Effusion. V. Angular Number Distributions of Gaseous CsCl from a Conical Orifice into Vacuum

Angular number distributions of CsCl(g) effusing from a divergent right conical orifice, located in the wall of an effusion cell, have been measured as a function of the state of the gas. The orifice had a circular gas opening with a diameter ${\mathrm{(d}}_S)$ of 0.3239 mm, a length of 9.524 mm, and a half‐angle of 15.93°. The effusion cell was constructed from oxygen‐free, high‐conductivity copper. Fifteen angular number distributions were measured with a range of Knudsen numbers (ratio of mean free path to orifice diameter $d_S)$ between 19.8 to 0.457. The angular number distribution data at large Knudsen numbers (molecular flow region) did not agree with theoretical angular number distributions. The fluctuation phenomenon, observed in similar experiments at low pressures in the molecular flow region with a right‐circular cylindrical orifice, was observed also with this conical orifice. As with long cylindrical orifices, a decrease in Knudsen number in the transition region decreased the probability of effusion in the forward direction.