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Executive Summary The Committee's mandate was: to evaluate the reliability of film badge results for personnel exposed to radiation during the atmospheric testing of nuclear weapons between 1945 and 1962; to recommend optimum procedures for deriv- ing best estimates of doses received by persons wearing them; and to quantify the uncertainty associated with these estimates. To accomplish these objectives the Committee reviewed volumes of reference reports and archival data for each of the nineteen test series, including examina- tion of a representative number of original films. The Committee identified, categorized, and quantified sources of uncertainty and developed a method for combining them into overall estimates of series-specific bias and uncertainty. The method allows uncertainty to be expressed as a continuous function of exposure.) Bias and uncertainty parameters for this function were determined for each test series. Even for early and less completely documented test series, the Committee found that estimates of exposure can be established within 95% confidence limits that rarely exceed a factor of 2 (i.e., from two times the exposure at the upper limit, to one-half the exposure at the lower limit) of the best exposure estimate. Usually this factor is less than 1.5. At very low exposures, relative uncertainties in film badge readings are largest, but these low exposures contribute very little to the accumulation of a substantial total exposure. When the term "exposure" is italicized it refers to the intensity of tic or gamma rays at the point in question. See Section 4.H for a more detailed deh~nitic~n. 1
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2 FILM BADGE DOSIMEIRY IN ATMOSPHERIC NUCLEAR TESTS The Committee applied methodology developed by the International Commis- sion on Radiation Units and Measurements to convert exposure measured by film badges (expressed in R) to dose equivalent (expressed in rem). The quantitative value of the deep-dose equivalent is 70 to 80% of the value of the exposure. Thus a best estimate of an exposure of 1 R converts to a best estimate of a deep-dose equivalent of 0.7 to 0.8 rem. Thus all previously reported values based on 1 rem/R were overestimated. The Committee had great difficulty in devising an optimal method for dealing with exposures reported as zero or less than the minimum detectable level (MDL) established for a particular film badge emulsion during a particular test series. The second recommendation that follows addresses this situation. The Commit- tee notes that the film badge readings reported as less than the MDL rarely can be realistically construed to contribute a total deep-dose equivalent of more than a few hundred millirem when the maximum number of reports at less than the MDL in any one individual's record are considered. The following paragraphs contain abbreviated summaries of the conclusions and recommendations of the Committee as a result of this study. The complete version of the conclusions and recommendations are presented at the end of this report. The text of the report develops the rationale relevant to each and should be referred to for a better understanding of the intent of the Committee in making these conclusions and recommendations. CONCLUSIONS Tractability of the Problem: Although not complete, extensive documentation is available. Despite deficiencies, it is possible to estimate dose equivalents for participants with reasonable certainty. A method is presented for doing so. Gamma Radiation from Fission Products and Activation Products: Exposure of participants was due primarily to x and gamma radiation; beta radiation and neutrons were not significant in terms of deep-dose equivalent. Capabilities and Limitations of Film Badge Dosimeters: While film badges improved throughout the period, they were adequate and reliable from the begin- ning of testing, particularly for measurement of exposures above 0.1 R. The reliability and precision generally improved throughout the period of testing. Bias and Uncertainty: Vanous sources of bias and uncertainty were identified, evaluated, and quantified on a series-specific basis. While the uncertainty in- creases with lower exposures, the overall uncertainty was small enough to make the data useful for consideration of potential biological effects in an individual participant. Methodology for Assessing Bias and Uncertainty: A method is presented for assessing bias and uncertainty in film badge exposure readings and for converting
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EXECUTIVE SUMMARY them to deep-dose equivalent values. This method is reasonable and of poten- tially broader application. Minimum Detectable Exposure Level: The minimum detectable level of radiation exposure can be established by a procedure presented in this report. For most test series, the minimum detectable level was determined to be approxi- mately 40 mR. Conversion from Exposure to Deep-dose Equivalent Deep-dose equivalent is the quantity of interest in evaluating the potential for biological effects from the radiation received by an individual involved in the weapons test series. Conver- sion from film badge readings to deep-dose equivalent is a necessary element in the evaluation of a participant's radiation exposure history. Hence the conversion method is included in this report RECOMMENDATIONS 3 The Committee recommends that the bias (B) and the uncertainty (K) be established for each reported exposure that is under investigation. The method for determining the bias and uncertainty is thoroughly discussed and tabulations of bias and uncertainty are included for each test series. Final evaluation of a participant's exposure should include the reporting of the B and K values and the conversion to deep-dose equivalent. The recommendation of the Committee is to allot one-half of the MDL for each zero appearing in the record when attempting to determine the total deep-dose equivalent. This will overestimate the true deep-dose equivalent and may not be appropriate under special circumstances as described in the body of the report. The recommended procedure for summing multiple film badge readings is included in the report. The total deep-dose equivalent can be represented as the sum of the individual deep-dose equivalents obtained from individual readings, estimating the upper and lower bounds of the range of uncertainn,r by summing the upper and lower confidence limits of the individual assessments. !
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