  An earthquake, Tohoku region Pacific Coast earthquake, occurred on the 11th
of March, 2011, and subsequent Fukushima nuclear power plant accidents have
been stirring natural radiation around the author's office in Fukushima Medical
University (FMU). FMU is located in Fukushima city, and is 57 km (35 miles)
away from northwest of the Fukushima Daiichi nuclear power plant. This paper
presents three types of radiation survey undertaken through the unprecedented
accidents at the campus and the hospital of FMU. First, a group of interested
people immediately began radiation surveillance; the group members were
assembled from the faculty members of "Life Sciences and Social Medicine" and
"Human and Natural Sciences". Second, the present author, regardless of the
earthquake, had serially observed natural radiations such as gamma radiation in
air with NaI scintillation counter, atmospheric radon with Lucas cell, and
second cosmic rays with NaI scintillation. Gamma radiation indicated most
drastic change, i.e., peak value (9.3 times usual level) appeared on March 16,
and decreased to 1.7 times usual level after two months. A nonlinear least
squares regression to this decreasing data gave short half-life of 3.6 days and
long half-life of 181 days. These two apparent half-lives are attributed to two
groups of radioisotopes, i.e., short half-life one of I-131 and long half-life
ones of Cs-134, Cs-137 and Sr-90. Also, atmospheric radon concentration became
high since a stop of ventilation, while second cosmic rays did not show any
response. Third, late April, 2011, a team of radiation dosimetry under the
direct control of Dean, School of Medicine, was established for the
continuation of radiation survey in the campus and the hospital of Fukushima
Medical University.
