capacity of 14,000 ma-hr powers each recorder.
The 12-hour recorder is driven by a 2-watt
motor operating at a speed of 6,000 rpm and regulated by a centrifugal governor. A 0.75-watt,
chronometrically governed motor rotating at 900 rpm operates the 60-hour recorder.
Both
recorders utilize gear reduction and worm-gear drive. The tape is guided in the conventional
manner. Metal friction plates on the feed spindle establish an average tape tension of about 4
ounces. Contacts on the recorder turn off the instrument when a conductive section of tape at
the end of the reel passes over them causing a circuit closure. Both recorders were developed
at NRDL in conjunction with the Precision Instruments Company, San Carlos, California.
The dose increments chosen for the low- and the high-range ionization chambers are 0.243
mr and 0.243 r, respectively. As radiation data is recorded on the two channels of the threechannel tape, pulses are recorded on the third channel at 3.75-second intervals to establish a
time reference for data reduction. The time pulses are generated by a cam-operated switch
driven by a low-power, 6-volt chronometrically governed motor. The accuracy of these pulses
{is =0.5 percent. The timer is manufactured by the Haydon Company and is used because ofits
known accuracy and high reliability.
The function of the control circuit is to start and stop the instrument.
tors and to the filaments is controlled by means of a latching relay.
Power to all the mo-
This relay can be activated
locally by a switch on the instrument or remotely by a contact closure through a cable into the
instrument. The instrument can be turned off by deactivation of the relay with the switch on
the instrument or by the tape-actuated turnoff switch on the recorder.
Mercury batteries are used to power the motors and the filaments, to take advantage of the
high current capacity and flat-discharge characteristics these batteries offer. In addition, a
mercury battery with very low current drain is used in the electrometer-calibration circuit to
restrict calibration shift to less than +1 percent during the expected life of the battery. Chamber bias and transistor bias are supplied by carbon batteries. With the exception of the motor
battery, the minimum battery life is in excess of 250 hours. However, the 12-hour recorder
can be operated in excesa of 26 hours and the 60-hour recorder in excess of 80 hours without a
battery change.
All components are designed to operate under the following maximum conditions: (1) a shock
of 15 g for 11 msec in all planes, (2) vibrations of 12 g at frequencies up to 45 cps in all planes,
(3) temperature within the detector of 120° F, (4) temperature within the main instrument assembly of 155° F, (5) ambient relative humidity of 100 percent, and (6) a static overpressure of 5
psi.
During the operation, satisfactory performance beyond these limits was frequently observed.
B.2 DECAY CURVES
Throughout this report, the tonization chamber decay curve in Reference 89, extrapolated to
early time by means of data in Reference 36, has been used repeatedly and has been referred
to as the standard decay curve. Since this entire curve ls not available in a single reference,
it is reproduced here (Figure B.5). In addition to the standard decay curve, the crystal decay
curve of Reference 120, the gammaintensity decay unit (GIDU) decay curve (Figure B.8), and
the IC decay curve S-IV (Section 3.3.1) have also been reproduced in Figure B.S. The GIDU
was installed aboard the DD-592 where it collected a total sample of deposited material for the
first 4 minutes after zero time.
This total sample was then conducted into a shielded chamber
where a GITR immediately started recording decay. The design and operation of this unit is
more fully described in Reference 86; however, the Umbrella decay from 6 minutes Is included
in this report for comparison with other decay curves (Figure B.6). For very early times, the
decay curve of Reference 87 is used and is also reproduced here for greater convenience
(Figure B.7).
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