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Geology topics

A. B. Tanner

Publications and source records attributed to A. B. Tanner.

18 recordsLinked to original sources
USGS1994

Geology and occurrence of radon

The accumulation of radon indoors is commonly due to movement of radon from adjacent soil and rock into a building foundation through joints, utility openings, cracks, or porous block walls. When air pressure inside the building is lower than that in the soil, pressure-driven flow of radonbearing soil gas can occur (see Chapter 2). Whether or not an indoor radon problem results depends on: (1) the radium concentration in the soil and underlying rock, (2) the ability of radon to escape from the solid material holding the parent radium, and (3) the ability of radon to move through the rock and soil fractures and pores.

Book chapter↗
USGS1991

Error in measuring radon in soil gas by means of passive detectors

Passive detection of radon isotopes depends on diffusion of radon atoms from the sites of their generation to the location of the detecting or collecting device. Because some radon decays en route to a passive detector in soil, the radon concentration measured by the detector must be less than the concentration in those soil pores where it is undiminished by diffusion to the detector cavity. The true radon concentration may be significantly underestimated in moist soils. -Author

Nuclear Geophysics↗
USGS1988

A tentative protocol for measurement of radon availability from the ground

A procedure is being tested in order to determine its suitability for assessing the intrinsic ability of the ground at a particular site to supply 222 Rn to a basement structure to be built on the site. Soil gas is sucked from a borehole probe through an alpha scintillation chamber and flow meter by a pump. The permeability of the soil is calculated from the flow rate and the pressure difference between the atmosphere and the borehole at the intake point. The diffusion coefficient is estimated from the water fraction in the soil pores. The upward migration distance for radon in such soil during one mean life is computed from an arbitrary steady pressure difference. This mean migration distance, multiplied by the measured radon concentration, gives the 'radon availability number'. Measurements at sites of known indoor radon concentration suggest that numbers below 2 kBq.m -2 indicate litte chance of elevated indoor radon and above 20 kBq.m -2 indicate that elevated indoor radon is likely. The range of uncertainty and the point-to-point and seasonal variations to be expected are under investigation.

Radiation Protection Dosimetry↗
USGS1988

A tentative protocol for measurement of radon availability from the ground

A procedure is being tested in order to determine its suitability for assessing the intrinsic ability of the ground at a particular site to supply radon (222Rn) to a basement structure to be built on the site. The mean migration distance, multiplied by the measured radon concentration gives the "Radon Availability Number' (RAN). Measurements at sites of known indoor radon concentration suggest that RANs below 2 kBq/m2 (5x104 pCi/m2) indicate little chance of elevated indoor radon and RANs above 20 kBq/m2 (5x105 pCi/m2) indicate that elevated indoor radon is likely. The range of uncertainty and the point-to-point and seasonal variations to be expected are under investigation. -from Author

Northeastern Environmental Science↗
USGS1986

Borehole field calibration and measurement of low-concentration manganese by decay gamma rays

The manganese concentration in the Arundel clay formation, Prince Georges County, Maryland, was determined from a borehole by using delayed neutron activation. The neutrons were produced by a 100 mu g 252 Cf source. The 847 keV gamma ray of manganese was detected continuously, and its counting rate was measured at intervals of 15 s as the measuring sonde was moved at a rate of 0.5 cm/s. The technique measured the concentration ratio of manganese to aluminum. This ratio, when combined with an estimate of the aluminum concentration of the clay, made it possible to determine the percentage concentration of manganese without using a test-pit calibration facility. The measurements were made by using an NaI(Tl) scintillation detector and a Ge(HP) solid-state detector cooled by solid propane. A two-pass technique had to be used with the scintillation detector because Compton background from the 1 779 keV photopeak of aluminum masked the manganese line. The Compton background did not interfere when the solid-state detector was used. The borehole measurements compared favorably with a chemical core analysis and were unaffected by water in the borehole.

