Fast neutrons measured in copper from the Hiroshima atomic bomb dome.

The first measurements of (63)Ni produced by A-bomb fast neutrons (above approximately 1 MeV) in copper samples from Hiroshima encompassed distances from approximately 380 to 5062 m from the hypocenter (the point on the ground directly under the bomb). They included the region of interest to survivor studies (approximately 900 to 1500 m) and provided the first direct validation of fast neutrons in that range. However, a significant measurement gap remained between the hypocenter and 380 m. Measurements close to the hypocenter are important as a high-value anchor for the slope of the curve for neutron activation as a function of distance. Here we report measurements of (63)Ni in copper samples from the historic Hiroshima Atomic Bomb Dome, which is located approximately 150 m from the hypocenter. These measurements extend the range of our previously published data for (63)Ni providing a more comprehensive and consistent A-bomb activation curve. The results are also in good agreement with calculations based on the current dosimetry system (DS02) and give further experimental support to the accuracy of this system that forms the basis for radiation risk estimates worldwide.

Neutron-induced 63Ni in copper samples from Hiroshima and Nagasaki: a comprehensive presentation of results obtained at the Munich Maier-Leibnitz Laboratory.

Those inhabitants of Hiroshima and Nagasaki who were affected by the A-bomb explosions, were exposed to a mixed neutron and gamma radiation field. Few years later about 120,000 survivors of both cities were selected, and since then radiation-induced late effects such as leukemia and solid tumors are being investigated in this cohort. When the present study was initiated, the fast neutron fluences that caused the neutron doses of these survivors had never been determined experimentally. In principle, this would have been possible if radioisotopes produced by fast neutrons from the A-bomb explosions had been detected in samples from Hiroshima and Nagasaki at distances where the inhabitants survived. However, no suitable radioisotope had so far been identified. As a contribution to a large international effort to re-evaluate the A-bomb dosimetry, the concentration of the radionuclide (63)Ni (half-life 100.1 years) has been measured in copper samples from Hiroshima and Nagasaki. These measurements were mainly performed at the Maier-Leibnitz-Laboratory in Munich, Germany, by means of accelerator mass spectrometry. Because the (63)Ni had been produced in these samples by fast A-bomb neutrons via the reaction (63)Cu(n,p)(63)Ni, these measurements allow direct experimental validation of calculated neutron doses to the members of the LSS cohort, for the first time. The results of these efforts have already been published in a compact form. A more detailed discussion of the methodical aspects of these measurements and their results are given in the present paper. Eight copper samples that had been significantly exposed to fast neutrons from the Hiroshima A-bomb explosion were investigated. In general, measured (63)Ni concentrations decreased in these samples with increasing distance to the hypocenter, from 4 x 10(6 ) (63)Ni nuclei per gram copper at 391 m, to about 1 x 10(5 ) (63)Ni nuclei per gram copper at about 1,400 m. Additional measurements performed on three large-distant copper samples from Hiroshima (distance to the hypocenter 1,880-7,500 m) and on three large-distant copper samples from Nagasaki (distance to the hypocenter 3,931-4,428 m) that were not exposed significantly to A-bomb neutrons, suggest a typical background concentration of about 8 x 10(4 ) (63)Ni nuclei per gram copper. If the observed background is accounted for, the results are consistent with state-of-the-art neutron transport calculations for Hiroshima, in particular for those distances where the victims survived and were included in the life span study cohort.

Olfactory bulb uptake and determination of biotransfer factors in the California ground squirrel (Spermophilus beecheyi) exposed to manganese and cadmium in environmental habitats.

Manganese (Mn) and cadmium (Cd) profiles in olfactory bulbs of California ground squirrels (Spermophilus beecheyi) trapped at Lawrence Livermore National Laboratory's Site 300 facility in California were determined with proton induced X-ray emission (PIXE). As a reference, Mn profiles in olfactory bulbs from laboratory rats exposed via nose-only inhalation to 0.53 mg/m3 Mn in the form of MnCl2 were also determined with PIXE. Atomic absorption spectrophotometry was used to measure soil Mn and Cd contents from the trapping sites and Mn and Cd contents in ground squirrel liver and leg muscle tissues. The data from laboratory rats revealed that Mn uptake into the olfactory bulb occurs via inhalation exposure. Data from ground squirrels and knowledge of the collection sites indicate that although several routes of exposure may occur, fossorial rodent olfactory uptake affords a significant exposure route to Mn and Cd in soils. Measured biotransfer factors (ratio of leg muscle tissue metal content to soil metal content) for Cd in ground squirrels were 10(3)-fold greater than exposure modeling estimates based on oral Cd uptake data from livestock. The measurements for ground squirrel tissues show that when conducting ecological risk assessments for natural habitats considerable care should be taken in selecting transfer factors. Specifically, transfer factors derived from data pertaining to comparable exposure pathways and ecological setting should be used wherever possible.