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Transitions between symmetric and asymmetric modes in the region of heavy actinides
... The main critical ingredient of the scission-point models [1][2][3][4][5][6][7][8][9][10][11][12] is the potential energy surface (PES), since any changes in the PES minima and their positions control all fission observables. Because of the same PES, the charge, mass, total kinetic energy (TKE), and neutron multiplicity distributions of fission fragments are correlated. ...
... The experimental data on fission of actinides and preactinides are well described with the scission-point type models [1][2][3][4][5][6][7][8][9][10][11][12]. The most important step of this model is the calculation of the potential energy of the dinuclear system (DNS) as a function of charge Z i , mass A i , deformations β i (the ratios between the major and minor semiaxes of the fragments) of the two fragments, and internuclear distance R between them [8][9][10][11]13]. ...
... The experimental data on fission of actinides and preactinides are well described with the scission-point type models [1][2][3][4][5][6][7][8][9][10][11][12]. The most important step of this model is the calculation of the potential energy of the dinuclear system (DNS) as a function of charge Z i , mass A i , deformations β i (the ratios between the major and minor semiaxes of the fragments) of the two fragments, and internuclear distance R between them [8][9][10][11]13]. The index i designates the light (L) or (H) heavy fragment. ...
For the electromagnetic-induced fission of even Th222–230 isotopes, the effect of the transition from a symmetric fission mode to an asymmetric one on the charge/mass, total kinetic energy, neutron multiplicity distributions, and probability for a given neutron multiplicity per fission event is explored within an improved scission-point model. The simultaneous description all these observables and correlations between them are presented.
... To describe the ratios N L,H /Z L,H and other fission observables, we employ an improved scission-point model [11][12][13][14], where the scission configurations are dinuclear systems (DNS) with two touching individual nuclei (fragments). The improved scission-point fission model is able to consistently and reliably describe several experimental observables in spontaneous and induced fission [11][12][13][14]. ...
... To describe the ratios N L,H /Z L,H and other fission observables, we employ an improved scission-point model [11][12][13][14], where the scission configurations are dinuclear systems (DNS) with two touching individual nuclei (fragments). The improved scission-point fission model is able to consistently and reliably describe several experimental observables in spontaneous and induced fission [11][12][13][14]. ...
... Thus, the model assumes that the fission observables are mainly established at the scission configurations. The most important step of this model is the calculation of the potential energy of the DNS as a function of charge Z i , mass A i , deformations β i (the ratios between the major and minor semiaxes of the fragments) of the two fragments, and internuclear distance R between them [11][12][13][14]. The potential energy ...
Within the improved scission-point fission model, it is shown that the average neutron number per proton is not the same in fission fragments and is not equal to that in a fissioning nucleus. For the induced fission of U238, Pu240, Cm244, and Cf250, the dependencies of the fission-fragment neutron-excess ratio on the shell structure and excitation energy of fragment are studied.
... (3) Along the Th chain, there is a transition from a symmetric fission mode to an asymmetric one, which should be described by the fission model. Our study of the fission process is based on an improved scission-point model [15][16][17][18]. The main critical ingredient of this model is the PES, since any changes in the PES minima and their positions control all fission observables. ...
... The most important step of the scission-point model is the calculation of the potential energy of the dinuclear system (DNS) as a function of charge Z i , mass A i , deformations β i (the ratios between the major and minor semiaxes of the fragments) of the two fragments, and internuclear distance R between them [15][16][17][18]. The index i designates the light (L) or (H) heavy fragment. ...
... of the system is calculated as the sum of the energies of the fragments [the liquid-drop (LD) energy U LD i plus shellcorrection energy δU shell i ] and energy V int = V C + V N of the fragment-fragment interaction [15][16][17][18]. The interaction potential consists of the Coulomb interaction potential V C of two uniformly charged ellipsoids and nuclear interaction potential V N taken in the double-folding form [19,20]. ...
For fissioning isotopes of thorium and uranium, the simultaneous description of the charge, mass, total kinetic energy, and neutron multiplicity distributions of fission fragments is presented within the improved scission-point model. Correlations between all these observables are analyzed. The influence of the transition from symmetric to asymmetric fission mode on the shape of neutron multiplicity distribution is studied.
... The most widely used theoretical model to study mass yields is the statistical model which was founded by Fong and Wilkins [1,2]. This model has been developed in many branches, such as the Gaussian model [3,4] and modified scission point models [6][7][8][9][10][11][12][13]. The time-dependent model has been significantly developed by Randrup [14][15][16] and others [17][18][19][20][21][22] to predict the shape of mass yields (symmetric or asymmetric modes). ...
... On the other hand, some researchers [6][7][8][9] added some terms to neutron kinetic energy or gamma endpoint energy, E (as the initial excitation energy), to obtain the excitation energy of the fissioning nucleus, E*, for example, Pasca [7,9] added the Q-factor and the difference between the potential energy of the fissioning nucleus and the potential energy of one of the fragments at the scission point to the initial excitation energy to obtain excitation energy (i.e., E* Q+E+U cn −U i ). Some others [10,11] took available energy as the difference between the potential energy of the fissioning system at the scission point and the energy of the excited compound nucleus, which is the sum of Q-factor and initial excitation energy (E* Q+E). ...
