Linked from
The 12 pages that link to Radium, each with the reason it gives.
ActiniumRelated: Radium occurs in the same decay chains and ores that contain trace actinium.
PoloniumRelated: The Curies identified radium alongside polonium in their work on uranium ores.
FranciumRelated: Radium borders francium in the periodic table and appears in its decay pathways.
PitchblendeBroader topic: Radium was isolated from pitchblende residues enriched in decay products.