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At least 19 recordsLinked to original sources
USGS1998

Consideration of measurement error when using commercial indoor radon determinations for selecting radon action levels

An examination of year-long, in-home radon measurement in Colorado from commercial companies applying typical methods indicates that considerable variation in precision exists. This variation can have a substantial impact on any mitigation decisions, either voluntary or mandated by law, especially regarding property sale or exchange. Both long-term exposure (nuclear track greater than 90 days), and short-term (charcoal adsorption 4-7 days) exposure methods were used. In addition, periods of continuous monitoring with a highly calibrated alpha-scintillometer took place for accuracy calibration. The results of duplicate commercial analysis show that typical results are no better than ??25 percent with occasional outliers (up to 5 percent of all analyses) well beyond that limit. Differential seasonal measurements (winter/summer) by short-term methods provide equivalent information to single long-term measurements. Action levels in the U.S. for possible mitigation decisions should be selected so that they consider the measurement variability; specifically, they should reflect a concentration range similar to that adopted by the European Community.

Conference Paper↗
USGS1959

α-Radioactivity of cerium-142

JOHNSON AND NIER 1 have measured the atomic masses of some of the rare-earth isotopes and have shown that the mass difference cerium-142—(barium-138 + helium-4) is equivalent to 1.68 ± 0.10 MeV. Similar results for the naturally occurring samarium and neodymium isotopes show that the α -active isotope of each element is the one having the largest possible decay energy. Rasmussen and others 2 suggest that the two or three neutrons just beyond the closed shell of 82 neutrons have decreased binding energies and hence the α -energy has a maximum about 84 neutrons. Johnson and Nier suggest that the α -decay of cerium-142 may take place with enough energy to be experimentally observable. Porschen and Riezler 3 examined a sample of un-enriched cerium ammonium citrate using nuclear track plates sensitive to α -particles. No α -activity was observed after a 30-day exposure of 1.2 mgm. of the cerium salt. In 1957 Riezler and Kauw 4 reported an alpha activity for an enriched sample of cerium-142. From their results they calculated a half-life of 5.1 × 10 15 years with an uncertainty factor of 2.

Nature↗
USGS1988

The effect of α-damage on fission-track annealing in zircon

The thermal stability of confined fission-track lengths in four zircon samples having different spontaneous track densities (i.e. different amounts of ??-damage) has been studied by one hour isochronal annealing experiments. The thermal stability of spontaneous track lengths is independent of initial spontaneous track density. The thermal stability of induced track lengths in pre-annealed zircon, however, is significantly higher than that of spontaneous track lengths. The results indicate that the presence of ??-damage lowers the thermal stability of fission-tracks in zircon. ?? 1988.

International Journal of Radiation Applications an↗
USGS1979

A practical method of estimating standard error of age in the fission track dating method

A first-order approximation formula for the propagation of error in the fission track age equation is given by PA = C[P2s+P2i+P2??-2rPsPi] 1 2, where PA, Ps, Pi and P?? are the percentage error of age, of spontaneous track density, of induced track density, and of neutron dose, respectively, and C is a constant. The correlation, r, between spontaneous are induced track densities is a crucial element in the error analysis, acting generally to improve the standard error of age. In addition, the correlation parameter r is instrumental is specifying the level of neutron dose, a controlled variable, which will minimize the standard error of age. The results from the approximation equation agree closely with the results from an independent statistical model for the propagation of errors in the fission-track dating method. ?? 1979.

Nuclear Tracks↗
USGS1984

Fission-track dating applied to mineral exploration

The partial to total resetting of fission-track ages of minerals in country rock near a mineralized area can be used to (1) locate a thermal anomaly, and (2) date the mineralizing event. Two mining districts in Colorado have been studied - Rico and Gilman. Rico is a precious- and base-metal mining district. Initial fission-track dating of a sill located about 6 km from the center of the district gave ages of 20 Myr and 65 Myr for apatite and zircon, respectively. The Eagle Mine in the Gilman District is the largest producer of zinc in the state of Colorado. Fission-track dating of zircon from a 70 Myr-old sill shows partial resetting of the zircon (45 Myr). The thermal anomaly identified by fission-track dating is seen in both districts far outside the area affected by obvious alteration. Based on the results of these two pilot studies, fission-track dating can be a useful exploration method for thermal anomalies associated with buried or otherwise poorly expressed mineral deposits.

