Using cosmic rays to monitor large scintillator arrays

Large arrays of scintillator-photomultiplier detectors are becoming the technique of choice to measure neutron spectrum from ICF implosions. A 32×30 array of detectors is currently under construction at LLE (MEDUSA). This array is at an angle of 26° relative to vertical and thus cosmic rays can be used to monitor individual channel performance. We will present: an analysis of the expected count rates and expected signal levels for single scintillator-photomultiplier detectors; a comparison of the above analysis to a test string of 30 detectors mounted in the MEDUSA frame; and the triggering scheme used to acquire data for routine operation of the instrument.