反符合方法用于降低内照射直接测量系统探测下限的研究

目的 目前肺部计数器在超铀核素的内照射直接测量方面存在探测下限较高的问题，本文采用反符合方法降低系统的本底，进一步降低系统探测下限。方法 在肺部计数器系统内建立宇宙射线探测器，采用反符合方法，研究宇宙射线中μ子等硬成分对肺部计数器系统本底的影响。该宇宙射线探测器主要由140 cm（长）×110 cm（宽）×5 cm（高）的大面积塑料闪烁体和反符合电路组成。结果 在6~2 MeV能量段，增加反符合探测器后系统的本底计数率由2.5 cps降至2.2 cps。测量时间1 800 s，系统对²⁴¹Am（59.5 keV）和²³⁹Pu（13.6 keV）的探测下限可达1.4 Bq和1 700 Bq。结论 用肺部计数器直接测量超铀核素的过程中，采用反符合方法降低宇宙射线硬成分可以较好地降低部分系统本底，在降低核素探测下限方面起到一定作用。

Study on detection limit of direct measurement system for internal exposure using anticoincidence method

Objective At present, there is a problem that the lower detection limit of lung counter is higher in the direct measurement of internal exposure of transuranic nuclides. In this paper, the anti-coincidence method is used to reduce the system's background and further reduce the detection limit of the system.Methods A new cosmic ray detector based on anti-coincidence method were established in the lung counter system to study the influence of hard components such as muon in cosmic rays on the background of the lung counter system. The cosmic ray detecting system was organized by a large area of plastic scintillator (140 cm (length)×110 cm(width)×5 cm(height)) and anti-coincidence circuit.Results For the energy between 6 keV and 2 MeV, the background count rate of this system decrease from 2.5 cps to 2.2 cps by using the anti-coincidence technique. And the detection limits of ²⁴¹Am (59.5 keV) and ²³⁹Pu (13.6 keV) after 1 800 seconds counting could reach 1.4 Bq and 1700 Bq, respectively.Conclusion In the process of direct measurement of transuranium nuclides with lung counter, the use of anti-coincidence method to reduce the hard component of cosmic rays can better reduce the background of some systems and play a role in reducing the lower limit of radionuclide detection.