Anomalous B 4 / 2 ratio in the yrast band of Os 167

Le résumé fourni par la source

Several instances of anomalously low values of the B ( E 2 ; 4 1 + → 2 1 + ) B ( E 2 ; 2 1 + → 0 gs + ) ratio ( B 4 / 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 B 4 / 2 ratios in even-even nuclei with the corresponding ratios of transition rates in neighboring odd-mass nuclei. However, until now only one case ( Os 169 ) has been observed with an unusually low corresponding B 4 / 2 ratio, approximately 1 σ below 1. Electromagnetic transition rates between excited states in the extremely neutron deficient nuclide Os 167 were measured using 15 single-crystal germanium detectors from the array coupled to the RITU gas-filled separator. The excited states of interest were populated via the Mo 92 ( Kr 78 , 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 i 13 / 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 + )

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