A study of the validity of the efficiency transfer method to calculate the peak efficiency using c-ray detectorsat extremely large distances

The full-energy peak efficiency (FEPE) curvesof the (2 x 2 and 3 x 3 ) NaI (Tl) detectors weremeasured at seven different axial positions from theirsurfaces. The calibration process was done using radioactivepoint sources, which produce a wide energy rangefrom 59.53 up to 1,408.01 keV. This work has beenundertaken to explain the effects of source energy andsourcE-to-detector distance on the detector efficiencycalculations. The study provides an empirical formula tocalculate FEPE based on the efficiency transfer method fordifferent detectors using the effective solid angle ratio atvery large distances and for higher energies. A remarkableagreement between the measured and calculated efficienciesfor the detectors at the sourcE-to-detector distances<35 cm and above that slight difference was observed.