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Operations & Facilities

What is an Isotope?

Radioactive isotopes are widely used in basic and applied science and engineering, most notably as environmental and industrial tracers, and for medical imaging procedures. The majority of the radioisotopes in use today are artificially created by the bombardment of a stable chemical element or compound with subatomic particles in either a particle accelerator or a nuclear reactor such as MNR. Reactor-based radioisotope production relies on the (n,y) nuclear transformation that occurs when a suitable target material is exposed to the neutron flux in the reactor core. An example of this is the production of lutetium-177 from lutetium-176.

Schematic representation of neutron capture event and direct production of radioisotopes.

A variation on this method is to generate a short-lived radioisotope that undergoes radioactive decay to yield the longer-lived radioisotope of interest. This strategy is used for the production of high specific activity iodine-125, which is a beta- decay product of xenon-125 formed when xenon-124 captures a neutron. A wide variety of radioisotopes can be produced at MNR by neutron irradiation of appropriate target materials.

Schematic representation of neutron capture event and indirect production of radioisotopes.

A wide variety of isotopes can be made at the McMaster Nuclear Reactor using by placing samples in-core or using the various “Rabbit” systems. Several well characterized sites with varying neutron fluxes are available for use, with graphite or beryllium reflected sites, or lead-shielded sites. Depending on the nature of the sample, cadmium lining is also available for fast neutron irradiations. To learn more about isotopes previously made in the reactor, check out the core irradiation page, or for specific questions contact

Reactor core schematic with the various irradiation sites available for isotope production