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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?

Answer.

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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