Investigation of the inverse-square law for gamma radiation

Investigation of the inverse-square law for gamma radiation

Equipment

Method

1. With the geiger counter far from the gamma source, start the stopwatch and geiger counter and after 20 minutes, record the total count reading. This is the background count.

2. Bring the source into the laboratory and set the distance X between the geiger counter and the gamma source to 0.600m, measured using the metre ruler. Start the stopwatch and geiger counter and take the count N after 5 minutes.

3. Reduce X by 0.100m and repeat this, reducing it by 0.100m each time down to 0.100m.

4. Repeat the experiment twice more and find and record the mean C for each X.

Graphs and calculations

1. Calculate and tabulate the count rate C for each X using C=N/t and do the same to find the background count rate. Then calculate and tabulate the corrected count rate C’ by subtracting the background count rate from C.

2. Plot a graph of  1/√C’ against X which should give a straight line, verifying the inverse square law