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 means of a pneumatic piston. For land-surface shots, grease-coated cellulose acetate disks wereused 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 charac- teristics. 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 im- prove collection and retention efficiency without hindering subsequent analyses. The collector was equipped with a sliding lid, to prevent samples from being altered by environmental conditions before or after collection, and designed in such a way that the top of the collecting tray was raised about Y, inch above the top of the instrument when the lid was opened. Upon recovery, each tray was sealed with a separate aluminum cover '/ inch thick which was left in place until the time of laboratory analysis. The samples collected by this instrument were used for chemical 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 place- ment until recovery. It was provided as a backup for the OCC, and the samples were intended to serve the same purposes. The RA wasa stock instrument (AN/UMQ-5B, RD108/UMQ-5) capable of recording wind speed and direction as a function of time. The Mark I and II trigger-control 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. was completely automatic. The Mark II had its own power and 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 experimenta) high-volumefilter unit (HVF), or incremental air sampler, was located on each of the ship platforms. It consisted of eight heads, each with a separate closure, and a single blower. The heads contained dimethyltere- phalate (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 sequen- tially 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 af 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 cress~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- tector (TOAD), one film-pack dosimeter (ESL), and one always-opentotal 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 thetotal 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 gam- 20