Half-life is the unit of measurement used to describe the life span of decaying things, such as radioactive materials.

As an example, if you have a bunch of carbon-14 atoms, they will eventually decay into carbon-12 and other particles. For half of that bunch of carbon-14 to decay, it takes 5,730 years. For half of the remaining carbon-14 to decay, it will take another 5,730 years. And another half of that in 5,730 years.

So after 11,460 years, you will have 1/4 of the original amount. After 17,190 years you will have 1/2 of 1/4, which is 1/8, and so on, until the amount is so microscopically small to measure, that it is considered zero.

Living creatures have both carbon-14 and carbon-12 in roughly equal amounts in their systems. The carbon is ingested while the creature lives. When the creature dies, they no longer are eating or drinking, so there is no replacement for the constantly decaying carbon-14 in them. The carbon-12 does not decay, and keeps building up because of the decay of the carbon-14.

This ratio of carbon-14 to carbon-12 present in the organism, and how it differs from the living 50/50 ratio, shows how long the creature has been dead, which is known as carbon dating. The higher the percentage of carbon-12 compared to percentage of carbon-14, the longer ago the creature died.

For a visual simulation, picture a cake. Somebody comes along and decides to eat half of it. Another person comes by five minutes later, and eats half of what's left. People keep walking past every five minutes and taking half of what is on the plate. Pretty soon, there are a bunch of crumbs, but the people keep going by at a regular pace and taking half. When is the cake all gone?

This is why it is more practical to measure the half-life and not the whole lifetime. If it was a really big cake, it would last a really long time. If it was only a $2 cake, it would last about a half hour, at most. They are both cake, both eaten at the same rate, and so have the same half-life of five minutes.

Half life is most often used to describe the amount of time it takes for one half of a radioactive material to decay into non-radioactive material. For example, the half life of carbon-14 is roughly 5730 years. If you have 1 kilogram of carbon-14, after 5730 years, you will now have half a kilogram of carbon-14 and half a kilogram of nitrogen-14. This period of 5730 years would be the half life of carbon-14.

...Radioactive half life is measured-

%100

one half life = %50

two half lives = %25

three =%12.5

four half lives= %6.25

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Different radi active elements have different Half lifes.

Uranium 238s half life is 4.51 billion years.

A measurement. It is the time it takes for a half of any bunch of atoms of the same type to decay (nuclear decay). Eg half life of iodine is 8 days, if you have 24 iodine atoms, after 8 days you will have 12, after another 8 days you will have 6 another 8 days and your will have 3, etc

...Half-life is a period time required to decay the material by it's half weight. In simplicity if there is a 1 Kg material and it's half -life is one day then after one day the half of the material (0.5Kg) would be decayed.

...Half-life is a term used in both physics and chemistry, it is usually used to describe the decay of radioactive substances. Half-life is the time it takes for a substance to lose half of it's value.

...Half-life is the amount of time that it takes something that is decaying to reduce by half. So if I have 4 of something and it decays to 2 in 1 hour, then the half-life is one hour.

...Half life is the time take for a radioactive substance to decay to half of it's original mass.

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