Calculation of the full-energy peak efficiency of NaI(Tl) detector using the efficiency transfer method for large radioactive cylindrical sources

• A new analytical approach for calculation of the FEPE is deduced.
• Separate calculation of factors which related to photon attenuation is introduced.
• The method depends on the calculation of the average path length and the efficiency transfer.
• 152Eu aqueous sources covering the energy range from 121up to 1408 keV were used.
• Remarkable agreement between measured and calculated efficiencies was achieved.

A new theoretical approach is introduced in this article to calculate the full-energy peak efficiency of cylindrical NaI(Tl) γ-ray detectors. This new approach depends mainly on an analytical calculation of the photon average path lengths inside the source-to-detector system. The effective solid angle Ω join mathematically with the efficiency transfer method (ET) to obtain a simple formula for the detection efficiency. The self attenuation factor of the source (with a radius greater than the detector's radius) matrix is also considered. In addition, the attenuation factors of the source container, the detector housing and any absorbing materials during the measurement are also included. Results are compared with those obtained from ETNA program and those measured by two different cylindrical NaI(Tl) detectors with resolution (FWHM) at 662 keV equal to 7.5% and 8.5%, respectively. 152Eu aqueous radioactive cylindrical sources covering the energy range from 121 keV up to 1408 keV are used. The measured and the calculated with ETNA program efficiencies are compared with those calculated with this new approach. The results are found satisfactory with negligible discrepancies.