of the fragments and their deformation energy. The deformation energy of the fragments should be calculated not using the elasticity values of the fragments according to the drop model, but, for very low deformations, the single particle elasticity values taking into account the magic effects, with a gradual transition to the drop values for deformations at which the levels of neighbouring shells intersect. The single-particle elasticity values can be obtained from the experimental data on the Coulomb excitation of the nuclei. In Vandenbosch's calculations of fragment deformation, the elasticity of the fragments was based on the condition of coincidence between the deformation energy of the fragments and the experimental values for their excitation energy. However, in this case the elasticity was assumed to be constant at all deformations, and for this reason, although the elasticity values found in Vandenbosch do show magic'effects, they differ considerably in magnitude from the experimental elasticity values (see above).. The calculations of Vandenbosch also failed to take into account the magic effects for non-deformed fragments that lead to a reduction in the energy of the magic nucleus. Therefore, according to these calculations fission should be symmetrical, since the elasticity and consequently also the deformation energy (at
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...
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.
Spontaneous breaking of supersymmetry
Energy Technology Data Exchange (ETDEWEB)
Zumino, B.
1981-12-01
There has been recently a revival of interest in supersymmetric gauge theories, stimulated by the hope that supersymmetry might help in clarifying some of the questions which remain unanswered in the so called Grand Unified Theories and in particular the gauge hierarchy problem. In a Grand Unified Theory one has two widely different mass scales: the unification mass M approx. = 10/sup 15/GeV at which the unification group (e.g. SU(5)) breaks down to SU(3) x SU(2) x U(1) and the mass ..mu.. approx. = 100 GeV at which SU(2) x U(1) is broken down to the U(1) of electromagnetism. There is at present no theoretical understanding of the extreme smallness of the ratio ..mu../M of these two numbers. This is the gauge hierarchy problem. This lecture attempts to review the various mechanisms for spontaneous supersymmetry breaking in gauge theories. Most of the discussions are concerned with the tree approximation, but what is presently known about radiative correction is also reviewed.
Spontaneous bacterial peritonitis
Institute of Scientific and Technical Information of China (English)
Anastasios Koulaouzidis; Shivaram Bhat; Athar A Saeed
2009-01-01
Since its initial description in 1964, research has transformed spontaneous bacterial peritonitis (SBP) from a feared disease (with reported mortality of 90%) to a treatable complication of decompensated cirrhosis,albeit with steady prevalence and a high recurrence rate. Bacterial translocation, the key mechanism in the pathogenesis of SBP, is only possible because of the concurrent failure of defensive mechanisms in cirrhosis.Variants of SBP should be treated. Leucocyte esterase reagent strips have managed to shorten the 'tap-toshot' time, while future studies should look into their combined use with ascitic fluid pH. Third generation cephalosporins are the antibiotic of choice because they have a number of advantages. Renal dysfunction has been shown to be an independent predictor of mortality in patients with SBP. Albumin is felt to reduce the risk of renal impairment by improving effective intravascular volume, and by helping to bind proinflammatory molecules. Following a single episode of SBP, patients should have long-term antibiotic prophylaxis and be considered for liver transplantation.
[Lazarus phenomenon: spontaneous resuscitation].
Casielles García, J L; González Latorre, M V; Fernández Amigo, N; Guerra Vélz, A; Cotta Galán, M; Bravo Capaz, E; de las Mulas Béjar, M
2004-01-01
A 94-year-old woman undergoing surgery for simple repair of a duodenal perforation experienced a sudden massive hemorrhage (1500 mL) when the duodenum was separated from adjacent structures. Hemodynamic stability was re-established when fluids were replaced. After the abdominal wall was closed, increased amplitude of the QRS wave was observed and heart rate slowed until there was no pulse. Electromechanical dissociation (EMD) was diagnosed and cardiopulmonary resuscitation was started. When EMD persisted after 40 minutes, resuscitative measures were stopped and the ventilator was disconnected, though orotracheal intubation and arterial and electrocardiographic monitoring were maintained. After 2 or 3 minutes, heart rhythm restarted spontaneously and arterial pressure waves reappeared on the monitor. The patient progressed well for 72 hours, after which she developed septic shock and multiorgan failure, dying 18 days later. The Lazarus phenomenon may be more common than the medical literature would indicate, possibly because a large gap in our understanding of the pathophysiology of the phenomenon underlies anecdotes about "miracles". As we wait for adequate international consensus on a protocol for monitoring the withdrawal of resuscitative measures, we should act prudently before definitively certifying death. The case we report occurred during a surgical intervention in which the patient had received general anesthesia. We believe that the causes that might explain the Lazarus phenomenon are quite different in that context than they would be in a nonsurgical setting, such that it would be useful to create a national database to keep a record of such intraoperative events. PMID:15495638
Spontaneous subgaleal aerocele.
