Radioactivity ofCo57

${\mathrm{Co}}^{57}$(270-day) has been prepared by the reactions ${\mathrm{Mn}}^{55}(\alpha , 2n)$ and ${\mathrm{Ni}}^{58}(p, 2p)$, separated chemically, and its disintegration studied with a magnetic lens and a scintillation spectrometer. ${\mathrm{Co}}^{57}$ decays by electron capture; an upper limit of 2×${10}^{-5\mathrm{}}$ positron per disintegration has been set. Positron groups previously assigned to ${\mathrm{Co}}^{57}$ presumably belong to one of the neighboring isotopes of cobalt. Gamma rays of 0.137 and 0.123 Mev have a relative abundance of 7 and 93 percent, and presumably are $E2\mathrm{}$ and $M1\mathrm{}$ transitions, respectively. A decay scheme is outlined.