Highly deformed 40^{40}Ca configurations in 28^{28}Si + 12^{12}C

The possible occurrence of highly deformed configurations in the $^{40}$Ca di-nuclear system formed in the $^{28}$Si + $^{12}$C reaction is investigated by analyzing the spectra of emitted light charged particles. Both inclusive and exclusive measurements of the heavy fragments (A $\geq$ 10) and their associated light charged particles (protons and $\alpha$ particles) have been made at the IReS Strasbourg {\sc VIVITRON} Tandem facility at bombarding energies of $E_{lab} (^{28}$Si) = 112 MeV and 180 MeV by using the {\sc ICARE} charged particle multidetector array. The energy spectra, velocity distributions, and both in-plane and out-of-plane angular correlations of light charged particles are compared to statistical-model calculations using a consistent set of parameters with spin-dependent level densities. The analysis suggests the onset of large nuclear deformation in $^{40}$Ca at high spin.Comment: 33 pages, 11 figure

Fusion and Binary-Decay Mechanisms in the 35^{35}Cl+24^{24}Mg System at E/A ≈\approx 8 MeV/Nucleon

Compound-nucleus fusion and binary-reaction mechanisms have been investigated for the $^{35}$Cl+$^{24}$Mg system at an incident beam energy of E$_{Lab}$= 282 MeV. Charge distributions, inclusive energy spectra, and angular distributions have been obtained for the evaporation residues and the binary fragments. Angle-integrated cross sections have been determined for evaporation residues from both the complete and incomplete fusion mechanisms. Energy spectra for binary fragment channels near to the entrance-channel mass partition are characterized by an inelastic contribution that is in addition to a fully energy damped component. The fully damped component which is observed in all the binary mass channels can be associated with decay times that are comparable to, or longer than the rotation period. The observed mass-dependent cross sections for the fully damped component are well reproduced by the fission transition-state model, suggesting a fusion followed by fission origin. The present data cannot, however, rule out the possibility that a long-lived orbiting mechanism accounts for part or all of this yield.Comment: 41 pages standard REVTeX file, 14 Figures available upon request -

Monte Carlo calculation of the de-excitation of fission fragments of Cf-252(sf) within multimodal random neck rupture model

The multimodal random neck rupture model has been employed to study the energy distribution in nuclear fission. Monte Carlo calculations have been carried out on the de-excitation of fission fragments of Cf-252(sf) using this model. In this study special attention has been paid to the law of conservation of energy. Results for the neutron multiplicities and kinetic energies, average gamma energies are in good agreement with the experimental data. Mass and charge distributions of secondary fission fragments are also well reproduced in the calculations

Nuclear level density with non-zero angular momentum

The statistical properties of interacting fermions have been studied for various angular momentum with the inclusion of pairing interaction. The dependence of the critical temperature on angular momentum for several nuclei, have been studied. The yrast energy as a function of angular momentum for (28)Si and (24)Mg nuclei have been calculated up to 60.0 MeV of excitation energy. The computed limiting angular momenta are compared with the experimental results for (26)Al produced by (12)C+(14)N reaction. The relevant nuclear level densities for non-zero angular momentum have been computed for (44)Ti and (136)Ba nuclei. The results are compared with their corresponding values obtained from the approximate. formulas

Microscopic study of spin cut-off factors of nuclear level densities

Level densities and spin cut-off factors have been investigated within the microscopic approach based on the BCS Hamiltonian. In particular, the spin cut-off parameters have been calculated at neutron binding energies over a large range of nuclear mass using the BCS theory. The spin cut-off parameters sigma(2)(E) have also been obtained from the Gilbert and Cameron expression and from rigid body calculations. The results were compared with their corresponding macroscopic values. It was found that the values of sigma(2)(E) did not increase smoothly with A as expected based on macroscopic theory. Instead, the values of sigma(2)(E) show structure reflecting the angular momentum of the shell model orbitals near the Fermi energy

Statistical treatment of low-energy nuclear level schemes

The level density parameter and the back shift energy El. are determined for nuclei with A-values across the whole periodic table from fits to complete level schemes at low excitation energy near the neutron binding energies. We find that the energy back shift E, shows complicated behavior and depends, on the type of the nucleus, even-even, odd mass, and odd-odd. The spin cut-off factor has also been investigated for nuclei mentioned above. The results are compared with the previous results and different experimental data on level densities

Possible exit channel effect on isomer yield ratios

Isomer yield ratio measurements in fission are important in understanding the fission process. With the development of new instrumental techniques, a large number of yield data are now available. The experimental data on isomer yield ratios in the thermal neutron induced fission of235U are compared with those calculated from the simple statistical model by Madland and England. The method of calculation has been extended to the isotopes having more than one isomeric state. The results may be explained according to the multi-exit-channel model of fission. © 1997 Akadémiai Kiadó

Proton and alpha pre-scission emission in the system 32S + 109Ag at 180 MeV

Charged-particles in coincidence with fission fragments (FF) and evaporationresidues (ER) have been measured for the system 180-MeV 32S + 109Ag leading to the composite system 141Eu at the excitation energy Ex 90 MeV. Energy spectra and multiplicities in both channels have been compared to the predictions of the statistical model by using the code PACE2. The best overall agreement was obtained, by using af /aν=1.12, a fission delay 12 < τd < 14 ( x 10−21s) and reduced alpha barriers in the relevant J-region for the fission channel. In addition to pre-scission particle measurements, we stress the importance of measuring particles in the ER channel. These latter allow to impose further constraints on the statistical model input parameters and to extract a more reliable picture on the presence of dynamical effects