Stopping Powers for Positrons and Electrons

Stopping cross sections for 20 keV positrons (S+) and electrons (S-) in a thin (61 ?g/cm2) Al target have been measured using an electrostatic analyzer. The results yield a ratio S+/S- = 1.15\ufffd0.08, in good agreement with the theoretically calculated value of 1.097. A marked dependence of the mean energy loss on an emergence angle has been observed for a thin target, and its origin is interpreted with the aid of Monte Carlo simulations.Peer reviewed: YesNRC publication: Ye

Study of astrophysically important resonant states in 30 S using the 32S(p,t)30 S reaction

A small fraction (< 1%) of presolar SiC grains is suggested to have been formed in the ejecta of classical novae. The 29P(p,γ)30S reaction plays an important role in understanding the Si isotopic abundances in such grains, which in turn provide us with information on the nature of the probable white dwarf progenitor’s core, as well as the peak temperatures achieved during nova outbursts, and thus the nova nucleosynthetic path. The 29P(p,γ)30S reaction rate at nova temperatures is determined by two low-lying 3+ and 2+ resonances above the proton threshold at 4399 keV in 30S. Despite several experimental studies in the past, however, only one of these two states has only been observed very recently. We have studied the 30S nuclear structure via the 32S(p,t) 30S reaction at 5 laboratory angles between 9° to 62°. We have observed 14 states, eleven of which are above the proton threshold, including two levels at 4692.7 ± 4.5 keV and 4813.8 ± 3.4 keV that are candidates for the 3+ and the previously “issing” 2+ state, respectively