A low-background detector for observing the disintegration of the deuteron by reactor antineutrinos

A detector is described which is capable of high-precision measurement of the cross sections for the disintegration of the deuteron via neutral and charged-current interactions with reactor antineutrinos ( anti νed→ anti νepn (NCD) and anti νed→e+nn (CCD)), as well as the inverse beta-decay reaction ( anti νep→e+n (CCP)). In a previous experiment, the background due to cosmic rays interacting in the materials surrounding the detector was high - around 300 per day, compared to a signal rate of 50 per day. Improvements to the active and passive shielding and to the data collection system have reduced this background rate to less than 50 per day. A new method of searching for neutrino oscillation using the ratio of measured to predicted cross sections for the neutral and charged-current reactions is also discussed. The method consists of measuring the CCP reaction, in addition to the CCD reaction and the NCD reaction, in the same target detector. The CCP reaction has a much higher rate and a higher detection efficiency than the CCD reaction, allowing a more precise measurement of the charged-current branch. With this method, the uncertainty in the ratio of measured cross sections should be reduced to ∼5%. (orig.)