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Experimental studies of transition radiation and optical bremsstrahlung

Description: This report summarizes research on the optical emission from thin films and bulk metals bombarded by 25 to 120 keV electrons carried out at Oak Ridge National Laboratory. Details concerning the experimental apparatus and theoretical calculations may be found in the references listed in this paper. Measurements have been carried out on the dependence of the emitted spectra on angle of observation, polarization, sample thickness, surface roughness, surface contamination, and incident electron energy. 13 refs.
Date: January 1, 1985
Creator: Arakawa, E.T.
Partner: UNT Libraries Government Documents Department

New neutron capture and transmission measurements for {sup 134,136}Ba at ORELA and their impact on s-process nucleosynthesis calculations

Description: We have made high-resolution neutron capture and transmission measurements on isotopically enriched samples of {sup 134}Ba and {sup 136}Ba at the Oak Ridge Electron Linear Accelerator (ORELA) in the energy range from 20 eV to 500 keV. Previous measurements had a lower energy limit of 3 - 5 keV, which is too high to determine accurately the Maxwellian-averaged capture cross section at the low temperatures (kT {approx} 6 - 12 keV) favored by the most recent stellar models of the {ital s}-process. Our results for the astrophysical reaction rates are in good agreement with the most recent previous measurement at the classical {ital s}-process temperature, kT = 30 keV, but show significant differences at lower 40 temperatures. We discuss the astrophysical implications of these differences.
Date: October 1, 1996
Creator: Koehler, P.E.; Spencer, R.R.; Winters, R.R.; Guber, K.H.; Harvey, J.A.; Hill, N.W. et al.
Partner: UNT Libraries Government Documents Department

Neutron Total Cross Sections of {sup 235}U From Transmission Measurements in the Energy Range 2 keV to 300 keV and Statistical Model Analysis of the Data

Description: The average {sup 235}U neutron total cross sections were obtained in the energy range 2 keV to 330 keV from high-resolution transmission measurements of a 0.033 atom/b sample.1 The experimental data were corrected for the contribution of isotope impurities and for resonance self-shielding effects in the sample. The results are in very good agreement with the experimental data of Poenitz et al.4 in the energy range 40 keV to 330 keV and are the only available accurate experimental data in the energy range 2 keV to 40 keV. ENDF/B-VI evaluated data are 1.7% larger. The SAMMY/FITACS code 2 was used for a statistical model analysis of the total cross section, selected fission cross sections and data in the energy range 2 keV to 200 keV. SAMMY/FITACS is an extended version of SAMMY which allows consistent analysis of the experimental data in the resolved and unresolved resonance region. The Reich-Moore resonance parameters were obtained 3 from a SAMMY Bayesian fits of high resolution experimental neutron transmission and partial cross section data below 2.25 keV, and the corresponding average parameters and covariance data were used in the present work as input for the statistical model analysis of the high energy range of the experimental data. The result of the analysis shows that the average resonance parameters obtained from the analysis of the unresolved resonance region are consistent with those obtained in the resolved energy region. Another important result is that ENDF/B-VI capture cross section could be too small by more than 10% in the energy range 10 keV to 200 keV.
Date: May 1, 2000
Creator: Derrien, H.; Harvey, J.A.; Larson, N.M.; Leal, L.C. & Wright, R.Q.
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

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

Characterization of Low-Energy (6-30 keV) Response of Polish TLDs (MTS-N, MCP-N) with Synchrotron Radiation and Determination of Some Fundamental TLD Quantities

Description: Relative to <sup>137</sup>Cs gamma rays, the response of MTS-N (<sup>Nat</sup>LiF:Mg,Ti-0.04 cm thick) increased from 0.4 to 1.4 between x-ray energies of 6 and 30 keV and that of MCP-N (<sup>Nat</sup>Lif:Mg, Cu, P-0.04 cm thick) increased from 0.02 to 1.2 between 6 and 26 keV. A mathematical model for TLD response was used with measured responses to determine overall TLD efficiency C(k) and efficiency relative to <sup>137</sup>Cs. The effective energy attenuation coefficient {mu}(k) and light attenuation coefficient f were also determined experimentally. The relative efficiency of MTS-N increased from 0.66 to 1.30 between 6 and 30 keV and that of MCP-N increased from 0.37 to 0.99 between 6 and 26 keV.
Date: November 17, 1998
Creator: Ipe, Nisy E.
Partner: UNT Libraries Government Documents Department

Near-field stacking of zone plates in the x-ray range.

