On the total photo-electric emission of electrons from metals as a function of temperature of the exciting radiation

Abstract

In the year 1913 K. T. Compton and O. W. Richardson ('Phil. Mag.,' vol. 26, p. 549 (1913)) published a paper containing an important investigation on the action of homogeneous mono-chromatic radiation on a number of metals. The essential characteristics of the photo-electric activity of various metals are set out in their experimental curves obtained by plotting photo-electric yield of electrons against exciting frequency. These curves contain double maxima in the case of extremely electro-positive elements like Na, and one maxium for a less electro-positive metal Al, while the curves for Pt exhibit no maximum in the range of frequencies covered by their experiments. Later investigations by Souder ('Phys. Rev.,' vol. 8, p. 327 (1916) and O. W. Richardson and A. F. A. Young ('Roy. Soc. Proc.,' A, vol. 107, p. 377 (1925)) have confirmed these general characteristics of photo-electric activity-frequency curves. A photo-electric maximum for the "selective" effect was observed by Pohl and Pringsheim ('Verh. d. Deutsch. Physik. Ges,' vol. 11. p. 1039 (1910)) as early as 1910 in the case of some electro-positive elements. The general shape of the humps in their curves appears to be a function of the angle of incidence of the exciting radiation; nevertheless, the position of the maximum is quite independent and definite. Lately, R. Döpel ('Zeits. für Phys.,' Vol. 33, p. 237 (1925)) has shown that a less electo-positive metal like Sr also shows the photo-electric maximum. It is therefore probable that all metals would exhibit such maximum. It is therefore probable that all metals would exhibit such maximum photo-electric effect if it were possible to extend the range of exciting frequencies far into the ultra-violet. The presence of double maxima in the curves for Na and K probably points to the existence of two photo-electric thresholds in these elements, as suggested by O. W. Richardson ('Proc. Phys. Soc. London,' vol. 36, p. 388 (1924)), and may lead to interesting developments in future. In the following Table I are collected the observed values of the long wavelength limit λ 0 and the wave-length λ m of the maximum photo-electric effect. A comparison of the figures in columns 1 and 3 shows that the frequencies v 0 and v m can be correlated within the range of accuracy and consistency attainable in photo-electric measurements by a simple relation, v m = 3/2 v 0 .