氮气低温除氡技术与极低水平氡测量方法研究

高纯低本底氮气在低本底实验中有重要作用，对氮气的放射性氡本底纯化技术和低本底氡测量方法进行研究非常重要。利用低温物理吸附技术，对氮气中的氡进行纯化，同时建立了静电收集结合低温富集法的氡测量装置， 能够测量氮气中10 μBq/m3的氡本底。利用氡测量装置测量了普通氮气中和纯化氮气中的氡，结果表明，纯化系统可以将氡本底为20 mBq/m3的氮气降低至(25.2±5) μBq/m3，即可将氡本底降低到纯化前的0.125%。研究还发现，纯化能力与氮气中氡本底相关，在氮气中氡本底为几十mBq/m3到几十μBq/m3范围内，随着氡本底的下降，纯化能力也随之下降。主要原因是，随着氮气中氡的分压降低，吸附能力下降。另外，在极低本底下由系统本底及泄露引入的氡污染影响显著增大。

Study of Low Temperature Radon Removal Technology and Low Background Radon Measurement in Nitrogen

High-purity and low-background nitrogen plays an important role in the low-background experiments, and it is necessary to study radioactive impurities removal technology and low-background radon measurement in nitrogen. The research uses low-temperature adsorption technology to remove radioactive impurities in nitrogen. At the same time, electrostatic collection and low-temperature enrichment methods are combined to measure ~10 μBq/m3 radon in nitrogen. The result shows that the purification system can reduce the radon background in nitrogen by 20 mBq/m3 to (25.2±5) μBq/m3, namely, can reduce the radon background by 800 times. It is also found that the purification capacity is related to the radon background in nitrogen. In the range of radon background from dozens of mBq/m3 to dozens of μBq/m3, the purification capacity decreases with the lower radon background. The main reason is that the adsorption capacity decreases with the lower partial pressure of radon. In addition, the influence of radon pollution caused by system background and leakage increases significantly under very low background.