... On the other hand, some researchers [6][7][8][9] added some terms to neutron kinetic energy or gamma endpoint energy, E (as the initial excitation energy), to obtain the excitation energy of the fissioning nucleus, E*, for example, Pasca [7,9] added the Q-factor and the difference between the potential energy of the fissioning nucleus and the potential energy of one of the fragments at the scission point to the initial excitation energy to obtain excitation energy (i.e., E* Q+E+U cn −U i ). Some others [10,11] took available energy as the difference between the potential energy of the fissioning system at the scission point and the energy of the excited compound nucleus, which is the sum of Q-factor and initial excitation energy (E* Q+E). ...
The photofission fragment mass yields of actinides are evaluated using a systematic statistical scission point model. In this model, all energies at the scission point are presented as a linear function of the mass numbers of fission fragments. The mass yields are calculated with a new approximated relative probability for each complementary fragment. The agreement with the experimental data is quite good, especially with a collective temperature T col of 2 MeV at intermediate excitation energy and T col = 1 MeV for spontaneous fission. This indicates that the collective temperature is greater than the value obtained by the initial excitation energy. The generalized superfluid model is applied for calculating the fragment temperature. The deformation parameters of fission fragments have been obtained by fitting the calculated results with the experimental values. This indicates that the deformation parameters decrease with increasing excitation energy. Also, these parameters decrease for fissioning systems with odd mass numbers.
... The statistical scission-point model relies on the assumption that the statistical equilibrium is established at scission where the observable characteristics of fission process are formed. So, the fissioning nucleus at scission-point is modeled by two nearly touching coaxial ellipsoids fragments [27]. Pasha [28] extracted the potential energies of fissioning isotopes of Ra, Ac, Th, Pa, and U as a function of the charge asymmetry coordinate. ...
... The charge distribution of fission fragments are studied in induced fission of even-even Thorium isotopes at high excitation energies [29]. Also, the mass and charge distributions of fragments were calculated for the electromagnetic-induced fission of some even-even isotopes [30] and heavy actinides [27]. In all recent works [27][28][29][30], the even-even fission fragments have been considered in the investigation of the charge and mass distribution of fission fragments. ...
... Also, the mass and charge distributions of fragments were calculated for the electromagnetic-induced fission of some even-even isotopes [30] and heavy actinides [27]. In all recent works [27][28][29][30], the even-even fission fragments have been considered in the investigation of the charge and mass distribution of fission fragments. The even-odd effects add some oscillations to the calculated results, so the pairing energy in calculations of fission fragments yields was neglected to obtain a smooth curve and also smeared each calculated yield with the Gaussian form. ...
The spontaneous fission fragments mass yield of $^{238}U$ is calculated with two models: WKB approximation model and statistical scission-point model. The results are compared with experimental data. This shows that the statistical scission-point model results are closer to the experimental data of the spontaneous fission fragments mass distributions than the WKB model. Also, experimental values are obtained by changing the deformation parameter for light fragments. The influence of temperature, deformation parameters, and pairing energy on the spontaneous fission fragments mass yield has been investigated within the statistical scission-point model. Adding the pairing correction energy to the total energy of the fission system adds some oscillations in theoretical results of fission fragments mass yields, also the inclusion of fission fragments temperature regardless of the pairing energy causes some theoretical results to be overestimated compared to the experimental data. It is seen that adding the pairing correction energy with the fragments temperature together leads to acceptable results compared to the experimental values. Therefore, the theoretical results of the systematic modified statistical scission-point model are in good agreement with the experimental values. This shows that although the statistical model is commonly used for the even-even isotopes, all isotopes can be investigated using the modified statistical model.
... Our aim is to predict the charge and mass distributions at large excitation energies. The fission observables are described using the improved scission-point model [16][17][18][19]. The statistical scission-point model [16][17][18][19] relies on the assumption that the statistical equilibrium is established at touching configuration where the observable characteristics of fission process are formed. ...
... The fission observables are described using the improved scission-point model [16][17][18][19]. The statistical scission-point model [16][17][18][19] relies on the assumption that the statistical equilibrium is established at touching configuration where the observable characteristics of fission process are formed. The reliability of this conclusion is supported by a good description of various experimental data (mass, charge, kinetic energy distributions, and neutron multiplicity) with the scission-point-type models [16][17][18][19][20][21][22][23][24][25][26][27][28]. ...
... The statistical scission-point model [16][17][18][19] relies on the assumption that the statistical equilibrium is established at touching configuration where the observable characteristics of fission process are formed. The reliability of this conclusion is supported by a good description of various experimental data (mass, charge, kinetic energy distributions, and neutron multiplicity) with the scission-point-type models [16][17][18][19][20][21][22][23][24][25][26][27][28]. ...
Using the improved scission-point model, the mass and charge distributions of fragments resulting from the fission of californium isotopes are calculated and compared with the available experimental data. The change of the shape of mass and charge distributions with increasing excitation energy is predicted for future experiments.
... The experimental data is increasingly available and theoretical support is urgently needed [15][16][17]. Using the method of Monte Carlo transport code Geant4 [18], we study in this work the reaction with two different physical models: the potential-driving model [19] and the G4ParaFission Model. Important and 237 Np(n, f) detailed information, such as the fission yield distributions, kinetic energy distributions, fission neutron spectrum and the total nubar, are compared with the nuclear data tables and experimental data, and the applicability of the potential-driving model is evaluated. ...
... Based on the potential-driving model [19], the driving potential D can be expressed as the sum of symmetric fission potential and asymmetric fission potential [20,21] ...
... and denote the widths of symmetric and asymmetric fission mass distribution, respectively. i is the index of different asymmetric fission potentials, and defines the relative contribution of each asymmetric fission potential [19]. ...
