Calibration of the Neutral Current Detection Array in the SNO experiment

Since November 25th, 2004, the Sudbury Neutrino Observatory has been taking production data in its third and final phase. For this phase a ‘Neutral-Current Detection (NCD) Array’, consisting of 36 strings of 3 He proportional counters and 4 strings of 4 He proportional counters, was deployed in SNOʼs D 2 O volume. It supplements the Cherenkov detector, consisting of 9456 photomultiplier tubes, present in the previous two phases by offering an independent measurement of the solar neutral current rate. The 3 He counters detect neutrons from neutrino-deuteron neutral current interactions in the D 2 O. We describe the calibration of this array.