Measurements of fast neutrons in Hiroshima by use of (39)Ar.
The survivors of the A-bomb explosions over Hiroshima and Nagasaki were exposed to a mixed neutron and gamma radiation field. To validate the high-energy portion of the neutron field and thus the neutron dose to the survivors, a method is described that allows retrospective assessment of the fast neutrons from the A-bombs. This is accomplished by the extraction of the noble gas argon from biotites separated from Hiroshima granite samples, and then the detection of the (39)Ar activity that was produced by the capture of the fast neutrons on potassium. Adjusted to the year 1945, activities measured in the first samples taken at distances of 94, 818, 992, and 1,173 m from the hypocenter were 6.9+/-0.2, 0.32+/-0.01, 0.14+/-0.02, and 0.09+/-0.01 mBq/g K, respectively. All signals were significantly above detector background and show low uncertainties. Considering their uncertainties they agree with the calculated (39)Ar activation in the samples, based on the most recent dosimetry system DS02. It is concluded that this method can be used to investigate samples obtained from large distances in Hiroshima, where previous data on fast neutrons are characterized by considerable uncertainties. Additionally, the method can be used to reconstruct the fast neutron fluence in Nagasaki, where no experimental data exist.
Nolte
Eckehart
E
Physics Department, Technical University of Munich, 85747 Garching, Germany.
Rühm
Werner
W
Loosli
H Hugo
HH
Tolstikhin
Igor
I
Kato
Kazuo
K
Huber
Thomas C
TC
Egbert
Stephen D
SD
D001128:Argon / Q000032:analysis*; D005214:Fast Neutrons; D007564:Japan; D009689:Nuclear Warfare; D011829:Radiation Dosage; D011834:Radiation Monitoring / Q000379:methods*; D011868:Radioisotopes / Q000032:analysis*; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D012990:Soil Pollutants, Radioactive / Q000032:analysis*
D011868:Radioisotopes; D012990:Soil Pollutants, Radioactive; D001128:Argon