Actinium-225
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.
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 | |
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.
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