Energy Distribution Of Fission Fragments Research Articles

Prompt-fission observable and fission yield calculations for actinides by TALYS

The nuclear reaction code TALYS adopts the Hauser-Feshbach statistical decay theory, to de-excite fission fragments. This involves for instance the evaporation of prompt fission neutrons and γ-rays. TALYS incorporates databases of primary fission fragment distribution which consists of primary fission fragment yield and data for excitation energy distribution of fission fragments. We conducted a sensitivity study on three parameters in TALYS and fitted them in order to reproduce experimental and evaluated data, in thermal neutron-induced fission of 235U. Moreover, we demonstrate a large-scale calculation of average prompt neutron and γ-ray multiplicities for 243 selected actinide isotopes.

SHELL EFFECTS IN THE FISSION OF <sup>236</sup>U* NUCLEI, FORMED IN THE REACTION <sup>232</sup>Th(α,f) AT INCIDENT ALPHA PARTICLES ENERGY OF 29 MeV

Mass and energy distribution of fission fragments of 236U* nuclei, formed in the reaction 232Th(α,f) at incident alpha energy of 29 MeV were studied to reveal the influence of shell effects. The experiment was carried out by 2E method at U-150M accelerator at Institute of Nuclear Physics, Almaty city. Acquired experimental data was decomposed into yields of separate shells, including deformed shells, assuming that the shell yield has the form of gauss distribution. The manifestation of deformed shells N84, Z52 and deformed shells Z36, Z38 was revealed.

Fission dynamics of excited compound nuclei in a wide range of fissile parameters produced in O16,18+X reactions within a stochastic approach

A stochastic approach based on four-dimensional Langevin equations has been used to simulate the fission dynamics of the excited compound nuclei $^{256}\mathrm{Fm}, ^{254}\mathrm{Fm}, ^{224}\mathrm{Th}, ^{215}\mathrm{Fr}, ^{213}\mathrm{Fr}, ^{200}\mathrm{Pb}, ^{187}\mathrm{Ir}, ^{172}\mathrm{Yb}, ^{170}\mathrm{Yb}, ^{162}\mathrm{Yb}, ^{142}\mathrm{Ce}$, and $^{125}\mathrm{Cs}$ produced in ${}^{16,18}\mathrm{O}+X$ reactions with projectile energies 158.8 and 288 MeV. The effect of nuclear dissipation was investigated in the dynamical simulation of fission process of these nuclei. The average prescission neutron multiplicity, the fission time, the average total kinetic energy of fission fragments, the mass and energy distribution of fission fragments, and the variation of the prescission neutron multiplicity with total kinetic energy of fission fragments have been calculated for these nuclei. The dynamical calculations have taken into account not only three shape collective coordinates introduced on the basis of the ``funny hills'' shape parameters but also orientation degree of freedom (spin about the symmetry axis), and in the dynamical calculations dissipation generated through the chaos-weighted wall and window friction formula and also the sum of the chaos-weighted wall and window friction formula with the two-body nuclear friction. Furthermore, the effect of dissipation coefficient of $K, {\ensuremath{\gamma}}_{K}$, were also considered in the dynamical calculations. Comparison of the theoretical results with the experimental data shows that the experimental data for compound nuclei produced with the projectile energy 158.8 MeV can be reproduced satisfactorily with the results of calculations by using the chaos-weighted wall and window friction formula, although the results of calculations of the average prescission neutron multiplicity, the fission time, and the variation of the pre-scission neutron multiplicity with total kinetic energy of fission fragments lie somewhat below the experimental data for heavy nuclei produced in reactions with projectile energy ${E}_{\mathrm{lab}}=158.8\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ and also for compound nuclei produced with the projectile energy 288 MeV. It was also shown that for reproducing experimental data for heavy nuclei produced in reactions with projectile energy ${E}_{\mathrm{lab}}=158.8\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ and also for nuclei produced with projectile energy ${E}_{\mathrm{lab}}=288\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ is suitable to use the sum of the chaos-weighted wall and window friction formula with the two-body nuclear friction in the Langevin equations. In other words, for simulations of fission dynamics of nuclei at high excitation energies and also for heavy nuclei it is suitable to use the sum of the chaos-weighted wall and window friction formula with the two-body nuclear friction in the Langevin equations.

