Scarcity of Low-Energy Levels ofBe8Appearing in Two Boron Reactions

Abstract

A careful search is made for evidence of possible excited states in ${\mathrm{Be}}^8$ in the reactions ${\mathrm{B}}^{11}(p, \alpha ){\mathrm{Be}}^8$ and ${\mathrm{B}}^{10}(d, \alpha ){\mathrm{Be}}^8$, by magnetic momentum analysis at a variety of angles and bombarding energies. In spite of observing the region corresponding to 3 to 8 Mev several times independently under different conditions, with several thousand counts per point on points spaced only about 100 kev apart, no indication was found of any of the states in this region reported by others on the basis of poorer statistics, mostly in other reactions. Each alpha-particle spectrum observed consists of a sharp ground-state peak and a broad peak of the alpha particles giving rise to the well-known 3-Mev excited state of ${\mathrm{Be}}^8$ superposed on a continuous background from the break-up of this state and from three-particle break-up. Peaks observed near the equivalent of 10 and 11 Mev in ${\mathrm{Be}}^8$ are identified as arising from a target impurity.