Electroluminescence in Xe-SF6 mixtures

Noble gas detectors that rely on electroluminescence (EL) are widely used in radiation detection and rare-event searches because they provide large signal amplification with low intrinsic fluctuations. The introduction of electronegative additives, such as SF 6 , modifies charge transport, opening the possibility of exploiting low diffusion through negative ion drift, but may suppress scintillation. In this work, EL production in Xe-SF 6 mixtures was studied as a function of reduced electric field and SF 6 concentration, using a GEM to induce electron detachment. Two complementary configurations were used to separate the contribution from light produced within the GEM holes and in the region after the GEM. Measurements show that, once the detachment threshold is reached, both charge and light signals increase with the electric field in the GEM region, with EL appearing before charge multiplication. In the scintillation region, after the GEM, a light signal can be observed that increases with the applied scintillation field, but remains much weaker than the one produced in the GEM region. In both regions, the effective EL yield is strongly reduced with respect to pure xenon and decreases as the SF 6 fraction increases. For higher SF 6 concentrations, the yield is approximately linear within the explored electric field range, whereas for lower concentrations it departs from linearity at higher fields. The onset of EL production was obtained and compared with the previously reported charge multiplication threshold and with a detachment cross-section prediction. Both thresholds shift to higher reduced electric fields as the SF 6 concentration increases and remain, within uncertainties, consistent with the prediction. These results demonstrate that EL is still possible in Xe-SF 6 mixtures, but is strongly quenched by the electronegative additive, highlighting the complex interplay of the microscopic processes in the detector. • Electroluminescence was studied in Xe-SF 6 mixtures over a range of fields and concentrations. • A GEM was used to induce electron detachment and probe light production. • Light is observed both inside the GEM holes and in the region after the GEM. • The effective electroluminescence yield is strongly reduced by SF 6 and decreases with increasing concentration. • The scintillation threshold shift to higher fields with SF 6 .