Neutron reflectometry on highly absorbing films and its application to ¹⁰ B ₄ C-based neutron detectors

Abstract

Neutron reflectometry is a powerful tool used for studies of surfaces and interfaces. The absorption in the typical studied materials is neglected and this technique is limited only to the reflectivity measurement. For strongly absorbing nuclei, the absorption can be directly measured by using the neutron-induced fluorescence technique which exploits the prompt particle emission of absorbing isotopes. This technique is emerging from soft matter and biology where highly absorbing nuclei, in very small quantities, are used as a label for buried layers. Nowadays, the importance of absorbing layers is rapidly increasing, partially because of their application in neutron detection; a field that has become more active also due to the 3He-shortage. We extend the neutron-induced fluorescence technique to the study of layers of highly absorbing materials, in particular 10B4C. The theory of neutron reflectometry is a commonly studied topic; however, when a strong absorption is present the subtle relationship between the reflection and the absorption of neutrons is not widely known. The theory for a general stack of absorbing layers has been developed and compared to measurements. We also report on the requirements that a 10B4C layer must fulfil in order to be employed as a converter in neutron detection.

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

“…The results show also that, apart from the near-surface region, the composition is homogenous for both coatings. The compositions of the near-surface regions of comparable B 4 C coatings were closer, as investigated in [45], where it was shown that surface oxidation extends to a maximum of 60 nm into the coatings.…”

Fast neutron sensitivity of neutron detectors based on Boron-10 converter layers

“…The Kapton (ρ = 1.42 g/cm 3 ) is composed of several elements, the macroscopic cross section is Σ mix = i N i σ i , the 10 B 4 C layer (ρ = 2.45 g/cm 3 ) as well. This density differs from the material data and refers to a measured value for the films employed in this detector [27]. The n p calculation for both compounds is reported in table 3.…”

The Multi-Blade Boron-10-based neutron detector for high intensity neutron reflectometry at ESS

“…It has been shown in [1] that the theoretical efficiency can be reached at an inclination of 10 degrees of the converter layer but it was not possible to prove this agreement at 5 degrees. Moreover, it has been shown in [71] that the inclination of 5 degrees does not affect the neutron detection efficiency due to neutron reflection at the layer surface. The neutron detection efficiency of the Multi-Blade detector at 5 degrees has been measured.…”