Health Physics: Nuclear Radiation
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how does radiation affect humans?
it can kill or damage living cells
what can nuclear radiation be used for?
- to sterilise medical instruments by killing germs
- to kill cancerous cells by placing an alpha source next to the tumour or by firing a beam of gamma rays at the tumour
radiation can be used for diagnosis, how?
- a radiactive tracer is injected into the patient
- the tracer is carefully chosen so that is will collect in the organ being studied and an image of the organ can be then be taken with a gamma camera
what is an atom?
- the smallest particle into which matter can be divided
- its made up of a central nucleus with orbiting electrons
what are the three types of nuclear radiation?
what happens what radiation passes through a material?
- some of its energy is absorbed by the material.
- the amount of absorption depends on the type of radiation and the material it is passing through
in an atom, what does the nucleus consist of?
- positively charged protonsuncharged neutrons
in an atom, what does the electrons do?
- orbit the nucleus at high speed
- they are negatively charged
what is alpha absorbed by? what is its range in air?
what is beta absorbed by? what is its range in air?
- 2-3mm aluminium
- a few metres
what is gamma absorbed by? what is its range in air?
- 2-3cm lead
- not aborbed in air
what is ionisation?
adding or taking away an electron from an uncharged atom
what is photographic fogging?
- its used in to detect radiation in a film badgein a film badge different section of a piece of photographic film are covered by various thicknesses and types of absorber
which radiation causes more ionisation?
what is ionisation used to detect radiation from?
the Geiger-Muller tube
what happens in the Geiger-Muller tube?
- when radiation enters the tube through the thin mica window it causes ionisation in the gas
- this allows the gas to conduct and a pulse of current passes between the electrodes
- this pulse of current is counted by the counter
how can the type of radiation be determined?
- by which sections of the film in a film badge are blackened
- the amount of radiation can be determined by how black the film is
what is scintillation?
- radiation can cause some materials to scintillate.
- the material absorbs the energy of the radiation and re-emits it as light.
scintillation is used to detect radiation in what?
what is a collimator?
- a large piece of lead with thousands of holes in it
- ensures that although gamma rays are given off in all directions, only parallel rays reach the detector
what is a detector?
converts radiation into light by scintillation
what is the electronics?
turn the pattern of light into an electrical signal, which can then be transmitted to a monitor for viewing
what is the activity of a radioactive source?
the number of atoms that decay each second
what is the half-life of a radioactive source?
the time taken for its activity to half
what is the activity of a radioactive source measured in?
how can the half-life of a radioactive source be measured?
by taking measurements of the activity of the source at regular intervals of time using a Geiger-Muller tube and counter
what happens to the activity of a radioactive source?
decreases with time
what safety precautions need to be taken when handling radioactive materials?
- always handle with forceps
- point source away from body
- store in lead container
- label all sources
- wash hands after use
what is the dose equivalent of a radioactive source?
a measure of the biological risk of the source
what is dose equivalent measured in?
what does the biological effect of radiation depend on?
- the type of absorbing tissue
- the type of radiation
- the total energy absorbed
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