The potential-driving model is used to describe the driving potential distribution and to calculate the pre-neutron emission mass distributions for different incident energies in the reaction. The potential-driving model is implemented in Geant4 and used to calculate the fission-fragment yield distributions, kinetic energy distribution fission neutron spectrum and the total nubar for the reaction. Compared with the built-in G4ParaFissionModel, the calculated results from the potential-driving model are in better agreement with the experimental data and evaluated data. Given the good agreement with the experimental data, the potential-driving model in Geant4 can describe well the neutron-induced fission of actinide nuclei, which is very important for the study of neutron transmutation physics and the design of a transmutation system.
... In this paper, we employ the improved version of the statistical scission-point model [4][5][6], to study the evolution of the charge (mass) distribution of fission fragments with increasing mass number and excitation energy of even-even isotopes of [254][255][256][257][258][259][260]264 Fm, [258][259][260][261][262][263][264] No, and 262-266 Rf. Our aim is to predict the transformation of the shape of charge distribution with increasing neutron number and excitation energy. ...
... The statistical scission-point model [4][5][6] relies on the assumption that the statistical equilibrium is established at scission of fissioning nucleus where the observable character-istics of fission are formed. The reliability of this conclusion is supported by a good description of various experimental data (mass, charge, kinetic energy distributions, and neutron multiplicity) with the scission-point models [4][5][6][7][8][9][10][11][12][13][14][15][16]. ...
... The statistical scission-point model [4][5][6] relies on the assumption that the statistical equilibrium is established at scission of fissioning nucleus where the observable character-istics of fission are formed. The reliability of this conclusion is supported by a good description of various experimental data (mass, charge, kinetic energy distributions, and neutron multiplicity) with the scission-point models [4][5][6][7][8][9][10][11][12][13][14][15][16]. The dinuclear system (DNS) [13,[17][18][19][20][21][22][23][24][25][26][27][28] is shown to be well suited for describing the scission configuration. ...
The charge (mass) distributions of fission fragments resulting from low- and high-energy fission of the even-even nuclei 254−260,264Fm, 258−264No, and 262−266Rf are studied with the statistical scission-point model. The calculated results are compared with the available experimental data. In contrast to the experimental data, the calculated mass distribution for 258Fm(s.f.) is strikingly similar to the experimental one for 257Fm(s.f.). The transformation of the shape of charge distribution with increasing isospin and excitation energy occurs gradually and in a similar fashion like that of the mass distribution, but slower. For 254Fm(i.f.), 257Fm(nth,f), and 260Fm(s.f.), the unexpected difference (symmetric or asymmetric) between the shapes of charge and mass distributions is predicted for the first time. At some critical excitation energy, the saturation of the symmetric component of charge (mass) yields is demonstrated.
... In the decay dynamics of excited CN induced, the fission fragments are found to fall either in the mass/ , or asymmetric (η A and η Z ≠ 0) regions, with the effect of the mass/charge numbers, excitation energy ( * E CN ) and angular momentum of compound nuclear system. To have a comprehensive understanding of the possible decaying fragments, the experimentalists have given the fission cross-sections and percentage yields of the most probable decaying fragments from the excited CN [1][2][3][4][5][6][7]. However, from the above analysis, it is difficult to identify the fission fragments. ...
... However, from the above analysis, it is difficult to identify the fission fragments. In this context, the theoretical investigations developed on the basis of micro/macroscopic calculations help to recognize the fission fragments [3,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. In the present work, we have opted the collective clusterization approach, which is used within the Dynamical Cluster-decay Model (DCM) [18][19][20]. ...
An idea to understand the fragmentation of a formed nuclear entity (i.e. compound nucleus), induced via heavy-ion reactions, is an interesting task especially at incident energies near, above and far away from the Coulomb barrier. In the present work, we are studying the decay dynamics of a formed nuclear entity i.e. ²²⁸U* compound nucleus (CN), via the radioactive beam of Aluminium-31 (³¹Al) striking on the stable Gold-197 (¹⁹⁷Au) target nucleus, for incident energies E c.m. = 106.2–163.2 MeV. A comprehensive knowledge regarding the probable decaying fragments from ²²⁸U* has been accumulated using the collective clusterization approach of the Dynamical Cluster-decay Model (DCM) in terms of mass and charge dispersion, which built up on the Quantum Mechanical Fragmentation Theory (QMFT). Through both of these dispersion cases, we have identified the decaying fragments in the fission and heavy-mass regions, at different scale of incident energies. Further, the fission cross-sections ( σfisTheo ) have been obtained for ³¹Al + ¹⁹⁷Au → ²²⁸U* reaction at the above said E c.m. (MeV) and compared with the experimental data. This study has been carried out using two different sets of Skyrme force parameters (SIII and SSk), which are employed within the semiclassical approach of Skyrme Energy Density Formalism. Unlike for energies below and near the barrier, a significant difference has been observed between calculated ( σfisTheo ) and experimental ( σfisExpt ) cross-sections for above barrier energies, with independent choice of Skyrme forces. Such discrepancy noticed has been addressed with the presence of quasi-fission (QF) event. Similar phenomena has also been seen for ¹⁹F-induced reaction forming the same CN (²²⁸U*).
... The model of actinides fission is mainly by asymmetric splitting including mass distributions and charge distributions, shown as bimodal shape, especially, low excitation energy. The scission point model as a typical statistical method can calculate and reproduce yield distributions [2][3][4][5][6][7][8][9]. The potential at the scission point is essentially given by the liquiddrop (LD) energy and shell energies of proton and neutron subsystems of the two nascent fragments and their interaction. ...
