41Ca in tooth enamel - Part I: A biological signature of neutron exposure in atomic-bomb survivors

A. WALLNER; W. RÜHM; G. RUGEL; N. NAKAMURA; A. ARAZI; T. FAESTERMANN; K. KNIE; H.J. MAIER; G. KORSCHINEK

RADIATION RESEARCH

RADIATION RESEARCH SOC

Año: 2010 vol. 174 p. 137 - 145

0033-7587

The detection of 41Ca atoms in tooth enamel using accelerator mass spectrometry is suggested as a method capable of reconstructing thermal neutron exposures from atomic bomb survivors in Hiroshima and Nagasaki. In general, 41Ca atoms are produced via thermal neutron capture by stable 40Ca. Thus, any 41Ca atoms present in the tooth enamel of the survivors would be due to neutron exposure from both, natural sources and radiation from the bomb. Tooth samples from 6 survivors in a control group were used to investigate the natural 41Ca content in tooth enamel, and 16 tooth samples from 13 survivors were used to estimate bomb-related neutron exposure. The results showed that the mean 41Ca/40Ca isotope ratio was (0.17± 0.05)×10−14 in the control samples, and increased to 2×10−14 for survivors who were proximally exposed to the bomb. The 41Ca/40Ca ratios showed an inverse correlation with distance from the hypocenter at the time of the bombing, similar to values which have been derived from theoretical free-in-air thermal-neutron transport calculations. Given that gamma-ray doses were determined earlier for the same tooth samples by means of the electron-spin-resonance technique (ESR, or electron paramagnetic resonance, EPR), these results can serve to validate neutron exposures which were calculated individually for the survivors, but which had to incorporate a number of assumptions (e.g. shielding conditions for the survivors).41Ca atoms in tooth enamel using accelerator mass spectrometry is suggested as a method capable of reconstructing thermal neutron exposures from atomic bomb survivors in Hiroshima and Nagasaki. In general, 41Ca atoms are produced via thermal neutron capture by stable 40Ca. Thus, any 41Ca atoms present in the tooth enamel of the survivors would be due to neutron exposure from both, natural sources and radiation from the bomb. Tooth samples from 6 survivors in a control group were used to investigate the natural 41Ca content in tooth enamel, and 16 tooth samples from 13 survivors were used to estimate bomb-related neutron exposure. The results showed that the mean 41Ca/40Ca isotope ratio was (0.17± 0.05)×10−14 in the control samples, and increased to 2×10−14 for survivors who were proximally exposed to the bomb. The 41Ca/40Ca ratios showed an inverse correlation with distance from the hypocenter at the time of the bombing, similar to values which have been derived from theoretical free-in-air thermal-neutron transport calculations. Given that gamma-ray doses were determined earlier for the same tooth samples by means of the electron-spin-resonance technique (ESR, or electron paramagnetic resonance, EPR), these results can serve to validate neutron exposures which were calculated individually for the survivors, but which had to incorporate a number of assumptions (e.g. shielding conditions for the survivors).