Ternary Fission Research Articles

Multi-modal fission in collinear ternary cluster decay of 252Cf(sf, fff)

We discuss the multiple decay modes of collinear fission in 252Cf(sf, fff), with three fragments as suggested by the potential energy surface (PES). Fission as a statistical decay is governed by the phase space of the different decay channels, which are suggested in the PES-landscape. The population of the fission modes is determined by the minima in the PES at the scission points and on the internal potential barriers. The ternary collinear decay proceeds as a sequential process, in two steps. The originally observed ternary decay of 252Cf(sf) into three different masses (e.g. 132–140Sn, 52–48Ca, 68–72Ni), observed by the FOBOS group in the FLNR (Flerov Laboratory for Nuclear Reactions) of the JINR (Dubna) the collinear cluster tripartition (CCT), is one of the ternary fission modes. This kind of “true ternary fission” of heavy nuclei has often been predicted in theoretical works during the last decades. In the present note we discuss different ternary fission modes in the same system. The PES shows pronounced minima, which correspond to several modes of ternary fragmentations. These decays have very similar dynamical features as the previously observed CCT-decays. The data obtained in the experiments on CCT allow us to extract the yields for different decay modes using specific gates on the measured parameters, and to establish multiple modes of the ternary fission decay.

True ternary fission

The study of the ternary fission of nuclei has received new interest recently. It is of general interest for nuclear dynamics, although the process is very rare. In the present work, we discuss the possibilities of true ternary fission (fragment masses $Ag30$) in $^{252}\mathrm{Cf}$ for different mass splits. These mass splits are strongly favored in a collinear geometry. Based on the three cluster model (TCM), it is shown that the true ternary fission into fragments with almost equal masses is one of the possible fission modes in $^{252}\mathrm{Cf}$. For general decays it is shown that the formation of the lightest fragment at the center has the highest probability. Further the formation of tin isotopes and/or other closed shell fragments are favored. For the decay products the presence of closed shell nuclei among the three fragments enhances the decay probabilities.

α-accompanied cold ternary fission ofPu238–244isotopes in equatorial and collinear configuration

The cold ternary fission of $^{238}$Pu, $^{240}$Pu, $^{242}$Pu and $^{244}$Pu isotopes, with $^{4}$He as light charged particle, in equatorial and collinear configuration has been studied within the Unified ternary fission model (UTFM). The fragment combination $^{100}$Zr+$^{4}$He+$^{134}$Te possessing the near doubly magic nuclei $^{134}$Te (N=82, Z=52) gives the highest yield in the alpha accompanied ternary fission of $^{238}$Pu. For the alpha accompanied ternary fission of $^{240}$Pu, $^{242}$Pu and $^{244}$Pu isotopes, the highest yield was found for the fragment combination with doubly magic nuclei $^{132}$Sn (N=82, Z=50) as the heavier fragment. The deformation and orientation of fragments have also been taken into account for the alpha accompanied ternary fission of $^{238-244}$Pu isotopes, and it has been found that in addition to closed shell effect, ground state deformation also plays an important role in determining the isotopic yield in the ternary fission process. The emission probability and kinetic energy of long range alpha particles have been calculated and are found to be in good agreement with the experimental data.

Isotopic yield in alpha accompanied ternary fission of 252Cf

The cold ternary fission of 252 Cf with 4 He as light charged particle (LCP) is studied with fragments in the equatorial and collinear configuration, taking the interacting barrier as the sum of the Coulomb and Proximity potential. The favorable fragment combinations are obtained from the cold valley plot and by calculating the yield for charge-minimized fragments. In both equatorial and collinear configurations, the highest yield is obtained for the fragment combination 116 Pd + 4 He + 132 Sn , which possess doubly magic nuclei 132 Sn (N = 82, Z = 50). The presence of doubly or near doubly magic nuclei (132 Sn , 130 Sn etc.) and higher Q value plays an important role in the alpha accompanied cold ternary fission of 252 Cf . The comparison of the relative yield for equatorial configuration with that of collinear configuration, points to the fact that equatorial configuration is the preferred configuration for the LCP (4 He ) accompanied ternary fission in 252 Cf isotope. The yields obtained for the alpha accompanied cold ternary fission of 252 Cf in equatorial and collinear configuration are compared with the experimental data. The emission probability of long range alpha (LRA) particle from 252 Cf isotope is predicted using our formalism and is found to be in agreement with experimental value.

