Considerations concerning targetry for radioisotope production at the NAC and the production of gallium-67, indium-111 and cadmium-109

Facilities for the routine production of radioisotopes utilizing the high-intensity proton beams of the separated-sector cyclotron of the NAC were developed. A target bombardment station was designed and built to facilitate the rapid exchange of targets. A closed-loop cooling-water system, which is characterized by its flexibility in terms of the independent control of each of three parallel cooling lines, was developed. The system provides for high cooling water flow rates to be maintained in radioisotope production targets requiring high or ultra-low back pressures. The most important considerations in developing a 'standardized' target holder for routine bombardment of solid targets at the NAC were addressed. The resulting target-holder design employs 1 mm thick layers of cooling water, flowing at high velocities across the target surfaces, to cool the target in a very efficient (almost 4π) cofiguration. Excitation functions were also measured to determine and optimize routes for the production of 67Ga, 111In and 109Cd. The well-known stacked-foil technique was used. Various target materials were investigated and several stacks of each were irradiated to cover the proton energy ranges 0-100 MeV (for 67Ga and 111In) and 0-200 MeV (for 109Cd). Thick-target production rates derived from the measured excitation functions were used to develop optimised production routes for the three radioisotopes. A theoretical approach to the development of a suitable production route for a particular radioisotope was evaluated. Theoretical cross-sections were calculated within the frame-work of the geometry-dependent hybrid model of preequilibrium particle emission in combination with the statistical model of equilibrium decay. The computer code ALICE/85/300 was used for this purpose and comparisons between experimental and theoretical cross-sections showed that the code has great potential to be used as a tool in planning an experimental investigation into a production route for a particular radioisotope. 47 figs., 19 tabs., 184 refs