Half Life Calculator
Calculate radioactive decay
Frequently Asked Questions
What is half-life and how is it calculated?
Half-life is the time required for a quantity to reduce to half its initial value. The formula is: N(t) = N₀ × (1/2)^(t/t½), where N₀ is the initial amount, t is elapsed time, and t½ is the half-life period.
How is half-life used in radioactive decay?
Each radioactive isotope has a characteristic half-life. Carbon-14 has a half-life of 5,730 years (used in dating). Uranium-238: 4.5 billion years. Iodine-131: 8 days. After 10 half-lives, less than 0.1% of the original material remains.
How does half-life apply to medication?
Drug half-life determines dosing frequency. Ibuprofen has a half-life of 2 hours, requiring frequent doses. Amoxicillin: 1 hour. Diazepam: 20-100 hours. After 5 half-lives, approximately 97% of the drug has been eliminated from the body.
How many half-lives until a substance is effectively gone?
After each half-life, 50% remains. After 5 half-lives: 3.125% remains. After 7: 0.78%. After 10: 0.098%. In practice, 7-10 half-lives is considered complete decay for most applications.
Can I calculate the half-life from decay data?
Yes. If you know the initial amount, remaining amount, and elapsed time: t½ = t × ln(2) / ln(N₀/N). For example, if 100g decays to 25g in 10 days, the half-life is 10 × 0.693 / 1.386 = 5 days.