What mathematical formula does this calculator use?

It applies the exponential decay law A(t) = A₀ · e^(−λt) or A(t) = A₀ · 2^(−t/T½), where λ = ln(2) / T½.

Can I use different time units for half-life and elapsed time?

Yes, you can independently select seconds, minutes, hours, days, or years for half-life and elapsed time.

What activity units are supported?

Supported units include Bq, kBq, MBq, GBq, Ci, mCi, µCi, and dpm (disintegrations per minute).

Does the calculation depend on the isotope type?

The calculation depends entirely on the numerical half-life value and unit you provide for your specific isotope.

What is the relationship between elapsed half-lives and remaining percentage?

Each elapsed half-life reduces the remaining activity by 50%; after n half-lives, the remaining fraction is (1/2)^n.

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Half-Life Activity Decay Calculator (A = A₀·e^(−λt))

Compute remaining radionuclide activity A(t) = A₀·2^(−t/T½) with λ = ln2/T½ in Bq/Ci/dpm units, for Tc-99m, F-18 and other isotopes.

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2 examples

Tc-99m: 800 MBq after 6 h (T½ = 6.01 h) → 400.46 MBq

A 800 MBq Tc-99m dose is injected, then imaging is delayed 6 hours. With t/T½ = 6/6.01 = 0.9983 half-lives the remaining activity is 800 × 2^(−0.9983) = 400.46 MBq (50.06 %) — essentially one half-life has passed.

{"result":"Decay: 800 MBq after 6 h (T½ = 6.01 h) → A = 400.46 MBq (50.06 % remaining).","metadata":{"result":{"remainingActivity":400.46,"remainingPercent":50.06,"elapsedHalfLives":1}}}

F-18 FDG: 370 MBq after 2 h (T½ = 109.77 min) → 173.43 MBq

A 370 MBq (10 mCi) F-18 FDG dose sits for 2 hours before scanning. After 120/109.77 = 1.093 half-lives the remaining activity is 370 × 2^(−1.093) = 173.43 MBq — 46.87 % of the dispensed activity.

{"result":"Decay: 370 MBq after 120 min (T½ = 109.77 min) → A = 173.43 MBq (46.87 % remaining).","metadata":{"result":{"remainingActivity":173.43,"remainingPercent":46.87,"elapsedHalfLives":1.09}}}

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7 options

SettingsAdjust formats, ranges, numbers, and modes.7

Initial Activity A₀numberRequiredActivity at t = 0 in the selected activity unit. Must be non-negative.Activity UnitselectRequiredUnit of the initial (and remaining) activity.Half-life T½numberRequiredPhysical half-life in the selected time unit. Must be greater than zero.Half-life T½selectRequiredTime unit of the half-life.Elapsed Time tnumberRequiredTime since the initial activity measurement. Must be non-negative.Elapsed Time tselectRequiredTime unit of the elapsed time.Decimal PlacesnumberOptional

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Half-Life Activity Decay Calculator (A = A₀·e^(−λt))

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Examples

1. Technetium-99m Diagnostic Scan Prep

2. Fluorine-18 FDG PET Tracer Decay

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