Radioactive Half-life Calculator

Radium half-life: N(t) = N₀·(1/2)^(t/T)

Radium is the prototypical radioactive element. Radium-226, the most stable natural isotope, has a half-life of 1,600 years and decays into Radon-222 (a radioactive gas). Radium-228 has a half-life of only 5.75 years. Using N(t) = N₀·(1/2)^(t/T): starting with 100 g of Ra-226, after 1,600 years 50 g remain; after 3,200 years, 25 g; and after 8,000 years (5 half-lives), about 3.13 g. Radium was discovered in 1898 by Marie and Pierre Curie; Marie went on to win two Nobel Prizes (Physics 1903, Chemistry 1911). Until the 1930s, radium was used in luminescent paints for watch dials — the "Radium Girls" who licked the brushes to point them suffered from severe jaw cancers (radium osteonecrosis), prompting the first US occupational-safety lawsuits.

Applications

Today radium's uses are primarily historical and educational; modern luminescent dials use tritium (³H) or non-radioactive photoluminescent compounds (GTLs). Ra-223 dichloride (Xofigo) is approved for bone metastases in advanced prostate cancer. Ra-226 contamination is still a concern in legacy industrial sites and old hospital sources, regulated in Brazil by CNEN.

FAQ

Why is radium so dangerous? It is a calcium analogue — the body deposits it in bones, where alpha emission causes osteosarcoma and aplastic anemia over years.

Does radium glow on its own? Pure radium emits a faint bluish glow from air ionization, but the bright green of antique dials came from zinc sulphide phosphor excited by Ra alpha particles.

How long until a Ra-226 source is safe? Roughly 10 half-lives (16,000 years) leaves ~0.1 % of activity — but radon daughters complicate disposal, so storage is essentially permanent.