著者
山崎 正勝
出版者
日本科学史学会
雑誌
科学史研究 (ISSN:21887535)
巻号頁・発行日
vol.60, no.297, pp.1-18, 2020 (Released:2021-10-06)

Hidehiko Tamaki, who engaged the uranium criticality calculations at the Riken during the Second World War, died on February 10, 2013, and the related materials at Tamakiʼs house were preserved at the Riken Archives in Wako City, Saitama Prefecture. The author takes up a handwritten manuscript by Tamaki that begins with "§1. Necessity of chain reaction and factors that hinder its realization," and examines it using reproduction calculation. It is shown that Tamaki had obtained the mixture ratio of uranium and water as moderator so that it let the amount of uranium used minimum. It was also pointed out that there was a discrepancy in the formula of the output energy evaluated under the condition of constant pressure. After presenting a method to avoid it, Rikenʼs reactor system was reexamined, and it is shown that there was a lack of the concept of controlling chain reactions including consideration of delayed neutrons and neutron absorbers such as the control rods of todayʼs nuclear reactors, so it was difficult to use it for power.