On D-3 days, the USS Munsee rechecked the old Wahoo array for possible mooring compo-
nents, and that evening the project indicated that it had no further need for its services. Roliup
proceeded rapidly. By D+5 days, essentially all project equipment, except that usec for data
reduction, was packed and ready for shipment.
2.2
INSTRUMENTS
2.2.1 Gamma-Intensity-Time Recorder (GITR). The primary instrument used by the project
was a portable, self-contained GITR (or std-GITR), which represents a further developmentof
a garoma-dcetecting instrument used during Operation Redwing (Reference 33), The instrument
(Reference 57) is 16 by 13 by 21 inches high, weighs approximately 55 pounds with power supply,
and consists of the following units: (1) a radiation detector and amplifier with time base, (2) a
recording system, (3) a battery pack, and (4) miscellaneous instrument control switches and
associated circuitry (Section B.1). The detector unit can be mounted either inside the recorder
case or aS a separate unit connected with the recorder by a cable not exceeding 25 feet in length
(Figures 1.4 and 2.3).
The sensitive element {s a low-range ionization chamber containing a
concentric, high-range chamber. The commonbase of these chambers contains the associated
recycling electrometer circuits.
Both chambers have nearly a 47 response and are independent of incident gamma energyto
within +20 percent from 100 kev to 1.3 Mev (Section C.1). The discharge of either chamber
fires its associated electrometer, giving a square-wave pulse that is amplified and recorded
on magnetic tape. The transducer automatically recycles to the original charged condition in
approximately 0.5 msec. Each recorded pulse represents an increment of gamma dose which,
by means of time pulses indicating tape speed, can be converted to dose rate. The dose incre-~
ments from the two chambers and the time base are recorded as three channels of information
on’a '4,-inch magnetic tape.
One of two types of tape transports can be coupled with the basic transducer unit, thus giving
two instruments: one with a tape speed of 0.25 in/sec, giving 12 hours of operation with a range
of 10 mr/hr to 10° r/hr; the other with a tape speed of 0.05 in/sec, giving 60 hours of operation
with a range of 10 mr/hr to 2x10‘ r/hr. All GITR’s were actuated by a signal from a triggercontrol box and shut themselves off automatically when the end of the tape was reached.
On a coracle installation, the detector was housed inside a watertight, 14-gage aluminum
case mounted directly on the deck (Figure 1.4). All coracle recorders were the 12-hour type
and were mounted below the deck inthe instrument well. This mounting arrangement was
selected after experimental checks of directional response with the detector mounted inside the
recorder proved to be unsatisfactory. The detector response to known deck activity, as indicated by IC collections, was experimentally determined using exact coracle geometry (Section
c.5).
For Wahoo, all shipboard GITR’s were of the 60-hour type to insure a GITR record that
would overlap the planned ship surveys. All shipboard GITR’s were mounted with the detector
and recorder installed separately. For Umbrella, two of the GITR’s aboard the EC-2 were
exchanged for 12-hour types in order to obtain the higher peak dose rate capability of these
instruments. No special determination of detector response to particular shipboard geometry
was attempted, although all locations were specifically selected to reduce anomalous contribu-
tions from ships’ structures.
2.2.2 Underwater GITR. The underwater GITR (UW- or sec-GITR) is a simple modification
of the standard GITR. The basic instrument consists of the 12-hour GITR described above with
its detector housed in a deck mounting case identical] to that used for the std-GITR (Figure 1.4).
The detector, however, was placed on a 25-foot cable and was mounted at the edge of the coracie in a dropping mechanism actuated by a small cylinder of carbon dioxide upon receipt of a
Signal from the trigger-control box (Figures 1.2 and 1.3). The detectors were so weighted and
the length of cable so chosen that after release they would be suspended approximately 6 feet
Oy
55