Neutron multiplicities in inelastic collisions of132Xe with197Au

Neutron multiplicities in inelastic collisions of132Xe with197Au

“…The discrepancy is not likely to be caused by angular momentum effects, but might be due to enhanced equilibrium or pre-equilibrium emission of charged particles (the JULIAN calculations imply an c~-multiplicity of about 1.0 for deep inelastic Au-like fragments, but no c~-emission from the Xe-like fragments, nor any significant proton emission). We believe now, that the present data are not sufficiently precise or detailed to draw firm conclusions on the presence of pre-equilibrium effects, in contrast to our previous suggestion [1]. In order to resolve this problem further experimental work is needed, including more sophisticated neutron measurements as well as studies of the competing gamma and charged particle channels.…”

“…The deduced absolute multiplicities, on the other hand, were about 25-30~o lower than expected from statistical evaporation calculations, or extrapolated from empirical data for fusion reactions of lighter systems. It was concluded that the bulk of the neutron emission occurs by statistical evaporation, but the low absolute multiplicities were interpreted as indirect evidence for pre-equilibrium effects [1]. Similar conclusions were also reached by Peter et al in an early study of the system 63Cu+ 19VAu, which indicated an excess of low energy neutrons at back angles and off the scattering plane [4].…”

“…Neutrons were detected in the vicinity of the fragment emission angles only, but not near the beam direction nor at angles off the scattering plane. As reported previously in a short note [1] the neutron multiplicities were found to increase in proportion to the kinetic energy loss, and their ratio was close to the fragment mass ratio over the whole range of Q-values. The deduced absolute multiplicities, on the other hand, were about 25-30~o lower than expected from statistical evaporation calculations, or extrapolated from empirical data for fusion reactions of lighter systems.…”

“…4. The upper spectrum is from scintillator N2 behind the In our previous work [1] we calculated the neutron attenuation by assuming the effective absorption coefficient to be the average of the absorption coefficients calculated from the total and nonelastic cross sections respectively. The measured attenuation corrections were found to be ~ 10 ~ larger than those predicted by these calculations and therefore the absolute multiplicities given here are 10 % higher than those given in Ref.…”

“…In particular, the observation of neutrons or light charged particles can yield information on the time scale of energy transfer (heat conduction) between the fragments, and on the mechanisms of energy dissipation and removal. In this paper we describe a measurement of neutron emission following the scattering of 7.5 MeV/u 132Xe ions from 197Au [1]. The choice of this system was governed partly by technical arguments, and partly by the expectation that highly excited nuclei in the A = 120-200 region should decay almost exclusively by * On leave from N.C. State University, Raleigh, N.C., USA ** Supported in part by GSI, Darmstadt, and by Bundesministerium fiir Forschung und Technologie of the Federal Republic of Germany neutron emission, with charged particle emission and fission playing only a minor part.…”