Measurement of radionuclides in biological tissues from occupationally exposed individuals
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Keratinous materials have the potential to be used in criminal investigation of individuals who participate in nuclear smuggling or in the production of clandestine nuclear weapons. To develop the keratin biomonitor, its response to well-documented actinide exposures needs to be studied. In addition to measurement of actinide concentrations, the isotope ratios 240Pu/239Pu, 235U/238U, and 236U/238U provide information that is useful for discriminating between actinide sources and americium measurement may provide information on the grade of the plutonium material an individual was exposed to. The measurement of radionuclides in brain tissue is of interest to the health physics community for developing internal dosimetry models. Examining the concentration of radionuclides in brain tissues may allow researchers to access the neurological outcomes associated with chronic internal exposure to radiation. ICP-MS analysis allows easy and accurate analysis of multiple elements. This work developed inductively coupled plasma mass spectrometry-based methods to measure the radionuclides 226Ra and 239Pu in brain tissue samples. This dissertation presents three methods to measure ultra-trace radionuclides in biological tissues. The methods involve chemical separation of radionuclides from matrix before analysis on inductively coupled plasma mass spectrometry (ICP-MS) instrumentation. Extraction chromatography, quadrupole ICP-MS, and multi collector ICP-MS were used to analyze plutonium, uranium, and americium in brain, hair, and nail tissues. Cation exchange chromatography and multi collector ICP-MS was used to measure radium in brain issue. Concentrations of 239Pu, 238U, and 241Am were measured in hair and nail samples from occupationally exposed individuals suggesting that hair and nail are a long-term excretion pathway for these actinides. The 240Pu/239Pu isotopic ratios indicated an exposure to weapons-grade plutonium. In several cases measured 235U/238U atom ratios were not consistent with natural uranium composition and 236U was measured indicating exposure to reprocessed uranium. The 239Pu concentration was measured in the right cerebral lobe of a former nuclear worker and the 240Pu/239Pu ratio was consistent with of weapons grade Pu. Results were consistent with previous alpha spectrometry measurement of the same sample. The concentration of 226Ra was measured in various regions of the brain tissue of a radium dial painter worker. This study found that 226Ra was uniformly distributed among cerebral gray matter, corpus collosum, and cerebellum tissue. The 226Ra concentration in cerebral white matter was elevated compared to other regions and mildly reduced in the brainstem. The concentrations of 226Ra and strontium in brain tissues were correlated, suggesting that they are transported across the blood brain barrier via the same mechanism.
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Ph. D.