Radioactivity
The Professional Development Service for Teachers is funded by the Department
of Education and Science under the National Development Plan
Radioactivity
This unit explores radioactivity and how
doctors can use radioactivity to diagnose and
treat illnesses
Objectives
By the end of this unit you should be able to
• Draw diagrams of atoms
• Understand what an isotope is
• Understand radioactive decay and write decay
equations
• Understand how doctors use radioisotopes to
diagnose illnesses
• Understand how doctors use radioisotopes to
treat cancer
• Have the basic knowledge needed for Expert
Group tasks
Task
To help you understand this topic you
will need to do some review work to find
out about atoms. In your groups
complete the worksheet given.
Atomic Theory Review
Aim of this review: To
describe the structure
of the atom, state the
location, relative charge,
and atomic mass of the
sub-atomic particles, and
define atomic number
and isotope. Draw the
Bohr structure of some
elements.
Now that you have reviewed
atomic theory try using
modeling clay or plasticine and
pipe cleaners, make a model of
(i) a lithium atom
(ii) a potassium atom
(iii) an aluminium atom.
Radioactive decay
Some atoms are radioactive this means
their nucleus is unstable and decays to
become more stable. When nuclei decay
they emit or get rid of something from
the nucleus
Unstable nucleus
Electromagnetic wave
particle
Atoms which emit electromagnetic radiation or
a particle by the spontaneous transformation of
their nucleus are called radioactive.
There are three types of radioactive decay
Alpha decay : This is when 2 protons and 2
neutrons leave the nucleus to help it become
stable
Look back at the table on your review sheet
what do we call something that has 2 protons
and 2 neutrons in the nucleus?
So an alpha particle is really ……………….nucleus
If 2 protons and 2 neutrons leave the nucleus
the nucleus will be transformed.
Beta Decay: This is when a neutron
in the nucleus turns into a proton
and electron. The electron then
leaves the nucleus.
Will the nucleus be transformed?
Explain why
Gamma Decay: Look back at the topic on X
rays .What are gamma rays?
If a gamma ray leaves the nucleus will it be
transformed?
Explain why
Types of radiation
• Alpha Particle (α)
-
• Beta Particle (β)
• Gamma Ray (γ)
You can represent alpha and beta decay as equations :the left hand
side of the arrow shows the number of protons and neutrons before
the decay and the right hand side shows the number after the decay.
The before and after “numbers ” must remain the same
Carbon 14 written
14
8C
is an isotope of Carbon what does this mean?
It is a radioactive isotope and it decays by beta decay .
The decay equation for Carbon 14 is shown below
14 C→ -1 e
8
0
+ 158N
14 particles before decay
15-1=14 particles after decay
8 protons before decay
8+0 =8 protons after decay
Problem
Cobalt 60 is a radioisotope that is
historically important for several
reasons. It is a product in radioactive
fallout from nuclear weapons. For many
years, the gamma radiation from this
decay was the main source for radiation
therapy for cancer.
Cobalt-60 decays by beta emission also.
Write a decay equation to show this.
Tracers
• 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.
Student Activity
Imagine the tubing
represents the gut. There is
a blockage in the gut
Instead of cutting the
patient to find the blockage
the patient drinks a liquid
containing a radioactive
tracer, the dye in this model
The gamma camera picks up
the image of the of the liquid
and the blockage is located
Preparing the Tracer
The tracer being injected into thhe
Patient
Gamma Camera
A gamma camera detects the radiation coming from the patient and
produces an image of where the radioactivity is in the body.
Obtaining the Image
• The gamma camera displays the
position of each gamma ray that it
detects.
• This is a bone scan made using
technetium-99.
• Can you see where the patient was
injected?
Tracers and their Uses
Bone :
99mTc
used to detect cancer, stress fractures
and bone graft success.
123 I used to access over-active and underThyroid:
active thyroids, as well as thyroid tumours,
cysts and goitres.
133Xe inhaled for ventilation studies (airways)
Lungs:
and 99mTc administered for perfusion studies
(blood flow).
201Tl used to study muscle performance.
Heart:
99mTc used to assess dementia and stroke
Brain:
damage.
Dilution analysis to access blood and water
volumes (the tracer mixes with certain body
fluids).
Body blood: 99mTc used to assess volume.
Red cells: 51Cr is attached to these.
Minerals: 24Na and 42K used to monitor body sodium
and potassium.
Radiotherapy
•
Rapidly dividing cells are particularly sensitive to damage by radiation.
For this reason, some cancerous growths can be controlled or
eliminated by irradiating the area containing the growth. External
irradiation can be carried out using a gamma beam from a radioactive
cobalt-60 source,
•
Internal radiotherapy is administered by planting a small radiation
source, usually a gamma or beta emitter, in the target area. Iodine-131
is commonly used to treat thyroid cancer, probably the most successful
kind of cancer treatment. It is also used to treat non-malignant thyroid
disorders. Iridium-192 implants are used especially in the head and
breast. They are produced in wire form and are introduced through a
tube called a catheter to the target area. After administering the
correct dose, the implant wire is removed to shielded storage.
•
Treating leukemia may involve a bone marrow transplant, in which case
the defective bone marrow will first be killed off with a massive (and
otherwise lethal) dose of radiation before being replaced with healthy
bone marrow from a donor.
Gamma Knife
This technique is
used for brain
surgery . Instead
of opening the
patient's head the
gamma rays from a
Cobalt 60 source
are focussed on
the tumour. The
location of the
tumour would have
been accurately
mapped earlier
using an MRI or CT
scan
The radiation must be
precisely targeted.
Metal windows restrict the
gamma ray beam size
This is the Gamma
Knife in position.
A polystyrene model
shows the position
that the patients
head would occupy.
A patient’s eye view
Planning the treatment
A medical physicist
decides how to
target the gamma
rays to destroy the
tumour and minimise
damage to other
tissue