A re-investigation of the decay of Eu 147 to Sm 147

Abstract

A re-investigation of the decay of Eu 147 has been undertaken; gamma-ray intensity measurements and gamma-gamma directional correlations have been performed using an isotopically and chemically pure source. Gamma-gamma directional correlations were measured for the 680-122 and 957-122 keV cascades; the data were consistent with the predominantly M1 assignment for the 680 keV transition based on internal conversion data. Evidence has been found for seven new gamma-ray transitions with energies of 1122, 1195, 1250, 1320, 1326, 1423 and 1448 keV. Gamma-gamma coincidence measurements performed on a chemically but not isotopically pure source of Eu 147 showed that the 1122 and 1250 keV transitions are in coincidence with the 198 keV transition and that the 1195, 1326 and 1423 keV transitions are in coincidence with the 122 keV transition. The energy of the previously reported 881 keV transition was measured and found to be 862 keV. This transition is shown to proceed from a level of 1060 keV; internal conversion coefficient data and gamma-gamma directional correlations indicate that the spin and parity of this level would be 3 2 + assuming a spin sequence for the three lowest levels of 7 2 −, 5 2 − and 3 2 − . The total positon feeding was determined to be (0.54±0.08)% of the total decay. The experimental results are compared with the theoretical results obtained by Schima employing quasi-particle states to account for the short-range forces and zero, one and two phonon states for the collective effects.