Transition probabilities and deformations in the doubly odd nucleus 152Eu

Abstract

In the (n, γ) reaction, nanosecond lifetimes of excited states of the N = 89 transitional nucleus 152Eu have been measured by the delayed coincidence method using a low-energy Ge(Li) detector. From the analysis of relative intensities in prompt and delayed γ-ray spectra, the following half-lives of isomeric states could be obtained for the first time: T 1 2 (141.83 keV) = 2.5 ± 0.5 ns, T 1 2 (158.05 keV) = 1.8 ± 0.4 ns, T 1 2 (160.88 keV) = 2.3 ± 0.4 ns and T 1 2 (180.63 keV) = 2.1 ± 0.6 ns. Further, it has been confirmed that the levels at 77.26 and 89.85 keV have nanosecond lifetimes T 1 2 > 30 ns. Absolute γ-ray transition probabilities available so far in this nucleus are compared with Weisskopf and Nilsson estimates, the latter being deduced for quadrupole deformation parameters ε 2 = 0.15, 0.20, 0.23 and 0.26 with the pairing effect taken into account. From the B( E2) value of the 71.03 keV transition, the average quadrupole deformation of ε 2 ≲ 0.18 for the corresponding excited states is concluded, which is smaller than ε 2 ≈ 0.25 established earlier for the ground state. Experimental matrix elements of allowed El transitions deviate from the relevant systematics in strongly deformed nuclei. The suggestion that these deviations are associated with strong configuration admixtures is supported by a new graphic systematization of allowed and forbidden B( E1) values in deformed odd-odd nuclei.