Search

The reduction of a 1‐mesityl‐2,5‐bis‐trimethylsilylchlorogermole 8 with KC8 is reported. While the reaction with one equivalent of KC8 gave the dimer with a Ge−Ge bond 10, excess of KC8 (four equivalents) resulted in the formation of the potassium salt of the germole dianion, 11 with reductive cleavage of the Ge−C bond. Careful reduction with two equivalents of KC8 in THF provided the potassium salt of the planar germolide 5. Its solid‐state structure revealed contact ion pairs with the potassium ion η5‐coordinated to the germacyclopentadienide ring. The molecular structure of the anion indicates a high degree of cyclic electron delocalization, in agreement with results from DFT calculations. Separation of the ion pair by complexation of the potassium ions with 18‐crown‐6 triggers the isomerization to germolide 6, which is characterized by a pyramidal coordination sphere of the germanium atom and a localized diene structure. The isomers 5 and 6 represent a rare example for a structurally manifested switch between a non‐aromatic and an aromatic state induced by an external stimulus, in this case the complexation of the counter cation. [ABSTRACT FROM AUTHOR]

Germanium (Ge) is a metal used in emerging energy technologies, communications, and defense, and has been deemed critical by the United States due to its essential applications and scarce supply. Germanium is recovered as a byproduct of zinc (Zn) sulfides, and mining and processing of these materials lead to waste that could act both as a source of extractable Ge and a source for exposure to humans and ecosystems. Yet the distribution, speciation, and mineral hosts of Ge in mining-impacted areas are poorly understood. The Tar Creek Superfund Site, a former Zn mining area and Ge producer, is a natural laboratory to understand the environmental behavior and economic implications of Ge in mine wastes. We studied the distribution and behavior of Ge in solid wastes at the Tar Creek Superfund Site using bulk and microanalytical techniques. In wastes at this site we find that Ge has been redistributed from its original host, sphalerite (ZnS), to the fine-grained weathering product hemimorphite (Zn 4 Si 2 O 7 (OH) 2 ·H 2 O), which impacts germanium's mobility, bioaccessibility, and potential for recovery. We provide chemical and mineralogical evidence of this redistribution, along with an evaluation of the oxidation state and molecular-scale substitution of Ge into sphalerite, hemimorphite, and quartz. Geochemical modeling shows that hemimorphite is more stable than sphalerite in waste piles and provides a stable secondary repository for Ge. However, hemimorphite is fine-grained, and if ingested or inhaled is readily soluble, with the potential to release Ge. Lastly, we discuss other sites internationally where similar behavior may be important. This study shows that weathering can have a significant impact on the distribution, speciation, and mineral hosts of Ge in mine wastes; directly influence mobilization from waste piles and subsequent availability to humans and ecosystems; and dictate metallurgical strategies to target Ge for recovery. [Display omitted] • Weathering in mine wastes has altered mineral hosts and speciation of germanium (Ge). • Ge exists in multiple oxidation states in sphalerite (ZnS), the original host mineral. • Hemimorphite, a Zn-silicate weathering product, hosts majority of Ge. • Presence in Zn-silicate has implications for mobility, bioavailability, and potential for recovery. [ABSTRACT FROM AUTHOR]

Both the peak and total detection efficiencies are generally needed in order to calculate sample activity from a gamma spectroscopic measurement, except in the case of isotope specific calibration. This is particularly true when the sample is in close proximity to the detector and corrections for cascade summing effects are required to avoid significant inaccuracy in the result. These corrections use the total detection efficiency to correct for summing-in and summing-out events, and the extent of the correction depends on both the geometry and the gamma cascade for the isotope in question. Experimentally determining the total efficiency is a labor intensive endeavor requiring multiple measurements with a set of single-gamma-emitting standards. Modeling the total efficiency vs. energy may be less time consuming, but is also likely to produce less confidence in the final result. Pacific Northwest National Laboratory's Radiation Detection and Nuclear Sciences group has constructed a low background 14-crystal HPGe array for sample measurement; in all measurements, samples will be in close proximity to the germanium crystals. This close geometry and the sheer number of efficiency calibrations required for the system have led us to investigate methods to simplify the efficiency calibration procedure. One method we are developing uses the γ-γ coincidence plane to isolate Compton scattering event populations, allowing experimental determination of total detection efficiency values from the measurement of a single mixed isotope standard. A description of the analysis and experimental results of this method are presented. [ABSTRACT FROM AUTHOR]

Abstract: We present measurement results of airborne fission products in Chapel Hill, NC, USA, from 62 d following the March 11, 2011, accident at the Fukushima Dai-ichi nuclear power plant. Airborne particle samples were collected daily in air filters and radio-assayed with two high-purity germanium (HPGe) detectors. The fission products 131I and 137Cs were measured with maximum activity concentrations of 4.2 ± 0.6 mBq/m3 and 0.42 ± 0.07 mBq/m3 respectively. Additional activity from 131,132I, 134,136,137Cs and 132Te were measured in the same air filters using a low-background HPGe detector at the Kimballton Underground Research Facility (KURF). [Copyright &y& Elsevier]

