The decay properties of actinium-225 are favorable for usage in targeted alpha therapy (TAT); clinical trials have demonstrated the applicability of radiopharmaceuticals containing 225Ac to treat various types of cancer.

As a member of the neptunium series, it does not occur in nature except as a product of trace quantities of 237Np and its daughters formed by neutron capture reactions on primordial 232Th and 238U.

[3] A team of physicists from Argonne National Laboratory led by F. Hagemann initially reported the discovery of 225Ac and identified its 10-day half-life.

[4] Independently, a Canadian group led by A. C. English identified the same decay scheme; both papers were published in the same issue of Physical Review.

[9] This is done by allowing some of the shorter-lived nuclides to decay; actinium isotopes are then chemically purified in hot cells and 225Ac is concentrated.

[10] The TRIUMF facility and Canadian Nuclear Laboratories have formed a strategic partnership around the commercial production of actinium-225.

Additionally, 225Ac has a median lethal dose several orders of magnitude greater than 213Bi because of its longer half-life and subsequent alpha emissions from its decay products.