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Electromagnetic spectrum: 9. The properties, uses and dangers of gamma radiation (ionising radiation)

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INDEX of physics notes: Properties and uses of electromagnetic radiation

9. The properties, uses and dangers of gamma radiation

The sources and properties of gamma radiation

In the breakdown of the unstable nucleus in radioactive decay, energy is released by the emission (usually) of three types of ionising radiation (nuclear radiation) called alpha particle radiation, beta particle radiation and gamma ionising radiation.

Gamma radiation emission often accompanies alpha and beta particle emission - its a way that a newly formed and temporarily unstable nucleus gets rid of its excess energy to become more stable.

Therefore you need a suitable radioisotope that gives out gamma radiation when the atoms decay.

When EM gamma radiation is absorbed, some of the wave energy is converted into heat, BUT gamma rays can cause ionisation - the process of knocking off outer electrons of atoms to create positive ions (see Part 10 ionisation for more details) - so gamma rays are an ionising radiation.

For more details on gamma radiation see:

What is Radioactivity? Why does it happen? Three types of atomic-nuclear-ionising radiation

Alpha, beta & gamma radiation - properties of radioactive nuclear emissions & symbols


The uses of gamma radiation

Gamma radiation can kill cells, but its not all bad news - sterilisation.

Radioactive gamma ray sources are used to sterilise medical equipment like surgical instruments at room temperature. If a microbe absorbs the gamma rays it is destroyed even if it is in a microscopic crevice - gamma rays are very penetrating! This is much more efficient that the old fashioned method of sterilising equipment in boiling hot water - the heat might damage delicate equipment.

Packaged food can be sterilised in the same way.

Any remaining microbes can be killed after the cooking and packaging processes and once sterilised and sealed no microbes can get in to rot and degrade the food.

This ensures the food is fresh for longer (longer shelf-life) and safe to eat without having to preserve it any other way e.g. cooking or freezing.

Medical uses

As with sterilisation, gamma rays can be used to kill harmful cells such as cancer cells.

A beam of gamma radiation is directed through the body onto the cancer cells to kill them. The dose must be the minimum required because its quite difficult to avoid killing some healthy cells too. With most cancer treatments using gamma radiation, your immune system takes a bit of battering and with some radiotherapy treatments you can lose your hair.

As with X-rays, most people would accept a risk of harm from gamma rays compared to the risk of leaving an untreated cancer. Unfortunately, unlike having an X-ray where the side-effects are negligible, the side-effects of gamma radiation radiotherapy are quite substantial, but in most cases temporarily. This is a classic case of risk versus benefit.

Since gamma radiation can damage and kill cells, some water treatment plants sterilise the water by exposing it to gamma radiation to kill harmful bacteria.

Gamma rays are so powerful and penetrating that they are transmitted through skin, soft tissue and even bone.

So gamma rays can be used in medical imaging techniques.

If you can introduce a radioactive tracer into the body by swallowing or injection, you can then monitor the movement of it.

Therefore gamma radiation is used in medical imaging to help doctors diagnose certain kinds of health issues.

The person is injected with a gamma emitter (radiotracer) which is so penetrating (unlike alpha and beta radiation) that it comes out of the body and monitored on a computer screen from the signals recorded by a gamma camera - a sort of digital camera which is outside of the body. Y

You can then follow where the tracer goes.

From the emitted gamma rays you can check on, for example, how efficient your blood circulation is, your lung efficiency, but you need to be injected with a gamma ray emitting radioisotope.

The radioactive tracer atom can be part of a molecule normally present in the body like urea or glucose. From where the tracer ends up doctors can see how efficient, or otherwise, how the organ in the body is working.

e.g. cancer growths use more glucose in respiration, they use more energy, therefore you see a 'hot spot' where more radioactive glucose has accumulated.

Positron emission tomography (PET scans) are used in medicine to produce highly detailed three-dimensional images of the inside of the human body.

for more details on PET scans and other uses of gamma radiation

... see Uses of radioactive isotopes including gamma radiation in industry and medicine notes


The dangers of gamma radiation - the highest frequency and highest energy of the EM spectrum

Gamma radiation (and X-rays) is the most dangerous of the ionising radiations and easily causing tissue damage. DNA can be damaged-altered interfering with cell function and cause mutations - leading to cancer.

Gamma rays have the highest EM radiation energy and are very deeply penetrating in their energy transfer to the absorbing material - which might be the deeper tissues and organs of the body.

To minimise the chance of harm from gamma-rays nurses and clinicians must take precautions e.g. protective clothing, operating gamma ray machines by remote control - all to prevent exposure to a large dose of radiation over time.

A high dose of gamma radiation kills many cells quickly causing 'radiation sickness' - a serious general malfunction of body leading to vomiting and hair loss, and can lead to death.

See Part 10 for general comments on the dangers of ionising radiation

Dangers of radioactive emissions - health and safety issues and ionising radiation

INDEX of notes: Properties and uses of electromagnetic radiation

Keywords, phrases and learning objectives for electromagnetic radiation spectrum

Be able to describe the properties of gamma rays and quote sources e.g. radioactive elements and know that gamma radiation is part of the electromagnetic spectrum.

Be able to describe and explain the uses of gamma radiation e.g. sterilisation of medical equipment, medical uses e.g. treatment to kill cancer cells, sterilising food or medical equipment, PET scans, radioactive tracers, but also be aware of the dangers of gamma radiation.


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INDEX of notes: Properties and uses of electromagnetic radiation