中文摘要：

大气中放射性气体氙同位素的活度浓度值是判断核裂变反应的关键数据,长期以来其准确测量一直是个难题.针对该问题,本文提出和定义了虚拟点源的概念,并使用LabSOCS软件模拟了不同尺寸气体体源和不同高度点源的探测效率,根据计算的数据建立了气体源体积和虚拟点源位置的函数关系.理论上证实了气体源体积和虚拟点位置有良好的线性关系,在理论上为解决虚拟源刻度技术提供了新的途径。

英文摘要：

The calibration methods for the radioactive Kr and Xe gases produce the key data for the judgment of nuclear fission reaction, whose accurate measurement has always been a difficult problem in operation for a long time. In order to obtain the accuracy, it is very important to calibrate the efficiencies of these gas sources, especially for proficiency test exercise of the laboratory, to analyze the CTBT samples of radioactive xenon, which are used to judge the nuclear test of the country and the measurement system. The relative measurement method has not realized in the experimental calibration, and the Monte Carlo method has large uncertainty also. Therefore, a new measurement method and experimental technology is needed. In order to avoid the above shortcomings, we need to develop a source-less efficient calibration method based on the virtual point source（VPS）. In the past, it was suggested that for point sources placed on the symmetry axis, a Ge（Li） or an HPGe cylindrical detector can be changed to an virtual point detector（VPD）, where all γ-ray interactions are considered to occur. This is not a real physical model but only a mathematical description. Aiming at the VPD, we put forward an innovative approach and define the concept of VPS. But, the concept is introduced in a volume source.In this concept, it is assumed that the total photons emission has occurred in a distance within the source described, and it is from the whole source to an imaginary point. If there is really a point located on the symmetry axis of the detector,whose efficiency is similar to that of the whole real volume source, the geometrical considerations used in calibrations of the source will be much simpler. The calibration process of the VPS is： firstly, a standard point source is placed at different position on the symmetry axis to obtain its full-energy peak efficiency. Secondly, the relationship between the height and the efficiency can be established. The position of the VPS can be deduced according to the full-ener