Electromagnetic transitions in some doubly odd deformed nuclei

Abstract Nanosecond lifetimes of excited states in doubly odd deformed nuclei have been determined by in-beam measurements applying the method of delayed γ-γ coincidences as well as by experiments in the radioactive decay with the method of delayed γ-ce coincidences, respectively. Analysing the time distributions and delayed γ-ray spectra, the following half-lives of isomeric states could be obtained for the first time: T 1 2 (63.7 keV in 160 Tb ) = 60 ± 5 ns , T 1 2 (138.7 keV in 160 Tb ) = 5.7 ± 0.5 ns , T 1 2 (82.0 keV in 156 Ho ) = 1.25 ± 0.20 ns , T 1 2 (87.2 keV in 156 Ho ) = 58.5 ± 3.5 ns , T 1 2 (139.2 keV in 158 Ho ) = 1.85 ± 0.10 ns , T 1 2 (38.3 keV in 162 Ho ) = 1.2 ± 0.2 ns , T 1 2 (179.9 keV in 162 Ho ) = 8.7 ± 0.2 ns , T 1 2 (342.8 keV in 164 Ho ) = 2.6 ± 0.2 ns , T 1 2 (295.1 keV in 166 Ho ) = 1.10±0.15 ns , T 1 2 (44.6 keV in 162 Tm ) = 1.40±0.15 ns , T 1 2 ,(163.4 keV in 162 Tm ) = 1.1 ± 0.1 ns , T 1 2 (220.1 keV in 178 Ta ) = 8.5 ± 1.0 ns , T 1 2 (289.5 keV in 178 Ta ) = 2.0 ± 0.5 ns , T 1 2 (392.8 keV in 178 Ta) ≈ 1 ns, T 1 2 (316.5 keV in 186 Re ) = 0.20 ± 0.10 ns , T 1 2 (300.2 keV in 188 Re ) = 1.5 ± 0.2 ns and T 1 2 (482.2 keV in 188 Re ) = 0.26 ± 0.10 ns . Furthermore, upper limits for the half-lives of fifteen excited states in 160 Tb, 164, 166 Ho and 186, 188 Re have been estimated. For eight isomeric levels in 186, 188 Re, the lifetimes earlier determined have been remeasured. Unlike previous studies, the existence of isomeric states at 87.2 keV in 156 Ho and at 179.9 keV in 162 Ho is suggested. Absolute γ-ray transition probabilities are deduced and compared with single-particle estimates according to Weisskopf and Nilsson, the latter also including pairing correlations. The K -, Ω- and f -forbidden transitions can qualitatively be explained in terms of configuration mixings. Experimental El, ΔK = 1 transition matrix elements in odd-odd deformed nuclei are supposed to be appreciably influenced by higher-order vibrational admixtures coupled via RPC and p-n interaction mixings.