Nuclear Tracks and Radiation Measurements (1982)↗
USGS1981

Fission-track dating of apatite and zircon: An interlaboratory comparison

Apatite and zircon separates from the Fish Canyon Tuff (K-Ar age, 27.9??0.7 Myr), San Juan Mtns., Colorado, have been given to over 50 laboratories for fission-track dating. Nineteen laboratories have reported fission-track ages that they have determined for apatites. Nine laboratories have reported their analysis of the zircons. The principal difference between the results reported by the laboratories reflects their choice of the decay constant. The laboratories which use a value of ??f ??? 7.0 ?? 10-17 yr-1 for the spontaneous-fission decay constant of 238U, report an average age for the apatite of 28.5??0.7 Myr, and those using ??f ??? = 8.4 ?? 10-17 yr-1 report an average age of 23.6??1.0 Myr. The average fission-track age for the zircons is 28.4??0.7 Myr. Only laboratories which use ??f ??? 7.0 ?? 10-17 yr-1 reported zircon data. ?? 1981.

Nuclear Tracks↗
USGS1985

Simulated fissioning of uranium and testing of the fission-track dating method

A computer program (FTD-SIM) faithfully simulates the fissioning of 238U with time and 235U with neutron dose. The simulation is based on first principles of physics where the fissioning of 238U with the flux of time is described by Ns = ??f 238Ut and the fissioning of 235U with the fluence of neutrons is described by Ni = ??235U??. The Poisson law is used to set the stochastic variation of fissioning within the uranium population. The life history of a given crystal can thus be traced under an infinite variety of age and irradiation conditions. A single dating attempt or up to 500 dating attempts on a given crystal population can be simulated by specifying the age of the crystal population, the size and variation in the areas to be counted, the amount and distribution of uranium, the neutron dose to be used and its variation, and the desired ratio of 238U to 235U. A variety of probability distributions can be applied to uranium and counting-area. The Price and Walker age equation is used to estimate age. The output of FTD-SIM includes the tabulated results of each individual dating attempt (sample) on demand and/or the summary statistics and histograms for multiple dating attempts (samples) including the sampling age. An analysis of the results from FTD-SIM shows that: (1) The external detector method is intrinsically more precise than the population method. (2) For the external detector method a correlation between spontaneous track count, Ns, and induced track count, Ni, results when the population of grains has a stochastic uranium content and/or when the counting areas between grains are stochastic. For the population method no correlation can exist. (3) In the external detector method the sampling distribution of age is independent of the number of grains counted. In the population method the sampling distribution of age is highly dependent on the number of grains counted. (4) Grains with zero-track counts, either in Ns or Ni, are in integral part of fissioning theory and under certain circumstances must be included in any estimate of age. (5) In estimating standard error of age the standard error of Ns and Ni and ?? must be accurately estimated and propagated through the age equation. Several statistical models are presently available to do so. ?? 1985.

Nuclear Tracks and Radiation Measurements (1982)↗
USGS1990

High temperature annealing of fission tracks in fluorapatite, Santa Fe Springs oil field, Los Angeles Basin, California

