Neutron Spectrometry With Scintillating Bolometers of LiF and Sapphire

Two scintillating bolometers of LiF (33 g) and Al 2 O 3 (50 g) at 20 mK, inside a lead shielding at the Canfranc Underground Laboratory, were irradiated with neutrons from a source of 252 Cf. The analysis of nuclear recoils registered by sapphire and (n, α) captures by 6 Li shows the feasibility of these cryogenic devices to measure the spectral flux of a neutron field. Data unfolding was done assuming that the spectral flux is a piecewise constant function defined on six energy groups. It can be solved by using non-negative least squares without additional assumptions on the neutron flux. The model provides consistent results with the spectra of the observed events in bolometers, giving a fast neutron flux of Φ(E > 0.1 MeV) = 0.20 n s -1 cm -2 with a 15% uncertainty after 3 hours of live time. After our analysis, it can be concluded that nuclear recoils in sapphire are more useful than (n, α) captures in LiF for spectrometry of fast neutrons.