Polonium haloes in mica

Abstract

GENTRY¹ has reported that some anomalous haloes found in ancient mica seem to arise from the α-decay of polonium isotopes only, without any observable long-lived β-emitting precursors. Fremlin² suggested that these might occur as a result of the diffusion of β-emitting radiogenic lead isotopes from relatively distant or widely dispersed uranium or thorium inclusions, and the absorption of the lead ions by small preexisting inclusions of foreign material. As Gentry³ pointed out, this would involve abnormally high diffusion rates for lead. We have carried out experiments that demonstrate the possibility of such high rates. Here we also discuss the reasons for the absence of an excess of observable tracks left in mica by the recoil of the lead daughter when α-decay takes place in the polonium isotopes.