  The proposed introduction of a soluble gadolinium (Gd) compound into water
Cherenkov detectors can result in a high efficiency for the detection of free
neutrons capturing on the Gd. The delayed 8 MeV gamma cascades produced by
these captures, in coincidence with a prompt positron signal, serve to uniquely
identify electron antineutrinos interacting via inverse beta decay. Such
coincidence detection can reduce backgrounds, allowing a large Gd-enhanced
water Cherenkov detector to make the first observation of supernova relic
neutrinos and high precision measurements of Japan's reactor antineutrino flux,
while still allowing for all current physics studies to be continued. Now, a
dedicated Gd test facility is operating in the Kamioka Mine. This new facility
houses everything needed to successfully operate a Gd doped water Cherenkov
detector. Successful running of this facility will demonstrate that adding Gd
salt to SK is both safe for the detector and is capable of delivering the
expected physics benefits.
