SIDEBAR 2.2Reactor and Accelerator Production of Mo-99/Tc-99m

Research reactors and accelerators produce neutrons, protons, and photons for medical isotope production (see Figure 2.2). This sidebar describes the operation and use of these technologies.

Research reactors generate neutrons primarily by fission of U-235 contained in the reactor fuel. These reactors are specifically designed to produce high neutron fluxes, typically on the order of 10¹⁴ neutrons/cm²/s for scientific research, technology development, or production. They have compact cores (typically less than a cubic meter in volume) that are surrounded by graphite, beryllium, or heavy water (deuterium oxide [D₂O]) to moderate (slow down) and reflect neutrons. The core and reflector typically contain numerous empty channels for material irradiations. Uranium or molybdenum targets can be inserted into these channels to produce Mo-99 through the reactions shown in Section 2.3.1.

Accelerators generate ion beams and accelerate them to high energies with oscillating electromagnetic fields. The accelerated particle beams can be used to irradiate various types of targets to produce Tc-99m or Mo-99. For example, Tc-99m can be produced by irradiating a target containing Mo-100 with protons (reaction (5) in Section 2.3.2). Alternatively, an electron beam can be used to irradiate a tungsten target to produce high-energy photons, which in turn can be used to irradiate a target containing Mo-100 to produce Mo-99 (reaction (4) in Section 2.3.2). A deuterium beam can be used to irradiate deuterium or tritium targets to produce neutrons, which in turn can be used to produce Mo-99 via reaction (3) in Section 2.3.2.

Research reactors are ideally suited for producing Mo-99 because of their large irradiation capacities. However, they are expensive to construct, license, and operate, and they produce radioactive waste. Accelerators are less expensive to construct and operate (typically one to two orders of magnitude less expensive than reactors, depending on size and supporting infrastructure) and produce little radioactive waste. However, accelerators cannot match the Mo-99 production capacity of reactors.