Actinium-225 dosage standard

Radioisotope attached to a cancer-targeting molecule, showing how the molecule attaches to a cancer cell and delivers alpha radiation.
Actinium-225 breaks down into six other elements, each of which emits certain types of radiation.
Client
NIST
Year
2025
Type
explanatory diagram
Field
radiopharmaceuticals / radioactivity measurement
Links
NIST story
Description
Two public-facing diagrams for a NIST story about an actinium-225 standard for cancer-drug dosage.

Context

Actinium-225 is used in targeted alpha therapy, where a radioactive isotope is attached to a molecule that seeks out cancer cells. Because the isotope decays through several daughter products, measuring the right activity is not as simple as reading one emission line.

NIST released a standard to help researchers and manufacturers calibrate instruments for actinium-225 dosage.

Approach

The first diagram explains the treatment idea in broad public language: radioisotope, targeting molecule, cancer cell, healthy cells, and alpha radiation. The second diagram shows the decay chain in a compact linear form, including the daughter elements and their alpha, beta, and gamma emissions.