The CYGNO experiment aims at the development of a large gaseous TPC with GEM-based amplification and an optical readout
by means of PMTs and scientific CMOS cameras for 3D tracking down to O(keV) energies, for the directional detection of rare
events such as low mass Dark Matter and solar neutrino interactions. The largest prototype built so far towards the realisation of the
CYGNO experiment demonstrator is the 50 L active volume LIME, with 4 PMTs and a single sCMOS imaging a 33×33 cm2 area for
50 cm drift, that has been installed in underground Laboratori Nazionali del Gran Sasso in February 2022. We will illustrate LIME
performances as evaluated overground in Laboratori Nazionali di Frascati by means of radioactive X-ray sources, and in particular
the detector stability, energy response and energy resolution. We will discuss the MC simulation developed to reproduce the detector
response and show the comparison with actual data. We will furthermore examine the background simulation worked out for LIME
underground data taking and illustrate the foreseen expected measurement and results in terms of natural and materials intrinsic
radioactivity characterisation and measurement of the LNGS underground natural neutron flux. The results that will be obtained
by underground LIME installation will be paramount in the optimisation of the CYGNO demonstrator, since this is foreseen to be
composed by multiple modules with the same LIME dimensions and characteristic
