IN-VIVO RADIATION DOSIMETRY USING PORTABLE L BAND EPR: ON-SITE MEASUREMENT OF VOLUNTEERS IN FUKUSHIMA PREFECTURE, JAPAN

Abstract

The aim of this study was to make direct measurements of the possible radiation-induced EPR signals in the teeth of volunteers who were residents in Fukushima within 80 km distance from the Fukushima Nuclear Power plant at the time of the disaster, and continued to live there for at least 3 month after the disaster. Thirty four volunteers were enrolled in this study. These measurements were made using a portable L-band EPR spectrometer, which was originally developed in the EPR Center at Dartmouth. All measurements were performed using surface loop resonators that have been specifically designed for the upper incisor teeth. Potentially these signals include not only radiation-induced signals induced by the incident but also background signals including those from prior radiation exposure from the environment and medical exposure. We demonstrated that it is feasible to transport the dosimeter to the measurement site and make valid measurements. The intensity of the signals that were obtained was not significantly above those seen in volunteers who had not had potential radiation exposures at Fukushima.

Figure 1.

The schema of Fukushima Prefecture is shown. On-site measurements were made at the locations marked by *. They were located at a distance of 70–80 km north-west from the Fukushima Nuclear power plant.

Figure 2.

Volunteers sat on the chair during the measurement. The time for each measurement was around 10 min including the tuning process.

Figure 3.

All measurements were performed using surface loop resonators that have been specifically designed for EPR measurements of the upper incisor teeth. The teeth were positioned by use of a bite plate system which gently held the upper lip and kept the resonator loop on the surface of the tooth. Bite plates are sterilizable and changed for each measurement.

Figure 4.

Typical EPR signal from volunteer (bracket shown). Arrowhead shows the signal from 15N-PDT as standard sample: sealed in a glass vial at a concentration of 8 mM in D₂O attached on the loop of the resonator.

Figure 5.

RIS ratio vs. radiation dose (air kerma of X-rays whose radical yield is four times that of Cs-137) of isolated incisors. Each dot indicates the intensity of the EPR signal from one tooth. There were no corrections applied for variations in tooth size, etc.

Figure 6.

RIS ratio of measured EPR signals from the volunteers in Fukushima. Average 0.087 ± 0.051.