Dr. Kalkstein: I might add just one thing to this: we are looking at this from a somewhat different angle. qualified as mass spectroscopists; we are not equipped, as it is expensive. We are not There are new means of alpha counting. Just about all of these things decay by alpha emission, or a certain fraction of the decays are by alpha emission. By separating out different elements, even where there are differences in the production of the heavy elements, one gets some discrimination, and then, even within a given element where there may be several isotopes decaying by alpha emission, there are means now by solid state devices where one can have a relatively cheap detector and one with sufficiently good resolution that one could make these measurements by alpha counting. There is some literature on both the method and results, and the first thing is to look at the results and get what you can out of them. We are trying to do this, too. It may turn out that we don't have to do much more measuring if the results give us what we want. Col, Russell: Are any of the particles you have been getting in the impactor-type samplers sufficiently large to be susceptable to electron microbeam analysis? Dr. Friend: There are particles ranging up to about 10 microns radius. micron and 10 microns radius. showed earlier. The population is very low between about 1 These particles appear to be of different nature from the persulphate which I Of course, there is speculation that these might be micrometeoritic material. Some of the sulphate particles do get up to around a micron radius or so, and these would also be amenable to electron microprobe. Dr. Kalkstein: This is being done; some of the sulphur data are just by X-ray fluorescence, but people are looking also at individual particles by electron microscope. Dr. Friend: For an individual particle, I don"t think anyone will ever quote less than 1-micron-diameter particles. You need a couple of microns or a big collection of many small particles. Floor: You are really saying that particles you can analyze are the background, natural aerosols in the stratosphere. We can discriminate the radioactive particles from background particles directly, and the preliminary data show that we have two quite different systems. I don't think that analysis of any of the particles over the particle spectrum would help you to determine constituents associated with the radioactive debris. Dr. Friend: If we take the natural stratospheric aerosol that we have right now and look at these particles, the signal we get is all sulphur from the electron microprobe. 92 There is so little mass of anything else there, although