B. Young

The use of radioactive nuclear beams to study the equilibration of the N Z degree of freedom in intermediate-energy heavy-ion reactions

Abstract The effect of the neutron to proton ratio of the colliding system on the isotope ratio of the emitted fragments (1 ⩽ Z ⩽ 5) was studied for for a variety of constant mass beam-target combinations. To extend the N Z ratio as far as possible, one of the projectiles employed, 40Cl, was a radioactive secondary beam. The isotopic ratios depend on the N Z of the target and beam in a way which is not consistent with N Z > equilibration on the timescale of the emission of intermediate-mass fragments.

Halflife measurements of the rp-process nuclei 61Ga, 63Ge, and 65As

Abstract Using the A1200 beam analysis device at the National Superconducting Cyclotron Laboratory, we have measured the halflives of several nuclei along the rp-process path near the proton-drip line. Halflife results for 61 Ga, 63 Ge, and 65 As (0.15±0.03 s, 95 −25 +23 ms, and 0.19 −0.07 +0.11 s, respectively) and their implications for the rp-process are presented.

Half-life measurements for Ga-61, Ge-63, and As-65 and their importance in the rp process

The [ital rp] process provides a mechanism whereby energy is generated and proton-rich nuclei are synthesized in various astrophysical environments. Understanding this process requires knowledge of the half-lives, binding energies, and reaction cross sections for the nuclei along its path, which for [ital A][approx gt]60 lies near the proton-drip line. Using the A1200 radioactive-beam facility at the National Superconducting Cyclotron Laboratory, we have performed an experiment to measure the [beta]-decay half-lives of several [ital T][sub [ital z]]=[minus]1/2 nuclei in this mass region by identification and implantation of projectile fragments followed by a rapid beam cutoff and observation of the [beta] decay. Using this technique, the half-lives of [sup 61]Ga, [sup 63]Ge, and [sup 65]As (0.15[plus minus]0.03 s, 95[sub [minus]20][sup +23] ms, and 0.19[sub [minus]0.07][sup +0.11] s, respectively) have been measured and are found to be consistent with expectations from [beta]-decay theory for decay between mirror states with [ital Q][sub [beta]][similar to]9 MeV. In addition, the proton-rich nucleus [sup 66]Se has been observed for the first time. The experimental method used for this measurement and the implications of these results for the [ital rp] process are discussed.

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.

Strong isomer production in fragmentation reactions

Abstract The population of the 0+ 0.228 MeV isomer of 26Al has been measured in projectile fragmentation reactions at E/A = 65, 80, and 100 MeV. For beams of 27Al and 28Si, the yield of the isomer was found to be approximately equal to that of the ground state, whereas for 40Ar beams it was much weaker. The significance and utility of the surprisingly high isomer yields is discussed.

Low-lying structure of Li10 in the reaction B11(7Li,8B)10Li

Momentum spectra have been measured for the reaction [sup 11]B([sup 7]Li,[sup 8]B)[sup 10]Li at 130 MeV and laboratory angles of 5[degree] and 3.5[degree]. There is strong evidence for the existence of a broad state in the unstable nucleus [sup 10]Li, corresponding to a single [ital p]-wave neutron resonance unbound to neutron decay by 538[plus minus]62 keV with wdith [Gamma][sub lab]=358[plus minus]23 keV. There is also weak evidence that the [sup 10]Li ground state may be either an [ital s]- or a [ital p]-wave resonance barely unbound to neutron decay with [ital S][sub [ital n]][ge][minus]100 keV and [Gamma][sub lab][lt]230 keV. The measured [ital Q] values for the reaction leading to these states are [minus]32 908[plus minus]62 keV and greater than [minus]32 471 keV, respectively. A comparison is made with previous measurements and theoretical predictions of the low-lying structure of the neutron-unstable nucleus [sup 10]Li.

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.

Low-lying structure of [sup 10]Li in the reaction [sup 11]B([sup 7]Li,[sup 8]B)[sup 10]Li

Momentum spectra have been measured for the reaction [sup 11]B([sup 7]Li,[sup 8]B)[sup 10]Li at 130 MeV and laboratory angles of 5[degree] and 3.5[degree]. There is strong evidence for the existence of a broad state in the unstable nucleus [sup 10]Li, corresponding to a single [ital p]-wave neutron resonance unbound to neutron decay by 538[plus minus]62 keV with wdith [Gamma][sub lab]=358[plus minus]23 keV. There is also weak evidence that the [sup 10]Li ground state may be either an [ital s]- or a [ital p]-wave resonance barely unbound to neutron decay with [ital S][sub [ital n]][ge][minus]100 keV and [Gamma][sub lab][lt]230 keV. The measured [ital Q] values for the reaction leading to these states are [minus]32 908[plus minus]62 keV and greater than [minus]32 471 keV, respectively. A comparison is made with previous measurements and theoretical predictions of the low-lying structure of the neutron-unstable nucleus [sup 10]Li.

Low-lying structure of Li-10 in the reaction B-11 (Li-7, B-8) Li-10

Momentum spectra have been measured for the reaction [sup 11]B([sup 7]Li,[sup 8]B)[sup 10]Li at 130 MeV and laboratory angles of 5[degree] and 3.5[degree]. There is strong evidence for the existence of a broad state in the unstable nucleus [sup 10]Li, corresponding to a single [ital p]-wave neutron resonance unbound to neutron decay by 538[plus minus]62 keV with wdith [Gamma][sub lab]=358[plus minus]23 keV. There is also weak evidence that the [sup 10]Li ground state may be either an [ital s]- or a [ital p]-wave resonance barely unbound to neutron decay with [ital S][sub [ital n]][ge][minus]100 keV and [Gamma][sub lab][lt]230 keV. The measured [ital Q] values for the reaction leading to these states are [minus]32 908[plus minus]62 keV and greater than [minus]32 471 keV, respectively. A comparison is made with previous measurements and theoretical predictions of the low-lying structure of the neutron-unstable nucleus [sup 10]Li.

Low-lying structure ofLi10in the reactionB11(7Li,8B)10Li

Momentum spectra have been measured for the reaction [sup 11]B([sup 7]Li,[sup 8]B)[sup 10]Li at 130 MeV and laboratory angles of 5[degree] and 3.5[degree]. There is strong evidence for the existence of a broad state in the unstable nucleus [sup 10]Li, corresponding to a single [ital p]-wave neutron resonance unbound to neutron decay by 538[plus minus]62 keV with wdith [Gamma][sub lab]=358[plus minus]23 keV. There is also weak evidence that the [sup 10]Li ground state may be either an [ital s]- or a [ital p]-wave resonance barely unbound to neutron decay with [ital S][sub [ital n]][ge][minus]100 keV and [Gamma][sub lab][lt]230 keV. The measured [ital Q] values for the reaction leading to these states are [minus]32 908[plus minus]62 keV and greater than [minus]32 471 keV, respectively. A comparison is made with previous measurements and theoretical predictions of the low-lying structure of the neutron-unstable nucleus [sup 10]Li.