B4C thin films for neutron detection

Abstract

Due to the very limited availability of B 4 C targets in an Ar discharge, using an industrial deposition system. The films were characterized with scanning electron microscopy, elastic recoil detection analysis, x-ray reflectivity, and neutron radiography. We show that the film-substrate adhesion and film purity are improved by increased substrate temperature and deposition rate. A deposition rate of 3.8 Å /s and substrate temperature of 400 C result in films with a density close to bulk values and good adhesion to film thickness above 3 lm. Boron-10 contents of almost 80 at. % are obtained in 6.3 m 2 of 1 lm thick 10 B 4 C thin films coated on Al-blades. Initial neutron absorption measurements agree with Monte Carlo simulations and show that the layer thickness, number of layers, neutron wavelength, and amount of impurities are determining factors. The study also shows the importance of having uniform layer thicknesses over large areas, which for a full-scale detector could be in total $1000 m

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].…”

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

“…However, the alternative and safe 10 B solid state neutron converter detector technology is still in the early stages of development. [15][16][17][18] A. Neutron detection by 10 …”

Elastic properties of B-C-N films grown by N2-reactive sputtering from boron carbide targets

“…Taking into account the empirical behavior in which lower Young's modulus correlate with higher linear thermal expansion coefficient, 47 B-C-N layers are suitable to constitute a functional graded material to solve the problem of delamination in the coating of polycrystalline aluminum (E ¼ 67.733 GPa) 48 with 10 B-enriched boron carbide films to be used in neutron detection. 15,49 The fact that the obtained elastic modulus for B-C-N films is in between that of boron carbide and aluminum lead to propose them as intermediate layers for the anchoring of B 4 C on aluminum in the design of new neutron detectors.…”

“…7 In the last few years, ternary systems based on B-C-N have been the subject of study, aimed to obtaining a combination of specific properties of boron carbide, cubic and hexagonal boron nitride oriented to the design and fabrication of materials 8 with high thermal and chemical stability, 9 low friction coefficient, 10 high hardness, [11][12][13] and good wear resistance. 14 On the other hand, the large absorption cross section for thermal neutrons of the 10 B isotope (that is 20% present in natural boron) allows a unique application of boron carbide in solid-state neutron detector for large-scale neutron source laboratories 15 and even for general purpose neutron detection. 16 Unfortunately, boron carbide and boron carbonitride thin films present delamination 17,18 when the film thickness lies about 0.5 lm.…”