[en] The theories of nuclear fission are guided by the extensive calculations of the potential energy surfaces (PES) in the multi-dimensional deformation space defining the shape of a deforming nucleus on the way to fission. Many approaches have been used for this. A well established technique is the microscopic-macroscopic (mic-mac) approach in which the macroscopic part is given by the liquid drop energy and the microscopic part is given in terms of Strutinsky shell correction. We have used the mic-mac approach to calculate the PES by using the Cassini ovaloid shape parameterization for nuclear potential. This formalism is due to Garcia et al. In this formalism, the single particle energies as a function of deformation parameters are calculated from an axially deformed Woods-Saxon potential. This single particle level scheme is used to calculate the shell and pairing corrections to the liquid drop energy (smooth macroscopic part) in Strutinsky approach

[en] Isomers can be viewed as a separate class of nuclei and offer interesting possibilities to study the behavior of nuclei under varied conditions of excitation energy, spin, life-time and particle configuration. We have completed a horizontal evaluation of nuclear isomers and the resulting data set contains a wealth of information which offers new insights in the nuclear structure of a wide range of configurations, nuclei approaching the drip lines etc. We now have reliable data on approximately 2460 isomers having a half-life ≥ 10 ns. A few of the systematics of the properties of nuclear isomers like excitation energy, half-life, spin, abundance etc. will be presented. The data set of semi-magic isomers strongly supports the existence of seniority isomers originating from the higher spin orbitals. (author)

[en] In this paper, we focus on the isomers that arise due to the seniority selection rules and the role played by generalized seniority when multi-j configurations are involved. In particular, we concentrate on explaining the B(E2) values in the semi-magic isomeric chains by using a simple approach. In this paper, we study the B(E2) variation of these isomers by using the generalized seniority scheme, applicable to many-j degenerate orbits. We show that the isomers known to arise mainly from the high-j intruder orbitals, do require the configuration mixing as an essential requirement

[en] The nuclear fission is one of the most complex nuclear phenomena in nature and many aspects remain only partially understood even now. The most exciting development in the 70's was the idea of existence of a second well. This was supported by many calculations and later on led to the discovery of fission isomers. We explore the occurrence of the second/third well by using a similar calculation. Because of the experimental difficulties, the observation of the third well is a very difficult task; yet it may now be attempted with the availability of modern detector arrays and separators

[en] In this paper, we study the 8⁺ isomer in ¹³⁰Cd (Z=48 and N=82), known to be arising from pure seniority g_9/2^-2 (two proton holes). We further compare it to the 10⁺ isomer in ²⁰⁶Hg (Z=80 and N=126), known to be arising from pure seniority h_11/2^-2 (two proton holes). Both the isomers result as the maximally aligned states from their respective dominant orbital. The new information in this region is limited due to the difficulties in populating large angular momenta for the neutron-rich nuclei

[en] Isomeric studies in neutron-rich nuclei are a powerful tool for exploring structure at the nuclear extremes. In this paper we discuss the systematic features of the excitation energies and transition probabilities of Sn isotopes in the region N = 50–82 and present their basic understanding in terms of generalized seniority. We further use generalized seniority as a probe to explore the neutron-rich $6^{+}$ seniority isomers in ^134–138Sn, and to validate the neutron single-particle energies beyond N = 82. We show that these isomers behave as generalized seniority isomers, where the so-called anomalous $\mathrm{B}(E2)$ behavior of the $6^{+}$ isomer in ¹³⁶Sn may be naturally explained. We support these results by shell model calculations, where the latest neutron single-particle energies of the N = 82–126 region have been used, and the i_13/2 neutron single-particle energy has been suitably modified in the renormalized charge-dependent Bonn interaction. This entails a possible new subshell closure at N = 112 due to the suggested higher location of the i_13/2 neutron orbital, also consistent with the choice of orbitals in the generalized seniority scheme. However, a small reduction in the f_7/2 two-body matrix elements is still required in the shell model calculations to consistently reproduce the experimental level energies as well as the transition probabilities in ^134–138Sn isotopes. (paper)

