CHAPTER X NUCLEAR CLOUD SAMPLING In the early days of sampling little was known about content of the cloud, the relationship between the content of the cloud and the efficiency or the yield of the nuclear detonation, nor the dangers associated with content of the cloud and "fallout," Along with cumlative experience, certain rules and formlae developed and cloud sampling became a prime means of judging the effectiveness of each device detonated. for determining efficiency evolved: fire-ball measurements, accurate, Three methods cloud sampling, alpha measurement, and Cloud sampling proved by far the most nearly Additionally, "tracer" elements were placed in the device itself to check the efficiency of the various components; however, sampling also gave the best readings from the "tracer"® elements and provided a means of determining how well each integral part of the device functioned. Los Alamos Scientific Laboratory officials have discovered no accurate means of forecasting the behavior of a device, Testing furnished the only means of determining the efficiency of a device, and cloud sampling was the most nearly positive method for this, Secondary benefits from cloud sampling occurred in fallout sampling, identification of particles, cloud phenomenology, the distribution of fission products, and, sometimes, determining alien successes with similar devices, To provide the scientist a usable sample required three important conditions : (1) It must comprise a large enough fraction of the total fission products and "unburned" material from the device to permit the desired measurements to be made reliably. 198 SWEH~-2-003) 4 Ve . AFWL/HO