© boardworks ltd 2003 ks4 radioactivity. © boardworks ltd 2003 background radiation background...

© Boardworks Ltd 2003

KS4 Radioactivity


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


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.

a) Draw a pie chart of this data.

b) Which source of radiation is the largest?

c) Suggest three possible ways radiation could get into the air.

d) Try to identify areas of high radioactivity.

Source

Percentage of total

radiation

Rocks 55%

Air 25%

Cosmic 15%

Building materials 5%

?


Marie Curie

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?

Marie Curie was a famous scientist.


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?


Springfield Nuclear Power Plant Safety

Rules:Any employee who fails to adhere to the rules below will be suspended:

1. Do not handle radioactive sources directly use tongs or a robotic arm.

2. Never point a radioactive source at a fellow worker or yourself.

3. When not in use store radioactive sources in lead-lined containers.

4. Always wear radiation protection suits.

5. Radiation badges should be worn to record exposure to radiation.

Mr. BurnzTask:

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.


Range of radiation investigation

You will use three sources of radiation: alpha, beta and gamma radiation.

1. Measure the background radiation reading using a radiation detector.

2. 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.

3. Record your results.

Questions:

1. Name three possible sources of the background radiation you recorded.

2. Which type of radiation had the shortest range?

3. Which type of radiation would be most dangerous 10m away from you? Why?


Penetrating power investigation


2. For each source separately, using tongs, place a piece of paper in between the detector and the source and then record the reading.

3. Repeat step two with a sheet of aluminium and the again with with a sheet of lead. Record your results.

Questions:

1. Which type of radiation was the least penetrating?

2. Which type of radiation would be most dangerous outside your body? Why?

3. Which type of radiation would be most dangerous inside your body? Why?



Thin mica Thin aluminiumstops BETA

Thick leadreduces GAMMA

Skin or paper stops ALPHA

The penetration power of the three types of radiation.


Magnetic field investigation


2. For each source separately, using tongs, place a magnet in between the detector and the source and then record the reading.

3. Record your results.

Questions:

1. Which types of radiation were affected by the magnetic field?

2. Which type of radiation was not affected by the magnetic field?

3. Beta radiation is high energy electrons. TV’s use electrons. Why should you not put your Hi-Fi loudspeakers too close to your TV?



The effects of a field on radiation

Gamma radiation has no mass or

charge so it is not deflected.

Beta radiation has a –1 charge and a small mass so is strongly

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.


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


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


Beta radiation -

high energy electron

Description:

High energy electron

Electric Charge:

-1


1/1860th

Penetration power:

Stopped by few mm of aluminium

Ionisation effect:

Weakly ionising


Strongly deflected


Gamma radiation -

Electromagnetic radiation

Description:

High energy electromagnetic radiation

Electric Charge:

0


0

Penetration power:

Reduced by several cm’s of lead or several metres of concrete

Ionisation effect:

Very weakly ionising


NO deflection


Match the radiation

Alpha

Beta

GammaHelium nuclei

High energy electron

Electromagnetic radiation

Stopped by paper or skin

Reduced by lead

Stopped by aluminium


Ionising radiation

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.

What happens if radiation is incident upon a living cell?

Ionising radiation can be used to kill cancer cells.

Radiation can ionise cells which causes cellular damage.


Ionisation questions

1. What is ionisation?

2. How is a neutral atom positively ionised?

3. How is a neutral atom negatively ionised?

4. What two effects on living cells can ionisation have?

5. Which type of radiation is the most ionising?

6. 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.


Which type of radiation is…..

1. The most penetrating?

2. The least penetrating?

3. Least dangerous outside the body?

4. Most dangerous inside the body?

5. High energy electrons?

6. Has a negative charge?

7. Is weakly ionising?

8. Has zero charge and zero mass?

9. Only reduced in intensity by lead and concrete?

Gamma

Alpha

Alpha

Alpha

Beta

Beta

Beta

Gamma

Gamma


Uses of radiation


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 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 Sourceunsterilised sterilised


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.

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.


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.

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.

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.

The isotope must have a short half life so the material does not become a long term problem.

The isotope must have a short half life so the material does not become a long term problem.

GM tube


Hydraulicram

detector

Thickness Control Mill

Electronic instructions to adjust rollers.

Beta Source

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.


Detecting radiation

Gieger-Muller Tube

Spark counter

Photographic film

Cloud chamber

What are the different methods?


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.


mica window

Argon gas

Geiger-Muller Tube

counter

collision & ionisation

radiation

124125

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.

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.

The Argon contains a little

bromine to act as a quenching agent and prevent

continuous discharge.

Good at detecting alpha and beta, not as good at detecting gamma.

Argon gas


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.

High voltage supply

Which type of radiation will be detected the best?

Why?


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.

Solid carbon dioxide

Radioactive source Cooled alcohol vapour


Which type of radiation is the most penetrating?

A. Alpha

B. Beta

C. Gamma

D. X rays


Which type of radiation is the most damaging inside the body?

A. Alpha

B. Beta

C. Gamma

D. X rays


Which type of radiation is the most dangerous outside the body?

A. Alpha

B. Beta

C. Gamma

D. X rays


Which of the following is not a use of radiation?

A. Pre-natal scans

B. Radiotherapy

C. Smoke detectors

D. Detecting leaks

© boardworks ltd 2003 ks4 radioactivity. © boardworks ltd 2003 background radiation background...

Documents

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