1. Use the term half-life in simple calculations, including the use of information in tables or decay curves.

The half-life of a radioactive substance is the time it takes for parent nuclei in a sample to halve. In other words, half-life of a radioactive substance is the time it takes for the count rate (on a Geiger-Muller counter) from the original substance to fall to half its initial level.

If we start with 1000 unstable nuclei and 10% disintegrate every hour, we would expect 100 nuclei to decay in the first hour leaving 900. Another 10% (900*10%=90) will decay in the next hour leaving 810 and so on. If we were to draw a table to record this decay, it would look like this:

decay
The disintegration rate is 10% per hour.

From the table above we can calculate the half-life of this particular radioactive substance to be somewhere between 6 to 7 hours (half of 1000 is 500 and it falls to 500 nuclei in the seventh hour).

In one half-life the number of nuclei decreases by half. In the second half-life it decreases by a further half and so on.

decay-curve.png
You can see the first, second, third and fourth half-lives marked here.

 

Notes submitted by Lintha

Click here to go to the next topic.

Click here to go back to the previous topic.

Click here to go back to the Science menu.

What Do You Think?

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.