133Ba活性炭滤盒自吸收修正方法研究

为了¹³³Ba滤盒体源活度的准确定值以及提高对碘监测仪探测效率刻度的准确性，本研究采用粒径为20~40目，堆积密度为0.47 g/cm³的优质椰壳活性炭，对体源不同活性炭层厚度的自吸收修正进行研究。使用MCNP蒙卡模拟程序，计算面源在不同活性炭层厚度t下的探测效率ε_t，以及无填充介质时的探测效率ε₀，建立随活性炭层厚度变化的自吸收修正曲线F（t），并通过实验验证模拟计算结果的有效性。通过模拟计算与实验，得到了面源在不同活性炭层厚度下的活性炭自吸收修正因子F（t），结果表明，模拟计算与实验结果相差在1%左右符合。对于¹³³Ba的356 keV γ能点，得出滤盒中活性炭的自吸收修正因子F（t），给出了活性炭滤盒体源自吸收修正的技术方法，并采用自吸收修正因子F（t）对自制的¹³³Ba活性炭滤盒体源的自吸收修正进行了理论计算，与实验测量结果比较，两者在2%以内符合，可利用实验得到的自吸收修正曲线F（t）进行活性炭滤盒体源的自吸收修正。

Self-absorption Correction in Gamma-ray of 133Ba Activated Carbon Filter Box Source

In order to ensure the quasi-determined value of the filter box source activity of the ¹³³Ba and to improve the accuracy of the iodine monitor detection efficiency scale, high-quality coconut shell activated carbon with a particle size of 20 to 40 mesh and a bulk density of 0.47 g/cm³ was used. The self-absorption correction of the thickness of different activated carbon layers in the body was studied. Using the MCNP Monte Carlo simulation program, the detection efficiency ε_t of the surface source at different thicknesses t of the activated carbon layer and the detection efficiency ε₀ of the unfilled medium were calculated. The self-absorption correction curveF（t） was established with the thickness of the activated carbon layer. And experiments verify the validity of the simulation results. Through simulated calculations and experiments, the self-absorption correction factor F（t） of the activated carbon under different activated carbon layer thickness was obtained. The results show that the difference between the simulation calculation and the experimental results is about 1%. For the 356 keV γ energy point of ¹³³Ba, the self-absorption correction factorF（t） of the activated carbon in the filter cartridge is obtained, and the technical method of the activated carbon filter cartridge originating from the absorption correction is given.F（t） is used to calculate the self-absorption correction of self-made ¹³³Ba activated carbon filter body. Comparing with the experimental results, the two are within 2%. Therefore, the self-absorption correction of the activated carbon cartridge body can be performed using the experimentally obtained self-absorption correction curveF（t）.