Alpha decay of 257100Fm

Abstract

The α-decay scheme of 257Fm has been investigated by measuring the α-particle, electron and γ-ray spectra of several sources containing ∼1000 257Fm α-disintegrations per minute. Five α-groups were identified: 6.756 MeV (0.60%), 6.695 MeV (3.5%), 6.520 MeV (93.6%), 6.441 MeV (2.0%) and 6.346 MeV (0.3%). γ-ray spectra were measured with Ge(Li) spectrometers and the intensity of the 179.4 keV γ-ray was found to be 8.7 ± 0.7 photons per 100 257Fm α-decays. A conversion-electron spectrum was measured with a cooled Si(Li) detector and transition multipolarities were derived. On the basis of the present investigation the 253Cf ground state has been assigned to the 7 2 +[613] single-particle state and the 257Fm ground state and the 241.0 keV state in 253Cf are assigned to the 9 2 +[615] orbital. The α-intensities and γ-ray branching ratios have been explained in terms of Coriolis mixing between the 7 2 +[613] and 9 2 +[615] states. Our observations are in agreement with the results of a previous study by Asaro and Perlman.