Skip to Content
Medical Term:


Pronunciation: rā′dē-ŭm

Definition: A metallic element, atomic no. 88, extracted in very minute quantities from pitchblende; 226Ra, its longest-lived isotope, is produced as an intermediate in the uranium series by the emission of an α particle from thorium-230 (ionium); 226Ra emits α particles and gamma rays with a half-life of 1,599 years breaking down to 222Rn; chemically, it is an alkaline earth metal with properties similar to those of barium. Its therapeutic action is similar to that of x-rays, since the α emission is filtered out.

[L. radius, ray]