Boron carbide coatings for neutron detection probed by x-rays, ions, and neutrons to determine thin film quality

• Due to the present shortage of He-3 and the associated tremendous increase of its price, the supply of large neutron detection systems with He-3 becomes unaffordable. Alternative neutron detection concepts, therefore, have been invented based on solid B-10 converters. These concepts require development in thin film deposition technique regarding high adhesion, thickness uniformity and chemical purity of the converter coating on large area substrates. We report on the sputter deposition of highly uniform large-area (B4C)-B-10 coatings of up to 2 mu m thickness with a thickness deviation below 4% using the Helmholtz-Zentrum Geesthacht large area sputtering system. The (B4C)-B-10 coatings are x-ray amorphous and highly adhesive to the substrate. Material analysis by means of X-ray-Photoelectron Spectroscopy, Secondary-Ion-Mass-Spectrometry, and Rutherford-Back-Scattering (RBS) revealed low impurities concentration in the coatings. The isotope composition determined by Secondary-Ion-Mass-Spectrometry, RBS, and inelastic nuclear reaction analysis of the converter coatings evidences almost identical B-10 isotope contents in the sputter target and in the deposited coating. Neutron conversion and detection test measurements with variable irradiation geometry of the converter coating demonstrate an average relative quantum efficiency ranging from 65% to 90% for cold neutrons as compared to a black He-3-monitor. Thus, these converter coatings contribute to the development of He-3-free prototype detectors based on neutron grazing incidence. Transferring the developed coating process to an industrial scale sputtering system can make alternative He-3-free converter elements available for large area neutron detection systems. (C) 2015 AIP Publishing LLC.

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