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Geology topics

F. E. Senftle

Publications and source records attributed to F. E. Senftle.

At least 37 records · Page 2Linked to original sources
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↗
USGS1974

Antiferromagnetic inclusions in lunar glass

The magnetic susceptibility of 11 glass spherules from the Apollo 15, 16, and 17 fines and two specimens of a relatively large glass spherical shell were studied as a function of temperature from room temperature to liquid helium temperatures. All but one specimen showed the presence of antiferromagnetic inclusions. Closely spaced temperature measurements of the magnetic susceptibility below 77 K on five of the specimens showed antiferromagnetic temperature transitions (Néel transitions). With the exception of ilmenite in one specimen, these transitions did not correspond to any transitions in known antiferromagnetic compounds.

Earth and Planetary Science Letters↗
USGS1973

Comparison of the magnetic properties of glass from Luna 20 with similar properties of glass from the Apollo missions

Magnetic susceptibility measurements have been made on four glass spherules and fragments from the Luna 20 fines; two at 300°K and two from 300°K to 4°K. From these data the magnetic susceptibility extrapolated to infinite field, the magnetization at low fields and also the saturation magnetization at high fields, the Curie constant, the Weiss temperature, and the temperature-independent susceptibility were determined. Using a model previously proposed for the Apollo specimens, the Curie constant of the antiferromagnetic inclusions and a zero field splitting parameter were calculated for the same specimens. The data show the relatively low concentration of iron in all forms in these specimens. In addition, the Weiss temperature is lower than that measured for the Apollo specimens, and can be attributed almost entirely to the ligand field distortion about the Fe 2+ ions in the glassy phase. The data further suggest that the Luna 20 specimens cooled more slowly than those of the Apollo missions, and that some of the antiferromagnetic inclusions in the glass may have crystallized from the glass during cooling.

Geochimica et Cosmochimica Acta↗
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↗
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↗
USGS1971

Analytical sensitivities and energies of thermal neutron capture gamma rays II

A table of the analytical sensitivities of the principal lines in the thermal neutron capture gamma-ray spectrum from 0 to 3 MeV has been compiled for most of the elements. A tabulation of the full-energy, single-escape, and double-escape peaks has also been made according to energy. The tables are useful for spectral interpretation and calibration.

Nuclear Instruments and Methods↗
USGS1970

Analytical sensitivities and energies of thermal-neutron-capture gamma rays

A table of the analytical sensitivities of the principal lines in the thermal-neutron-capture gamma ray spectrum has been compiled for most of the elements. In addition a second table of the full-energy, single-escape, and double-escape peaks has been compiled according to energy for all significant lines above 3 MeV. Lines that contrast well with adjacent lines are noted as prominent. The tables are useful for spectral interpretation and calibration.

Nuclear Instruments and Methods↗
USGS1970

Magnetic studies of lunar samples

The remanent magnetism of a lunar type C breccia sample includes a large viscous component with a time constant of several hours, and a high coercivity remanence, possibly acquired by impact processes on the lunar surface. Ilmenite(?) and metallic iron in breccias, and ferrous and metallic iron in glass beads separated from lunar fines (type D) were identified by high-field and low-temperature experiments. The iron appears to occur in a wide range of grain sizes including the single domain and multidomain states.

Science↗
USGS1968

Van vleck paramagnetism in orthorhombic TiO2 (Brookite)

The magnetic susceptibility of the orthorhombic form of titanium dioxide has been measured from 5 to 300°K. After deducting the temperature-dependent component, which is probably due to defects or impurities, and the free-ion diamagnetic component, the Van Vleck paramagnetism was estimated to be 33× 10 − 6 emu/mole. Comparison is made between this value and the Van Vleck paramagnetism of strontium titanate and the two tetragonal forms of titanium dioxide: rutile and anatase.

