Radiation: Shields up

Physics
Radiation: Shields up
Unless astronauts can be protected from exposure to dangerous levels of
radiation it might mean there will only ever be one way tickets to Mars.
In this lesson you will investigate the following:
• What is radiation?
• When is radiation dangerous?
• If radiation causes cancer how can it be used to treat cancer?
​Let’s see if a new protective shield will deflect the cosmic attacks.
This is a print version of an interactive online lesson.
To sign up for the real thing or for curriculum details
about the lesson go to www.cosmosforschools.com
Introduction: Radiation
In space it’s the stuff you can’t see that can kill you!
A vacuum that would make your eyes pop out and a temperature cold enough to freeze air are obvious dangers, but just as deadly
is the invisible stream of cosmic radiation that could kill you even if you never went outside your spacecraft.
High-energy charged particles are beamed out when stars explode, hurtling across the cosmos and tearing through anything in
their path, including the bodies of astronauts.
Then there are the less energetic particles that stream from the Sun – still powerful enough to present a serious cancer risk.
Scientists are thinking about how we can protect astronauts from these rays as they travel to Mars, a trip that will take more than
two years.
They've come up with the Space Radiation Superconductive Shield (SR2S) – a giant magnetic shield designed to wrap around
spacecraft and deflect cosmic rays much like the Earth's magnetic field protects the planet.
It’s a great idea, but there’s one problem. Such a shield would use so much energy that there wouldn’t be enough left to power
other vital operations on the spacecraft, like temperature control and air circulation.
So the scientists are experimenting with superconductors that allow electrical current – electrons – to flow freely. So freely that they
don’t use any energy at all. The shields can be charged by the Sun and stay charged for years.
Oh, and superconductors only work at very low temperatures. But that’s no problem in space, where the temperature is -263° C.
So, shields up, ready for Mars!
Read or listen to the full Cosmos magazine article here.
Geiger counters are used to check for radiation leaks from drums of radioactive material.
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Question 1
Identify: What does radiation make you think of? Use the mind map below to show everything you know about radiation or that
you've heard about it.
Sub Idea...
Sub Idea...
Radiation
Sub Idea...
Sub Idea...
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Gather: Radiation
What is radiation?
Radiation at work – from left, an infrared thermal imaging device showing heat loss from a building; a microwave oven; a
radio telescope in New Mexico, USA; and a 3D X-ray of a hand.
0:00
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Question 1
Define: What is radiation?
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Question 2
Complete: Use information from the video to fill in the table below, explaining the helpful roles of some types of wave radiation.
Also, indicate whether each type of radiation is ionizing or non-ionizing.
Type of electromagnetic
radiation
Is useful for...
Ionizing or non-ionizing
Visible light
Infrared radiation
Microwaves
Radio waves
Ultraviolet radiation
Not applicable
X-rays
Gamma rays
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Not applicable
Question 3
Select: Ionizing radiation:
can be particles or waves.
transfers energy to atoms that it strikes.
removes electrons from atoms that it strikes.
All of the above.
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Question 4
Recall: Beta particles are:
less ionizing than both alpha particles and
gamma rays.
more ionizing than both alpha particles and
gamma rays.
more ionizing than alpha particles and less
ionizing than gamma rays.
Waves
Radiation can consist of waves or particles. Stars, including our Sun, emit both.
Wave radiation, commonly known as electromagnetic (EM) radiation, includes visible light and radiation from numerous artificial
sources such as electric power cables, cooking devices, televisions, radios and mobile phones.
Different types of EM radiation carry different amounts of energy. Those with high energy, such as X-rays and gamma rays,
are ionizing and so are dangerous to humans. The key things to remember are that EM waves:
have no mass,
have no electric charge,
travel at the speed of light in a vacuum, and
may be either ionizing or non-ionizing depending on their energy.
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Question 5
Interpret: Use the diagram above to help fill in the missing words in the sentences below. Type them into the right hand column.
X-rays have shorter wavelengths and ____________ energy than UV radiation.
Radio waves have ____________ wavelengths and ____________ energy than gamma rays.
Microwaves have ____________ wavelengths and ____________ energy than visible light.
EM waves with shorter wavelengths have ____________ energy than EM waves with longer
wavelengths.
