The radioactive decays of 6.7 min 179mW and 38 min 179W

Abstract

The decays of 6.7 min 179mW and 38 min 179W have been studied by means of high resolution γ-ray and electron spectroscopy using Ge(Li) and Si(Li) detectors, a broad-range transport solenoid electron spectrometer and γ-γ coincidences with Ge(Li) detectors. The decay of 38 min 179W occurs by a fast beta transition (log ft 4.6) and by a first-forbidden beta transition (log ft 6.9) followed by a 30.7 keV and by a 133.9 keV γ-transition, respectively. The [521] 1 2 − 6.7 min 179mW decays mainly by an isomeric transition of 221.5 keV (M3) and a competing 101.6 keV (E4)-120.1 (E2) keV cascade to the 179W ground state. A small fraction of the decay of the 6.7 min isomer is observed to proceed by beta transitions to levels in 179Ta. The results are interpreted in terms of the Nilsson model and the following intrinsic proton states are proposed in 179Ta: [404]if 7 2 + giound state; [514]if 9 2 − 30.67 keV; [402]if 5 2 + 238.7 keV; [411]if 1 2 + 520.4 keV; and [541]if 5 2 − , K = 1 2 at 741.5 keV. The [541] if 1 2 − band is observed to have approximately the same large decoupling parameter ( a > 4) as has been found in 173,175Lu.