Chapter 7.17.1. Radiochemical Analysis and Radioactivity Measurements

All nuclear instrumentation is calibrated with standard sources obtained from or traceable to the National Institute of Standards and Technology (NIST). The equipment is usually checked daily with secondary counting standards to ensure proper operation. Samples are periodically analyzed in duplicate or with the addition of known amounts of a radionuclide to check precision and accuracy. When a nuclide was not detected, the result is given as "less than" (<) the detection limit by the analytical method used. The detection limits were chosen so that the measurement uncertainty at the 95 % confidence level is equal to the measured value. The air and water detection limits for all radionuclides for which measurements were made are given in Table 7. 1. The relative error in a result decreases with increasing concentration. At a concentration equal to twice the detection limit, the error is about 50% of the measured value and at ten times the detection limit, the error is about 1O %.

Average values are usually accompanied by a plus-or-minus (±) limit value. Unless otherwise stated, this value is the standard error at the 95 % confidence level calculated from the standard deviation of the average. The ± limit value is a measure of the range in the concentrations encountered at that location; it does not represent the conventional uncertainty in the average of repeated measurements on the same or identical samples. Since many of the variations observed in environmental radioactivity are not random but occur for specific reasons (e.g., seasonal variations), samples collected from the same location at different

TABLE 7.1 Detection Limits ______________________________________________________________ Nuclide or Air Water Activity (fci/m3) (Pci/L) ______________________________________________________________ Americium-241 - 0.001 Beryllium-7 5 - Californium-249 - 0.001 Californium-252 - 0.001 Cesium-137 0.1 1 Curium-242 - 0.001 Curium-244 - 0.001 Hydrogen-3 100 100 Lead-2 1 0 1 - Neptunium-237 - 0.001 Plutonium-238 0.0003 0.001 Plutonium-239 0.0003 0.001 Radium-226 - 0.1 Radium-228 - 0.1 Strontium-89 0.1 2 Strontium-90 0.01 0.25 Thorium-228 0.001 - Thorium-230 0.001 Thorium-232 0.001 - Uranium-234 0.0003 0.01 Uranium-235 0.0003 0.01 Uranium-238 0.0003 0.01 Uranium - natural 0.02 0.2 Alpha 0.2 0.2 Beta 0.5 1 ____________________________________________________________

times are not replicates. The more random the variation in activity at a particular location, the closer the confidence limits will represent the actual distribution of values at that location. The averages and confidence limits should be interpreted with this in mind. When a plus-or-minus value accompanies an individual result in this report, it represents the statistical counting error at the 95 % confidence level.

Standard and intercomparison samples distributed by the Quality Assurance Branch of the EPA are analyzed regularly. Results of ANL's participation in the EPA program during 1994 are given in Table 7.2. In the table, the comparison is made between the EPA value, which is the quantity added to the sample by that laboratory, and the value obtained in the ANL laboratory. Certain information may assist in judging the quality of the results, including the fact that typical uncertainties for the ANL analyses are 2 % to 50 %, depending on the concentration and the nuclide, and the uncertainties in the EPA results are 2 % to 5 % (ANL estimate).

In addition, participation continued in the DOE Environmental Measurements Laboratory Quality Assurance Program (DOE-EML-QAP), a semi-annual distribution of four different sample matrices containing various combinations of radionuclides that are analyzed. Results for 1994 are summarized in Table 7.3. In the table, the EML value, which is the result of duplicate determinations by that laboratory, is compared with the average value obtained in the ANL laboratory. Information that will assist in judging the quality of the results includes the fact that typical uncertainties for ANL's analyses are 2% to 50% and that the uncertainties in the EML results are 1% to 30% (depending on the nuclide and the amount present). For most analyses for which the differences are large (>20%), the concentrations were quite low and the differences were within the measurement uncertainties.

TABLE 7.2 Summary of EPA Samples, 1994 _________________________________________________________________ Type of Number Average Difference Sample Analysis Analyzed from Added __________________________________________________________________ Air Filter Total Alpha 1 21 Total Beta 1 33 Strontium-90 1 2 Cesium- 137 1 2 Water Total Alpha 4 34 Total Beta 4 23 Hydrogen-3 2 3 Cobalt-60 3 3 Zinc-65 2 11 Strontium-89 3 4 Strontium-90 3 0 Ruthenium-106 1 9 Iodine-131 1 3 Cesium- 134 3 7 Cesium-137 3 10 Barium-133 2 4 Radium-226 4 2 Radium-228 4 2 Total Uranium 4 6 Plutonium-239 1 5 ___________________________________________________________ TABLE 7.3 Summary of DOE-EML-QAP Samples, 1994 ___________________________________________________________ Percent Difference From EML Value ----------------------------------- Radionuclide Air Filters Soil Vegetation Water _____________________________________________________________ Hydrogen-3 - - - 3 (2) Potassium-40 - 10 (2) 5 (2) - Manganese-54 9 (2) - - 6 (2) Cobalt-57 15(2) - - Cobalt-60 5 (2) - 8 (2) 13 (2) Strontium-90 13(2) 24 (2) 9 (2) 8 (2) Ruthenium- 106 42(1) - - - Antimony-125 6 (2) - - - Cesium-134 14(1) - - 4 (2) Cesium-137 5 (2) 9 (2) 10 (2) 12 (2) Cerium-144 20(2) - - 15 (1) Uranium-234 6 (2) 13 (2) 7 (2) Uranium-238 9 (2) 13 (2) - 9 (2) Plutonium-238 9 (2) 18 (2) 4 1 (1) 9 (2) Plutonium-239 10(2) 6 (2) 1 3 (2) 4 (2) Americium-241 5 (2) 14 (2) 1 1 (2) 3 (2) _________________________________________________________________ Note: The value in parentheses is the number of samples.