• ASHOK KUMAR

Articles written in Pramana – Journal of Physics

• Elastic scattering of electrons by argon atoms

The partial wave method with a central potential has been applied to investigate the elastic scattering of electrons by the argon atoms in the intermediate energy range (100 eV − 1 keV). The central potential includes the effects of the static field, exchange and polarization. The results are in good accord with recent experimental data.

• Magnetic susceptibility of heavy rare-earth sesquioxides

Measurement of magnetic susceptibility of the powder samples of heavy rare-earth (Tb, Dy, Ho, Er, Tm and Yb) sesquioxides have been reported in the temperature range 300 to 900 K. Curie-Weiss law behaviour has been observed for all samples. The Curie constant, the paramagnetic Curie temperature and the magneton number for magnetic ions in each material have also been evaluated.

• Back-bending in182,184,186osmium

The high spin yrast states uptoJ=22+ in182,184,186Os are studied in a microscopic variational approach with number-conserved projected states. The energy spectra, quadrupole, moments andB (E2) values are calculated by employing the Hamiltonian with quadrupole plus pairing interactions. The results of the calculations are in fair agreement with the available experimental data.

• High spin yrast states in even platinum isotopes

The high spin yrast states up toJ=20+ in184, 186Pt and190, 192, 194Pt are studied in a microscopic approach of variation with number-conserved projected states. The energy spectra, quadrupole moments andB(E2) values are calculated by employing the Hamiltonian with quadrupole plus pairing interactions. The results of the calculations are in fair agreement with the available experimental data.

• The quadrupole plus pairing interaction model in large configuration space for W, Os and Pt nuclei

The equilibrium deformations of tungsten, osmium and platinum nuclei are studied with the self-consistent quadrupole plus pairing interaction model by considering all the nucleons in nucleus explicitly. It is shown that similar results can be obtained by performing calculations with or without the assumption of an inert core. The only difference is in the strength of the quadrupole and pairing interactions to be employed in the respective calculations. The experimental static quadrupole moments and theB (E2) values are correctly reproduced by performing calculations with bare nucleon charge for all the nucleons.

• Elastic scattering ofα-particles from20Ne

A relatively simple procedure using nuclear interaction calculated microscopically from two-nucleon potential employing equivalence of resonating group method and generator coordinate method has been used to calculate the differential cross-sections (DCS) forα +20Ne elastic scattering atElab=18.0, 20.2, 21.9, 23.0 and 27.2 MeV. The absorption effects due to the opening of the non-elastic channels are taken into account approximately by the sharp cut-off of lower partial waves. The anomalous large oscillations of the DCS at backward angles atElab=18.0 and 27.2 MeV are reproduced. The calculated results are in fair agreement with the experimental data.

• Level structures in the odd-odd nucleus180Re

Experimental data on energy levels of the odd-odd deformed nucleus180Re obtained from radioactive-decay and heavy-ion reaction studies are analysed to deduce spin-parity and configuration assignments for the six observed rotational bands based on the selection rules for fast beta transitions, criteria for the relative-energy ordering of the triplet and singlet bandheads, two-particle-plus-rotor model calculations including Coriolis mixing, rotational energy systematics involving staggering features, and considerations of gyromagnetic ratios, signature splittings and rotational band alignments.

• Trace formula for level density of a spherical billiard

A trace formula for the oscillating part of the level density for a spherical billiard has been obtained in spherical polar coordinates. The Jacobian of stability and the length of the orbits are obtained from the classical mechanics of the problem. The same formula is applicable to both the planar and the diametric orbits. Numerical results have been obtained with this formula and compared with the results from exact quantum theory, EBK quantization, and Balian and Bloch.

• Magnetic rotation and chiral symmetry breaking

The deformed mean field of nuclei exhibits various geometrical and dynamical symmetries which manifest themselves as various types of rotational and decay patterns. Most of the symmetry operations considered so far have been defined for a situation wherein the angular momentum coincides with one of the principal axes and the principal axis cranking may be invoked. New possibilities arise with the observation of rotational features in weakly deformed nuclei and now interpreted as magnetic rotational bands. More than 120 MR bands have now been identified by filtering the existing data. We present a brief overview of these bands. The total angular momentum vector in such bands is tilted away from the principal axes. Such a situation gives rise to several new possibilities including breaking of chiral symmetry as discussed recently by Frauendorf. We present the outcome of such symmetries and their possible experimental verification. Some possible examples of chiral bands are presented.