Effects of isospin and dissipation coefficient of the K coordinate in simulation of fission dynamics of excited compound nuclei

A stochastic approach based on four-dimensional (4D) dynamical model has been used to simulate the fission process of the excited compound nuclei [Formula: see text]Fr, [Formula: see text]Fr and [Formula: see text]Fr produced in fusion reactions. Effects of isospin and dissipation coefficient of the [Formula: see text] coordinate, [Formula: see text], on estimation of the evaporation residue (ER) cross-section, the prescission neutron multiplicity, the variance of the mass and energy distributions of fission fragments and the anisotropy of fission fragments angular distribution have been investigated for the excited compound nuclei [Formula: see text]Fr, [Formula: see text]Fr and [Formula: see text]Fr. Three collective shape coordinates [Formula: see text] plus the projection of total spin of the compound nucleus to the symmetry axis, [Formula: see text], were considered in the 4D dynamical model. In the 4D dynamical model, the magnitude of the dissipation coefficient of [Formula: see text], [Formula: see text], was considered as a free parameter and its magnitude inferred by fitting measured data on the ER cross-section. Results of the extracted dissipation coefficients of [Formula: see text] for different isotopes of Fr were shown that the magnitude of the dissipation coefficient of [Formula: see text] increases with decreasing isospin of fissioning compound nucleus. It was also shown that the prescission neutron multiplicity and the anisotropy of fission fragments angular distribution increase with increasing isospin whereas the variance of the mass and energy distributions of fission fragments decrease with increasing isospin of fissioning compound nucleus. Furthermore, it was shown that the calculated values of prescission neutron multiplicity and the variance of the mass distribution of fission fragments for the excited compound nuclei [Formula: see text]Fr, [Formula: see text]Fr and [Formula: see text]Fr decrease with the dissipation strength of [Formula: see text], whereas the variance of the energy distribution of fission fragments and the anisotropy of fission fragments angular distribution increase with the dissipation strength of [Formula: see text].

Measurement of mass and total kinetic energy distribution of fission fragments using newly developed compact MWPC detectors

Two large area (12.5 cm × 7.5 cm) position sensitive compact multiwire proportional counter detectors have been developed for the study of fission reactions for bombarding energies near the Coulomb barrier. Each detector provides one negative fast signal (anode signal) which is used for the time of flight measurement, in addition to four position signals. The timing signal from anode and delayed timing signal from position frames are processed through non-inverting and inverting fast preamplifiers developed in-house. These preamplifiers are based on monolithic microwave integrated circuits. The position resolutions were measured using a mask made of aluminium. The X and Y-position resolutions were found to be ≈ 1.3 and 1.4 mm respectively. The time spread obtained from the sum spectra of position signals extracted from both the ends of the same position frame, was ≈ 1.6 ns. The detectors were used successfully in an in-beam experiment to detect the fission fragments in the 19F+238U reaction. The time correlation spectra between two anode signals provide clean identification of fission events. Difference of those recorded time was used to measure the mass distribution and hence the total kinetic energy distribution of the fission fragments.

Fully microscopic scission-point model to predict fission fragment observables

We present an upgraded version of the SPY model, called SPY2 for version 2 of the scission point yield, to estimate mainly the yields and the kinetic energy distributions of fission fragments: The theoretical framework is similar to our previous version, i.e., a statistical scission point model, but this version is based on fully microscopic nuclear ingredients describing the fragments properties at the scission point. These include the static properties of some 7000 nuclei at 120 axial quadrupole deformations, such as binding energies, proton densities, single-particle level schemes, and states densities, coherently calculated within the constrained Hartree-Fock-Bogoliubov model on the basis of the Skyrme BSk27 interaction. The use of microscopic ingredients has been extended to the proton density distribution and the nuclear states densities. Considering realistic proton densities of fragments allows us to improve the definition of the scission point as well as the prediction of the kinetic energy distribution and to link the kinetic energy to the diffuseness of the fragments' proton density. New microscopic nuclear states densities improve the general coherence of the model, in particular regarding the inclusion of the odd-even pairing effect. In this updated SPY2 version, the calculation of the fission yields and kinetic energy distributions is significantly improved and found to be in relatively good agreement with experiments, at least qualitatively. A detailed study is performed for three well known fissioning systems, namely, thermal neutron induced fission of $^{235}\mathrm{U}$ and $^{239}\mathrm{Pu}$ and spontaneous fission of $^{252}\mathrm{Cf}$. A systematic analysis of the fission mode as well as mean fragments deformation and total kinetic energies has been performed for some 2000 fissioning nuclei with $78\ensuremath{\le}Z\ensuremath{\le}110$ lying between the proton and neutron drip lines.

