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2. Gamma-Ray Measurements
Pages 14-30

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From page 14...
... The agreement in 1986 between the TL measurements and DS86 calculations was generally good and within the estimates of uncertainty for the DS86 calculations (Roesch 1987~. Quartz, like any material used in thermoluminescent dosimetry, contains quantitative radiation-exposure history from the time of its initial annealing at high temperature.
From page 15...
... The second, or additive, technique attempts to correct for an initial nonlinearity in the dose-response relationship of quartz by irradiating multiple samples of the extracted quartz at increasing doses, and correcting the measurements of the original sample in the nonlinear or supralinear region. The third, predose, technique and its variations use a lower-energy electron trap in quartz near 110°C, which fades rapidly and is not found in normal samples.
From page 16...
... These four factors and their effects on the quality of TL measurements are discussed in more detail in the following sections. Fading Figures 2-2 and 2-3, from The Effects of Nuclear Weapons (Gras stone and Dolan 1977)
From page 17...
... Although temperature of that magnitude would certainly affect the TL signal after exposure, there are no data to confirm fading of a signal when the radiation exposure and the radiant energy occur at nearly the same moment. It is not known
From page 18...
... Some of the TL measurements were performed by Edwin Haskell, who indicates that the predose technique used precludes any effect of fading (Haskell 2000~. Moreover, if there were fading, the depth-dose curves in tile would not be consistent with the gamma-ray energy attenuation (Haskell 2000~.
From page 19...
... 19 N N N N N N ____—_ ~ ~ It ~ g g Cal ~ O U)
From page 20...
... the DS86 calculations included a component for backscatter and the backscatter signal enhancement is probably less than 5% at 1000 m ground distance. Quartz Energy Response All TL materials yield a different that is increasing light output with decreasing gamma ray energy.
From page 21...
... Delayed gamma rays contribute most of the exposure and dose from the burst. Figures 2-8 and 2-9 show the cumulative distributions of downward and forward fluence at several ground ranges.
From page 22...
... FIGURE 2-8 Hiroshima: cumulative gamma-ray vs. energy by distance (downward fluence)
From page 24...
... Thus background is extremely important especially at the larger distances. The most important of the other three factors that potentially affect the TL measurements is considered to be the increase in the magnitude (light output)
From page 25...
... FIGURE 2-10 Hiroshima TL measurements. Original reported units roentgens, tissue, air, quartz converted to RA tissue kerma (Cullings 2000~.
From page 26...
... Their arithmetic mean and standard deviation are 0.058 + 0.089 Gy, as shown in Figure 2-10. The replicate data are important because they demonstrate the acknowledged precision of TL measurements, which, in general, is 20-30%.
From page 27...
... I_ 1000 1500 Ground Distance (meters) 2000 2500 FIGURE 2-13 Nagasaki TL measurements (corrected)
From page 28...
... 2000 2500 FIGURE 2-15 Hiroshima residuals (mean - DS86) /DS86; original measurement values and values corrected by 0.8.
From page 29...
... FIGURE 2-16 Nagasaki TL measurements averaged over 100-m intervals. 2500 Figure 2-15 shows that the TED measurements in Hiroshima appear to be about 20% lower than the DS86 calculation out to 1300 m, then 20% higher at ground distances greater than 1300 m.
From page 30...
... If there are actually more fast neutrons at distances in Hiroshima than has been estimated in DS86 they should result in some increase also in the gamma-ray dose at distances because of neutron-capture reactions producing gamma rays. The four factors inherent in TL measurement uncertainty described cannot be evaluated quantitatively, but the agreement of the TL measurements with DS86 calculations is striking and provides support for the present estimates of gammaray dose.


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