1.2. Production of Radioisotopes

Abstract

Publisher Summary This chapter describes the production of radioisotopes. At present, radioisotopes of almost every element can be produced, and approximately 200 radioisotopes are commercially available. For most uses, purchase from a commercial supplier is the easiest and most economical way of obtaining radioisotopes; special production should be considered only when the desired characteristics (e.g., short half-life, nonstandard chemical form, exceptional radiochemical purity, or very high specific activity) demand it. The most important characteristics to consider while deciding which radioisotope to use are (1) specific activity, (2) radiochemical purity, (3) chemical and physical form, and (4) chemical purity. Artificial radioisotopes are produced by nuclear reactions. The probability that a nuclear reaction will occur is usually expressed in terms of a cross section σ , which has the dimension of an area. The increase of the concentration of a particular radioisotope under irradiation depends on (1) flux Ф , (2) number of target nuclei n d present at the start of the irradiation, (3) cross section σ 1 , of the target nuclei for the desired reaction, (4) reaction cross section σ 2 , of the product nuclei, which may be destroyed by the capture of further bombarding particles, (5) decay constant λ 1 , of the product nuclei, and (6) irradiation time t. The majority of useful radioisotopes are produced by thermal-neutron capture in a nuclear reactor because the cross sections for these reactions and the availability and cost of thermal neutrons are favorable.