Ac 225

 Yes — Actinium-225 is often described as one of the most expensive materials in the world, but that statement needs context.

Why Actinium-225 is so expensive

• It’s extremely rare — only tiny amounts exist naturally.
• It’s mostly artificially produced in nuclear reactors or particle accelerators.
• Production is slow and complex, often starting from thorium-229 or irradiated radium.
• It has a short half-life (~10 days), so it must be used quickly and continuously produced.
• Demand is rising for targeted alpha cancer therapy, especially for metastatic cancers.

Estimated price

Numbers vary widely, but commonly cited figures:

• ~$20–30 million per gram
• Some estimates go above $100 million per gram depending on purity and availability

That puts it in the same category as:

• Californium-252
• Antimatter (theoretical pricing)
• Tritium (high but less than Ac-225)

Important nuance

Calling it “the most expensive material” is not strictly accurate, because:

• Antimatter is vastly more expensive (but not practical to buy)
• Some synthetic isotopes can exceed it temporarily due to scarcity
• Actinium-225 is usually considered the most expensive practical material used in medicine

So the claim is mostly true in a practical sense, especially in nuclear medicine, but not universally the absolute most expensive substance known.

Want to know:

•  why it’s used for cancer treatment, or
•  how it’s produced, or
•  comparison with antimatter?