Ibe, M O N; Onu, D O; Igwe, N N
2014-01-01
Apart from reporting about a case of spontaneous subgaleal aerocele this paper looks at the possible causes and management also. A 35-year-old Igbo-Nigerian female, about 4 weeks post-natal, with a 10-month old steadily and gradually enlarging mass around the back of her head, including both temporal regions was referred to us. Plain skull radiographs showed air in this mass. Needle puncture produced air leading to immediate and complete flattening of the lesion. A few hours after this procedure while still in the hospital premises, she had generalized convulsions, for which she was hospitalized and treated. With no further attacks, her request for discharge the following day was granted. At the next visit, 7 days later, there was a re-accumulation, which was treated the same way as previously and with the same result. She has not reported back since then, though she was advised to visit us again in 7 day-time. This lesion should be considered when masses on the head are presented. Our health institutions should have adequate investigative facilities. PMID:24553041
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
International Nuclear Information System (INIS)
The main results of studying the properties of “instantaneous” neutrons and γ photons during the fission of 233,235U(nth, f) and 239Pu(nth, f) nuclei and spontaneous fission of 252Cf, which were performed on the WWR-M reactor at the St. Petersburg Nuclear Physics Institute, Russian Academy of Sciences, are presented. Along with obtaining the main characteristics of the instantaneous radiation from fission fragments, these studies were also aimed at gaining deeper insight into such exotic processes as the emission of break neutrons and γ photons from a fissioning nucleus near the break point. These investigations were performed on different experimental setups using different analytical methods. This approach allowed us not only to find but also to reduce to minimum possible systematic effects. The yields of break neutrons were found to be about (5–7) × 10−2 of the total number of neutrons per 233,235U(n, f) fission event and approximately twice as much for 239Pu(n, f) and 252Cf. The coefficient of T-odd asymmetry for γ photons is in agreement with the estimate obtained on the assumption that the observed effect is mainly related to the γ photons emitted by excited fragments with highly oriented angular momenta. This fact gave grounds to conclude that the desired break γ photons cannot be reliably selected (within the obtained experimental accuracy) against the much larger background of γ photons from fission fragments.
Process of spontaneous combustion of solid fuels
Energy Technology Data Exchange (ETDEWEB)
Postrzednik, S.; Bialecki, R.; Nowak, A. (Politechnika Slaska, Gliwice (Poland))
1988-01-01
Reviews literature on coal spontaneous combustion and oxidation. The following aspects are discussed: low-temperature oxidation, medium and high-temperature oxidation, theories of spontaneous coal combustion (bacteria theory, phenol theory, water-coal system theory, water adsorption theory), factors that influence spontaneous combustion (coal rank, petrology, porosity, moisture content, storage method, storage temperature, air circulation, macrostructure and geometry of the system for storage of coal), effects of mineral content on coal hazards of spontaneous combustion, physicochemical phenomena that influence spontaneous combustion, laboratory investigations into spontaneous combustion, experimental methods used in laboratory investigations, forecasting energy effects of spontaneous combustion, mathematical models of coal spontaneous combustion. 94 refs.
Stochastic resonance in nuclear fission
International Nuclear Information System (INIS)
Fission decay of highly excited periodically driven compound nuclei is considered in the framework of Langevin approach. We used residual-time distribution (RTD) as a tool for studying the dynamic features in the presence of periodic perturbation. The structure of RTD essentially depends on the relation between Kramers decay rate and the frequency ω of periodic perturbation. In particular, the intensity of the first peak in RTD has a sharp maximum at certain nuclear temperature depending on ω. This maximum should be considered as fist-hand manifestation of stochastic resonance in nuclear dynamics
Fission fragment excited laser system
McArthur, David A.; Tollefsrud, Philip B.
