Multi-layer boron thin-film detectors for neutrons

Intrinsic efficiencies of multi-layer boron-10 thin-film detectors were studied theoretically and experimentally. For multi-layer schemes based on an optimized single-layer film thickness, the practical efficiency is limited to about 42% for thermal neutrons. This is about half the efficiency of a moderated ³He detectors in commercial use for portal monitoring. The efficiency limitation is due to charged particle loss in the boron layers and substrates. The same loss mechanism will prevent all substrate-based boron detectors from ever reaching the intrinsic efficiencies of high-pressure ³He tubes, independent of substrate geometry and material composition. Experimental data also indicate that the multi-layer detector configuration can have an efficiency approaching the theoretical limit. Excellent n/γ discrimination has also been achieved using an ionization chamber.