True ternary fission of 252Cf(sf), the collinear decay into fragments of similar size

The ternary decay in 252Cf(sf, fff), with three cluster fragments of different masses (e.g.132Sn,52-48Ca,68-72Ni), has been observed by the FOBOS group in JINR. This work has established a new decay mode of heavy nuclei, the collinear cluster tripartition, (CCT). This "true ternary fission" of heavy nuclei has been predicted many times in theoretical works during the last decades. In the present report we discuss true ternary fission (FFF) into three nuclei of almost equal size (e.g. Z=98 → Zi = 32, 34, 32) and other fission modes in the same system. The possible fission channels for 252 Cf(sf) are predicted from potential-energy (PES) calculations. These PES's show pronounced minima for several ternary fragmentation decays, suggesting a variety of collinear ternary fission modes. The FFF-decays have very similar dynamical features as the previously observed collinear CCT-decays, the central fragment has very small kinetic energy. The data of the cited experiment allow the extraction of the yield for some FFF-decays, by using specific gates on the measured parameters.

34Si accompanied ternary fission of 242Cm in equatorial and collinear configuration

Taking the interacting potential as the sum of Coulomb and proximity potential, 34 Si accompanied cold ternary fission of 242 Cm has been studied with fragments in the equatorial and collinear configuration. The cold valley plots (plot of driving potential versus mass number of fragments) and the calculations on the yields for the charge minimized fragments have been used to obtain the favorable fragment combinations. Thus, our study on the 34 Si accompanied ternary fission of 242 Cm reveals the role of near doubly magic shell closures (of 130 Sn , 132 Te , 134 Te , etc.) in cold ternary fission. The comparison of relative yield reveals that in 34 Si accompanied ternary fission of 242 Cm , collinear configuration is preferred than the equatorial configuration. The relative yield for binary exit channel is found to be higher than that of ternary fragmentation (both equatorial and collinear configuration). The predicted yield for the binary fragmentation of 4 He and 34 Si from 242 Cm are in agreement with the experimental data.

The emission probabilities of long range alpha particles from even–even 244–252Cm isotopes

The alpha accompanied cold ternary fission of even–even 244Cm, 246Cm, 248Cm, 250Cm and 252Cm isotopes has been studied by taking the interacting barrier as the sum of the Coulomb and proximity potential with the fragments in equatorial configuration. The favorable fragment combinations are obtained from the cold reaction valley plot and by calculating the relative yield for the charge minimized fragments. In the alpha accompanied ternary fission of the 244Cm isotope, the highest yield is found for the fragment combination 110Ru+4He+130Sn, which possess near doubly magic nuclei 130Sn. For the ternary fission of 246Cm, 248Cm, 250Cm and 252Cm isotopes with 4He as the light charged particle, the highest yield is obtained for the fragment combination with doubly magic nuclei 132Sn as the heavier fragment. The emission probabilities and kinetic energies of long range alpha particles have been computed for the 242,244,246,248Cm isotopes and are found to be in good agreement with the experimental data. The relative yields for the 4He accompanied ternary fission (equatorial and collinear) of 242–252Cm isotopes are compared with the corresponding yield for binary fission. The effect of deformation and orientation of fragments in the 4He accompanied ternary fission of 244–252Cm isotopes are studied. Our study reveals that the ground state deformation has as an important role in the alpha accompanied ternary fission as that of the shell effect.

Collinear versus triangular geometry: A ternary fission study

We study in this work the preference of the arrangements of fragments leading to ternary fission. Earlier experimental investigations on this subject have established the fact that the emission of a third particle happens in a direction perpendicular to the direction of the fission axis. Recently, within the missing mass approach, it has been reported that for fragments of comparable masses, the so-called collinear cluster tripartition (CCT), collinear emission of the fragments occurs. The ternary potential energy surface (PES) of three-body fragmentation of $^{252}\mathrm{Cf}$ is studied. The PESs are calculated for the fragment arrangements starting from a collinear configuration to a triangular configuration by varying the angle between the end fragments with respect to the fragment positioned in the middle. Furthermore, the role of the positioning of the three fragments is analyzed. Our results indicate that there is a clear preference for an arrangement in which the lightest fragment is positioned in the middle. Furthermore, for all possible third fragments, collinear geometry is found to be favored over orthogonal geometry.

Publisher's Note: Nucleation and cluster formation in low-density nucleonic matter: A mechanism for ternary fission [Phys. Rev. C <b>90</b>, 011601(R) (2014)

Publisher's Note: Nucleation and cluster formation in low-density nucleonic matter: A mechanism for ternary fission [Phys. Rev. C <b>90</b>, 011601(R) (2014)

Nucleation and cluster formation in low-density nucleonic matter: A mechanism for ternary fission

Ternary fission yields in the reaction 241Pu(nth,f) are calculated using a new model which assumes a nucleation-time moderated chemical equilibrium in the low density matter which constitutes the neck region of the scissioning system. The temperature, density, proton fraction and fission time required to fit the experimental data are derived and discussed. A reasonably good fit to the experimental data is obtained. This model provides a natural explanation for the observed yields of heavier isotopes relative to those of the lighter isotopes, the observation of low proton yields relative to 2H and 3H yields and the non-observation of 3He, all features which are shared by similar thermal neutron induced and spontaneous fissioning systems.

