9.5.6 Nav-Rad Instruments.
The M/V Horizon and the two destroyer escorts were equipped
with special radiation detectors, which were mounted atop the pilot house of each ship. Figure
2.3 shows a schematic representation of the sensing head. Each device had two sensing elements
shielded in the manner of the ship’s running lights by a 2-inch lead separation. The shielding
arrangement was designed in this fashion, so that the readings from the sensing heads would
give a good indication of the direction of radioactive water.
Fach of the two sensing elements in each head was made up of fourteen Anton 315 G-M tubes
arranged in cylindrical geometry and wired in parallel. The circuit was similar to that used in
the Horizon’s sensitive probe.
Each of the sensing elements was connected to its own micro-
ammeter, located in the wheel house. If the port meter read higher than the starboard meter,
this meant that the more-highly contaminated water was on the port side of the ship. A rangeselector switch was provided in the wheel house for switching through four different ranges.
The total range of the instrument covered the values from 0.01 to 500 mr/hr.
2.5.6 Water Sampling.
Water-surface samples were taken in polyethylene buckets.
procedure has long been used by oceanographers.
This
The only precaution necessary is that all
sampling containers be rinsed two or three times before the sample is taken.
stored in polyethylene bottles.
Samples were
For depth samples, the Horizon used standard Nansen bottles that had been coated inside and
out with polyester resin. The Nansen bottle is a tin-dipped brass cylinder containing a valve at
each end. While the bottle is being lowered, both valves are open and water flows freely through
the bottle. After it is lowered to the desired sampling depth, the bottle is reversed by a messenger sent down the hydrographic wire. This reversal closes both valves at once, and the
water sample is trapped in the bottle. When a cast is made, ten to fifteen bottles can be placed
on the wire, so that as many different depths can be sampled at once. All depth samples for
Projects 2.63 and 2.64 were taken by this method.
2.5.7 Marker Drogues.
The marker drogues consisted simply of a mast with a numbered
board and flag supported by an automobile inner tube with an aviator’s parachute attached to the
bottom. The drag of the parachute in water was so large that the drogue essentially remained
tied to the spot of water in which it was launched. The drogues launched by the YAG 39 had, in
addition to flag and numbered board, a light and a radar target, so that they could be followed
The use of drogues during the surveys was not as extensive as was originally planned, due to
the hazard that freely floating drogues presented to the deep-moored skiff installations.
2.5.8 Decay Tank. In order to measure the effective radioactive decay, it was decided to
collect a single large sample and to measure its decay using the probe. Calculations indicated
that over 95 percent of the radiation measured at a point in water, containing uniformly distributed radioactive products, would be contributed by those photons emitted within a 24, -foot
radius,
On this basis, a cylindrical steel tank, 5 feet high and 5 feet in diameter, was constructed.
A valved opening was installed in the bottom for releasing the sample. The top contained three
Openings: one for manual access to the tank interior, one for the shaft of the mixing propeller,
and cne in the center to permit insertion and removal of the detector probe.
A rack was erected
on tcp over the center hole, so that the probe could be clamped into position with the Geiger tubes
in exact center of the tank.
This tank was installed on the fantail of the M/V Horizon.
Observations during Operations Castle and Wigwam had indicated that the radioactive particles
in water had a tendency to plate out on metal surfaces. To avoid this, two steps were taken:
(1) all of the inside surfaces of the tank were coated with polyester resin of the type used in
bonding fiber glass, and (2) an attempt was made to “gel” the water sample in the tank to prevent the settling or migration of particles to any surface. By experimentation, it was found that
at least in small quantities (several gallons), sea water could be so gelled by the addition of
Sodium silicate followed by reduction of the pH to 9.0 by the addition of hydrochloric acid.
In actual practice, involving the 700 gallons in the tank, it was found that a firm gel was not
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