AS Science In Society 1.7
Teacher Notes
Introduction
This activity should help students develop a clearer understanding of
the different sources of radiation to which they are exposed and an
appreciation of their relative magnitude. The values in most cases are
averages and there is a considerable range even within one medical
procedure or geographical region.
The activity
It is important to check that students understand the concept of
effective dose before starting. The textbook page 112 or the activity
‘Radioactivity units’ provide the necessary information.
Students should work through the sheet in pairs or alone. Remind them
that these are only estimates. They need not get too concerned about
exactly how many hours they spent flying or what the gamma dose is in
their area.
Suggested answers to questions
1. The average value for the UK is 2.7 mSv per year but individual
doses will depend mainly on where they live.
2. Average values have been used for exposures. The maps include
very wide areas and there is a range of values within each area.
Medical procedures vary depending amongst other things on the
age of the equipment and the type of information needed. The dose
from nuclear installations will vary from time to time and particularly
if there is a leak, however small. Contamination via diet will have a
major effect.
3. Artificial sources are assumed to contribute to about 15% of the total
average dose. This will depend on location and personal
circumstances.
4. The largest artificial source for most people is from medical
procedures.
5. Radon is the largest natural source, around 50% of the total
average dose.
6. The slight increase in the average dose is due to the increased use
of medical procedures involving radiation, particularly CT scans.
7. The effective dose measures the potential for damage to our cells
and takes into account the greater ionising power of α particles as
well as the different susceptibility of different organs.
Page 1
Science Explanations
Db Radioactive atoms decay,
emitting radiation. The decays occur
randomly but with a definite
probability. As they proceed, the
number of radioactive atoms left in
a sample falls, so the rate of
emission drops. The number of
emissions per second is called the
activity of the source (in becquerel).
Df When radiation is absorbed it
ceases to exist as radiation, instead
causing heating. Shorter
wavelength radiation, ultraviolet, Xrays and gamma rays, can bring
about chemical changes by
breaking up molecules into
fragments. The fragments are often
electrically charged particles which
we call ions. Radiation that
produces ions is called ionising
radiation.
Dg All three types of emission can
cause damage to the molecules in
living cells, either killing the cells or
causing mutations in the genes.
Alpha does most damage (per
centimetre of their path), followed
by beta, then gamma. The radiation
dose equivalent (in sievert) which a
person receives is a measure of the
amount of damage caused by the
radiation within their body.
Dh Effects of radioactivity can be
spread in two ways: by irradiation
(the emissions from a radioactive
substance striking and being
absorbed by another object); and by
contamination (the transfer of
pieces of the radioactive substance
itself on to, or into, another object).
How science works
Ge Several factors can influence a
person’s willingness to accept a
specific risk. Most people are more
willing to accept a process or
situation that has some risk if they
get direct benefit from it and if they
choose it voluntarily rather than
having it imposed.
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.7
Teacher Notes
8. Gamma rays produce a lower effective dose, they do less damage. Contamination by radioactive
gases in the lungs allows α particles to penetrate directly into the lung cells. The main source is
Polonium, a decay product of radon.
9. Suggestions include;
A worker in the nuclear industry who lives near Sellafield and spends her spare time fishing.
An international footballer with a home in Cornwall, frequent flights and regular CT scans to assess
fitness.
Risk
1. The UK average gives a risk of 2.7 mSv gives an increased annual risk of cancer of 1 in 7 400.
2. This makes it lower than smoking, but higher than road accidents or accidents in the home.
3. Workers in the nuclear industry accept the risk voluntarily. They are generally well paid whereas the
public receives no benefit from exposure to risk.
4. Medical procedures with exposures above 1 mSv include Spine X-ray, barium meal, CT scans,
nuclear medicine and radiotherapy. The additional slight risk associated with most of these
procedures is less than the risk to health of not diagnosing or treating a potentially serious health
problem. The additional lifetime risk of extra exposure in any one year is negligible.
Acknowledgements
This activity is developed and updated from ideas in a similar SATIS 14 - 16 activity.
