Improving the Design of an Alpha Particle Detector Collimator*

The BL3 experiment will be performed to investigate a 4.3 σ discrepancy between measurements of the neutron lifetime using a cold neutron beam versus trapped ultracold neutrons. An important aspect of BL3 is measurement of the neutron capture flux by detecting the alpha and triton particles from reaction with a thin Li-6 foil in the neutron beam. Thus, the precise positioning of alpha detectors and apertures is required for detection efficiency and uniformity. A detector support has been redesigned for the BL3 apparatus which rigidly mounts to the vacuum chamber and allows PIPS detector to be swapped out without accessing the apertures. This design uses kinematic couplings to make fine adjustments to the aperture orientation, and allows for precision mounting of caustic apertures, which allow for enhanced detection uniformity.