Mechanism of the 31P(p, γ) 32S reaction in the giant dipole resonance region

Abstract

The radiative capture of protons by 31P has been studied in the energy range E p = 9.5–11.5 MeV and the gamma rays to the ground and first excited states of 32S were analysed. Excitation functions and angular distributions were measured in energy steps of 20 keV. It was found that the angular distributions are almost invariant with energy and are slightly forward peaked indicating an E2 intensity of order one per cent. From the Legendre polynomial coefficient A 2 A 0 the channel spin s = 0 and s = 1 fractions of the cross section were separated for ground state gamma rays; it is observed that s = 0 accounts for ≈ 75 % of the γ 0 integrated strength. There are large variations in gamma-ray yield as a function of energy and an analysis in terms of statistical fluctuation theory shows that ≈ 90 % of the cross section is due to a “direct interaction” mechanism. A large correlation between the γ 0 and γ 1 yields is observed.