DECAY OF 155SM

The beta decay of 155Sm has been studied using Ge(Li), Si(Li) and NaI detectors singly and in two-parameter experiments. The half-life has been measured to be 22.4±0.3 min. The energies and intensities of 49 gamma rays have been determined. These data and the results of the coincidence experiments have led to the identification of the levels at 0.0 ( 5 2+[413]), 78.5 ( 7 2, 5 2+[413]), 104.26 ( 5 2-[532]), 169.0 ( 7 2-[532]), 245.68 ( 3 2+[411]), 307.4 ( 5 2, 3 2+[411]), 391.4 ( 7 2, 3 2+[411]), 768.23( 3 2+), 876.9, 911.2, 922.8 1096.9, 1101.6, 1106.7, 1263.0 and 1301.4 keV in 155Eu. The numbers in parentheses give the spins and parities and the Nilsson description of the levels whenever possible. The branching ratios of the gamma rays from the 768.2 and 817.6 keV states and the absence of these levels in the deuteron spectra of the 155Sm(3He, d)155Eu reaction lead to a rejection of the previously proposed identification of the state at 768.2 keV with the Nilsson 1 2+[411] orbital. Evidence is adduced to show that the 768.2, 817.6 and 911.2 keV states are the 3 2+, 5 2+and 7 2+ members of a rotational band based on either a 3 2+[422] hole state or on the β-vibrational state associated with the 3 2+[411] orbital. © 1969.