The level scheme of 137Pr; evidence for prolate nuclear shape

The level scheme of ¹³⁷Pr was investigated by means of the γ-rays following the β-decay of ¹³⁷Nd as well as by prompt γ-rays accompanying (α, xn) reactions. We measured γ-ray single spectra, γγ coincidences (both in-beam and off-beam), angular distributions of prompt γ-rays and conversion electrons. About 100 γ-rays were assigned to the 38 min decay of ¹³⁷Nd most of which fit into a scheme of 26 deduced levels. From in-beam experiments we tentatively assigned an $\text{11}\text{2}$^? level which is the basis of a strong cascade of stretched E2 transitions with a probable level sequence of $\text{23}\text{2}$^? ?$\text{19}\text{2}$^? ?$\text{15}\text{2}$^? ?$\text{11}\text{2}$^?. The interpretation of this cascade in the framework of a strong coupling model indicates a prolate deformation of ¹³⁷Pr. Another indication for such a deformation was obtained from the very low energy (75 keV) of the first $\text{3}\text{2}$⁺ level which could not be interpreted in an intermediate coupling model, but is suggested by a Nilsson scheme.