Detection of radioxenon and radioargon produced by underground nuclear explosions is one of the primary methods by which the Comprehensive Nuclear-Test–Ban Treaty (CTBT) monitors for nuclear activities. However, transport of these noble gases to the surface via barometric pumping is a complex process relying on advective and diffusive processes in a fractured porous medium to bring detectable levels to the surface. To better understand this process, experimental measurements of noble gas and chemical surrogate diffusivity in relevant lithologies are necessary. However, measurement of noble gas diffusivity in tight or partially saturated porous media is challenging due to the transparent nature of noble gases, the lengthy diffusion times, and difficulty maintaining consistent water saturation. Here, the quasi-steady-state Ney–Armistead method is modified to accommodate continuous gas sampling via effusive flow to a mass spectrometer. An analytical solution accounting for the cumulative sampling losses and induced advective flow is then derived. Experimental results appear in good agreement with the proposed theory, suggesting the presence of retained groundwater reduces the effective diffusivity of the gas tracers by 10–1000 times. Furthermore, by using a mass spectrometer, the method described herein is applicable to a broad range of gas species and porous media.

中文翻译：

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一种通过连续监测质谱法测量紧密和部分饱和多孔介质中气体扩散率的实验方法

探测地下核爆炸产生的放射性氙和放射性氩是《全面禁止核试验条约》（CTBT）监测核活动的主要方法之一。然而，通过气压泵将这些稀有气体输送到地表是一个复杂的过程，它依赖于裂缝多孔介质中的对流和扩散过程，以将可检测水平带到地表。为了更好地理解这一过程，需要对相关岩性中的惰性气体和化学替代扩散率进行实验测量。然而，由于惰性气体的透明性质、漫长的扩散时间以及难以保持一致的水饱和度，在致密或部分饱和的多孔介质中测量惰性气体扩散率具有挑战性。这里，对准稳态 Ney-Armistead 方法进行了修改，以适应通过流出流到质谱仪的连续气体采样。然后推导出考虑累积采样损失和诱发的平流的解析解。实验结果与提出的理论非常吻合，表明保留地下水的存在将气体示踪剂的有效扩散率降低了 10-1000 倍。此外，通过使用质谱仪，本文所述的方法适用于广泛的气体种类和多孔介质。表明保留地下水的存在将气体示踪剂的有效扩散率降低了 10-1000 倍。此外，通过使用质谱仪，本文所述的方法适用于广泛的气体种类和多孔介质。表明保留地下水的存在将气体示踪剂的有效扩散率降低了 10-1000 倍。此外，通过使用质谱仪，本文所述的方法适用于广泛的气体种类和多孔介质。