α decay studies of very neutron-deficient francium and radium isotopes

Very neutron-deficient francium and radium isotopes have been produced in fusion evaporation reactions using 63Cu and 65Cu ions on 141Pr targets and 36Ar ions on 170Yb targets. The gas-filled recoil separator RITU was employed to collect the fusion products and to separate them from the scattered beam. The activities were implanted into a position-sensitive silicon detector after passing through a gas-counter system. The isotopes were identified using spatial and time correlations between the implants and decays. Two new α decaying radium isotopes, 201Ra and 202Ra, were identified. The α decay energy and half-life of 203Ra were measured with improved precision. The α decay properties measured for the francium isotopes 201Fr, 202Fr, 203Fr, and 204Fr were confirmed, in many cases with improved precision. For the first time, a (πs1/2 -1)1/2+ proton intruder state was identified in francium isotopes, namely in 201Fr and tentatively in 203Fr. The measured decay properties for the neutron-deficient odd-mass Fr isotopes suggest an onset of substantial deformation at N = 112. ©2005 The American Physical Society.