Effects of rotation of fissioning nuclei in the angular distributions of prompt neutrons and gamma rays originating from the polarized-neutron-induced fission of 233U and 235U nuclei

The results of an experiment devoted to searches for effects of rotation of fissioning nuclei in the angular distributions of prompt neutrons and gamma rays originating from the polarized-neutron-induced fission of 233U nuclei are presented. The effects discovered in these angular distributions are opposite in sign to their counterparts in the polarized-neutron-induced fission of 235U nuclei. This is at odds with data on the relative signs of respective effects in the angular distribution of alpha particles from the ternary fission of the same nuclei and may be indicative of problems in the model currently used to describe the effect in question. The report on which this article is based was presented at the seminar held at the Institute of Theoretical and Experimental Physics and dedicated to the 90th anniversary of the birth of Yu.G. Abov, corresponding member of Russian Academy of Sciences, Editor in Chief of the journal Physics of Atomic Nuclei.

True ternary fission, the collinear decay into fragments of similar size in the 252Cf(sf) and 235U(nth, f) reactions

The collinear cluster decay in 252Cf(sf, fff), with three cluster fragments of different masses (e.g. 132Sn, 52–48Ca, 68–72Ni), which has been observed by the FOBOS group in JINR, has established a new decay mode of heavy nuclei, the collinear cluster tripartition (CCT). The same type of ternary fission decay has been observed in the reaction 235U(nth, fff). This kind of “true ternary fission” of heavy nuclei has been predicted many times in theoretical works during the last decades. In the present note we discuss true ternary fission (TFFF) into three nuclei of almost equal size (e.g. Z=98→Zi=32, 34, 32) in the same systems. The possible fission channels are predicted from potential-energy (PES) calculations. These PES's show pronounced minima for several ternary fragmentation decays, e.g. for 252Cf(sf) and for 235U(nth, f). They suggest the existence of a variety of collinear ternary fission modes. The TFFF-decays chosen in this letter have very similar dynamical features as the previously observed collinear CCT-decays. The data obtained in the above mentioned experiments allow us to extract the yield for these TFFF-decays in both systems by using specific gates on the measured parameters. These yields are a few 1.0⋅10−6/(binary fission).

Peculiarities of cluster formation in true ternary fission of 252Cf and 236U*

The existence of a new type of cluster decay called ‘collinear cluster tri-partition’ (CCT) is discussed by an analysis of the landscape of the potential energy surface (PES). The total energy of the ternary system is found as a sum of the binding energies of fragments and nucleus–nucleus interaction between them. The pre-scission state of the ternary system is assumed to be arranged as a chain of the three fragments along a straight line. Minima and valleys of the PES are determined by variation of the proton and neutron distributions between them. Pre-scission prompt emission of neutrons is assumed and PES is calculated for the cases of emission of two neutrons. The presence of the valley corresponding to the formation of the isotopes of Sn with masses A = 130–136 is inherent for all PES calculated for CCT for spontaneous fission of and fission induced by neutrons of . There are local minima indicating the formation of Ca, Fe, Ni, Ge and Se isotopes having magic proton or/and neutron numbers, such as 20, 28 and 50. The analysis shows that the experimentally observed is formed as the edge fragment of the ternary system connecting to Sn by Si and Ca isotopes at fission of and , respectively.

Light charged particle accompanied ternary fission of 242Cm using the Coulomb and proximity potential

The cold ternary fission of 242Cm with 4He , 10Be and 14C as light charged particle has been studied by taking the interacting barrier as the sum of Coulomb and proximity potential with the fragments in equatorial configuration. The favorable fragment combinations are obtained from the cold valley plot (plot of driving potential vs. mass number of fragments) and by calculating the yield for charge minimized fragments. The maximum yield in the 4He accompanied ternary fission is obtained for the fragmentation channel 104Mo + 134Te + 4He and for the 10Be accompanied ternary fission, the maximum yield is found for the fragmentation channel 98Zr + 134Te + 10Be . It is to be noted that, in the case of 14C accompanied ternary fission, the maximum yield is obtained for the fragmentation channel 94Sr + 134Te + 14C and the next higher yield is found for the fragmentation channel 96Zr + 132Sn + 14C . Thus, the fragment combinations with maximum yields reveal the role of doubly magic and near doubly magic nuclei in cold ternary fission.

