Measurement of Environmental Radiation and Exposure Dose
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*Masaharu OKAN®
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The main objectives of measuring environmental
~-padiation was to keep the ships personnel from undur
exposure to the dangerous effects of external nuclear
radiation and to provide future references for other
‘measurements of radiation contamination.
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Two types of scintillation counters were used as the
environmental radiation monitor. One was an ordinary
scintillation counter with a sodium iodide crystal,
11/2" in diameter and 1 1/2" long, with the discrimination level set at approximately 20 KeV of the electron
energy value. This instrument was placed at the starboard
side of the bridge, and the counts printed on paper
every 15 minutes. The other scintillation counter was
used for exposure dose monitoring. This type had a
specially designed shield surrounding the crystal to
correct energy characteristics. With this device, a
dose rate as low as 0.1 uar/hr in the energy range of 0.1 MeV
to 2 MeV could be measured by simply reading the counting
rate.
The dose rate in the chart room during measurements
made with this instrument was 0.7-1.0 ar/pr, excluding
‘on the survey vessel using the scintillation counter.
These values are shown in Table 1.
dosimeters were used.
Table 2.
Peears peerere
In order to measure total exposure doses during the
Surveys on the ship, pocket dosimeters and the glass
The values found are shown in
4
* Institute of Physical and Chemical Research
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| cosmic radiation and contamination of the detector head.
Other surveys were made of radioactive contamination