centreted by evaporation. Yurthermore, for three of the shots the ‘gamples were not received until 3 to 6 days after detonation and even oe the fourth shot the fallout sample was not received at the site Jaboretory until late in the day after the detonation, For these reasons, the characterization of the fallout itself in many respects was not achieved, However, it is doubtful whether a coa- ‘plete characterization of fallout material from some of the shots would igve been feasible even with satisfactory collection methods, Accorj to some eyewitness reports, it would appear that the fallout frea t 1 (at least at distances of the order of 30 to 50 miles fros ground : ) consisted of dry particles, while that from Shot 2, at the same ‘Gistances appeared to consist of a fine aerosol which in itself would ‘produce practically negligible volume in the collector bottles (some eollector bottles were, in fact, dry). For Shot 4 early, invisible fall- wut arrived on the YAG 39. ‘ In sumery, it should be borne in mind that the results of sone of the following analyses ani experiments do not apply to material as it actually fell at the collection sites, but rather to the total sampled gaterial as received at the site laboratory and which in the majority of eases underwent important changes before it could be examined. This ‘gpplies especially to the physical state separations and chemical states ef Np and I. §$.2 PHYSICAL STATE SEPARATIO, This part of the investigation sought to separate the fallout material recovered as an aqueous suspension into three fractions: eolloidal, and solid, and then to determine the distribution of the ionic, gamma omitting activity and also the distribution of inactive elements among the three fractions. The solid fraction was defined as that material which was removed by centrifugation for 15 min at 2500 RPM (980 g). The ionic fraction was defined as that part of the supernatant which passed through a cellophane ultrafilter membrane of pore size 12 to 40 As the colloidal fraction was that part which was stopped by the sembrane. 3.2.1 Physical Treatment of Samples A 10 to 16 ml aliquot was taken from the original sample with rapid stirring. 4 volumetric’ pipette with its tip broken off to sample the suspended particles was used in this sampling. The slurry aliquot Was placed directly in a weighed, graduated cone-point centrifuge tube, which was then reweighed to obtain both the weight and the volume of the sample. In addition, an aliquot of the original slurry was taken with a micropipet whenever possible for gamma counting; for samples with appreecieble quantities of suspended solida the aliquot for gamma counting was taken from the acidified material used in the neptunium procedure. The slurry sample was centrifuged for 10 min at 2500 RPh. The pH of the supernatant was measured immediately, A small aliquot of the supernatant was taken for a gamma count and a 5- or 10-ml aliquot was Placed in an ultrafilter, The ultrafilter was a modification of one 33