A low-noise current-mode preamplifier for gamma asymmetry measurements

The NPDGamma experiment will measure with high accuracy a very small parity-violating directional asymmetry A γ in the emission of gamma rays from the capture of polarized cold neutrons by protons. High event rates and systematic error considerations require the use of current mode detection with vacuum photo-diodes and low-noise solid-state preamplifiers. The preamplifier requirements, design, and measured properties are described.