Author: Luke, Scott, & Tim

Scott found a good source for 6-inch 4-atm ³He neutron detector tubes a few years back. So we wanted to take one of them and turn it into our standard detector system for making absolute neutron rate measurements of our various neutron producing endeavors. This chronicles the empirical design, construction and calibration of that detector.

Over a decade ago Tim purchased 1500 lbs of pure polyethylene in the form of eight 2-inch thick slabs from a guy in New Mexico. Six of the slabs were cut up into 2x4x8 bricks for convenient stacking, and you will see them in use elsewhere in photos on this site. One slab was left in tact to create a large volume detector someday. That day has arrived.

First, we needed to determine the optimal geometry (other than a cylinder). We empirically accomplished this by stacking the bricks around the side, front and back of the detector to give the highest response from a fix distance ²⁵²Cf source (Tim is the custodian of a small calibrated ²⁵²Cf source at UMD). Once that geometry was determined we designed the monolithic moderator.