Asymmetric fission of Ni56

Cross sections for the two-body channels populated in the S32+Mg24 reaction at Ec.m.=60.8 MeV have been measured by use of a coincidence technique which allows correction for secondary light-particle evaporation. The data show reaction yields with full equilibration of energy and mass-asymmetry coordinates. These results suggest an asymmetric fission mechanism and are contrary to what is expected from the previously proposed "orbiting" mechanism in light systems

Structure in the E2 quasicontinuum spectrum of Dy154

The evolution of the quasicontinuum spectrum with neutron number has been investigated in the sequence of isotopes Dy152,154,156. The three nuclei display a pronounced collective E2 component. In Dy154 this component shows a splitting into two distinct parts, signifying a structural change along the cascade above the yrast line. The E2 and statistical components are reproduced in simple -cascade calculations; in Dy152 and Dy156 only rotational bands are included, whereas in Dy154 additional vibration-like transitions are required to reproduce the two E2 peaks

Evolution of nuclear structure with increasing spin and internal excitation energy in 152Dy

The total γ ray spectrum emitted by 152Dy has been measured in two different reactions and decomposed into its constituent parts. From the measured decay times, multiplicities, multipolarities and spectral shapes, the average decay path has been reconstructed. The yrast single-particle structures have been shown to give way to highly collective bands at internal excitations energies > 1.5 MeV. A model, which takes into account the competition between statistical and collective decay at high spin and temperature, has been used to fit all features of the data, yielding Qt=7.0+2.5-1.5 e b for the collective bands

Structural changes along and above the yrast line of Dy154

States in Dy154 have been located up to I=48+ and their lifetimes measured. Marked structural changes occur along the yrast line with a transition from prolate to oblate shape, followed by an unexpected return to moderate collectivity at the highest spins. Structural changes with increasing energy above the yrast line are also observed

Level structure of 148Gd up to I=44

The level scheme of 148Gd has been extended to I=44 by use of a Compton-suppressed Ge spectrometer array. Up to I=38 the observed level spectrum consists of spherical and oblate states of aligned-particle type. A change in structure along the yrast line is indicated at higher spins, where fast E2 transitions suggest the onset of collectivity

Evidence for superdeformation in 148Gd

γ-γ transition energy correlation measurements were performed in 148Gd using Compton-suppressed Ge detectors. A broad first ridge was observed for 1.00<Eγ<1.42 MeV. The deduced moment of inertia I(2)=78 h ℏ2MeV- is consistent with superdeformation in 148Gd. The results can be explained by cranked Strutinsky calculations

Fusion-fission in the /sup 16/O + /sup 40,44/Ca and /sup 32/S + /sup 24/Mg reactions

In measurements of fully-damped yields for the /sup 16/O + /sup 40,44Ca and /sup 32/S + /sup 24/Mg reactions, evidence for a fusion-fission reaction mechanism were found. The experiments were performed at the Argonne tandem-linac booster facility. Reaction products with masses 22 < A < 36 for the /sup 16/O + /sup 40,44Ca reactions and 10 < A < 28 for the /sup 32/S + /sup 24/Mg reaction were detected and identified using the time-of-flight technique. The /sup 16/O + /sup 40,44Ca reactions were measured at several center-of-mass energies from 49.5 to 62.5 MeV, while the /sup 32/S + /sup 24/Mg data were obtained at a single energy of E/sub cm/ = 60 MeV. The resulting total kinetic energies (calculated assuming two-body kinematics), angular distributions, and mass distributions of the fragments are found to be consistent with a fusion-fission reaction mechanism. An alternative explanation of the yields in terms of a deep-inelastic scattering mechanism is ruled out by the asymmetric nature of the mass distributions: the maximum cross section for the /sup 32/S + /sup 224/Mg reaction is detected in the mass 12 channel whereas the maximum cross sections for deep-inelastic scattering would be expected to occur near the target-projectile mass partition. For the /sup 32/S + /sup 4/Mg reaction at E/sub cm/ = 60 MeV, the fission cross sections is found to be approximately 6% of the evaporation-residue cross section. These results indicate that at higher energies fission competes with light particle evaporation in compound nuclear decay - even in these light systems. 8 refs

Damped reactions in medium mass nuclei

The use of online Hypertexts, like "Les Chants de Maldoror" (Lautréamont), is a mean for literary research, of course, but also a mean for thinking and creating exercices for Learning of French as a second Language. Some examples in this paper may help to concieve the interest of these possibilities. The exercices we give as examples, with morpho-syntaxic or semantic purpose, are depending on the needs of the students and on their reactivity in the use of computers. Please Note : This paper contains some dynamic links, mainly to the Lautréamont hypertext