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- 24 April 2014 11:45 am , Vol. 344 , #6182
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Finding Less Risky Ways to Make Medical Isotopes
13 June 2013 6:10 pm
Is nuclear medicine a cover for countries intent on acquiring nuclear weapons? For years, that question has clouded efforts to expand production of medical radioisotopes, many of which are made in nuclear reactors that run on highly enriched uranium (HEU)—the fissile material in a bomb—or use HEU as targets for generating radioisotopes. A report released today by AAAS, the publisher of ScienceInsider, highlights a growing range of alternative methods of radioisotope production that would make it harder for would-be proliferators to lay hands on fissile material.
The safer methods could help defuse tensions surrounding nations with nuclear ambitions, analysts say. Iran, for instance, has been engaged in a decadelong standoff with the United States and its allies over its nuclear program and has cited the need to produce medical isotopes and power as key justifications for its efforts. One confidence-building measure might be for Iran to explore medical isotope production that avoids using or producing fissile material. In this respect, if U.S. State Department negotiators "can sell the idea of Iran participating in advanced nuclear technologies [that steer clear of fissile material], then maybe you've got something," says Mark Jansson, special projects director at the Federation of American Scientists in Washington, D.C. In laying out the alternatives, the report's authors, he says, "have done a fantastic job."
Radioisotopes are widely used in medical imaging and for irradiating certain kinds of tumors. They were long seen as a dividend of nuclear technology and were an important reason that the world's nuclear powers in the 1950s and 1960s promoted the construction of research reactors around the world. Medical isotopes can also be produced in cyclotrons or spallation neutron sources, for example, but dedicated facilities were prohibitively expensive—until the wide embrace of a technology called positron emission (PE) scanning in the 1980s. High demand for the short-lived medical isotopes used in PE tomography scanning has driven down the cost of hospital-based ion accelerators. As a result, "accelerator technology is far less expensive and more capable than in the past," notes the report, authored by Derek Updegraff and Seth A. Hoedl of AAAS's Center for Science, Technology, and Security Policy.
Their report focuses on the world's most widely used medical isotope: technetium-99m (Tc-99m), which is used in about 80% of all nuclear medicine procedures: some 30 million procedures a year. Tc-99m is popular in nuclear medicine because it is readily incorporated into a variety of chemical compounds that can concentrate the radioisotope in various tissue types for imaging. Hospitals that use Tc-99m purchase its parent radioisotope, molybdenum-99 (Mo-99), which is a decay product of uranium-235. The main way that Mo-99 is now produced is to irradiate uranium targets in a research reactor. It doesn't have to be that way: The AAAS report notes that Mo-99 can be created by a photonuclear reaction on Mo-100, or Mo-99 can be skipped entirely by producing Tc-99m directly by bombarding Mo-100 with protons. The latter approach is now being tested by a cyclotron maker in Canada, the report notes. "The proliferation risk with accelerators is dramatically lower," Updegraff says.