Spectroscopy and high-spin structure ofFr210: Isomerism and potential evidence for configuration mixing

Abstract

The structure of 210 Fr has been established up to an excitation energy of ∼5.5 MeV and spins of ∼25 , via time-correlated γ-ray spectroscopy and using the 197 Au(18 O ,5n) 210 Fr reaction with pulsed beams at an energy of 97 MeV. A significantly different level scheme has been obtained compared to previous publications. Several isomers are reported here, including a J π = (23) + , τ = 686(9)-ns state at 4417 keV and a 10 − , 29.8(11)-ns state at 1113 keV. The former isomer has been associated with the π (h 3 9/2 i 2 13/2)ν(p −2 1/2 f −1 5/2) configuration and decays via proposed E3 transitions with strengths of 8.4(3) and 21.2(8) W.u. There are only very few known cases of a high-spin isomer decaying via two parallel E3 transitions. Indeed, this is not seen in other Fr nuclei, and consequently these strengths differ from related decays in the neighboring isotopes. However, by examining the systematics of E3 transitions in trans-lead nuclei, we suggest that the weaker of the two transitions decays to a mixed 20 − state. Systematics of the 10 − isomer are also discussed. Comparisons are made between the observed spectrum of states and those predicted from semiempirical shell-model calculations.

The Heavy Ion Accelerator Facility: Research Achievements and Aspirations

“…Refs. [15,16] and references therein). Highlights of recent work include the addition of LaBr 3 detectors for lifetime measurements on the subnanosecond time scale, and experiments to eliminate possible alternative explanations of recent evidence of isomer depletion due to nuclear excitation by electron capture [17].…”

High-spin spectroscopy and shell-model interpretation of the N < 126 radium isotopes Ra212 and Ra<

“…Further physical considerations can facilitate the determination of the electric or magnetic nature of many identified transitions. There is a wellestablished occurrence of E3 transitions from isomeric states in neighboring nuclides [8,9,16]. Consequently, any transitions found to exhibit a large A 2 /A 0 coefficient without a discernible state lifetime can be considered to be E2 in nature.…”