The two-dosimeter algorithm (TDA) is an improved method for estimating the effective dose (E) in unknown radiation fields. For such fields, energy spectrum and radiation geometry are not known, although the radiation source characteristics are specified. The two dosimeter algorithm can be used to overcome these limitations, however, resulting in significant dose overestimations for Laterals (LATs), Overhead (OH) and Underfoot (UF) beam directions. This study attempts to design a Thermoluminescent Dosimeter (TLD)-based tool that does not overestimate E for the mentioned radiation directions, by putting a shield on the dosimeter. The shape, materials, and size of the shield were appropriately selected so that the response of the dosimeters was similar to the body when it is irradiated to the external exposure. The shape of the shield was chosen as a half ellipsoid positioned on top of a cylinder with an elliptical surface with appropriate sizes. Aluminum oxide (Al2O3) and Chrysoberyl (BeAl2O4) were considered as materials for the shield. Dosimeters responses have been tested for 0.08, 0.3, and 1 MeV photon energies with various beam directions. Results showed that, by applying these new dosimeters, the two-dosimeter algorithms Eest= 0.97 Rf +0.42 Rb and Eest= 0.51 Rf + 0.22 Rb were obtained for dosimeters with Al2O3 and BeAl2O4 shields, respectively. Using this novel approach, more than 80% of Eest was in the -10% to 100% span that is an ideal range of TDA for all photon energies and beam directions. There were overestimations in the order of 200% to 280%, for few irradiation angles, which is much less than the overestimation of the previous algorithm and dosimeters without shield (580%).

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