Application of low-background gamma-ray spectrometry to monitor radioactivity in the environment and food

Gamma Radioactivity Detection Limits and Associated Radionuclide Intakes Study in Artificial Human Urine Using Sodium-iodide and High-purity Germanium Detectors

The performance of several gamma detectors was investigated for emergency urine bioassay screening of two radionuclides of concern: 131 I and 137 Cs. Unspiked artificial urine samples were measured for 10 min each on four different gamma detectors: 80% relative efficiency high-purity Ge detector in standard shielding, 102% low-background high-purity Ge detector equipped with top muon shield, 78% high-purity Ge well detector in standard shielding, and 4″ × 4″ NaI well detector in standard shielding. The measured gamma spectra were analyzed in two ways: (1) for the 364-keV peak region of 131 I and 662-keV peak region of 137 Cs and (2) for the total counts in the full energy spectrum (50-2,048 keV). The results were analyzed using the principles of signal detection theory according to the Currie's formalism extended by a complete uncertainty propagation. This enabled calculation of the detection capability in terms of detection limit (Bq L -1 ) of urine, the latter referred to as minimum detectable activity. The NaI well detector had the lowest minimum detectable activities for total spectra, whereas the high-purity Ge well detector had the lowest peak minimum detectable activity values. Minimum detectable inhalation and ingestion intakes from urine bioassay were calculated from the minimum detectable activity values for urine collection 1 d, 1 wk, and 1 mo past the initial intake. The calculated intakes were compared with annual limits on intake. The results are interpreted with respect to a large-scale radiological emergency response.

Application of modern anticoincidence (AC) system in HPGe γ-spectrometry for the detection limit lowering of the radionuclides in air filters

The use of active and passive shields can substantially reduce the Minimum Detectable Activity (MDA) of the γ-ray counting systems, rejecting events induced by cosmic-rays or by environmental radioactivity. However, the size and geometry of the samples lead to limitations in the background reduction in routine measurements. The Minimum Detectable Activity (MDA) values for low energy of γ-ray emitting radionuclides (<200 keV) deposited in three typical air filter geometries have been compared for anticoincidence and single HPGe detector mode of γ-spectrometry systems. The relative increase in the Figure Of Merit (FOM) values from to 10-37% has been achieved for AC counting mode for radionuclides of ²¹⁰Pb, ²³⁴Th, ²³⁵U and ²²⁶Ra deposited on the three kinds of air filters.

Long-term monitoring of radioactivity in fish from New York waters

As part of an environmental surveillance program operated by the New York State (NYS) Department of Health, measurements of various radionuclides in aquatic life (primarily fish) collected from waterways in NYS have occurred for decades. An investigation was undertaken to gain a better understanding of the occurrence, activity levels, and extent of radionuclide variations in aquatic life obtained from local waterways in relation to concentrations reported in fish from sites outside NYS (e.g., Pacific Ocean tuna). The man-made isotopes (137)Cs and (90)Sr were detectable at activities below 1 Bq/kg in the edible portions of fish from most NYS waterways, with the exception of greater activities in fish collected downstream of Brookhaven National Laboratory. Calculated effective doses resulting from eating the fish, estimated as 11-390 nSv/yr for (137)Cs and 0.3-7.9 nSv/yr for (90)Sr, are considered extremely low.