A 12-Channel Semiconductor Counter System for the NBS Electron Scattering Spectrometer

A 12-channel array of lithium-drifted silicon detectors for detecting high energy electrons in the focal plane of a magnetic spectrometer is described. The detectors are movable along the focal plane and are backed up by two large stationary plastic scintillators. The scintillators are placed one behind the other, such that a count is recorded when a triple coincidence occurs between both scintillators and a single semiconductor detector. The system has a momentum resolution of 0.036 percent, determined by the detector size and the spectrometer momentum dispersion. Discriminator curves have been obtained which show sufficiently flat plateaus to afford stable counting conditions for electron momentum greater than 20 MeV/C. Detector efficiency measurements have also been made which show that the relative efficiencies of the detectors are stable and known to less than two percent of their values. An electron scattering experiment is now in progress using these detectors.