Studies of Radioactivity Produced by the Hiroshima Atomic Bomb: 1. Neutron-Induced Radioactivity Measurements for Dose Evaluation

A Review of Forty-Five Years Study of Hiroshima and Nagasaki Atomic Bomb Survivors I. DOSIMETRY

Abstract

This review summarizes measurements made of ¹⁵²Eu and ⁶⁰Co radioactivity induced by neutron radiation from the Hiroshima atomic bomb (A-bomb) with the goal of estimating the neutron dose released by the bomb. Prior to these measurements, A-bomb-irradiated specimens such as rocks and pieces of concrete, which had not been shielded were collected. The specific radioactivity obtained (in bequerels per gram of Eu or Co) were compared with those calculated from DS86 neutrons. Findings of usefulness of ¹⁵²Eu data within 700 m ground range are reported and systematic differences between measured activities and calculations are discussed. The ¹⁵²Eu data were also useful for the discussion of circular asymmetry, and there was no asymmetry within the experimental errors. This review also covers the similar difference found in ³²P data, which were measured immediately after the A-bomb, along with the other ¹⁵²Eu and ⁶⁰Co data. The need for more measurements of ¹⁵²Eu activity in samples farther away from the hypocenter in order to verify the DS86 calculations is also discussed.