1. Radioactivity

2. Background radiation
Background radiation is the radiation all around us. Working in pairs try to think of five possible sources of background radiation.
You have FIVE minutes!!
Rocks
Air
Building materials
Outer space
Food

3. Percentage of total radiation
Background radiation is higher in some places than in others, it depends where you are on the Earth’s surface.
Task: The sources of radiation for a location are shown.
Draw a pie chart of this data.
Which source of radiation is the largest?
Suggest three possible ways radiation could get into the air.
Try to identify areas of high radioactivity.
Source
Percentage of total radiation
Rocks
55%
Air
25%
Cosmic
15%
Building materials 5%  ?

4. Marie Curie Marie Curie was a famous scientist.
Try to find out about her life.
When and where did she live?
What work she did do?
What problems did she had to overcome?
What famous prizes she was awarded?

5. Safety first
There are several types of radiation. They differ in what effects they have and their nature.
All radioactive sources must be handled safely.
Do you know what the hazard symbol for radiation is?
As well as the normal laboratory safety instructions you follow are there any extra rules concerning radioactivity?

6. Springfield Nuclear Power Plant Safety Rules:
Any employee who fails to adhere to the rules below will be suspended:
Do not handle radioactive sources directly use tongs or a robotic arm.
Never point a radioactive source at a fellow worker or yourself.
When not in use store radioactive sources in lead-lined containers.
Always wear radiation protection suits.
Radiation badges should be worn to record exposure to radiation.
Mr. Burnz
Task:
Working in pairs write down the three safety rules from above that would be most relevant in your school saying why you chose them. Also say which safety rule you think is the most important and why.

7. Range of radiation investigation
You will use three sources of radiation: alpha, beta and gamma radiation.
Measure the background radiation reading using a radiation detector.
For each source separately, using tongs, move the source slowly away from the radiation detector until the reading on the detector is the same as that for background radiation. This is the range of the radiation.
Record your results.
Questions:
Name three possible sources of the background radiation you recorded.
Which type of radiation had the shortest range?
Which type of radiation would be most dangerous 10m away from you? Why?

8. Penetrating power investigation
You will use three sources of radiation: alpha, beta and gamma radiation.
Measure the background radiation reading using a radiation detector.
For each source separately, using tongs, place a piece of paper in between the detector and the source and then record the reading.
Repeat step two with a sheet of aluminium and the again with with a sheet of lead. Record your results.
Questions:
Which type of radiation was the least penetrating?
Which type of radiation would be most dangerous outside your body? Why?
Which type of radiation would be most dangerous inside your body? Why?

9. The penetration power of the three types of radiation.  
Skin or paper
stops ALPHA
Thin aluminium
stops BETA
Thick lead
reduces GAMMA
Thin mica

10. Magnetic field investigation
You will use three sources of radiation: alpha, beta and gamma radiation.
Measure the background radiation reading using a radiation detector.
For each source separately, using tongs, place a magnet in between the detector and the source and then record the reading.
Record your results.
Questions:
Which types of radiation were affected by the magnetic field?
Which type of radiation was not affected by the magnetic field?
Beta radiation is high energy electrons. TV’s use electrons. Why should you not put your Hi-Fi loudspeakers too close to your TV?

11. The effects of a field on radiation
Beta radiation has a –1 charge and a small mass so is strongly deflected
Gamma radiation has no mass or charge so it is not deflected.
Alpha radiation has a +2 charge but a RAM of 4 so is only weakly deflected.
The effect of a magnetic or electric field on radiation depends upon the nature of the radiation.

12. Using your results from the previous three investigations, fill in the table below:
Alpha
Beta
Gamma
Penetrating power
Range of radiation
Most dangerous outside of body
Most dangerous inside of body
Affected by a magnetic field
least
medium
most
shortest
medium
longest
least
medium
most
most
medium
least
yes
yes no

13. Alpha radiation -  Helium nuclei Description:
2 neutrons, 2 protons (helium nuclei)
Electric Charge: +2
Relative Atomic Mass: 4
Penetration power:
Stopped by paper or a few cm of air
Ionisation effect:
Strongly ionising
Effects of Magnetic/Electric Field:
Weakly deflected
Helium nuclei

14. Beta radiation -  high energy electron Description:
Electric Charge: -1
Relative Atomic Mass:
1/1860th
Penetration power:
Stopped by few mm of aluminium
Ionisation effect:
Weakly ionising
Effects of Magnetic/Electric Field:
Strongly deflected
high energy electron

15. Gamma radiation -  Electromagnetic radiation Description:
High energy electromagnetic radiation
Electric Charge:
Relative Atomic Mass:
Penetration power:
Reduced by several cm’s of lead or several metres of concrete
Ionisation effect:
Very weakly ionising
Effects of Magnetic/Electric Field:
NO deflection
Electromagnetic radiation

16. Match the radiation Electromagnetic radiation Stopped by paper or skin
Alpha
High energy electron
Reduced by lead
Beta
Helium nuclei
Gamma
Stopped by aluminium

17. Ionising radiation
What happens if radiation is incident upon a living cell?
Radiation can ionise cells which causes cellular damage.
If the exposure is high, it can kill the cell.
If the exposure is lower it can cause cancer.
The higher the exposure, the higher the risk of cancer.
Alpha is the most ionising radiation, gamma is the least.
Ionising radiation can be used to kill cancer cells.