Investigation of 238U in the (n, n′γ) reaction

An irradiation of 238U with a beam of reactor fast neutrons permits revealing about 550 gamma transitions associated with the respective (n, n′γ) reaction and with fission fragments. The use of all known data on gamma radiation from fission fragments makes it possible to identify gamma transitions belonging to 238U with a high probability. The scheme of levels and gamma transitions is composed for 238U. New levels (including those of spin-parity Jπ = 0+) at excitation energies below 2 MeV are proposed. The low-lying levels in the rotational band for two-phonon octupole excitations are determined. It is found that a hybrid state is formed upon the crossing of this band and the band based on two-quasiparticle excitations. This hybrid state must involve excitations of both types. A small value of the rotational-band parameter in the isomer of energy 2559.0(4) keV is explained by the contribution to this state from two-quasiparticle configurations belonging to the 1k17/2 subshell. The same circumstance may also be responsible for an enhanced yield of ternary fission for this isomer.

Mechanisms of formation of P-odd, P-even and T-odd asymmetries in the angular distributions of products of binary and ternary fission induced by cold polarized neutrons

The experimentally measured P-odd, T-even; P-even, T-even; and P-even, T-odd asymmetries in the angular distributions of products of binary and ternary fission induced by cold polarized neutrons are classified, and the mechanisms of their appearance are studied. Basic asymmetries in the angular distributions of binary-fission fragments are found theoretically and are used to construct induced asymmetries in the angular distributions of prescission and evaporated third particles emitted in true and delayed ternary fission. If effects associated with the collective rotation of the polarized fissile system are disregarded, P-odd, T-even; P-even, T-even; and P-even, T-odd asymmetries in the angular distributions of prescission and evaporated photons are proven to be absent, and the coefficients of the analogous asymmetries in the angular distributions of prescission and evaporated neutrons are calculated for this case. The features of the coefficients of induced P-even, T-odd asymmetries are studied for evaporated photons and neutrons associated with taking into account the quantum rotation of the polarized fissile system.

Dynamics of collinear ternary fission in the fragmentation of252Cf

With the observation of the collinear cluster tripartition in 252 Cf, we discuss various features of the true ternary fission (collinear fission). The conditions for collinear ternary decay with three clusters are explained. We discuss the potential energy surfaces for ternary decay and conditions for the collinear decay.

Nuclear spin-orbit interaction and T-odd angular correlations in ternary fission

T-odd angular correlations in ternary fission of 233U and 235U nuclei by slow polarized neutrons are not related to TRI (time reversal invariance) violation, but are caused by an effective spin-orbit interaction in the final state.

The comparison of binary- and ternary-fission configurations close to the instant of scission

A new way to bring into comparison the binary- and ternary-fission configurations is proposed. The method is founded on recently discovered ROT effect. The angle of fission axis deflection from its initial orientation at the moment of scission comes into existence as a result of dividing system rotation and carries information about fissioning nucleus deformation. The comparison of proper angles for binary and ternary fission can be used to estimate the difference in the rupture configurations.

(A = 10)-Accompanied spontaneous ternary fission of californium isotopes

The ternary fission of 238-256Cf even-A isotopes is studied in the framework of the three-cluster model within the spherical approximation. The study is confined to those decays in which the accompanied light charged particle is of mass A = 10. The most probable ternary fission path is obtained as the one that has a peak in the Q-value and a minimum in the driving potential, with respect to the mass and charge asymmetries. Assuming both equatorial and collinear configurations of the different emissions of the light charged particles with A = 10, the ternary fission of 252Cf is found to be most favored with 10Be. The predicted favorable fragmentation channels of the 10Be-accompanied ternary fission of 238-256Cf, even-A, isotopes are discussed in detail. The closed-shell structure of the produced heaviest fragment is found to play a key role for the detected most favorable channels. A nucleus with a closed neutron shell or even doubly closed shell always appears as the heaviest nucleus in the favored channel of the ternary fission of all mentioned isotopes. As the isospin asymmetry of the isotope increases, the width of its cold fission valley around the symmetric mass region decreases, with more shifting towards the centre of the symmetric region. Neither the most favorable ternary emissions nor the behavior of the ternary fragmentation potential changed with the type of nuclear interaction potential (Yukawa, folding potential with Migdal force, and proximity 77). Also, almost no change is observed according to the method of emission of the fragments (equatorially or collinearly) or when the calculations are performed without inserting the nuclear interaction potential.