Heavy-ion emission from light nuclei

Abstract

Reactions involving the emission of heavy ions leading to low-lying states of the residual nucleus have been studied using 42 MeV α-particles incident on light target nuclei. The heavy ions resulting from these reactions were identified by mass number using the time-of-flight technique. With this method, products with a mass number as high as A = 14 could generally be separated from neighbouring isobars. Reactions leading to different particle masses from a particular target were studied simultaneously. Angular distributions and total cross sections were obtained for the reactions 12C( 4He, 6Li) 10B, 12C( 4He, 7Be) 9Be, 16O( 4He, 6Li) 14N, 16O( 4He, 7Li) 13N, 16O( 4He, 7Be) 13C and 16O( 4He, 9Be) 11C. A comparison of the experimental angular distributions and cross sections with statistical model calculations was carried out. We show that as the mass of the emitted heavy ion increases for a particular reaction, the fractional contribution of compound-nuclear processes increases. Considerable compound nuclear contributions to all the reactions studied are indicated. Comparison of the calculated and experimental results for the 16O( 4He, 7Be) and 16O( 4He, 7Li) reactions with those for the reaction 16O( 4He, 8Be) 12C indicate that there is no enhancement of the latter reaction due to α-clustering. Evidence is given for the conservation of isotopic spin in complex reactions proceeding through a short-lived compound nucleus. The possible astrophysical significance of low-energy α-particle-induced reactions in the nucleosynthesis of Li, Be and B is discussed.