Actinium-225

Actinium-225, ²²⁵Ac

Cherenkov radiation from a sample of Ac-225 (17 mCi), photo by Dr Andrew R Burgoyne at ORNL
General
Symbol	225Ac
Names	actinium-225, 225Ac, Ac-225
Protons (Z)	89
Neutrons (N)	136
Nuclide data
Natural abundance	trace
Half-life (t1/2)	9.920 d
Isotope mass	225.023229(5) Da
Excess energy	21637±5 keV
Parent isotopes	225Ra (β−) 229Pa (α) 225Th (EC)
Decay products	221Fr
Decay modes
Decay mode	Decay energy (MeV)
α	5.9351
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.