The yield distributions of neutron-induced fission of actinides were calculated and evaluated by using the improved scission-point model with considering octupole deformation of fragments. We studied the influence of the octupole deformation on the asymmetric yields of actinides fission. The more probable scission configuration is the pear-shaped heavy fragments rather than more spherical shape. We used the improved scission model to calculate the peak of charge and neutron distributions and compared results with the experimental data. The results confirm that the main asymmetric fission mode of the heavy actinides fission is indeed characterized by “ZH≈54.” The protons configuration of heavy fragment plays a dominant role in asymmetric fission of actinides.
... The model of actinides fission is mainly by asymmetric splitting including mass distributions and charge distributions, shown as bimodal shape, especially, low excitation energy. The scission point model as a typical statistical method can calculate and reproduce yield distributions [2][3][4][5][6][7][8][9]. The potential at the scission point is essentially given by the liquiddrop (LD) energy and shell energies of proton and neutron subsystems of the two nascent fragments and their interaction. ...
Novel measurements of the neutron energy spectra of the ⁹ Be( d , n ) ¹⁰ B reaction with a thick beryllium target are performed using a fast neutron time-of-flight (TOF) spectrometer for the neutron emission angles and , and the incident deuteron energies are 250 and 300 keV, respectively. The neutron contributions from the ⁹ Be( d , n ) ¹⁰ B reaction are distributed relatively independently for the ground state and the first, second, and third excited states of ¹⁰ B. The branching ratios of the ⁹ Be( d , n ) ¹⁰ B reaction for the different excited states of ¹⁰ B are obtained for the neutron emission angles and , and the incident deuteron energies are 250 and 300 keV, respectively. The branching ratio of the ⁹ Be( d , n ) ¹⁰ B reaction for the third excited state decreases with increase in the incident deuteron energy, and the branching ratios for the ground state and the second excited state increase with increase in the neutron emission angle.
For the neutron-induced fission of nuclei U235,238, the evolution of the shape of fission-fragment neutron multiplicity distribution with increasing excitation energy is explored within the improved scission-point model. For a wide range of incident neutron energies, the dependence of an average number of neutrons emitted per a fission event on the excitation energy is studied.
The improved scission-point statistical model based on the dinuclear system approach is employed to describe spontaneous fission, electromagnetic-, neutron-, charged-particle- and heavy-ion-induced fission of even–even pre-actinides, actinides and superheavy nuclei and to analyze the correlations between various observables. The key element of the model is the calculation of potential energy surfaces. The evolution of fission observables with increasing excitation energy is shown to be related with the widening and migration of the minima in the potential energy surface. Conservation of asymmetric shapes of mass and charge distributions of the fission fragments at high enough excitation energies of fissioning nuclei Hg, Pb, Rn, Ra, Th, U, Cf, Fm and No is predicted. At some critical excitation energy, the saturation of the symmetric component of charge and mass yields is demonstrated. For fissioning [Formula: see text]Hg, [Formula: see text]Fm and [Formula: see text]No, transitions from two-peaked to single-peaked mass distributions are predicted. The origin of the transition between asymmetric and symmetric fission modes with variations of neutron number and excitation energy is explored. For [Formula: see text]Hg(i.f.), [Formula: see text]Hg(i.f.), [Formula: see text]Fm(i.f.), [Formula: see text]Fm([Formula: see text], [Formula: see text]) and [Formula: see text]Fm(s.f.), the unexpected difference (symmetric or asymmetric) between the shapes of charge and mass distributions is predicted for the first time. The dependence of the neutron excess ratio of fission fragments on the fragment charge number is studied. A method is suggested for experimental verification of the multi-chance fission assumption. A possible explanation of the anomaly in charge yield of Mo/Sn fragments in the fission reaction [Formula: see text]U([Formula: see text], [Formula: see text]) at low excitation energies found by [Formula: see text]–[Formula: see text] coincidence spectroscopy is presented.
Atomic nuclei are quantum many-body systems of protons and neutrons held together by strong nuclear forces. Under the proper conditions, nuclei can break into two (sometimes three) fragments which will subsequently decay by emitting particles. This phenomenon is called nuclear fission. Since different fission events may produce different fragmentations, the end-products of all fissions that occurred in a small chemical sample of matter comprise hundreds of different isotopes, including α particles, together with a large number of emitted neutrons, photons, electrons and antineutrinos. The extraordinary complexity of this process, which happens at length scales of the order of a femtometer, mostly takes less than a femtosecond but is not entirely over until all the lingering β decays have completed – which can take years – is a fascinating window into the physics of atomic nuclei. While fission may be more naturally known in the context of its technological applications, it also plays a crucial role in the synthesis of heavy elements in astrophysical environments. In both cases, simulations are needed for the many systems or energies inaccessible to experiments in the laboratory. In this context, the level of accuracy and precision required poses formidable challenges to nuclear theory. The goal of this article is to provide a comprehensive overview of the theoretical methods employed in the description of nuclear fission.
