Chapter 2 PROCEDURE 2.1 OPERATIONS Project 2.1 participated in Shots Cherokee, Zuni, Flathead, Dakota (limited), Navajo, and Tewa, For every shot except Dakota, all possible stations were instrumented with every avail- able type of detector of appropriate range. For Shot Dakota, stations were loaded with photo- graphic-type dosimeters just prior to shot time, and these were recovered at the instrumentation time for Shot Navajo. Stations were instrumented as late as possible prior to shot time and recovered as soon as rad~safe conditions permitted. 2.2 INSTRUMENTATION 2.2.1 Photographic Dosimeter. The primary detector consisted of film exposed in the NBStype film holder. This consisted of a bakelite container with an 8.25-mm wall thickness covered with a 1.07-mm layer of tin and a 0.3-mm layer of lead. The lead and tin acted asfilters to suppress the lower energies sufficiently to keep the response linear above 115 kev. Below 115 kev, the gamma radiation was attenuated excessively, and exposure caused by gammas below 115 kev was small compared to that above 115 kev (Reference 12). The thickness of bakelite was determined experimentally on the assumption that the spectrum from a 10-Mev betatron was similar to the initial radiation of the device (Reference 13). The electron equilibrium layer presented a source of electrons that might have been scattered into the emulsion to replace those electrons produced by gamma radiation absorbed near the surface of the film and lost without being detected. In the energy range from 115 kev to 10 Mev, the dosimeter was considered accurate to within 420 percent with the film types used on this operation (References 14 and 15). For Shot Cherokee, film was exposed both with and without NBS holders to obtain an indication of the presence of low gamma-energy components in initial radiation, since bare films showed maximum sensitivity to gamma energies at about 60 kev. Two dental-size film packets, each containing from oneto three different film emulsions, could be placed in the holder. A lead strip of 0.78-mm thickness was wrapped around the outer edge of the holder to cover the seam. The holder was placed in a sealed plastic can to protect the film from weather while in the field. The primary film packets used were Du Pont 553 containing Emulsions 502, 510, and 606, and an Eastman packet containing a special microfilm (SO 1112) and spectroscopic-type 548-0 doublecoat film. These packets were individually sealed in polyethylene bags. In addition, Eastman spectroscopic-type 548-0 single~coat was used when very-high exposures were anticipated. Table 2.1 lists the ranges of the films, and Figures 2.1, 2.2, and 2.3 show examples of the calibration curves. The films were stored in a refrigerator at Site Elmer and withdrawn as needed. Sets of calibration films were exposed to the Co®calibration source from 30 minutes to 12 hours after each detonation. Films were processed about a week after each event, thereby minimizing pos- sible errors caused by latent image fading. Variations caused by temperature, aging, and processing technique were compensated for by the calibration film. Factors that caused variation in density from event to event were the latent image fading of Eastman 548-0 film and the small variation in the temperature of the developer solution, In Shots Dakota, Navajo, and Tewa, an increase in the background density equivalent to about 200 mr was noted on the Dupont Emul- sion 502, The use of calibration film in each of these events compensated for this background density increase. 14