with the data from Shot Lassen normalized in the same manner as was done for the 730-yard
data. The theoretical estimate of AFSWC TR-58-13 is also shown.
The break in the curve, that is, the point at which the nitrogen-capture effect disappears and
the fission-product portion of the curve predominates, appears normally at about 0.4 seconds.
The appearance of this break in the data obtained at 550 yards at approximately 0.2 second makes
the time scale of this instrument suspect. As dependence on tape speed was the only time reference utilized this error was entirely possible.
Figure 3.3 shows the measurements obtained at 750 yards, along with the Lassen data normalized as was done previously at 1 second. The measurements obtained at 550 yards are also
plotted in Figure 3.3; however, a constant multiplier of [wo was used to shift the time axis of the
TABLE 3.1 INITIAL-GAMMA DOSE RATE VERSUS TIME
Time
sec
0.025
550 Yards
Experimental
Corrected
Dose Rate
Dose Rate
r/sec
16.1
Time
r/sec
sec
<
750 Yards
Experimental
Corrected
Dose Rate
Dose Rate
r/sec
0.025
§.36
0.05
7.36
0.05
2.58
0.075
§.11
0.075
1.61
0.1
2.77
0.1
1.12
9.2
0.861
0.2
0.180
r/sec
0.3
0.569
0.3
0.0703
0.4
0.472
0.4
0.0450
0.5
0.424
0.5
0.0383
0.6
0.389
0.6
0.7
0.0328
0.8
0.317
0.8
0.0299
0.9
0.292
0.9
0.0289
1.0
0.264
0.265
1.0
0.0269
0.0270
1.5
0.186
0.187
1.5
0.0214
0.0215 ©
0.7
0.356
0.0347
2
0.142
0.143
2
0.0181
0.0182
3
0.0944
0.0958
3
0.0133
0.0134
4
0.0778
0.0796
4
0.0114
0.0116
5
0.0639
0.0659
5
0.0103
0.0105
6
0.0556
0.0579
6
0.0083
0.0085
7
0.0503
0.0529
7
0.00778
0.00803
8
0.0439
0.0466
8
0,00694
0.00721
9
0.0394
0.0429
9
0.00667
0.00698
10
0.0350
0.0390
10
0.00639
0.00673
15
0.0253
0.0297
14
0.00556
0.00605
20
0.0197
0.0246
20
0.00472
0.00541
22
0.0192
0.0245
30
0.00403
0.00512
30
0.0144
0.0210
°36
0.00397
0.00539
40
0.0122
0.0209”
data and the intensity was decreased to match the 750-yard measurements at 1 second. The intensities out to 20 seconds no longer suffer from the instrumentation error and follow the Lassen
data with close agreement.
Figure 3.4 shows the percent of the measured initial-gamma dose accumulation as the function
of time at the 750-yard location. The heavy line in the figure shows the unrealistically steep approach to 100 percent that results from the leveling off of the measured data. If a decay similar
to that of Shot Lassen is assumed, the dashed line illustrates the integrated gamma dose under
these conditions.
As a result of the measurements obtained, the shape of the curve for fission-product doserate decayfor very-low-yield weapons was further defined. The agreement between data obtained from Operation Plumbbob (Shot Lassen) and the adjusted data obtained from Shot Hamilton
was found to be good.
As the total dose can be accurately predicted and the fraction of the initial
31