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The detailed guide below is currently available in English.
The half-life decay formula
Radioactive substances do not decay by a fixed amount per unit time — they lose a fixed fraction per half-life. That gives exponential decay: N = N₀ × 0.5t/h, where N₀ is the starting quantity, h is the half-life, and t is the elapsed time. After one half-life 50% remains, after two only 25%, after three just 12.5%. The constant that replaces the half-life in calculus work is the decay constant λ = ln 2 ÷ h, which converts the same process into N = N₀e−λt.
자주 묻는 질문
Does the material ever fully disappear?
Mathematically it only approaches zero, halving forever. Practically, after about ten half-lives roughly 0.1% remains, which most fields treat as negligible.
Can I use any time unit?
Yes — just enter the half-life and the elapsed time in the same unit. A half-life of 5 with an elapsed time of 10 works identically whether that means 5 days and 10 days or 5 years and 10 years.