[en] The initial distribution of Tl(I) and Tl(III) species, and its change on heating, have been investigated in solid thermal neutron-irradiated Th₄Cl₆. An initial ratio of 5/1 for ²⁰⁴Tl(I)/²⁰⁴Tl(III) is found and this remains constant for integral gamma-doses of 3 to 12 MRad. The variation of the ²⁰⁴Tl(III) fraction with temperature is found identical to that observed in labelled Tl₄Cl₆ for which a genuine isotopic exchange has previously been described. It is concluded that the recoil species are rapidly converted, after the recoil processes, into stable ions