Frank E. Senftle

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

Abstract 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.

SOME NATURAL VARIATIONS IN THE RELATIVE ABUNDANCE OF COPPER ISOTOPES

Abstract The relative isotopic abundance of copper has been measured in a number of minerals and a few plant materials. Suites of samples from Michigan and the Colorado Plateau have been examined in more detail to determine if local variations due to isotopic exchange or diffusion could be found. The relative isotopic abundance of copper in specimens from several other localities was also determined. The variations noted were small but in some cases were felt to be significant because they were larger than the experimental error (0·1 per cent in the ratio). A total spread of −1 to +8 parts per mil compared to the standard was found in the specimens tested.

Magnetic susceptibility of tektites and some other glasses

Abstract The magnetic susceptibility at several magnetic field strengths of about thirty tektites from various localities have been measured. The susceptibility ranges from 2 × 10−6 to about 7.9 × 10−6 e.m.u./g. Tektites from a given locality have similar susceptibilities. The intensity of magnetization of all the tektites measured is zero or very small. For comparison, the same measurements have been made on about thirty obsidians. The magnetic susceptibilities cover approximately the same range, but the intensity of magnetization of the impurity was found to be much higher. By heating the obsidians to 1450°C the intensity of magnetization was reduced to zero. From the above data, it is shown that the tektites must have been heated well above 1400°C, and that essentially all the iron is in solution. On the other hand, the evidence shows that obsidians have not been heated much above this temperature, and that there is a significant amount of undissolved iron in the glass, probably as magnetite. Further, if tektites are extraterrestrial, they probably entered the earths atmosphere as a glass.

Theoretical effect of diffusion on isotopic abundance ratios in rocks and associated fluids

Abstract Diffusion is considered as a possible process of isotope fractionation taking place throughout geologic time. Both diffusion in solids and diffusion in liquids are taken as possible mechanisms, the latter being more important. Arguments are presented to show that if significant fractionation takes place within a crystal by outward diffusion under solid-state conditions, enrichment will be evident only in elements of minor concentration. Similar conclusions are inferred for solid-state diffusion across a boundary or for diffusion in liquids. No isotopic enrichment can be expected in relatively large bodies of diffusion transported material. Although the necessary data to confirm these conclusions are scanty, it seems worth while to undertake further work in this direction.

The 57Fe Mossbauer parameters of pyrite and marcasite with different provenances

Eighteen pyrite and twelve marcasite samples which have different provenances have been investigated to determine the systematics of the influence of mineralogical and geological factors on the 57Fe Mossbauer spectra at 298 K. The following results have been obtained: there is no ambiguity in distinguishing single phase pyrite from single phase marcasite by means of 57Fe Mossbauer spectroscopy at 298 K. At 298 K the average electric quadrupole splitting, 〈ΔEQ〉, and average isomer shift, 〈δ〉, with respect to Fe metal, are 0.6110 ± 0.0030 mm s−1 and 0.313 ± 0.008 mm s−1, respectively, for the 18 pyrites; 〈ΔEQ〉 = 0.5030 ± 0.0070 mm s−1 and 〈δ〉 = 0.2770 ± 0.0020 mm s−1 for the 12 marcasites. At 77 K, ΔEQ is 0.624 mm s−1 for pyrite and 0.508 mm s−1 for marcasite. In distinguishing pyrites from marcasites, spectra obtained at 77 K are not warranted. The Mossbauer parameters of pyrite and marcasite exhibit appreciable variations, which bear no simple relationship to the geological environment in which they occur but appear to be selectively influenced by impurities, especially arsenic, in the pyrite lattice. Quantitative and qualitative determinations of pyrite/marcasite mechanical mixtures are straightforward at 298 K and 77 K but do require least-squares computer fittings and are limited to accuracies ranging from ±5 to ±15 per cent by uncertainties in the parameter values of the pure phases. The methodology and results of this investigation are directly applicable to coals for which the presence and relative amounts of pyrite and marcasite could be of considerable genetic significance.

A study of the natural α-recoil damage in zircon by infrared spectra

Abstract Natural α-recoil damage of 30 natural zircon specimens from Ceylon have been examined by studying the infrared absorption spectra from 1 to 15 μm. Two synthetic zircon specimens were also studied as undamaged reference specimens. The ir absorption coefficient at 6 μm (1666 cm−1) was found to be a function of radiation damage. The ir data can be explained by a dual damage mechanism. The initial damage process produces degradation of the v 3 vibrational mode in the ir spectra which can be explained by deformation of SiO4 tetrahedra, whereas the predominant effect of the advanced stage of radiation damage is the breakdown of the zircon lattice into SiO2 and ZrO2 which causes a skewing of the v 3 absorption band. These data substantiate the model of Pellas and clarify the dualistic nature of the radiation damage mechanism.

Absolute Method of Measuring Magnetic Susceptibility

An absolute method of standardization and measurement of the magnetic susceptibility of small samples is presented which can be applied to most techniques based on the Faraday method. The fact that the susceptibility is a function of the area under the curve of sample displacement versus distance of the magnet from the sample, offers a simple method of measuring the susceptibility without recourse to a standard sample. Typical results on a few substances are compared with reported values, and an error of less than 2% can be achieved.

Quartz Helix Magnetic Susceptibility Balance Using the Curie‐Cheneveau Principle

A quartz spring balance is described which can be used to measure the magnetic susceptibility of submilligram amounts of sample. The magnetic field is supplied by a moving permanent magnet, and the susceptibility is determined by the deflection of the spring observed in a measuring microscope. The apparatus is calibrated by a comparison standard (platinum) and results are shown for platinum, nickel aluminate, lead, manganese, and sucrose. A precision of better than 2% can be obtained on submilligram amounts of paramagnetic substances having a magnetic susceptibility of from 1 to 50×10−6 emu/g. On weakly paramagnetic or diamagnetic substances comparable precision can be obtained on less than 10 mg amounts of sample.

Chemical oxidation of anthracite with hydrogen peroxide via the Fenton reaction

Solutions of 30% H2O2 ranging from pH = 0 to pH = 11.5 have been used to oxidize anthracite at room temperature. The inorganic impurities, primarily pyrite, catalysed the oxidation and reduction of H2O2 (the Fenton reaction) to form the hydroxyl radical; the oxidation of the organic matter was minimal and was observed only in strong acidic solutions (pH < 1.5). After acid demineralization, samples of the same anthracite underwent a significant enhancement of oxidation in both acid and alkaline solutions (pH = 0.4–11.5). As all the iron had been removed from the surface and the reactions were completed in a much shorter time, the oxidation mechanism must have been of a different nature than that for the untreated anthracite. A qualitative model based on the catalytic decomposition of H2O2 by activated carbon sites in the coal surface is used to explain the oxidation of the demineralized anthracite.

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

Abstract 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.