Optimized VUV-photon detection with acetone/CaF2 proportional counters for use in inverse photoemission

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Abstract
The detection of vacuum-ultraviolet photons in inverse-photoemission experiments is usually carried out with gas-filled counting tubes. Iodine/argon gas fillings have been used for Geiger-Müller-type photon detection. Later, the gas filling was replaced by acetone to increase stability and the operation was changed to proportional mode. While doing this, the counting tube geometry was not necessarily changed. We carried out a systematic study to understand the photon-detection process in acetone-filled counting tubes and to optimize the geometry accordingly. In the range of optimal gas pressures, we found that the photon mean free path in acetone is in the order of a few millimeters instead of a few centimeters in the iodine/argon case. As a consequence, the position of the cathode wire close to the entrance window becomes a critical parameter for optimizing the detection efficiency.

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