The Luna experiment

LUNA is a pilot project initially focused on the 3 He ( 3 He , 2 p ) 4 He cross section measurement within the thermal energy region of the Sun (15–27 KeV ). A compact high current 50 KV ion accelerator facility including a windowless gas target system, a beam calorimeter and four detector telescopes has been built, tested and installed underground at the Laboratori Nazionali del Gran Sasso. The sensitivity has been improved by more than four orders of magnitude, as compared to the previous experiment. In particular, thanks to the cosmic ray suppression, we could attain a background level of less than 1 event per week, a rate similar to the one expected from 3 He ( 3 He ,2 p ) 4 He at the lower edge of the Sun thermal energy region