Interactive training · Targeted alpha therapy
Actinium-225 Decay Explorer
Explore daughter ingrowth, emission pathways and changing activities following an initially purified Ac-225 sample. Select a radionuclide to inspect its properties.
Interactive 3D decay chain
Select a nucleus to inspect its transition. Gold arrows = alpha; cyan = beta. Half-lives are shown under each nucleus on larger screens. Particle motion is illustrative, not a time-scaled simulation.
Bi-213: β− (~97.8%) → Po-213; α (~2.2%) → Tl-209
Schematic nuclei, not representations of true nucleon positions or emissions. Branch widths and animation speed do not encode probabilities, half-lives, gamma emissions, or particle ranges. Use the activity plot below to examine simplified daughter ingrowth.
Decay-chain activity
Relative activity: daughter activity / initial Ac-225 activity. No units of administered activity.
Inspect a radionuclide
- Half-life
- 45.6 minutes
- Emission
- ~97.8% β−, ~2.2% α
- Activity relative to initial Ac-225
- 0.716
Major beta branch produces Po-213; minor alpha branch produces Tl-209. A 440 keV photon is relevant to some measurement approaches.
Starts with Ac-225 only (no daughters). Closed, well-mixed system with no biological clearance, chemical separation or daughter escape. Dynamics use a simplified five-state decay model; At-217 and Po-213 activities are treated as instantaneous equilibrium with their immediate precursors after the initial seconds. These approximations do not capture millisecond/microsecond transients. The chart is not a dose, detector response, dose calibrator correction factor or treatment planning tool. Approximate emissions and half-lives are for education; consult evaluated nuclear data for quantitative applications.
Reference: Bismuth-213 for Targeted Radionuclide Therapy (2021) and NIST Ac-225 activity measurements (2025).