Manganese-57

A previously unknown isotope, 1.7-minute ${\mathrm{Mn}}^{57}$, was produced by an ($n, p$) reaction on isotopically enriched ${\mathrm{Fe}}^{57}$. It was identified by chemical separations, by measurement of its formation cross section, by investigation of possible impurity effects, and by comparison of its gamma spectrum with that of ${\mathrm{Co}}^{57}$. It decays principally by 2.6-Mev negatron emission to the 131-kev excited state of ${\mathrm{Fe}}^{57}$, which in turn decays to either the ground or the 14-kev state of ${\mathrm{Fe}}^{57}$ with approximately equal probability. The gamma-ray spectrum also indicates the presence of a weak 690-kev gamma ray, and possible weak gamma rays of 350 kev and 220 kev. It is shown that a previous assignment of a 7.2-day activity to ${\mathrm{Mn}}^{57}$ is very probably in error.