Tapan Mukhopadhyay

Chaos modified wall formula damping of the surface motion of a cavity undergoing fissionlike shape evolutions

The chaos weighted wall formula developed earlier for systems with partially chaotic single particle motion is applied to large amplitude collective motions similar to those in nuclear fission. Considering an ideal gas in a cavity undergoing fission-like shape evolutions, the irreversible energy transfer to the gas is dynamically calculated and compared with the prediction of the chaos weighted wall formula. We conclude that the chaos weighted wall formula provides a fairly accurate description of one body dissipation in dynamical systems similar to fissioning nuclei. We also find a qualitative similarity between the phenomenological friction in nuclear fission and the chaos weighted wall formula. This provides further evidence for one body nature of the dissipative force acting in a fissioning nucleus.

Photonuclear reactions of actinide and pre-actinide nuclei at intermediate energies

Photonuclear reaction is described with an approach based on the quasideuteron nuclear photoabsorption model followed by the process of competition between light particle evaporation and fission for the excited nucleus. Thus fission process is considered as a decay mode. The evaporation-fission process of the compound nucleus is simulated in a Monte Carlo framework. Photofission reaction cross sections are analysed in a systematic manner in the energy range {approx}50-70 MeV for the actinides {sup 232}Th, {sup 233}U, {sup 235}U, {sup 238}U, and {sup 237}Np and the pre-actinide nuclei {sup 208}Pb and {sup 209}Bi. The study reproduces satisfactorily well the available experimental data of photofission cross sections at energies {approx}50-70 MeV and the increasing trend of nuclear fissility with the fissility parameter Z{sup 2}/A for the actinides and pre-actinides at intermediate energies ({approx}20-140 MeV)

Photonuclear reactions of actinides in the giant dipole resonance region

Abstract.Photonuclear reactions at energies covering the giant dipole resonance (GDR) region are analyzed with an approach based on nuclear photoabsorption followed by the process of competition between light-particle evaporation and fission for the excited nucleus. The photoabsorption cross-section at energies covering the GDR region is contributed by both the Lorentz-type GDR cross-section and the quasi-deuteron cross-section. The evaporation-fission process of the compound nucleus is simulated in a Monte Carlo framework. Photofission reaction cross-sections are analyzed in a systematic manner in the energy range of ∼ 10-20 MeV for the actinides 232Th , 238U and 237Np . Photonuclear cross-sections for the medium-mass nuclei 63Cu and 64Zn , for which there are no fission events, are also presented. The study reproduces satisfactorily the available experimental data of photofission cross-sections at GDR energy region and the increasing trend of nuclear fissility with the fissility parameter Z2/A for the actinides.

Coherent stochastic resonance in the case of two absorbing boundaries.

The coherent stochastic resonance is observed and studied with a multistep periodic signal in a continuous medium having two absorbing boundaries. The general features of this process are exhibited. The universal features at the resonance point are demonstrated. The kinetic behaviors around the resonance point are also presented.

{gamma} induced multiparticle emissions of medium mass nuclei at intermediate energies

A comprehensive analysis of multiparticle emissions following photon induced reactions at intermediate energies is provided. Photon induced reaction is described in the energy range of {approx}30-140 MeV with an approach based on the quasideuteron nuclear photoabsorption model followed by the process of competition between light particle evaporation and fission for the excited nucleus. The evaporation-fission process of the compound nucleus is simulated in a Monte-Carlo framework. The study shows almost no fission events for the medium mass nuclei and reproduces the available experimental data of photonuclear reaction cross sections satisfactorily at energies {approx}30-140 MeV.

Coherent Stochastic Resonance in One Dimensional Diffusion with One Reflecting and One Absorbing Boundaries

It is shown that the single-step periodic signal (periodic telegraph signal) can not produce coherent stochastic resonance for diffusion on a segment with one absorbing and one reflecting end points while the multi-step periodic signal does. The general features of this process are exihibited. The resonant frequency is found to decrease and the mean first passage time at resonant frequency increases linearly, as we increase the length of the medium. The cycle variable is shown to be the proper argument to express the first passage probability at resonance. A formula for first passage probability at resonance is derived in terms of two universal functions, which clearly isolates its dependence on the length of the medium.

Mass and charge distribution in232Th(α, f) reaction in the projectile energy range 28 to 72 MeV

The cumulative yields for 13 short-lived neutron rich nuclei in the mass rangeA=99 toA=118, produced via the232Th (α, f) reaction were determined at four incident beam energies covering the range from 28 to 72 MeV usingγ-spectroscopy of fission products. The charge distribution parameter Zp was determined for theA=99 mass chain at all the four incident beam energies of 28.5, 39.7, 50.8 and 71.4 MeV and was found to fit into a description of fission process with unchanged charge division (UCD). The measured cumulative yields were converted into chain yields assuming UCD and the yieldmass distribution was obtained at all the above energies. The mass distribution remains asymmetric even at 71.4 MeV, the highest energy studied in this work. The excitation energy dependence of the mass and the charge distribution and of the cumulative yields indirectly suggests that the fission has predominantly proceeded from a relatively low level of excitation allowing most of the excitation energy to be carried away by light particles prior to scission.

Chaotic dynamics of single particles in axially symmetric nuclear shapes

Abstract The spectral statistics of single particle motion in deformed cavities with axial symmetry are presented. Considering cavities with Legendre-polynomial deformations P 2 to P 6 , a systematic study of the fluctuation measures of the energy spectra is performed. For each deformation type the evolution of the fluctuation measures with increasing deformation indicating an order-to-chaos transition is observed. The nature of such transitions is found to be in agreement with earlier classical phase space calculations.

Angular distributions of neutron-nucleus collisions

We derive the total and the differential cross sections with respect to angle for neutron-induced reactions from an analytical model having a simple functional form to demonstrate the quantitative agreement with the measured cross sections. The energy dependence of the neutron-nucleus interaction cross sections are estimated successfully for energies ranging from 5 to 600 MeV. In this work, the effect of the imaginary part of the nuclear potential is treated more appropriately compared to our earlier work. The angular distributions for neutron scattering also agree reasonably well with the experimental data at forward angles.

Erratum: Cross sections of neutron-induced reactions [Phys. Rev. C 82, 044613 (2010)]

The first equation of Eqs.(3) in [1] was used to describe the mass number and energy dependence of experimental total neutron cross sections for the first time in [2], while the second and third ones for scattering and reaction cross sections in [3]. We are sorry for the omission of these two references which were not in our knowledge. In fact we derived these equations and Eq.(4) of Ref.[12] [J.D. Anderson and S.M. Grimes, Phys. Rev. C 41, 2904 (1990) [4]] of our paper [1] as follows. From partial wave analysis of scattering theory, we know the standard expressions for scattering σsc and reaction σr cross sections as