Change of Conductance of Selenium due to Electronic Bombardment

Effect of electronic bombardment on the conductance of selenium.—A low-resistance selenium cell about 1 inch square made by pressing Se between twenty double turns of fine Pt wire, was mounted in a vacuum tube with a grid and an oxide-coated, equipotential, electrically heated cathode and subjected to bombardment by electron currents up to $400\mu$-amp. at potentials up to 95 volts. The increase of conductance $\Delta C$ with current $I$ and with voltage $V$, is found to agree well with the theoretical formula $\frac{\Delta C}{C}=\sqrt{1+kIV}-1\mathrm{}$, derived on the basis of the free electron theory of conduction, assuming that the impinging electrons increase the number of free electrons throughout the whole volume of the Se by ionizations proportional both to the number of electrons and to the energy of each, i.e. to $\mathrm{IV}$. The constant $k$ is the ratio of the ions created per watt to the number of ions produced spontaneously per sec. and comes out 98.5.