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

TL;DR

This paper introduces a novel offline method to produce and trap francium atoms by implanting a $^{225}$Ac beam, enabling long-term studies despite lower flux compared to traditional sources.

Contribution

The authors demonstrate a new technique for offline francium trapping using $^{225}$Ac decay, offering a longer-term, albeit lower flux, source for precision measurements.

Findings

Achieved 34% release efficiency of $^{221}$Fr from the foil.

Laser cooling efficiency is 8+10-5 times lower than from a mass-separated beam.

Provides a long-term francium source suitable for offline experiments.

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 $^{225}$Ac, $t_{1/2} = 9.920(3)$ days, in a foil, allows use of the decay products, i.e.$^{221}$Fr, $t_{1/2} = 288.0(4)$ s. $^{221}$Fr is ejected from the foil by the $\alpha$ decay of $^{225}$Ac. 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 $^{221}$Fr 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 $^{221}$Fr 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.