An aerogel Cherenkov detector for multi-GeV photon detection with low sensitivity to neutrons

We describe a novel multi-GeV photon detector which operates under an intense flux of neutrons. It is composed of lead–aerogel sandwich counter modules. Its salient features are high photon detection efficiency and blindness to neutrons. Monte Carlo (MC) simulations show that the efficiency for photons with energy larger than 1 GeV is expected to be higher than 99.5% and that for 2 GeV/|$c$| neutrons is less than 1%. Performance of photon detection with an underlying large flux of neutrons was measured by a partial detector with 12 modules. We confirm the efficiency for photons with energy |$>1$| GeV is consistent with the MC expectation within an uncertainty of 8.2%.