First Excited State ofMn55

Abstract

The spin of the first excited state of ${\mathrm{Mn}}^{55}$ at 128 kev has been measured in the electric excitation process with 3-Mev alpha particles. Determinations of the $K$ conversion coefficient and the angular distribution of the gamma rays lead to a spin assignment of $\frac{7}{2^{-}}$ for the excited state and multipolarity $M1\mathrm{}$ for the transition to the ground state. The $K$ conversion coefficient (${\alpha }_K=0.0144\mathrm{}\pm 0.003$) was measured by comparison with the known coefficient of the 137-kev transition in ${\mathrm{Ta}}^{181}$. The spin, parity, and transition probability are consistent with those expected for a rotational state.