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Unit P3: Applications of physics
Topic 3 Production, uses and risks of ionising
radiation from radioactive sources
Student Notes
Unit P3: Applications of physics
Topic 3
Production, uses and risks of ionising
radiation from radioactive sources
We Are Learning To
3.2 Describe the properties of alpha, beta, gamma, positron and neutron
radiation
3.3 Recall the relative masses and relative electric charges of protons,
neutrons, electrons and positrons
3.4 Recall that in an atom the number of protons equals the number of
electrons
Mass number (nucleon number)
The mass number is the total number of protons and neutrons. the
particles found in the nucleus are sometimes called nucleons, so the
mass number is sometimes called the nucleon number.
Atomic number (proton number)
The atomic number tells you the number of protons in the nucleus. This
number is also called the proton number. Atoms always have the same
number of electrons as protons.
E.g.
mass number (nucleon number)
14
Atomic number (proton number)
6
C
All atoms are made up of electrons, protons and
neutrons
Particle
Proton
Relative charge +1
Neutron Electron
0 (neutral) -1
Relative mass
1
1
Position
Nucleus Nucleus
0.0005 (negligible)
Shell
Protons and neutrons are found
in the nucleus of an atom
Electrons move around the nucleus
of an atom in energy shells
10 neutrons (0 charge)
Mass number
Atomic number
19
9
9 protons (9+)
9 electrons (9-)
F
Relative masses and relative electric charges of
protons, neutrons, electrons and positrons
Particle
Relative Mass
Relative Charge
Proton
1
1
Neutron
1
0
Electron
0
-1
Positron
0
+1
Types of radiation
Alpha Particle
(α)
+
4
He
2
Beta Particle (β-) -10 β
Positron
(β+)
0
1
β
Gamma Ray (γ)
Neutron (n)
1
n
0
0γ
0
ALPHA, BETA and GAMMA.
Each type is capable of penetrating different
materials:



Sheet of
paper
Few mm of
aluminium
Few cm of
lead
Note:
Neutrons have no charge and so are not directly ionising but
they are as penetrating as gamma rays
Property
Alpha
Beta
Ability
to ionise
Very
ionising
Moderately
ionising
Range
in air
Travels a few 50cm to 1 m
centimetres
Gamma
Weakly
Ionising
Travels a few
kilometres
Unit P3: Applications of physics
Topic 3
Production, uses and risks of ionising
radiation from radioactive sources
We Are Learning To
3.5 Describe the process of β- decay (a neutron becomes a proton plus an electron)
3.6 Describe the process of β+ decay (a proton becomes a neutron plus a
positron)
3.9 Describe the features of the N-Z curve for stable isotopes
3.10 Identify isotopes as radioactive from their position relative to the stability
curve
3.11 Recall that nuclei with high values of Z (above 82) usually undergo alpha
decay
3.12 Recall that an isotope above the curve has too many neutrons to be stable
and will undergo β- decay
3.13 Recall that an isotope below the curve has too many protons to be stable and
will undergo β+ decay
Isotopes of an element have the same atomic number but
different atomic mass. Some isotopes are radioactive and
emit radiation.
Why do you think carbon is shown as
table?
in the periodic
Belt of stability
4
He
2
x
Isotopes that lie below the curve
have too few neutrons to be stable.
These nuclei emit a positron.
Isotopes that lie above the curve
have too many neutrons to be
stable. These nuclei emit an
electron.
All nuclei with a proton number
above 82 are unstable. These
radioactive isotopes emit alpha
particle.
0
-1
β
x
x
0
1
β
82
Unit P3: Applications of physics
Topic 3
Production, uses and risks of ionising
radiation from radioactive sources
We Are Learning To
3.14 Recall that the proton and neutron each contain three particles called quarks
3.15 Describe the arrangement of up and down quarks in protons and neutrons
3.16 Use given data to explain the arrangement of up and down quarks in protons
and neutrons in terms of charge and mass
3.17 Explain β- decay as a process that involves a down quark changing into an up
quark (a neutron becomes a proton and an electron)
3.18 Explain β+ decay as a process that involves an up quark changing into a
down quark (a proton becomes a neutron and a positron)
Fundamental Particles
A fundamental particle is a particle that is not made up of smaller
particles.
Some examples of
fundamental Particles
Some examples of non
Fundamental Particles
Electron
Neutron
Positron
Proton
Quark
1. Quarks have about 1/3 of the mass of a nucleon (proton/neutron).
2. Quarks also have charge!
+2/3
-1/3
Compared to an electron with a
negative charge of -1, an up quark has
a charge +2/3e and a down quark has
a charge –1/3e So quarks have
fractions of the charge of an electron.
