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Bismuth germanate's role in the new revolution in gamma-ray spectroscopy

Description: Some of the considerations on how to effectively incorporate bismuth germanate into complex detection systems are covered, and some of these new systems now in operation or under construction are discussed. Significant achievements in gamma ray spectroscopy are reviewed as well as some recent results based on data taken with coincidence arrays of germanium detectors and Compton-suppression spectrometers. Then the first impact of bismuth germanate detectors on our understanding of the properties of nuclei that have high energy and very high angular momentum states are addressed. (LEW)
Date: January 1, 1983
Creator: Johnson, N.R.; Baktash, C. & Lee, I.Y.
Partner: UNT Libraries Government Documents Department

Spiral order in Ba{sub 2}CuGe{sub 2}O{sub 7}

Description: The quasi 2-D square-lattice antiferromagnet Ba{sub 2}CuGe{sub 2}O{sub 7} was studied by neutron scattering and bulk magnetic techniques. An incommensurate magnetic spiral structure with the propagation vector (1+{xi}, 1+{xi}, 0)({xi}=0.027) was observed below T{sub N}=3.26 K. Spin dynamics can be adequately described by conventional spin-wave theory with two exchange constants: nearest- neighbor in-plant antiferromagnetic coupling J{sub 1}{approx}0.48 meV and interplane ferromagnetic interaction J{sub 3}{approx}0.013 meV. This set of exchange parameters apparently fails to explain the spiral order. The non-centrosymmetric crystal structure suggests that the incommensurate phase may be the result of a Dzyaloshinskii-Moriya instability of the Neel ground state.
Date: August 1, 1996
Creator: Zheludev, A.; Shirane, G.; Sasago, Y.; Koide, N. & Uchinokura, K.
Partner: UNT Libraries Government Documents Department

Role of structure in ion movement of glasses. Final report, July 1, 1990--December 31, 1995

Description: The ion movement in inorganic glasses is key to their optimum use in various applications such as solid electrolytes, durable nuclear waste form, stable insulation in electronic devices etc. The primary objective of this project was to understand ion movement in relation to the physical structure of inorganic glasses. Five different glass forming systems were selected for systematically varying different aspects of the structure and determining their influence on ion dynamics: (1) binary Rb and K germanate glass series; (2) mixed (Rb, Ag) and (Rb, K) germanate glass series (3) high purity quartz amorphized by neutron irradiation (4) sodium triborate glasses with different melt conditions and (5) heavy metal fluoride glasses. A two-pronged research program was developed: on the one hand dc ionic conductivity and ac relaxation were measured for a variety of oxide and fluoride glasses as a function of composition, temperature and frequency to characterize long and short range ion transport phenomena. The ion movement was also observed in terms of nuclear spin relaxation rate at University of Dortmund, Germany. On the other hand, the structure was characterized by high resolution x-ray photoelectron spectroscopy (XPS) at Lehigh, infra-red (IR) and Raman spectroscopy at National Hellenic Research Foundation, Athens, Greece, and extended x-ray absorption fine structure (EXAFS) experiments at National Synchrotron Light Source, Brookhaven National Laboratory. The most significant results of the project are briefly summarized.
Date: May 1, 1996
Creator: Jain, H.
Partner: UNT Libraries Government Documents Department

Anomalous x-ray scattering studies of short-, intermediate- and extended-range order in glasses

Description: The authors present the formalism of anomalous x-ray scattering as applied to partial structure analysis of disordered materials, and give an example of how the technique has been applied, together with that of neutron diffraction, to investigate short-, intermediate- and extended-range order in vitreous germania and rubidium germanate.
Date: August 1998
Creator: Price, D. L.; Saboungi, M. L.; Armand, P. & Cox, D. E.
Partner: UNT Libraries Government Documents Department

Extended-range order in glasses

Description: A new type of order is identified in complex glasses, characterized by diffraction peaks at values of the wave vector below those typical of intermediate-range order. Combined neutron and anomalous x-ray diffraction studies of one glass exhibiting this behavior, vitreous rubidium germanate, indicate it to be associated with chemical ordering of the two cations with respect to each other.
Date: March 1, 1994
Creator: Ellison, A. J. G.; Price, D. L.; Saboungi, M. L.; Egami, T.; Hu, Rui-Zhong & Howells, W. S.
Partner: UNT Libraries Government Documents Department

Detector design for high-resolution MeV photon imaging of cargo containers using spectral information

