Neutron reflectometry on highly absorbing films and its application to 10B4C-based neutron detectors

TL;DR

This paper extends neutron reflectometry to highly absorbing 10B4C layers, enabling better characterization of neutron detectors and advancing understanding of neutron absorption and reflection in such materials.

Contribution

It develops a theoretical framework for neutron reflectometry on strongly absorbing layers and demonstrates its application to 10B4C, a material relevant for neutron detection.

Findings

The theory accurately describes neutron reflection and absorption in absorbing layers.

Experimental validation confirms the model's effectiveness.

Guidelines for 10B4C layer properties suitable for neutron detectors.

Abstract

Neutron reflectometry is a powerful tool used for studies of surfaces and interfaces. In general the absorption in the typical studied materials can be neglected and this technique is limited to the measurement of the reflectivity only. In the case of strongly absorbing nuclei the number of neutrons is not conserved and 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, generally in very small quantities, are used as a label for buried layers. Nowadays the importance of highly absorbing layers is rapidly increasing, partially because of their application in neutron detection; a field that has become more and more active also due to the 3He-shortage. In this manuscript we extend the neutron-induced fluorescence technique to the study of thick layers of highly absorbing materials; in particular 10B4C. The theory of neutron reflectometry is a commonly studied topic, however the subtle relationship between the reflection and the absorption of neutrons is not widely known, in particular when a strong absorption is present. The theory for a general stack of absorbing layers has been developed and compared to measurements. This new technique has potential as a tool for characterization of highly absorbing layers. We also report on the requirements that a 10B4C layer must fulfill in order to be employed as a converter in neutron detection.