Spectroscopy and high-spin structure of 209 Fr

Abstract

Excited states in Fr209 have been studied using the Au197(O16,4n)Fr209 reaction with pulsed beams and I-ray and electron spectroscopy. A comprehensive scheme has been established up to an excitation energy of about 6 MeV and spins of about 49/2. Several isomers have been identified including a JÏ€=25/2+, Ï.,=48(3) ns state at 2130 keV and a 606(26) ns, 45/2- state at 4660 keV. The latter state decays via an enhanced E3 transition with a strength of 28.8(12) W.u. It can be identified with a similar isomer in the heavier odd isotopes Fr211 and Fr213, arising from the maximal coupling of the five valence protons in the Ï€h9/23i13/22 configuration. The systematics of the yrast states in the odd-A isotopes are discussed, including the presence of states arising from the main proton configurations coupled to the p1/2, f5/2, and i13/2 neutron holes. Shell-model configurations are assigned to many of the observed states. The isotopic assignment differs from earlier work, which is shown to be erroneous.