TABLE 5.2 Predicted vs Observed Particle Size Separations by Stendard Sleves Size Range of Sieves Cry $3 53-62 dy fon . 74-88 88-105 105-125 125-149 62.4 &s.8 113 116 172 215 159-177 Number of Particles Sounted 239 321 228 . 369 150 181 381 __186 The frection from the 62-74 pp sieve hed a particularly broad distribution, so that all data associated with it should be viewed 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 frengible or agglomerated particles. A comparison of czlibrated size with observed size is given in Table 5.3. TARLE 5.3 Predicted vs Observed Particle Size Separations by Roller Analyzer Calibrated Size Range (p) 0-5 5-10 10-20 20-30 20-40 ay Number of (yp) Particles Counted 5.08 10.3 23.3 29.5 43,7 “He 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 fron experimental limitations as to the size and specific activity of a particle which mzy be cetected as hot. *This discussion of autoradiograph errors is due to Mr. Robert J. “French of these Laboratories, 38 SECRET —- RESTRICTED DATA