Annealing of fission tracks is a kinetic process dependent primarily on temperature and to a laser extent on time. Several kinetic models of apatite annealing have been proposed. The predictive capabilities of these models for long-term geologic annealing have been limited to qualitative or semiquantitative at best, because of uncertainties associated with (1) the extrapolation of laboratory observations to geologic conditions, (2) the thermal histories of field samples, and (3) to some extent, the effect of apatite composition on reported annealing temperatures. Thermal history in the Santa Fe Springs oil field, Los Angeles Basin, California, is constrained by an exceptionally well known burial history and present-day temperature gradient. Sediment burial histories are continuous and tightly constrained from about 9 Ma to present, with an important tie at 3.4 Ma. No surface erosion and virtually no uplift were recorded during or since deposition of these sediments, so the burial history is simple and uniquely defined. Temperature gradient (???40??C km-1) is well established from oil-field operations. Fission-track data from the Santa Fe Springs area should thus provide one critical field test of kinetic annealing models for apatite. Fission-track analysis has been performed on apatites from sandstones of Pliocene to Miocene age from a deep drill hole at Santa Fe Springs. Apatite composition, determined by electron microprobe, is fluorapatite [average composition (F1.78Cl0.01OH0.21)] with very low chlorine content [less than Durango apatite; sample means range from 0.0 to 0.04 Cl atoms, calculated on the basis of 26(O, F, Cl, OH)], suggesting that the apatite is not unusually resistant to annealing. Fission tracks are preserved in these apatites at exceptionally high present-day temperatures. Track loss is not complete until temperatures reach the extreme of 167-178??C (at 3795-4090 m depth). The temperature-time annealing relationships indicated by the new data from Santa Fe Springs conflict with predictions based on previously published, commonly used, kinetic annealing models for apatite. Work is proceeding on samples from another area of the basin that may resolve this discrepancy.

International Journal of Radiation Applications an↗
USGS1990

Timing of uplift peripheral to the Red Sea, Saudi Arabia

A Prominent escarpment is found along the western margin of the Arabian Shield. Elevations along this escarpment are up to 3200 m above the Red Sea. Between the Red Sea and the crest of the escarpment is a relatively featureless coastal plane that is ??? 50 km across. The coastal plane abruptly gives way to the steep mountainous terrain, the elevation of which increases abruptly towards the high crest. The elevation slowly decreases to the east of the high crest. Forty-four apatite fission-track ages have been determined on rocks from the Proterozoic Arabian Shield in southwestern Saudi Arabia. These ages range from 13.8 to 568 Ma. In general, the youngest ages are found at low elevations along the base of the escarpment near the eastern edge of the coastal plane. The oldest ages are from along and to the east of the crest. The fission-track data from Saudi Arabia show that there was a period of minor uplift and cooling during the Cretaceous. This was followed by a relatively stable period which lasted until the Mid to Upper Miocene. The latest uplift and erosion began slightly younger than 13.8 Ma. This latest episode resulted in a minimum uplift of 3 km and is related to the Red Sea Rift. Samples totally annealed prior to this latest episode of uplift and cooling have not yet reached the surface.

International Journal of Radiation Applications an↗
USGS1993

Possible secondary apatite fission track age standard from altered volcanic ash beds in the middle Jurassic Carmel Formation, Southwestern Utah

Secondary age standards are valuable in intra- and interlaboratory calibration. At present very few such standards are available for fission track dating that is older than Tertiary. Several altered volcanic ash beds occur in the Middle Jurassic Carmel Formation in southwestern Utah. The formation was deposited in a shallow marine/sabhka environment. Near Gunlock, Utah, eight ash beds have been identified. Sanidines from one of the ash beds (GUN-F) give a single-crystal laser-probe 40Ar/39Ar age of 166.3??0.8 Ma (2??). Apatite and zircon fission track ages range from 152-185 Ma with typically 15-20 Ma errors (2??). Track densities in zircons are high and most grains are not countable. Apatites are fairly common in most of the ash beds and have reasonable track densities ranging between 1.2-1.5 ?? 106 tracks/cm2. Track length distributions in apatites are unimodal, have standard deviations <1??m, and mean track lengths of about 14-14.5 ??m. High Cl apatites (F:Cl:OH ratio of 39:33:28) are particularly abundant and large in ash GUN-F, and are fairly easy to concentrate, but the concentrates contain some siderite, most of which can be removed by sieving. GUN-F shows evidence of some reworking and detriaal contamination based on older single grain 40Ar/39Ar analyses and some rounding of grains, but the apatite population appears to be largely uncontaminated. At present BJK has approximately 12 of apatite separate from GUN-F. ?? 1993.

