Actinium-225

Actinium-225, 225Ac
Cherenkov radiation from a sample of Ac-225 (17 mCi), photo by Dr Andrew R Burgoyne at ORNL
General
Symbol225Ac
Namesactinium-225, 225Ac, Ac-225
Protons (Z)89
Neutrons (N)136
Nuclide data
Natural abundancetrace
Half-life (t1/2)9.920 d
Isotope mass225.023229(5) Da
Excess energy21637±5 keV
Parent isotopes225Ra (β)
229Pa (α)
225Th (EC)
Decay products221Fr
Decay modes
Decay modeDecay energy (MeV)
α5.9351
Isotopes of actinium
Complete table of nuclides

Actinium-225 (225Ac, Ac-225) is an isotope of actinium. It undergoes alpha decay to francium-221 with a half-life of 10 days, and is an intermediate decay product in the neptunium series (the decay chain starting at 237Np). Except for minuscule quantities arising from this decay chain in nature, 225Ac is entirely synthetic.

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. However, the scarcity of this isotope resulting from its necessary synthesis in cyclotrons limits its potential applications.