Atividade A(t) meia-vida
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
The A(t) half-life calculator determines the remaining radioactive activity of a substance after a given time using the formula A(t) = A₀·(1/2)^(t/t½). It's critical in fields requiring exponential decay predictions, such as nuclear medicine, geological dating, or radioactive waste management.
It operates with three main variables: A₀ (initial activity), t (elapsed time), and t½ (substance's half-life). For instance, if a sample has a 10-year half-life and 30 years pass, the activity will be A₀·(1/2)^3, or 1/8 of the original. The formula assumes a constant exponential decay pattern, valid for stable radioactive elements.
Use this tool in scenarios like: dose planning in nuclear medicine, safety calculations in nuclear power plants, or predicting residual activity in archaeological samples. Caution: don't confuse half-life with safe storage time; some elements may produce hazardous decay products even after their parent isotope's half-life.
Ensure the correct half-life value for the isotope is used, and confirm time units match. This calculator doesn't replace specialized analysis in complex cases involving multiple isotopes or combined decay processes.
Frequently asked questions
How to input fractional half-life values?
Enter decimal numbers directly. For example, 15 days and half would be 15.5. The calculator automatically processes fractions in the exponential formula.
What if the calculated time is less than the half-life?
The formula still applies. A time shorter than t½ will produce a decay factor (t/t½) less than 1, maintaining activity above 50% of the initial amount.
Can this calculator be used for beta or alpha decay?
Yes, the formula works for all types of radioactive decay as long as the isotope's specific half-life is known.
What time units are supported?
The calculator accepts seconds, minutes, hours, days, or years. Ensure all input units are consistent for accurate results.
How to interpret results with fractions of nanocuries?
Decimal values represent proportional activity. Use scientific notation for results requiring more than 4 decimal places, such as in radiotracer studies.