Review of FDOH Lab Data
A review of the instrument quality control charts for all four instruments reported to have been used for the measurements revealed no out-of-control conditions. NAREL also reviewed reports of FDOH’s participation in the Department of Energy’s Mixed Analyte Performance Evaluation Program (MAPEP) for both their fixed and mobile laboratories. All results were within the acceptable ranges.
Further review of the RADIUM.NLB gamma library provided by FDOH revealed some significant differences in gamma-ray intensities compared to the NAREL library:
FL Intensity %
NAREL Intensity %
Relative Difference (%)
These library differences should tend to cause values obtained by NAREL to be lower than those obtained by FDOH for 234Th and 226Ra, and higher for 228Ac. When more than one gamma-ray is found for a radionuclide, both the FDOH and NAREL gamma-analysis software systems calculate a weighted average of the individual results obtained for those gamma-rays. Since NAREL uses consistently lower gamma-ray intensities for all three 228Ac gamma-rays, the average difference between the FDOH and NAREL results can be expected to be most pronounced for 228Ac.
NAREL selected at least one gamma spectrum file provided by FDOH for each of the four detectors reported to have been used for FDOH’s analysis, and reanalyzed the spectra using Genie2K for PCs, version 3.1A. The energy, FWHM, and efficiency calibrations stored in each spectrum file, together with background spectra and the radium nuclide library provided by FDOH. NAREL used the Library (Gamma-M) peak search engine that FDOH stated that they had used and obtained comparable, but not identical, results.
NAREL does not routinely use Genie2K for gamma spectrometry and therefore has not attempted to optimize the many user-definable variables that can affect the results of peak searches and quantitative analysis. At NAREL, all of these parameters remain set to the factory defaults, thus results obtained are not expected to correspond exactly with those obtained elsewhere.
NAREL’s data quality review of FDOH’s data, instrument control charts and spectral files revealed no observable problems or data quality issues. Statistical tests performed on the paired results from FDOH and NAREL showed no significant differences for 226Ra, 40K and 238U/234Th. A statistically significant difference was found for 232Th/228Ra with NAREL’s results being higher than FDOH’s results. While the difference is statistically significant from a measurement perspective, it may have little practical significance given the levels of the radionuclides and the issue being investigated.