  A multi-cell He gas-scintillator active target, designed for the measurement
of photoreaction cross sections, is described. The target has four main
chambers, giving an overall thickness of 0.103 $\mathrm{g/cm^{2}}$ at an
operating pressure of 2 MPa. Scintillations are read out by photomultiplier
tubes and the addition of small amounts of $\mathrm{N}_{2}$ to the He, to shift
the scintillation emission from UV to visible, is discussed. First results of
measurements at the MAX IV Laboratory tagged-photon facility show that the
target has good timing resolution and can cope well with a high-flux photon
beam. The determination of reaction cross sections from target yields relies on
a Monte Carlo simulation, which considers scintillation light transport,
photodisintegration processes in $^{4}\mathrm{He}$, background photon
interactions in target windows and interactions of the reaction-product
particles in the gas and target container. The predictions of this simulation
are compared to the measured target response.
