Hogue M G, Roberts D W, Burkett J L
1Savannah River Nuclear Solutions, LLC, Bldg. 730-1B, Rm. 110, Aiken, SC 29808.
Health Phys. 2018 Dec;115(6):769-772. doi: 10.1097/HP.0000000000000918.
The relative response of neutron rem detectors has previously been shown to increase after prolonged exposure to a neutron flux. This increase has been referred to as the "soak factor." The cause of the increased response has been previously unexplained. This note reports on a search for the underlying cause of the increased response. Testing involved gamma-ray spectroscopy of activated neutron rem detector components and testing of instrument response at various rates of neutron flux and accumulated fluence. The proposed primary cause of the increased response is activation of copper in the brass collar at the fill end of the gas-filled detector tube. This component allows for attachment of the extension housing on the tube containing BF3 or He gas. Under a neutron flux, some of this copper activates to Cu. In addition, Mn was detected in activated components but does not seem to be a significant contributor to the detector response. Cadmium isotopes did not appear to be significant. The activated component causes an increase in indicated neutron dose rate due to decay photons from activated components. Photons normally have little impact on neutron rem detector readings because the electrical pulses produced in the probes are below the lower-level discriminator. However, the photon pulses do impact the overall count rate when they occur simultaneously with normally uncounted, lower amplitude, wall-effect neutron pulses.
中子rem探测器的相对响应先前已表明，在长时间暴露于中子通量后会增加。这种增加被称为“浸泡因子”。响应增加的原因先前一直未得到解释。本报告介绍了对响应增加的根本原因的探寻。测试包括对活化的中子rem探测器部件进行伽马射线能谱分析，以及在不同中子通量率和累积注量下测试仪器响应。响应增加的主要原因据推测是充气探测器管填充端黄铜套中的铜被活化。该部件用于将延长外壳连接到装有BF3或He气的管子上。在中子通量作用下，部分这种铜会活化为Cu。此外，在活化部件中检测到了锰，但它似乎对探测器响应的贡献不大。镉同位素似乎也不显著。活化部件由于活化部件的衰变光子导致指示的中子剂量率增加。光子通常对中子rem探测器读数影响很小，因为探测器探头中产生的电脉冲低于下限甄别器。然而，当光子脉冲与通常未计数的、幅度较小的壁效应中子脉冲同时出现时，确实会影响总计数率。
