Levels in Gd156 excited in the decay of 5.6 d Tb156

The decay of 5.6 day Tb156 has been studied by means of a six gap β-ray spectrometer, scintillation spectrometers, and coincidence techniques. Conversion electron and γ-ray coincidence measurements have been used extensively for obtaining quantitative estimates of γ-ray intensities. A description of the electronic equipment is given, including a scaler and gate unit, which improves the performance of a relatively slow (τ = 700 μsec) multichannel analyzer. 24 transitions are assigned to Tb156.

Multipole orders are given in most cases. The following levels are proposed and their quantum numbers (K, I, π) given in parenthesis: 89 keV (0, 2+), 199 keV (0, 4+), 584 keV (0, 6+) 1126 keV (tentative), 1152 keV (2, 2+), 1246 keV (2, 3+), 1507 keV (4, 4+), 1620 keV (4, 5+), 1931 keV (3−), and 2042 keV (4−).

Violation of K-selection rules and significant deviations from the expected branching ratios for transitions to a rotational band are observed. These features are discussed in terms of a probable mixing of the rotational bands.