• Measurement of peak ﬂuence of neutron beams using Bi-ﬁssion detectors

Fission fragments and other charged particles leave tracks of permanent damage in most of the insulating solids. Damage track detectors are useful for personal dosimeters and for ﬂux/dose determination of high-energy particles from accelerators or cosmic rays. A detector that has its principal response at nucleon energy above 50 MeV is provided by the ﬁssion of Bi-209. Neutrons produce the largest percentage of hadron dose in most high-energy radiation ﬁelds. In these ﬁelds, the neutron spectrum is typically formed by low-energy neutrons (evaporation spectrum) and high-energy neutrons (knock-on spectrum). We used Bi-ﬁssion detectors to measure neutron peak ﬂuence and compared the result with the calculated value of neutron peak ﬂuence. For the exposure to 100 MeV we have used the iThemba Facility in South Africa.

• Main injector particle production experiment at Fermilab

The main injector particle production (MIPP) experiment at Fermilab uses particle beams of charged pions, kaons, proton and antiproton with beam momenta of 5–90 GeV/c to measure particle production cross-sections of various nuclei including liquid hydrogen, MINOS target and thin targets of beryllium, carbon, bismuth and uranium. The physics motivation to perform such cross-section measurements is described here. Recent results on the analysis of NuMI target and forward neutron cross-sections are presented here. Preliminary cross-section measurements for 58 GeV/c proton on liquid hydrogen target are also presented. A new method is described to correct for low multiplicity inefficiencies in the trigger using KNO scaling.

• Characteristics of disintegration of different emulsion nuclei by relativistic 28Si nuclei at 3.7 A GeV

An analysis of the data based on 924 inelastic interaction events induced by 28 Si nuclei in a nuclear emulsion is presented. The nuclear fragmentation process is studied by analysing the total charge (𝑄) distribution of the projectile spectators for different emulsion target groups along with the comparison of Monte Carlo Glauber model results. Probability distributions for total disintegrated events as a function of different projectile masses are shown and compared with cascade evaporation model results at same energy per nucleon. Further, mean multiplicities of different charged secondaries for different classes of events are presented and for each event, variation of mean multiplicities as a function of total charge (𝑄) is also presented. The pseudorapidity distributions and normalized pseudorapidity distributions of the produced charged particles in nucleus–nucleus collisions at 3.7 A GeV are analysed for total disintegration (TD) as well as minimum-bias events.

• Physics potential of the ICAL detector at the India-based Neutrino Observatory (INO)

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies andpath lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial toaddress some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations.We describe the simulation framework, the neutrino interactions in the detector, and the expected responseof the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Itscharge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles.

• Rapid Communication: $\Delta\upsilon = 2$ seniority changing transitions in yrast $3^{−}$ states and $B(E3)$ systematics of Sn isotopes

We show for the first time that the generalized seniority scheme explains reasonably well the $B(E3)$ systematics for the $(0^{+} → 3^{−}_{1})$ transitions in the Sn isotopes, which are odd-tensor $E3$ transitions connecting different seniority states $(\Delta\upsilon = 2)$. Additionally, we also present large scale shell model (LSSM) calculations to support our interpretation. The generalized seniority scheme points to the octupole character of these 3− states in Sn isotopes.

• Test of isospin conservation in thermal neutron-induced fission of $^{245}Cm$

We have recently shown that the general trends of partition-wise fission fragment mass distribution in heavy-ion-induced compound nuclear (CN) fission of heavy nuclei can be reproduced reasonably well by using theconcept of isospin conservation, hence providing a direct evidence of isospin conservation in neutron-rich systems [Jain et al, Nucl Data Sheets 120, 123 (2014); Garg and Jain, Phys. Scr. 92, 094001 (2017); Jain and Garg, EPJ Web of Conference 178, 05007 (2018); Garg et al, Phys. Scr. 93, 124008 (2018)]. In this paper, we test the concept of isospin conservation to reproduce the fission fragment mass distribution emerging from thermal neutron-inducedCN fission reaction, $^{245}\rm{Cm}(n_{th}, f)$. As earlier, we use Kelson’s conjectures [I Kelson, Proceedings of the Conference on Nuclear Isospin (Academic Press, New York, 1969)] to assign isospin to neutron-rich fragments emitted in fission, which suggest the formation of fission fragments in isobaric analogue states. We calculate the relative yields of neutron-rich fragments using the concept of isospin conservation and basic isospin algebra. The calculated resultsreproduce the experimentally known partition-wise mass distributions quite well. This highlights the usefulness of isospin as an approximately good quantum number in neutron-rich nuclei. This also allows us to predict the fragment distribution of the most symmetric Cd–Cd partition and the heavier mass fragment distributions, both not measured so far.

• # Pramana – Journal of Physics

Current Issue
Volume 92 | Issue 6
June 2019