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Dr Leonard Dietz, MS, Bio Retired research physicist with 30+ years at Knolls Atomic Power Laboratories in Schenectady, New York, 1955 – 1983. The mass spectrometer laboratory routinely analyzed 24-hour urine collections from radiation workers for their uranium content. Influential in development of Mass Spectrometry and assists UMRC in the development of methodology and interpretation of data. Mr. Dietz is also active in presentation and publication of research findings. Methodology and the Difficulties of Testing for DU
Natural uranium contains three isotopes of atomic masses (U234, U235 and U238); DU contains these three isotopes - plus a trace amount of U236. More than 99% of the uranium, whether depleted or natural, consists of U238. The U234, U235 and U236 isotopes exist in different, but known, proportions in both depleted and natural uranium. The different ratios of the isotopes are unique fingerprints that allow the DU fraction to be calculated accurately, even though it always is mixed with natural uranium. A typical concentration of natural uranium in urine is 0.1 part per billion, or 0.1 microgram (millionth of a gram) of natural uranium per liter of urine. Its concentration can fluctuate in a given individual. For different individuals it can vary over a range of 0.01 to 1.0 microgram per liter. It is well known that almost all of the DU particles formed when a high velocity cannon penetrator hits armor are in a ceramic uranium oxide form, which has very low solubility in lung fluid. The biological half-life for ceramic DU particles in the lung is 4 years at least. The low solubility makes it difficult for the chemist to insure that all of the DU is dissolved before extracting uranium from the urine sample. Starting with 0.5 liter or even 1.0 liter of urine, the chemist evaporates the liquid down to near dryness. Then the residue is processed with some very corrosive chemical reagents: hydrofluoric acid, perchloric acid, a mixture of concentrated nitric and hydrochloric acids, and other powerful chemicals. This is to insure that all of the ceramic DU is dissolved. This whole process is very time-consuming and for safety reasons the chemistry must be done with great care in a well-ventilated fume hood. Every sample that is analyzed is a separate scientific experiment and must be calibrated against a uranium standard. Chemical reagent blanks must be run periodically. In case a bioassay sample tests positive for the presence of DU, a second run of the sample is made on the mass spectrometer to verify the first result. These additional mass spectrometer analyses are necessary to keep the measurement process under tight control and they rarely show up in the final reported analytical results. We are very lucky to have university laboratories that are willing and qualified to do this kind of scientific isotope analysis of DU. One cannot just send a few liters of urine to any laboratory and expect to receive accurate results. The geochemist at the Canadian laboratory had to spend a significant amount of time developing a reliable chemical separation technique before she began to do the DU bioassay analyses. The other factor to consider is that the DU analysis is just a minor fraction and is not the reason the laboratory is in business. Its mission is to support geology research and not only DU research. Surface ionization mass spectrometers exist largely in government atomic energy facilities and in some universities, not typically in commercial laboratories. Not many universities are willing to accept samples from outside researchers. Everyone must appreciate the high quality scientific work that the scientists and chemists are doing, so patience is called for. Trying to put pressure to get faster results can only be counterproductive and will slow down the work. |
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