1 Need draw only one diagram. Just say replace paper with aluminum .
2 absorption by air is not directly measured so got to say count rate C
3 show the two diff values as C1 -C2=C3 where C3 is the count rate due to beta only.
4 handle the source with tongs,do not point the source at anyone and store away source in a lead box when not in use.
5 good design : make sure the source has long half life, high energy beta may still pass through aluminum, the distance d should be measured from the same refrerence point on the GMtube . Repeating measurement and averaging is important in this expt.
SAMPLE
To investigate how the count rate C of beta depends on the distance d between the Source and GM tube keeping the source power constant.
Procedure:
1 Set up the experiment as shown above.
2 Measure the distance d using a ruler.
3.Place a sheet of paper between the source and Gm tube and record the count rate C1 Using the rate meter.
4. Record the count rate C2 when the paper is replaced by an aluminium sheet.
5 The count rate C of beta particles can be found by the formula C1- C2.
6 Repeat steps 2-5 to obtain 6 sets of readings by varying the distance d .
7. Plot a graph of lg C against lg d. If the graph is linear , the relationship C=kdn is valid. where lg k is the intercept and gradient is n.
Reliability : Use the same source , ensuring that it has a long half life.
Repeat the expt to get average reading.
Safety measures:
1. Handle the source with tongs
2. Do not point the source at anyone.
3. Keep the source in lead box after use.