Description: Monte Carlo simulations of a pixelated detector array of inorganic scintillators for high spatial resolution imaging of 1-9 MeV photons are presented. The results suggest that a detector array of 0.5 cm x 0.5 cm x 5 cm pixels of bismuth germanate may provide sufficient efficiency and spatial resolution to permit imaging of an object with uncertainties in dimension of several mm. The cross talk between pixels is found to be in the range of a few percent when pixels are shielded by {approx} 1mm of lead or tungsten. The contrast at the edge of an object is greatly improved by rejection of events depositing less than {approx} 1 MeV. Given the relatively short decay time of BGO, the simulations suggest that such a detector may prove adequate for the purpose of rapid scanning of highly-shielded cargos for possible presence of high atomic number (including clandestine fissionable) materials when used with low current high duty factor x-ray sources.
Date: February 1, 2010
Creator: Descalle, M A; Vetter, K; Hansen, A; Daniels, J & Prussin, S G
Partner: UNT Libraries Government Documents Department

Magnetic Excitation of CuGeO{sub 3} under Applied Pressure

Description: Magnetic excitations of the spin-Peierls compound CuGeO{sub 3} under applied pressure of 2 GPa have been studied. The dispersion along the chain direction up to zone boundary has been obtained. The spin-Peierls gap energy increases to 4.2 meV and the zone boundary energy decreases to 14.1 meV. The pressure dependence of dispersion relation can be interpreted by the increase of the next-nearest-neighbor intra-chain interaction under applied pressure causing the increase of both the spin-Peierls gap energy and transition temperature.
Date: July 31, 1997
Creator: Nishi, M.; Kakurai, K.; Fujii, Y.; Yethiraj, M.; Tennant, D. A.; Nagler, S. E. et al.
Partner: UNT Libraries Government Documents Department

High-temperature borate liquids: physical properties of glass-forming compositions

Description: Several experimental routes can be used to develop a better understanding of the polymeric constitution (polyanionic and/or polyhedral distribution) of borate, germanate, and silicate glasses. Spectral, chemical, physical-chemical, and mechanical property information can be determined directly for the glass compositions of interest. Generally, only physical-chemical information is readily accessible for the corresponding high temperature liquids. It will be shown that information on each state of matter has its own particular merits. Most of the evidence thus far published suggests an excellent agreement between polyhedral distributions in an oxide glass and its corresponding high temperature liquid state. There is no well known oxide glass forming system for which such a state of affairs does not exist. In spite of this, occasional efforts are put forth which ignore some of what is known for oxide liquids, glasses, and crystals. Such attempts therefore invariably imply, if only indirectly, that significant changes occur in the polyhedral distributions close to the glass transition temperature region. Specific examples to be discussed will include efforts that avoid well known coordination change equilibria such as BO/sub 3/ reversible BO/sub 4/ and GeO/sub 4/ reversible GeO/sub 6/.
Date: May 6, 1977
Creator: Riebling, E.F.
Partner: UNT Libraries Government Documents Department

Radiation dosimetry through spectral definition

Description: We have developed a fieldable instrumentation system for determining from measured flux spectra, both the neutron and gamma ray dose rate distributions associated with radioactive sources. This system includes the sensors, the computer-based data acquisition and analysis hardware, and the requisite software for unfolding the sensor response functions to obtain the flux spectra, and for folding the resultant flux spectra with appropriate flux spectrum-to-dose conversion factors. We use bismuth germanate scintillators that have experimentally measured and analytically interpolated response functions to determine the gamma ray flux spectra, and a suite of neutron sensors, based on proton recoil and /sup 3/He capture, to determine the neutron flux spectra. In addition, gamma ray peak identification is done using HPGe sensors. We describe the equipment and procedures and present some recent results. 10 refs., 15 figs.
Date: January 1, 1985
Creator: Dowdy, E.J.; Moss, C.E.; Robba, A.A.; Evans, A.E.; Lucas, M.C.; Shunk, E.R. et al.
Partner: UNT Libraries Government Documents Department

Efficiency of a bismuth-germanate scintillator: comparison of Monte Carlo calculations with measurements

Description: Monte Carlo calculations of a bismuth-germanate scintillator's efficiency agree closely with experimental measurements. For this comparison, we studied the absolute gamma-ray photopeak efficiency of a scintillator (7.62 cm long by 7.62 cm in diameter) at several gamma-ray energies from 166 to 2615 keV at distances from 0.5 to 152.4 cm. Computer calculations were done in a two-dimensional cylindrical geometry with the Monte Carlo coupled photon-electron code CYLTRAN. For the experiment we measured 11 sources with simple spectra and precisely known strengths. The average deviation between the calculations and the measurements is 3%. Our calculated results also closely agree with recently published calculated results.
Date: January 1, 1983
Creator: Hsu, H.H.; Dowdy, E.J.; Estes, G.P.; Lucas, M.C.; Mack, J.M.; Moss, C.E. et al.
Partner: UNT Libraries Government Documents Department

