Calculadora de Meias-Vidas
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
N = N₀·(½)^(t/t½)
About this calculator
The Half-Life Calculator determines the remaining amount of a radioactive substance after a given time, using the exponential decay formula: N = N₀·(½)^(t/t½). Here, N is the final amount, N₀ is the initial amount, t is the elapsed time, and t½ is the half-life. This tool is essential in nuclear physics, nuclear medicine, archaeological dating (carbon-14), and radioactive waste management.
Usage is straightforward: enter the initial amount, elapsed time, and half-life. The calculator applies the formula and returns the remaining amount. For example, if a sample of iodine-131 (half-life 8 days) starts with 100 grams, after 16 days it will be 25 grams. This is because 16 days equal two half-lives, halving the amount twice.
Use this calculator whenever you need to predict radioactive decay. Common scenarios include: estimating the activity of a radioisotope in medical exams, calculating the time needed for toxic waste to reach safe levels, or determining the age of organic fossils via radiometric dating. Remember that the model assumes pure decay without external interference.
Important precautions: ensure time units are consistent (use the same period for t and t½). The formula is exponential, so small input errors can cause large result differences. Additionally, the half-life of some isotopes may vary under extreme environmental conditions, but for most practical cases, tabulated values are reliable.
Frequently asked questions
What is half-life?
Half-life is the time required for half of the atoms in a radioactive sample to decay. Each substance has its own half-life, ranging from seconds to billions of years.
How to use the calculator for carbon-14 dating?
Enter the initial amount of carbon-14 (typically found in living organisms), the current amount measured in the sample, and the half-life of carbon-14 (5,730 years). The calculator will provide the time elapsed since the organism's death.
Can I use different units for time and half-life?
No. Both must be in the same unit (days, years, etc.). If you enter time in hours and half-life in years, the result will be incorrect. Convert to the same unit before use.
Does the calculator work for exponential growth?
No, it is specific to decay. For growth, use the formula N = N₀·2^(t/t½), which represents doubling every period.
What does it mean if the result is zero?
If the elapsed time is much longer than the half-life, the value may be so small that the calculator rounds to zero. This indicates that virtually all material has decayed.