Geophysics↗
USGS1984

Inter-pulse high-resolution gamma-ray spectra using a 14 MeV pulsed neutron generator

A neutron generator pulsed at 100 s-1 was suspended in an artificial borehole containing a 7.7 metric ton mixture of sand, aragonite, magnetite, sulfur, and salt. Two Ge(HP) gamma-ray detectors were used: one in a borehole sonde, and one at the outside wall of the sample tank opposite the neutron generator target. Gamma-ray spectra were collected by the outside detector during each of 10 discrete time windows during the 10 ms period following the onset of gamma-ray build-up after each neutron burst. The sample was measured first when dry and then when saturated with water. In the dry sample, gamma rays due to inelastic neutron scattering, neutron capture, and decay were counted during the first (150 ??s) time window. Subsequently only capture and decay gamma rays were observed. In the wet sample, only neutron capture and decay gamma rays were observed. Neutron capture gamma rays dominated the spectrum during the period from 150 to 400 ??s after the neutron burst in both samples, but decreased with time much more rapidly in the wet sample. A signal-to-noise-ratio (S/N) analysis indicates that optimum conditions for neutron capture analysis occurred in the 350-800 ??s window. A poor S/N in the first 100-150 ??s is due to a large background continuum during the first time interval. Time gating can be used to enhance gamma-ray spectra, depending on the nuclides in the target material and the reactions needed to produce them, and should improve the sensitivity of in situ well logging. ?? 1984.

Nuclear Instruments and Methods In Physics Researc↗
USGS1977

Importance of neutron energy distribution in borehole activation analysis in relatively dry, low-porosity rocks

To evaluate the importance of variations in the neutron energy distribution in borehole activation analysis, capture gamma-ray measurements were made in relatively dry, low-porosity gabbro of the Duluth Complex. Although sections of over a meter of solid rock were encountered in the borehole, there was significant fracturing with interstitial water leading to a substantial variation of water with depth in the borehole. The linear-correlation coefficients calculated for the peak intensities of several elements compared to the chemical core analyses were generally poor throughout the depth investigated. The data suggest and arguments are given which indicate that the variation of the thermal-to-intermediate-to-fast neutron flux density as a function of borehole depth is a serious source of error and is a major cause of the changes observed in the capture gamma-ray peak intensities. These variations in neutron energy may also cause a shift in the observed capture gamma-ray energy.

Geoexploration↗
USGS1977

In situ analysis of coal using a 252CF-Ge(Li) borehole sonde

A borehole sonde using a 252 Cf neutron source and a Ge(Li) gamma-ray detector was field tested in a coal bed in Belmont County, Ohio, to ascertain whether such a device could be useful as a coal-exploration tool. In continuous motion, the sonde was used to accumulate successive spectra over short time intervals. The intensities of the capture gamma rays from hydrogen and of the decay gamma rays from aluminum were determined simultaneously in each spectrum. A log of the intensities versus depth shows the depth and thickness of the coal bed. With the sonde stationary at points above, in, and below the coal bed, capture gamma rays were measured to show the variation in concentration of certain elements. From the spectrum recorded in the bed, a complete ultimate analysis, the percent ash content, and the heat content were determined without recourse to an external standard. With the sonde stationary at points above, in, and below the coal bed, capture gamma rays were measured to show the variation in concentration of certain elements. From the spectrum recorded in the bed, a complete ultimate analysis, the percent ash content, and the heat content were determined without recourse to an external standard. These experiments show that it is feasible to use a 252 CfGe(Li) borehole sonde as an aid in coal exploration.

Open-File Report↗
USGS1976

Intrinsic germanium detector used in borehole sonde for uranium exploration

A borehole sonde (~1.7 m long; 7.3 cm diameter) using a 200 mm 2 planar intrinsic germanium detector, mounted in a cryostat cooled by removable canisters of frozen propane, has been constructed and tested. The sonde is especially useful in measuring X- and low-energy gamma-ray spectra (40–400 keV). Laboratory tests in an artificial borehole facility indicate its potential for in-situ uranium analyses in boreholes irrespective of the state of equilibrium in the uranium series. Both natural gamma-ray and neutron-activation gamma-ray spectra have been measured with the sonde. Although the neutron-activation technique yields greater sensitivity, improvements being made in the resolution and efficiency of intrinsic germanium detectors suggest that it will soon be possible to use a similar sonde in the passive mode for measurement of uranium in a borehole down to about 0.1% with acceptable accuracy. Using a similar detector and neutron activation, the sonde can be used to measure uranium down to 0.01%.