Particles
Particle radiation consists of various high-speed subatomic particles. They can be individual particles or, as in the case of alpha
radiation, small groups of particles stuck together. They all have mass, although this can be very small. For example the electrons
that make up beta radiation have very little mass.
Particle radiation includes cosmic rays from outer space – mostly high-energy protons. On Earth we are most familiar with positively
charged alpha particles and negatively charged beta particles. Both come from naturally occurring minerals – for example alpha
particles are emitted by uranium and beta particles by strontium.
The key things to remember are that radiation particles:
have mass,
can have positive or negative electric charges, or can be electrically neutral,
travel at high speeds less than the speed of light, and
are ionizing.
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Question 6
Match: Using information you have learnt from the lesson so far:
label boxes describing or showing alpha particles with an "a", and
label boxes describing or showing beta particles with a "b".
Ionizing radiation
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Question 7
Identify: The graphic above shows a radiation source producing three different types of ionizing radiation: alpha particles, beta
particles and gamma waves. The radiation beams are directed through electrically charged plates before being detected.
Identify each type of ionizing radiation and explain your choice.
Radiation
beam
A
B
C
Type of ionizing Explanation
radiation
Process: Radiation
Radiation in space
0:00
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Question 1
Remember: Galactic cosmic rays cause tremendous damage to
human cells. Which of the following are reasons for this?
Galactic cosmic rays have high velocity
Galactic cosmic rays have no mass
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Question 2
Recollect: Which of the following bodily organs or systems can
be affected by ionizing radiation?
Nervous system
Genitals
Eyes
Galactic cosmic rays have negative electric charge
Glands
Galactic cosmic rays have positive electric charge
Gastrointestinal system
Galactic cosmic rays have high mass
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Question 3
Calculate: In a round trip to Mars, how much more radiation
would astronauts be exposed to compared to an average CT
scan?
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Question 4
Recall: The Earth is protected from most radiation coming from
the Sun and other stars just by the ozone layer in its
atmosphere. about 70 times more
True
about 700 times more
False
about 7 times more
Question 5
Consider: Why do you think galactic cosmic rays can cause so many different types of illness in humans?
Good radiation, bad radiation
When high-energy radiation ionizes atoms it often also destroys the molecules those atoms make up, like DNA. The body can repair
low levels of this damage but at higher levels there are two possible outcomes:
1. Short-term high-level exposure can cause irreparable cell damage – enough to kill cells within 24 hours. Called radiation
poisoning, this sort of damage often causes death.
2. Long-term lower-level exposure can destabilize DNA molecules without killing cells, but the cells become cancerous,
replicating out of control. Radiation causes cancer in most parts of the body but whole-body exposure is most often linked
with leukaemia – cancer of the bone marrow.
In spite of these effects, high doses of X-rays, gamma rays or particle radiation are used by doctors to cure cancer. They direct the
radiation at cancerous cells to kill them. This is called radiation therapy, or radiotherapy. More than 50 per cent of people with
cancer undergo radiotherapy as part of their treatment. Ionizing radiation, good and bad. Radioactive spills at nuclear power plants are very dangerous and must be contained
as soon as possible. However ionizing radiation is also used to treat cancer, as in the photo at right.
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Question 6
Calculate: When radiotherapy is prescribed it is very important that the radiation is accurately targeted to the correct area and that
an appropriate dose is delivered. This is called the absorbed dose (D), calculated as follows:
E
D =
m
where:
E is the energy of the radiation, expressed in joules (J), and
m is the mass of body tissue irradiated, in kilograms (kg). D, therefore, is measured in joules per kilogram (J/kg).
Calculate:
i) the absorbed dose received by a 150 g tumour irradiated with 12 J of gamma-ray energy. ii) the absorbed dose received by an 8 g tumour irradiated with 0.25 J of gamma-ray energy.
Hint: don't forget the units!
Did you know?
The typical gamma-ray radiation dose required to treat a solid skin tumour ranges from 60 to 80 J/kg, whereas lymphomas –
tumours formed from cancerous white blood cells blocked in the lymph nodes – are treated with 20 to 40 J/kg. This big difference
is related to the ratio of mature to immature cells in the different types of tissue, how often the cells replicate, and how long
replication takes.
