Abstract
To fully understand the radiation effects of the atomic bombing of Hiroshima and Nagasaki among the survivors, radiation from neutron-induced radioisotopes in soil and other materials should be considered in addition to the initial radiation directly received from the bombs. This might be important for evaluating the radiation risks to the people who moved to these cities soon after the detonations and probably inhaled activated radioactive “dust.” Manganese-56 is known to be one of the dominant radioisotopes produced in soil by neutrons. Due to its short physical half-life, 56Mn emits residual radiation during the first hours after explosion. Hence, the biological effects of internal exposure of Wistar rats to 56Mn were investigated in the present study. MnO2 powder was activated by a neutron beam to produce radioactive 56Mn. Rats were divided into four groups: those exposed to 56Mn, to non-radioactive Mn, to 60Co γ rays (2 Gy, whole body), and those not exposed to any additional radiation (control). On days 3, 14, and 60 after exposure, the animals were killed and major organs were dissected and subjected to histopathological analysis. As described in more detail by an accompanying publication, the highest internal radiation dose was observed in the digestive system of the rats, followed by the lungs. It was found that the number of mitotic cells increased in the small intestine on day 3 after 56Mn and 60Co exposure, and this change persisted only in 56Mn-exposed animals. Lung tissue was severely damaged only by exposure to 56Mn, despite a rather low radiation dose (less than 0.1 Gy). These data suggest that internal exposure to 56Mn has a significant biological impact on the lungs and small intestine.
Highlights
After the atomic bombing of Hiroshima and Nagasaki, Japan, initial radiation directly produced during or shortly after the explosions and residual radiation contributed towards a radiation exposure of the survivors (Imanaka et al 2008)
The initial activities of neutron-activated MnO2 powder were similar in Experiments 1 and 2, the radiation doses of each organ received in Experiment 2 were substantially lower than those received in Experiment 1, i.e., the small intestine received 1330 mGy in Experiment 1 while 150 mGy in Experiment 2
These results might demonstrate that, to understand the radiation effects among the survivors of the atomic bombing of Hiroshima and Nagasaki, it is important to include the effects of residual radiation in addition to those of the initial radiation directly received from the bombs
Summary
After the atomic bombing of Hiroshima and Nagasaki, Japan, initial radiation directly produced during or shortly after the explosions and residual radiation contributed towards a radiation exposure of the survivors (Imanaka et al 2008). There are two sources of residual radiation: (1) neutron-activated radioisotopes from materials on the ground and (2) radioactive fallout containing fission products and residual fissile materials from the bombs. Understanding the former is important for evaluating the risks to those people who moved to these cities soon after the detonations and might have inhaled radioactive dust (Kerr et al 2013, 2015; Imanaka et al 2008). In terms of radiation exposure, 56Mn (physical half-life: 2.58 h), which emits both β particles and γ rays, is one of the most important radioisotopes produced after the atomic bomb explosion in Hiroshima
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