4.3 Background radiation Flashcards
Background radiation
The radiation that exists around us all the time.
It is important to remember that radiation is a natural phenomenon.
Radioactive elements have always existed on Earth and in outer space.
However, human activity has added to the amount of radiation that humans are exposed to on Earth.
Types of background radiation
There are two types of background radiation:
Natural sources (Rocks, Cosmic rays from space, Foods)
Man-made sources (Fallout from nuclear weapons testing and nuclear accidents, Exposure from medical testing)
Measuring radiation dosage
It is important to regulate the exposure of humans to radiation.
The amount of radiation received by a person is called the dose and is measured in sieverts (Sv).
One sievert is a very big dose of radiation.
It would cause acute radiation poisoning.
People would normally receive about 3 mSv (0.003 Sv) in one year.
To protect against over-exposure, the dose received by different activities is measured.
A dosemeter measures the amount of radiation in particular areas.
Short half life values
If an isotope has a short half-life, the nuclei will decay very quickly
This means that the isotope will emit a lot of radiation in a short amount of time.
If only a small amount of the isotope is used, having a short half-life can be advantageous, as the material will quickly lose its radioactivity.
If a large amount is used, however, the levels of radiation emitted could make handling the isotope extremely dangerous.
Long half life values
If an isotope has a long half-life then a sample of it will decay slowly.
Although it may not emit a lot of radiation, it will remain radioactive for a very long time.
Sources with long half-life values present a risk of contamination for a much longer time.
Radioactive waste with a long half-life is buried underground to prevent it from being released into the environment.
Medical tracers
A tracer is a radioactive isotope that can be used to track the movement of substances, like blood, around the body.
Gamma emitters are usually used for this purpose.
Gamma rays are highly penetrating and so will be able to pass through the body and be detected outside the body.
This allows an internal image of the body to be created.
Since gamma rays are less ionising than some other forms of radiation, the harm caused to the patient is also minimised.
As well as choosing a gamma emitter:
The amount of isotope used is kept to a minimum to reduce people’s exposure to radiation.
Isotopes are chosen that have short half-lives of around a few hours: Long enough to carry out the procedure, but not so long that they cause long term harm.
Radiotherapy
Radiotherapy is the name given to the treatment of cancer using radiation
Although radiation can cause cancer, it is also highly effective at treating it.
Radiation can kill living cells.
Some cells, such as bacteria and cancer cells, are more susceptible to radiation than others.
During external radiotherapy, beams of gamma rays are directed at the cancerous tumour.
The machine rotates to target the tumour from different angles.
This minimises the exposure of healthy tissue to the gamma rays and minimises damage to healthy cells.
During internal radiotherapy, small pellets of radioactive materials can also be inserted into a tumour exposing it directly to radiation.
Sterilising medical equipment
Gamma radiation is widely used to sterilise medical equipment.
Gamma is most suited to this because:
It is the most penetrating out of all the types of radiation.
It is penetrating enough to irradiate all sides of the instruments.
Instruments can be sterilised without removing the packaging.
Risks of nuclear radiation
The use of radiation in medicine carries risk.
Radiation can:
Kill or damage living cells.
Cause cancer.
Cause mutations.
As a result, its use needs to be kept to a minimum.
However, the benefits of using radiation in medicine can out weigh the potential risks.