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Question 7
Speculate: Before patients start radiotherapy a team of specialists discuss the best way to treat their cancer. Imagine you are
accompanying a friend to a medical appointment where they will be told about their upcoming treatment. What do you think would
be some good questions to ask?
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Question 8
Consider: Your friend will be told about the side effects of radiotherapy that they may experience. For example, apart from
the nausea, skin pain and diarrhoea mentioned in the video there can also be hair loss, mouth ulcers, sexual dysfunction, appetite
loss and general fatigue. There is even the possibility that the radiotherapy could cause new cancers to form. Why do people accept these side effects as part of their treatment? Are there situations where you think the benefits of
radiotherapy might not outweigh the side effects? Explain your answer.
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Apply: Radiation
Experiment: How to identify mystery radiation
Background
The three common types of ionizing radiation – alpha, beta and gamma rays – vary widely in their ability to penetrate materials and
damage living tissue. In this part of the lesson you will remotely control a real life radiation laboratory at La Trobe University,
Melbourne, Australia, to investigate how effectively different types of material block different types of radiation.
Ionizing radiation is invisible so a specialized detection instrument is used. A Geiger counter measures the number of ionizing
events – or counts – per second.
The insights gained from this type of experiment can be used in many ways, from developing safe medical treatments to finding
new ways of storing radioactive waste – and protecting astronauts on future missions to Mars!
Aims
To compare the effectiveness of different types of material in blocking alpha, beta and gamma radiation.
To identify a mystery source of radiation.
To compare the effects of different types of radiation on living tissue.
Procedure
1. Open the FarLabs website at the nuclear turntable experiment, here.
2. Your teacher will inform you which experimental station to use. Click the button for your turntable.
3. Type in the session password given to you by your teacher to activate the turntable.
4. The buttons listed under Source allow you to control the left hand turntable to position different radiation sources under the
Geiger counter. The buttons listed under Absorber allow you to control the right hand turntable to bring sheets of various
materials between the radiation source and the Geiger counter, or to let the radiation pass without obstruction. First, select
Alpha and None. You may see the turntables rotating into position via the live webcam.
5. Monitor the Geiger counter measurement as recorded on the graph for about 15 seconds and estimate the average number
of counts per second as shown on the vertical axis. Record this number in the table below.
6. Now select Plastic as the Absorber and watch as the right hand turntable shifts position, bringing the sheet of plastic between
the radiation source and the Geiger counter. You should notice a sudden decrease in the amount of radiation being detected.
Wait at least 15 seconds for the vertical scale of the graph to adjust to the new level of radiation. Then estimate the new count
rate and enter it into the table below.
7. Use the control buttons to record the data needed to fill in the remaining blank cells in the table. For the moment ignore
the columns marked %P, which relate to Question 2.
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Question 1
Record: Enter your data into the following table.
Absorber ► None
Source
counts/s
Plastic
counts/s
Thin Al
%P
Alpha
Beta
–
72
Gamma
–
94
Thick Al
Lead
counts/s
%P
counts/s
%P
counts/s
%P
–
2
–
1
–
0.3
–
20
–
0.5
–
80
–
90
Unknown
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Question 2
Calculate: A useful measure of the effectiveness of a radiation barrier is percentage penetration (%P). This tells you how much of the
radiation manages to get through the material. For example, a %P value of 70 means that 70% of the radiation passes through the
barrier and 30% is absorbed. To calculate percentage penetration for the data you have just collected, use the following equation:
count rate with absorber (counts/s)
%P
=
count rate with no absorber (counts/s)
×
100
Use a calculator to complete the %P columns in the table above. Note that several values have been provided for you, based on
past experimental data. You can type any notes into the text space below.
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Question 3
Identify: The graph in the sketchpad below illustrates some generic percentage penetration values for the various combinations of
source and absorber that you have investigated. Based on the relative shapes of the graphs, use your own data to identify the three
types of ionizing radiation and type your answers into the sketchpad.
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Question 4
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Question 5
Deduce: Use the data you have gathered and the graph above
Think: Why do you think that gamma radiation is so much more
to figure out the most likely candidate for the unknown
radiation source.
penetrative than the two other types of radiation?
