Читать книгу Essentials of Nuclear Medicine Physics, Instrumentation, and Radiation Biology - Rachel A. Powsner - Страница 65

Cyclotrons are circular devices (Figure 3.5) in which charged particles such as protons and alpha particles are accelerated in a spiral path within a vacuum. The power supply provides a rapidly alternating voltage across the dees (the two halves of the circle). This produces a rapidly alternating electric field between the dees that accelerates the particles, which quickly acquire high kinetic energies. They spiral outward under the influence of the magnetic field until they have sufficient velocity and are deflected into a target.

Figure 3.2 Transient equilibrium.

Figure 3.3 Transient equilibrium in a ⁹⁹Mo–^99mTc generator.

A deflector is used to direct the particles out through a window of the cyclotron into a target. Some of the particles and kinetic energy from these particles are incorporated into the nuclei of the atoms of the target. These energized (excited) nuclei are unstable.

Figure 3.4 Secular equilibrium.

Figure 3.5 Cyclotron.

Indium‐111 (¹¹¹In) is produced in a cyclotron. The accelerated (bombarding) particles are protons. The target atoms are cadmium‐112 (¹¹²Cd). When a proton enters the nucleus of a ¹¹²Cd atom, the ¹¹²Cd is transformed into ¹¹¹In by discharging two neutrons. This reaction can be written as:

or

Other examples of cyclotron reactions include ¹²¹Sb(α,2n)¹²³I, ⁶⁸Zn(d,n)⁶⁷Ga, and ¹⁰B(d,n)¹¹C, where the symbols α and d denote alpha particles and deuterons (proton plus neutron) respectively.