Offline trapping of 221Fr in a magneto-optical trap from implantation of an 225Ac ion beam

Abstract

We demonstrate a new technique to prepare an offline source of francium for trapping in a magneto-optical trap. Implanting a radioactive beam of 225Ac, t1/2 = 9.920(3) days, in a foil, allows use of the decay products, i.e. 221Fr, t1/2 = 288.0(4) s. 221Fr is ejected from the foil by the α decay of 225Ac. This technique is compatible with the online accumulation of a laser-cooled atomic francium sample for a series of planned parity non-conservation measurements at TRIUMF. We obtain a 34 % release efficiency for 221Fr from the recoil source based on particle detector measurements. We find that laser cooling operation with the source is 8+10-5 times less efficient than from a mass-separated ion beam of 221Fr in the current geometry. While the flux of this source is two to three orders of magnitude lower than typical francium beams from ISOL facilities, the source provides a longer-term supply of francium for offline studies.