Time Correlated gamma-ray Spectroscopy and High-Spin Structure of the Odd-Odd Nucleus ²¹⁰Fr

Abstract

The structure of ²¹⁰Fr has been studied with the ¹⁹⁷Au(¹⁸O, 5n)²¹⁰Fr reaction. Experiments were performed using the 14UD Pelletron accelerator at the Heavy- Ion Accelerator Facility at the ANU to provide an ¹⁸O beam at an energy of 97 MeV. Several structural features have been discovered including the presence of four isomers. A high-spin isomeric state, with spin more likely being 23⁺, has been identified at ∼4.4 MeV with a lifetime of 686(17) ns that decays by two γ-rays at 573.5 and 663.6 keV that are very likely to have either M2 or E3 multi-polarity. The measured strengths in the case of E3 assignments are approximatively 8 and 21 W.u., respectively. These would be less enhanced than is observed in the decay from the high spin isomers in ²⁰⁹Fr and ²¹¹Fr that are believed to be from a related configuration. Another isomer at ∼1 MeV with Jπ=10⁻ and lifetime of ∼30 ns is found to decay via a hindered E1 transition that is j-forbidden. Possible configurations of excited states in ²¹⁰Fr are discussed within the semi-empirical shell model. Comparisons are made with calculations performed using the code Sesame developed at the ANU.