ARTIFICIALLY CREATED RADIOISOTOPES have been available for biological and medical studies since 19351 when they were first produced by cyclotron bombardments. Since the end of World War II and since the volumed production of isotopes by nuclear reactors as well as cyclotrons, they have been available for much more widespread use. In the past few years, these materials have been distributed in ever-increasing numbers of shipments from the Oak Ridge reactor facilities. Through the efforts of a number of drug companies, which have taken over standardization and preparation of pharmaceutical grade products from the Oak Ridge materials, many of the isotopes are available now in convenient form for use of a qualified physician, even though he may have relatively limited radioisotope laboratory facilities.
There are over 100 elements in the periodic table, and radioisotopes of each of these are available. A great many of them are of convenient