first chemically separating the plutonium and uranium from the gross gample and then submitting the separated fractions to mass spectrographic and se analyses. Extremely low levels of uranium and plutonium can be getermined in this manner. 3. Certain induced activities such as iron, beryllium, nickel, co- palt, etc. were also chemically separated from the gross sample and ingividually assayed. These results are discussed in Chapter 3, Section 3.15¢ The detailed analytical and assay procedures for this complex array of data can be found in References 10, l1, 12, 13, 14, and 15. 2.3+2 Radiochemical; Gas. The principal gases of interest in Castle gas samples included C™ (measured as C'40,), A®4 Kr, Xe 134, and H8 (measured as H?,0). Since the gas samples occurred in varying volumes, at least two separation systems capable of handling the varied volumes were required. A larger gas-separation system was utilized for the B-31 and the B-36 Squeegee samples, and a smaller separation train was utilized for the snap and F-84G Squeegee samples. Carrier for krypton and xenon was used in all samples separated; occasionally, samples wre spiked with D,O0 as a tracer for the tritium measuremnts. Separation, decontamination, and sample cross~contamination problems are discussed in detail in References 3, 4, and 5- Upon separation of the desired gas fractions, accurate assay or counting is required. Separations were ac~ complished at Tracerlab, Inc., and assay was principally done at the Argonne National Laboratory, Chicago, Illinois. Current separation end assay procedures are sufficiently sensitive to measure background quantities (Reference 11). It was hoped that Castle tests would give gas fractions sufficiently high above background to explore and test the usefulness of these quantities in terms of interpreting phenomena associated with the nuclear explosions. 2-3-3 Physicaland Petrographic. The primary prerequisite for physical and petrographic studies of particulate nuclear debris was the separation of the radioactive particles from the filter-paper medium and other inert particles. When individual particles were separated, they were observed under optical microscopes and their size determined. These individual particles were then examined for color, shape, and X-ray diffraction patterns, and also for specific beta and alpha activity. In some instances, the composition of the particles was measured when pertinent to the overall evaluation of these analyses. Occasionally, individual particles were subjected to nuclear film studies to observe low-level alpha activity by studying the tracks produced by the radiations. This technique was sometimes useful for detecting the presence of polonium. 14