Table 1. Survey of Samplers and Sampling Methods Fallout Trays/surface collectors 1. a. b. c. Always-open collector (gross or total collector) Open-close collector Gross-fallout collector adem Sequential collectors Differential fallout collector Incremental collector Intermittent fallout collector Special incremental collector Sticky surfaces a. Tape fallout monitor Aerosol monitors a. db. c. Il. Cascade impactor Electrostatic precipitator Conifuge Cloud Filter units (presumably isokinetic) an or & 1. ACC type V asbestos fiber IPC 1478 impregnated cellutose Membrane filters Glass fiber Sticky wires Cascade impactors Electrostatic precipitators Ill. Miscellaneous Hi-vols Scoops Resuspension samplers Radar (remote measurement) Core drills Fallout samplers are either passive or active, with the great majority of samples taken in the passive mode. By active sampling, we mean sampling by means of impactors, precipitators, conifuge, etc. The other samplers mentioned are, then, passive. The always-open collector remains uncovered during an event. This collector may be a tray, or a bottle with a funnel. With this type of collector, the fallout may become considerably diluted with extraneous dust entering the collector from the base surge and as a result of wind action before, during, and after the actual collection period. Furthermore, no information can be obtained (without parallel and independent appropriate radiological monitoring equipment} about the time of first arrival of fallout particles and the time of cessation of fallout. An improvement is the gross-fallout collector, consisting of a bottle with a funnel equipped with a lid that automatically opens at shot time. This lid is then replaced about 12 hours later. A further improvement is the open-close collector which not only can be automatically opened, but which also can be automatically closed. However, some dilution of fallout particulates still occurs even with this last type of collector. More detailed information is provided by sequential samplers. Differential, incremental, and intermittent fallout collectors are different types of collectors that are programmed to expose sequentially new collecting surfaces for equal increments of time. After some tests, 20 or more sequential samples have been collected at any one location. The “special incremental collector" has been adapted to shipboard use in the Pacific by the addition of a provision whereby the samples are automatically delivered to a laboratory below deck. Sometimes the bottom of the fallout trays was coated with a thin layer of grease to prevent the collected particles from being blown away. Other trays were lined with plastic, so that the sample could be removed by simply lifting the plastic sheet out of the tray. Sometimes the trays contained small nylon pebbles to simulate a soil surface. Whereas these sequential samplers are usually trays of one sort or another, a movable sticky tape has also been used as a sequential sampler. Mostly, however, this type of collector (tape fallout monitor) was used in conjunction with a radiation monttor to corroborate time-of-arrival data from the intermittent fallout collectors or similar devices. Among the less frequently used active samplers, the "conifuge" needs special mention. This is a particle-sizing device consisting of a pair of rotating concentric cones separated by a narrow annular space. The particles are introduced into this space, and follow trajectories determined by their mass and the centrifugal force resulting from the rotating cones. Thus segregated, the particles deposit on the surface of the outer cone. Impactors, mostly Casella, some Anderson, were used frequently to obtain a separation of the fallout into size fractions and to obtain mass distribution. 227