Determination of Nb-93m content in pressure vessel steel by liquid scintillation counting 1069 views

<p>The unintended presence of low niobium (Nb) impurity&nbsp;levels in reactor pressure vessel steels suggests the&nbsp;possibility of Nb's use as a fast neutron in-situ dosimeter,&nbsp;using the Nb⁹³ ( n, n') Nb^93m reaction.</p> <p>This project investigated the use of a Liquid&nbsp;scintillation Counter (LSC) to measure very low Nb⁹³&nbsp;activities. The first phase of this project involved the&nbsp;development of a UVA Nb solution standard in order to&nbsp;establish both counting efficiencies and "quench" for Nb in&nbsp;the LSC. In the second phase, Nb was radiochemically&nbsp;separated from "typical" U.S. pressure vessel steels that&nbsp;had been neutron-activated for the University of California&nbsp;at Santa Barbara. Finally, an enhanced Beckman LS200 LSC&nbsp;was used to determine the Nb^93m activity obtained from&nbsp;various steel samples of interest.</p> <p>The Minimum Detectable Amount (MDA) (95% confidence&nbsp;interval) for Nb^93m was determined to be o. 04 ± o. 01 Bq/g for&nbsp;a counting period of 100 hours, in the presence of typical&nbsp;impurity levels of iron and tantalum. Unfortunately, even&nbsp;though this low MDA indicates that much of the Nb^93m activity&nbsp;data collected are valid, poor reproduction of the radiochemical&nbsp;separation procedure, and the minute Nb levels in&nbsp;U.S. pressure vessel steels did not permit elemental Nb&nbsp;determination. Therefore, calculation of exposed neutron&nbsp;fluence and use as an in-situ dosimeter are not possible.&nbsp;&nbsp; </p>

MSNE (Master of Science Nuclear Engineering)

Pressure vessels; Niobium; Liquid scintillation counting

English

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1992-01-01