Nuclear Instruments and Methods↗
USGS1976

Field experiments to test neutron interaction techniques in boreholes in relatively dry, low porosity rock

Depending on the technique, there are a number of problems associated with in situ neutron activation elemental analyses in boreholes. Several techniques of using delayed and capture gamma rays for in situ borehole spectral analysis were tried in a relatively dry gabbro. Using copper as a test element the best results using a delayed gamma-ray method were obtained by independent uniform neutron irradiation of the borehole followed by a delay time of about 16 hours before spectral analysis. The results obtained for several other elements measured by both delayed and capture gamma-ray methods, however, showed poor correlation with the chemical analyses. The change in the nonthermal compared with thermal neutron flux density in the rock appears to be the most serious cause of the poor correlation observed. This in turn affects the gamma-ray peak intensities and energies. Errors in the driller's log, poor correspondence between the core chemistry and the sample, and interstation interference also contributed substantially to the poor results.

Open-File Report↗
USGS1976

Intrinsic germanium detector used in borehole sonde for uranium exploration

A borehole sonde using a 200-mm 2 planar intrinsic germanium detector, mounted in a cryostat cooled by removable canisters of frozen propane, has been constructed and tested. The sonde is especially useful in measuring X- and low-energy gamma-ray spectra (40-400 keV). Laboratory tests in an artificial borehole facility indicate its potential for in-situ uranium analyses in boreholes irrespective of the state of equilibrium in the uranium series. Both natural gamma-ray and neutron-activation gamma-ray spectra have been measured with the sonde. Although the neutron-activation technique yields greater sensitivity, improvements being made in the resolution and efficiency of intrinsic germanium detectors suggest that it will soon be possible to use a similar sonde for measurement of the natural radiations of uranium in a borehole down to the 0.1 percent range with acceptable accuracy.

Open-File Report↗
USGS1972

A probe for neutron activation analysis in a drill hole using 252Cf, and a Ge(Li) detector cooled by a melting cryogen

A sonde has been built for high-resolution measurement of natural or neutron-induced gamma rays in boreholes. The sonde is 7.3 cm in diameter and about 2.2 m in length and weighs about 16 kg. The lithium-compensated germanium semiconductor detector is stabilized at −185 to −188°C for as much as ten hours by a cryostatic reservoir containing melting propane. During periods when the sonde is not in use the propane is kept frozen by a gravity-fed trickle of liquid nitrogen from a reservoir temporarily attached to the cryostat section. A 252 Cf source, shielded from the detector, may be placed in the bottom section of the sonde for anlysis by measurement of neutron-activation or neutron-capture gamma rays. Stability of the cryostat with changing hydrostatic pressure, absence of vibration, lack of need for power to the cryostat during operation, and freedom of orientation make the method desirable for borehole, undersea, space, and some laboratory applications.

Nuclear Instruments and Methods↗
USGS1972

Radiative-neutron-capture gamma-ray analysis by a linear combination technique

The linear combination technique, when applied to a gamma-ray spectrum, gives a single number indicative of the extent to which the spectral lines of a sought element are present in a complex spectrum. Spectra are taken of the sought element and of various other substances whose spectra interfere with that of the sought element. A weighting function is then computed for application to spectra of unknown materials. The technique was used to determine calcium by radiative-neutron-capture gamma-ray analysis in the presence of interfering elements, notably titanium, and the results were compared with those for two popular methods of peak area integration. Although linearity of response was similar for the methods, the linear combination technique was much better at rejecting interferences. For analyses involving mixtures of unknown composition the technique consequently offers improved sensitivity.

Nuclear Instruments and Methods↗
USGS1972

A comparison of radiative capture with decay gamma-ray method in bore hole logging for economic minerals

The recent availability of borehole logging sondes employing a source of neutrons and a Ge(Li) detector opens up the possibility of analyzing either decay or capture gamma rays. The most efficient method for a given element can be predicted by calculating the decay-to-capture count ratio for the most prominent peaks in the respective spectra. From a practical point of view such a calculation must be slanted toward short irradiation and count times at each station in a borehole. A simplified method of computation is shown, and the decay-to-capture count ratio has been calculated and tabulated for the optimum value in the decay mode irrespective of the irradiation time, and also for a ten minute irradiation time. Based on analysis of a single peak in each spectrum, the results indicate the preferred technique and the best decay or capture peak to observe for those elements of economic interest.

Nuclear Instruments and Methods↗