2025

Zanon, I.; Doncel, M.; Cederwall, B.; Grahn, T.; Illana, A.; Appagere, G.; Auranen, K.; Bäck, T.; Bogdanoff, V.; Briscoe, A. D.; Cederlöf, E. A.; González-Briz, G.; Greenlees, P. T.; Makwana, R. Jashbhai; Joukainen, H.; Julin, R.; Jutila, H.; Knežević, D.; Luoko, J.; Luoma, M.; McCarter, A.; Singh, B. S. Nara; Pakarinen, J.; Plaza, A. M.; Rahkila, P.; Ruotsalainen, P.; Sarén, J.; Sullivan, C.; Tegnér, P.-E.; Uusikylä, E.; Uusitalo, J.; Zimba, G. L.

Several instances of anomalously low values of the 𝐵⁡(𝐸⁢2;4+1→2+1)𝐵⁡(𝐸⁢2;2+1→0+gs) ratio (𝐵4/2)<1 have previously been observed in several nuclei among the highly neutron deficient W-Os-Pt isotopes with even numbers of neutrons and protons. The relatively large number of cases suggests a striking new phenomenon that currently has no theoretical explanation. A clue to its origin might be achieved by comparing the 𝐵4/2 ratios in even-even nuclei with the corresponding ratios of transition rates in neighboring odd-mass nuclei. However, until now only one case (169Os) has been observed with an unusually low corresponding 𝐵4/2 ratio, approximately 1⁢𝜎 below 1. Electromagnetic transition rates between excited states in the extremely neutron deficient nuclide 167Os were measured using 15 single-crystal germanium detectors from the jurogam 3 array coupled to the RITU gas-filled separator. The excited states of interest were populated via the 92Mo⁢(78Kr,2⁢pn) fusion-evaporation reaction and studied by selecting the rare reaction channel via recoil-𝛼-decay tagging. The lifetimes of low-lying states were measured using the recoil distance Doppler shift method with the APPA plunger device. From the measured lifetimes in the rotational-like band structure assigned to the 𝜈⁢𝑖13/2 yrast intruder configuration, the 𝐵⁡(𝐸⁢2;17/2+→13/2+) and 𝐵⁡(𝐸⁢2;21/2+→17/2+) values were deduced, resulting in the ratio 𝐵⁡(𝐸⁢2;21/2+→17/2+)𝐵⁡(𝐸⁢2;17/2+→13/2+)=0.49⁢(10). The results were compared with previous measurements in the Os isotopic chain and theoretical mean-field calculations, implying that the odd neutron valence particle has limited, if any, influence on the 𝐵4/2 values for this particular single-particle configuration.