稀土废渣现场γ射线剂量率分段计算方法

在现场γ射线剂量率筛选的过程中,由放射性核素的活度限值到剂量率限值的计算是其中重要部分。在稀土冶炼过程中,伴生的天然放射性232 Th、238 U、235 U系列平衡被破坏,使得稀土废渣现场γ射线剂量率的计算工作加大。本文基于核素的衰变规律和化学特性,将232 Th、238 U、235 U天然放射性系列进行分段处理,通过计算各段衰变子系的γ剂量率来求得整个衰变系列的γ射线剂量率,提出现场γ射线剂量率分段计算方法。在封闭的环境下,232 Th、238 U、235 U系列的主要辐射子系可在较短时间内达到衰变平衡,从而避免非平衡状态下衰变系列各代子体核素的活度随时间变化的问题,减小计算量,并基于蒙特卡罗方法建立各段衰变子系的比活度与现场γ剂量率之间的关系,利用实验室测量的各衰变核素的比活度,实现对现场γ射线剂量率的计算。

The On-Site Gamma-Ray Dose Rate Piecewise Calculation Method for Rare Earth Tailings

In the process of gamma ray dose rate screening,the calculation from the activity limit of radionuclides to the dose rate limit is an important part.The balance of decay series of 232 Th,238 U and 235 U in rare earth tailings is broken during smelting,which makes the calculation of on-site gamma-ray dose rate of rare earth tailings more complicated.The on-site gamma-ray dose rate calculation method is based on the decay law and chemical characteristics of nuclides,and the gamma-ray dosimetry of 232 Th,238 U and 235 U natural radioactive series is processed in stages,and the gamma-ray dosimetry of the whole decay series is obtained by calculating the gamma-ray dosimetry of each decay sub-series.In the closed environment,the main radiation subsystems of 232 Th,238 U and 235 U series have the characteristics of reaching the decay equilibrium in a short time,so as to avoid the problem that the activity of the nuclides of each generation of the decay series varies with time in the non-equilibrium state and reduce the calculation amount.Based on the monte carlo method,the relationship between the specific activity of each decay subsystem and the field gamma dose rate was established.Then,the gamma-ray dose rate can be calculated if the specific activity of each radionuclide is measured in the laboratory.