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# Half Life Calculator

The following tools can generate any one of the values from the other three in the half-life formula for a substance undergoing decay to decrease by half.

## Half Life Calculator

Please provide any three of the following to calculate the fourth value.

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## Half Life, Mean Lifetime, and Decay Constant Conversion

Please provide any one of the following to get the other two.

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## Definition and Formula

Half-life is defined as the amount of time it takes a given quantity to decrease to half of its initial value. The term is most commonly used in relation to atoms undergoing radioactive decay, but can be used to describe other types of decay, whether exponential or not. One of the most well-known applications of half-life is carbon-14 dating. The half-life of carbon-14 is approximately 5,730 years, and it can be reliably used to measure dates up to around 50,000 years ago. The process of carbon-14 dating was developed by William Libby, and is based on the fact that carbon-14 is constantly being made in the atmosphere. It is incorporated into plants through photosynthesis, and then into animals when they consume plants. The carbon-14 undergoes radioactive decay once the plant or animal dies, and measuring the amount of carbon-14 in a sample conveys information about when the plant or animal died.

Below are shown three equivalent formulas describing exponential decay:

where
N0 is the initial quantity
Nt is the remaining quantity after time, t
t1/2 is the half-life