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J. N. Rosholt

Publications and source records attributed to J. N. Rosholt.

6 recordsLinked to original sources
USGS2002

Quantitative radiochemical method for determination of major sources of natural radioactivity in ores and minerals

When an ore sample contains radioactivity other than that attributable to the uranium series in equilibrium, a quantitative analysis of the other emitters must be made in order to determine the source of this activity. Thorium-232, radon-222, and lead-210 have been determined by isolation and subsequent activity analysis of some of their short-lived daughter products. The sulfides of bismuth and polonium are precipitated out of solutions of thorium or uranium ores, and the α -particle activity of polonium-214, polonium-212, and polonium-210 is determined by scintillation-counting techniques. Polonium-214 activity is used to determine radon-222, polonium-212 activity for thorium-232, and polonium-210 for lead-210. The development of these methods of radiochemical analysis will facilitate the rapid determination of some of the major sources of natural radioactivity.

Analytical Chemistry↗
USGS2002

Quantitative radiochemical methods for determination of the sources of natural radioactivity

Study of the state of equilibrium of any natural radioactive source requires determination of several key nuclides or groups of nuclides to find their contribution to the total amount of radioactivity. Alpha activity measured by scintillation counting is used for determination of protactinium-231, thorium-232, thorium-230, and radium-226. The chemical procedures for the separations of the specific elements are described, as well as the measurement techniques used to determine the abundances of the individual isotopes. To correct for deviations in the ore standards, an independent means of evaluating the efficiencies of the individual separations and measurements is used. The development of these methods of radiochemical analysis facilitates detailed investigation of the major sources of natural radioactivity.

Analytical Chemistry↗
USGS2002

Automatic measurements and computations for radiochemical analyses

In natural radioactive sources the most important radioactive daughter products useful for geochemical studies are protactinium-231, the alpha-emitting thorium isotopes, and the radium isotopes. To resolve the abundances of these thorium and radium isotopes by their characteristic decay and growth patterns, a large number of repeated alpha activity measurements on the two chemically separated elements were made over extended periods of time. Alpha scintillation counting with automatic measurements and sample changing is used to obtain the basic count data. Generation of the required theoretical decay and growth functions, varying with time, and the least squares solution of the overdetermined simultaneous count rate equations are done with a digital computer. Examples of the complex count rate equations which may be solved and results of a natural sample containing four alpha-emitting isotopes of thorium are illustrated. These methods facilitate the determination of the radioactive sources on the large scale required for many geochemical investigations.

Analytical Chemistry↗
USGS1973

Lead isotope systematics and uranium depletion in the Granite Mountains, Wyoming

Isotopic composition and concentration of lead in whole rock and microcline and concentration of uranium and thorium in whole-rock samples of granite from the Granite Mountains, Wyoming, have been determined. The lead isotopic composition in the whole rocks was found to be highly radiogenic with a range in Pb 206 /Pb 204 of 19.58 to 42.27; the corresponding range in microclines is 15.39 to 22.44. A Pb 206 /Pb 204 versus Pb 207 /Pb 204 plot of the whole-rock data yields an apparent isochron age of 2,790 ± 80 m.y. as the time of crystallization of the granite. Chemically determined values of U 238 /Pb 204 in the whole rocks lie between 3.3 and 18.4 and are too low to account for the amount of radiogenic lead observed. A material balance of lead, thorium, and uranium components indicates that an average of approximately 75 percent of the amount of uranium required to produce the radiogenic lead was removed from the rocks, whereas, on the average, there was no apparent loss of thorium. Loss of uranium from the granite is demonstrated to extend at least to a depth of 165 ft in a drill core. The average uranium loss from the samples analyzed represents about 20 g uranium per 1,000 kg of rock that apparently was removed during the Cenozoic and that probably constitutes the major source of uranium now in ore deposits in central Wyoming basins. The lead isotopic composition of the microclines indicates that lead was mobilized within the granite and was isolated in the feldspar during a thermal event about 1,640 + 120 m.y. ago. However, there is no evidence that the whole rocks themselves became open systems at that time. Whole-rock and microcline isochrons intersect at Pb 206 /Pb 204 and Pb 207 /Pb 204 of 13.77 and 14.86, respectively, indicating a characteristic U 238 /Pb 204 of 8.96 in the source region of the granite magma.

Wyoming↗
USGS1970

Nuclear methods applied to uranium geochemistry

Stable and radioactive daughter products produced from nuclear disintegrations of uranium have proved useful in fundamental studies of the geochemistry of uranium in igneous rock and sedimentary environments and in ore deposits. Information gained from geochemical studies of uranium migration has been used to develop models for attempts to date archeological, geological, and oceanographic environments represented by samples of bone, wood, charcoal, continental and marine carbonates, marine sediments, and glacially derived soils. Recent improvements of nuclear instrumentation and techniques allowed accurate measurements of natural radioactive isotopes, and it is now believed that radioactive equilibrium between the long-lived isotopes of the two uranium decay series is more the exception than the rule in nature. It was assumed that the 234U and 238U isotopes were in equilibrium until Thurber confirmed that considerable separation between 234U daughter and 238U parent exists in nature. It now has been documented that the 234U content may range from 60% deficient to 500% in excess relative to 238U. An excess of 15% of 234U isotope in sea water is well documented. A summary of previous work has shown that geochemical fractionation of the radioactive nuclides in 238U and 235U decay series takes place in the hydrologic environment, resulting in depletion of 230Th and 231Pa with respect to their parents, 238U, 234U, and 235U, in water and a complementary enrichment of these daughter nuclides in some sediments. Subsequent assimilation of Uranium, essentially free of radioactive daughters, occurs in some specific types of deposits such as carbonates and phosphates.

IEEE Transactions on Nuclear Science↗