β−Decay and Cosmic‐Ray Half‐Life of54Mn

A superconducting solenoid electron spectrometer operated in the lens mode was adapted to search for the β- decay of 54Mn. The Compton electron and other instrumental backgrounds were largely reduced by special shielding of the absorber system. An improved procedure was developed to select the events by momenta. An upper limit of less than 3.9 × 10-5 has been established for the intensity of the β- branch. This would define the partial half-life of the 54Mn β- decay to be greater than 2.2 × 104 yr. The implications of this result for the 54Mn cosmic-ray chronometry problem are discussed.