Calibration of CsI Detectors for the NPDG Experiment

The NPDGamma experiment at Oak Ridge National Lab will measure the asymmetry in gamma production in the reaction: neutron + proton -$>$ deuteron + gamma. The parity violating component of this reaction is measured from the correlation of neutron spin and $\gamma $ momentum. In order to detect this asymmetry, 48 cesium iodide scintillators are arranged in a cylinder around a liquid parahydrogen target in a beam of polarized neutrons. The detector efficiency was calibrated using a rotating Cs$^{137}$ source of known intensity. The output voltage output as a function of the rotation angle was fit using a Fourier series expansion plus a linear background term. The amplitude was the ratio of signal to energy deposited in V/MeV/s, essentially an efficiency for each detector. The calibration procedure will be presented, as well as the complete data analysis. Supported by NSF under grant PHY-0855584.