In this paper, the transitions between symmetric and asymmetric modes are investigated for the fission of actinides within the scission point model. All effective energies in fission are investigated in detail, separately. This indicates that the interaction energy and the liquid-drop energy do not change much in the symmetric region, so they cannot play a major role in the transition of actinide fission modes. Additionally, the sum of shell correction of complementary fragments at zero excitation energy is plotted over the fission fragment mass numbers. Also, the mass distributions of actinides fission are calculated within the scission point model. There is a good agreement between the calculated mass distribution and the total shell correction distribution. This indicates that the minimum total shell correction energy at the excitation energy corresponds to the maximum mass distribution for actinides fission, especially for the fermium 258 fission. Therefore, the main reason for the formation of fission mode in the actinides fission is the total shell correction energy of the complementary fission fragments at the zero excitation energy.
The fission fragment mass-yields are evaluated for pre-actinide and actinide isotopes using a
systematic statistical scission point model. The total potential energy of the fissioning systems at
the scission point is presented in approximate relations as functions of mass numbers,
deformation parameters and the temperature of complementary fission fragments. The collective
temperature, Tcoll, and the temperature of fission fragments, Ti, are separated and the effect of
collective temperature on mass yields results is investigated. The fragment temperature has been
calculated with the generalized superfluid model. The sum of deformation parameters of
complementary fission fragments has been obtained by fitting the calculated results with the
experimental data. To investigate the transitions between symmetric and asymmetric modes
mass yields for pre-actinide and heavy actinides are calculated with this model. The transition
from asymmetric to symmetric fission is well reproduced using this systematic statistical scission
point model. The calculated results are in good agreement with the experimental data with
Tcoll = 2MeV at intermediate excitation energy and with Tcoll = 1MeV for spontaneous fission.
Despite the Langevin model, in the scission point model, a constraint on the deformation
parameters of fission fragments has little effect on the results of the mass yield.
The cold and spontaneous fission fragments mass yield of 252Cf is calculated using the statistical scission point model. The results are compared with the available experimental data and the calculated results of the WKB model. This comparison indicates that the fission fragments mass distribution obtained by the statistical method are well agreed with the experimental data than the WKB model. The finite-range liquid-drop (FRLDM) as a macroscopic model with shell effects and pairing energy was used as the microscopic energy. On the other hand, for the microscopic energy, the deformation energy is substituted by the temperature dependence of the nuclear excited energy. The shell correction energy as a function of mass and atomic numbers of fission fragments is formulated in our systematic approach. The deformation parameters and the fragment temperature are obtained by fitting the calculated results with the experimental data. Analysis of calculated results of fragments mass yields clear that the pairing energy has relatively weak effect on cold fission fragments yields against spontaneous fission, although the deformation parameters are effective on cold fission fragments yield than the spontaneous fission.
Spectroscopic data for all nuclei with mass number A=212 have been evaluated and the corresponding level schemes from radioactive decay and reaction studies are presented. Highlights from this evaluation include the first observation of ²¹²Hg by 2010Al24 and the first measurement of the ground state half-life by 2012Be28 and 2016Ca25. The first measurement of the β− decay of ²¹²Tl populating excited states in ²¹²Pb has been performed by 2014Mo02. Knowledge of excited levels and their half-lives in ²¹²Po has been significantly extended in the transfer reaction studies of 2010As01,2010As03 and 2016Ko03,2017Ko38. A new (9⁻) isomer which α decays in ²¹²At was observed by 2007Ku30. The level scheme of ²¹²Rn was significantly extended through the (HI,xnγ) reaction studies of 2009Dr12 and 2008Dr01. New levels in ²¹²Ra were identified in a transfer reaction experiment by 2018Pa04. Finally, the α decay of both the ground state and an isomer in ²¹⁶U populating ²¹²Th was reported for the first time by 2015Ma37 and 2015De22.
Using the improved scission-point model, the mass and charge distributions of fission fragments of the compound nuclei Hg*180,182,190,198 and Pb*202 formed in complete fusion reactions Ar36+Sm144, Ca40+Nd142, Ar36+Sm154, α+Pt194, and Ca48+Sm154 are studied and compared with available experimental data. The transition is explained from the mass-asymmetric distribution in fissioning Hg*180,182,190 to the mass-symmetric distribution found in fissioning Hg*198 and Pb*202. The retention of the asymmetric mass distributions is treated in the case of fissioning Hg*180,182,190 with increasing excitation energy. In the fissioning Hg*198 and Hg*182, completely different shapes are predicted for charge and mass yields.
The fission of even-even fermium nuclides Fm250−260 at low excitation energy was studied using Langevin equations of three-dimensional nuclear-shape parametrization. The mass distributions of fission fragments show a dramatic change from an asymmetric shape for the lighter fermium isotopes to sharp symmetric fission for the heavier isotopes. The time evolution of the nuclear shape on the potential surface reveals that the lighter fermium isotopes showing asymmetric fission are trapped in the second minimum for a substantial length of time before overcoming the second saddle point. This behavior changes dramatically for the compact symmetric fission found in the heavier neutron-rich fermium nuclei that disintegrate immediately after overcoming the first saddle point, without feeling the second barrier, resulting in a fission time two orders of magnitude shorter.
The three-dimensional Langevin model plus a constraint on the heavy fragment deformation is used to study the fission dynamics for uranium and plutonium isotopes at low excitation energies. The potential energy surface is calculated with the macroscopic-microscopic model based on the two-center shell model. The Werner-Wheeler approximation is used to calculate the inertia tensor and the wall-and-window model is applied to calculate the friction tensor. In this work, the influence of the model parameters on the fission fragment mass distribution is investigated. The fission fragment mass distributions for U234,236,239 and Pu240 at low excitation energies are calculated and compared with the results of gef code as well as the evaluated data of ENDF/B-VIII.0. A nice agreement is found in the comparison, in which the incorporation of the constraint on the heavy fragment deformation plays an important role. In addition, the dependence of the mass distribution on the excitation energies for n+U235 fission is also studied within the model. Furthermore, the correlation between the elongation and mass asymmetry at the scission point and the correlations of the fission time with both the elongation and mass asymmetry are studied. This study may shed light on understanding the dynamics of the superlong channel for symmetric fission and the standard channels for asymmetric fission in the gef model and other phenomenological fission models.
