Negative parity levels in the even-even nucleus Dy 160

Abstract

The conversion electron spectrum of Tb 160 has been studied in the Chalk River air-cored ρ√2 β-ray spectrometer at resolution settings of 0.04 % to 0.1 %. Gamma-conversion electron coincidence experiments have been made to establish the positions of the levels in Dy 160. The level scheme based on the present results is 0(0+), 86.7 (2+), 283.6 (4+), 965.8 (2+), 1048.8 (3+), 1264.4 (2-), 1286.5 (3-), 1358.2 (2-), and 1398.5 keV (3-). This is similar to that of Nathan in the positive parity levels but differs in the negative parity levels. Particular attention has been paid to determining the intensities of weak transitions in the decay scheme. The relative quantum transition probabilities have been deduced from the conversion line measurements using Sliv's theoretical conversion coefficients. The agreement between the observed transition probabilities from the positive parity levels and the theoretical predictions of the Unified Model is greatly improved if a small amount of K = 0 band is assumed mixed in the K = 2 gamma-vibrational band. The relative transition probabilities from the negative parity levels are not consistent with K being a good quantum number in discussing these levels. The possibility of interaction between the negative parity levels is briefly discussed.