Photoelectric Yields in the Extreme Ultraviolet

The photoelectric yields for various surfaces (Ni, W, Mg, W-O and Constantan) illuminated by the extremely short wave-length radiation given out by the positive columns in He, Ne and A respectively, have been determined. The effect of the extremely short wave-length radiation was separated from that of the complete radiation by the use of a quartz disk which, when inserted, cut off all radiations, below 1500A. The yields obtained (in electrons per 100 quanta) range from 11 in the case of Constantan and He, to 0.14 in the case of Mg (surprisingly) and Ne. The yields, e.g., for well degassed Ni for He, Ne and A, were 4.4, 1.6 and 0.6 respectively; those for the other surfaces except Mg varied with the gas in the same general way. Thus the maximum in the yield for most ordinary metal surfaces probably lies on the short $\lambda$ side of 584A. W-O gave greater yields than W (except in A) and in general undegassed metals gave yields several times greater than well degassed ones. The size of the yields suggests that the photoelectric emission from probe and cathode surfaces in the rare gases may be considerable importance.