249 research outputs found
Possible dynamic effects in the particle decay of 59Cu compound nuclei,
No full textThe slopes of the energy spectra of p, d, t, and α particles emitted from 59Cu nuclei formed in the reaction of 32S+27Al at a bombarding energy of 150 MeV are described by statistical-model calculations in which the deformation is frozen during the first two steps of the deexcitation chain. The resultant fits to the high-energy portions of the spectra are comparable to those previously obtained by modifying the spin dependence of the level density, suggesting that dynamic effects may be important in evaporation from light nuclei
Fission Probability in the Reaction of �����B with ��������Au at Projectile Energies of 130 to 320 MeV
No full textProgram year: 1982-1983Digitized from print original stored in HDRAngular distributions of fission fragments for the reaction of �����B + Au at bombarding energies of 130, 180, 225, and 320 MeV were obtained. Integration of these cross-sections was carried out, but problems with the first three energies prevent us from reporting absolute data at this time. The total fission cross-section for the 320 MeV case was 1.2 ���.16 barns which lends evidence to the possibility of a drop in collective character at energies/nucleon comparable to the Fermi energy
The decay of deformed 59Cu nuclei
No full textThe light charged particle emission following the fusion of 32S with 27Al at 100–150 MeV bombarding energies in 10 MeV steps has been studied. Energy spectra and angular distributions of p, d, t, and alpha particles as well as light-particle–light-particle coincidences have been measured. The light charged particle data and the published evaporation residue distributions are compared with statistical model calculations. The comparison shows that the statistical model describes well the experimental observables if account is taken of changes in the level density and barrier apparently due to the onset of deformations at high spins. The spectra of α particles emitted from narrow windows of angular momentum with 28ħ≤Jave≤34ħ have been obtained by means of a subtraction procedure and analyzed to extract emission barriers and level density enhancement factors. The deduced barrier lowering with respect to the spherical barrier is somewhat greater than that predicted by assuming rotating liquid drop model (RLDM) shapes. The level density enhancement factor is comparable with that determined in the past for statistically deformed nuclei
Level densities and barriers of deformed 59Cu nuclei
No full textThe spectra of α particles emitted from narrow windows of angular momentum with 28ħ≤Jav≤34ħ show systematic deviations from spectra calculated using the statistical model as the spin of the emitter increases to values for which strong deformations are predicted. The barrier reduction and the enhancement of the level density needed to reproduce the experimental spectra have been determined
Dynamic evolution and the caloric curve for medium mass nuclei
No full textSelf-consistent coalescence model analyses of light particle emission have been used to follow the evolution of the
temperatures and densities of Af110 nuclei produced in violent collisions induced by four different 47 AMeV projectiles.
The degree of expansion of the emitting system increases with increasing projectile mass. The caloric curve derived for these
expanding Af110 nuclei plateaus near Ts7 MeV. The plateau extends from 3.5 to 6.9 MeVru excitation energy. q2000
Published by Elsevier Science B.V. All rights reserved
Determination of the temperatures of hot nuclei from “first chance” emission spectra
No full textThe “first chance” spectra of light charged particles and neutrons emitted from 160Yb produced in the 60Ni+100Mo reaction have been isolated. The same initial temperature for the different evaporated particles and a decrease of the Coulomb barriers for the charged particles are observed. The inverse level density parameter K=A/a reaches a value of 13.8±0.7 MeV at ETH≈236 MeV, confirming the decrease of the parameter a at excitation energies above 150 MeV
Production and deexcitation of highly excited 67Ga
No full textThe energy spectra and angular distributions of alpha particles and protons emitted from 67Ga compound nuclei at excitation energies of 110 to 116 MeV formed in four different reactions have been measured. The populated angular momentum ranges deduced from fusion cross section information correspond to 0–24 ħ for 4Cu, 0–38 ħ for 12Mn, 0–48 ħ for 16V, and 0–50 ħ for 40Al. The experimental data are analyzed using the angular-momentum-dependent statistical model and the rotating liquid drop model. Average multiplicities and barriers are extracted for different zones of angular momentum. Comparisons with the models indicate large deformations of the 67Ga nuclei at the higher angular momenta and suggest large deformation related increases in the nuclear level density and decreases of emission barriers. The p/α ratio decreases with increasing angular momentum less than expected for spherical emitters at the higher angular momenta. The average α emission barriers are found to be close to those which are calculated for emission from the tips of prolate deformed nuclei such as those predicted by the liquid drop model. The experimental proton barriers appear somewhat smaller than those calculated using the liquid drop model shapes
Reactions of 265 MeV Nitrogen on Carbon
No full textProgram year: 1983-1984Digitized from print original stored in HDRSingles and coincidence energy spectra were obtained for �����N projectiles at 265 MeV incident on a ����C target. Model calculations were done for this system using the computer program LILITA and comparisons were made between the calculated and experimental spectra. From these comparisons we determined that the lower energy heavy fragments were predominantly fusion residues but that fusion accounted for a relatively small portion of the total reaction cross section. Plots of light particle energy versus heavy fragment energy were produced for coincidence events to determine what other reaction mechanisms may be occurring
Shapes of 59Cu nuclei at moderate excitation energies and spin
No full textContinuum γ-ray spectra from the decay of 59Cu formed at excitation energies of 54 and 74 MeV and angular momenta up to 40ħ have been measured and analyzed. The parameters of the giant dipole resonance have been extracted using the statistical model. The giant dipole resonance parameters for the lower excitation energy agree well with published data for spherical 63Cu nuclei. At the higher excitation, the giant dipole resonance strength distribution is not described by a single Lorentzian fit in disagreement with the findings for 63Cu at the same excitation energy. This seems to be correlated with the onset of spin driven deformations as recently evidenced from the shapes of evaporative particle spectra
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