1976-01-01
A laser system and method for exciting lasing action in a molecular gas lasing medium which includes cooling the lasing medium to a temperature below about 150 K and injecting fission fragments through the lasing medium so as to preferentially excite low lying vibrational levels of the medium and to cause population inversions therein. The cooled gas lasing medium should have a mass areal density of about 5 .times. 10.sup.-.sup.3 grams/square centimeter, relaxation times of greater than 50 microseconds, and a broad range of excitable vibrational levels which are excitable by molecular collisions.
Spectroscopy of heavy fissionable nuclei
Indian Academy of Sciences (India)
S K Tandel
2015-09-01
Structural studies of heavy nuclei are quite challenging due to increased competition from fission, particularly at high spins. Nuclei in the actinide region exhibit a variety of interesting phenomena. Recent advances in instrumentation and analysis techniques have made feasible sensitive measurements of nuclei populated with quite low cross-sections. These include isomers and rotational band structures in isotopes of Pu ( = 94) to Rf ( = 104), and octupole correlations in the Th ( = 90) region. The obtained experimental data have provided insights on various aspects like moments of inertia and nucleon alignments at high spins, quasiparticle energies and evolution of quadrupole and octupole collectivity, among others. An overview of some of these results is presented.
A definition of scission points and consequences on some fission distributions
International Nuclear Information System (INIS)
A quantitative definition of scission points occurring in a fission process at low energy (spontaneous or induced by low-energy neutron, γ, charged particle) is proposed. It is based on the concept of a negligible nuclear mutual energy versus its Coulomb counterpart. Practical ways by which one may approximately, albeit mostly in a microscopic fashion (Skyrme-Hartree-Fock-BCS), calculate the total energy at scission and their mutual energy parts is presented in a limited yet relevant collective variable space. For a given fragmentation, we present some modeling of the probability for the fissioning system to lie at a given point in the fragment deformation space. From this probability, one deduces the distributions of total fragment-deformation, excitation or Coulomb energies for a given couple of fragments. To yield these distributions some approximations are made and discussed on the sharing of the energy gained in the descent towards scission between kinetic and excitation energies. Some calculational results using the Skyrme effective interaction and related to the spontaneous fission of the Cf252 nucleus are shown for given fragmentations. Calculated in the orientation-pumping mechanism alone, the average fragment spins are found to be compatible with the available experimental data. (authors)
Effect of inertia parameters on static fission path
International Nuclear Information System (INIS)
Properties of static (minimum potential) fission path in the formalism of Hofmann are investigated. It is pointed out that the inertial parameters greatly affect the fission path and hence the penetrability. The difficulty of determining fission path is discussed
Absolute Energy Calibration of Solid-State Detectors for Fission Fragments and Heavy Ions
International Nuclear Information System (INIS)
Detailed measurements of the pulse-height response of silicon solid-state detectors to energetic heavy ions and fission fragments have been made. These studies have now led to a reliable method of absolute energy calibration of solid-state detectors for fission fragments, as well as to a better understanding of the somewhat peculiar response characteristics of the detectors to fission fragments and heavy ions. The use of silicon solid-state detectors in fragment kinetic energy measurements in recent years has been widespread; at the same time, questions have been raised about the detailed interpretation of such measurements because of the increasing evidence for anomalous behaviour in charge production, charge collection and charge multiplication in the case of densely ionizing particles. The present report discusses systematics and possible origins of these effects. Application of the absolute energy calibration method, which takes into account the mass and energy dependence of the response, is based simply on a Cf252 or U235 fragment pulse- height spectrum. Our studies were carried out with mono-energetic Br71, Br81 and I127 ions of energies from 30 to 120 MeV, and with fission fragments from spontaneous fission of Cf252 and neutron-induced fission of U235 and Pu239. It is shown that for a given fragment mass, over a wide energy range, the fragment energy versus pulse-height relationship is of the form E = ax + b, where E is the fragment energy and x is the measured pulse height. A dependence of pulse height on fragment mass has also been established, which leads to an energy versus pulse-height relationship, for the range of fission-fragment masses and energies, of the form E = (a + a'm)x + b + b'M, where M is the fragment mass. The effect of detector window and of detector type, resistivity and electric field have been studied. Guides to the selection of detectors and to their use with fission fragments are given. The effect of the more exact calibration