Thermal neutron response and theoretical comparison of LiF coated aluminized Mylar

Abstract

Thin layers of LiF were deposited on a 2.0µm thick aluminized BoPET (i.e. Mylar) in thicknesses of 4.5, 9.9, and 14.0µm using an electron beam evaporator. These coatings were thinner than the summed triton and alpha particle range from the 6Li(n,t)4He reaction, which allows both particles to escape a suspended absorber sheet simultaneously and measured in a proportional gas region concurrently. Each thickness of the LiF coated Mylar sheets were positioned separately in a test chamber that had a single anode wire positioned on each side of the absorber sheets. The thermal neutron response pulse-height spectra were collected for each LiF thickness and are presented and discussed. The coatings became fragile at thicknesses greater than 5.0µm and would flake off of the Mylar sheets. Additionally, the ideal LiF coating thickness that maximizes the intrinsic thermal neutron detection efficiency is greater than 5.0µm, which is discussed in a greater detail in the text. Overall, the detectors are capable of achieving thermal-neutron detection efficiencies greater than 30% for a 5 layer device and 60 % for 20 layers, but these devices are complex to fabricate due to flaking of the LiF coatings. Additional research is required to eliminate flaking by possibly using additional mechanical structures or adhesive materials.