Radioactivity

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Radioactivity
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Radioactivity
This unit explores radioactivity and how doctors
can use radioactivity to diagnose and treat
illnesses
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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

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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.
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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.
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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.
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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
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Unstable nucleus
Electromagnetic wave
particle
Atoms which emit electromagnetic radiation or a
particle by the spontaneous transformation of
their nucleus are called radioactive.
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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.
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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
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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
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Types of radiation

• Alpha Particle (a)

• Beta Particle (ß)

• Gamma Ray (?)

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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 148C
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
148C? -10e 158N 14
particles before decay 15-114 particles
after decay 8 protons before decay 80
8 protons after decay
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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.

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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.

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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
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Preparing the Tracer
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The tracer being injected into thhe Patient
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Gamma Camera
A gamma camera detects the radiation coming from
the patient and produces an image of where the
radioactivity is in the body.
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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?

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Tracers and their Uses

• Bone 99mTc used to detect cancer, stress
  fractures and bone graft success.
• Thyroid 123 I used to access over-active and
  under-active thyroids, as well as thyroid
  tumours, cysts and goitres.
• Lungs 133Xe inhaled for ventilation studies
  (airways) and 99mTc administered for perfusion
  studies (blood flow).
• Heart 201Tl used to study muscle performance.
• Brain 99mTc used to assess dementia and stroke
  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.

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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.

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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
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Planning the treatment

• A medical physicist decides how to target the
  gamma rays to destroy the tumour and minimise
  damage to other tissue