mum tape transport speed of the GITOUT, the time interval between successive radi... .
pulses can become shorter than 200 msec, at which point radiation puises will be lost auring
the print-out operation. Thus, the maximum dose rates that can be read out by the timebetween-pulse method without electronic stretching are 280 r. hr and 280 mr, hr for the high-
and low-range channels, respectively. Higher dose rates can be read out only after tapes are
rerecorded at speeds higher than those used for the original recording so that the physical
spacing between radiation pulses on the tape is expanded. This process is called electronic
stretching.
The time-between-pulse method was used for all ASEL tapes and on all NRDL
tapes in the 100- to 2,000-r,hr dose rate range where difficulties resulted from the crossover
between the low- and high-range channels. All peak dose rates were measured by a modified
time-between-pulse method in which a sweep-calibrated oscilloscope trace of the radiation
pulses was photographed in the neighborhood of peak and the minimum distance between successive pulses converted to peak rate (Reference 65).
The direct plotting capability of the GITOUT was used only to obtain qualitative dose rate
information for the preliminary report (FTR~1621).
Al! GITR dose rates reproduced in this
report were obtained by converting digital print-out information into dose rate, which was then
plotted against the total number of counting intervals converted from playback to real time.
For the ASEL records, digital time-between-pulse information was converted to dose rate using a calibration curve for each detector (Section C.2). The resulting dose rates were similarly plotted against real time. This readout and plotting procedure is estimated to be within the
Stated limits of accuracy.
For the higher dose rates, the time resolution of radiation pulses ts approximately +10
msec on the NRDL tapes, whereas the resolution on the ASEL tapes is +0.1 msec. Although
high resolution is possible between any two events on a given tape, the time of the entire gam-
ma record relative to zero time for the detonation cannot be as precisely determined. The
project received EG&G radio signals at minus 5 minutes, minus 1 minute, and minus 5 sec-
onds, the two latter signals being used to determine time relative to zero time. According to
EG&G (References 84 and 85), the accuracy of these keyed signals is + 0.05 second relative to
zero time; however, a delay as great as 0.25 second can be experienced between the time of
the keyed signal and closure of the signal relay in the EG&G radio receiver. All delays in the
coracle control box are at least an order of magnitude less than those enumerated. Zero time
for the ASEL tapes was determined on the assumption that this instrument received its starting signal at minus 5 seconds; the accuracy of this assumption ts within +0.05 to —0.30 second.
Zero time for all NRDL tapeswas determined by means of a timing blank which started at
minus 1 minute and ceased at minus 5 seconds (Section 2.2.7). Although this procedure synchronized all instruments within a coracle, it did not permit the determination of zero time
with an accuracy greater than +1.25 seconds.
All gamma dose rates were plotted on semilogarithmic paper, and Straight lines were drawn
between the points. These plots were later used to calculate the cumulative dose by a process
of numerical integration. Both the use of semilogarithmic presentation and the construction of
Straight lines on such a plot contain inherent errors that depend on the actual shape of the dose
rate curve. In determining cumulative doses, a linear dose rate function was assumed over
each increment of time. If the dose rate is actually a logarithmic function of time, then the
logarithmic presentation {s correct, but the linear averaging technique employed \(s high by a
factor dependent upon the distance between data points. If, on the other hand, the dose rate is
actually a linear function of time, then construction of straight lines on a semilogarithmic plot
is incorrect and the linear averaging is low by a factor dependent upon the distance between
data points. However, a high density of plotted points reduces the errors inherent in either
assumption.
For the linear averaging technique employed, the area under the curve can be as much as
30 percent low for a time interval so selected that the dose rate falls exactly midway between
two plotted points a decade apart. If the separation of the plotted points is reduced by a factor
of 10, the calculated area uncer the curve would be 2.4 percent low, with continued increases
82