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Geology topics

G. R. Boynton

Publications and source records attributed to G. R. Boynton.

At least 19 recordsLinked to original sources
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↗
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↗
USGS1975

Canister cryogenic system for cooling germanium semiconductor detectors in borehole and marine probes

High resolution intrinsic and lithium-drifted germanium gamma-ray detectors operate at about 77–90 K. A cryostat for borehole and marine applications has been designed that makes use of prefrozen propane canisters. Uses of such canisters simplifies cryostat construction, and the rapid exchange of canisters greatly reduces the time required to restore the detector to full holding-time capability and enhances the safety of a field operation where high-intensity 252 Cf or other isotopic sources are used. A holding time of 6 h at 86 K was achieved in the laboratory in a simulated borehole probe in which a canister 3.7 cm diameter by 57 cm long was used. Longer holding times can be achieved by larger volume canisters in marine probes.

Nuclear Instruments and Methods↗
USGS1972

Borehole activation analysis by delayed and capture gamma rays using a 252Cf neutron source

Theoretical analysis and experimental comparison of the radiative capture and delayed gamma-ray activation techniques indicate the latter to be more efficient for the detection of copper, whereas the radiative capture method is preferable for nickel. A conservative lower detection limit for both copper and nickel is '-0.5%. Borehole spectra by both techniques were made in a copper- and nickel-bearing gabbro, utilizing a Ge(Li) propane-cooled detector. Al, Mn, Na, Mg, Cu, and V were readily activated and detected by the delayed method. H, Fe, Si, and Ni were not usually present in the delayed spectra but they responded well in the capture mode. It is shown that the borehole sonde can be configured to permit simultaneous delayed and capture spectra, permitting detection of all of these elements. Simulated borehole experiments indicate that, in the delayed gamma-ray mode, an infinite sample is achieved when the ore layer has a vertical thickness of ∼20 cm and a horizontal distance of '10 cm into the wallrock. The depth resolution is thus relatively good but horizontal penetration through the wallrock is limited. © 1972 Society of Economic Geologists, Inc.

Economic Geology↗