Photoelectric Properties of Barium and Calcium

With a photoelectric cell in which Ba was fractionated and repeatedly distilled, values of φ₀ at room temperature, as obtained by Fowler's method, were found to be 2.520 and 2.510 electron volts, the difference being attributed to either differences in crystal structure or chemical purity. For both conditions of the surface, the cell showed extraordinary constancy of work function. Measurements 100^∘{}C above room temperature yielded a temperature coefficient of (2.2±{}0.7)×{}10^-5 ev/^∘{}K. The absolute photoelectric yield of the surface was determined. The optical reflection coefficient was found to vary from 43 percent at 4000A to 63 percent at 7000A. The work function of a Ca surface prepared by single distillation was 2.706 ev. After repeatedly heating the surface to 100^∘{}C the data did not fit Fowler's theoretical curve. The departures were consistent with the assumption that, after heating, the surface was not homogeneous. Analysis of the data gave evidence of two emitting surfaces having work functions differing by approximately 0.2 ev.