TABLE 5.2 Predicted vs Observed Particle Size Separztions by Stendard Steves Size Range of Sieves (i) Wh§3 53-62 62-74 74-88 88-105 105-125 125-149 145-177 dy Number of Particles _(y Counted 62.4 85.8 79.5 113 116 172 215 239. 321 228 32? 369 150 181 381 286, The frection from the 62-74 i sieve had a particularly broad distribution, so that all data associated with it should be viewed “ale with great suspicion. The Roller analyzer, used here for particles smaller than 50 p, provides sharper size separations less sensitive to particle shape than the sieves. On the other hand it is more likely to break up frangible or agglomerated particles. A comparison of celiorated size with observed size is given in Table 5.3. ARLE 5.3 Predicted vs Observed Particle Size Separations by Roller Analyzer Calibrated © Size Range () 5-10 - 10420 20=30 30-40 dy Namber of (py) Particles Counted 10.3 3.3 29.5 43,7 743 376 1089 429 From recent autoradiographic studies it has been found that the experimental determination of the per cent active particles in the lower size range may require a correction under certain conditions.*® This results from experimental limitations as to the size and specific activity of a particle which mey be detected as hot. *This discussion of autoradiograph errors is due to Mr. Robert J. ‘French of these Laboratories. 38 SECRET —- RESTRICTED DATA