J. Stevenson

Impact parameter dependence of high energy gamma ray production in heavy-ion collisions☆

Abstract High energy photons ( E γ ⩾30 MeV) have been measured in coincidence with light particles observed in a multidetector array for the 40 Ar+ 51 V system at a bombarding energy of E A =65 MeV . Double differential cross sections were obtained as a function of the midrapidity charge representation of the centrality of the collision. The inverse slope parameter increases with centrality more strongly than predicted by a BUU model.

High energy gamma ray emission in heavy ion collisions

Abstract It has been known for the last two years that in heavy ion collisions at intermediate energies (20 γ > 20 MeV) gamma rays. Initially these were thought to be due to coherent nucleus-nucleus bremsstrahlung. Current theoretical work assumes the production mechanism to be incoherent nucleon-nucleon bremsstrahlung.

Mass dependence of pion production in heavy ion collisions near, but below threshold☆

Abstract We have measured the inclusive cross section for production of negative pions near mid-rapidity in 20 Ne + NaF , 139 La + 139 La and 197 Au + 197 Au collisions at E = 183 and 236 MeV/u. Au + Au is the heaviest system from which subthreshold pion production has been measured to date. The dependence of the pion cross section on pion energy, beam energy and associated charged particle multiplicity is consistent with previous results both above and below threshold. The dependence of the cross section on the mass of the colliding system varies only slightly as the beam energy is reduced below threshold, in contrast to some previous measurements. Comparison with theory suggests that at these energies the pion production process is still dominated by nucleon-nucleon collisions.

A Technique for Proton Drip-Line Studies via Fusion-Evaporation Reactions

A survey of the evaporation-residue cross-sections from fusion reactions in the mass region 56 < A < 100 was begun to investigate the utility of this process for producing proton-rich nuclei of astrophysical importance for future decay studies. The initial study was the fusion of an E/A = 8 MeV 36Ar beam with a 40Ca target using the K500 cyclotron at the National Superconducting Cyclotron Laboratory, Michigan State University. The details of the new S320 spectrograph focal-plane detection system developed to identify the evaporation products are presented, along with preliminary experimental results.

Study of beta decay half‐lives and beta‐delayed multi‐particle final states at Michigan State University

The first five years of operation of the Reaction Product Mass Separator (RPMS) at Michigan State University has produced information important for understanding the structure of many nuclei in the p and sd shells. We discuss the design and operation of the RPMS. The products of projectile fragmentation‐like reactions leave the mass separator with a much greater range than products separated with standard on‐line separators. We have taken advantage of this extended range distribution by implanting exotic species within silicon detectors, and detecting the decay products directly. Using this technique, we have measured the beta‐decay half‐lives of 14Be, 15B, 17B, 17C and 19N. We have also measured the beta‐delayed alpha emission from 18N. By containing the total charged‐particle decay energy of nuclear states left excited by beta decay within a single silicon detector, we have measured beta decay branching ratios of 9C, which always produces a delayed three‐body final state. These new measurements yield be...