Linked from
The 8 pages that link to Thorium-232, each with the reason it gives.
RadonRelated: Its chain produces thoron, a radon isotope with a much shorter half-life.
ThoriumBroader topic: It accounts for nearly all naturally occurring thorium.
Thorium fuel cycleRelated: It is the starting material irradiated to initiate the cycle.
GeoneutrinoRelated: Its decay chain is another principal source of geoneutrinos.
Radiogenic heatBroader topic: Its slow decay makes it a persistent source of planetary heat.