Abstract: Intensity Modulated Radiation Therapy (IMRT) is a technique widely used in the treatment of patients with prostate cancer, the most commonly occurring male cancer in the United States and Western Europe. The technique has many attractive features, promising improved radiotherapy over that provided by conventional techniques, including enabling the tumour to be treated with a uniform high dose, capability for shaping the radiation beams to match the shape of the tumour and potentially improving patient outcome. However, there are a number of concerns involving high photon energy IMRT (>10MV), including greater radiation leakage and the possibility of photo-neutron production. The aim of the present study is to investigate the potential of Ge-doped optical fibre thermoluminescent (TL) dosimetry in determining typical out-of-field doses for high energy IMRT. Commercial Ge-doped optical fibres have been employed as the TL dosimeters, offering features such as high sensitivity, cost-effectiveness and small size. Extensive measurements have been made, examining reproducibility, sensitivity, energy response and linearity with dose. Screening for sensitivity to dose of the individual fibres and subsequent selection has led to an overall coefficient of variation (CV) of better than 4 %. Use has been made of an anthropomorphic phantom (RANDO) for photon irradiation measurements delivered over the range of nominal energies 6–15MV as typically used in IMRT treatment of prostate cancer. Comparison has been made with TLD-100 measurements, the latter being corrected at 15MV for their response to thermal neutrons. The study has demonstrated the Ge-doped optical fibre TL dosimeters to offer good potential for use in IMRT radiotherapy when using 6MV photons, also indicating a need to correct their response to neutrons when conducting 15MV irradiations. [Copyright &y& Elsevier]

We have used the EBIT-I electron beam ion trap at the Lawrence Livermore National Laboratory and a duplicate Orion High Resolution X-ray Spectrometer (OHREX) to measure the relative efficiency of a spherically bent quartz (1011) crystal (2d = 6.687 Å) and a spherically bent germanium (111) crystal (2d = 6.532 Å). L-shell X-ray photons from highly charged molybdenum ions generated in EBIT-I were simultaneously focussed and Bragg reflected by each crystal, both housed in a single spectrometer, onto a single CCD X-ray detector. The flux from each crystal was then directly compared. Our results show that the germanium crystal has a reflection efficiency significantly better than the quartz crystal, however, the energy resolution is significantly worse. Moreover, we find that the spatial focussing properties of the germanium crystal are worse than those of the quartz crystal. Details of the experiment are presented, and we discuss the advantages of using either crystal on a streak-camera equipped OHREX spectrometer. [ABSTRACT FROM AUTHOR]

Until recently, high-purity germanium (HPGe) was used only by small, select teams of specialists in field applications for nuclear materials detection in national defense, treaty verification, and interdiction applications. Recent advances in technology of hardware and software has enabled widespread deployment of HPGe-based tools which dramatically expand the envelope of information available to personnel previously outside the ‘circle’ of nuclear measurement experts. This paper describes the technological advances as well as the practical implications of these new tools for counter-terrorism, non-proliferation, homeland security, and post-accident triage applications. [ABSTRACT FROM AUTHOR]

The Duckmantian-aged Amos coal bed is a thin (<51 cm) coal bed that occurs in lobate southwest-trending pods separated by thin sandstones in the Western Kentucky coalfield. The coal bed, which is comprised of up to two benches and a rider coal, is low in ash yield (<6%) and sulfur content (<1%). The coal tends to be thin (<40 cm), but it was heavily mined in the 1980s because it could be combusted as mined.Geochemical analysis of the Amos coal bed shows higher concentrations of B and Ge than other Western Kentucky coal beds. High total B concentrations as well as high B/Be, both considered to be indicators of marine environments, increase toward the top of the coal bed. Most of the B values for the Amos samples range from 66 to 103 ppm (whole coal basis) indicating deposition in a brackish environment. High Ge concentrations in coals have been considered to be a function of seam thickness and proximity to the top and bottom of the coal bed. Thin coals, such as the Amos, are dominated by the coal bed margins and, therefore, have a tendency to have relatively high Ge concentrations. In the case of the Amos coal bed, the lower bench has a higher Ge content, suggesting that the substrate was a more important source of Ge than the roof rock. [Copyright &y& Elsevier]

The article presents the author's views regarding the state of the semiconductor industry in the U.S. The author states that the industry has transformed several areas, including biotechnology, medicine, education and communications. He mentions the invention of the germanium junction transistor amplifier in 1948. He adds that innovative technology is hampered by financial problems. He concludes that the industry will continue to expand but doubts that it is already a mature industry.

Unlabelled: We have developed a methodology for calibrating (68)Ge radioactivity content in a commercially available calibration source for activity calibrators in a way that is traceable to the national standard. Additionally, the source was cross-calibrated for equivalent (18)F content by direct comparison with the national standard for (18)F in the same geometry., Methods: Sources containing standardized (68)GeCl(4) or (18)F-FDG solutions were prepared at the National Institute of Standards and Technology (NIST) with mock syringe blanks used in the construction of a commercially available epoxy-based (68)Ge calibration source. These sources and several NIST-constructed epoxy-based (68)Ge mock syringes were then used as artifact standards to determine calibration factors for NIST-maintained activity calibrators and secondary standard ionization chambers to enable calibration of the actual commercial sources. A direct comparison between the solution-based (68)Ge sources and the (18)F-FDG sources allowed for an empiric determination of the relative response for these radionuclides in several commercial activity calibrators. Potential measurement effects due to differences between the solution composition and the epoxy and theoretic (68)Ge-to-(18)F response ratios were studied by Monte Carlo simulation., Results: The calibration factors developed in this study enabled NIST to calibrate epoxy-based mock syringe sources with a relative combined standard uncertainty of 0.52%. The direct comparisons of the (68)Ge and (18)F standards in the various ionization chambers allowed the activity to be expressed in terms of equivalent (18)F activity with a relative combined standard uncertainty of about 0.9%., Conclusion: The ability for NIST to calibrate these epoxy-based mock syringes enabled, for the first time to our knowledge, the direct traceability to the national (68)Ge standard to be established for this type of source. Through a direct comparison with the NIST (18)F standard, the determination of the relative response ratios in activity calibrators enabled the equivalent (18)F activity to be determined in a way that was also traceable to the national (18)F activity standard.