In order to utilize the advantages of the electron microscope for the study of respirable particles, it is desirable to have an instrument capable of sampling from atmospheres having very sparse dispersions of particles at a rate sufficiently high to result in precipitation densities of approximately one particle per 10/u² of microscope screen for a 10 minute sampling period. In order to avoid qualitative or quantitative alteration of the aerosol, it was desired that the instrument collect the sample directly on an electron microscope screen rather than on a filter material for subsequent transfer to the screen. This paper summarizes work aimed at the development of such an instrument.

Soil chemistry studies have been carried on at Hanford for a number of years in support of the disposal of low and intermediate level liquid wastes to the ground. Equilibrium type experiments were carried out to investigate the mechanisms of the reactions of Sr, Cs, and rare earth ions with soils (1, 3, 4, 5). Experiments were also conducted with simulated and actual wastes in soil columns and an empirical method was developed for prediction of radionuclide breakthrough from ground disposal facilities into ground water on the basis of short, laboratory soil columns and equilibrium experiments (6,7). In this method it is assumed that the shape and position of the breakthrough curve is the same under laboratory conditions as in the larger scale field case. It is also assumed that the "column volume" or amount of soil effectively used for fission product sorption is that directly under a disposal facility without considering any spreading of waste solutions. These assumptions are known to be on the conservative side, but the degree of conservativeness is not known.