Used for both proton decay searches and neutrino physics, large water
Cherenkov (WC) detectors have been very successful tools in particle physics.
They are notable for their large masses and charged particle detection
capabilities. While current WC detectors reconstruct charged particle tracks
over a wide energy range, they cannot efficiently detect neutrons. Gadolinium
(Gd) has the largest thermal neutron capture cross section of all stable nuclei
and produces an 8 MeV gamma cascade that can be detected with high efficiency.
Because of the many new physics opportunities that neutron tagging with a Gd
salt dissolved in water would open up, a large-scale R&D program called EGADS
was established to demonstrate this technique's feasibility. EGADS features all
the components of a WC detector, chiefly a 200-ton stainless steel water tank
furnished with 240 photo-detectors, DAQ, and a water system that removes all
impurities in water while keeping Gd in solution. In this paper we discuss the
milestones towards demonstrating the feasibility of this novel technique, and
the features of EGADS in detail.