  Performance and characteristics of a band-pass photon detector using acetone
gas and CaF_2 window (acetone/CaF_2) have been studied and compared with an
ethanol/MgF_2 detector. The optimal operating conditions are found to be 4 mbar
acetone pressure and 745+/-20 V anode voltage. The count rate obtained by us is
about a factor of 3 higher than what has been reported earlier for the acetone
detector. Unlike other gas filled detectors, this detector works in the
proportional region with very small dead time (4 micro sec). A detector
band-pass of 0.48+/-0.01 eV FWHM is obtained.
