VALIDATION OF IN SITU OBJECT COUNTING SYSTEM (ISOCS) MATHEMATICAL EFFICIENCY CALIBRATION SOFTWARE
VALIDATION OF IN SITU OBJECT COUNTING SYSTEM (ISOCS) MATHEMATICAL EFFICIENCY CALIBRATION SOFTWARE
复制标题
原位物体计数系统 (ISOCS) 数学效率校准软件的验证
DOI：
10.1016/s0168-9002(98)01115-2
复制
发表时间：
1999
影响因子：
1.4
通讯作者：
M. Field
中科院分区：
文献类型：
--
作者：
R. Venkataraman;F. Bronson;V. Abashkevich;B. Young;M. Field
ISOCS校准方法是一种方便的工具，用于校准探测器效率作为能量的函数，用于各种各样的源的几何形状和活动分布。ISOCS方法包括探测器的堪培拉表征、源几何数据的用户输入以及使用这些数据来产生效率校准的ISOCS软件。在表征过程中，开发了探测器的MCNP模型。然后，使用NIST可追溯源的测量结果对模型进行独立验证。给出验证模型，探测器的响应特性被映射到覆盖半径为50 m的球体内的任何位置，以探测器为中心，并且在50 keV-7 MeV的光子能量范围内。ISOCS软件包含一系列数学模型，可以模拟各种样品形状。该软件将每个源区域划分为多个体素。在每个体素内，以准随机方式定义点位置。在给定的能量下，计算每个体素的探测器效率，同时考虑到由于源内部和外部的吸收体引起的衰减。所有体素的效率在给定能量下相加。为了确定这种校准方法的准确性，进行了大量的测试（约109）。在这些测试中的每一个中，将参考效率校准与相同几何形状下的ISOCS效率校准进行比较。参考校准来自完整的MCNP计算，或来自多能量放射源。测试被分为三种不同的计数几何，即，现场，实验室，准直几何。每种几何结构的数据进一步分为低能（<150 keV）和中高能（> 150 keV）组。ISOCS/真实效率的平均比率为（i）场几何结构为1.01±0.007，（ii）实验室几何结构为0.97±0.007，（iii）准直几何结构为1.09±0.014。通过分析真实效率的相对不确定度和比值的相对标准偏差，估计现场、实验室和准直几何形状的ISOCS平均相对标准偏差分别为6.5%、5.4%和10.5%。从该验证过程中识别出影响数据的各种偏倚来源。在表征过程和算法方面进行了改进，这些改进将在ISOCS效率校准软件的未来版本中实施。
The ISOCS calibration method is a convenient tool for calibrating the detector efficiency as a function of energy for a wide variety of source geometries and activity distributions. The ISOCS method consists of a Canberra characterization of the detector, user input of source geometry data, and the ISOCS software which uses these to produce the efficiency calibration. During the characterization, an MCNP model of the detector is developed. The model is then independently validated using measurements with a NIST traceable source. Given the validated model, the response characteristics of the detector are mapped out to cover any location inside a sphere of radius 50m, centered on the detector, and over a photon energy range of 50keV–7MeV. The ISOCS software contains a series of mathematical models that can simulate a wide variety of sample shapes. The software divides each source region into a number of voxels. Inside each voxel, a point location is defined in a quasi-random fashion. At a given energy, the detector efficiency is calculated for each voxel, taking into account the attenuation due to absorbers both inside and outside the source. The efficiencies for all the voxels are summed up at the given energy. To determine the accuracy of this calibration method, a large number of tests (about 109) were performed. In each of these tests, a reference efficiency calibration was compared to an ISOCS efficiency calibration at the same geometry. The reference calibration was either from a full MCNP calculation, or from a multi-energy radioactive source. The tests were categorized into three different counting geometries, namely, Field, Laboratory, and Collimated geometry. The data for each geometry were further divided into low energy (<150keV) and intermediate to high-energy (>150keV) groups. The mean ratio of ISOCS/True efficiencies was (i) 1.01±0.007 for the Field geometries, (ii) 0.97±0.007 for the Laboratory geometries, and (iii) 1.09±0.014 for the Collimated geometries. By analyzing the relative uncertainties in the True efficiencies, and the relative standard deviation in the ratios, the average relative standard deviation due to ISOCS is estimated to be 6.5%, 5.4%, and 10.5%, for the Field, Laboratory, and Collimated geometries, respectively. Various sources of bias affecting the data have been identified from this validation process. Improvements have been made in the characterization process and in the algorithms, which will be implemented in future versions of the ISOCS efficiency calibration software.