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Origin of the 871-keV gamma ray and the ``oxide'' attribute

Description: This work concludes the investigation of the oxide attribute of current interest for the characterization of stored plutonium. Originally it was believed that the presence of oxide could be ascertained by measurement of the 871-keV line in a high-resolution gamma-ray spectrum. However, recent work has suggested that the 871-keV gamma ray in plutonium oxide arises from the reaction {sup 14}N({alpha},p){sup 17}O rather than the inelastic scattering reaction {sup 17}O({alpha},{alpha}{prime}){sup 17}O*. This conclusion, though initially surprising, was obtained during efforts to determine the relative importance of americium and plutonium alpha-particle decay for the production of the 871-keV gamma ray. Several questions were raised by previous experiments: What role, if any does {sup 17}O have in the generation of the 871-keV gamma ray? How does sufficient nitrogen come to be present in plutonium oxide? Under what conditions is the 871-keV gamma ray measurable in plutonium oxide? This paper describes the answers to these questions.
Date: March 22, 2000
Creator: Peurrung, AJ; Arthur, RJ; Geelhood, BD; Scheele, RD; Elovich, RJ & Pratt, SL
Partner: UNT Libraries Government Documents Department

Formation of a metastable crystalline phase during ion irradiation of spinel

Description: We have examined the radiation resistance of magnesio-aluminate spinel by irradiating single crystals of MgAl{sub 2}O{sub 4} with 400 keV Xe++ions at 100 K. At low irradiation doses, the material transformed into a metastable crystalline phase with half the lattice spacing of the original crystal. Electron diffraction analysis revealed that this structural change can be explained in terms of the redistribution of cations among octahedral, tetrahedral, and three- fold coordinated interstitial sites of the close-packed anion lattice. Corresponding to this transformation, the hardness and elastic modulus increased with dose to values about 10% greater than those of unirradiated spinel. We believe that the formation of this metastable phase plays an important role in determining the radiation resistance of spinel.
Date: December 31, 1995
Creator: Devanathan, R.; Yu, Ning; Sickafus, K. & Nastasi, M.
Partner: UNT Libraries Government Documents Department

Damage growth in MgAl{sub 2}O{sub 4} crystals by Xe ion irradiations

Description: We have studied damage kinetics in single crystal MgAl{sub 2}O{sub 4} (spinel) with (l00) orientation under 370 keV Xe ion irradiations at temperatures of {minus}100 and 400C. In-situ Rutherford Backscattering Spectrometry (RBS) and ion channeling have been used to monitor the damage accumulation in spinel following sequential Xe ion irradiations. A significant temperature effect on the irradiation damage has been found. Channeling data show that at {minus}100C, the irradiated spinel layer reaches the same level as in a random spectrum at a dose of 8 {times} 10{sup 15} Xe/cm{sup 2} (20 DPA for peak damage), while at 400C, the near surface region (50 nm) remains single-crystalline up to 2 {times} l0{sup l6} Xe/cm{sup 2}.
Date: December 31, 1993
Creator: Yu, Ning; Nastasi, M.; Hollander, M. G.; Evans, C. R.; Maggiore, C. J.; Sickafus, K. E. et al.
Partner: UNT Libraries Government Documents Department

Synthesis and properties of GaAs nanocrystals in SiO{sub 2} formed by ion implantation

Description: GaAs nanocrystals have been formed by sequential ion implantation. Sequence of Ga and As ion implantation (ie, Ga + As or As + Ga) is found to affect the size distributions of GaAs nanocrystals significantly. Nanocrystal sizes are much bigger in the samples with Ga implanted first than those with As implanted first. This phenomenon is explained by the different diffusion behaviors of Ga and As species. Different precipitate regions have been observed in the samples implanted with Ga first and then As. Optical absorption measurements show that Ga particles have already formed in the as-implanted stage.
Date: December 1, 1995
Creator: Zhu, J.G.; White, C.W.; Budai, J.D.; Withrow, S.P.; Wallis, D.J. & Henderson, D.O.
Partner: UNT Libraries Government Documents Department

Fragmentation of biomolecules using slow highly charged ions

Description: We present first results of biomolecular fragmentation studies with slow highly charged ions (HCI). A layer of the tripeptide RVA was deposited on gold targets and irradiated with slow (few 100 keV) ions, e.g. Xe{sup 50+} and Xe{sup 15+}, extracted from the LLNL EBIT (electron beam ion trap). The secondary ions released upon ion impact were mass analyzed via Time-Of-Flight Secondary-Ion-Mass-Spectrometry (TOF-SIMS). The results show a strong dependence of the positive and negative ion yields on the charge state of the incident ion. We also found that incident ions with high charge states cause the ejection of fragments with a wide mass range as well as the intact molecule (345 amu). The underlying mechanisms are not yet understood but electron depletion of the target due to the high incident charge is likely to cause a variety of fragmentation processes. 6 refs., 2 figs.
Date: November 1, 1996
Creator: Ruehlicke, C.; Schneider, D.; Balhorn, R. & DuBois, R.
Partner: UNT Libraries Government Documents Department

