  We present a vacuum ultraviolet (VUV) band-pass photon detector for inverse
photoemission spectroscopy. A SrF2 window is used due to its high-energy cutoff
of the optical transmission being 9.7eV, and acetone is selected as filling gas
with the photoionization threshold also being 9.7eV. The structure of the
detector described in detail is based on a Geiger-M\"uller type counter with an
MgF2 window and argon as amplification gas. Its energy resolution can be tuned
continuously from 46meV with a normal temperature situation to 105meV at 215K.
Meanwhile, the signal intensity of the detector is adjusted accordingly to find
an optimal operation program for our inverse photoemission system which is
being constructed. The ratio of acetone vapor and argon is varied carefully.
Background signals and the response of time are analyzed. The detector is
normalized by deuterium lamp in combination with a grating monochromator.
