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