Enter your Initial Activity, Half-Life, and Elapsed Time (with their respective units) into the Radioactive Decay Calculator, and it'll calculate your sample's Remaining Activity along with the Decay Constant (λ), Fraction Remaining, Half-Lives Elapsed, and Activity Lost — or pick a Common Isotope to auto-fill the half-life.
Remaining Activity
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Decay Constant (λ)
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Fraction Remaining
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Half-Lives Elapsed
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Activity Lost
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Radioactive decay is the spontaneous breakdown of unstable atomic nuclei, releasing radiation. It follows exponential decay law: N(t) = N₀ × e^(-λt), where N₀ is initial activity, λ is decay constant, and t is time.
Common conversions: 1 Ci = 3.7 × 10¹⁰ Bq, 1 mCi = 3.7 × 10⁷ Bq, 1 μCi = 3.7 × 10⁴ Bq. The calculator automatically handles unit conversions for accurate results.
Common biological tracers include Carbon-14 (dating, metabolism), Phosphorus-32 (DNA/RNA labeling), Sulfur-35 (protein studies), Iodine-125 (protein binding), and Tritium (water tracing).
Half-life calculations are highly accurate for pure isotopes. However, in biological systems, effective half-life may differ due to biological elimination processes combined with physical decay.
Always account for decay when planning experiments, storage, and disposal. Longer-lived isotopes require extended safety protocols, while short-lived ones may decay to safe levels quickly.
Temperature has no effect on radioactive decay rates. Decay is a nuclear process independent of chemical or physical conditions like temperature, pressure, or chemical bonding.
The decay constant (λ) and half-life (t₁/₂) are inversely related: λ = ln(2)/t₁/₂ ≈ 0.693/t₁/₂. A larger decay constant means shorter half-life and faster decay.
Calculate remaining activity at your experiment date, ensure sufficient activity for detection, and account for decay during long experiments. Order isotopes close to use date for maximum activity.