Study of mass yield and kinetic energy distribution of fission fragments from fission of the excited compound nucleus 254Fm produced in fusion reaction

A stochastic approach based on four-dimensional Langevin fission dynamics has been used to calculate the anisotropy of fission fragment angular distribution, the mass and energy distribution of fission fragments, the yield and variance of the mass distribution of fission fragments, the fission cross section and the pre-scission neutron multiplicity for the compound nucleus 254Fm produced in the reaction 16O + 238U. In the dynamical calculations dissipation coefficient of K , \( \gamma_k\) , was considered as a free parameter and its magnitude inferred by fitting measured data on the anisotropy of fission fragments angular distribution. It was shown that the results of the anisotropy of fission fragments angular distribution for the compound nucleus 254Fm are in good agreement with the experimental data by using values of dissipation coefficient of K, equal to \(\gamma_{k}=(0.076-0.088)\) (MeV zs)-1/2. We also calculated the above-mentioned experimental data for the compound nucleus 254Fm by using \(\gamma_{k}=(0.076-0.088)\) (MeV zs)-1/2 and results of the calculations compared with the experimental data. A comparison of the theoretical results with the experimental data showed that the results of calculations are in good agreement with the experimental data, although at high energy the difference between the results of calculations with the experimental data for the variance of the mass distribution of fission fragments and the pre-scission neutron multiplicity is slightly high. It was also shown that at high energy the variance of the mass distribution of fission fragments and the pre-scission neutron multiplicity can be reproduced for the compound nucleus 254Fm by using values of dissipation coefficient of K equal to \(\gamma_{k}=0.098\) (MeV zs)-1/2 and \(\gamma_{k}=0.065\) (MeV zs)-1/2, respectively.

Searching for the Superasymmetric Fission Mode of 248Cf, 254Fm, and 260No in Reactions 22Ne + 232Th, 238U; 16O + 232Th, 238U

The mass and energy distributions of fission fragments in reactions 16O + 232Th, 16O + 238U, 22Ne + 232Th, and 22Ne + 238U are measured to investigate the role of closed proton and neutron shells in the fission of 248Cf, 254Fm, and 260No nuclei at excitation energies of 40–45 MeV. Experiments are performed on the U-400 cyclotron at the Flerov Laboratory of Nuclear Reactions (Dubna, Russia) using the CORSET double-arm time-of-flight spectrometer. For compound nucleus 260No* formed in the reaction 22Ne + 238U, an increase in the fragment yields is observed in the superasymmetric mass region 52/208 amu, which corresponds to the formation of fissioning pairs of two double-magic nuclei, 48Ca and 208Pb. Superasymmetric fission at a mass yield level of 10−5 was not observed for compound nuclei 248Cf and 254Fm* formed in reactions 16O + 232Th, 16O + 238U, and 22Ne + 232Th at an initial excitation energy of 40−45 MeV. Bimodal fission was observed for the 260No*compound nucleus at an initial excitation energy of 41 MeV. In the symmetric mass split, both fission fragments are in this case close to double-magic 132Sn.

Fission fragments and primary electrons’ energy distribution in helium-3 plasma irradiated by neutron flux

Boltzmann kinetic equations governing energy spectra distribution of fast particles in nuclear inducedplasma are defined and presented for continuous fissionable plasma interacting with neutrons.The formation of electrons energy distribution crucially depends on energy distribution of fissionfragments and cannot be treated separately and their distributions self consistently affect on electronsenergy spectra time evolution and their degradation in space. So the self-consistent system of Boltzmannkinetic equations for both electrons and fission fragments are proposed and discussed for helium-3plasma. Primary electrons spectra analytical expressions are derived and the first order approximationpresented on the assumption that energy spectra of protons and tritium nuclei have monochromatic energyspectra created by helium-3 fissioning in neutron flux. Any gas irradiated by highly energetic particlesdemonstrates its modified chemical abilities as well as a great variety of energy transformation channelsincluding the selection of some definite chemical reactions leading to innovative transformation intechnology [1-5]

Theoretical study of different features of the fission process of excited nuclei in the framework of the modified statistical model and four-dimensional dynamical model

