An underground nuclear explosion (UNE) generates radioactive gases that can be transported through fractures to the ground surface over timescales of hours to months. If detected, the presence of particular short-lived radionuclides in the gas can provide strong evidence that a recent UNE has occurred. By drawing comparisons between sixteen similar historical U.S. UNEs where radioactive gas was or was not detected, we identified factors that control the occurrence and timing of breakthrough at the ground surface. The factors that we evaluated include the post-test atmospheric conditions, local geology, and surface geology at the UNE sites. The UNEs, all located on Pahute Mesa on the Nevada National Security Site (NNSS), had the same announced yield range (20–150 kt), similar burial depths in the unsaturated zone, and were designed and performed by the same organization during the mid-to-late 1980s. Results of the analysis indicate that breakthrough at the ground surface is largely controlled by a combination of the post-UNE barometric pressure changes in the months following the UNE, and the volume of air-filled pore space above the UNE. Conceptually simplified numerical models of each of the 16 historical UNEs that include these factors successfully predict the occurrence (5 of the UNEs) or lack of occurrence (remaining 11 UNEs) of post-UNE gas seepage to the ground surface. However, the data analysis and modeling indicates that estimates of the meteorological conditions and of the post-UNE, site-specific subsurface environment including air-filled porosity, in combination, may be necessary to successfully predict late-time detectable gas breakthrough for a suspected UNE site.

地下核爆炸（UNE）产生放射性气体，这些气体可在数小时至数月的时间内通过裂缝传输到地面。如果检测到，气体中存在特定的短寿命放射性核素可以提供强有力的证据证明最近发生了UNE。通过对16个历史悠久的美国UNE（有或没有探测到放射性气体）之间的比较进行比较，我们确定了控制地面穿透发生和时间的因素。我们评估的因素包括UNE站点的测试后大气条件，当地地质和地表地质。UNE都位于内华达国家安全局（NNSS）的Pahute Mesa上，其宣布的产量范围相同（20-150 kt），在非饱和带的埋葬深度相似，由同一组织在1980年代中后期设计和执行。分析结果表明，地面的突破在很大程度上受到UNE之后几个月内UNE后的大气压力变化以及UNE上方的充气孔隙空间体积的综合控制。在概念上简化了包括这些因素的16个历史UNE中的每一个的数值模型，它们成功地预测了UNE后地下气体渗漏的发生（5个UNE）或不发生（剩余11个UNE）。但是，数据分析和建模表明，结合气象条件和UNE后特定地点的地下环境（包括充气孔隙）的估计，