Nuclear reaction modelling: Capture reactions

The (n, γ) reactions can serve as the means of production of some radiopharmaceuticals, either directly (89Sr, 103Pd, 153Sm and others) or via suitable generators and/or precursors (e.g. 125Xe serves as a precursor for 125I). This reactor-based method of production is well established in some cases (89Sr and 125I) but more often, the necessary radionuclide is preferentially produced by other reactions (e.g. see Refs [4.1, 4.2]). A primary aim is not only to create the desired radionuclide but to produce sufficient amounts that are uncontaminated by other isotopes that arise from either the target impurities or competing reactions. Nuclear reactions evolve through several very different regions with increasing incident energy, beginning with the thermal and resonance regions before reaching the continuum. Whereas the thermal and, especially, the resonance regions are of vital importance to isotope production in reactors where the (n, γ) reactions take practically the whole strength, the continuum region is of much less interest because of the very low cross-sections, the main strength being taken away by the open nucleon channels. Correspondingly, experimental data in the continuum are rare, so that reliable predictions of the excitation functions based on model calculations are very important.