A type of particle accelerator (circular) that uses a magnetic field to force particles to move in circular paths, causing them to repeatedly pass through a small region where they are accelerated by an electric field.
The cyclotron was invented in the early 1930s by the American scientist Ernest Lawrence, who was awarded the Nobel Prize in Physics in 1939 for this invention. From its invention until the mid-1940s, the cyclotron dominated the field of high-energy accelerators. Even today, with much more powerful accelerators available, cyclotrons are still used for certain research and practical purposes, including production of radioactive isotopes for preparation of various diagnostic radiopharmaceuticals.
The cyclotron consists of two half-cylinders, each called “Dee” (due to their shape, which resembles the letter D), with different electric potentials, thus creating an electric field between them, which accelerates charged particles as they pass through. A magnetic field is present across the entire cyclotron, including the Dees, which causes the charged particles to move in a circular motion, bringing them repeatedly back to the acceleration region. Because the rotation frequency of a charged particle in a magnetic field does not change with its speed, an electric field that oscillates at the same frequency is oriented to accelerate the charged particle towards the other half-cylinder every time the particle exits one of the Dees.
Cyclotrons are mainly used to produce radioactive isotopes by bombarding stable nuclei (isotopes) with particles such as protons and deuterium nuclei, which have sufficient energy to overcome the repulsive forces between them and the target nuclei. This bombardment creates a nuclear reaction, allowing the nuclei to merge (with or without emission of other particles) to form a new type of nucleus. This process has been vital for studying nuclear structure and the interactions governing it, and has yielded important reaction products (isotopes). In this way, radioactive isotopes of known atoms were first produced and put to use in various applications, including medical needs. Later, new elements were discovered by this method, the first being technetium, followed by transuranic elements, most notably plutonium. Today, cyclotrons are used for producing radioactive isotopes, mainly for medical purposes, as well as for various applied research needs.
Currently, there are four cyclotrons in Israel. Two of them are located at Hadassah Ein Kerem Hospital and are operated by S.R.Y. The devices are used for ongoing production and research purposes. The majority of production is dedicated to fluorine-18, which is used to label numerous radiopharmaceuticals for hospitals across Israel for the diagnosis of cancer and other diseases using PET (positron emission tomography) imaging.
