High purity materials as targets for radioisotope production: Needs and challenges

摘要

Radionuclides have become powerful and indispensable tools in many endeavours of human activities, most importantly in medicine, industry, biology and agriculture, apart from R&D activities. Ready availability of radionuclides in suitable radiochemical form, its facile detection and elegant tracer concepts are responsible for their unprecedented use. Application of radioisotopes in medicine has given birth to a new branch, viz. nuclear medicine, wherein radioisotopes are used extensively in the diagnosis and treatment of variety of diseases including cancer. Artificial transmutation of an element employing thermal neutrons in a reactor or high energy particle accelerators (cyclotrons) are the routes of radioisotope production world over. Availability of high purity target materials, natural or enriched, are crucial for any successful radioisotope programme. Selection of stable nuclides in suitable chemical form as targets with desired isotopic and chemical purity are among the important considerations in radioisotope production. Mostly the oxide, carbonate or the metal itself are the preferred target forms for neutron activation in a research reactor. Chemical impurities, particularly from the elements of the same group, put a limitation on the purity of the final radioisotope product. Whereas the isotopic impurities result in the production of undesirable radionuclidic impurities, which affect their effective utilization. Isotope Group, BARC, is in the forefront of radioisotope production and supply in the country, meeting demands for gamut of radioisotope applications indigenously for over four decades now. Radioisotopes such as 131I, 99Mo, 32P, 51Cr, 153Sm, 82Br, 203Hg, 198Au etc are produced in TBq quantities every month and supplied to several users and to Board of Radiation and Isotope Technology (BRIT). Such a large production programme puts a huge demand on the reliable sources of availability of high purity target materials which are at present mostly met through import. Availability of suitable target materials, their purity considerations and our efforts in finding sources of raw materials for sustaining the radioisotope programme are discussed here.