  In the last few years many detector technologies for thermal neutron
detection have been developed in order to face the shortage of 3He, which is
now much less available and more expensive. Moreover the 3He-based detectors
can not fulfil the requirements in performance, e.g. the spatial resolution and
the counting rate capability needed for the new instruments. The Boron-10-based
gaseous detectors have been proposed as a suitable choice. This and other
alternatives technologies are being developed at ESS. Higher intensities mean
higher signals but higher background as well. The signal-to-background ratio is
an important feature to study, in particular the gamma-ray and the fast neutron
contributions. This paper investigates, for the first time, the fast neutrons
sensitivity of 10B-based thermal neutron detector. It presents the study of the
detector response as a function of energy threshold and the underlying physical
mechanisms. The latter are explained with the help of theoretical
considerations and simulations.