18. Ionisation questions What is ionisation?
How is a neutral atom positively ionised?
How is a neutral atom negatively ionised?
What two effects on living cells can ionisation have?
Which type of radiation is the most ionising?
Which type of radiation is the least ionising?
When a neutral atom loses or gains electrons and hence charge.
By losing electrons.
By gaining electrons.
Kill cells or cause cancer.
Alpha radiation.
Gamma radiation.

19. Which type of radiation is…..
The most penetrating?
The least penetrating?
Least dangerous outside the body?
Most dangerous inside the body?
High energy electrons?
Has a negative charge?
Is weakly ionising?
Has zero charge and zero mass?
Only reduced in intensity by lead and concrete?
Gamma
Alpha
Alpha
Alpha
Beta
Beta
Beta
Gamma
Gamma

20. Uses of radiation

21. Sterilisation
Gamma rays are used to kill bacteria, mould and insects in food. This can be done even after the food has been packaged. It can affect the taste, but supermarkets like it because it lengthens the shelf life.
Gamma rays are also used to kill bacteria on hospital equipment. It is particularly useful with plastic equipment that would be damaged by heat sterilisation.
Gamma Source
unsterilised
sterilised

22. Radiotherapy
A carefully controlled beam of gamma rays can be used to kill cancer cells. It must be directed carefully to minimise the damage to normal cells.
However, some damage is unavoidable and this can make the patient ill.
It is therefore a balancing act - getting the dose high enough to kill the cancerous cells, but as low as possible to minimise the harm to the patient.

23. Leak detection in pipes
The radioactive isotope is injected into the pipe. Then the outside of the pipe is checked with a Geiger-Muller detector, to find areas of high radioactivity. These are the points where the pipe is leaking. This is useful for underground pipes that are hard to get near.
GM tube
The isotope must have a short half life so the material does not become a long term problem.
The radioactive isotope must be a gamma emitter so that it can be detected through the metal and the earth where the pipe leaks. Alpha and beta rays would be blocked by the metal and the earth.

24. Thickness Control Mill
A radioactive source is on one side of the material and a detector on the other.
If too much radioactivity is getting through, then the material is too thin and the rollers open up a bit to make the material thicker.
If not enough radioactivity is detected then the rollers compress to make the material thinner.
This method is used in the manufacture of lots of sheet materials: plastics, paper, sheet steel.
Beta Source
detector
Hydraulic
ram
Electronic instructions to adjust rollers.
This is because the amount of Beta particles received at the detector varies according to the thickness the medium.

25. Detecting radiation What are the different methods? Gieger-Muller Tube
Spark counter
Photographic film
Cloud chamber

26. Photographic film
1. What happens to film when radiation is incident upon it?
It darkens.
2. Can photographic film tell you the type of radiation incident upon it?
No, just the amount of radiation received.
3. What can this be used for?
Can be used in radiation badges, that record the exposure of workers to radiation. Different windows detect different types of radiation.

27. Geiger-Muller Tube counter 124 125
The detector is a metal tube filled with gas. The tube has a thin wire down the middle and a voltage between the wire and the casing.
Good at detecting alpha and beta, not as good at detecting gamma.
collision & ionisation
The Argon contains a little bromine to act as a quenching agent and prevent continuous discharge.
radiation
Argon gas
Argon gas
mica window
When the radioactivity enters the tube, it ionises the gas in the tube. This produces a pulse of current which is amplified and passed to a counter.
counter
124
125

28. The Spark Detector
The spark detector consists of a metal grid and a metal strip. A high voltage is applied between the grid and the strip. The voltage is increased until electrical arcing (sparking) across the gap just occurs.
When ionising radiation is placed close to the detector there is a marked increasing in the amount of sparking.
Which type of radiation will be detected the best?
Why?
High voltage
supply

29. Cloud chamber
Cloud chambers show the actual paths of the ionising particles. They rely on ionisation. The cloud chamber is cooled and then is super-saturated with alcohol. If an ion is formed a droplet of condensation appears. Best for alpha radiation as alpha most ionising; then Beta which shows faint traces, but cloud chambers are not as good for gamma as gamma is only weakly ionising.
Cooled alcohol vapour
Radioactive source
Solid carbon dioxide

30. Which type of radiation is the most penetrating?
Alpha
Beta
Gamma
X rays 

31. Which type of radiation is the most damaging inside the body?
Alpha
Beta
Gamma
X rays

32. Which type of radiation is the most dangerous outside the body?
Alpha
Beta
Gamma
X rays 

33. Which of the following is not a use of radiation?
Pre-natal scans
Radiotherapy
Smoke detectors
Detecting leaks