Actinium-225
Cherenkov radiation from a sample of Ac-225 (17 mCi) | |
| General | |
|---|---|
| Symbol | 225Ac |
| Names | actinium-225 |
| Protons (Z) | 89 |
| Neutrons (N) | 136 |
| Nuclide data | |
| Natural abundance | trace |
| Half-life (t1/2) | 9.919 d |
| Isotope mass | 225.023229 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 | 5.935 |
| 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 near 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 (emitting four alpha particles within about an hour) 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. Another such isotope, bismuth-213, is produced necessarily (given its short half-life) from the decay of actinium-225 in a generator and immediate use; it gives only the last of the four alpha particles, requiring a larger amount of actinium, but may be preferred if available.