Figure 2–17 shows that the TLD measurements in Nagasaki are uniformly about 20% lower than the DS86 calculation. The exception at both cities occurs in measurements at greater than 2000 m, where the error in the measurement technique is estimated to be of the order of 100%. Given the overall uncertainty of about 20% for the TLD technique (precision, sample orientation, etc.) there is good agreement of the gamma-ray measurements with DS86 calculations.

Other sources of radiation might provide a small contribution to the TL signal. Neutron activation of short-lived nuclides, such as sodium and calcium, could have added to the TL signal. Fallout from the bomb might have contributed a small amount. There were two tornadoes at Hiroshima within a relatively short time after the burst, and fallout was probably washed away.

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 gamma-ray dose.

The committee suggests that the working group consider reevaluating the TL measurement data with particular emphasis on whether the energy response of the TL was properly accounted for and on background considerations.

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