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 U235 and Pu239 and spontaneous fission of Cf252. 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≤Z≤110 lying between the proton and neutron drip lines.
Using the improved scission-point model, the charge distribution of fission fragments is studied in neutron-induced fission of the U238 nucleus. A possible explanation of the anomaly in charge yield of Mo and Sn fragments is presented.
Transfer- and fusion-induced fission in inverse kinematics has proved to be a powerful tool to investigate nuclear fission, widening information on the fission fragments and access to unstable fissioning systems with respect to other experimental approaches. An experimental campaign is being carried out at GANIL with this technique since 2008. In these experiments, a beam of U238, accelerated to 6.1 MeV/u, impinges on a C12 target. Fissioning systems from U to Cf are populated through inelastic scattering, transfer, and fusion reactions, with excitation energies that range from a few MeV up to 46 MeV. The use of inverse kinematics, the SPIDER telescope, and the VAMOS spectrometer allow the characterization of the fissioning system in terms of mass, nuclear charge, and excitation energy, and the isotopic identification of the full fragment distribution. This work reports on new data from the second experiment of the campaign on fission-fragment yields of the heavy actinides U238, Np239, Pu240, Cm244, and Cf250, which are of interest from both fundamental and application points of view.
The potential-energy surfaces of an extended set of heavy and superheavy even-even nuclei with 92≤Z≤126 and isospins 40≤N−Z≤74 are evaluated within the recently developed Fourier shape parametrization. Ground-state and decay properties are studied for 324 different even-even isotopes in a four-dimensional deformation space, defined by nonaxiality, quadrupole, octupole, and hexadecapole degrees of freedom. Nuclear deformation energies are evaluated in the framework of the macroscopic-microscopic approach, with the Lublin-Strasbourg drop model and a Yukawa-folded mean-field potential. The evolution of the ground-state equilibrium shape (and possible isomeric, metastable states) is studied as a function of Z and N. α-decay Q values and half-lives, as well as fission-barrier heights, are deduced. In order to understand the transition from asymmetric to symmetric fission along the Fm isotopic chain, the properties of all identified fission paths are investigated. Good agreement is found with experimental data wherever available. New interesting features about the population of different fission modes for nuclei beyond Fm are predicted.
For fissioning isotopes of Ra, Ac, Th, Pa, and U, the potential energies as a function of the charge asymmetry coordinate are extracted from the experimental charge distributions of the fission fragment and compared with the calculated scission-point driving potentials. The role of the potential energy surfaces in the description of the fission charge distribution is discussed.
The mass, charge and isotopic distributions of fission fragments are studied within an improved scission-point statistical model in the reaction 235U+n at different energies of the incident neutron. The available experimental data are well reproduced and the energy-dependencies of the observable characteristics of fission are predicted for future experiments. The calculated mass distribution of 238U+n is also compared with experimental data.
An effective method to calculate the potential energy of a dinuclear system is suggested. The nuclear part of the nucleus-nucleus potential is taken in the double folding form. The analytical expressions obtained allow one to simplify the calculations of interaction between two nuclei except the nuclei near the drip lines. The relationship between the double folding potential and the proximity potential is found. The influence of a deformation and a relative orientation of nuclei on the interaction potential is investigated. The method is applied to the calculations of the energies of the dinuclear and trinuclear systems.
The secondary-beam facility of GSI provided the technical equipment for a new kind of fission experiment. Fission properties of short-lived neutron-deficient nuclei have been investigated in inverse kinematics. The measured element distributions reveal new kinds of systematics on shell structure and even–odd effects and lead to an improved understanding of structure effects in nuclear fission. The relevance of these studies for some presently considered applications is described. Prospects for future experiments are discussed.
We have measured the mass and kinetic-energy distributions from the spontaneous fission of ²âµâ¸Fm, ²âµâ¸No, ²âµâ¹Md, ²â¶Â°Md, and ²â¶Â°(104). All are observed to fission with a symmetrical division of mass. The total-kinetic-energy distributions strongly deviated from the Gaussian shape characteristically found in the fission of all other actinides. When the total-kinetic-energy distributions are resolved into two Gaussians, the constituent peaks lie near 200 and 233 MeV. We conclude that both low- and high-energy fission modes occur in four of the five nuclides studied. We call this property bimodal fission.'' Even though both modes are possible in the same nuclide, one generally predominates. We offer an explanation for each mode based on shell structures of the fissioning nucleus and of its fragments. The appearance of both modes of fission in this region of the nuclide chart seems to be a coincidence in that the opportunity to divide into near doubly magic Sn fragments occurs in the same region where the second fission barrier is expected to drop in energy below the ground state of the fissioning nucleus. Appropriate paths on the potential-energy surface of deformation have been found by theorists, but no physical grounds have been advanced that would allow the near equal populations we observe traveling each path. We suggest that this failure to find a reason for somewhat equal branching may be a fundamental flaw of current fission models. Assuming the proposed origins of these modes are correct, we conclude the low-energy, but also mass-symmetrical mode is likely to extend to far heavier nuclei. The high-energy mode will be restricted to a smaller region, a realm of nuclei defined by the proximity of the fragments to the strong neutron and proton shells in ¹³²Sn.
