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Determination of Uranium Series Activity Before Secular Equilibrium Is Established

Wilson, Charles A. IV1; Matthews, Kenneth L. II2; Hamideh, Amin M.3; Wang, Wei-Hsung4

doi: 10.1097/HP.0000000000001073

Timely achievement of uranium series’ secular equilibrium is not always feasible. Our objective is to mathematically justify methods for early uranium series gamma spectroscopy measurements that can accurately predict naturally occurring radioactive material equilibrium activities long before equilibrium is established. It was believed that, regardless of prior 222Rn escape, after sealing a sample for a few hours the activities of 222Rn, 226Ra, and 238U could theoretically be determined with a single measurement of both 214Pb and 214Bi. However, when accounting for error, this theory did not work as expected (CV = 14.0 in 226Ra simulation). A similar approach published by Li et al. in 2015 proved to be much more reliable with the error considered, using 214Pb activities measured at two different times gave significantly improved results when tested the same way (CV = 0.29 in 226Ra simulation). Because both 214Pb and 214Bi activities are typically available when using gamma spectrometry, we combine these approaches and further increased the accuracy of the calculated activities (CV = 0.21 in 226Ra simulation).

1Louisiana State University Center for Advanced Microstructures and Devices (CAMD)

2Louisiana State University Department of Physics and Astronomy

3Louisiana State University Radiation Safety Office

4Louisiana State University Center for Energy Studies.

The authors declare no conflicts of interest.

Charles A. Wilson IV is the radiation safety officer at Louisiana State University’s Center for Advanced Microstructures and Devices (CAMD). He recently earned his Ph.D. studying environmental health physics in the Department of Environmental Sciences at LSU. He earned his master’s degree in medical physics and health physics from LSU in 2012. Charles was President of the Deep South Chapter of the HPS and a former Chair of the HPS Student Support Committee and Society Support Committee. He presently serves on the Program Committee and the IRPA task force. His email is

Online date: May 21, 2019

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