Investigation of the 7 H-system in the experiment conducted at the fragment separator ACCULINNA-2 in the 8 He( 2 H, 3 He) 7 H reaction requires to detect the recoil 3 He ions with energy down to 6 MeV. For this purpose two particle telescopes are used, with each telescope having in front a thin (20-μm) Si strip detector ( ). The maps of thickness heterogeneity of the thin detectors were determined by measuring the energy losses of the 226 Ra α-particles. The adopted thickness normalization method provides a good identification of the 3 He nuclei being recorded in the presence of a high 4 He background. Two approaches were used for calculating the energy losses of the identified 3 He and 4 He reaction ejectiles and reconstructing their energy values available at the exit from the deuterium target. The developed techniques were applied for the 7 H missing-mass reconstruction.