A Simple Rotating-Cell Double-Beam Unit for Spectrometers

Abstract

RECORDING spectrometers employing A.C. radiation beams are generally used in conjunction with amplifiers which are tuned to be selective at the chopping frequency used in the instrument. When absorbing material is placed in the radiation beam, alternate pulses of zero radiation I₀, and of (total radiation minus absorbed radiation) I_A, are sent into the monochromator at a controlled frequency ν_c. If the intensity of the radiation beam passing through the reference or blank cell int the monochromator is I_B, and if the beam is made to alternate between the two cells with the frequency ν_c, the A.C. impulse falling on the detector will be a function of the difference between I_B and I_A and not of the difference between I₀ and I_A. A spectrometer employing such a system will in effect be a double-beam instrument.