Sakae iaCRE
Per Terr eey
CHAPTER5
ANALYSIS OF RESULTS
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The voltage-calibration trace and foil-calibration trace that were made just prior to
closing each station showed that all densitometers were in satisfactory operating condition.
These calibrations were made both as a final check on the serviceability of the densitometers
and also to check the calibration during the record run.
The causes of the functional failures at Stations 690.01, 690.03, and 690.04 are not
definitely known. However, there are several possible explanations. At Station 690.01 there
may have been a faulty contact between the recording-unit outlet and the cable connected to the
H-5 sec timing (EG&G) relay. Hence the control relay in the recording unit which was to close
the camera powercircuit was not actuated.
At Station €90.03 a situation opposite to that at Station 690.01 appeared to have occurred.
The camera and all other circuits designed to close at H—-5 sec were turned on. However,
oscillator- and filament-battery voltages after recovery indicated that they were never turned
on (at R—1 min). This time the control cakle connected to the H—1 min timing relay may have
made poor contact.
The densitometer at Station 690.04 operated well but with reversed timing sequence. The
designed timing sequence was for the timing oscillators and oscilloscope-filament circuits to
close at H—1 min. The camera power waa to be turned on at H-5 sec. The film record showed
that the camera had already been running about 58 sec when the timing marks appeared and
the oscilloscope filaments were turned on. Since ali the densitometcrs were connected in an
identical manner, the timing relays at Station 690.04 could have been marked in reverse.
The record obtained at Station 690.02 agreed with predictions. The time of release of the
last calibration foil had been measured in the laboratory to be about 2.9 sec after the master
timing relay closed at H-5 sec. The break in the beta trace at about 1.1 sec after the release
of the last foil was therefore taken as the zero-time mark, The break in the beta trace was
believed to have been used by a sudden burst of gamma radiation at the instant of explosion.
This momentary lerge background gamma radiation superimposed on the beta signa) was
sufficient to deflect the electron beam off the face of the oscilloscope.
The quick recovery of the beta trace to its prezero-time level proved that the predicted
low gamma radiation rate was indeed correct and that its consequence, namely, elimination of
lead shielding and of a second phototube for subtracting background radiation, was justified.
Except for the short break (for about 0.30 sec) in the beta trace at zero time, the betatrace level was essentially constant from H—1.03 sec (time of release of last calibration foil)
until H + 9.86 sec (time of blast arrival). This was interpreted to mean not only negligible
background radiation but also the absence of dust-loading in the air (thermal dust prior to
blast arrival). It also indicated phototube fatigue was negligible during the period of measurement.
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