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

Abstract

Boron carbide coatings for neutron detection probed by x-rays, ions, and neutrons to determine thin film quality He and the associated tremendous increase of its price, the supply of large neutron detection systems with 3 He becomes unaffordable. Alternative neutron detection concepts, therefore, have been invented based on solid 10 B 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 10 B 4 C coatings of up to 2 lm thickness with a thickness deviation below 4% using the Helmholtz-Zentrum Geesthacht large area sputtering system. The 10 B 4 C 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 RutherfordBack-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 10 B 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 3 He-monitor. Thus, these converter coatings contribute to the development of 3 He-free prototype detectors based on neutron grazing incidence. Transferring the developed coating process to an industrial scale sputtering system can make alternative 3 He-free converter elements available for large area neutron detection systems.

Neutrons for industry

“…Transferring the presented preparation process to a large-scale industrial system would deliver highly uniform 10 B 4 C neutron converter coatings for alternative, 3 He-free large-area neutron detection systems. Similar progress has been reported by a collaboration of several groups with the ESS [73,74].…”

Low-temperature growth of boron carbide coatings by direct current magnetron sputtering and high-power impulse magnetron sputtering

“…Natural boron contains 20 % 10 B, but the isotope separation is relatively easy and [95 % 10 B-enriched material is commercially available. In previous publications [3,12,13], direct current magnetron sputtering (DCMS) was shown to provide suitable deposition processes for the production of 10 B 4 C large area neutron detectors. 10 B 4 C is the preferred material, instead of 10 B, 10 BN, or other 10 Bcontaining compounds, due to its relatively high boron content in combination with excellent wear resistance and thermal and chemical stability [14][15][16][17].…”

Neutron detectors for the ESS diffractometers

“…The inclination of the boron-layer leads to an increase of the effective absorption film thickness by a factor proportional to 1/sin(η) and thus, to a larger detection efficiency for a single converter layer. For example, the detection efficiency for a thermal neutron striking a 3 µm thick layer at 90 • (normal incidence) is ∼5 %, but increases to 60% when the layer is positioned at 5 • with respect to the direction of the incident neutron [73,74]. Moreover, the wire pitch seen by the incoming neutron becomes smaller by a factor proportional to sin(η), which at first glance improves the position resolution and the counting rate capability of the detector by 1/sin(η) [57].…”