Bismuth germanate scintillators: applications in nuclear safeguards and health physics

Description: Bismuth germanate (BGO) scintillators are preferable to NaI(Tl) scintillators or germanium detectors for some applications in nuclear safeguards and health physics. The first system, which consists of eight scintillators and a computer-based data acquisition system, is very efficient. The second, which consists of one scintillator and a small analyzer, is less efficient but portable. A computer code that uses measured response functions and photopeak efficiencies, unfolds the BGO distributions measured with these systems to determine gamma-ray flux spectra and dose rates. One application of these systems is the accurate determination of flux spectra and dose rates from containers of uranium or plutonium. A second application determined these quantities from a replica of Little Boy, the device exploded over Hiroshima. 7 refs., 6 figs.
Date: May 1, 1985
Creator: Moss, C.E.; Dowdy, E.J. & Lucas, M.C.
Partner: UNT Libraries Government Documents Department

Improvements in the energy resolution and high-count-rate performance of bismuth germanate

Description: Several methods for improving the energy resolution of bismuth germanate (BGO) have been investigated. It is shown that some of these methods resulted in a substantial improvement in the energy resolution. In addition, a method to improve the performance of BGO at high counting rates has been systematically studied. The results of this study are presented and discussed.
Date: January 1, 1985
Creator: Koehler, P.E.; Wender, S.A. & Kapustinsky, J.S.
Partner: UNT Libraries Government Documents Department

Performance of BGO in a high radiation environment

Description: Bismuth Germanate (Bi/sub 4/Ge/sub 3/O/sub 12/), an inert, high Z, and non-hygroscopic material, with a short radiation length L/sub RAD/ = 1.1 cm, has been proposed as the scintillator in a 4..pi.. electromagnetic calorimeter at LEP. Recently long BGO crystals have become available and studies of the effect of radiation have been made by several groups. We report here on the decrease of the light output of long BGO crystals due to irradiation by /sup 60/Co ..gamma..-rays and 25 MeV electrons with doses from 50 to 5000 rad and on the performance of a 4 x 4 matrix of BGO crystals located at small angles (5 to 9 mrad, a high radiation environment) at the e/sup +/e/sup -/ storage ring PEP at SLAC. All crystals used are 2 x 2 x 23 or 2 x 2 x 24 cm/sup 3/, have all six faces polished, and are wrapped in white teflon tape. 9 references, 11 figures.
Date: May 1, 1984
Creator: Bobbink, G.J.; Engler, A.; Kraemer, R.W.; Nash, J.; Sutton, R.B.; Gearhart, R.A. et al.
Partner: UNT Libraries Government Documents Department

Compensation for crystal penetration in high resolution positron tomography

Description: We have characterized the effects of crystal penetration by annihilation photons in circular ring positron tomographs. They are most serious in high resolution instruments having small detectors. When annihilation photons are not normally incident and penetrate some distance into the scintillator before interacting, the measurement of their transverse position becomes uncertain. This penetration of photons into the detector material before interaction is a statistical process which leads to significant displacement and anisotropy of the point spread function. The subject of this work is mathematical correction of emission datasets by performing a two-dimensional spatially variant deconvolution of the emission data in sinogram format. Examples for the Donner 600-Crystal Positron Tomograph are presented, and the amplification of statistical errors resulting from the correction procedure is also discussed. 7 refs., 9 figs., 2 tabs.
Date: November 1, 1988
Creator: Huesman, R.H.; Salmeron, E.M. & Baker, J.R.
Partner: UNT Libraries Government Documents Department

EVALUATION OF THE IMPACT OF THE DEFENSE WASTE PROCESSING FACILITY (DWPF) LABORATORY GERMANIUM OXIDE USE ON RECYCLE TRANSFERS TO THE H-TANK FARM

