Quality assurance of temporal variability of natural decay chain and neutron induced background for low-level NORM analysis

Twenty-one high purity germanium (HPGe) background spectra were collected over 2 years at Los Alamos National Laboratory. A quality assurance methodology was developed to monitor spectral background levels from thermal and fast neutron flux levels and naturally occurring radioactive material decay series radionuclides. ²³⁸U decay products above ²²²Rn demonstrated minimal temporal variability beyond that expected from counting statistics. ²³⁸U and ²³²Th progeny below Rn gas displayed at most twice the expected variability. Further, an analysis of the 139 keV ⁷⁴Ge(n, γ) and 691 keV ⁷²Ge(n, n') spectral features demonstrated temporal stability for both thermal and fast neutron fluxes. (author)