Collective 2+ 1 excitations in 206Po and 208,210Rn

Abstract

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Lifetimes of the 41+ states of Po206 and Po204<

“…These values suggest a constant, or slightly increasing trend with respect to the B(E2; 2 + 1 → 0 + 1 ) value in 204 Pb, instead of the expected more rapid increase, should the seniority regime persist. Based on this observation and QRPA calculations [12], it has been suggested that, at least for the 2 + 1 states of the polonium isotopes, a moderate collectivity sets in immediately when moving away from the closed proton shell [12]. Thus, the energy level pattern and the evolution of the B(E2; 8 + 1 → 6 + 1 ) values suggest that the non-collective seniority regime persists for the N = 122 isotones, as suggested in Refs.…”

“…Thus, the energy level pattern and the evolution of the B(E2; 8 + 1 → 6 + 1 ) values suggest that the non-collective seniority regime persists for the N = 122 isotones, as suggested in Refs. [5,10], while the newly measured values of the B(E2; 2 + 1 → 0 + 1 ) in 206 Po and 208 Rn indicate a moderate collectivity [12]. This suggests that the transition from single-particle seniority-type mode to collective mode develops differently for low-and high-spin states.…”

“…and 13(6) W.u. have been reported for the N = 122 isotones 206 Po and 208 Rn, respectively [12]. These values suggest a constant, or slightly increasing trend with respect to the B(E2; 2 + 1 → 0 + 1 ) value in 204 Pb, instead of the expected more rapid increase, should the seniority regime persist.…”

“…In order to shed more light on this process we have measured the lifetimes of the 4 + 1 states of 206 Po and 204 Po which determine the E2 transition strengths for the seniority-preserving transition 4 + 1 (ν = 2) → 2 + 1 (ν = 2). Until now, these data were missing due to experimental difficulties that stem from the fact that the 4 + 1 states of these nuclei are positioned between the long-lived 8 + 1 states (τ (8 + 1 ; 206 Po) = 335(6) ns [13] and τ (8 + 1 ; 204 Po) = 202 (7) ns [14]) and the short-lived 2 + 1 states (τ (2 + 1 ; 206 Po) = 3.7 +2.8 −1.7 ps [12]).…”

A revised B(E2;2+ 1 $ \rightarrow$ → 0+ 1) value in the semi-magic nucleus 210Po

“…The conservation of seniority imposes a number of simple rules [3,4,6,7] that can be exploited for tracing the evolution from seniority-like behaviour to collectivity with increasing number of valence nucleons [8,9]. Nuclei with two valence nucleons serve as reference points, providing the properties of the basic j 2 configurations such as the energies of states with υ = 2 and the absolute E2 transition strengths for the seniority-changing transition (∆υ = 2) 2 + 1 → 0 + 1 and the seniority-preserving transitions (∆υ = 0) within the υ = 2 multiplet.…”