Determination of the Relative Spectral Sensitivity of Phototubes*

The determination of the relative spectral response of phototubes usually involves the calibration of the spectrum from a monochromator and subsequent exposure of the phototubes thereto. To avoid the well-known difficulties of radiometry, involving monochromators, thermocouples and/or thermopiles, galvanometers, and amplifiers, an alternative method is developed. Instead of using the calibrated spectrum from a monochromator as a radiation standard, known radiation samples are obtained from the combination of an accurately calibrated tungsten lamp with each of a conveniently spaced set of narrow band interference filters of the Fabry-Perot type.