Conservation of Isobaric Spin in the ReactionBe9(p, α)Li6

Abstract

The reaction ${\mathrm{Be}}^9(p, \alpha ){\mathrm{Li}}^6$ involves transitions to the ground state and first excited state of ${\mathrm{Li}}^6$ which are shown to display only a gradual dependence on proton energy and no indication of resonance at the known gamma-ray resonance at 2.565 Mev which goes by way of the second excited state of ${\mathrm{Li}}^6$. This may be explained in terms of conservation of isobaric spin and verifies that the second excited state of ${\mathrm{Li}}^6$ has isobaric spin $T=1\mathrm{}$ (or odd charge parity) as does also the resonant state of the compound nucleus ${\mathrm{B}}^{10}$. The lack of resonance in the two alpha groups does not provide a very sensitive test of the purity of isobaric spin in the resonant state, because the contribution of an impurity would be superposed on a background, but the sharpness with which the gamma resonance falls off on the low-energy side does indicate that neighboring $T=0\mathrm{}$ states have remarkably little $T=1\mathrm{}$ admixture. The observations were made by means of a 16-in. two-dimensional focusing magnetic spectrometer, the construction and characteristics of which are described.