Conditions for equivalence of Statistical Ensembles in Nuclear Multifragmentation

Statistical models based on canonical and grand canonical ensembles are extensively used to study intermediate energy heavy ion collisions. The underlying physical assumption behind canonical and grand canonical models is fundamentally different, and in principle agree only in the thermodynamical limit when the number of particles become infinite. Nevertheless, we show that these models are equivalent in the sense that they predict similar results if certain conditions are met even for finite nuclei. In particular, the results converge when nuclear multifragmentation leads to the formation of predominantly nucleons and low mass clusters. The conditions under which the equivalence holds are amenable to present day experiments.Comment: 5 pages, 5 figure

Effect of transients in nuclear fission on multiplicity of prescission neutrons

Transients in the fission of highly excited nuclei are studied in the framework of the Langevin equation. Time-dependent fission widths are calculated which show that after the initial transients, a steady flow towards the scission point is established not only for nuclei which have fission barriers but also for nuclei which have no fission barrier. It is shown from a comparison of the transient time and the fission life time that fission changes from a diffusive to a transient dominated process over a certain transition region as a function of the spin of the fissioning nucleus. Multiplicities of prescission neutrons are calculated in a statistical model with as well as without a single swoop description of fission and they are found to differ in the transition region. We however find that the difference is marginal and hence a single swoop picture of fission though not strictly valid in the transition region can still be used in the statistical model calculations.Comment: 15 pages including 7 figures, to appear in The European Physical Journal

Effect of secondary decay on isoscaling: Results from the canonical thermodynamical model

The projectile fragmentation reactions using $^{58}Ni$ $\&$ $^{64}Ni$ beams at 140 MeV/n on targets$^{9}Be$ $\&$ $^{181}Ta$ are studied using the canonical thermodynamical model coupled with an evaporation code. The isoscaling property of the fragments produced is studied using both the primary and the secondary fragments and it is observed that the secondary fragments also respect isoscaling though the isoscaling parameters $\alpha$ and $\beta$ changes. The temperature needed to reproduce experimental data with the secondary fragments is less than that needed with the primary ones. The canonical model coupled with the evaporation code successfully explains the experimental data for isoscaling for the projectile fragmentation reactions

Constraints on Density Dependent MIT Bag Model Parameters for Quark and Hybrid Stars

We compute the equation of state (EoS) of strange quark stars (SQSs) with the MIT Bag model using density dependent bag pressure, characterized by a Gaussian distribution function. The bag pressure's density dependence is controlled by three key parameters namely the asymptotic value ($B_{as}$), $\Delta B(=B_0 - B_{as})$, and $\beta$. We explore various parameter combinations ($B_{as}$, $\Delta B$, $\beta$) that adhere to the Bodmer-Witten conjecture, a criterion for the stability of SQSs. Our primary aim is to analyze the effects of these parameter variations on the structural properties of SQSs. However we find that none of the combinations can satisfy the NICER data for PSR J0030+0451 and the constraint on tidal deformability from GW170817. So it can be emphasized that this model cannot describe reasonable SQS configurations. We also extend our work to calculate structural properties of hybrid stars (HSs). With the density dependent bag model (DDBM), these astrophysical constraints are fulfilled by the HSs configurations within a very restricted range of the three parameters. The present work is the first to constrain the parameters of DDBM for both SQS and HSs using the recent astrophysical constraints on tidal deformabiity from GW170817 and that on mass-radius relationship from NICER data.Comment: Accepted for publication in Nuclear Physics

Evaporation residue cross-sections as a probe for nuclear dissipation in the fission channel of a hot rotating nucleus

Evaporation residue cross-sections are calculated in a dynamical description of nuclear fission in the framework of the Langevin equation coupled with statistical evporation of light particles. A theoretical model of one-body nuclear friction which was developed earlier, namely the chaos-weighted wall formula, is used in this calculation for the 224Th nucleus. The evaporation residue cross-section is found to be very sensitive to the choice of nuclear friction. The present results indicate that the chaotic nature of the single-particle dynamics within the nuclear volume may provide an explanation for the strong shape-dependence of nuclear friction which is usually required to fit experimental data.Comment: 12 pages including 4 figure

A statistically motivated choice of process parameters for the improvement of canthaxanthin production by Dietzia maris NIT-D (accession number: HM151403)

Dietzia maris NIT-D, a producer of canthaxanthin, is isolated during routine screening of pigment producing bacteria. The effects of process parameters, namely temperature, pH, shaker speed, percentage inoculum, medium volume, and concentration of glucose on the canthaxanthin production are studied by using response surface design methodology. The optimal conditions are temperature = 30 degrees C, pH = 5.9, shaker speed = 125 rpm, inoculum = 1.9 %, volume = 50 mL, and glucose = 15 g L-1, resulting in a canthaxanthin production of 152 mg L-1, which is 25% higher than that of a recently reported study

Prescission neutron multiplicity and fission probability from Langevin dynamics of nuclear fission

A theoretical model of one-body nuclear friction which was developed earlier, namely the chaos-weighted wall formula, is applied to a dynamical description of compound nuclear decay in the framework of the Langevin equation coupled with statistical evaporation of light particles and photons. We have used both the usual wall formula friction and its chaos-weighted version in the Langevin equation to calculate the fission probability and prescission neutron multiplicity for the compound nuclei $^{178}$W, $^{188}$Pt, $^{200}$Pb, $^{213}$Fr, $^{224}$Th, and $^{251}$Es. We have also obtained the contributions of the presaddle and postsaddle neutrons to the total prescission multiplicity. A detailed analysis of our results leads us to conclude that the chaos-weighted wall formula friction can adequately describe the fission dynamics in the presaddle region. This friction, however, turns out to be too weak to describe the postsaddle dynamics properly. This points to the need for a suitable explanation for the enhanced neutron emission in the postsaddle stage of nuclear fission.Comment: RevTex, 14 pages including 5 Postscript figures, results improved by using a different potential, conclusions remain unchanged, to appear in Phys. Rev.