Improvements to the neutron detector for the BL3 experiment

The BL3 experiment is being developed to resolve the discrepancy between previous in-flight decay measurement of the neutron lifetime and measurements using trapped UCNs.  One of the leading systematic uncertainties is the measurement of the neutron fluence through the Penning trap.  I will describe improvements to the neutron monitor to achieve a more uniform detection efficiency across the beam profile, including the possibility for 100% uniformity with a novel "caustic aperture".