Absolute Neutron Flux Measurement to Calibrate Neutron Monitor Efficiencies in the BL3 Experiment

The BL3 Experiment is a next-generation neutron lifetime experiment aiming to achieve 0.3 second precision on the lifetime using the Sussex-ILL-NIST beam method. This method employs a quasi-Penning trap to count decayed neutrons and a monitor to measure the escaping neutron flux. The neutron beam is incident on a thin LiF foil target inside the neutron monitor which measures the rate of alpha and triton emission from neutron capture. To calibrate the efficiency of this monitor to 0.01%, we will use an absolute flux measurement device in series with the monitor on a monochromatic beam to repeatedly determine the efficiency throughout the lifetime of the experiment. The absolute flux is determined through a four-step calibration procedure measuring both alpha and gamma emissions from neutron capture on a boron foil of varying thicknesses. Alpha emission is measured with silicon PIPS detectors and gamma emission is measured with high purity germanium detectors. The current status of the detector evaluation and data acquisition hardware is presented in this talk.