What Is a Cyclotron?
A Cyclotron is an accelerator for charged particles (negatively charged electrons, positively charged protons, ions, etc.) that repeatedly swirls the charged particles to increase their speed.
A cyclotron is a type of accelerator that accelerates particles by applying a potential difference that switches at high speed to the gap between two straight sections of electrodes (dee electrodes), which are shaped like the letter D in the alphabet.
Uses of Cyclotrons
Cyclotrons are used in a variety of fields to take advantage of the effects that occur when accelerated charged particles collide with a target (e.g., to produce isotopes that do not exist naturally, to modify semiconductors, etc.). One example is the production of short-lived radiolabeled compounds for PET (Positron Emission Tomography).
Radiolabeled compounds used in PET have short lifetimes and must be manufactured in cyclotrons as they are used. Recently, medical facilities are increasingly equipped with small cyclotrons for PET.
Another application is to improve the performance of semiconductors by semiconductor irradiation. Semiconductors can be modified by irradiating them with charged particles to improve their electrical properties.
Other applications include the production of radioisotopes for use in SPECT (Single Photon Emission Computed Tomography), research radioisotopes, radiopharmaceuticals, and nuclear physics research.
Principle of the Cyclotron
Cyclotrons use the force exerted on charged particles as they pass through a magnetic field (Lorentz force). The backbone of a cyclotron is a disk-shaped part consisting of two Dee electrodes in the shape of the letter D. The image of a circular shape is formed by pasting the vertical bars of the D and the flip side D together.
The D electrode is placed in a magnetic field created by an electromagnet. This is to make use of the Lorentz force to move the ions. When a charged particle is introduced into the magnetic field of the cyclotron, the Lorentz force causes the particle to bend and move in a circular orbit. At this time, they will orbit in a circular path along the shape of a disk formed by two dee electrodes.
Halfway around the disk, the particle reaches another dee electrode, at which point a potential difference is created between the electrodes to accelerate the particle. When the particles return to the original electrode after completing half the circumference, the potential difference can be reversed to accelerate them again. This process is repeated to accelerate the charged particles.
As the speed of the charged particle increases, the radius of gyration increases, allowing the particle to be extracted from the periphery of the disk.
Other Information on Cyclotrons
1. Limit of Acceleration
As the speed of the charged particle approaches the speed of light, its mass increases due to relativity effects, making it more difficult to bend. Therefore, the radius increases beyond the initial calculation, and acceleration cannot be achieved as originally designed. Therefore, there is a limit to the acceleration using a cyclotron.
Synchrocyclotrons and synchrotrons were therefore considered. Synchrocyclotrons are cyclotrons that enable acceleration up to high speeds by slowing down the switching of the electric field according to the speed of the ions.
Synchrotrons, on the other hand, are constructed with a different concept than cyclotrons. Unlike cyclotrons, which gradually increase the orbit radius, synchrotrons accelerate by changing the strength of the magnetic field and the period of electric field switching while maintaining a constant circular orbit.
2. Advantages of Cyclotrons
Although cyclotrons have limitations in acceleration, one advantage that synchrotrons do not have is the ability to continuously accelerate particles by pouring them into the cyclotron one after another.
They can also produce high intensity particle beams. These features are suitable for the production of isotopes and the modification of semiconductors, and the features are successfully used in applications.