Graduate Thesis Or Dissertation
 

The use of delayed neutron counting for uranium analysis in biological tissue and its application to a pharmacokinetic study in weanling rats

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  • Delayed neutron counting (DNC) is a variation of neutron activation analysis applicable only to fissionable elements. Briefly, it involves exposing a sample to the neutron flux in a reactor to induce fission, then quickly retrieving the sample to count the delayed fission neutrons emitted. These are proportional to the amount of the fissionable element in the sample. This technique has been used for over two decades to assay uranium in geological and water samples. I investigated its applicability to biological tissues, specifically soft tissues and bones. Only the simplest sample preparation was required. Samples needed only to be freeze dried , weighed and encapsulated in polyvials before activation. This allowed rapid preparation of large numbers of samples at low cost (about half that of conventional chemical analyses). The minimum level of detection (MLD) for ¹/₂ gram samples was about 10 nanograms for natural uranium. Precision was comparable to values attained for other methods of uranium analysis. Accuracy was determined by using a relative accuracy. Prepared standard solutions were analyzed for uranium content by an outside laboratory and then all counting data were compared to these values. The effects on precision and accuracy of a variety of factors in sample preparation, activation, and neutron counting were evaluated. DNC appears to have substantial advantages for uranium analysis over conventional methods, while achieving similar precision, accuracy, and MLD. The DNC method was used to study the uptake, distribution, and clearance of an acute dose of uranium in weanling rats. The dose was administered by gavage. Animals were killed and various tissues were collected at several times post gavage. The absorption of uranium in the GI tract occurred primarily in the stomach within 15 minutes, and appeared to be dependent upon the acidity of the stomach contents. Uranium absorbed from the GI tract entered the blood and deposited in the skeleton. Uptake and loss in the skeleton followed two patterns. A transitory uptake was observed in the skull, while a slower, longer term uptake associated with bone growth or degree of bone mineralization was observed in the remainder of the skeleton. Uptake and loss in the kidney followed a similar pattern as observed for the skeleton (excluding the skull). In addition, the relative distribution of uranium in the skeleton, i.e., the fractional burdens of the individual bones of the skeleton, appeared to be independent of time post gavage, age, route of administration, and sex.
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