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NaI (Tl) detectors have been widely used during the recent years based on their response to γ-rays, which is significant mainly for the elemental analysis of neutron-induced prompt γ-rays. The detector functions significantly influence the analysis results, especially the detector efficiency. The present study focused on this problem and has been made of the contribution of the full-energy peak attenuation in the calculation of the detector efficiency. An empirical formula has been derived to calculate the full-energy peak attenuation for 3″×3″ NaI (Tl) well-type detector using isotropic radiating axial point sources. The measured efficiency values are used in this method to find the peak attenuation coefficient for this particular source-to-detector geometry. In addition, the obtaining values were used to calculate the detector full-energy peak efficiency, and compared it with the measured ones. The calculated values of the detector efficiency are found to be in a good agreement with experimental data. This gives indication about the ability to extend the calculated efficiency values to build an efficiency curve as a function of γ-ray energy as not many radioactive sources exist for the standardization process.

The incidence of cancer throughout the world is increasing with the prolonged life expectancy that has resulted from improvements in standards of living. About half of all cancer patients receive radiotherapy, either as part of their primary treatment or in connection with recurrences or palliation. The International Atomic Energy Agency (IAEA) has estimated that approximately 2500 teletherapy machines were in use in 1998 in developing countries and that 10000 such machines may be needed by 2015. The preparation of this Safety paper was initiated as a result of an expected increase in the construction of radiotherapy facilities, and in response to Member States that have requested practical guidance regarding the design and shielding of such facilities. In this work, The Harshaw Model 4500 Manual TLD Reader was used for Thermo Luminescence Dosimetry (TLD) by using a set of 20 chips Dosimeter TLD-100. A comprehensive set of measurements were performed for five different sites inside and outside the accelerator. The obtained results showed agreement with published data in some location while the results of the working staff site were within the limits of the recommended permissible dose where it was about 0.5 m Sievert per year.