Practical 5 - Investigaion of the varation of intensity of gamma radiation with distance

Question 1

Setting up

Answer 1

1. Set up the Geiger-Muller tube and attach it to the scaler.
2. Clamp a metre rule to the bench and line it up with your zero point (in the Geiger-Muller tube).
   3.With some Geiger-Muller tubes, the gamma radiation will pass through the side. So set the Geiger-Muller tube up at right angles to the metre rule. The zero point is then the axis of the tube.

Question 2

Method

Answer 2

1. Measure the background count with the source far away.
2. Start with the gamma source 10 cm from the zero point.
3. Increase the distance and take measurements of count rate at 20 cm, 30 cm, 40 cm, 60 cm
   and 80 cm.
   4.Correct the count rates for the background count.
4. Plot a graph of corrected count-rate against distance.

Question 3

Inverse square law equation

Answer 3

I = I0/4pir^2

Question 4

Io

Answer 4

Intensity of source (initial intensity)

Question 5

What’s the correction factor that we need to include in this practical?

Answer 5

For the systemic error that needs to be added to all readings —> the distance between the sensor and the end of the Geigner tube

Question 6

Is count rate equal to intensity?

Answer 6

No, just proportional

Question 7

Why is count rate proportional to intensity?

Answer 7

More gamma rays = greater intensity = count rate increases

Question 8

What’s the count rate counting?

Answer 8

The number of ionisations that occur in the Geigner tube

Question 9

How do we get to the final equation that we use to plot the graph?

Answer 9

C = Co/4pi(s+d)^2

(s+d)^2 = Co/4pi x 1/C

s + d = sqrtCo/4pi x 1/sqrtC

sqrtCo/4\pi is a constant, e.g K

r = K x 1/sqrtC - d

Question 10

What goes on the axes, what’s the gradient and what’s the intercept with this experiment’s graph?

Answer 10

r = K x 1/sqrtC - x/k
y = mx + c

So

r = y-axis
K = gradient
1/sqrtC = x-axis
-x/K = intercept

Question 11

Is the emission of radioactivity able to be predicted? Why?

Answer 11

No - the emission of radioactivity occurs spontaneously and unpredictable
It’s impossible to predict

Question 12

What is radioactive decay unaffected by?

Answer 12

External conditions like chemical reactions, pressure and temperature