Investigation of Higher Count Rate and Helium-3 Alternative Beam Monitors for Neutron Scattering Facilities

Beam monitors are an important diagnostic tool at neutron science facilities. At high flux neutron scattering facilities, neutron beam monitors with very low intrinsic efficiency (10^-5) are presently selected to keep the counting rate within a feasible range, even when a higher efficiency would improve the counting statistics and yield a better measurement of the incident beam. This report outlines a beam monitor with a parallel-plate avalanche chamber design that is capable of measuring a high count rate without saturation. Several designs of the beam monitor using different electrode materials and different neutron conversion materials were constructed and tested. The different designs had efficiencies ranging from 9.8 x 10^-7 to 1.2 x 10^-3 for thermal neutrons. One of the designs measured 1 x 10⁶ cps, which means it is possible to measure neutron fluxes over 10⁹ cps without saturation while maintaining a 10^-3 efficiency.