The kinetic energy distribution of coincident fragments from spontaneous fission of 257Fm has been measured with silicon detectors. The data reveal two significant features: (1) The mass-yield distribution is markedly more symmetric than for slightly lighter nuclei (e.g., 252Cf, 254Cf); (2) the average total kinetic energy increases monotonically with the approach to symmetric fission.
Pre-neutron-emission fragment-mass and total-kinetic-energy distributions and the mass-energy correlations in the spontaneous-fission decay of 2.30-sec 252No have been deduced from measured energies of coincident fragment pairs using silicon surface-barrier detectors. The 252No for these measurements was produced in the 241Am(15N, 4n) reaction and deposited on 40-μg cm-2 carbon foils using a He-jet technique. From an analysis of 154 correlated fission events, the average pre-neutron-emission total-kinetic energy, 〈TKE〉, was found to be 202.4±1.2 MeV. The mass distribution is decidedly asymmetric, similar to that observed for 252Cf spontaneous fission, although a maximum in the 〈TKE〉 curve as a function of fragment mass occurs for near-symmetric mass divisions as it does for the heavier isotopes of fermium. The measured spontaneous-fission-decay branching fraction for 252No is 26.9±1.9% and the measured total half-life is 2.30±0.22 sec. The measured and deduced fission charàcteristics for 252No are compared with those for the Cm, Cf, and Fm nuclides as well as with recent theoretical predictions.RADIOACTIVITY, FISSION 252No(α, sf) measured fragment-fragment coin E, T1/2, Eα, α/sf, σ for 241Am(15N, 4n) reaction; deduced pre-neutron fragment masses, energies, and total kinetic E distribution. Enriched target.
Within an improved scission point model, experimental data on the relative yield, mean value and variance of the total kinetic-energy distribution of fission fragments are described. It is shown that for a fixed mass and charge fragmentation, the potential energy of the scission configuration has several minima as a function of the deformation parameters of the fragments. The scission at these minima leads to a relatively enhanced yield of the fragments with a certain TKE and creates fine structures in the TKE-mass distribution which are different from those produced by the odd-even effect.
Within the scission point model the bimodality in fission of actinides is demonstrated to be related to different neighboring
charge and mass splittings. This phenomenon is peculiar not only for the fission of heavy nuclei like 256,258Fm and 256,258,262No but also for fission of lighter actinides like 236U, 240Pu and 252Cf. The experiments are suggested to prove our interpretation of bimodality.
We present calculated potential-energy surfaces and fission half-lives for heavy even and odd nuclei between Pu and Z = 110. We base our study on the macroscopic-microscopic model. For the macroscopic part we use the Yukawa-plus-exponential (finite-range) model and for the microscopic part a folded-Yukawa (diffuse-surface) single-particle potential. To remove some deficiences of the model that were associated with describing the transition from a single nuclear system to two different nuclear systems that occurs in the scission region, we have included the following new features. We have increased the smoothing range in the Strutinsky method from 1.0 × ħω0 to 1.4 × ħω0 and we use shape-dependent Wigner and A0 terms. The effects of these two improvements are large, up to a magnitude of about 10 MeV close to scission. However, since the changes due to the two improvements have different signs, the results obtained in our previous study are approximately retained. To allow studies of the fission properties of odd nuclei we have also added the possibility of calculating the specialization energies associated with the odd particles. This allows us to calculate fission half-lives also for odd systems for fission along both the new and old fission paths. In most cases we find good agreement between calculated and experimental half-lives. Our results show that we have obtained a good understanding of the fission properties also of odd heavy nuclei.
Nuclei undergoing fission can be described by a multi-dimensional potential-energy surface that guides the nuclear shape evolution--from the ground state, through intermediate saddle points and finally to the configurations of separated fission fragments. Until now, calculations have lacked adequate exploration of the shape parameterization of sufficient dimensionality to yield features in the potential-energy surface (such as multiple minima, valleys, saddle points and ridges) that correspond to characteristic observables of the fission process. Here we calculate and analyse five-dimensional potential-energy landscapes based on a grid of 2,610,885 deformation points. We find that observed fission features--such as the distributions of fission fragment mass and kinetic energy, and the different energy thresholds for symmetric and asymmetric fission--are very closely related to topological features in the calculated five-dimensional energy landscapes.
- A N Andreyev
- M Huyse
- P Van Duppen
A.N. Andreyev, M. Huyse, P. Van Duppen, Rev. Mod. Phys. 85 (2013) 1541.
- I V Ryzhov
I.V. Ryzhov, et al., Phys. Rev. C 83 (2011) 054603.
- K.-H Schmidt
K.-H. Schmidt, et al., Nucl. Phys. A 665 (2000) 221;
K.-H. Schmidt, et al., Nucl. Phys. A 693 (2001) 169.
- D C Hoffman
- S Hofmann
- G Münzenberg
D.C. Hoffman, J. Alloys Compd. 213/214 (1994) 67;
S. Hofmann, G. Münzenberg, Rev. Mod. Phys. 72 (2000) 733.
- M G Itkis
- N A Kondrat'ev
- S I Mul'gin
- V N Okolovich
- A Ya
- G N Rusanov
- Smirenkin
M.G. Itkis, N.A. Kondrat'ev, S.I. Mul'gin, V.N. Okolovich, A.Ya. Rusanov, G.N. Smirenkin, Sov. J. Nucl. Phys. 53
(1991) 757.
