A major hope for discovering subsurface uranium ore is that measurable concentrations of the radioactive gas 222Rn can be recognized near the surface of the earth. Integrated measurements, made over several weeks, show promise of giving greater reproducibility than short-term measurements, which are more subject to meteorologic variability.
The use of improved methods of integrated radon measurements—free of 220Rn, of thermal-track fading, and of moisture-condensation effects—allow readings to be made that generally are highly stable over time. At a site 16 km north of Thoreau, New Mexico, readings at a depth of 60 cm, taken over a 9-month interval for a set of 55 positions, give different but nearly constant monthly readings at each position, the typical standard deviation being 14%. Superimposed on that stable pattern have been two periods during which spatially grouped radon readings increased by a factor of two or more over their normal values. The simplest tenable description of the source of the increases is sporadic puffs of upflowing gas, originating at as yet unknown depths. The measurements are consistent with an upward velocity of flow of ~10-3cm/sec.