Immediately following the passage of the blast wave, one team moved into the area, marked
the 10 r/hr point on the east line, and measured the dose rate at each stake on that line outside
of this point. At 15 minutes following the shot (H+15 minutes), four additional teams made similar surveys on all four lines and the other team made a general survey as for Shot Hamilton.
Additional surveys were made up to H+6.5 hours when the area was evacuated for another shot.
A survey for alpha contamination was made after Hamilton D+1 day at the 96 alpha-monitoring
pads adjacent to the film-badge stake stations. Operational conditions, such as late shifting of
ground zero and time limitations before and after the shot, precluded any alpha surveys for Shot
Humboldt.
INSTRUMENTATION
Incremental-Gamma~Dose Recorders. The incremental-gamma-dose recorder used was a
modified Emmett device as employed by Project 2.5 during Operation Plumbbob. This device
is essentially a conveyor belt of film badges, each of which is exposed in turn from an underground shield and returned thereto. A typical station cross-section: is shown in Figure 5, and
a line drawing of the mechanism is presented as Figure 6. A complete description of the Emmett device is given in Reference 3.
Since the Emmett device does not have a fast-enough time resolution to differentiate the various initial gamma pulses from very-low-yield bursts, it was decided to changethe traveling
speed of the film badges in order that each badge would be exposed for 1 minute. (The device
so modified ran for 20 minutes and could provide fallout-arrival data or early-decay data.)
By:
spacing the film badges so that some were in the probe above ground at zero time, it was possible to obtain total gamma doses during the first 3, 15, and 30 seconds.
The speed of the Emmett device, as modified by this project, was sensitive to battery voltage.
Consequently, freshly charged batteries were employed, and the speed was set by ad-
justing a resistance in series with the motor just before the assembly was loweredinto the
ground. The speed setting was verified by timing the drive-sprocket revolutions with a stop
watch.
Dry runs over the entire cycle of operation showed that the speed did not vary by more
than +5 percent.
.
Figures 7, 8, and 9 are photographs of steps in the installation of an Emmett station. In
Figure 7, the instrument rack complete with film probe is lowered into the undergroundshield.
In Figure 8, the rack and probe are in place along with sand-bag shielding. The top of the probe
wasscrewed in place after the 30-second-exposure film badges were checked for proper position
at the top of the probe.
Figure 9 shows the completely installed station, with the blast shield in
place and the timing wire connected. (The smaller cylindrical tube was originally used during
Operation Plumbbobto protect an ionization chamber. It was not used by this project. )
Film-Badge Station. The film badges were placed in National Bureau of Standards (NBS)
holders, which were inserted, in turn, in plastic cigarette cases for dust and moisture protection.
A discussion of the NBS holder is contained in Reference 9.
All film badges within 300
yards from ground zero were also placed inside of electrical “condulets” or pipe nipples for
blast, missile, and thermal protection.
A condulet is a small, weather-proof, iron, electrical-junction box. The model used by this
project incorporated female pipe threads to facilitate fastening to iron-pipe stakes.
(The condu-
lets were previously treated to remove cadmium plating and so minimize neutron-capture photons. }
The film packs were mounted on top of 3-foot~long pipes driven into the ground. For Shot
Hamilton, several stations were extended to 6 feet elevation to clear a shadow-shielded area
behind a dike to the east of ground zero. Figure 10 illustrates a typical station.
Table 3 lists the ranges covered by the individual films in the film badge.
Field-Survey Instrumentation. The field-survey teams used the AN-PDR/39 for gamma
readings and the Eberline PAC-3G alpha survey instrument for alpha readings. These instruments are described in References 11 and 4 respectively.
16