PGNAA方法测量元素的非线性规律研究

瞬发伽玛中子活化分析(prompt gamma neutron activation analysis, PGNAA)在线分析仪广泛应用于水泥、煤炭等工业控制领域，由于工业现场产量的变化，导致皮带上物料的厚度不恒定，当物料厚度变化时，在线分析仪的测量结果会出现偏差。为消除在线分析仪测量不同厚度物料的测量偏差，通过理论分析和蒙特卡罗模拟(MCNP)研究中子自屏蔽和伽玛自衰减影响，并寻求修正模型。根据探测器接收特征伽玛射线的计算公式进行理论分析，利用蒙特卡罗软件建立PGNAA在线分析仪装置模型，分别模拟Al₂O₃、SiO₂、CaO、Fe和水泥生料等物料随厚度变化的特征射线计数，以水泥在线分析仪为例，寻求修正模型。结果表明，特征伽玛射线强度不随物料厚度增加而线性增长，按照线性标定方法的在线分析仪测量误差增大，各元素平均相对误差大于10%；根据水泥生料各元素的特征射线计数与物料厚度之间的关系，建立适用于测量水泥生料的多项式厚度修正模型。与线性标定相比，修正后分析仪测量误差降低30%以上，可为煤质、烧结料、铝土矿等块状物料的PGNAA元素检测提供修正方法。

Nonlinear Study of Elemental Measurements by PGNAA Method

Prompt gamma neutron activation analysis (PGNAA) is a kind of high sensitivity to nondestructive testing technology. Application of the technology of on-line PGNAA analyzer is widely used in industrial control fields such as cement, coal, which has advantages of fast response and high precision of analysis. The thickness of the material on the belt is often not constant due to the change of industrial field production. When the material thickness changes, the measurement results of the on-line analyzer will deviate. In order to eliminate the measurement deviation of materials with different thickness measured by on line analyzer, the reason of deviation is studied through theoretical analysis and Monte Carlo simulation, and the correction model is sought. First, through the theoretical analysis, according to the calculation formula of gamma ray detector characteristics, mainly due to the self-shielding effect of neutron and self-attenuation gamma rays of the material inside, the neutron field distribution and gamma receiving efficiency change, then lead to feature gamma counting nonlinear increase with the increase of thickness. Then, on-line PGNAA analyzer device model is built by using the Monte Carlo software (MCNP), and the changes of characteristic ray count of Al₂O₃, SiO₂, CaO, Fe and cement raw materials with thickness are simulated respectively. Simulation and experimental results show that the characteristics of gamma radiation intensity is not linear with the increase of the thickness of the material. The on-line analyzer measurement error increases by linear calibration method, the average relative error is more than 10%. Finally, taking cement on-line analyzer as an example, the modified model is sought. According to the relationship between the characteristic ray count of each element of cement raw material and the material thickness, a polynomial thickness correction model suitable for measuring cement raw material is established. Compared with linear calibration, the measurement error of the modified analyzer is reduced by more than 30%. The modified method can be applied to PGNAA detection of lump materials such as coal, sintering materials and bauxite.