Film Badge Dosimetry in Atmospheric Nuclear Tests (1989) / Chapter Skim
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5 Quantification of Personnel Film Badge Uncertainties
5 Quantification of Personnel Film Badge Uncertainties
Pages 61-79
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From page 61... ...
The uncertainty assessment is accomplished by developing an approach for calculating upper and lower limits for the exposure and deep-dose equivalent based on any film badge reading obtained during atmospheric nuclear tests. The method of calculation is intended to assure that there is a high probability that the limits include the actual exposure and deep-dose equivalent received by the individual.
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From page 62... ...
The assessment in this report is based on the use of lognormal distributions for describing uncertainties from individual sources. The lognormal distribution is one in which the logarithms of the estimated values follow symmetric normal distributions, and is symmetric on a multiplicative scale; that is, the probability that an estimated value exceeds F times the median value, is the same as the probability that a value is less than 1/F times the median value.
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From page 63... ...
represents a much greater amount of uncertainty; the range 0.25 to 4 is now required to cover 95% of the probability. Combining Several Sources of Uncertainty in One Badge Reading The approach used to combine uncertainties is based on the assumption that the uncertainties from specific sources follow independent lognormal distributions.
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From page 65... ...
It is useful to define the GSD and 95% uncertainty factor from source i as Si and Ki respectively, where Si = e i, Ki = Sit 96, and to define the overall GSD and 95% uncertainty factor by S = es and K = Sib, respectively. Example: A film badge reading, obtained in test A, provides an exposure estimate of O.X R
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From page 66... ...
Special Problems in the Application of Uncertainty Analyses to Film Badge Dosimetry Because uncertainties in film badge readings are often expressed in a form that is symmetric on an additive scale (e.g., + 50%) , the use of the lognormal distribution in this report merits comment.
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From page 67... ...
P% limits for the individual film badge readings may in many cases provide useful limits, especially if the number of readings is small and/or the estimated exposures are small. The confidence level associated with such an interval will be 2 P%, and, because intervals obtained in this manner do not account for possible cancelling of uncertainties as exposures are summed, they will generally be wider than necessary.
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From page 68... ...
Even under the best controlled laboratory conditions, laboratory uncertainties are a strong function of exposure level, particularly at low exposure levels. This behavior is evident from the general mathematical form of the variation of film optical density, D, with exposure:
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From page 69... ...
For the Du Pont Type 502 film illustrated in Figure 4-3, Do = 2.8, and it= 0.25 with exposure expressed in R; other films of comparable sensitivity to that of the Type 502 film should yield similar values. If it is assumed that the standard deviation of the measured optical density does not depend on exposure, and is given by a constant c' *
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From page 70... ...
Under less favorable conditions in some test series the minimum K is even larger. In almost all cases, the intrinsic uncertainty dominates at low exposures.
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From page 71... ...
. It should be noted that the expression "minimum detectable level" is often used in a less precise sense; thus the MDL values indicated in various documents describing test series may not satisfy the above definition exactly.
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From page 72... ...
Note that this treatment of laboratory uncertainties at low doses is a departure from the use of the lognormal distribution in that it allows for the inclusion of zero in the confidence limits. Laboratory uncertainties may be better described by the symmetric normal distribution than by the lognormal distribution.
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From page 73... ...
Therefore, film badge readings for aircraft personnel are more reproducible measures of exposure than for ground personnel, and perhaps more accurate as well. Nevertheless, in order to provide a conservative estimate of uncertainty, the same values of K are adopted as for Wound personnel in most test series.
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From page 74... ...
Aircraft ground crews who often encountered radiation as they cleaned aircraft flown in proximity to nuclear tests, or as they removed air filters used to collect radioactive debris from detonation clouds, are estimated to have bias and uncertainty values associated with their dosimetry readings that are similar to those of other ground personnel.
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From page 75... ...
Environmental conditions during the use of film badges in atmospheric testing were similar within each of two categories, continental and oceanic testing locations. Except for the first nuclear detonation, TRINITY, in an arid New Mexico location, the remaining continental atmospheric test series were conducted in Nevada at either Frenchman Flat or nearby Yucca Flat in a semi-desert environment.
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From page 76... ...
The Committee therefore related film badge readings to deep-dose equivalents that are more relevant to health effects. By converting film badge exposure to deepdose equivalent, the film badge readings from atmospheric nuclear tests are easily compared to current results for other activities, including underground weapons testing, nuclear power plant operation, diagnostic radiology, and nuclear medicine.
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From page 77... ...
Hp(10) is the dose equivalent from penetrating radiation to soft tissue located at a depth of 10 mm in the body.
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From page 78... ...
Weighting is based on the relative risk of a stochastic death per unit dose equivalent to the various tissues or organs. The effective dose equivalent is thus the quantity that most closely associates exposure to radiation with the risk of an adverse biological effect.
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From page 79... ...
. Table 54 The Ratio of the Red Bone Marrow-Dose Equivalent to the Deep-Dose Equivalent, HptlO)
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