Radioactive Decay Calculator
Calculate remaining quantity after radioactive decay: N = N0 x e^(-lambda x t), lambda = ln(2)/half_life.
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Enter the initial quantity (atoms, grams, or activity), the half-life, and the elapsed time. Both time values must use the same units. The calculator uses N = N0 x e^(-0.693t/half_life) to find the remaining amount.
About the Radioactive Decay Calculator
Radioactive decay is the spontaneous transformation of an unstable atomic nucleus. It follows first-order kinetics with a constant half-life characteristic of each isotope. Applications include carbon dating, nuclear medicine, nuclear power, and geological age determination.
Frequently Asked Questions
What is a half-life?
A half-life is the time it takes for half of a radioactive sample to decay. After one half-life, 50% remains. After two, 25%. After three, 12.5%. The half-life is constant for each isotope regardless of the amount present.
What units should I use for time and half-life?
Both must use the same units (years, days, hours, seconds, etc.). Common half-lives: carbon-14 = 5,730 years, iodine-131 = 8.02 days, uranium-238 = 4.47 billion years.
What is the decay constant lambda?
Lambda = ln(2)/half-life = 0.693/half-life. It represents the probability of a single nucleus decaying per unit time. A larger lambda means faster decay (shorter half-life).