Page 2
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.7
Student sheets
Introduction
Everyone is exposed to ionising radiation. This radiation comes from both natural and artificial sources.
The average annual dose for a member of the public in the UK is about 2.7 mSv. Your own dose
depends on where you live and on what you do. You can make an estimate of your own annual dose
using the information in this activity.
(Remind yourself of how radiation doses are measured, from your text book p 112)
The dose you receive is made up of radiation from natural sources - cosmic rays, ground and buildings
and food and drink and from artificial sources - nuclear power and medical treatments. You will find all
the information you need in Figures 1 - 6. Use the record sheet to total your dose from all sources. Then
answer the questions.
Natural Sources
Cosmic rays
Cosmic rays are high energy radiation from outer space. About 500 000 cosmic rays pass through the
average person every hour. The atmosphere protects us from the full effect, so the higher you live or the
higher you fly the greater the dose.
Average annual dose at sea level
0.30 mSv
Additional exposure for every 100m you live above
sea level
Air travel long haul per hour in air
0.010 mSv
Air travel short haul per hour in air
0.003 mSv
0.004 mSv
Figure 1 Cosmic radiation exposure
Radiation from the air
Radon is a radioactive gas. It is formed by the decay of uranium and thorium in rocks, soil and building
materials. Out of doors it blows away, but indoors it can build up to significant concentrations and is
breathed into the lungs where it decays, producing α particles which have a high effective dose. About
30 000 atoms disintegrate in our lungs each hour. Estimate your radiation dose from radon using Figure
2.
Page 1
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.7
Student sheets
Figure 2 Radon dose
Figure 3 Gamma ray dose
Gamma rays
Some radioactive elements are found in the soil and in rocks. They include isotopes of uranium, thorium
and potassium. These elements all emit gamma rays as they decay. Over 200 million gamma rays pass
through the average person each hour. Some rocks are more radioactive than others. Building materials
are extracted from the earth so they may also be radioactive. Make an estimate of your exposure to
gamma rays from Figure 3. The exposure given in Figure 3 assumes that you spend 10% of your time
out of doors.
Radiation from food and drink
We receive radiation from our food and drink, mainly from the radioactive isotope K-40. Your dose will
depend on your diet. About 15 million potassium-40 atoms disintegrate inside us each hour. An average
dose value is assumed to be 0.25 mSv per year although this will vary from 0.10 mSv up to as high as
1.0 mSv. Use the average value in your record sheet.
Artificial Sources
Radiation from medical treatments
X-rays, CT scans and other medical procedures all increase our exposure to radiation. Use the values in
Figure 4 to calculate your exposure in the last year.
Diagnostic test
Chest X-ray
Spine X-ray
Pelvis X-ray
Head X-ray
Barium meal
CT scan head
CT scan body
Dental X-ray
Nuclear medicine (radioactive substance
administered before scanning)
Radiotherapy
Figure 4
Page 2
Typical effective dose / mSv
0.02
1.00
0.70
0.20
7.20
2.00
9.00
0.005
1.50
40 000
source HPA
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.7
Student sheets
Radiation from Nuclear power
Waste from nuclear power stations may increase your radiation dose in
two ways: you will experience direct radiation and any locally produced
food you eat or air, soil or water you ingest will result in contamination.
The average dose from nuclear power in Britain is 0.002 mSv. However
for those living close to a nuclear power station or processing plant it
may be much higher. The map in Figure 5 shows where these are.
5
Use Figure 6 to estimate your additional dose if you live within 10km of
one of the following sites. If the site is not listed or there is no dose
given you can assume that the dose is insignificant. You may well
decide that some doses are too small to be significant and leave them
out. Remember we are only making an estimate. There is considerable
uncertainty in most of the data.
