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Calcimator

Radioactive Decay Calculator

Calculate remaining radioactive activity from initial activity, half-life, and elapsed time.

Inputs

Bq

Results

Remaining Activity

314,980.26 Bq

Fraction Remaining0.32
Percent Decayed68.5%
Half-Lives Elapsed1.67
Decay Constant (λ)0 /unit time
Mean Lifetime (τ)43.28
Time to 1% Remaining199.32
Time to 0.1% Remaining298.97
How to Use This Calculator
  1. Enter Initial Activity, Half-Life, and Time Unit.
  2. Set Elapsed Time.
  3. Review the Remaining Activity (Bq) result.
  4. Use Fraction Remaining and Percent Decayed (%) to inform your decision.
  5. Use the chart to visualize the results and explore different scenarios by adjusting inputs.

What each input means

Initial Activity
Initial radioactive activity in becquerels (disintegrations per second). 1 Ci = 3.7×10¹⁰ Bq.
Half-Life
Time for activity to decrease by half. Set the unit below.
Time Unit
1=Seconds, 2=Minutes, 3=Hours, 4=Days, 5=Years
Elapsed Time
Time elapsed since the initial activity measurement, in the same unit as the half-life.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Initial Activity = 1000000, Half-Life = 30, Time Unit = 5, Elapsed Time = 50 = 4 input(s) provided
  2. Calculate Remaining Activity
    Remaining Activity
    314980.262 = 314980.262
  3. Calculate Fraction Remaining
    Fraction Remaining
    0.315 = 0.315
  4. Calculate Percent Decayed
    Percent Decayed
    68.5 = 68.5%

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