Evaporation residue cross section, fission probability, anisotropy of fission fragment angular distribution, mass and energy distributions of fission fragments and the pre-scission neutron multiplicity for the excited compound nuclei and produced in fusion reactions have been calculated in the framework of the modified statistical model and multidimensional dynamical model. In the dynamical calculations, the dynamics of fission of excited nuclei has been studied by solving three- and four-dimensional Langevin equations with dissipation generated through the chaos-weighted wall and window friction formula. Three collective shape coordinates plus the projection of total spin of the compound nucleus to the symmetry axis, were considered in the four-dimensional dynamical model. A non-constant dissipation coefficient of was applied in the four-dimensional dynamical calculations. A comparison of the results of the three- and four-dimensional dynamical models with the experimental data showed that the results of the four-dimensional dynamical model for the evaporation residue cross section, fission probability, anisotropy of fission fragment angular distribution, mass and energy distributions of fission fragments and the pre-scission neutron multiplicity are in better agreement with the experimental data. It was also shown that the modified statistical model can reproduce the above-mentioned experimental data by choosing appropriate values of the temperature coefficient of the effective potential, and the scaling factor of the fission-barrier height, .

Scission-point model predictions of fission-fragment mass and total kinetic energy distributions for 236U and 252Cf

The total deformation energy at the moment of the neck rupture for 236 U and 252 Cf is calculated using the Strutinsky's prescription and nuclear shapes described in terms of Cassinian ovals generalized by the inclusion of four additional shape parameters: α1 , α2 , α3 , and α4 . The corresponding fragment-mass distributions are estimated supposing that each point in the deformation space is occupied according to a canonical distribution. The energy distributions of fission fragments are calculated assuming the point-charge approximation for the Coulomb interaction of fission fragments. Finally, an alternative definition of the nuclear scission point configuration relying on the minimization of liquid drop energy (optimal shape method) is used. Both definitions lead, for these two nuclei, to a reasonably good agreement with the experimental data.

Fabrication and characterization of carbon-backed thin 208Pb targets

Thin carbon-backed isotopically enriched 208Pb targets were required for our experiment aimed to study the reaction dynamics for 48Ti+208Pb system, populating the near super-heavy nucleus 256Rf, through mass-energy correlation of the fission fragments. Purity and thickness of the targets are of utmost importance in such studies as these factors have strong influence on the measurement accuracy of mass and energy distribution of fission fragments. 208Pb targets with thickness ranging from 60 μg/cm2 to 250 μg/cm2 have been fabricated in high vacuum environment using physical vapor deposition method. Important points in the method are as follows:•208Pb was deposited using resistive heating method, whereas carbon (backing foil) deposition was performed by using the electron beam bombardment technique.•Different characterization techniques such as Particle Induced X-ray Emission (PIXE), Energy Dispersive X-Ray Fluorescence (EDXRF) and Rutherford Backscattering Spectrometry (RBS) were used to assert the purity and thickness of the targets.•These targets have successfully been used to accomplish our experimental objectives.

Theoretical investigation of shape parametrization’s effects on characteristics of fission fragments in 18O-induced fission of 154Sm, 197Au, 238U and 246Cm

The multi-dimensional Langevin equations are employed to investigate mass and energy distributions of fission fragments. The calculations have been performed with two different shape classes of parametrization, namely Funny Hills and Cassinian Ovaloids. It was shown that inclusion of the Funny Hills parameterizations in the dynamical model produced considerable increase in neutron multiplicity as compared with available experimental data for 18O-induced fission of 154Sm, 197Au, 238U and 246Cm. The proposed shape-dependent multi-dimensional dynamical model reproduces well experimental data for mass distribution, neutron multiplicity and average kinetic energy of fission fragments over a wide range of mass–energy regions.

Bimodal fission of Hs*

Mass and energy distributions of fission fragments obtained in the reactions 22Ne + 249Cf, 26Mg + 248Cm, and 22Ne + 238U have been measured. A special attention will be paid on the properties of mass-energy distribution of fission fragments obtained in the reaction 26Mg + 248Cm at an excitation energy of 35 MeV. At this energy shell effects should become more effective in fission, the TKE distribution of symmetric fragments obtained in the reaction 26Mg + 248Cm differs strongly from a Gaussian shape. Besides a low-energy component, a high-energy component, not foreseen in the LDM, arises. This is attributed to the fact that both fission fragments are close to the spherical neutron shell N = 82. It means that for the compound nucleus 274Hs*, formed in the reaction 26Mg + 248Cm, the phenomenon of bimodal fission was observed for the first time. For the compound nucleus 260No* formed in the reaction 22Ne + 238U at the initial excitation energy of 41 MeV the bimodal fission as well as superasymmetric fission were observed.

