Cosmic ray measurement of the ⁵⁴Mn β^- partial half-life

Abstract

In the fully stripped cosmic rays, the electron capture decay of ⁵⁴Mn (τ_1/2=312d) is strongly suppressed. In this situation the β^- decay channel dominates; however, this half-life has never been measured in the laboratory. Some lower limits have been placed on it previously. Using the cosmic-ray data from the Ulysses spacecraft high-energy telescope (HET) and a self-consistent model of the galactic transport of cosmic rays, this partial lifetime can be determined. The best-fit β^- partial decay lifetime is dependent on the interstellar gas density, but is constrained to be between 1-2×10⁶ yr. This is consistent with, but much more restrictive than, earlier limits placed on the lifetime (>~3×10⁴ and >~2.95×10⁵ yr) from direct and indirect methods, respectively. This determination using the cosmic-ray data requires laboratory verification for which there appears to be interest.