How it works
A cyclotron is a particle accelerator. It is an electrically powered machine which produces a beam of charged particles that can be used for medical, industrial and research processes. As the name suggests, a cyclotron accelerates charged particles in a spiral path, which allows for a much longer acceleration path than a straight line accelerator.
A cyclotron body consists of electrodes, called 'dees' because of their shape, in a vacuum chamber. This vacuum chamber is flat and sits in a narrow gap between poles of a large magnet which creates a perpendicular magnetic field. A stream of charged particles is fed into the centre of the chamber and a high frequency alternating voltage is applied across the electrodes. This voltage alternately attracts and repels the charged particles causing them to accelerate.
The magnetic field moves the particles in a circular path and, as they gain more energy from the accelerating voltage, they spiral outwards until they reach the outer edge of the chamber.
Modern cyclotrons accelerate negative ions created in a plasma. When these negative ions reach the outer edge of the chamber the excess electrons are stripped off the ions forming positive particles such as a proton or deuteron, which can then be extracted from the cyclotron as a beam. The size of the vacuum chamber determines the length of the spiral path and hence the amount of energy attained by the particle.
Medical cyclotrons produce proton beams which are used to manufacture radioisotopes used in medical diagnosis. Radioisotopes produced in a cyclotron decay by either positron emission or electron capture. Positron emission tomography (PET) and single photon emission computed tomography (SPECT), which utilises the gamma rays associated with electron capture, are two imaging techniques that rely on cyclotron-produced radioisotopes.
Cyclotrons and nuclear reactors
It depends on the radioactive properties required whether a nuclear reactor or a cyclotron is used to produce a radioisotope.
Atoms with extra protons in the nucleus are called neutron-deficient and are produced in a particle accelerator such as a cyclotron. Atoms with extra neutrons in the nucleus are called neutron-rich and are produced in a nuclear reactor, such as OPAL
Neutron-rich and neutron-deficient radioisotopes decay by different means and hence have different properties and different uses. Radioisotopes made in cyclotrons complement those made in a reactor. Both types of radioisotopes are needed to service all of Australia's nuclear medical needs.
Radioisotopes are an essential part of radiopharmaceuticals. In fact, they have been used routinely in medicine for diagnostic imaging and in some cases therapy for more than 30 years.
Nuclear medicine uses small amounts of radiation to provide information about a person's body and the functioning of specific organs, ongoing biological processes, or the disease state of a specific illness. In most cases, the information is used by physicians to make an accurate diagnosis. In certain cases radiation can be used to treat disease.