Y. K. Gupta

Angular momentum dependence of the nuclear level-density parameter around Z ~ 50

{alpha}-particle evaporation spectra and {gamma}-ray multiplicities were measured for various target-projectile systems corresponding to residual nuclei in the range of Z{sub R}=48-55 and with excitation energy in the range of 30-40 MeV. The high-energy part of the evaporation spectra were analyzed using the statistical model code PACE2 to derive values of the inverse level-density parameter (K). The K values were found to be in the range of 9.0-10.5 for all systems. Angular momentum dependence of the inverse level-density parameter was investigated using the {gamma}-ray multiplicity data. It is seen that there are strong variations in K as a function of angular momentum for many systems. Present results provide important input information for a systematic understanding of the statistical properties of nuclei at moderate excitation energies and angular momenta.

Fission fragment angular distributions in the {sup 9}Be + {sup 232}Th reaction

Fission fragment angular distributions have been measured for a {sup 9}Be + {sup 232}Th system at four different beam energies around the Coulomb barrier. The experimental results on fission fragment anisotropies have been compared with predictions of the standard statistical saddle-point model (SSPM) and the preequilibrium fission (PEQ) model including projectile ground-state spin. It is observed that both SSPM and the PEQ model fail to reproduce the experimental results, indicating that projectile breakup may affect the fission fragment anisotropies.

Nuclear level-density parameters of nuclei in the Z{approx}70 and A{approx}180 mid-shell regions

{alpha}-particle evaporation energy spectra have been measured as a function of {gamma}-ray fold for various target-projectile systems leading to residual nuclei in the range of Z{approx}70 and A{approx}180 with excitation energy of 30-40 MeV. The inverse level-density parameter K was determined for various nuclei by comparing the high-energy part of the {alpha}-particle evaporation spectra with PACE2 predictions. It is observed that the inverse level-density parameter remains constant for all systems studied in this work within statistical errors in the angular momentum range of 15-30 ({Dirac_h}/2{pi}). The fold-gated {alpha}-particle energy spectra in these systems are well reproduced by the PACE2 code with a level-density parameter value of A/(8.2{+-}1.1) MeV{sup -1}.

Evidence for Coulomb effects on the fusion barrier distribution for deformed projectile nuclei

Coulomb effects during the interaction of light deformed projectile nuclei with a heavy collision partner have been predicted to modify the fusion barrier distribution leading to a hindrance in the sub-barrier fusion cross section. In order to verify this experimentally, we have determined the fusion barrier distributions from the measurement of quasielastic excitation functions for {sup 16}O(spherical)+{sup 115}In, {sup 28}Si(oblate)+ {sup 115}In, and {sup 30}Si(prolate)+ {sup 115}In systems. For {sup 16}O+{sup 115}In system, the fusion barrier distribution is single peaked, whereas for {sup 28}Si+{sup 115}In and {sup 30}Si+{sup 115}In systems, one observes broadening and well defined structures in fusion barrier distribution, which could be explained by coupled-channel calculations performed using the CCFULL code after including deformation and Coulomb effects on the projectile in the field of target nucleus.