Research of boron lined honey-neutron detector realized with atomic layer deposition

Boron lined gaseous detector is one of the alternative detector types that possibly replace the helium-3 counter. The most important problem in the realization of boron-lined gaseous detector is how to plate thin boron film on the surface of large area substrate. Though methods of PVD (physical vapor deposition) can plate B₄C layer effectively with good thickness uniformity and adhesion, they suffer from the drawback that the area of substrate, typically 0.1 m² in once coating process, is far smaller than required in SANS (small angle neutron scattering) spectrometry. ALD (Atomic layer deposition) technique, which is a kind of CVD (chemical vapor deposition) method, can plate boron on the surface of large aspect ratio (at most 2000:1) substrate, so it can accommodate large area substrates. Honeycomb detector, which is composed of many small honeycomb cells with 6 mm side length, has very large surface area and is placed inside the reaction chamber of ALD machine to deposit boron layer on the surface of it to realize high detection efficiency. BBr₃ and H₂O are used as precursors to form B₂O₃ layer and diethyl zinc and H₂O are used as precursors to form ZnO film, the passivation layer. 0.04 mg/cm² of B₂O₃ is deposited after 2250 cycles of growth. The boron lined honeycomb then is filled with 95% argon + 5% CO₂ to be a proportional counter. Its neutron sensitivity is tested under the thermal neutron field provided by a photoneutron source. The preliminary result shows that the neutron sensitivity of the honeycomb detector would be 1.26 × 10^-2 cm² (for one cell) and 1.15 cm² (for the whole detector).