Si28(He4,O16)O16Reaction

Abstract

Cross sections and angular distributions have been measured for ${\mathrm{Si}}^{28}$ (${\mathrm{He}}^4$,${\mathrm{O}}^{16}$)${\mathrm{O}}^{16}$ reaction leading to the ground state and to several of the excited states of one of the product nuclei. The reaction where both product nuclei are left in excited states has also been observed. The differential cross sections are quite small, of the order of 1 μb/sr. The reaction products were identified by simultaneous detection and two-dimensional analysis of both reaction products. The results are discussed in terms of the statistical theory of compound nuclear reactions. The observed angular distribution is consistent with the expectation that only the compound states with the highest available angular momentum ($J\sim 14$) contribute to the exit channel where both ${\mathrm{O}}^{16}$ product nuclei are in their ground state. A statistical-model analysis of the absolute cross sections yields a value for the level density parameter $a$ of $(0.15\mathrm{}\pm 0.02)A$ for mass numbers $A$ in the region of 28-31. Deviations in the relative yields from that predicted by statistical theory are discussed in terms of possible shell-structure effects on nuclear deformabilities.