Institute of Radiation Protection

Dose reconstruction for A-bomb survivors

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, ⁶³Ni had been detected in copper samples from Hiroshima. Because this ⁶³Ni had been produced by fast neutrons from the A-bomb, its concentration can be used to reconstruct fast neutron fluences relevant for the neutron dose to survivors (see Rühm et al. 2000, Straume et al. and Fig.1, Nature, Rühm et al. 2007).

More recently we developed an alternative method that also 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 ³⁹Ar activity that was produced by the capture of the fast neutrons on potassium. First measurements on samples taken at distances of 94 m, 818 m, 992 m, and 1173 m from the hypocenter in Hiroshima were already measured. The resulting ³⁹Ar signal decreased with increasing distance which suggests that fast neutrons from the a-bomb explosion have been measured, indeed. All signals were significantly above background and show low uncertainties. Considering their uncertainties they agree with the calculated ³⁹Ar 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.

Another effort was made to measure ⁴¹Ca in tooth enamel of atomic bomb survivors. This radionuclide has a phyical half-life of about 100,000 years, and was produced by thermal neutrons from the atomic bomb. Accelerator mass spectrometry was used, and ⁴¹Ca was detected in enamel samples from 13 surivors. It is concluded that this method allows - for the first time - to detect an individual biological signature of the neutrons present at the time of the bombing. The measured signal was consistent with state-of-the-art simulations that were also used for the current DS02 dosimetry system.

References:

W. Rühm, A. Wallner, H. Cullings, S.D. Egbert, N. El-Faramawy, T. Faestermann, D. Kaul, K. Knie, G. Korschinek, N. Nakamura, J. Roberts and G. Rugel. ⁴¹Ca in tooth enamel -Part II: A Means for Retrospective Biological Neutron Dosimetry in atomic-bomb survivors. Radiat Res 174, 146-154 (2010).

A. Wallner, W. Rühm, G. Rugel, N. Nakamura, A. Arazi, T. Faestermann, K. Knie, H. J. Maier and G. Korschinek. ⁴¹Ca in tooth enamel Part I: A biological signature of neutron exposure in atomic-bomb survivors. Radiat Res 174, 137-145 (2010).  

A. A. Marchetti, J. E. McAnnich, G. Rugel, W. Rühm, G. Korschinek, R. E. Martinelli, T. Faestermann, K. Knie, S. D. Egbert, A. Wallner, C. Wallner, K. Tanaka, S. Endo, M. Hoshi, K. Shizuma, S. Fujita, H. Hasai, T. Imanaka and T. Straume. Fast Neutrons Measured in Copper from the Hiroshima Atomic Bomb Dome. Radiation Research 171, 118-122 (2009)

K. Komura, M. Hoshi, S. Endo, T. Imanaka, S.D. Egbert, W. Rühm, H. Fukushima, S. Fujita. Atomic bomb induced 152Eu: reconciliation of discrepancy between measurements and calculation. Health Physics 92 (4), 366-370, 2007

W. Rühm, K. L. Carroll, S. Egbert, T. Faestermann, K. Knie, G. Korschinek, R. E. Martinelli, A. A. Marchetti, J. E. McAninch, G. Rugel, T. Straume, A. Wallner, C. Wallner, S. Fujita, H. Hasai, M. Hoshi, K. Shizuma (2007) Neutron-induced 63Ni in Copper Samples from Hiroshima and Nagasaki – A Comprehensive Presentation of Results Obtained at the Munich Maier-Leibnitz Laboratory. Radiat Environ Biophys 46: 327-338

Nolte E, Rühm W, Loosli HH, Tolstikhin I, Kato K, Huber TC, Egbert SD (2006) Measurements of fast neutrons in Hiroshima by use of 39Ar. Radiat Environ Biophys 44: 261-271

Straume T, Rugel G, Marchetti AA, Rühm W, Korschinek G, McAninch JE, Carroll K, Egbert S, Faestermann T, Knie K, Martinelli R, Wallner A, Wallner C, Fujita S, Shizuma K, Hoshi M, Hasai H. (2003) Measuring fast neutrons in Hiroshima at distances relevant to atomic-bomb survivors. Nature 424, 539-542, and (2004) Nature 430, 483.

Rühm W, Knie K, Rugel G, Faestermann T, Marchetti AA, McAninch JE, Straume T, Wallner C, Korschinek G (2000) Detection of 63Ni by means of accelerator mass spectrometry for estimating the fluence of fast neutrons from the Hiroshima atomic bomb. Health Phys 79: 358;