Study of fission dynamics of 215Fr and 213Fr produced in fusion reactions with three-dimensional Langevin equations

A stochastic approach that treats fission dynamics on the basis of three-dimensional Langevin equations was used to calculate the average pre-scission neutron multiplicities, fission probabilities, mass and energy distribution of fission fragments, and the dependences of the multiplicities of pre-scission neutrons on the masses of fission fragments and their kinetic energies for compound nuclei 213Fr and 215Fr. In these calculations, dissipation was generated through the chaos weighted wall and window friction formula. Comparison of the theoretical results with the experimental data showed that three-dimensional Langevin equations with dissipation generated through the chaos weighted wall and window friction formula make it possible to satisfactorily reproduce the experimental data.

DYNAMICAL SIMULATION OF FISSION FRAGMENTS AVERAGE KINETIC ENERGY IN HEAVY-ION FUSION–FISSION REACTIONS

Monte Carlo simulation based on the three-dimensional Langevin equations and one-body dissipation mechanism has been applied to highly excited compound nucleus to investigate the kinetic energy distribution of fission fragments. The effect of center to center distance between nascent fragments and other dynamical parameters (elongation, neck thickness and mass asymmetry) on average kinetic energy of fragments also studied. Finally, obtained results using this approach are compared with earlier theoretical and experimental data for a few typical systems.

Proton-induced fission on actinide nuclei at energies 27 and 63 MeV

Measurements of proton-induced fission on 232Th, 238U, 237Np, 239Pu and 241Am nuclei at proton energies of 26.5 MeV and 62.9 MeV were performed at the Louvain-la-Neuve cyclotron facility. Neutrons were detected with the multidetector DEMON. Mass and energy distributions of fission fragments, neutron angular distribution and multiplicities and total fission cross sections were determined. The relative contributions of pre-equilibrium neutron emission and compound nucleus evaporation, as well as of post-scission evaporation from the fission fragments were analyzed with moving multisource fits and were also compared with the predictions of the nuclear-reaction model code TALYS. Detailed comparisons with the data indicate that there is still room for improvement in this code.

Determination of the fission fragment excitation energy with allowance for neutron multiplicity

The study of the excitation energy distribution of fission fragments as a function of their mass and charge is important for revealing the nuclear fission mechanism and useful for many applications. To measure directly the excitation energy of primary fission fragments (before emission of neutrons) is a great problem. A method of obtaining these excitation energies from calculated neutron multiplicities and experimental values for differential yields of fragment pairs after emission of neutrons is considered. The Empire-II code was used to calculate neutron multiplicities as a function of various characteristics of the nuclear structure, fission process, and fission fragment deexcitation.

Dynamical description of the moments of the energy distribution of fission fragments and scission of a fissile nucleus

A multidimensional stochastic approach to fission dynamics on the basis of three-dimensional Langevin equations is applied systematically to calculating the first four moments of the energy distribution of fission fragments over a broad range of Coulomb parameter values (700 < Z2/A1/3 < 1700). For the scission of a fissile nucleus into fragments, use was made of various criteria traditional in modern fission theory: the vanishing of the neck radius at the scission instant and the equality of the neck radius to about 0.3R0 at this instant. In calculating the energy distribution, both of the criteria used lead to a fairly good description of experimental data on the first two moments and to a satisfactory description of data on the third and fourth moments of the distribution. However, the quality of the description of available experimental data is insufficiently good for giving preference to any of these criteria. Within three-dimensional Langevin dynamics, it is shown that the vanishing-radius criterion leads to unexpectably good agreement with experimental data on the first four moments of the energy distribution. A modified version of one-body dissipation where the coefficient that takes into account the reduction of the wall-formula contribution was set to ks = 0.25 was used in the calculations.

Analysis of fusion-fission process with neutron evaporation in superheavy mass region

The fusion-fission process for the synthesis of superheavy elements is discussed on the basis of fluctuation-dissipation dynamics. Recently, experiments at Dubna on fission of superheavy nuclei were carried out, and the mass and total kinetic energy distributions of fission fragments were measured. The fusion-fission cross section was derived from the experiments. We analyze the data using a three-dimensional Langevin calculation. We present a clear understanding of the competition between the fusion and the quasifission. We emphasize that a one-or two-dimensional model of Langevin calculation is not sufficient to estimate the fusion cross section in the superheavy mass region. Also, experiments on the emission of neutrons in correlation with fission fragments were conducted. It is useful to investigate the fusion-fission dynamics. We take into account the neutron emission with a Langevin calculation and compare it with experimental data. Finally, we discuss the evaporation residue cross section for superheavy elements.