© Boardworks Ltd 2004 1 of 20 © Boardworks Ltd 2005 1 of 35 KS4 Physics Radioactivity

© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20051 of 35

KS4 Physics

Radioactivity


Radioactivity

Contents

Background radiation

Safety rules

Uses of radiation

Summary activities

Types of 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

(cosmic)

Food


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) Find out about areas of high radioactivity.

Source

Percentage of total

radiation

Rocks 55%

Air 25%

Cosmic 15%

Building materials

5%


The sources of radiation for a particular location are shown:


Marie Curie

Try to find out about her life:

When and where did she live?

What work did she do?

What problems did she have to

overcome?

Which famous prizes was she

awarded?

Marie Curie was a famous scientist.


Radioactivity

Contents


Safety rules

Uses of radiation

Summary activities

Types of radiation


Safety first

There are several types of radiation. They differ in their effects and physical 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?


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. Store radioactive sources in lead-lined containers when not in use.

4. Always wear radiation protection suits.

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

Task: Working in pairs choose three of the safety rules that would be most relevant in your school and explain why you chose them. Also say which safety rule you think is the most important and why.

Safety rules


Radioactivity

Contents


Safety rules

Uses of radiation

Summary activities

Types of radiation


Use three sources of radiation: alpha, beta and gamma.

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. 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?

Range of radiation 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. Repeat this with a sheet of aluminium and again with a sheet of lead. Record your results.

Penetrating power investigation

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?



Thin mica Thinaluminiumstops beta

Thick leadreduces gamma

Skin orpaper stops

alpha

Penetrating power of the three types of radiation


alpha

beta

gammahelium nuclei

High-energy electron

electromagnetic radiation

stopped by paper or skin

reduced by lead

stopped by aluminium

Match the radiation



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

Magnetic field investigation

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. TVs use electrons. Why should you not put your hi-fi loudspeakers too close to your TV?



Gamma radiation has no mass or

charge so it is not deflected.

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

Alpha radiation has a +2 charge but a RAM of 4 so it

is only weakly deflected.

The effect of a magnetic or electric field on radiation depends upon the type of radiation.

The effects of field on radiation

+

–


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

Results table


Alpha (α) radiation

Description: 2 neutrons, 2 protons

Electric charge: +2

Relative atomic mass: 4

Penetration power: Stopped by paper or a few cm of air

Ionization effect: Strongly ionizing

Effects of magnetic/electric field: Weakly deflected

helium nuclei


Description: High-energy electron

Electric charge: -1

Relative atomic mass: 1/1860

Penetration power: Stopped by a few mm of aluminium

Ionization effect: Weakly ionizing

Effects of magnetic/electric field: Strongly deflected

Beta (β) radiation

high-energy electron


Gamma () radiation

electromagnetic radiation

Description: High-energy electromagnetic radiation

Electric charge: 0

Relative atomic mass: 0

Penetration power: Reduced by several cms of lead or several metres of concrete

Ionization effect: Very weakly ionizing

Effects of magnetic/electric field: Not deflected


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 ionizing radiation; gamma the least ionizing.

What happens to living cells when exposed to radiation?

Ionizing radiation can be used to kill cancer cells.

Radiation can ionize cells, which causes cellular damage.

Ionizing radiation


Radioactivity

Contents


Safety rules

Uses of radiation

Summary activities

Types of radiation


Uses of radiation


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.

Sterilization

gamma sourceunsterilized sterilized

Gamma rays are also used to kill bacteria on hospital equipment. It is particularly useful with plastic equipment that would be damaged by heat sterilization.


A carefully controlled beam of gamma rays can be used to kill cancer cells. It must be directed carefully to minimize the damage to normal cells.

Radiotherapy

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 minimize the harm to the patient.


A radioactive isotope is injected into the pipe. Then the outside of the pipe is checked with a Geiger-Müller 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

Leak detection in pipes

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.


hydraulicram

detector

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, such as plastics, paper and sheet steel.

Thickness control mill


Geiger-Müller tube

spark counter

photographic film

cloud chamber

What are the different methods of detecting radiation?

Detecting radiation


1. What happens to film when it is exposed to radiation?

It darkens.

2. Can photographic film tell you the type of radiation that it has been exposed to?

No, just the amount of radiation received.

3. What can this be used for?Can be used in radiation badges, which record the exposure of workers to radiation. Different windows on the badge detect different types of radiation.

Photographic film


mica window

counter

radiation

collision & ionization

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 ionizes the gas in the tube. This produces a pulse of current, which is amplified and passed to a counter.

It is good at detecting alpha and beta radiation, but not as good at detecting gamma radiation.

argon gas

Geiger-Müller tube


A 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.

Which type of radiation will be detected most easily?

Why?

Spark detector

high-voltage supply

When ionizing radiation is placed close to the detector there is a marked increase in the amount of sparking.


Cloud chambers show the actual paths of the ionizing particles. They rely on ionization. The cloud chamber is cooled and is then super-saturated with alcohol.

solid carbon dioxide

radioactivesource

cooledalcoholvapour

Cloud chamber

When an ion is formed a droplet of condensation appears. Cloud chambers are good for showing alpha radiation as this is the most ionizing. Beta radiation shows faint traces. Cloud chambers are not good for showing gamma radiation, as it is only weakly ionizing.


Radioactivity

Contents


Safety rules

Uses of radiation

Summary activities

Types of radiation


Glossary

alpha radiation – Positively charged particles made up of two protons and two neutrons. It is the least penetrating of the three main types of radiation.

background radiation – Constant low-level radiation from food and environmental sources.

beta radiation – High-energy electrons emitted by some radioactive materials. It is more penetrating than alpha radiation but less penetrating than gamma radiation.

cloud chamber – A device that shows the paths of ionizing particles. It is good at detecting alpha radiation.

gamma radiation – Short wavelength electromagnetic radiation emitted during radioactive decay. It is the most penetrating of the three main types of radiation.

Geiger-Müller tube – A device used to detect and measure radiation from radioactive materials.

ionizing radiation – High-energy radiation capable ofionizing substances through which it passes.


Anagrams


Multiple-choice quiz

Documents

© Boardworks Ltd 2004 1 of 20 © Boardworks Ltd 2005 1 of 35 KS4 Physics Radioactivity