S. Musolino, D. T. Coulter, H. Tedla
May 1, 2011
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Health Physics
Abstract
THE NATIONAL Academy of Sciences’ 2008 study evaluated technologies and made recommendations for replacing existing high-activity radioactive materials that might be used for malevolent purposes. Their report recognized the possibility of substituting such materials with nonradionuclide alternatives and developing new technologies; the authors expressed great concern about cesium chloride, including proposing discontinuing its licensing and usage. They also recommended caution in implementing alternatives to ensure the preservation of the original material’s essential functions (NAS 2008). The widespread use of cesium chloride is a vital component of radiobiological and medical research and of clinical medicine, so that any decision to eliminate its use has far-reaching implications in these fields. Currently, and for the near future, there is no alternative to it in many applications. The Cs monoenergetic spectrum has been the reference standard for radiobiological research for over 60 y and is the basis for national and international standards for dosimetry and instrument calibration; it cannot simply be replaced by x-rays. Indeed, any move away from using the Cs spectrum would necessitate years of repetition of impractical and fundamental radiobiological studies to redefine and verify another standard. Its elimination would impose great difficulties and financial hardship on clinical-medical applications. There is no obvious alternative to it for the millions of radiation instruments requiring frequent calibration and whose use is essential for regulatory compliance to protect people and the environment and for homeland security. Indeed, the outright removal of cesium chloride would create havoc. While there are viable options for some procedures that are not spectrumdependent, such as blood irradiation, using accelerators and x-ray machines is expensive, much less reliable, and their maintenance is very costly. Furthermore, most operators do not want these machines in hospitals where space is at a premium because typically they encompass three times more space to accommodate their chillers and associated equipment. It is common knowledge that the intelligence community has reported that terrorist groups have expressed interest in carrying out radiological terrorism. To deal with this threat, the Nuclear Regulatory Commission issued Emergency Orders in 2005, including one that required Increased Controls to upgrade the security of high-activity sources of radioactive materials (Table 1, U.S. NRC 2005). Subsequently, licensees nationwide implemented these requirements, thereby vastly reducing the risk of a malicious diversion. So what would happen if there were a terrorist incident with radioactive material? The dispersal pattern inevitably would be a function of the following parameters (Harper et al. 2007):