Angular Correlations for the ReactionBe9(He3, α)Be8(16.92)→α+α

Abstract

Angular correlations for the ${\mathrm{Be}}^9({\mathrm{He}}^3, 3\alpha )$ reaction proceeding via the 16.92-MeV state of ${\mathrm{Be}}^8$ have been obtained by measuring the energies of two $\alpha$ particles in coincidence. The measurements were made by varying the angle of observation of the breakup $\alpha$ particle, a constituent of ${\mathrm{Be}}^8$(16.92), with respect to the angle of emission of the initial $\alpha$ particle fixed at laboratory angles of 0°, 20°, 40°, 60°, 90°, and 140°. These measurements were carried out in the initial reaction plane and in the plane perpendicular to the reaction plane. The observed angular correlations involving the formation of the ${\mathrm{Be}}^8$(16.92) are consistent with the assignment of $J^{\pi }=2^{+}$ for this state and exclude the possibility of $J^{\pi }=0^{+}$. The distorted-wave pickup description was used in the analysis of the angular correlations from the reaction ${\mathrm{Be}}^9({\mathrm{He}}^3, \alpha ){\mathrm{Be}}^8\mathrm{}\left(16.92\right)\mathrm{}\to 2\alpha$, which was assumed to be a two-step process in which the first step is a direct pickup.