- A cyclotron is a type of particle accelerator that uses a combination of a static magnetic field and a rapidly alternating electric field to accelerate charged particles—typically protons, deuterons, or other ions—to high energies in a spiral trajectory. Invented in 1930 by physicist Ernest O. Lawrence, the cyclotron became a groundbreaking tool in both nuclear physics research and medical applications, particularly in the production of short-lived radioisotopes used in diagnostic imaging and cancer treatment.
- The basic structure of a cyclotron includes two hollow, semi-circular electrodes known as “dees” (because of their D-like shape) placed in a vacuum chamber and positioned between the poles of a large electromagnet. A radiofrequency (RF) alternating voltage is applied between the dees, creating an oscillating electric field in the gap between them. When a charged particle, typically emitted from a central ion source, enters the gap, it is accelerated by the electric field. Once inside a dee, the particle moves in a semi-circular path due to the perpendicular magnetic field, which forces it into a spiral. Each time the particle crosses the gap between the dees, it gains more energy and travels in a larger radius, eventually reaching the outer edge, where it can be extracted and directed to a target or beamline.
- Cyclotrons can produce particles with energies ranging from a few million electron volts (MeV) to several hundred MeV, depending on the design. These high-energy particles are used to bombard target materials, initiating nuclear reactions that generate radioisotopes. In medical applications, cyclotrons are vital for producing positron-emitting isotopes like fluorine-18, carbon-11, nitrogen-13, and oxygen-15, all of which are essential for positron emission tomography (PET) imaging. Because many of these isotopes have very short half-lives (e.g., fluorine-18 has a half-life of about 110 minutes), cyclotrons are often located near or within major medical centers to ensure timely radiotracer production and use.
- Beyond medicine, cyclotrons are employed in materials science, nuclear physics experiments, and radiation therapy, particularly proton therapy for cancer treatment. In this context, cyclotrons are used to generate high-energy proton beams that can be precisely targeted to destroy tumor tissue while sparing surrounding healthy tissue, reducing side effects compared to traditional radiation therapy.
- Modern cyclotrons vary in size and complexity. Compact medical cyclotrons are designed for hospital use and automated to produce radiotracers with minimal operator intervention. Research-grade cyclotrons, on the other hand, are much larger and capable of accelerating a wider range of particles to higher energies. Advances in superconducting magnets, automation, and computer control systems have further improved the efficiency, reliability, and safety of cyclotron operations.
