Vacuum Chamber Metrology and Detector Housing Design for the BL3 Experiment

The BL3 Experiment aims to measure the lifetime of the neutron to a precision of 0.3 s and investigate the systematics of beamline measurements. To calculate the neutron capture flux in the system we detect alpha particles emitted by the neutron beam on a Li6 target. The alpha detectors must be held in a known geometry and be positioned reproducibly to within 1 part in 10,000. We used a coordinate measuring machine (CMM) to collect point cloud data of our as-built vacuum chamber and fit the data together using least squares minimization. We then constructed an as-built 3D model of the physical chamber. To compensate for deviations from the ideal chamber model the detector supports include a vacuum compatible 3D printed stainless steel adapter. The design of each adapter is custom to hold the detector in the desired pose despite imperfections in the position of the flange that the housing assembly is mounted on. After installing the detector housings inside of the physical chamber, we used the CMM to measure the position at which each housing holds its detector to confirm correct placement.