[en] CaF₂:Tm thermoluminescent dosimeters (TLD-300) show two well separated peaks (peak 3 and peak 5) and are used to separate the neutron and gamma dose in mixed neutron-gamma fields by mean of the two-peaks method equation. Solving this equation for the neutron sensitivity ratio k₃/k₅ of the two main peaks the following expression is obtained: k₃/k₅ = [1/(1 - (D_γ/R₅)] . [1 - (R₃/R₅)] (eq. 1) where R₃ and R₅ are the measured responses of peak 3 and peak 5 in the mixed field and D_γ is the gamma absorbed dose. Further, since by definition of the neutron sensitivity k for TLDs k₃/k₅ results independent from the surrounding media, from eq. (1) the R₃/R₅ ratio is expected to be independent from the medium as well. The R₃/R₅ ratio for TLD-300 ribbons (3.2 x 3.2 x 0.9 mm³ dimension) was thus studied as function of several encapsulating materials (teflon, polyethylene, PVC, perspex, aluminium, iron, stainless steel, copper and lead) irradiated using three different neutron energy spectra (Am-Be, 14 MeV (D-T), and d(48.5) + Be). The experimental results pointed out that the measured R₃/R₅ ratio changes within ±20%. If the analysis is restricted to Tissue Equivalent (T.E.) materials teflon, polyethylene, PVC and perspex, the R₃/R₅ ratio is constant within ±7%. In this work, using literature's data for k₃/k₅ and R₃/R₅ ratio, the validity of eq. (1) is tested for T.E. materials and this gave some insight about the still open problem whether the neutron sensitivity of TLD-300 is constant or not upon the neutron energy. (author)