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Medical Survey of Japanese Exposed to Fall-out Radiation in 1954
A Report after 10 Years
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Introduction
On 1 March 1954 a thermo-nuclear test explo-
sion was performed at Bikini lagoon by U.S.
authorities. At chat time, one Japanese fishing
boat, the 5th “ Fukuryu-maru” (Lucky Dragon)
was about 90 miles east of the explosion centre.
The twentythree Japanese fishermen on board,
aged 18-39, saw a huge red light in the west
and heard a detonation sound several minutes
later while they were fishing for tunas.
After
this explosion, a large amount of radio-active
substance fell on the neighbouring area. At
about 7:00 a.m. white matter began to fall,
which continued for approximately 3 hours.
They gave up fishing and returned to their
harbour on !4 March 1954.
After landing, all the fishermen were found
to have been injured by the radioactive materials.
deposited in the cabins, on the deck, etc.
(3)
Internally from the radioactive materials
entering various organs.
The diameter of the fall-out materials ranged
19-460 2, mainly 100-4004".
The radiochemical
analysis of the materials was performed at several
laboratories.
According to data from Prof.
Kimura's laboratory’', on 26 March
rare-earth
elements contributed about 50% of the total
radioactivity and uranium contributed about
205. The specific activity of the material was
0.37 mCi/g on 23 April.
By extrapolation of this
data, a value of 1.4Ci/g was obtained as the
specific activity at 7:00a.m. on 1 March. The
March. They were discharged from both hos-
estimation of irradiation dose, especially that
from body surface and internally deposited
radioactive materials, was difficult. However,
externally irradiated dose for 14 days was estimated as 170-700R, about half or more being
pitals in May 1955, except one fatal case who
died on 23 September 1954.
tion was based on the results of the experimental
After being discharged, they took rest at their
reproduction of ash-fall, and on detailed inves-
Although some of them
tigation of each patient’s behaviour on the boat.
continued ¢o work as fishermen, most of them
gave up fishery and got new jobs. Because of
The dose to each person differed depending on
his behaviour and the position of his cabin.
The integrated dose to the thyroid from '"'I
was inferred as about 20-120 rad on 4 persons
who were examined 2-3 times for external countings of radioactivity in the thyroid region during
the 4-7 weeks after the initial exposure.
Urine samples of patients were collected and
transferred to the Health and Safety Laboratory
of U.S. A. E. C. for radiochemical analysis several
times.’ Significant amounts of radioactivity
were found in the urine samples collected at
about 4+ weeks after the explosion. Radiochemical
analysis of these samples indicated that "Sr and
Seven of them were hospitalized to the Tokyo
University Hospital, and the other sixteen to
the First National Hospital of Tokyo by 28
home for some period.
their varied status in occupations, financial situations and of the widely distributed addresses, it
was not always possible to get all of them
nde
three ways:
(1) From the radioactive materials adhering
to the body surface.
(2) Externally from the radioactive materials
together for the annual examinations as planned.
i. Summory of the Past Findings
Wehave reported medical data of these people
several times'’’””. The following is a brief sum-
mary of the past findings.
A. State of Irradiation and the Estimated Dose
The persons were irradiated in the following
irradiated on the Ist day (Table |). This estima-