Number of Half-Lives
Compute how many half-lives have elapsed, n = t/T½, and the fraction of radioactive material remaining, (1/2)ⁿ, from the elapsed time and the half-life. With each half-life the amount halves: after 1 half-life 50% remains, after 2 it is 25%, after 10 less than 0.1%. It is the intuitive way to assess how much of a source (or contamination) is left. Enter the elapsed time and the half-life.
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Número de meias-vidas
A maneira mais intuitiva de pensar no decaimento radioativo é contar meias-vidas: n = t/T½. A cada meia-vida que passa, a quantidade de material radioativo cai pela metade, independentemente de quanto havia. Após 1 meia-vida resta 50%; após 2, restam 25%; após 3, 12,5%; após 10 meias-vidas, menos de 0,1% (a regra prática é que após ~7 meias-vidas a fonte já caiu a menos de 1%, sendo muitas vezes considerada desprezível). A fração restante é (1/2)ⁿ. Esse raciocínio é usado para decidir quanto tempo guardar um rejeito radioativo até ele ser seguro, ou quando um radiofármaco perdeu utilidade. Note que o decaimento é exponencial, não linear — nunca chega exatamente a zero, apenas se aproxima. Informe o tempo decorrido e a meia-vida.
Related Tools
Decay Constant
Compute the radioactive decay constant, λ = ln(2)/T½, from the half-life (T½). The constant λ is the probability of a nucleus decaying per unit time — the larger it is, the more unstable the isotope and the shorter its half-life. It links the half-life (time for half the nuclei to decay) to the activity and to the exponential decay law. Enter the isotope's half-life.
Effective Half-Life
Compute the effective half-life of a radionuclide in the body, 1/Teff = 1/Tbio + 1/Tphys, combining the physical half-life (radioactive decay) with the biological one (elimination by the organism). Since both processes reduce the amount simultaneously, the effective half-life is always shorter than either. It is essential in internal dosimetry in nuclear medicine and radiation protection. Enter the biological and physical half-lives.
Caffeine Half-Life Calculator
Find out how much caffeine is still in your body after a few hours, using the roughly 5-hour half-life. Enter the dose and the time elapsed.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.