Calculadora de Meia-Vida
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
t½ = ln2/λ ; N(t) = N₀·(½)^(t/t½)
About this calculator
The Half-Life Calculator determines the time required for half of the atoms in a radioactive sample to decay, or the remaining amount after a period. The half-life (t½) is a characteristic constant for each isotope, given by t½ = ln2 / λ, where λ is the decay constant. To calculate the remaining quantity N(t) after time t, use N(t) = N₀ × 0.5^(t/t½), where N₀ is the initial quantity.
This tool is useful in areas such as nuclear medicine (radiopharmaceutical dosing), archaeological dating (carbon-14), nuclear waste management, and chemical kinetics studies. For example, knowing the half-life of iodine-131 (8 days), you can calculate how much remains after 24 days to plan a treatment.
Important considerations: the formula assumes pure exponential decay, unaffected by external factors. In biological samples, metabolic clearance can alter the effective rate. Also, half-life is a statistical average; for very small samples, fluctuations may occur. Always use consistent units (same time unit for t and t½).
Frequently asked questions
What is half-life?
Half-life is the time required for half of the atoms in a radioactive sample to decay, transforming into another element.
How to calculate the remaining amount after several half-lives?
Divide the total time by the half-life to get the number of half-lives. The remaining fraction is 0.5 raised to that number.
Does the calculator work for any isotope?
Yes, as long as you enter the correct decay constant or half-life. Each isotope has a specific value.
Can I use this calculator for carbon-14 dating?
Yes, but note that the half-life of carbon-14 is approximately 5730 years. The calculator gives the remaining amount, which can be used to estimate the sample's age.