Hm. Araujo et al., STUDY OF BIALKALI PHOTOCATHODES BELOW ROOM-TEMPERATURE IN THE UV VUV REGION/, IEEE transactions on nuclear science, 45(3), 1998, pp. 542-549
Two photomultiplier tubes with bialkali photocathodes and fused silica
windows (2 '' Philips XP2020Q and 1-1/8 '' Hamamatsu R1668) were stud
ied between room temperature and -160 degrees C, illuminated in de mod
e in the UV/VUV wavelength range. The photomultipliers were operated a
s diodes, with direct measurement of the current of photoelectrons, in
order to study in detail the effects associated to the photocathode.
The influence of light intensity, applied voltage and illuminated area
on the response as a function of temperature were investigated. The i
ncrease of the electrical resistivity of the emissive layer upon cooli
ng proved to be responsible for a loss of linearity of the photocathod
e response, leading ultimately to the complete absence of signal at lo
w temperature. A simplified model is presented that accounts for some
experimental results. An unexpected increase of response below room te
mperature was also found at 170 nm.