• S K Patra

      Articles written in Pramana – Journal of Physics

    • A relativistic mean-field study of magic numbers in light nuclei from neutron to proton drip-lines

      T K Jha M S Mehta S K Patra B K Raj Raj K Gupta

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      In an axially deformed relativistic mean-field calculation of single-particle energy spectra ofN = 8 (Li-Mg) andN = 14,16 (C-Mg) isotonic chain and the one- and two-neutron separation energies of various isotopes of Li-Mg, new magic numbers are found to exist atN = 6 andN = 16 and/orN = 14, which are in addition to theN = 8 andN = 20 magic numbers. In neutron-rich nuclei, the shell gap atN = 6 is larger than atN = 8 and a large gap is observed forN = 16 or 14 for the neutron-rich andN = 14 for proton-rich nuclei. Large shell gaps are also found to exist atN = 14 and 16 orN = 16 alone for nuclei near theβ-stability line. The above results are independent of the parameter sets TM2, NL3 and NL-SH used here. Similarly, new large shell gaps are predicted atZ = 616 and/or 14 for protons.

    • Shape change in Hf, W and Os-isotopes: A non-relativistic Hartree-Fock versus relativistic Hartree approximation

      Z Naik B K Sharma T K Jha P Arumugam S K Patra

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      We have investigated the ground-state structures of even-even Hf, W and Os isotopes within the framework of a deformed non-relativistic Hartree-Fock and a relativistic mean field formalism. A majority of the nuclei are predicted to be prolate in shape in the relativistic calculations. On the other hand, contrary to the relativistic results, we predict a shape change in a cyclic order in the non-relativistic calculations. However, in both the cases, the magnitude of the quadrupole deformation parameter agrees well with the experimental data. We also evaluated the hexadecapole deformation parameter for Hf, W and Os isotopes and irrespective of the shape change in quadrupole moments, we find a cyclic change in hexadecapole shape from positive to negative and vice versa in both the relativistic and non-relativistic formalisms.

    • Potential energy surfaces forN =Z,20Ne-112Ba nuclei

      M S Mehta T K Jha S K Patra Raj K Gupta

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      We have calculated the potential energy surfaces forN = Z,20Ne-112Ba nuclei in an axially deformed relativistic mean field approach. A quadratic constraint scheme is applied to determine the complete energy surface for a wide range of the quadrupole deformation. The NL3, NL-RA1 and TM1 parameter sets are used. The phenomenon of (multiple) shape coextistence is studied and the calculated ground and excited state binding energies, quadrupole deformation parameters and root mean square (rms) charge radii are compared with the available experimental data and other theoretical predictions.

    • Fission decay properties of ultra neutron-rich uranium isotopes

      L Satpathy S K Patra R K Choudhury

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      The fission decay of highly neutron-rich uranium isotopes is investigated which shows interesting new features in the barrier properties and neutron emission characteristics in the fission process. 233U and 235U are the nuclei in the actinide region in the beta stability valley which are thermally fissile and have been mainly used in reactors for power generation. The possibility of occurrence of thermally fissile members in the chain of neutron-rich uranium isotopes is examined here. The neutron number $N = 162$ or 164 has been predicted to be magic in numerous theoretical studies carried out over the years. The series of uranium isotopes around it with $N = 154-172$ are identified to be thermally fissile on the basis of the fission barrier and neutron separation energy systematics; a manifestation of the close shell nature of $N = 162$ (or 164). We consider here the thermal neutron fission of a typical representative 249U nucleus in the highly neutron-rich region. Semiempirical study of fission barrier height and width shows that 250U nucleus is stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. On the basis of the calculation of the probability of fragment mass yields and the microscopic study in relativistic mean field theory, this nucleus is shown to undergo exotic decay mode of thermal neutron fission (multi-fragmentation fission) whereby a number of prompt scission neutrons are expected to be simultaneously released along with the two heavy fission fragments. Such properties will have important implications in stellar evolution involving 𝑟-process nucleosynthesis.

    • The effect of nonlinearity in relativistic nucleon–nucleon potential

      B B Sahu S K Singh M Bhuyan S K Patra

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      A simple form for nucleon–nucleon (NN) potential is introduced as an alternative to the popular M3Y form using the relativistic mean field theory (RMFT) with the non-linear terms in 𝜎 -meson for the first time. In contrast to theM3Y form, the new interaction becomes exactly zero at a finite distance and the expressions are analogous with the M3Y terms. Further, its applicability is examined by the study of proton and cluster radioactivity by folding it with the RMFT-densities of the cluster and daughter nuclei to obtain the optical potential in the region of proton-rich nuclides just above the double magic core 100Sn. The results obtained were found comparable with the widely used M3Y $NN$ interactions.

    • A pilgrimage through superheavy valley

      M Bhuyan S K Patra

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      We searched for the shell closure proton and neutron numbers in the superheavy region beyond 𝑍 = 82 and 𝑁 = 126 within the framework of non-relativistic Skryme–Hartree–Fock (SHF) with FITZ, SIII, SkMP and SLy4 interactions. We have calculated the average proton pairing gap $\Delta_p$, average neutron pairing gap $\Delta_n$, two-nucleon separation energy $S_{2q}$ and shell correction energy $E_{\text{shell}}$ for the isotopic chain of 𝑍 = 112–126. Based on these observables, 𝑍 = 120 with 𝑁 = 182 is suggested to be the magic numbers in the present approach.

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