Y12 Homework on Radioactivity

The formatting for the tables is slightly askew but you can work it out.

Nuclear Physics

1. Radon has a proton number of 86 and a nucleon number of 220. It emits an α-particle to become Thorium A (polonium), which emits another α particle to become Thorium B (radioactive lead). Thorium B then emits a β-particle to become Thorium C (bismuth). What is (a) the proton number and (b) the nucleon number of Thorium C?

2. When a Boron nucleus 105B is bombarded with a neutron a nucleus of Lithium 73Li, is produced, together with another particle. What are the proton number, the nucleon number and the name of this particle?

3. A ’snap-shot’ photograph of a cloud chamber shows 40 well-defined alpha particle tracks. A second ’snap-shot’ taken 2 min later shows only 10 tracks. What is the half-life of the alpha source?

4. A lead container has a narrow slit and sources inside emit α, β and γ rays. A powerful magnetic field is applied. Draw a labelled sketch to show what happens – the rays emerge vertically upwards in the plane of the paper and the field is applied so that the flux passes at right angles into the plane of the paper.

5. A Geiger-Muller tube connected to a rate meter is held near a radio-active source. The corrected count rate (allowing for background count) is 400 Bq. 40 min later the corrected count rate is 25 Bq. What is the half-life of the source?

6. A rate meter records a background count rate of 2 Bq. When a radioactive source is held near the count rate is 162 Bq. If the half-life of the source is 5 min, what will the recorded count rate be 20 min later?

7. A patient suffering from cancer of the thyroid gland is given a dose of radioactive iodine 131, with a half-life of 8 days, to combat the disease. He is temporarily radioactive and his nurses must be changed regularly to protect them. If his radioactivity is initially 4 times the acceptable level, how long is it before the special nursing rota can be dropped?

8. An experiment to determine the half-life of a radioactive gas using a Geiger-Muller tube and a rate meter gave the following results:

Background count rate; 1 Bq
Time/s
0
20
40
60
80
100
120
140
160
Recorded count rate/Bq
71
55
43
34
26
20
16
12
10
Plot a graph and estimate the half-life of the gas.

9. Thoron gas was introduced into a ’decay chamber’ attached to a pulse electroscope. The times at which successive pulses occurred were recorded, giving the following results:
Pulse number
1
2
3
4
5
6
7
8
9
10
Time/s
8
17
28
40
55
75
100
135
200
500
Draw a ’pulse number-time’ graph and estimate the half-life of Thoron.

10. An ionisation chamber was connected to a pulse electroscope and an alpha source held near it. Beyond a certain distance no pulses were produced. For smaller distances the pulse rate varied as follows:
Distance from source /cm
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Number of pulses per min
100
90
68
44
26
14
8
4
1

Plot a graph and estimate the range of the alpha particles.