Whole-body counter survey results 4 months after the Fukushima Daiichi NPP accident in Minamisoma City, Fukushima

TL;DR

This study measured radiocesium body burdens in 566 residents of Minamisoma, Fukushima, four months after the nuclear accident, using a chair-type WBC with developed background compensation methods, finding doses below 1 mSv.

Contribution

It introduces a novel background compensation method for chair-type WBC units and validates it with well-shielded units, enabling accurate dose assessment post-accident.

Findings

All subjects had estimated doses below 1 mSv.

Developed background correction methods for chair-type WBC.

Validated methods with well-shielded WBC data.

Abstract

Using the first WBC unit installed in Fukushima Prefecture after the accident, the radiocesium body burdens of 566 high-risk residents of Minamisoma city were measured in July 2011 at the Minamisoma Municipal General Hospital. The analysis of the data was challenging because this chair-type WBC unit did not have sufficient shielding against background gamma rays, and methods had to be developed to reliably compensate for the body-attenuated background radiation. Fortunately, data for repeated tests of hospital staff members using both the chair-type and well-shielded FASTSCAN WBC units, installed in September 2011, were available, and could be used to check the validity of the analysis. The CEDs of all subjects, estimated under the assumption of acute inhalation in March 2011, were found to be less than 1 mSv.