Research into nuclear physics has enabled the development of science and technology that directly benefits us. Here are just a few examples of how nuclear processes and ionising radiation are being used to improve our lives.
X-rays – are the most common form of ionising radiation used in medicine. In the body calcium, Z=20, in bones absorb x-rays very efficiently, while soft tissue and fat absorb x-rays less efficiently. The difference in absorption efficiency creates the contrast in an x-ray picture, allowing doctors to see inside the body without the need for surgery. In this way x-rays are useful for checking broken bones, but they can also be used to identify other medical problems. A chest x-ray can be used to diagnose lung diseases such as pneumonia and mammograms use x-rays to screen for breast cancer.
X-rays are also used in a type of computed tomography, more commonly known as a CT scan. This imaging technique builds up a highly detailed picture by taking x-ray images from different angles to give a series of image cross sections (or slices) through the part of the body being scanned.
Radiotherapy – is the use of ionising radiation to treat cancer. Almost half the people in the UK with cancer have radiotherapy as part of their treatment. Radiotherapy can be carried out externally, usually with a high energy beam of x-rays, or internally. Internal radiotherapy is when a radioactive liquid is swallowed or injected, or a small piece of radioactive material is placed temporarily in or close to the cancerous cells. This is known as brachytherapy.
PET scan – positron emission tomography (PET) is an imaging technique that also shows how processes in the body are functioning. A small amount of radioactive tracer is injected into the body, most commonly fluorine, Z=18, which is a radioactive sugar. This tracer undergoes beta decay emitting a positron, the antimatter partner of the electron. When a positron interacts with an electron they annihilate and give off a pair of γ-rays travelling in opposite directions. The scanner detects these pairs of γ-rays and builds up a sequence of 2D images of the tracer concentration. A 3D image can be built up with the help of an x-ray CT scan, which is performed by the same machine at the same time.
Nuclear power stations generate energy through nuclear fission, the splitting apart of heavy atomic nuclei. When elements like uranium, Z=92, fission, the large nucleus splits into smaller ‘daughter’ nuclei releasing a lot of energy, which can be harnessed to produce electricity. Nuclear fuel is very energy dense with 1 tonne of uranium = 20,000 tonnes of coal and it is a low-carbon method of producing electricity. There are 16 operational nuclear reactors in the UK and they provide approximately 15% of the UK’s electricity.
Nuclear batteries use the decay of radioactive nuclei to generate electricity. They are very expensive, but have a high energy density and last an extremely long time. Nuclear batteries are therefore extremely useful as power sources for equipment where there is no opportunity to ‘change the batteries’ such as pacemakers and spacecraft.
Using nuclear techniques to identify different stable and radioactive isotopes in archaeological relics and works of art, enables the histories of these artefacts to be discovered. As different radioactive isotopes decay at different rates there are a lot of different methods that can be used to reliably date an object from the creation of the Earth, right up to the present day. One of the most well known forms of radioactive dating is carbon, Z=6, dating.
The radioactive isotope of carbon used in dating is carbon-14, which has 6 protons and 8 neutrons. This isotope exists naturally on Earth and is taken up by plants and animals while they are alive. During an organisms life the ratio of carbon-14 and the stable carbon-12 is roughly constant, but once it dies, the amount of carbon-14 is reduced by radioactive decay at a known rate and is not replaced. By measuring the ratio of carbon isotopes in a sample the date of death can be estimated. Similar nuclear methods can also be used to determining the origin of artefacts, helping archaeologists better understand the trade, cultural contacts and influences between ancient settlements.
The most common domestic smoke alarms use a radioactive isotope of the element americium, Z=95, to detect smoke. In a smoke detector a very small americium-241 source emits alpha particles into an ionisation chamber that is open to the air. The air in this chamber becomes ionised, allowing a very small electrical current to flow. If smoke is present this current drops and the alarm sounds.
A wide variety of household items are sterilised using ionising radiation; from plastic materials, cables, wires and car parts; to food packaging and even gemstones. The radiation, usually γ-rays, destroys bacteria, viruses, fungi, mould, insects and eggs using much less energy that sterilisation through heating. Medical equipment and supplies are also sterilised using ionising radiation, as sterilisation can occur after packaging, reducing the risk of contamination further. Some foods can be sterilised using γ-rays. In the UK fruit, vegetables, cereals, bulbs, tubers, dried aromatic herbs, spices, vegetable seasonings, poultry, fish and shellfish can be irradiated, but they must be clearly labelled.