Proton
u
(remember a proton has a charge of +1)
u + u + d
2/3 + 2/3 + (-1/3)
= +1
u
Neutron
d
u
(remember a neutron has no charge)
d + u + d
(-1/3) + 2/3 + (-1/3)
=0
d
d
Beta particle β- emission
n
p
decays
u
u
d
-1/3
u
d
+ 2/3
d
+
+
β-
β-1
Positron (β+) emission.
p
n
decays
u
u
+2/3
+
u
d
d
-1/3
d
+
β+
β+
+1
Unit P3: Applications of physics
Topic 3
Production, uses and risks of ionising
radiation from radioactive sources
We Are Learning To
3.7 Explain the effects on the atomic (proton) number and mass
(nucleon) number of radioactive decays (α, β and γ decay)
3.8 Use given data to balance nuclear equations
3.19 Recall that nuclei that have undergone radioactive decay
often undergo nuclear rearrangement with a loss of energy as
gamma radiation
Alpha Particle Emission
238
92
U 
Uranium-238
4
2
He +
Alpha particle
234
90
Th
Thorium-234
Beta emission
14
6
C 
Carbon-14
0
-1
β
Beta particle
+
14
7
N
Nitrogen-14
Positron Emission
18
9
F 
Fluorine-18
o
+1
β
Positron
+
18
8
O
Oxygen-18
Gamma Emission
Gamma radiation is sometimes emitted from
a radioactive nucleus after either a beta,
positron or alpha particle has been emitted.
238
92

U
234
90
0
0
γ
γ
+
Th
He +
4
2
0
0
Explain what is happening to a nucleus during gamma
emission.
Answer:
Nucleus releases excess energy in the form of
gamma radiation, following nuclear rearrangement.
Nuclear fission
Kr
1n 235
+
0
92
U
139
56
Ba
94
+
36
Ba
1n
+ 0
Kr 3
Unit P3: Applications of physics
Topic 3
Production, uses and risks of ionising
radiation from radioactive sources
We Are Learning To
3.20 Describe the dangers of ionising radiation in terms of tissue
damage and possible mutations
3.21 Explain the precautions taken to ensure the safety of people
exposed to radiation, including limiting the dose for patients and
the risks to medical personnel
Equivalent dose
The unit which incorporates both the energy and
the biological harm of radiation is the Sievert
Measured in Sievert (Sv), or the millisievert (1 Sv = 1000 mSv).
Type of exposure
Equivalent dose
of radiation (mSv)
flight from London to Madrid
0.01
chest X-ray
0.02
average annual dose from natural radiation in UK
3.00
annual dose in Cornwall from natural radiation
8.00
maximum permitted annual dose for an employee
20.00
dose which causes immediate radiation sickness
1000.00
dose causing death in 50% of population
4000.00
Equivalent dose of radiation (mSv)
The average person in the UK receives 2.7 mSv
of ionising radiation a year
nuclear workers receive 3.6 mSv
air crew receive 4.6 mSv
European annual limit of 20 mSv set for a worker in a nuclear power
plant.
News:
Recent research has shown that male pilots have slightly higher rates of
several cancers compared with the national average. However, women
seem to be at greater risk. Air hostesses have twice the risk of breast
cancer compared to the average flier.
Workers who work with radiation every day e.g.
hospital staff/nuclear power plant workers need to:
(1) monitor the dose they are being exposed to staff wear special badges that monitor their
exposure.
(2) take precautions to reduce the dose they are
exposed to - leave the room or go behind a lead or
thick concrete shield whilst a patient is being given
radiation treatment
Is ionising radiation harmful?
Ionising radiation can damage DNA.
This could cause…
1. Cancer
2. Inflammation
3. Cell death
4. Damage to genes can lead to mutations in offspring
Cells are more sensitive to radiation during cell division than at
other times.
Cells which divide frequently (e.g. the gut walls) are more
sensitive than those which rarely divide (e.g. nervous tissue).
Unit P3: Applications of physics
Topic 3
Production, uses and risks of ionising
radiation from radioactive sources
We Are Learning To
3.22 Compare and contrast the treatment of tumours using radiation applied
internally or externally
3.23 Describe palliative care including the use of radiation in some
instances
3.24 Explain some of the uses of radioactive substances in diagnosis of
medical conditions, including PET scanners and tracers
3.25 Explain why isotopes used in PET scanners have to be produced nearby
Radiation in hospitals - treatment:
Radiotherapy is often used to treat cancers, as the radiation can
kill cancer cells (or tumours). The radiation can be applied:
1. Internally (with the source
inside the patient, right by the
tumour). A beta source such
as iodine-131 can be used.
1. Externally (with the source
outside the patient). A
gamma source or high
frequency X-rays is used.
Radiotherapy – treatment of cancer
 The tumour is exposed to gamma radiation at
different angles.
 This gives normal cells a low dose of radiation,
while the tumour receives a high dose.
 However, levels have to be carefully monitored
so that healthy cells are not damaged as well.
Rotating
gamma source
tumour
In some patients radiation treatment may not be able to destroy the cancer.
Sometimes it is used only to reduce suffering (palliative care).
