TABLE OF CONTENTS Upon determining the production reaction and irradiation conditions, one must select an appropriate target material. Indeed in special cases, for example when reaching very high specific activity or ultra high purity is the goal, the effort required in target design can be as demanding as the rest of the experiment. There are several general factors to be considered.
Pure metals or elements are generally best. If these are not suitable due to the constraints below, favorable materials also include alloys as well as simple compounds such as oxides, carbonates, halides, etc. The form must also be compatible with post-irradiation processing. Thus, easily dissolved compounds are sometimes preferable over metal targets.
There can be substantial sample heating during irradiation. Incident particles impart energy and some nuclear reactions are exothermic. Although thermal neutrons do not transfer much energy, fast neutrons can. Additionally, some of the energy of prompt gammas from (n, ?) reactions generated in the sample, fuel elements, reactor containment, and other nearby samples can be absorbed in the sample. The gamma heating is proportional to sample mass and can be substantial for samples in excess of a gram. Target cooling is thus essential in reactors in order to prevent target overheating and possible destruction. In addition, the target material should have good thermal conductivity and a high melting point. For these reasons organic compounds and aqueous solutions cannot usually be used.
The target must not decompose...
