  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.
