Shichijo Kazuko, Takatsuji Toshihiro, Fukumoto Manabu, Nakashima Masahiro, Matsuyama Mutsumi M, Sekine Ichiro
Division of Tumor and Diagnostic Pathology, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan.
Faculty of Environmental Science, Nagasaki University, Nagasaki, Japan.
Heliyon. 2018 Jun 29;4(6):e00666. doi: 10.1016/j.heliyon.2018.e00666. eCollection 2018 Jun.
Radiation doses received by Hiroshima and Nagasaki atomic bomb survivors has been evaluated from data related only to external exposure because there was no reliable evidence for internal exposure in atomic bomb victims. However, we assumed that the contribution of internal exposure cannot be ruled out.
Autoradiography was carried out with the 70-year old paraffin-embedded specimens taken from Nagasaki atomic bomb victims who died within 5 months after the bombing. After exposure to photo emulsion for 6 months alpha-tracks were revealed in the specimens. We confirmed the alpha-tracks were emitted from deposited plutonium (Pu) in reference to the track length of the 8.787 MeV alpha-particle of thorium series from Polonium-212. Radioactivity concentration of Pu was obtained by counting alpha-tracks. The absorbed dose of each cell nucleus penetrated by an alpha-particle was estimated by calculating the absorbed energy from the particle.
Using old paraffin embedded sections processed about 70 years ago, we demonstrated for the first time that conditions in the aftermath of the bombing led to internal exposure to alpha-particles emitted from Pu, the fissile material of the Nagasaki atomic bomb. Dose rate of internal exposure was higher in the victims exposed outdoors than those indoors. Radioactivity concentration was relatively uniform among organs examined in a victim.
Pu was deposited in the bodies of the Nagasaki A-bomb victims presumably via various routes. Organ dose from Pu of the Nagasaki A-bomb victims studied was during their surviving period, which is lower compared with external exposure. However, the impact to the individual cell nucleus by a single alpha-particle might not be negligible, It would be meaningful; to analyze the relationship of the impact of internal exposure at the cellular level and organ dose. The 70-year old pathological specimens utilized in our study are an invaluable source for understanding internal radiation exposure and are crucial in elucidating experimentally unreproducible phenomena.
广岛和长崎原子弹幸存者所接受的辐射剂量一直是根据仅与外部照射相关的数据来评估的，因为当时没有可靠证据表明原子弹受害者存在体内照射。然而，我们认为不能排除体内照射的影响。
对从长崎原子弹爆炸后5个月内死亡的受害者身上获取的、保存了70年的石蜡包埋标本进行放射自显影。将标本暴露于感光乳剂6个月后，在标本中发现了α径迹。参照钋-212钍系8.787 MeVα粒子的径迹长度，我们确认这些α径迹是由沉积的钚（Pu）发出的。通过计数α径迹获得钚的放射性浓度。通过计算粒子吸收的能量来估计被α粒子穿透的每个细胞核的吸收剂量。
利用约70年前处理的陈旧石蜡包埋切片，我们首次证明了爆炸后的情况导致了对长崎原子弹裂变材料钚发出的α粒子的体内照射。户外暴露的受害者体内照射剂量率高于室内受害者。在一名受害者的多个被检查器官中，放射性浓度相对均匀。
钚可能通过多种途径沉积在长崎原子弹受害者体内。本研究中长崎原子弹受害者钚的器官剂量在其存活期间，与外部照射相比更低。然而，单个α粒子对单个细胞核的影响可能不可忽略。分析细胞水平的体内照射影响与器官剂量之间的关系是有意义的。我们研究中使用的70年历史的病理标本是了解体内辐射暴露的宝贵资源，对于阐明实验上无法重现的现象至关重要。
