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that excessively contaminated water could be observed as a result of
the sediment deposited in the water and could be evaluated adequately
using only a PDR/39 survey-type meter.
milliliter.
The average activity varied from 1 x 10°™"
Air samples collected in fall-out areas by vacuum-type air fil-
ters and cascade impactor slides constituted another type of sample
analysed in the field laboratory. Upon those occasions when fallout was detected on board the USS Bairoko portable air samplers were
periodically turned on as a means to determine whether fall-out was
still occurring,
The entire filter paper was counted and the activity
shop on board the Bairoko, was utilized to evaluate the inhalation
Y
mining the percentage of the total activity associated with, particles
less than 5 microns in diameter, The air samples collected:on Ma
1, when the USS Bairoko received a substantial fall-gut fro
indicated activities ranging from 455 to 27ho cpm/ft
of air.
cascade impactor data was also obtained during the fall-out that
occurred on the Bairoko.
d
e onl
An average of 65 per cent of the activity
was found to be associated with particles less than 5 microns in diameter,
Decay rate measurements and energy determinations were made on
various types of samples throughout the operation in an effort to
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obtain detailed information on the fundamental properties of the
radioactive particulate matter. Gamma energies were difficult to
obtain accurately due to the low counting efficiency of GM tubes for
gamma radiation and the apparent low energies involved. The latter
also made beta energy determinations more difficult.
Gamma energies
measured on very active samples varied from 600 to 25 kev.
gemma energies measured were somewhat surprising.
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varied from 0.2 to 2.2 mev.
LAINMe8 AiReadeNT aM TBARS
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Air samplers were also used by the initial
<A cascade impactor, installed in the radiac repair
hazard associated with the radioactive particulate matter by deter-
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to 5 x 10
microcuries per milliliter. No ship's drinking water was found to
contain any detectable radioactive material.
noted in cpm/ft? of air,
Ad S am RAaeMG Gt
a
The maxim contamination en-
countered in the lagoon anchorages was 8.4 x 1079 micpocuries per)
The low
Beta energies
Log-log plots of cpm vs time after detonation were utilized to
cotain decay rate data.
Sarples studied included fall-out samples
on the Bairoko; water samples from the lagoon and drinking water
senples from Rongelap; crater Samples; andi air samples,
The following
results represent a cross-section of the different types of samples
studied and the calculated slope of the line obtained by plotting the
log of the activity versus the log of the time after detonation.
Fall-out sample on flight deck Bairoko wat) rr"
12h
oe
26 ow-
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