Description: When processing High Level Waste (HLW) glass, the Defense Waste Processing Facility (DWPF) cannot wait until the melt or waste glass has been made to assess its acceptability, since by then no further changes to the glass composition and acceptability are possible. Therefore, the acceptability decision is made on the upstream feed stream, rather than on the downstream melt or glass product. This strategy is known as 'feed forward statistical process control.' The DWPF depends on chemical analysis of the feed streams from the Sludge Receipt and Adjustment Tank (SRAT) and the Slurry Mix Evaporator (SME) where the frit plus adjusted sludge from the SRAT are mixed. The SME is the last vessel in which any chemical adjustments or frit additions can be made. Once the analyses of the SME product are deemed acceptable, the SME product is transferred to the Melter Feed Tank (MFT) and onto the melter. The SRAT and SME analyses have been analyzed by the DWPF laboratory using a 'Cold Chemical' method but this dissolution did not adequately dissolve all the elemental components. A new dissolution method which fuses the SRAT or SME product with cesium nitrate (CsNO{sub 3}), germanium (IV) oxide (GeO{sub 2}) and cesium carbonate (Cs{sub 2}CO{sub 3}) into a cesium germanate glass at 1050 C in platinum crucibles has been developed. Once the germanium glass is formed in that fusion, it is readily dissolved by concentrated nitric acid (about 1M) to solubilize all the elements in the SRAT and/or SME product for elemental analysis. When the chemical analyses are completed the acidic cesium-germanate solution is transferred from the DWPF analytic laboratory to the Recycle Collection Tank (RCT) where the pH is increased to {approx}12 M to be released back to the tank farm and the 2H evaporator. Therefore, about 2.5 kg/yr of GeO{sub ...
Date: August 15, 2011
Creator: Jantzen, C. & Laurinat, J.
Partner: UNT Libraries Government Documents Department

Connection between NMR and electrical conductivity in glassy chalcogenide fast ionic conductors

Description: The work documented in this thesis follows the traditional order. In this chapter a general discussion of ionic conduction and of glassy materials are followed by a brief outline of the experimental techniques for the investigation of fast ionic conduction in glassy materials, including NMR and impedance spectroscopy techniques. A summary of the previous and present studies is presented in the last section of this introductory chapter. The details of the background theory and models are found in the Chapter II, followed by the description of the experimental details in Chapter III. Chapter IV of the thesis describes the experimental results and the analysis of the experimental observations followed by the conclusions in chapter V.
Date: November 1, 1995
Creator: Kim, K.H.
Partner: UNT Libraries Government Documents Department

Monte Carlo calculations of the optical coupling between bismuth germanate crystals and photomultiplier tubes

Description: The high density and atomic number of bismuth germanate (Bi/sub 4/Ge/sub 3/O/sub 12/ or BGO) make it a very useful detector for positron emission tomography. Modern tomograph designs use large numbers of small, closely-packed crystals for high spatial resolution and high sensitivity. However, the low light output, the high refractive index (n=2.15), and the need for accurate timing make it important to optimize the transfer of light to the photomultiplier tube (PMT). We describe the results of a Monte Carlo computer program developed to study the effect of crystal shape, reflector type, and the refractive index of the PMT window on coupling efficiency. The program simulates total internal, external, and Fresnel reflection as well as internal absorption and scattering by bubbles.
Date: October 1, 1981
Creator: Derenzo, S.E. & Riles, J.K.
Partner: UNT Libraries Government Documents Department

Performance of a PET detector module utilizing an array of silicon photodiodes to identify the crystal of interaction

Description: We present initial performance results for a new multi-layer PET detector module consisting of an array of 3 mm square by 30 mm deep BGO crystals coupled on one end to a single photomultiplier tube and on the opposite end to an array of 3 mm square silicon photodiodes. The photomultiplier tube provides an accurate timing pulse and energy discrimination for the all the crystals in the module, while the silicon photodiodes identify the crystal of interaction. When a single BGO crystal at +25{degree}C is excited with 511 key photons, we measure a photodiode signal centered at 700 electrons (e{sup {minus}}) with noise of 375 e{sup {minus}} fwhm. When a four crystal / photodiode module is excited with a collimated line source of 511 key photons, the crystal of interaction is correctly identified 82% of the time. The misidentification rate can be greatly reduced and an 8{times}8 crystal / photodiode module constructed by using thicker depletion layer photodiodes or cooling to 0{degrees}C.
Date: November 1, 1992
Creator: Moses, W. W.; Derenzo, S. E.; Nutt, R.; Digby, W. M.; Williams, C. W. & Andreaco, M.
Partner: UNT Libraries Government Documents Department

A positron tomograph with 600 BGO (bismuth germanate) crystals and 2. 6 mm resolution

