Half-life converter
Convert a half-life into a mean lifetime or a decay constant, and see how long it takes until almost nothing is left.
That's about the same as carbon-14. Only one percent would be left after about 38,070 years.
What it means
How long does it last?
Half-life is a property of the nucleus alone. Heat, pressure and chemistry do not change it, which is what makes radiometric dating work.
Every unit
Your half-life in every unit
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Three things worth knowing
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Mean lifetime = half-life ÷ 0.693
So carbon-14’s 5,730-year half-life is an 8,267-year mean lifetime. The mean is longer because the few atoms that survive a long time drag the average up.
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Rutherford noticed the pattern
In 1900 he saw that radioactive samples always lost the same fraction in the same time, whatever they started with. That made the half-life the natural way to describe decay.
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Two half-lives is not all of it
It is three quarters, not everything. Getting to 1% takes about 6.6 half-lives, and it never quite reaches zero.
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Background
About half-life
A half-life is the time for half the atoms in a sample to decay. It never changes: after two half-lives a quarter is left, after ten about a thousandth.
The decay constant λ is the chance per second that any one atom goes, and the mean lifetime is how long an average atom survives — longer than the half-life, by a factor of 1/ln2.