ABSTRACT
The Slepian device is the predecessor of modern day photomultiplier tubes (PMTs). The photocathode work function and the wavelength of photons impinging upon the photocathode generally determine the electron cutoff energy for a PMT. The photomultiplier tube is an extremely important tool in radiation detection because it is the device that allowed scintillation materials to become practical detectors. Because photoelectrons are ejected into vacuum from the side of the photocathode material opposite that upon which light is incident, this type of photocathode is sometimes called a transmission photocathode. The dark current of a PMT is the current that flows in the cathode or anode circuits in the absence of light. The dark current flow of electrons is a source of random electromagnetic fields that add to electronic noise. A thermally dependent source of sporadic electrons is thermionic emission of electrons from the surfaces of the photocathode and dynodes.
