Abstract:
The properties of photomultiplier tubes (PMTs) have been investigated experimentally. The flux of cosmic rays has been used as a source of signals detected directly by a PMT (without a scintillator). The number of detected events versus the size of the PMT’s transparent front window has been studied. To this end, modified FEU-167 multipliers (FEU-167M) have been fabricated in which all parameters have been kept unchanged except for the size of the front window, which has been decreased. It has been found that the number of detected signals is roughly proportional to the surface area of the window. Hence, a signal induced by background cosmic rays arises in the glass of the PMT’s front screen. This circumstance should be taken into consideration when operating with different PMTs.
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