it because the distribution of rare earths in vaporizing meteoritic material is likely to be very consistent, However, it may not be exactly what we have seen in the earth's crust or in certain specific types of meteorites. So all we need to do is measure the effects and change of ratio, due to an addition of one added carrier in this region, and look at two. So, say you change the potential for gathering Europium by a factor of 2; you can dis- criminate the added tracer in that sample. get a signal above the background. You push the total mass of the tracer up to the point where you can The background work certainly has to be done, and this is a tough low-level problem, more because of the background in the collector than from what may be the high stratosphere. Dr. Kalkstein: I think the natural background can be taped just by looking at what is there and putting up more than there is by a large factor. We have been thinking of ways of suggesting cooperative experiments with the Russians, and, if we have to go to large payloads, maybe this is the way we can cooperate. IPC tape, and we find that everything is in IPC paper. We also have neutron-activated The difficulty with neutron activation is that, for certain elements anyway, it is so sensitive that you have really got to be careful how you handle your samples, what is in your samples, and what material you use to collect your samples on. I really think that this is where the big problem is if one wants to get into this. Dr. Friend: For instance, I happen to have some results. ash samples. In the experiment that we did, we used Mylar to wrap up the We analyzed the Mylar, which you might think to be very clean material. This was all handled with rubber gloves with no powder to put on them, and in as dust-free an atmosphere as we could manage, Copper came out 10°® grams; zinc, 10°! grams; phosphorous, 10°! grams; calcium 10°°, grams; cobalt, 10°? grams; and soon. 96 We did not measure uranium.