Radioactive Decay Calculator
Calculate remaining activity, decay constant, and half-lives elapsed. Presets for common isotopes.
Forward Decay Calculator
A = A0 × (1/2)(t / t½)
Results
Remaining Activity
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Remaining %
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Decay Constant λ
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Half-Lives Elapsed
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Activity vs. Time (10 Half-Lives)
How this was calculated
Equation: A(t) = A0 × (1/2)^(t / t_half) = A0 × e^(-λt)
The decay constant λ = ln(2) / t_half. The number of half-lives elapsed = t / t_half.
Reverse mode: t = t_half × log2(A0 / A_final)
Assumptions: First-order decay. No ingrowth from parent isotopes. Activity units are consistent.
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Book a free strategy call →Understanding Radioactive Decay
Radioactive decay is the spontaneous transformation of an unstable atomic nucleus into a more stable configuration, emitting radiation in the process. The rate of decay is characterized by the half-life, the time required for half of the radioactive atoms in a sample to decay. This is a first-order process: the activity (disintegrations per second) decreases exponentially with time.
The decay constant λ = ln(2) / t_half relates the half-life to the exponential decay rate. Common applications include radiometric dating (C-14), medical imaging (Tc-99m), cancer therapy (Co-60, I-131), nuclear power (U-238, Cs-137), and radiation protection.
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