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.
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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.
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
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.
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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.
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
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
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.
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.
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.
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)
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
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
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
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
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%
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
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
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.
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.
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
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)
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
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.
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.
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...
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
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
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
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
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
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)
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...
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
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
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
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
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.
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.
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 ...
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)
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
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
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.
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
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
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...
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
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
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
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.
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...
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
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
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
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
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
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
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
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
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
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
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
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
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
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.)
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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.
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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)
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
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
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
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)
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
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
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
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
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
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?
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
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
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.
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)
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
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
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
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.
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
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
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
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
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
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)