Changes in spectral sensitivity of multiplier phototubes resulting from changes in temperature

The change in cathode spectral sensitivity of Westinghouse WX 4582 (S-11) and RCA 1P21(S-4) multiplier phototubes was measured across the visible spectrum, i.e., from 400 nm to 700 nm, for various temperature changes, both increases and decreases. Two methods were used for these measurements, viz., an adaptation of the Hardy spectrophotometer and the use of an environmental chamber. A decrease in temperature usually caused an increase in sensitivity in the short wavelength part of the spectrum and a decrease (as much as 90% at 700 nm) in the long wavelength part of the spectrum, with the crossover point (no appreciable change of sensitivity with change of temperature) at about 590 nm. An increase in temperature was accompanied by a reversal of spectral sensitivity changes, i.e., a decrease in the short wavelength part of spectrum and an increase in the long wavelength part of the spectrum. The change in cathode sensitivity varied with different types of phototubes and with phototubes of the same type.