Preparation of Radioisotopes and Labelled Compounds:

During early days in the beginning till 1940, radioisotopes were isolated from naturally occurring radioactive decay series of uranium and thorium.  In 1913 George de Von Hevesy first isolated ²¹⁰Pb from uranium decay series and used it for the determination of solubility of PbSO₄.  However, it was only after 1934 that extensive efforts were made to prepare radioisotopes by suitable nuclear reactions.  Majority of radioisotopes used by analytical chemists are man made and so there is a need for their preparation from stable target materials. The production of radioisotopes involves target preparation, irradiation, target processing, and isolation and specification of the radioisotopes including determination of its specific activity.  The handling of radioisotopes requires special techniques and care.

In India, sole supplier of radioisotopes is Board of Radiation and Isotope Technology (BRIT), Mumbai. Actually these are made by neutron irradiation in a nuclear reactor such as APSARA and CIRUS at the Bhabha Atomic Research Centre (BARC), Mumbai and processed by the Isotope Group of BARC, Mumbai. Most common method of preparing radioisotopes is by neutron irradiation. This topic will be dealt in more details in the next Unit 13 where its analytical aspects will be discussed.

Availability of high fluxes of 10¹² - 10¹³ n.cm^-2 s^-1 at these reactors makes it possible to produce high level of radioactivity required by analytical chemists. Some radioisotopes have ¹³⁷Cs and ¹³¹I are also separated from fission products of uranium in a nuclear reactor. However, if some workers need specific radioisotopes for research or other purposes these may be imported from UK, USA or other countries.