137Cs Concentration in Soil Samples from an Early Survey of Hiroshima Atomic Bomb and Cumulative Dose Estimation from the Fallout

Abstract

Low background gamma-ray measurement has been performed to determine the 137Cs content in soil samples collected in a very early survey of the Hiroshima atomic bomb. These soil samples were collected just 3 d after the explosion within 5 km from the hypocenter and were not exposed to the global fallout from nuclear weapon tests. Out of 22 samples, 137Cs was detected for 11 samples, and their radioactivities ranged from 0.16-10.6 mBq g-1 at the time of the measurement. A comparison of the 137Cs deposition with the rainfall area within Hiroshima city indicates that the rainfall area was wider than the previously proposed one. Cumulative exposure by the fallout has been estimated to be 0.31 mC kg-1 (0.12 R) in Hiroshima city except for the heavy fallout area and at most 1.0 mC kg-1 (4 R) in the heavy fallout area.

Gamma-ray thermoluminescence measurements: a record of fallout deposition in Hiroshima?

“…The Hiromoto house BB excess TLD dose sample is very near to the extremely high Nishi-o-hashi 137 Cs #7 sample and the dose at Nishi-ohashi is almost half of the Hiromoto house excess TLD. Most of the other samples noted by the present authors as being in excess are near to detectable samples measured by Shizuma et al (1996Shizuma et al ( , 2011, which did not have 137 Cs results as high as the sample just noted from Nishi-o-hashi. (Shizuma et al 1996).…”

“…Most of the other samples noted by the present authors as being in excess are near to detectable samples measured by Shizuma et al (1996Shizuma et al ( , 2011, which did not have 137 Cs results as high as the sample just noted from Nishi-o-hashi. (Shizuma et al 1996). 137 Cs activities measured by Shizuma are indicated by relative radius of circles.…”

“…In 1996, Shizuma et al (1996Shizuma et al ( , 2011 reported assays of 137 Cs in 22 soil samples (average of *25 g each) from Hiroshima soil collected from 28 locations taken several days after the bombing, well before the typhoons that (Uda et al 1953;Takeshita 1975). Survey ratios are given as total measurement exposure rate to background exposure rate at about 3 years after the explosion.…”

“…This dose depends on what one assumes for fission-product fractionation for 137 Cs. Shizuma et al (1996Shizuma et al ( , 2011 plotted the relative 137 Cs measurements on the rainfall area map of Masuda (1989Masuda ( , 2011 trying to find a correlation with the amount of rainfall on that day. It appears there may be a correlation with the occurrence of rain, but not necessarily its amount.…”

Answer to the comments by Eric J. Grant et al. in “Radiation unlikely to be responsible for high cancer rates among distal Hiroshima A-bomb survivors”

“…The reasons that the effects of residual radiation in Hiroshima prefecture have been ignored or discounted include (1) there were no direct measurements of particulate radioactivity in the fallout immediately after the explosion, and (2) although there are measurement data for radioactive substances (cesium 137) in the soil, including that contained in radioactive rain collected during the 3 days following the explosion in Hiroshima [4], the values in other data were low, with the exception of the Koi and Takasu area, as pointed out by Grant et al However, nearly all subsequent measurements of residual radiation were made following the Makurazaki typhoon on 17 September 1945 and a subsequent typhoon on 9 October. The possibility that these values were low because much of the radioactive substances in the soil had already been washed away cannot be ruled out.…”