Radionuclide production

This article continues from the earlier article "An Introduction to Nuclear Medicine" where the general principles of nuclear medicine were discussed. Radionuclides are required in both diagnostic and therapeutic nuclear medicine procedures. Naturally occurring radionuclides are generally not suitable for diagnostic and therapeutic procedures due to their typically long half-lives or less than ideal physical or chemical characteristics; therefore appropriate radionuclides need to be produced. The common methods of radionuclide production for nuclear medicine include: fission, neutron activation, cyclotron and generator. Fission occurs in a nuclear reactor where neutrons are used to bombard fission nuclides such as uranium-235 (235U) or plutonium-239 (239Pu). Fission results in the splitting of the large nucleus into smaller fission fragments along with the release of gamma radiation and high energy neutrons. Neutron activation also takes place in a nuclear reactor. The neutrons are used to bombard stable nuclides to form other radionuclides. There are disadvantages with this process so other production means are oft en preferred. Cyclotrons are used to accelerate charged particles such as protons (p), deuterons (d), triton (t) and alpha (alpha) particles to high velocities to penetrate the orbital electrons of the target atom and interact with the nucleus. Generators produce the most commonly used radionuclide in nuclear medicine, technetium-99m (99mTc). The radionuclide generator sees the decay of a long half-life parent radionuclide to a short half-life daughter radionuclide. The daughter is the radionuclide used in nuclear medicine. An understanding of radionuclide production will assist in the understanding of both diagnostic and therapeutic nuclear medicine procedures.