- D C Hoffman
D.C. Hoffman, et al., Phys. Rev. C 41 (1990) 631.
- S Cwiok
- P Rozmej
- A Sobiczewski
- Z Patyk
- P Möller
- J R Nix
- W J Swiatecki
S. Cwiok, P. Rozmej, A. Sobiczewski, Z. Patyk, Nucl. Phys. A 491 (1989) 281;
P. Möller, J.R. Nix, W.J. Swiatecki, Nucl. Phys. A 492 (1989) 349;
- U Brosa
- S Grossmann
- A Müller
U. Brosa, S. Grossmann, A. Müller, Phys. Rep. 197 (1990) 167.
- J Randrup
- P Möller
J. Randrup, P. Möller, Phys. Rev. C 88 (2013) 064606;
- N Carjan
- F A Ivanyuk
- Yu Ts
- G M Oganessian
- Ter-Akopian
N. Carjan, F.A. Ivanyuk, Yu.Ts. Oganessian, G.M. Ter-Akopian, Nucl. Phys. A 942 (2015) 97.
- C Simenel
- A S Umar
C. Simenel, A.S. Umar, Phys. Rev. C 89 (2014) 031601(R);
- G Scamps
- C Simenel
- D Lacroix
G. Scamps, C. Simenel, D. Lacroix, Phys. Rev. C 92 (2016) 011602(R);
- Y Tanimura
- D Lacroix
- S Ayik
Y. Tanimura, D. Lacroix, S. Ayik, Phys. Rev. Lett. 118 (2017) 152501.
- T Matsuse
- C Beck
- R Nouicer
- D Mahboub
T. Matsuse, C. Beck, R. Nouicer, D. Mahboub, Phys. Rev. C 55 (1997) 1380.
- S J Sanders
- A Szanto De Toledo
- C Beck
S.J. Sanders, A. Szanto de Toledo, C. Beck, Phys. Rep. 311 (1999) 487.
- S Panebianco
- J.-L Sida
- H Goutte
- J.-F Lemaître
- N Dubray
- S Hilaire
S. Panebianco, J.-L. Sida, H. Goutte, J.-F. Lemaître, N. Dubray, S. Hilaire, Phys. Rev. C 86 (2012) 064601.
- M Caamaño
M. Caamaño, et al., Phys. Rev. C 92 (2015) 034606.
- J Maruhn
- W Greiner
J. Maruhn, W. Greiner, Z. Phys. 251 (1972) 431.
- D A Shaughnessy
D.A. Shaughnessy, et al., Phys. Rev. C 61 (2000) 044609.
- D A Shaughnessy
D.A. Shaughnessy, et al., Phys. Rev. C 65 (2002) 024612.
- J P Unik
J.P. Unik, et al., in: Physics and Chemistry of Fission, vol. II, IAEA, Vienna, 1974, p. 25.
- C Romano
C. Romano, et al., Phys. Rev. C 81 (2010) 014607.
- D C Hoffman
D.C. Hoffman, et al., Phys. Rev. C 21 (1980) 972.
- E Cheifetz
E. Cheifetz, et al., Phys. Rev. C 4 (1971) 1913.
- G M Ter-Akopian
G.M. Ter-Akopian, et al., Phys. Rev. C 55 (1997) 1146.
- K.-H Schmidt
K.-H. Schmidt, et al., Nucl. Phys. A 665 (2000) 221;
- D C Hoffman
D.C. Hoffman, J. Alloys Compd. 213/214 (1994) 67;
- S Hofmann
- G Münzenberg
S. Hofmann, G. Münzenberg, Rev. Mod. Phys. 72 (2000) 733.
- S Cwiok
- P Rozmej
- A Sobiczewski
- Z Patyk
S. Cwiok, P. Rozmej, A. Sobiczewski, Z. Patyk, Nucl. Phys. A 491 (1989) 281;
- H Paşca
- A V Andreev
- G G Adamian
- N V Antonenko
H. Paşca, A.V. Andreev, G.G. Adamian, N.V. Antonenko, Phys. Rev. C 94 (2016) 064614.
- H Paşca
- A V Andreev
- G G Adamian
- N V Antonenko
H. Paşca, A.V. Andreev, G.G. Adamian, N.V. Antonenko, Phys. Lett. B 760 (2016) 800.
- H Paşca
- A V Andreev
- G G Adamian
- N V Antonenko
- Y Kim
H. Paşca, A.V. Andreev, G.G. Adamian, N.V. Antonenko, Y. Kim, Phys. Rev. C 93 (2016) 054602;
- A V Andreev
- G G Adamian
- N V Antonenko
A.V. Andreev, G.G. Adamian, N.V. Antonenko, Phys. Rev. C 86 (2012) 044315;
- A V Andreev
- G G Adamian
- N V Antonenko
- A N Andreyev
A.V. Andreev, G.G. Adamian, N.V. Antonenko, A.N. Andreyev, Phys. Rev. C 88 (2013) 047604.
- G G Adamian
- N V Antonenko
- W Scheid
G.G. Adamian, N.V. Antonenko, W. Scheid, in: Christian Beck (Ed.), Clusters in Nuclei, vol. 2, in: Lect. Notes
Phys., vol. 848, Springer-Verlag, Berlin, 2012, p. 165.