Nuclear Tracks and Radiation Measurements↗
USGS2021

Using fission-track radiography coupled with scanning electron microscopy for efficient identification of solid-phase uranium mineralogy at a former uranium pilot mill (Grand Junction, Colorado)

At a former uranium pilot mill in Grand Junction, Colorado, mine tailings and some subpile sediments were excavated to various depths to meet surface radiological standards, but residual solid-phase uranium below these excavation depths still occurs at concentrations above background. The combination of fission-track radiography and scanning electron microscope energy-dispersive X-ray spectroscopy (SEM-EDS) provides a uniquely efficient and quantitative way of determining mineralogic associations of uranium that can influence uranium mobility. After the creation of sample thin sections, a mica sheet is placed on those thin sections and irradiated in a nuclear research reactor. Decay of the irradiated uranium creates fission tracks that can be viewed with a microscope. The fission-track radiography images indicate thin section sample areas with elevated uranium that are focus areas for SEM-EDS work. EDS spectra provide quantitative elemental data that indicate the mineralogy of individual grains or grain coatings associated with the fission-track identification of elevated uranium. For the site in this study, the results indicated that uranium occurred (1) with coatings of aluminum–silicon (Al/Si) gel and gypsum, (2) dispersed in the unsaturated zone associated with evaporite-type salts, and (3) sorbed onto organic carbon. The Al/Si gel likely formed when low-pH waters were precipitated during calcite buffering, which in turn retained or precipitated trace amounts of Fe, As, U, V, Ca, and S. Understanding these mechanisms can help guide future laboratory and field-scale efforts in determining long-term uranium release rates to groundwater.

Colorado↗
USGS2007

Simulation and Particle-Tracking Analysis of Selected Ground-Water Pumping Scenarios at Vogtle Electric Generation Plant, Burke County, Georgia

The source of ground water to production wells at Vogtle Electric Generation Plant (VEGP), a nuclear power plant in Burke County, Georgia, was simulated under existing (2002) and potential future pumping conditions using an existing U.S. Geological Survey (USGS) MODFLOW ground-water flow model of a 4,455-square-mile area in the Coastal Plain of Georgia and South Carolina. Simulation results for three steady-state pumping scenarios were compared to each other and to a 2002 Base Case condition. The pumping scenarios focused on pumping increases at VEGP resulting from projected future demands and the addition of two electrical-generating reactor units. Scenarios simulated pumping increases at VEGP ranging from 1.09 to 3.42 million gallons per day (Mgal/d), with one of the scenarios simulating the elimination of 5.3 Mgal/d of pumping at the Savannah River Site (SRS), a U.S. Department of Energy facility located across the Savannah River from VEGP. The largest simulated water-level changes at VEGP were for the scenario whereby pumping at the facility was more than tripled, resulting in drawdown exceeding 4-8 feet (ft) in the aquifers screened in the production wells. For the scenario that eliminated pumping at SRS, water-level rises of as much as 4-8 ft were simulated in the same aquifers at SRS. Results of MODFLOW simulations were analyzed using the USGS particle-tracking code MODPATH to determine the source of water and associated time of travel to VEGP production wells. For each of the scenarios, most of the recharge to VEGP wells originated in an upland area near the county line between Burke and Jefferson Counties, Georgia, with none of the recharge originating on SRS or elsewhere in South Carolina. An exception occurs for the scenario whereby pumping at VEGP was more than tripled. For this scenario, some of the recharge originates in an upland area in eastern Barnwell County, South Carolina. Simulated mean time of travel from recharge areas to VEGP wells for the Base Case and the three other pumping scenarios was between about 2,700 and 3,800 years, with some variation related to changes in head gradients because of pumping changes.

