Work was completed on the high-temperature, high efficiency air filter. Technical assistance was given at a large-scale, privately financed run of an all-glass medium. Full-size filers have been produced in quantity and are offered by manufacturers; it is considered that commercial manufacture has been established. A survey was made of air sampling practices at 37 laboratories. Analysis of the survey results indicated that 22 different kinds of air-sampling filer media were in use among the laboratories questioned. We have recommended that air-assay practice be simplified by use of fewer media. A group of five media has been proposed as adequate for meeting all requirements. Laboratory work was done on the development of a high-efficiency, low-ash, all-purpose, air-assay paper. Two methods of approach were tried. In one an effort was made to produce cellulose fibrils in sufficient quantity and quality to act as the fine-fiber component of a filter. Only moderate success was attained. Better promise was shown by combining synthetic organic microfibers with cellulose fibers in a wet-formed sheet. No plant work was undertaken on this item.

During an experiment involving alpha phase annealing (at 610 to 655 deg C for 5 and 10 min) of beta-quenched uranium, it was determined that the relatively coarse, irregular shaped grains (0.08 to 0.150 mm in diameter) in the beta-quenched structure, were replaced by fine equiaxed grains (0.04 to 0.09 mm in diameter).

As part of the recent intensified study of variables involved in the beta heat treatment of production uranium, the writer undertook a qualitative examination of the effects of heating and quenching media on the hydrogen content of pieces heat treated in slug form. Because of the limited amount of time available the work was necessarily restricted in scope. For the same reason no detailed study of any single heat treatment was attempted: rather, a number of beta treating schedules were selected so that estimates of the degree of hydrogen occlusion to be expected during a large variety of beta heat treating schedules would be possible.