Investigation of a lithium foil multi-wire proportional counter for potential 3He replacement

The recent shortage in the supply of 3He for neutron detection has caused a large surge in research for a viable replacement. 6Li has a large cross section for the absorption of thermal neutrons and emits two relatively short-ranged interaction products. Li foil can now be manufactured thin enough to allow both reaction products to escape the foil. Ten layers of natural Li foil were placed in a multi-wire continuous flow gas chamber with a single anode wire between each foil. Four different thicknesses, 30, 50, 75 and 120 μm, were tested in a thermalized neutron beam. The intrinsic thermal neutron detection efficiencies of 10 layers of 30, 50, and 75 μm thick Li foil were measured to be 8.1, 11.1, and 15.7 percent. The n/γ ratio was found to be 1.25×107 using a 137Cs gamma-ray source. Additionally, neutron response pulse-height spectra of the four foil thicknesses are presented and compare well to simulated response spectra. Theoretical calculations show that thermal neutron detection efficiencies above 70 percent are achievable using enriched 6Li foils for the same detector geometries.