- ©2001. AAPG/DEG
Measurement of terrain-emanated natural uranium gamma radiation is difficult because of the inclusion by the measuring device of radiation from the decay of atmospheric radon. This paper presents the results of a 7-year study of time variations of the components of the natural gamma radiation. Accurate measurement and removal of the atmospheric equivalent uranium (eU) decay fraction provides the terrain-emanated eU radiation. Variations in equivalent thorium (eTh), eU, and potassium-40 (40K) natural radiation have been measured over this 7-year period at one location at 5-min intervals. Atmospheric diurnal changes in the concentrations of radon gamma-emitting daughters are observed to exceed surface-emanated eU radiation by more than 400% in the absence of rainfall and up to ∼3000% in rainfall. Gamma radiation from rainfall-deposited thoron daughters has been seen to increase the surface-emanated eTh radiation by more than 70%. Two different field vehicles currently contain the measurement systems. Data reduction requires the use of environmentally measured gamma ray standard spectra for eTh, eU, and 40K decay and cosmic radiation, plus measurement and use of vehicular system radiation backgrounds. Using these measurement methods, gamma radiation emitted from the earth's surface can be accurately determined day or night, except during and for up to1.5 days following rainfall. Monthly variations of the components of the natural gamma radiation are presented together with daily variations for six selected months of the measurement period.
Robert S. Foote is president of Geoscience & Technology, Inc., and Geoscience International, Inc., geophysical service companies that specialize in analysis of high-sensitivity measurement of the earth's magnetic field. He received his master's degree in nuclear physics from the University of Illinois in 1948. He was employed at National Bureau of Standards high-energy physics laboratory from 1949 to 1955, and worked in the Texas Instruments Central Research & Engineering laboratory from 1957 to 1968. He was active in the USDOE NURE program for determining the U.S. uranium potential with Geodata International, Inc., in the 1970s and started Geoscience & Technology, Inc., in 1984. He has several patents and has published several papers relating the application of sedimentary residual magnetic field anomalies in the semi-shallow subsurface environment and exploration drill cuttings magnetic susceptibility to the discovery of oil and gas.
Nathan Frick is Vice President of Systems at Geoscience & Technology, Inc., and Geoscience International, Inc., and is currently finishing work on a master's degree in physics at the University of Texas at Arlington. His interests include neural networks, stochastic processes, music, and computational quantum mechanics.