Calibration of well-type NaI(Tl) detector using a point sources measured out the detector well at different axial distances

The high efficiency of well-type detector is one of its important advantages, when it is used to determine the low level activity of radiation in many different fields. In the present work the full-energy peak efficiency of 3"× 3" NaI(Tl) well-type scintillation detector was calculated. The calculations were based on the efficiency transfer principle and a new straightforward analytical definition to compute the effective solid angle between a point source and the detector surfaces Moreover, the effective solid angle ratio subtended by the well-type detector and a point source located out the detector cavity at various distances was calculated, the attenuation of the photon by the source-detector system [detectorendcap,deadlayer and holder material] was considered and determined. This method is easily useful in setting up the efficiency calibration curve for well-type detectors when the source is outside. The computed efficiency values are found to be in a good agreement with the experimental data obtained in the case of radiating γ -ray standard point sources.