arXiv subjects

B. K. Agrawal

Publications and source records attributed to B. K. Agrawal.

97 records · Page 6Linked to original sources

arXiv1998

Equation of state for finite nuclei and liquid-gas phase transition

We construct the equation of state (EOS) of finite nuclei including surface and Coulomb effects in a Thomas-Fermi framework using a finite range, momentum and density dependent two-body interaction. We identify critical temperatures for nuclei below which the EOS so constructed shows clear signals for liquid-gas phase transition in these finite systems. Comparison with the EOS of infinite nuclear matter shows that the critical density and temperature of the phase transition in nuclei are influenced by the mentioned finite size effects.

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arXiv1998

Isotope thermometery in nuclear multifragmentation

A systematic study of the effect of fragment$-$fragment interaction, quantum statistics, $γ$-feeding and collective flow is made in the extraction of the nuclear temperature from the double ratio of the isotopic yields in the statistical model of one-step (Prompt) multifragmentation. Temperature is also extracted from the isotope yield ratios generated in the sequential binary-decay model. Comparison of the thermodynamic temperature with the extracted temperatures for different isotope ratios show some anomaly in both models which is discussed in the context of experimentally measured caloric curves.

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arXiv1997

Level density and level density parameter in medium heavy nuclei including thermal and quantal fluctuation effects

In a realistic application of the SPA + RPA theory for calculation of the nuclear level densities we find that quantal fluctuation corrections (RPA) are important even up to temperature $T = 2.0 MeV$. This leads to a good agreement between calculated numbers and the available experimental data for $^{104}Pd$ and $^{114}Sn$, particularly the excitation energy ($E^*$) dependence. Furthermore, we also argue that $a=S^2/4E^*$ is the only correct definition of the level density parameter in the present context which is also consistent with the Bethe like level density formula.

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arXiv1995

SPA+RPA approach to canonical and grandcanonical treatments of nuclear level densities

Using an exactly solvable pairing model Hamiltonian in the static path approximation together with small-amplitude quantal fluctuation corrections in random phase approximation (SPA+RPA), we have analyzed the behaviour of canonical (number projected) and grandcanonical treatments of nuclear level densities as a function of temperature and number of particles. For small particle numbers at a low temperature, we find that though the grandcanonical partition function in SPA+RPA approach is quite close to its exact value, the small errors in its estimation causes significant suppression of level density obtained using number projected partition function. The results are also compared with the smoothed out exact values of level density. Within this model study, it appears that due to saddle point approximation to multiple Laplace-back transform, the grandcanonical treatment of level density at low temperature may be reliable only for relatively large number of particles.

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arXiv1993

On the angular momentum dependence of nuclear level densities

Angular momentum dependence of nuclear level densities at finite temperatures are investigated in the static path approximation(SPA) to the partition function using a cranked quadrupole interaction Hamiltonian in the following three schemes: (i) cranking about x-axis, (ii) cranking about z-axis and (iii) cranking about z-axis but correcting for the orientation fluctuation of the axis. Performing numerical computations for an $sd$ and a $pf$ shell nucleus, we find that the x-axis cranking results are satisfactory for reasonably heavy nuclei and this offers a computationally faster method to include the angular momentum dependence at high temperatures in the SPA approach. It also appears that at high spins inclusion of orientation fluctuation correction would be important.

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arXiv1993

Temperature induced alignment in hot rotating nuclei

Employing a cranking Hamiltonian, in the static path approximation to the partition function, we have studied the behaviour of the moment of inertia of $^{64}Zn$ at a few values of temperatures as a function of the rotation frequency. At a low temperature T = 0.5 MeV and J=16 rotational alignment of $0g_{9/2}$ orbitals takes place. But at a high temperature T = 2.0 MeV about 40 - 45$\%$ of all the angular momenta are generated by the alignment of the same orbitals. This should imply a decrease in collectivity for all the spins at high temperatures.

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arXiv1993

Thermal properties of a rotating nucleus in a fluctuating mean field approach

The static path approximation to the path integral representation of partition function provides a natural microscopic basis to deal with thermal fluctuations around mean field configurations. Using this approach for one-dimensional cranking Hamiltonian with quadrupole- quadrupole interaction term we have studied a few properties like energy, level density, level density parameter($a$) and moment of inertia as a function of temperature and spin for $^{64}Zn$ taking it as an illustrative example. We have also investigated the effects of variation in interaction strength on the level density and the parameter $a$ as a function of temperature. The moment of inertia, $\cal I$ versus rotational frequency, $ω$ plot shows a sudden rise in the value of $\cal I$ due to rotation alignment of $0g_{9/2}$ orbitals at $ω\approx 1.0$ MeV for a small temperature T $\sim 0.5$ MeV. At high T $\sim$ 2.0 MeV about 40-45$\%$ of each angular momentum is generated by alignment of $0g_{9/2}$ orbitals with an interesting result that at $ω\sim 1.0$ MeV and spin J $\sim$ 16 the moment of inertia has almost a constant, temperature independent value.

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