Vendor B Dosimeter (CR-39) Response Curve Demonstrating the Decrease in Sensitivity to Neutrons with Energy Below 100 keV 43 Vendor C Dosimeter (TLD) Response Curve • 45 Schematic Representation of Neutrons Incident on TLD Albedo Dosimeter 46 Vendor D Dosimeter (TLD) Response Curve • 48 Additionally, there are those staff members of the represented power companies and dosimeter vendors whose cooperation and support made this study possible.
Two identical spherical calorimeters, one constructed of carbon (graphite) and the other of A-150 plastic, were used to measure kerma while activation foils of aluminium and gold were used to measure neutron fluence. The calorimeters were constructed specifically for the purpose of measuring neutron kerma. The amount of extraneous material around the calorimeters was kept to a minimum in order to reduce the absorption and scattering of neutrons before they reached the cores of the calorimeters. Neutrons were produced by the rotating target neutron source (RTNS-II) at the Lawrence Livermore National Laboratory, using the d-T interaction. The detectors were placed at an angle of 45<o with respect to the deuteron beam line, where the most probable neutron energy was computed to be 14.6 MeV. The effects of gamma rays and low energy neutron contamination were accounted for, along with the neutron absorption and scattering that occurred in the enclosure, jacket, and core of each calorimeter. The measured value of the kerma factor for carbon was found to be 1.8 ± 0.16 x 10-11 Gy.cm, about 10% lower than the calculated value.
A study of the uncertainty of dosimeter results is required by the national accreditation programs for each dosimeter model for which accreditation is sought. Typically, the methods used to determine uncertainty have included the partial differentiation method described in the U.S. Guide to Uncertainty in Measurements or the use of Monte Carlo techniques and probability distribution functions to generate simulated dose results. Each of these techniques has particular strengths and should be employed when the areas of uncertainty are required to be understood in detail. However, the uncertainty of dosimeter results can also be determined using a Model II One-Way Analysis of Variance technique and accreditation testing data. The strengths of the technique include (1) the method is straightforward and the data are provided under accreditation testing and (2) the method provides additional data for the analysis of long-term uncertainty using Statistical Process Control (SPC) techniques. The use of SPC to compare variances and standard deviations over time is described well in other areas and is not discussed in detail in this paper. The application of Analysis of Variance to historic testing data indicated that the accuracy in a representative dosimetry system (Panasonic® Model UD-802) was 8.2%, 5.1%, and 4.8% and the expanded uncertainties at the 95% confidence level were 10.7%, 14.9%, and 15.2% for the Accident, Protection Level-Shallow, and Protection Level-Deep test categories in the Department of Energy Laboratory Accreditation Program, respectively. The 95% level of confidence ranges were (0.98 to 1.19), (0.90 to 1.20), and (0.90 to 1.20) for the three groupings of test categories, respectively.
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