-13- velocity, higher collection efficiency, smaller collection area, more reproducible performance and higher altitude capability, has been built and flown several times by General Mills, Inc. The others, still in the preliminary design stage, promise high efficiency with lower resistance to air flow, low weight, and still greater concentration of the sample. Several flights have been made with /stratospheric air liquefaction system designed by the Chicago Midway Laboratories to collect whole air samples for calibrating the routine collectors. Fig. 15 shows the collector. The total weight of a typical flight train is close to a ton. Results of analysis of the samples collected by this liquid air system are now being evaluated. . A device is also being developed to collect separate particle size fractions in the stratosphere for radiochemical analysis. It is hoped that the development of high-altitude particulate sampling devices will contribute not only to the solution of our own practical problem: but also to a wide range of basic studies on such subjects as global exchange processes, meteoritic accretion and others. 5. Hardtack Tracer Experiment In order to help in distinguishing among various possible routes of transport of debris from test detonations, the AEC has recently added the isotopes tungsten-185 and rhodium-102 to the list of analyses performed. These isotopes resulf’from neutron activation of materials present in certain nuclear devices. As far as is known, the proportions of these radioactivities to the fission products in the debris resulting from the Hardtack test series conducted in the Pacific Proving Ground last DOE ARCHIVES spring and summer. were appreciably higher than from other sources. isotopes can therefore serve as tracers for #™ Hardtack debris. These (9