Skip to content

Half Life

Half Life, other than being a fantastic game, is the time it takes for a radioactive substance to halve it's radioactivity / for the nuclei in a sample to decay. This can be anything from a few seconds, to billions of years.

Use to calculate radiation level

The Half Life of a sample can be used to calculate the radiation level of said sample between two given times.

For example:

1
2
3
4
5
6
7
8
9
An isotope has a half life of 2 hours. It starts with a radiation level of 1600
counts/sec. What will the radiation level be after 6 hours?

First establish how many half-lifes that is: 6 / 2 = 3 half lifes

start   2 hours   4 hours   6 hours
1600 -> 800    -> 400    -> 200 counts/sec

Therefor the radiation level will be 200 counts/sec after 6 hours.

Use radiation level to calculate half life

The Half Life of a sample can be established by using two radiation levels and the time between the readings.

For example:

1
2
3
4
5
6
7
An isotope started with a radiation level of 1600 counts/sec, after 4 hours it had a
radiation level of 400 counts/sec. What is the isotope's half life?

start   1 half life   2 half lifes
1600 -> 800        -> 400

In 4 hours there were 2 half lifes - therefor a half life is 4/2 = 2 hours.
Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Mozilla Public License 2.0.