Determining a Correlation in Field and Lab Measurements of Cs-137 Concentrations in Deer at the Savannah River Site

Abstract

The Savannah River Site (SRS) hosts controlled hunts on their land to help control the population of deer and wild pigs. All of the animals harvested are measured for Cs-137 in the field to estimate the dose the hunter could receive from that animal. Flesh samples are taken from every tenth animal and sent to an onsite radiological lab for more sensitive measurements of the Cs-137 concentrations. The dose a hunter may receive from the deer or hogs is calculated using the field data; however, over the past few years, this data was found to be biased and lower than the lab data. Previously, this bias was adjusted by using a correction factor based on the weight of the animal. Over the summer, a comparison of the data from measured deer/hog samples was performed in an attempt to find a better correlation between the field and lab data to replace the current correction factor. Data from the past three years were used to help look at the possible sources of bias in the field data. A comparison between the NaI(Tl) detector readings and the source concentrations during calibration found a strong linear relationship. There was no correlation found between the weight of the deer and the readings from both the field and the lab. A definitive correlation was not found and two new correction factors were determined based on the concentration levels. For concentration below 2.00 pCi/g the correction factor is 1.44, and above 2.00 pCi/g the factor is 1.56. The previous weight-based correction factor was not technically correct and was replaced by the new correction factors based on concentrations. The new concentration-based correction factors will need to be revised on an annual basis as more data is collected. Funding Source: Department of Energy