Physical Review↗
USGS1966

Mineral exploration and soil analysis using in situ neutron activation

A feasibility study has been made to operate by remote control an unshielded portable positive-ion accelerator type neutron source to induce activities in the ground or rock by “in situ” neutron irradiation. Selective activation techniques make it possible to detect some thirty or more elements by irradiating the ground for periods of a few minutes with either 3-MeV or 14-MeV neutrons. The depth of penetration of neutrons, the effect of water content of the soil on neutron moderation, gamma ray attenuation in the soil and other problems are considered. The analysis shows that, when exploring for most elements of economic interest, the reaction 2 H(d,n) 3 He yielding ∼ 3-MeV neutrons is most practical to produce a relatively uniform flux of neutrons of less than 1 keV to a depth of 19″–20″. Irradiation with high energy neutrons (∼ 14 MeV) can also be used and may be better suited for certain problems. However, due to higher background and lower sensitivity for the heavy minerals, it is not a recommended neutron source for general exploration use. Preliminary experiments have been made which indicate that neutron activation in situ is feasible for a mineral exploration or qualititative soil analysis.

Nuclear Instruments and Methods↗
USGS1966

Absence of neutral alkali atoms in rhodizite

The formula CsB 12 Be 4 Al 4 O 28 has been proposed by others for the mineral rhodizite. Electron-spin-resonance and magnetic susceptibility measurements prove the absence of neutral cesium atoms. An ionic formula CsB 11 Be 4 Al 4 O 26 (OH) 2 is proposed.

Science↗
USGS1964

Submicroscopic spherules and color of tektites

Magnetic susceptibility measurements of 18 tektites from various strewn fields have been made as a function of temperature from 77°K to room temperature. A relatively large temperature-independent component of the magnetic susceptibility was observed in all cases, and an analysis of the data shows that this component is the result of submicroscopic iron spherules in the tektites. An analysis of the color of tektites in terms of the magnetic measurements and also of the optical absorption spectra suggests that the basic color of all tektites is green or greenish-blue, and that the brown to black coloration in some tektites is due to finely dispersed Fe 2 O 3 and/or many metallic spherules, both probably of colloidal size.

Geochimica et Cosmochimica Acta↗
USGS1963

Antiferromagnetism of UO2⋅2H2O

Magnetic susceptibility measurements have been made on UO 2 · x H 2 O for x =1.78 to x =2.13, and from 77° to 375°K. As the value of x decreased the susceptibility increased. Both these data and structural arguments imply that the formula of this compound is U(OH) 4 rather than the dihydrate form. Based on this concept the data have been corrected for diamagnetism and also small amounts of UO 2 and H 2 O which were present. The molar susceptibility of U 4+ in U(OH) 4 is nearly an order of magnitude less than in other uranium compounds, and it is suggested that this is probably due to superexchange between adjacent uranium atoms through intervening oxygen atoms.

Journal of Chemical Physics↗
USGS1962

Oxygen adsorption and the magnetic susceptibility of ice at low temperatures

WHEN dealing with the magnetic susceptibility of tumour tissue 1 , we reported the magnetic susceptibility of ice at various temperatures from 273° K. down to 77° K. Since this publication, the authors have made many susceptibility measurements of ice, using the same equipment, and have obtained similar results, that is, a relatively large increase in diamagnetism below 150° K. Normal diamagnetism is not dependent on temperature, and hence further experiments were made of the magnetic susceptibility of ice at low temperatures in an attempt to determine some extraneous cause of the increased diamagnetism.

Nature↗
USGS1962

Temperature dependence of decay time and intensity of alpha pulses in pure and thallium-activated cesium iodide

The intensity and decay time of Po 210 alpha particle scintillations produced in pure and thallium‐activated cesium iodide have been measured with a fast electronic system as a function of temperature down to 77°K. Three modes of decay due to alpha excitation have been observed for CsI(Tl), and two for CsI. Other than the 7‐ and 0.55‐μsec modes (at room temperature) reported in the literature for CsI(Tl), an additional temperature‐independent mode of about 1.3 μsec has been detected between 77 and 150°K. In CsI a fast temperature‐dependent mode of decay (≈100 nsec) was observed between 100–200°K in addition to the known principal mode.

Review of Scientific Instruments↗