1.7-Mev State inBe9

Abstract

Evidence is presented concerning the 1.7-Mev state in ${\mathrm{Be}}^9$ and its characteristics, which are currently in doubt because of the extreme weakness of the anomaly observed in charged-particle reactions. On the basis of this evidence, the state now appears to be well established, and its spin and parity are probably ${\mathrm{½}}^{+}$ or ${\mathrm{½}}^{-}$. The evidence in favor of the ${\mathrm{½}}^{+}$ assignment, corresponding to an intermediate-coupling parameter $\frac{a}{K}$ of ∼2.75 for ${\mathrm{Be}}^9$, comes from the final-state-interaction analysis in the present paper of the results of three different charged-particle reactions at Indiana University and the Massachusetts Institute of Technology, from the agreement between the scattering length for neutrons on ${\mathrm{Be}}^8$ resulting from this analysis and the predictions of Ford and Bohm, and from the continuity of $\frac{a}{K}$ with mass number. In addition, experiments on the mirror nucleus ${\mathrm{B}}^9$ by Marion et al. seem to be in disagreement with the existence of a ${\mathrm{½}}^{-}$ state in this region. The evidence in favor of the ${\mathrm{½}}^{-}$ assignment, corresponding to $\frac{a}{K}\sim 1.5$, comes from the static magnetic moment of ${\mathrm{Be}}^9$ and the photodisintegration data of Connors and Miller.