β+decay and cosmic-ray half-life ofMn54

${}_{}{}^{54}{}_{}{}^{}\mathrm{Mn}$ has previously been observed in cosmic rays where is it expected to decay by ${\beta }^{+}$ and ${\beta }^{\mathrm{-}}$ transitions with a half-life of a few million years. The present experiment to measure the ${\beta }^{+}$ decay branch in the laboratory establishes an upper limit of 4.4×${10}^{\mathrm{-}8}$ for the branching ratio, and a lower limit of 13.3 for the logft value of this second forbidden unique transition. If it is assumed that the ${\beta }^{\mathrm{-}}$ decay branch has the same logft value, then its partial half-life must be greater than 4×${10}^4$ years.