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How to Calculate the Half-life from the Count Rate.

Calculations using Half-life.

There are two types of calculation using half-life.

1. If you know the half-life of a material, you can calculate
what the
count rate will be at some time in the future.
The method for this is shown on the previous page.

2. If you are given two count rates and you
know how long it takes to get from one to the other,
then you can calculate the half-life of the material.
The method for this is shown below.

How the Half-life can be Calculated from the Count Rate.

Question.
The count rate of a material is 2016 Bq.
After 35 days it has fallen to 63. What is the half-life?

Put the count rate in boxes and use arrows to represent the half-life.
After each half-life the count rate is halved.

In going from 2016 to 63 there are 5 half-lives.
If 5 half-lives take 35 days, each half-life is
35 ÷ 5 = 7 days.
The half-life of the material is 7 days.

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