Well-type NaI(Tl) detector efficiency using analytical technique and ANGLE 4 software based on radioactive point sources located out the well cavity

•A new analytical approach for calculation of the full-energy peak efficiency is deduced.•The method depends on the calculation of the photon path length.•Separate calculation of factors which related to photon attenuation is introduced.•The effective solid angle between source-to-detector is calculated.•Remarkable agreement between measured and calculated efficiencies was achieved.

Well-type detectors play an important role in qualitative and quantitative analysis of low-activity samples, thanks to their pronouncedly high efficiency; this is particularly the case with scintillation detectors. In this work a theoretical approach to calculations of full-energy peak efficiencies of well-type detectors is elaborated. The approach is based on the concept of the effective solid angle and the efficiency transfer principle. In parallel, ANGLE 4 software was employed to the same aim, using point sources positioned on 2″ × 2″ NaI(Tl) detector axis outside the detector well cavity. The theoretically obtained and ANGLE 4 calculated efficiency values were compared to the measured ones. These comparisons supported/confirmed both the theoretical concept and ANGLE 4 Software validity in well-type scintillation detectors calibration.