Cyclotron and Production of PET Radionuclides

Abstract

99 More than 3000 nuclides are known, of which approximately 270 are stable and the remainder are radioactive. The majority of radionuclides are artificially produced in the cyclotron and reactor. In PET technology, only positron-emitting radionuclides are required, and only a few positron emit-ters of all radionuclides have been suitably utilized in the clinical studies. These radionuclides include 11 C, 13 N, 18 F, 15 O, etc. and are produced in the cyclotron. The operation of a cyclotron and the production of useful positron emitters are described below. Cyclotron Operation In a cyclotron (Figure 6-1), charged particles (S) are accelerated in circular paths within the two D-shaped hollow metallic electrodes called the dees (A and B) under vacuum by means of an electromagnetic field. Charged particles can be either positive ions (e.g. proton, deuteron, a particle) or negative ions (e.g. negatively charged hydrogen atom, H-). The following is a description of a cyclotron to accelerate H-particles (negative ion cyclotrons). The ions are obtained from an ion source (S) positioned at the center of the cyclotron. The ion source is a small chamber located between two negative high-voltage (V) (1 to 3kV) tantalum cathodes. The hydrogen gas flows (4 to 10mL/min) into the chamber. Electrons emitted from the cathodes and constrained by the magnetic field of the main magnet interact with the hydrogen atoms to form a plasma in the chamber that consists of 3 entities: protons, negatively charged hydrogen atoms Hand nd neutral hydrogen atoms. In some cyclotrons, the gas is ionized by applying 20 kV DC, producing proton and H-. Protons or negative hydrogen ions (H-) are pulled out of the ion source chamber through a narrow slit by the electrostatic force depending on the polarity of the dees. The two dees (A and B) are half-pie-shaped, troughlike, hollow copper structures connected to an alternating high-voltage (30KV) oscillator oper