  The xenon secondary scintillation yield was studied as a function of the
electric field in the scintillation region, in a gas proportional scintillation
counter operated at room temperature. A large area avalanche photodiode was
used for the readout of the VUV secondary scintillation produced in the gas,
together with the 5.9 keV x-rays directly absorbed in the photodiode. The
latter was used as a reference for the determination of the number of charge
carriers produced by the scintillation pulse and, thus, the number of VUV
photons impinging the photodiode. A value of 140 photons/kV was obtained for
the scintillation amplification parameter. The attained results are in good
agreement with those predicted, for room temperature, by Monte Carlo simulation
and Boltzmann calculations, as well as with those obtained for saturated xenon
vapour, at cryogenic temperatures, and are about a factor of two higher than
former results measured at room temperature.
