With regard to the adequacy of radioassay techniques, as I said, I think they are good, but I think calibrations have to be polished up considerably so that any laboratory could look at a given sample and say with confidence that they have so many fissions attributable to this or that source. Dr. Martell: May I comment on your remarks about tungsten isotopes differing for various sources? Welooked at this briefly but, unfortunately, the only two isotopes that have been studied to any extent are 181 and 185, which show a maximum variation of a factor of 2 if you examine their production in the single, very high altitude shot, and consider the total production of each of them in the lower altitude shots taken as a group. very much in altitude. They don't differ A factor of 2 isn't very much to play with if you are attempting to make an inner com- parison to get ratios for these two isotopes and other components of these two sources, especially when you add to this the fact that you are comparing radioassay data from two or more laboratories. Col. Russell: That is true. However, if you remember, I mentioned that the Tungsten 188 went into the analysis and that the Tungsten 188-to-185 ratio differed by a factor of something like 5 or 6. The high yield tungsten-bearing shot would be expected, I think, to go considerably higher than the others. Dr. Kalkstein: One thing with regard to Tungsten 188 is that is was produced in a lesser amount, by a factor of about 10, than 181 or 185. This makes 188 a difficult measurement, particularly if we are not seeing it yet. Looking at our radium data in the early days and worrying about the amount of tungsten was a means of saying that this was Orange. In the early balloon samples rhodium went up somewhat, but tungsten just wasn't there. With Tungsten 185 and 181 as with Rhodium 102, you don't have to know much about the tracer you are using if you want to do just relative measurements. Conversely, if you want to make comparisons with other isotopes - if you want to compare with other labs - then it is rather important to know the decay scheme and how you are going from cpm to dpm to atoms. Tungsten 181 is particularly bad in this respect, and I suspect that there will be very poor agreement between laboratories. The reason is the following: the best value for the L-to-K electron ratio. are emitted. If one looks at the table of isotopes, one finds Tungsten 181 decays by electron capture and both L and K X-rays If you count K X-rays, which are what most of us are counting, the energy is about 57 kev. want to talk about dpm, you have to correct for the L X-rays. If you This reference, let's say, gives an L-to-K ratio of 1.5, so, you have to multiply K X-ray count by 2-1/2 to compute the number of electron capture events or the total X-rays out. Actually, there is some reason to doubt this reference. Early work has shown that there were gamma rays of about 130 kev and 150 kev in low abundance associated with Tungsten 181. The man who made measurements of the L-to-K ratio said that he looked for these gamma rays and didn't find them. He then actu- ally measured L X-ray abundances and K X-ray abundances, and came out with the L-to-K ratio of 1.5. measurements are very difficult to make. These It is a difficult experiment, and my feeling is that it was poorly done. The implications are the L-to-K ratios are the best means to use where there aren't other means available for measuring disintegration energies for electron capture. energy of 90 kev. The L-to~-K ratio also led this author to disintegration If there really were 150-kev gamma rays subsequent to decay, then energy for disintegration between ground states has to be greater than 90 kev, perhaps greater than 150 kev. 88 This L-to-K ratio as a