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Abstract Water can become contaminated as a result of a leak from a nuclear facility, such as a waste facility, or from clandestine nuclear activity. Low-level on-line radiation monitoring is needed to detect these events in real time. A Bayesian control chart method, Shiryaev-Roberts (SR) procedure, was compared with classical methods, 3- σ and cumulative sum (CUSUM), for quantifying an accumulating signal from an extractive scintillating resin flow-cell detection system. Solutions containing 0.10–5.0 Bq/L of 99Tc, as T 99 cO 4 − were pumped through a flow cell packed with extractive scintillating resin used in conjunction with a Beta-RAM Model 5 HPLC detector. While T 99 cO 4 − accumulated on the resin, time series data were collected. Control chart methods were applied to the data using statistical algorithms developed in MATLAB. SR charts were constructed using Poisson (Poisson SR) and Gaussian (Gaussian SR) probability distributions of count data to estimate the likelihood ratio. Poisson and Gaussian SR charts required less volume of radioactive solution at a fixed concentration to exceed the control limit in most cases than 3- σ and CUSUM control charts, particularly solutions with lower activity. SR is thus the ideal control chart for low-level on-line radiation monitoring. Once the control limit was exceeded, activity concentrations were estimated from the SR control chart using the control chart slope on a semi-logarithmic plot. A linear regression fit was applied to averaged slope data for five activity concentration groupings for Poisson and Gaussian SR control charts. A correlation coefficient (R 2) of 0.77 for Poisson SR and 0.90 for Gaussian SR suggest this method will adequately estimate activity concentration for an unknown solution. Highlights • Shiryaev-Roberts (SR) procedure uses less volume than classical control charts. • Poisson SR uses least volume but could be confused as a false positive. • Gaussian SR has low false positive rate and continuous increasing trend. • Activity concentration can be estimated from SR control chart slope. [ABSTRACT FROM AUTHOR]

Californium-252 is used as a neutron calibration source for passive neutron correlation counting. Source age and isotopic information are needed to make decay corrections to the neutron emission rate due to the influence of 250Cf. Gamma-ray signatures present in the spectrum from spontaneous fission products and odd-numbered Cf isotopes can be used with high accuracy to confirm or query declared values on a technical data sheet. This method is good practice for independently verifying the content of 252Cf calibration sources. • Demonstrate the use of high-resolution gamma-ray spectroscopy to characterize Cf-252 sources. • Calculate source age from spontaneous fission products and isotopic ratios from odd-numbered Cf isotopes. • Perform associated uncertainty analyses for source age and isotopic ratios. • Confirmation of source age and isotopic ratios from the technical data sheet. [ABSTRACT FROM AUTHOR]