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sci.radioactive-decay Calculator
Calculates radioactive decay activity A = A₀ e^(−λt) and remaining quantity from initial activity and decay constant λ = ln2/t½. After each half-life, activity halves — ¹³¹I (t½ = 8 days) used in thyroid cancer treatment decays to <1% in 53 days.
Inputs
Initial Activity Bq
Reference formula or conversion factor shown for context.
Half Life Days
Reference formula or conversion factor shown for context.
Elapsed Days
Duration of the process. Make sure units match the rate inputs (seconds, minutes, or hours).
Results
remaining activity (Bq)
Rate of radioactive decay events per second (becquerels or curies). Decreases exponentially with time.
percent remaining
Sample size or count used in the calculation.
half-lives elapsed
Reference formula or conversion factor shown for context.
decay constant λ (per day)
Sample size or count used in the calculation.
A(t) = A₀ × (½)^(t/t½)
Reference formula or conversion factor shown for context.
I-131 half-life
Time for half the radioactive material to decay. After 10 half-lives, less than 0.1% of the original material remains.