Cyclotron particle

The cyclotron accelerates charged particles in a spiral path to high energies, crucial in nuclear physics and medicine.

About this subject

The cyclotron is a particle accelerator invented by Ernest Lawrence in 1932, for which he won the Nobel Prize in Physics in 1939. Unlike linear accelerators, it uses a constant magnetic field and an oscillating electric field to make particles move in spiral paths, gaining energy each turn. This compact geometry allows energies up to tens of MeV (megaelectron-volts) for protons and light nuclei, making it essential in nuclear physics research and the production of radioisotopes for medical imaging, such as FDG in PET scans.

Acceleration occurs inside two hollow metal D-shaped electrodes called 'dees', immersed in a perpendicular magnetic field. Every half-cycle, the polarity of the dees reverses, pushing the particle to the opposite dee. The electric field frequency is tuned to the cyclotron frequency (ω=qB/m) to maintain synchrony. The 'lo-fi disposable camera' style evokes the aesthetic of experimental records from the 1930s to 1960s, when disposable cameras captured sparks and tracks in cloud chambers, associated with the discovery of new particles.

Beyond fundamental research, modern cyclotrons are used in proton therapy for cancer treatment, delivering high-precision beams. The largest cyclotron ever built, at Los Alamos National Laboratory, was 18 meters in diameter. Interestingly, Lawrence's idea was based on a concept by Norwegian physicist Rolf Widerøe, but the practical implementation and experimental success came from Lawrence and his student M. Stanley Livingston.

Frequently Asked Questions

What is the difference between a cyclotron and a linear accelerator?

In a cyclotron, particles follow a spiral path under a constant magnetic field and an oscillating electric field, allowing continuous acceleration in a compact space. In a linear accelerator, particles travel a straight line through multiple electrodes, usually requiring a longer length.

How is a cyclotron used in medicine?

It produces short-lived radioisotopes like fluorine-18, used in PET scans. It also forms the basis for proton therapy, a cancer treatment that precisely irradiates tumors.

Can particles in a cyclotron reach the speed of light?

No, because relativistic effects increase effective mass, altering the cyclotron frequency. For very high energies, a synchrocyclotron or other accelerators that adjust the frequency are used.