at the top of the ascending elevator for an equal increment of time, varying from 2 to 15 minutes
for different instruments; after exposure it was pushed horizontally across to the descending
elevator by meansof a pneumatic piston.
For land-surface shots, grease-coated cellulose ace-
tate disks were used as collecting surfaces; for water-surface shots these were interspersed
with disks carrying chloride-sensitive films. This instrument also furnished data on the time
of arrival, rate of arrival, peak and cessation of fallout and, in addition, provided samples for
measurements of single-particle properties, particle-size distribution, and radiation characteristics.
The OCC, shown with the top cover removed in Figure 2.6, contained a square aluminum
tray about 2 inches deep and 2.60 square feet in area, Each tray was lined with a thin sheet of
polyethylene to facilitate sample removal and filled with a fiberglass honeycomb insert to improve collection and retention efficiency without hindering subsequent analyses. The collector
was equipped with a sliding lid, to prevent samples from being altered by environmental condi-
tions before or after collection, and designed in such a way that the top of the collecting tray
was raised about '4 inch above the top of the instrument whenthe lid was opened. Upon recovery,
each tray was sealed with a separate aluminum cover Y, inch thick which wasleft in place until
the time of laboratory analysis.
The samples collected by this instrument were used for chemi-
cal and radiochemical measurements of total fallout and for determinations of activity deposited
per unit area.
The AOC, was an OCC tray assembly which was continuously exposed from the time of placement until recovery. It was provided as a backup for the OCC, and the samples were intended
to serve the same purposes.
The RA was a stock instrument (AN/UMQ-5B, RD108/UMQ-5) capable of recording wind
speed and direction as a function of time.
The Mark I and I trigger-controil units were central panels designed to control the operation
of the instruments in the major sampling array. The Mark I utilized ship power and provided
for manual control of OCC’s and automatic control of IC’s. The Mark II had its own power and
was completely automatic. A manually operated direct-circuit trigger was used for the ship
installations and a combination of radio, light, pressure and radiation triggers was used on the
barges and Site How.
In addition to the instruments described above, an experimental high-volumefilter unit (HVF),
or incremental air sampler, was located on each of the ship platforms. It consisted af eight
heads, each with a separate closure, and a single blower. The heads contained dimethylterephalate (DMT) filters, 3 inches in diameter, and were oriented vertically upward. Air was
drawn through them at the rate of about 10 cubic feet per minute as they were opened sequentially through the control unit.
The instrument was designed to obtain gross aerosol samples
under conditions of low concentration and permit the recovery of particles without alteration
resulting from sublimation of the DMT.
Sets of instruments consisting of one incremental and one total-fallout collector belonging to
Project 2.65 and one gamma dose recorder belonging to Project 2.2 were also placed on the ship
platforms and either on or near the barge and Site How platforms.
eventual cross-correlation of data possible.
These were provided to make
:
2.2.2 Minor Sampling Array. The minor array (Figure 2.7) was mounted in two ways. On
the skiffs, a telescoping mast and the space within the skiff were used for the instruments. On
the rafts and islands, a portable structure served both as a tower and shield against blast and
thermal effects. However, all arrays included the same instruments: one time-of-arrival de-
(aot,(TOAD), one film-pack dosimeter (ESL), and one always-open total collector, Type 2
AOC,).
{
The TOADconsisted of an ionization-chamber radiation trigger and an 8-day chronometric
clock started by the trigger. With this instrument, the time of arrival was determined by sub-
tracting the clock reading from the total period elapsed between detonation and the time when
the instrument was read.
The ESL was a standard Evans Signal Laboratory film pack used to estimate the gross gam20