Measuring fast neutrons in Hiroshima at distances relevant to atomic-bomb survivors

Abstract

Data from the survivors of the atomic bombs serve as the major basis for risk calculations of radiation-induced cancer in humans. A controversy has existed for almost two decades, however, concerning the possibility that neutron doses in Hiroshima may have been much larger than estimated. This controversy was based on measurements of radioisotopes activated by thermal neutrons that suggested much higher fluences at larger distances than expected. For fast neutrons, which contributed almost all the neutron dose, clear measurement validation has so far proved impossible at the large distances (900 to 1,500 m) most relevant to survivor locations. Here, the first results are reported for the detection of 63Ni produced predominantly by fast neutrons (above about 1 MeV) in copper samples from Hiroshima. This breakthrough was made possible by the development of chemical extraction methods and major improvements in the sensitivity of accelerator mass spectrometry for detection of 63Ni atoms (refs 8-11). When results are compared with 63Ni activation predicted by neutron doses for Hiroshima survivors, good agreement is observed at the distances most relevant to survivor data. These findings provide, for the first time, clear measurement validation of the neutron doses to survivors in Hiroshima.

The cancer epidemiology of radiation

“…Radiation source data from weapons tests in combination with sophisticated computational techniques for radiation transport and shielding, together with measurements of induced long-lived radioactivity in the environment, were used to determine the radiation dose to each organ of each survivor. The dosimetry system has undergone revision over the years and the latest revision has just been completed although it is not anticipated that substantial changes from the last, 1986, version (DS86) will occur (Straume et al, 2003). The findings presented in this paper are based on the DS86 dosimetry system.…”

Characteristic expression of fukutin in gastric cancer among atomic bomb survivors

“…The LSS cohort from the RERF is based on the DS02 system, which was established by the Joint US-Japan Working Group, a collaboration among American, German and Japanese universities together with national laboratories (20). This group revised the gamma ray and neutron fluence calculations of source terms from the previous DS86 system (20,23,24). It may be hypothesized that the difference in estimation strategies for radiation exposure led to the discrepancy between the two cohorts.…”

Accelerator mass spectrometry – from DNA to astrophysics

“…However, the much higher energies available at this facility allows one to perform isobar separation for AMS experiments not possible at the smaller machines. Examples are 53 Mn [6], 60 Fe [7], and 63 Ni [8]. Somewhat in between the small and large machines is the Vienna Environmental Research Accelerator (VERA), a dedicated AMS facility based on a 3-MV tandem accelerator [9].…”