though most of their data are described fairly well by this behavior. The most notable deviation is the forward angle point (28° cm.) at 980 Mev, for which the value of O(1OOO)//>(A)>(0) is (0.84±0.11)X10-31 cm 2 /sr compared to an average value of 1.25 or 1.3X10" 31 cm 2 /sr for their data at 1010 Mev, and 1.02 to 1.15 X 10~3 1 cm 2 /sr for the other angles at 980 Mev. This rapid decrease in the forward angle cross section toward low photon energies was not observed in our experiment.The difference of roughly 25% between the Cornell average for [_p(W00)/p{k)~]

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A small rectangular dc electrostatic separator with the dimensions 1×1×2m3 is used to investigate the voltage breakdown in the vacuum of a dc electrostatic separator with the electrodes 400 mm in diameter. The electrodes are made of several materials to which voltages are applied up to 400 kV. The chamber is evacuated to 1×10-6 Torr with a turbo-molecular pump and an ion pump. A gas is fed to the chamber to obtain a curve of maximum voltage as a function of the pressure, a P-V curve. The P-V curves are obtained by varying the kind of gas, the material of the cathode and the gap spacing etc. Speculations are given for the voltage breakdown mechanism in the vacuum of the separator, and condition for the optimization of the design of dc electrostatic separators are also given.