1) THE BASICS Easy marks are available here. Lets start
with the idea of half life. The half life of an element tells us two very important things.
Number of atoms
Lets say we a new element Xon is discovered.
It is radioactive and has a half life of 1 day. On Monday at 12.00pm we count
the number of Xon atoms we have - its 1000. On Tuesday 12.00pm we count the number of
Xon atoms we have - its 500. We do the same thing on Wednesday 12.00pm - we have
250 left. How many do you think we will count on Thursday. You can see that if
the element Xon has a half life of 1 day. It means every day the number of atoms of Xon we
have is reduced by a half.
Activity
Lets say we decide to investigate further , and find out how many atoms seem to disappear
(decay) in a minute. On Monday at 12.00pm we count the number of atoms which decay in one minute.
We find that 32 atoms disappear in 1 minute. On Tuesday at 12.00pm we do the same thing-
16 now disappear in one minute. On Wednesday 12.00pm we have 8 atoms disappearing in one minute.
How many do you think decay on Thursday at 12.00pm. You can see that the element Xon has a half
life of 1 day. It means that every day the number of atoms decaying in a set amount of time is
reduced by a half. It looks like the element is becoming less activity. In fact the number
of atoms decaying in a set time is called the activity.
If you've understood that,
you have understood half -life. Now you need to get to grips with the equations, understand
the technical terms connected with this idea and all the marks for these questions are available .
That in a nutshell is half life.
Radioactivity
2) GOING INTO IT A LITTLE DEEPER .
Background radiation
- the disintegrations that go on all around us regardless of the source we are investigating.
If you want to get an accurate radiation count you should subtract the average background
radiation count from any measurements you make.
Alpha beta and gamma radiation
( a, ß and ?) Different types of radiations. What ever is radiated it makes no
difference to how half life works.
Activity -The standards units are
counts per second (Becquerel) but actually any time interval can be used.
Decay Constant (?) - just think of this as the opposite of half life. It has units
of s-1
Random- You must remember that its not quite as simple
as it says in the basics. Radioactive decay is a random process so you wont get 345
exactly half the number left ( or half the activity) if you check back after 1 half life.
Its impossible to say if a particular atom will decay or when the next decay will take place.
Half lifes and Activities are averages.
3) MORE STUFF HERE. Learn how to use the equations.
To test yourself . Try completing the activity
here It contains questions which cover all the
bits about Radioactivity that you need to know.