A uranium‐bearing granitic rock of known radon emanation was deformed to failure under uniaxial stress. Radon emanation and microcrack activity were recorded continuously during the test. Radon concentration in the closed system was measured by an alpha detector. A decrease in emanation was observed during the initial loading of the sample and is interpreted as associated with the closure of pre‐existing cracks within the rock. At a uniaxial stress equal to approximately one‐half the ultimate strength, a temporary increase (50%) in the radon emanation was observed that correlated with an increase in microcracking within the sample. When the stress was removed for several hours, the original emanation was restored. However, once the specimen failed, a temporary emanation increase of 120% was observed. The emanation then decreased to a level nearly 5% greater than the prefailure specimen emanation.

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