Site
direct
liquid waste
radiation/mSv contamination
from eating
fish and shell
fish/mSv
0.43
0.15
atmospheric
discharges
contamination
mainly via
food/mSv
0.07
Springfields
0.007
0.018
0.007
Chapelcross
Amersham
Bradwell
Heysham
Dungeness
Hinkley
Point
Hunterston
Sizewell
0.043
0.10
0.45
0.020
0.38
0.040
0.044
0.041
0.005
0.02
Sellafield
and Drigg
0.0590.008
0.007
0.014
0.072
0.008
0.010
0.010
0.005
0.028
0.014
Trawsfynydd 0.010
Wylfa
0.034
0.011
total
Figure 5
Notes
dose
depends
largely on
amount of
fish in diet
dose
depends
largely on
amount of
fish in diet
the newest
nuclear
power
station in
the UK
0.014
Figure 6 - Radiation dose in mSv close to nuclear installations.
source defra and hpa
Radiation from other artificial sources
The fallout from tests of nuclear weapons up to 1980 and from the Chernobyl disaster in 1986 has been
falling and is now only around 0.004 mSv per year so need not be included.
Page 3
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.7
Student sheets
The radiation we receive from products such as smoke detectors and watches is only about 0.0001mSv
a year and need not be included.
Questions
1. What is your total annual dose in millisieverts, mSv?
2. Why do we call this an estimate, not a certain value? Identify two major sources of error.
3. What percentage of your total dose comes from artificial sources?
4. What is the largest artificial source of radiation in your annual dose?
5. What is the largest natural source in your annual dose?
6. Estimates of the average annual dose in the UK have recently been increased from 2.6 mSv to
2.7 mSv. Suggest which source is the main contributor to this increase.
7. Explain why we are more interested in the effective dose we receive, measured in mSv, than in
the energy transferred to our body, measured in Gy.
8. The 200 000 000 gamma rays that pass through the average person per hour are less dangerous
than the 30 000 atoms that disintegrate in our lungs each hour. Why?
9. Write a short description of the job and the lifestyle of someone who would have a significantly
higher dose than yourself. You might imagine their work, where they live, what they eat, their
travel and what medical care they receive.
Radiation Risk
Radiation damage to cells is one of the risk factors for cancer. It is assumed that the risk is proportional
to the dose with no safe threshold. This assumption has yet to be confirmed but is widely used.
It is assumed that a dose of 1mSv per year increases the annual risk of cancer by 1 in 20 000.
Over a lifetime this would mean an increased risk of cancer of 65/20000 or 1 in 300 (assuming a life of
65 years).
1. Calculate your increased annual risk of cancer from your radiation dose.
2. Compare this risk with those from other causes as given in Figure 7 and insert your risk in the
correct order in the table
Outcome
Lung cancer caused by smoking 20
cigarettes a day
Annual risk
1 in 200
Death in road accident
1 in 17 000
Accident at home
1 in 25 000
Murder
Figure 7
Page 4
1 in 100 000
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.7
Student sheets
3. The statutory dose limit for the public in the UK is 1 mSv a year. This means that a member of the
public should not be exposed to more than 1 mSv from artificial sources. Workers in the nuclear
industry are allowed to be exposed to 20 mSv a year. Explain why there is such a difference in the
allowable risks.
4. Which medical exposures give a dose above the statutory limit? Explain why these are permitted
despite the increased risk.
August 2008
Page 5
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.7
Student sheets
Estimating your radiation dose
A
mSv/year
1
Dose from
cosmic
rays
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Page 6
B
mSv/year
Average does at
sea level
Air travel (Figure 1)
Total dose from cosmic rays in
a year
Dose from
Dose indoors from
ground and radon (Figure 2)
buildings
Dose from gamma
rays
(Figure 3)
Total dose from grounds and
buildings
Dose from
Average dose in
food and
Britain
drink
Total dose from all natural
sources
Dose from
medical
treatments
(Figure 4)
Chest X-ray
Dental X-ray
All other treatments
(CT scan, other Xray radiotherapy)
Total dose from medical
treatments in a year
Dose from
nuclear
installations
Average dose in
Britain
Additional dose if
living near to a
nuclear
installation
(Figure 6)
Total dose from nuclear
installations
Total dose from all artificial
sources
My total radiation
dose/mSv/year
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges