Figure 3.5 is a composite of themeasurements made with the DT-60/PD dosimeters, NBS
film packs, and LSD film stacks. Each datum point is the numerical average of the corrected
readings obtained by a particular dosimeter technique at the slant distance indicated. The NBS
and LSD data obtained along the 0-degree axis was plotted without distinguishing between dosimeters placed in pipes or on-stakes, because all films were calibrated both inside and outside of
the pipes. The DT-60’s were probably not sensitive enough to record these differences; therefore, data obtained in pipes and at stake stations were plotted the same as iefilms. The line
drawnis a least-squares fit of the data points shown.
The measurements along the 0-degree axis are consistently higher than along the 85-degree
axis. The slightly higher dose (10 to 15 percent) on the high-neutron axis is, for the most part,
attributable tothe increased nitrogen-capture gamma dose on this axis. The weapon orientation
and a 4~inch-thick, 11-inch-diameter beryllium shadow shield adjacent to the weapon on the 85degree axis accounted for the higher neutron output on the O-degree axis. Also presented in
Figure 3.5
is a theoretical curve for initial-gamma dose (Reference 6) obtained by assuming a
0.001-kt detonation and a relative air density (NACA atmosphere) of 0.88. Using TM-23-200
(Reference 17) and a relative air density of 0.9 the theoretical dose is approximately a factor of
two lower than the experimental measurements shown in Figure 3.5.
No corrections were applied to the total-dose measurements in Figure 3.5 for the increased
radiation dosages actually recorded, because of_neutron-induced activity present in the soil and
in the pipes in which the close-in dosimeters were placed.
any dosages received from fallout.
Also, no corrections were made for
The cable to which the standard 3-inch-steel-pipe holders
were attached was drawn back beyond 500 yards at approximately H +5 minutes. The film
badges and associated equipment were removed from the pipes within 30 minutes after shot time.
Dose-rate measurements on each pipe were negligible, except for the one at 55 yards for which
the dose rate was only 1 r/hr at approximately 5 minutes after the shot. Dose rates from fallout at distances greater than 300 yards were negligible. Film badges and associated equipment
attached to stakes beyond 300 yards were removed within 2 hours after shot time. On this basis,
it is believed that any dose received by the detectors other than initial-gamma dose was negligible.
The NBS and LSD data presented in Figure 3.5 was corrected for the contribution of the neutrons to the film blackening. This effect can be attributed to both the low-energy neutrons and
to the total neutron rep dose resulting primarily from the higher-energy neutrons.
Experiments
that have measured these effects have shown that little error is introduced in the range of useful
film exposure by assuming an average film type and using a single correction factor for each
effect on the films. The total initial gamma dose film data points for a particular slant distance
as shownin Figure 3.5 were derived from the following equations:
gold neutron flux
r dose = film reading — TSR Wem? 0.038 (neutron rep dose)
The corrections used were (Reference 5): film sensitivity to gold neutrons,
film R, and film sensitivity to high-energy neutrons as a percentage of neutron rep
dose, 3.8 + 2.4,
The gold neutron flux for the 0-degree axis was obtained from Reference 18.
No gold flux
measurements were made along the 85-degree axis; consequently this correction to the meas-
ured fitm dose was based on the 0-degree-axis gold measurements. The rep dose used in the
corrections was based on the sulfur-activation measurements as presented in Figures 3.6 and
3.7.
.
The DT-60/PD dosimeter data presented in Figure 3.5 was corrected for the effect of neutrons
on the dosimeter reading. The DT-60/PD dose as read by the reader is:
Reader dose = true dose + 6.8 nth
where nth is the neutron rep dose at a particular slant range due to thermal neutrons, and 6.8
is an experimentally determined coefficient (Reference 19). The thermal (gold) neutron flux
was obtained from Reference 18 and was converted to dose using the fact
35
Mage 3G Devetd