Positron annihilation spectroscopy (PAS). Positron annihilation measurements have been carried out using a 22NaCl source (strength ~ 10 ?Ci) and sealed in a 1.5 ?m (micro-meter) thick nickel foil. The sealed source has been placed amidst two identical plane faced samples (8 mm diameter × 1 mm thick pellet) for both the positron annihilation lifetime (PAL) as well as Doppler broadening measurements. The PAL have been calculated with a conventional fast-fast coincidence assembly which comprises of two gamma-ray detectors (25 mm long and 25 mm tapered to 13 mm diameter BaF2 scintillator, optically coupled with XP2020 Q photomultiplier tube) and two differential discriminators having constant fraction (Fast ComTech; model 7029A) which has time resolution (full width at half maximum) of ~ 220 ps measured by the prompt gamma ray of 60Co source. Approximately ten million coincidence counts have been detected and recorded in a multichannel analyzer. The recorded lifetime spectrum has been examined using the computer code PATFIT-88 with proper source corrections. The room temperature Doppler broadening of positron annihilation radiation (DBPAR) experiment has been carried out by a single HPGe detector (Efficiency: 12%; Type: PGC 1216sp of DSG, Germany) which have an energy resolution of 1.15 keV at 514 keV of 85Sr. The DBPAR spectra have been recorded in a dual ADC based – multiparameter data acquisition system (MPA-3 of FAST ComTec, Germany). The Doppler broadening of annihilation at 511 keV ?-ray spectrum has been examined by evaluation of the line-shape parameters (S-parameter).27,28 The S-parameter is defined as the ratio of counts in the central area (~511 keV) under the photo peak ( | 511 keV – E? | ? 0.85 keV ) to the whole area under the photo peak ( | 511 keV – E? | ? 4.25 keV ). The S-parameter mainly reflects the fraction of positrons that are being annihilated by the lower momentum electrons with reference to the total electrons annihilated. The contribution of the S-parameter is crucially because of the occurrence of open volume defects where the positrons get annihilated.