Light yield measurements were performed at room temperature (RT) under the excitation of 662 keV c-rays from a 137Cs source using a photomultiplier (PMT) based-setup described in the signal from a Photonis XP5200B PMT anode was sent to a CANBERRA 2005 preamplifier and then to a Tennelec TC 243 spectroscopy amplifier. The PC-based multichannel analyzer (Tukan 8 k MCA) was used to record the pulse height spectra. The photoelectron yield, expressed as a number of photoelectrons per MeV (phe/MeV) of energy deposited in the crystal, was determined bymeans of a single photoelectron method . In this method the number of photoelectrons is measured by comparing the position of a full energy peak of c-rays detected in the crystals with that of the single photoelectron peak from the PMT photocathode. To improve the light collection efficiency the samples were coupled to the PMT window with silicone grease and covered with several layers of Teflon tape. The measurements of LY non-proportionality and energy resolution were carried out for a series of X/c-rays emitted by different radioactive sources in the energy range from 32.1 to 1274.5 keV. The total mass attenuation coefficient at 59.5 and 662 keV c-rays was determined using the good geometry arrangement of source (100 mCi 241Am and 15 mCi 137Cs), absorber (1 mm thick BGO sample) and NaI:Tl detector. A narrow beam of c-rays is defined by circular apertures (£4 mm) in the Pb-collimators of source and detector, placed at a distance of 40 cm.