[en] The nuclear fission is one of the most complex nuclear phenomena in nature and many aspects remain only partially understood even in the 75^th year of its discovery. The third minimum has been discussed in the literature for many nuclides like thorium isotopes. The mic-mac approach with Cassini Ovaloid Shape parameterization for the nuclear potential has been utilized to calculate the potential energy surfaces in the actinides. This formalism is due to Garcia et al. The aim of the work is to search for the triple-humped fission barrier which may support the existence of hyper-deformed isomers. The paper look into such a hyper-deformed isomer near the magic numbers predicted around the 3:1 shapes. For the anisotropic-oscillator, the deformed magic numbers for the axes ratio 2:1 are 2, 4, 10, 16, 28, 40, 60, 80, 110, 140 and 182, which are also upwardly modified due to the spin-orbit term as recently shown for the super-deformed nuclei similar to the harmonic oscillator potential for spherical magic numbers. As we go to the higher deformation at 0.86 with axes ratio 3:1, the numbers become 2, 4, 6, 12, 18, 24, 36, 48, 60, 80, 100, 120, 150, 180, and 210. The spin-orbit interaction will modify these numbers upwards too. Therefore, the search for the third well near those magic numbers which lie in the actinide region is focussed. The potential energy surfaces are calculated for the nuclei having Z = 93 to 96 and N ∼ 150 for the search of triple-hump barrier. The calculations show that the third well corresponding to the 3:1 shell structure begins to appear in the deformation range 0.7-0.8 near neutron number 150 and above. The outer barrier decreases as we go from Z=93 to 95 due to increasing Coulomb energy contribution to the barrier. It starts to be more flat and leads to the existence of the deeper third well in the neutron-rich side of the particular isotopic chain. These calculations show that the Am nuclides may be the best candidates for third minimum. The deepest third minimum is observed in ²⁵⁰Am with a depth of 1.29 MeV. The next possible candidate is ²⁵¹Am. However, the experimentally accessible isotopes may be ^244,245Am. These nuclides have sufficiently deep minimum to observe hyper-deformed isomer. However, further calculations are in progress to establish this

[en] Nuclear isomers are the excited metastable states of nuclei, which have gained attention due to wide range of possible applications, both fundamental and applied. Seniority isomers, identified in semi-magic nuclei, have now been placed in a separate class due to their properties. In this paper, we extend our studies to include the energy systematics of the nuclear isomeric states arising from the i_13/2 intruder orbital in the Z = 82 isotopic chains and contrast it with the Z=50 chain of isomers arising from the h_11/2 intruder orbital

[en] Following on from our earlier paper Garg and Jain (2017 Phys. Scr. 92 094001) containing some initial results, we present a detailed discussion and complete results in this paper, which provide the first direct evidence for the validity of isospin as a nearly good quantum number in neutron-rich systems. The evidence comes from the reproduction of the general features of the partition-wise relative yields of neutron-rich fission fragments produced in two heavy-ion induced fusion fission reactions, namely ²⁰⁸Pb (¹⁸O, f) and ²³⁸U (¹⁸O, f), by using the concept of isospin conservation. To fix the isospin values and use the isospin algebra, we invoke what we term Kelson’s conjectures. We present a consistent scheme for isospin assignments based on these considerations. Our calculated results confirm that isospin behaves as an approximately good quantum number in neutron-rich systems, in this case, the fission fragments. (paper)

[en] In this paper, we have tried to overcome the ambiguities in assigning the isospin values (T, T_3) and considered all the possibilities allowed by the isospin selection rules. Also, the concept of Isobaric Analog States (IAS) has been used to assign the isospin to each fragment. We also use the neutron multiplicity data for each fission partition as given by Bogachev et al., to take into account the weight of various n-emission channels. We are, thus, able to reproduce the total relative yields of fission fragments quite well