BATSE observations of BL Lac objects

Description: The Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory has been shown to be sensitive to non-transient hard X-ray sources in our galaxy, down to flux levels of 100 mCrab for daily measurements, 3 mCrab for integrations over several years. We use the continuous BATSE database and the Earth Occultation technique to extract average flux values between 20 and 2OO keV from complete and radio- and X-ray- selected BL Lac samples over a 2 year period.
Date: June 1, 1998
Creator: Connaughton, V.; Laurent-Muehleisen, S.; McCollough, M.A & Robinson, C.F.
Partner: UNT Libraries Government Documents Department

Plastic flow induced by single ion impacts on gold

Description: In situ TEM was used to follow RT irradiation of thinned bulk and 62nm thick gold films with Xe ions at 50-400 keV. Energy spikes from single ion impacts give rise to surface craters and holes which exist until annihilated by subsequent ion impacts. Video recording provided details with a time resolution of 33 ms. Craters were produced on the irradiated surface at all ion energies and on the opposite surface when the ions had enough energy to traverse the specimen. Crater sizes were as large as 12nm for the higher energy irradiations. On average, about 6% of impinging ions result in craters. A single 200 keV Xe ion may produce a hole in thin gold foils. Hole formation involves the movement by plastic flow of massive amounts of material, on the order of tens of thousand Au atoms per ion impact. Individual ion impacts also result in a filling of both holes and craters as well as a thickening of the gold foil. Change in morphology during irradiation is attributed to a localized, thermal-spike induced melting, coupled with plastic flow under the influence of surface forces.
Date: December 1996
Creator: Birtcher, R. C. & Donnelly, S. E.
Partner: UNT Libraries Government Documents Department

Precision Measurements of {sup 56}Fe Cross Sections for the 847-keV Gamma Transition

Description: At the First Research Coordination Meeting of the IAEA/NDS CRP on Measurement, Calculation and Evaluation of Photon Production Data an experiment to measure with high precision the cross sections of the production of the 847-keV gamma ray due to inelastic neutron scattering with iron was proposed and discussed. The main justification for the proposed improved precision was the need for improved calculations of radiation transport through thick iron components of nuclear reactors. Present evaluated data for the subject reaction in the ENDF/B-VI files have evaluated uncertainties {approx} 10%; consequently, the results of computation of deep penetration of radiation in iron can have quite large uncertainties -- larger than 100%, for example, for an attenuation of {approximately} three orders of magnitude -- which can be a serious problem when one considers the magnitude of the radiation field inside a pressure vessel. This report describes progress toward obtaining more precise data. 13 refs., 1 fig.
Date: December 31, 1997
Creator: Dickens, J.K.
Partner: UNT Libraries Government Documents Department

Sputtering of Au induced by single Xe ion impacts

Description: Sputtering of Au thin films has been determined for Xe ions with energies between 50 and 600 keV. In-situ transmission electron microscopy was used to observe sputtered Au during deposition on a carbon foil near the specimen. Total reflection and transmission sputtering yields for a 62 nm thick Au thin film were determined by ex-situ measurement of the total amount of Au on the carbon foils. In situ observations show that individual Xe ions eject Au nanoparticles as large as 7 nm in diameter with an average diameter of approximately 3 nm. Particle emission correlates with crater formation due to single ion impacts. Nanoparticle emission contributes significantly to the total sputtering yield for Xe ions in this energy range in either reflection or transmission geometry.
Date: December 6, 1999
Creator: Birtcher, R. C. & Donnelly, S. E.
Partner: UNT Libraries Government Documents Department

Neutron Capture and Neutron Total Cross Sections Measurements for {sup 27}Al at the Oak Ridge Electron Linear Accelerator

Description: We have used the Oak Ridge Electron Linear Accelerator (ORELA) to measure neutron total and capture cross sections of {sup 27}Al in the energy range from 100 eV to {approximately}400 keV. We report the resonance parameters as well as the Maxwellian average capture cross sections.
Date: August 30, 1999
Creator: Guber, K.H.; Harvey, J.A.; Hill, N.W.; Koehler, P.E.; Leal, L.C.; Sayer, R.O. et al.
Partner: UNT Libraries Government Documents Department

A comparative study of radiation damage in Al{sub 2}O{sub 3}, FeTiO{sub 3}, and MgTiO{sub 3}

Description: Oriented single crystals of synthetic alpha-alumina ({alpha}-Al{sub 2}O{sub 3}), geikielite (MgTiO{sub 3}) natural ilmenite (FeTiO{sub 3}) were irradiated with 200 keV argon ions under cryogenic conditions (100 K) to assess their damage response. Using Rutherford backscattering spectrometry combined with ion channeling techniques, it was found that ilmenite amorphized readily at doses below 5{times}10{sup 14}, alumina amorphized at a dose of 1-2{times}{sup 15}, and geikielite was amorphized at {approximately}2{times}10{sup 15} Ar cm{sup {minus}2}. The radiation damage response of the ilmenite crystal may be complicated by the presence of hematite exsolution lamellae and the experimentally induced oxidation of iron. The relative radiation-resistance of geikielite holds promise for similar behavior in other Mg-Ti oxides.
Date: December 31, 1995
Creator: Mitchell, J.N.; Yu, Ning; Sickafus, K.E.; Nastasi, M.; Taylor, T.N.; McClellan, K.J. et al.
Partner: UNT Libraries Government Documents Department

