Investigations of photoelectric effects occupy an important place in studies of semiconductors. Recently investigations of photoconductivity and photoelectromotive forces have been intensified in step with the general development of semi conductor physics. An important feature of current work is an approach which combines several experimental methods of investigating photoconductivity by meas uring a number of the parameters which govern it (e. g., quantum yield, lifetime, etc.). In other words the study of steady-state photoconductiv ity is being replaced by the study of photoconductivity kinetics. Another important feature is the extension of the studies beyond pure ly photoelectric phenomena by the use of radiations other than light. Such an extension is justified not only by practical requirements but also by the close similarity between the ionization processes produced by different radiations. It can be shown that the charge carriers liberated by light and other radiations are not unique as far as their behavior in a crystal lattice is concerned. This can be seen from the following considerations.