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2 为什么要限制γ射线可透钢厚度的下限值(如AB级~(192)Ir定为30mm)?下限值降至10mm行不行?为什么采用内透中心法或偏心法时γ射线可透厚度的下限可降为表1所示值的一半? 表1 ~(192)Irγ射线能谱(基线) 答:要回答这个问题,先要从放射性同位素的γ射线能谱谈起。以~(192)Ir为例,其能谱较复杂,至少由24根能谱线组成,其基线和相对强度如表1所示。从表中可见,它主要包含三组能量:0.31.0.47和0.61MeV,而第一组占优势。与此能谱有关的~(192)Irγ射线在宽束条件下的有效吸收系数(中等钢厚度)见表2。为供比较,表3列出了200和300kVX射线吸收系数的实验值和计算值。
2 Why should limit the lower limit of the thickness of γ-ray permeable steel (such as AB class (192) Ir is set to 30mm)? The lower limit dropped to 10mm line not? Why using the endoprosthesis method or eccentric method γ-ray The lower limit of penetration can be reduced to half of the value shown in Table 1. Table 1 ~ (192) Ir 射 ray spectrum (baseline) A: To answer this question, we first talk about the γ-ray energy spectrum of radioisotopes. Taking Ir (192) as an example, its energy spectrum is more complex and consists of at least 24 energy spectrum lines. The baseline and relative intensities are shown in Table 1. It can be seen from the table that it mainly contains three sets of energy: 0.31.0.47 and 0.61 MeV, while the first group is dominant. Table 2 shows the effective absorption coefficient (medium steel thickness) of ~ (192) Irγ rays in this wide beam. For comparison, Table 3 lists the experimental and calculated values for the absorption coefficients of 200 and 300 kV X-rays.