Gamma-ray spectrometer utilizing xenon at high pressure

Description: A prototype gamma-ray spectrometer utilizing xenon gas near the critical point (166{degrees}C, 58 atm) is under development. The spectrometer will function as a room-temperature ionization chamber detecting gamma rays in the energy range 100 keV2 MeV, with an energy resolution intermediate between semiconductor (Ge) and scintillation (NaI) spectrometers. The energy resolution is superior to that of a NaI scintillation spectrometer by a substantial margin (approximately a factor 5), and accordingly, much more information can be extracted from a given gamma-ray spectrum. Unlike germanium detectors, the spectrometer possesses the capability for sustained operation under ambient temperature conditions without a requirement for liquid nitrogen.
Date: August 1, 1994
Creator: Smith, G. C.; Mahler, G. J.; Yu, B.; Kane, W. R. & Markey, J. K.
Partner: UNT Libraries Government Documents Department

Structural change of graphite during electron irradiation

Description: Highly oriented pyrolytic graphite was irradiated at room temperature with 300-keV electrons. High resolution transmission electron microscopy and electron energy loss spectroscopy were employed to study the structure of electron-irradiated graphite. Results consistently indicated absence of long-range order periodicity in the basal plane, and loose retention of the c-axis periodicity. Structure was modeled based on a mixture of sixfold and non-sixfold atom rings. Formation of non-sixfold atom rings was related to the observed buckling and discontinuity of the original graphite basal plane.
Date: December 31, 1992
Creator: Koike, J. & Pedraza, D. F.
Partner: UNT Libraries Government Documents Department

Cusp electron production in 75--300 keV He{sup +} + Ar collisions

Description: Cusp-electron production has been investigated in collisions of 75--300 keV He{sup +} with Ar. The relative contributions from electron capture to the continuum (ECC), transfer ionization (TI), and electron loss to the continuum (ELC) to the total cusp electron production were measured. Over the energy range investigated, ECC was found to decrease from about 86% to 80%, TI decreased from about 12% to 1%, and ELC increased from about 2% to 20%. The present results are consistent with earlier work for He{sup +} and O{sup q+} projectiles.
Date: December 31, 1992
Creator: Plano, V. L.; Sarkadi, L.; Zavodszky, P.; Berenyi, D.; Palinkas, J.; Gulyas, L. et al.
Partner: UNT Libraries Government Documents Department

Electron beam energy deposition and VUV efficiency measurements in rare gases

Description: Reliable techniques for the determination of the energy/cm$sup 3$ deposited by an e-beam into a gas as well as the energy/cm$sup 3$ radiated have been developed in order to obtain dependable data on the VUV fluorescence efficiency for rare gas excimers. Spatially resolved total stopping calorimetry in the gas at the cell foil was used to characterize the energy distribution in the e-beam (approximately 200 kV, few Amp/cm$sup 2$, approximately 1 $mu$sec) transmitted by a ''hibachi''-supported 1-mil Ti foil. By using these data, suitable input for a 3-D Monte Carlo electron transport code (SANDYL) was generated. The spatial distribution of energy deposition in the gas was then calculated taking into account multiple scattering and cell geometry. The validity of the SANDYL technique is substantiated by excellent agreement between the measured and calculated energy flux on a vertical stack of five fast risetime ( less than 1 msec) calorimeters at several depth positions [0 less than Z(cm) less than 15] in the gas [1 less than P(atm) less than 3]. Calibrated optical components were used in a well defined geometry that permitted calculation of the effective radiating volume observed. By using the above techniques, high absolute efficiencies (10--30 percent) have been measured for rare gas VUV continua emission which can photolytically produce group VI metastables [e.g., 0($sup 1$S), S($sup 1$S)] of interest as fusion visible-laser candidates.
Date: November 1, 1975
Creator: Turner, C.E. Jr.; Hoff, P.W. & Taska, J.
Partner: UNT Libraries Government Documents Department

Cu(n,x$gamma$) reaction cross section for incident neutron energies between 0.2 and 20.0 MeV

Description: Differential cross sections for the neutron-induced gamma-ray production from copper have been measured for incident neutron energies between 0.2 and 20.0 MeV. The Oak Ridge Linear Accelerator (ORELA) was used to provide the neutrons and a NaI spectrometer to detect the gamma rays at 125$sup 0$. The data presented are the doubly differential cross section, d$sup 2$sigma/d$Omega$dE, for gamma-ray energies between 0.3 and 10.6 MeV for coarse intervals in incident neutron energy. The integrated yield of gamma rays of energies greater than 300 keV with higher resolution in the neutron energy is also presented. The experimental results are compared with previous measurements made at ORELA and with the Evaluated Neutron Data File (ENDF/B-IV, MAT 1295). 41 figures, cross section tables. (auth)
Date: February 1, 1976
Creator: Chapman, G.T.
Partner: UNT Libraries Government Documents Department