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Using Half-life to Calculate the Count Rate.

Calculations using Half-life.

There are two types of calculation using half-life.

1. 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 on the next
page.

2. 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 below.

How Half-life
can be used to Calculate the Count Rate.

Question.

The half-life of a material is 3
hours.

If the initial count rate is
544 Bq,

what will the count rate be after 15
hours?

Answer.

Put the count rate in
boxes and use arrows to represent the half-life.

We are told that the half-life of the material is 3
hours.

In 15 hours there are 15 ÷
3 half-lives

= 5
half-lives.

After each half-life the count rate is
halved.

After five half-lives the count
rate is 17
Bq.

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