In present work, the validity of the virtual point detector (VPD) model for the NaI(Tl) detectors is studied and confirmed in the photon energy range of 60–1408 keV. The full energy peak efficiency (FEPE) of two NaI(Tl) detectors, which have scintillation crystal dimensions of 5.08 × 5.08 cm and 7.62 × 7.62 cm respectively, is measured for “point-like” radioactive sources on the symmetry axis with source-to-detector distances in the range of 2–40 cm. It is found that the VPD model is valid to fit too well to the experimental FEPE for the two surveyed NaI(Tl) detectors. The dependence of the VPD position on the incident photon energy for the NaI(Tl) detectors with different scintillation crystal dimensions is shown based on experimental data. A semi-empirical equation involving incident photon energy and source-to-detector distance is proposed to calculate the FEPE for the NaI(Tl) detectors. The calculated results for the two surveyed NaI(Tl) detectors by this equation are in a good agreement with experimental results for photon energies in the range of 344–1408 keV. However, the difference between experimental and calculated results is quite significant for source-to-detector close geometries for photon energies lower than 344 keV.

在目前的工作中，对NaI（Tl）探测器的虚拟点探测器（VPD）模型的有效性进行了研究，并在60-1408 keV的光子能量范围内得到了证实。在对称轴上测量“点状”放射源的两个NaI（Tl）探测器的全能量峰值效率（FEPE），该探测器的闪烁晶体尺寸分别为5.08×5.08 cm和7.62×7.62 cm。到探测器的距离范围为2–40 cm。发现对于两个被调查的NaI（Tl）检测器，VPD模型有效地太适合实验FEPE。根据实验数据，显示了VPD位置对具有不同闪烁晶体尺寸的NaI（Tl）检测器的入射光子能量的依赖性。提出了一个包含入射光子能量和源到探测器距离的半经验方程，以计算NaI（Tl）探测器的FEPE。该方程对两个被调查的NaI（Tl）探测器的计算结果与344-1408 keV范围内光子能量的实验结果非常吻合。但是，对于低于344 keV的光子能量，对于源到探测器的紧密几何形状，实验结果与计算结果之间的差异非常显着。