[Illustration: _This radioisotope powered swimsuit heater uses
plutonium-238 to produce 420 watts of heat. Water, heated by the
decay of ²³⁸Pu, is pumped through plastic veins partially visible in
the undergarment. The cylinder under the diver’s arm contains 4
capsules of ²³⁸Pu, and a battery-pump assembly is contained in the
box at his feet. After preliminary tests at the Naval Medical
Research Institute in Bethesda, Maryland, the unit will be used in
Sealab III, the Navy’s underwater research laboratory. The heater
was developed by the AEC Division of Isotopes Development._]
The ocean is both a complex and a harsh environment and its study has
always demanded that designers of seaworthy instruments and sampling
devices be both ingenious and experienced in shipboard requirements.
Until recently, these devices tended to be rugged and simple, if not
indeed crude. More refined, electronic instrumentation has begun to
appear in recent years, but most designs still fail to pass the test of
use at sea. Even among those that do pass, there is persistent
difficulty in separating desired information-carrying signals from
background and system-induced “noise”. This has been a specific problem
with current meters designed to be moored in the open ocean and also
with one quite sophisticated gamma-ray detector.
To meet the clear need for improved devices, as well as to support its
own research and increase utilization of nuclear materials and
techniques, the AEC Division of Isotopes Development encourages the
development of oceanographic instrumentation. This comparatively young
technology already has produced exciting results. The future may be even
more revealing as nuclear energy is applied more and more to the study,
exploration, and exploitation of the ocean.
Instruments that have been developed under the AEC program include a
current meter, a dissolved-oxygen-content analyzer, and a
sediment-density meter. A new, fast method for determining the mineral
content of geological samples also has been perfected.
The DEEP WATER ISOTOPIC CURRENT ANALYZER (DWICA) was developed under a
contract with William H. Johnson Laboratories, Inc. It relies on
radioisotope drift time over a fixed course to measure seawater flow
rates ranging from 0.002 to 10.0 knots. The device embodies 12 radiation
sensors spaced equally in a circle around a radioisotope-injection
nozzle. Current direction can be determined to within 15 degrees. The
mass of tracer isotope injected is very small—less than 10 picograms[12]
per injection—and the instrument can store enough tracer material to
operate for a year. The tracer can be injected automatically at
intervals from 2 to 20 minutes, depending on the current. The device
sits on the sea floor, where its orientation to magnetic north can be
determined within 2.5 degrees.
[Illustration: _The Deep Water Isotopic Current Analyzer._]
Isotope Reservoir and equipressure system
Electric logic circuitry
Pressure protective case
Compass
Sensor ring
Flow baffle plate
Isotope injection point
[Illustration: The Deep Water Isotopic Current Analyzer.]
A SEDIMENT DENSITY PROBE, developed under an AEC contract by Lane-Wells
Company, employs gamma-ray absorption and backscatter properties[13] to
determine the density of the sediments at the bottom of lakes, rivers,
or the ocean, without the necessity of returning a sediment sample to
the surface. It is expected that it can be modified to sense the water
content of the sediments. These determinations are valuable not only for
research, but also for activity that requires structures on the ocean
floor, such as petroleum exploration and naval operations.
[Illustration: _The Sediment Density Probe. The drawing shows the
complete probe._]
The unit consists of a rocket-like tube 26 feet long and about 4 inches
in diameter, containing a gamma-ray-emitting cesium-137 source, a lead
shield, and a radiation detector. The device is lowered over the side of
a ship and allowed to penetrate the sediment. Once in place, the gamma
ray source, shield, and detector move together up and down, inside the
probe, for a distance of 11 feet, stopping every 24 inches for 4 minutes
to take a measurement. Gamma rays are absorbed in any material through
which they pass, according to its density. A low radiation count at the
detector indicates a high-density sediment: More radiation is absorbed
and less is reflected back to the detector. Conversely, a high count
indicates low density. Data are recorded on special cold-resistant film.
A number of different sediment measurements can be made in several
locations before the unit must be returned to the surface.
[Illustration: _Oxygen analyzer equipment includes the deep-sea
probe (large device, center, including a special Geiger counter, the
electronic assembly, a pump, and power supplies), cable for
transmission of Geiger counter signals (back), and portable scaler
(left)._]
[Illustration: _The latter is also shown aboard a research vessel
(inset) during tests made at sea._]
OXYGEN ANALYZER The amount of dissolved oxygen in any part of the ocean
is a basic quantity that must be determined before some kinds of
research can be undertaken. For example, oxygen concentration is
important in determining the life-support capability of seawater and in
measuring deep-water mixing. In the past this measurement has had to be
determined by laborious chemical methods that may subject the water
sample to contamination by exposure to atmospheric oxygen. Under an AEC
contract, the Research Triangle Institute has developed a dissolved
oxygen analyzer that relies on the quantitative oxidation by dissolved
oxygen of thallium metal containing a known ratio of radioactive
thallium-204.
The seawater sample passes through a column lined with thallium. The
thallium is oxydized and goes into solution. It then passes between two
facing pancake-shaped radiation counters that record the level of beta
radiation from the thallium-204. Since the rate of oxidation, and
therefore the rate of release of the thallium to solution, is
proportional to the amount of dissolved oxygen in the water, it is
simple to calibrate the device to show oxygen content. The system is
sensitive enough to detect one part of oxygen in 10 billion of water.
And, the device can be towed and take readings at depths of up to one
mile, an added advantage that obviates the chances of surface-air
contamination.
NEUTRON ACTIVATION ANALYSIS Nuclear energy is contributing to the more
accurate and more rapid analysis of minerals in the sea in at least two
different ways. The first employs neutron activation analysis, which we
have already mentioned. This method is valuable not only in analyzing
sediments cored from the ocean floor, but also in the detection and
quantitative analysis of trace elements in the water. Knowledge of the
role of all natural constituents in the ocean is essential to an
understanding of the complex interrelationships of the ocean
environment, as we have seen. Identification of trace elements also is a
necessary preliminary to determining the effects of purposely introduced
radionuclides. Collection of the minute quantities of trace elements is
very difficult at best. Once they have been collected and concentrated,
neutron activation analysis provides a means for their identification
and measurement.
X-RAY FLUORESCENCE is another technique, used to identify the mineral
content of ore or sediment. This system was developed (for the purpose
of spotting gold being smuggled through Customs) by Tracerlab Division
of Laboratory for Electronics, Inc. (LFE), under an AEC contract.
Similar equipment was developed simultaneously in England for use by
prospectors, geologists and mining engineers. It now may be used at sea
in analyzing samples from the sea floor. As is often the case with
isotope-based devices, its operation is really quite simple. When
excited by radiation from an isotope (or any other radiation source),
each element produces its own unique pattern of X-ray fluorescence, that
is, it radiates characteristic X rays. By varying filters and measuring
the count rate, oceanographers can detect and measure materials, such as
tin, copper, lead, and zinc. The British unit is completely
transistorized, battery powered, and weighs only 16.5 pounds.
RHODAMINE-B DYE The AEC also has improved oceanographic research in ways
that do not involve the use of nuclear energy. Some years ago under the
joint sponsorship of the AEC Division of Reactor Development and
Technology and the Division of Biology and Medicine, the Waterlift
Division of Cleveland Pneumatic Tool Company developed instrumentation
and techniques for detecting the presence of the red dye, rhodamine-B,
in concentrations as low as one-tenth part per billion. This method is
now widely used both for groundwater studies and in the study of
currents, diffusion, and pollution in rivers, lakes, and the ocean. In
many cases, rhodamine-B is a better tracer in water than radioisotopes,
due to the greater ease with which it is detected.