Georgia↗
USGS2012

Polar and brown bear genomes reveal ancient admixture and demographic footprints of past climate change

Polar bears (PBs) are superbly adapted to the extreme Arctic environment and have become emblematic of the threat to biodiversity from global climate change. Their divergence from the lower-latitude brown bear provides a textbook example of rapid evolution of distinct phenotypes. However, limited mitochondrial and nuclear DNA evidence conflicts in the timing of PB origin as well as placement of the species within versus sister to the brown bear lineage. We gathered extensive genomic sequence data from contemporary polar, brown, and American black bear samples, in addition to a 130,000- to 110,000-y old PB, to examine this problem from a genome-wide perspective. Nuclear DNA markers reflect a species tree consistent with expectation, showing polar and brown bears to be sister species. However, for the enigmatic brown bears native to Alaska's Alexander Archipelago, we estimate that not only their mitochondrial genome, but also 5–10% of their nuclear genome, is most closely related to PBs, indicating ancient admixture between the two species. Explicit admixture analyses are consistent with ancient splits among PBs, brown bears and black bears that were later followed by occasional admixture. We also provide paleodemographic estimates that suggest bear evolution has tracked key climate events, and that PB in particular experienced a prolonged and dramatic decline in its effective population size during the last ca. 500,000 years. We demonstrate that brown bears and PBs have had sufficiently independent evolutionary histories over the last 4–5 million years to leave imprints in the PB nuclear genome that likely are associated with ecological adaptation to the Arctic environment.

Proceedings of the National Academy of Sciences↗
USGS1978

Mineral resources of the Cabinet Mountains Wilderness, Lincoln and Sanders Counties, Montana

This report describes the differential array, of seismometers recently installed at the Hollister, California, Municipal Airport. Such an array of relatively closely spaced seismometers has already been installed in El Centro and provided useful information for both engineering and seismological applications from the 1979 Imperial Valley earthquake. Differential ground motions, principally due to horizontally propagating surface waves, are important in determining the stresses in such extended structures as large mat foundations for nuclear power stations, dams, bridges and pipelines. Further, analyses of the records of the 1979 Imperial Valley earthquake from the differential array have demonstrated the utility of short-baseline array data in tracking the progress of the rupture wave front of an earthquake.

Open-File Report↗
USGS1978

Uranium in waters and aquifer rocks at the Nevada Test Site, Nye County, Nevada

Previous chemical, geological, and hydrological information describing the physical and chemical environment of the Nevada Test Site (a Federal reserve for the testing of nuclear explosive devices) has been combined with new radiochemical and isotope data for water and rock samples in order to explain the behavior of uranium during alteration of thick sequences of rhyolitic volcanic rocks and associated volcaniclastic sediments. A model is proposed in which uranium mobility is controlled by two competing processes. Uranium is liberated from the volcanic rocks through dissolution of the glassy constituents and is carried in solution as a uranyl carbonate complex. Uranium is subsequently removed from solution by adsorption on secondary oxides of iron, titanium, and manganese, as observed in fission-track maps of aquifer rocks. The model explains the poor correlation of dissolved uranium with depth within tuffaceous sequences in which percolation of ground water is predominantly downward. Good positive correlation of dissolved uranium with dissolved Na, total dissolved solids, and total carbonate supports the glass dissolution model, while inverse correlation of dissolved uranium with U 234 /U 238 ratios of waters implies uranium is being absorbed by a relatively insoluble, surficial phase. Alpha radioactivity of Test Site water is primarily caused by high U 234 contents, and beta activity is highly correlated with dissolved K (K 40 ). Small amounts of dissolved radium, Pb 210 , and Po 210 are present but no evidence was found for alpha activity sources related to nuclear testing (Pu, U 235 ). A filtered but unacidified carbonate solution of uranium was found to be stable (± 10 percent of original U concentration) for years when stored in acid-washed polyethylene bottles.

Nevada↗