Beta particles
Gamma rays
Alpha particles
Extension questions
Equivalent dose
Earlier in this lesson you learned that the absorbed dose is a measure of how much radiation energy is absorbed by a certain
amount of living tissue, measured in joules per kilogram (J/kg). During radiotherapy treatments the absorbed dose needs to be
carefully monitored so that just enough radiation is applied to kill the cancerous cells without causing too much damage to the
healthy cells.
A better measure of the damaging effect of radiation is the equivalent dose because different types of radiation have different
biological effects for the same absorbed dose. In other words, the same amounts of energy from different types of radiation have
different effects. The equivalent dose (in the special unit of sieverts or Sv) can be calculated using the following simple formula:
equivalent dose (Sv) = absorbed dose (J/kg) x radiation weighting factor
The radiation weighting factor is 1 for both beta particles and gamma rays and 20 for alpha particles, which means that absorbed
alpha radiation is twenty times more dangerous to living tissue.
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Question 6
Reflect: Why do you think that alpha particles are significantly more damaging than the other two types of radiation?
Did you know?
An equivalent dose of 4 Sv is usually lethal. The maximum allowed radiation exposure for NASA astronauts over their career is
about 1 Sv, while flight attendants can receive radiation exposure of approximately 1.5 x 10-3 Sv per year. The miniscule amount of
1 x 10-8 Sv is the approximate equivalent dose produced by the naturally occurring potassium in a typical banana.
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Question 7
Calculate: In 2006 the ex-Russian spy Alexander Litvinenko
suddenly fell ill and died in hospital three weeks later. It was
later discovered that he had been poisoned by ingesting a lethal
dose of the radioactive element polonium, which emits alpha
particles as it decays. As you found in the turntable experiment,
alpha radiation is easily blocked by barriers such as the skin and
this made it easy for Litvinenko's killers to handle safely. On the
other hand, it causes far more damage once it enters the body
and is absorbed by living tissue.
Using the equation above, calculate the absorbed dose of alpha
radiation (in J/kg) that would be required to produce an
equivalent dose of 4 Sv.
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Career: Radiation
Growing up, Dr Peter Karamoskos’ dad used to buy him books about the “hows” and “whys” of science – in fact, from a series
called the How and Why Wonder Books. Now, as the public representative for the Australian Radiation Health Committee (RHC), Peter
explores how and why the ionizing radiation used in medical imaging affects people’s health.
The RHC advises the Australian Radiation Protection and
Nuclear Safety Agency on radiation health matters and makes
sure that legislation across the country adheres to a standard
safety framework. Peter’s job is to look at radiation research
others have done and communicate the findings to politicians
and legislators.
Before his job at the RHC Peter worked as a radiologist and
nuclear medicine physician for over 20 years, using imaging
technologies like X-rays and MRIs to diagnose and treat
diseases. Peter chose radiology at the start of his career
because it gave him the opportunity to use high-tech equipment
(“Which any science student knows is very cool,” he says) and,
ultimately, to help people (“Which is even cooler!”).
The radiation in medical imaging is the biggest source of nonnatural ionizing radiation that most people are exposed to.
Peter knows that it can do a lot of good, but if it’s not respected
and dealt with properly it can do a lot of harm too. It’s a big
responsibility, but that’s part of what inspires Peter – he loves
that he is making a difference in people’s lives.
Peter believes that you should surround yourself with smart
people and those you admire because it helps make you a
better person. As a keen cyclist he rides a couple of hundred
kilometres a week with his friends through the hills around
Melbourne. His friends are even fitter than he is and they make
sure he doesn’t slack off!

Question 1
Consider: ​
Peter thinks that using high-tech equipment to help people is "very cool", but while technology can do a lot of good it
also has the potential to cause harm. Think of some examples of useful technologies and consider whether there are any risks
associated with them. If so, how can you protect yourself?
Cosmos Lessons team
Lesson authors: Samantha Webber and Hayley Bridgwood
Introduction author: Bill Condie
Profile author: Megan​
Toomey
Editors: Jim Rountree, Campbell Edgar
Art director: Wendy Johns
​
Education director: Daniel Pikler
Image credits: iStock, Shutterstock, Reuter
Video credits: SciShow, superpowersunit, TomoNews US,
kuresurem, YouTube
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