Description: We describe the imaging performance of the Donner 600-Crystal Positron Tomograph, a single 600 cm diam ring of 3 mm wide bismuth germanate (BGO) crystals coupled individually to 14 mm phototubes. With a pulse height threshold of 200 keV and a slice thickness of 5 mm, the sensitivity is 7024 eventssec per ..mu..Ciml in a 20 cm cyliner of water. The measured rates for 18 ..mu..Ciml are 95,000 truessec plus 20,000 randomsec. A 0.3 mm diam /sup 22/Na line source near the center of the tomograph has a circular point spread function (PSF) with a full-width at half-maximum (fwhm) of 2.6 mm. At 5 cm from the center the PSF is elliptical with a fwhm of 2.7 mm tangential )times) 3.2 mm radial. At 10 cm the PSF has a fwhm of 2.8 mm tangential )times) 4.8 mm radial. Attenuation data are accumulated with a 20 mCi /sup 68/Ge orbiting transmission source and 100 million coincident events are collected in 200 sec. 20 refs., 9 figs., 5 tabs
Date: October 1, 1987
Creator: Derenzo, S.E.; Huesman, R.H.; Cahoon, J.L.; Geyer, A.B.; Moses, W.W.; Uber, D.C. et al.
Partner: UNT Libraries Government Documents Department

Fieldable computer system for determining gamma-ray pulse-height distributions, flux spectra, and dose rates from Little Boy

Description: Our system consists of a LeCroy 3500 data acquisition system with a built-in CAMAC crate and eight bismuth-germanate detectors 7.62 cm in diameter and 7.62 cm long. Gamma-ray pulse-height distributions are acquired simultaneously for up to eight positions. The system was very carefully calibrated and characterized from 0.1 to 8.3 MeV using gamma-ray spectra from a variety of radioactive sources. By fitting the pulse-height distributions from the sources with a function containing 17 parameters, we determined theoretical repsonse functions. We use these response functions to unfold the distributions to obtain flux spectra. A flux-to-dose-rate conversion curve based on the work of Dimbylow and Francis is then used to obtain dose rates. Direct use of measured spectra and flux-to-dose-rate curves to obtain dose rates avoids the errors that can arise from spectrum dependence in simple gamma-ray dosimeter instruments. We present some gamma-ray doses for the Little Boy assembly operated at low power. These results can be used to determine the exposures of the Hiroshima survivors and thus aid in the establishment of radation exposure limits for the nuclear industry.
Date: January 1, 1984
Creator: Moss, C.E.; Lucas, M.C.; Tisinger, E.W. & Hamm, M.E.
Partner: UNT Libraries Government Documents Department

Performance of a PET detector module utilizing an array of silicon photodiodes to identify the crystal of interaction

Description: We present initial performance results for a new multi-layer PET detector module consisting of an array of 3 mm square by 30 mm deep BGO crystals coupled on one end to a single photomultiplier tube and on the opposite end to an array of 3 mm square silicon photodiodes. The photomultiplier tube provides an accurate timing pulse and energy discrimination for the all the crystals in the module, while the silicon photodiodes identify the crystal of interaction. When a single BGO crystal at +25[degree]C is excited with 511 key photons, we measure a photodiode signal centered at 700 electrons (e[sup [minus]]) with noise of 375 e[sup [minus]] fwhm. When a four crystal / photodiode module is excited with a collimated line source of 511 key photons, the crystal of interaction is correctly identified 82% of the time. The misidentification rate can be greatly reduced and an 8[times]8 crystal / photodiode module constructed by using thicker depletion layer photodiodes or cooling to 0[degrees]C.
Date: November 1, 1992
Creator: Moses, W.W.; Derenzo, S.E. (Lawrence Berkeley Lab., CA (United States)); Nutt, R.; Digby, W.M.; Williams, C.W. & Andreaco, M. (CTI, Inc., Knoxville, TN (United States))
Partner: UNT Libraries Government Documents Department

High-spin research with HERA (High Energy-Resolution Array)

Description: The topic of this report is high spin research with the High Energy Resolution Array (HERA) at Lawrence Berkeley Laboratory. This is a 21 Ge detector system, the first with bismuth germanate (BGO) Compton suppression. The array is described briefly and some of the results obtained during the past year using this detector facility are discussed. Two types of studies are described: observation of superdeformation in the light Nd isotopes, and rotational damping at high spin and excitation energy in the continuum gamma ray spectrum.
Date: June 1, 1987
Creator: Diamond, R.M.
Partner: UNT Libraries Government Documents Department

HERA, the Berkeley Array, and early results

Description: As in all fields of spectroscopy, high resolution is of geat importance in nuclear ..gamma..-ray studies. Also important are a good response function and good efficiency, so as to be able to obtain high-order coincidences when observing de-excitation cascades. The design of the Berkeley High Energy-Resolution Array is discussed and some first results are given. 5 refs., 6 figs.
Date: September 1, 1985
Creator: Diamond, R.M.
Partner: UNT Libraries Government Documents Department