Internal radiotherapy known as Brachytherapy
prostate
cancer
In this treatment, radioactive ‘seeds’ are inserted through fine needles directly
into the prostate under anesthetic. This enables high doses of radiation to be
delivered directly to the prostate without affecting surrounding structures. As a
consequence the side effects tend to be less pronounced.
Internal radiotherapy
Treatment is given in one of two ways:
1. Brachytherapy - putting solid radioactive material (the source)
close to or inside the tumour for a limited period of time.
If you’re having brachytherapy, you only need to stay in isolation while the radioactive source is in
place. Once it has been removed, the radioactivity disappears and it’s perfectly safe to be with
other people.
This doesn’t apply to brachytherapy for prostate cancer, as the radioactive seeds are not
removed. With prostate brachytherapy the radiation affects only the area a few millimetres around
the seeds, so there’s no danger of it affecting other people.
2. Radioisotope treatment - by using a radioactive liquid, which is
given either as a drink or as an injection into a vein.
If you’re having treatment with a radioisotope the radioactivity will disappear gradually, so you will
need to stay in isolation until the radiation in your body has dropped to a safe level. Before you
leave hospital, the staff will check that most of the radioactivity in your body has gone. After you
leave hospital you should be able to carry on with your life normally, but there may be a few
restrictions about contact with children and pregnant women for a few more days.
Chemotherapy
Chemotherapy is often used in combination with
radiotherapy when the cancer is widespread, or if it is
thought there is a significant risk of the cancer returning.
Chemotherapy involves the use of powerful cancer-killing
medicines. These medicines damage the DNA of the
cancerous cells, interrupting their ability to reproduce.
Palliative care
When an illness is incurable a patient may still receive
treatment - this is called palliative care.
e.g. radiotherapy may still be given to a patient who can’t be
cured of cancer. Radiotherapy is given to try to reduce the size
of the tumour to help reduce pain and improve the patients
quality of life.
Iodine-123 is a radioactive tracer
Decay curve
Use the graph to
find Iodine-123
half-life?
Radioactive Tracers – used for diagnosis
• Radioactive tracers can be used to see how well organs in your
body are working or to find areas of disease.
e.g. radioisotopes of iodine or technetium.
• Often these are mixed with a drug that collects in a particular
organ in the body.
• If we then inject the drug into the body, then by detecting the
radiation, we can examine that organ.
Gamma camera
Radioactive Tracers – used for diagnosis
Gamma camera
A gamma camera
detects the radiation
coming from the
patient and produces
an image of where
the radioactivity is in
the body.
When a radioactive chemical is used in this way it is not normally
harmful, because:
it has a short half-life and so decays before it can do much damage
Emitters of gamma radiation are used because gamma radiation can
penetrate through the body.
A PET scan reveals areas with high levels of chemical
activity, such as high glucose metabolism.
breast cancer
Unit P3: Applications of physics
Topic 3
Production, uses and risks of ionising
radiation from radioactive sources
We Are Learning To
3.1 Evaluate the social and ethical issues relating to the use of radioactive
techniques in medical physics
May 2008
The gift of a pioneering medical scanner to the
NHS has met with opposition because the donor,
the Royal Bank of Scotland, wants first call on up
to 25 per cent of its use for bank staff. The rest of
the time the three-dimensional CT scanner - the
first of its kind in Britain and one of only a handful
in Europe - would be available for NHS patients.
Cheltenham Imaging Centre
Linton House Clinic
Thirlestaine Road, Cheltenham,
Gloucestershire, GL53 7AS
Tel: 01242 535910
NEW DIAGNOSTIC SERVICES AT
CHELTENHAM IMAGING CENTRE
THE WORLD’S FIRST & ONLY DESIGNED
OPEN PET/CT SCANNER
£798 PER PATIENT SCAN REGARDLESS OF
BODY AREAS
INCLUDING REPORT & CD FOR EASY PC
MANIPULATION
The transparency in waiting times is
part of the government's attempts to
achieve an 18-week maximum wait
from GP to treatment, including all
diagnostic tests, by 2008.
Social and Ethical Implications of Medical Care
within the NHS.
Read the following news articles regarding finances
Hospital refuses patient cancer drug!
Doctors believe a new drug will
prolong the life of a man with kidney
cancer, but the local hospital trust
refuses to pay for the treatment. Instead
the man has had to sell his home to
cover the cost.
Cancer patients denied new drug!
The use of Herceptin could cost the
NHS £17 million a year. However,
recent studies show that Herceptin is
not being prescribed by all health care
trusts, making cancer treatment a
"postcode lottery".
What do you think?
Social and Ethical Implications of Medical Care
New treatments increase costs within the NHS:
 Each PET scan costs between £750 and £1,000 per patient.
 Post-operative breast cancer radiotherapy costs £2,000 per
patient.
 MRI scans cost from £350 per patient.
Can the NHS continue to afford to
treat smokers for lung cancer?