Description: We use Fresnel zone plates as focusing optics in hard x-ray microprobes at energies typically between 6 and 30 keV. While a spatial resolution close to 0.1 {micro}m can currently be achieved, highest spatial resolution is obtained only at reduced diffraction efficiency due to manufacturing limitations with respect to the aspect ratios of zone plates. To increase the effective thickness of zone plates, we are stacking several identical zone plates on-axis in close proximity. If the zone plates are aligned laterally to within better than an outermost zone width and longitudinally within the optical near-field, they form a single optical element of larger effective thickness and improved efficiency and reduced background from undiffracted radiation. This allows us both to use zone plates of moderate outermost zone width at energies of 30 keV and above, as well as to increase the efficiency of zone plates with small outermost zone widths particularly for the energy range of 6-15 keV.
Date: September 20, 2002
Creator: Maser, J.; Lai, B.; Yun, W.; Shastri, S. D.; Cai, Z.; Rodrigues, W. et al.
Partner: UNT Libraries Government Documents Department

plutonium isotopic analysis in the 30 KeV to 210 KeV range

Description: Low-Energy Gamma-ray Spectroscopy (LEGS) is a nondestructive assay (NDA) technique developed in the 1980s. In 1999, it was modified to include a physical-based model for the energy dependent efficiency. It uses the gamma rays in the energy range from approximately 30 keV to 210 keV, except the 100-keV region. This energy region provides intense, well-separated gamma rays from the principal isotopes of plutonium. For applications involving small quantities (mg to g) of freshly separated plutonium in various chemical forms, it is ideally suited for accurate real-time or near real-time isotopic analysis. Since the last modification, LEGS has been incorporated into the FRAM code (Fixed-energy Response-function Analysis with Multiple efficiency), version 4. FRAM v4 is capable of analyzing the peaks in the whole energy range from 30 keV to 1 MeV, including the X-ray region. The new capability of analyzing the peaks in the 100-keV region greatly enhances the plutonium analysis in the 30 keV to 2 10 keV ranges of the traditional LEGS. We now can analyze both the freshly separated and aged plutonium with greater accuracy.
Date: January 1, 2001
Creator: Vo, Duc T. & Li, T. K. (Tien K.)
Partner: UNT Libraries Government Documents Department

X-ray spectral properties of {gamma}-ray bursts

Description: The authors summarize the spectral characteristics of a sample of 22 bright gamma-ray bursts detected with the gamma-ray burst sensors aboard the satellite Ginga. This instrument employed a proportional and scintillation counter to provide sensitivity to photons in the 2--400 keV range, providing a unique opportunity to characterize the largely unexplored X-ray properties of gamma-ray bursts. The photon spectra of the Ginga bursts are well described by a low energy slope, a bend energy, and a high energy slope. In the energy range where they can be compared, this result is consistent with burst spectral analyses obtained from the BATSE experiment aboard the Compton Observatory. However, below 20 keV they find evidence for a positive spectral number index in approximately 40% of their burst sample, with some evidence for a strong rolloff at lower energies in a few events. They find that the distribution of spectral bend energies extends below 10 keV. The observed ratio of energy emitted in the X-rays relative to the gamma-rays can be much larger than a few percent and, in fact, is sometimes larger than unity. The average for their sample is 24%.
Date: September 1, 1997
Creator: Strohmayer, T.E.; Fenimore, E.E.; Murakami, Toshio & Yoshida, Atsumasa
Partner: UNT Libraries Government Documents Department

An electromagnetic helical undulator for polarized x-rays

Description: Linearly and circularly polarized x-rays have been very successfully applied to the study of the properties of materials. Many applications can benefit from the availability of energy-turnable, high-brilliance x-ray beams with adjustable polarization properties. A helical undulator that can generate beams of variable (linear to circular) polarization has been designed and built by the Budker Institute of Nuclear Physics and the Advanced Photon Source. The first harmonic of this 12.8-cm-period device will cover the energy range from 0.4 keV to 3.5 keV. An important feature of this fully electromagnetic device is that it will allow one to generate 100% horizontally (K{sub x}=O)or vertically (K{sub y}=O) plane-polarized radiation, which will enable many experiments otherwise not technically feasible. With symmetric deflection parameters (K{sub x}=K{sub y}), the on-axis radiation will be circularly polarized, with a user-selectable handedness. The polarization can be changed at rates up to 10 Hz.
Date: October 28, 1999
Creator: Gluskin, E.; Vinokurov, N.; Tcheskidov, V.; Medvedko, A.; Evtushenko, Y. Kolomogorov, V.; Vobly, P. et al.
Partner: UNT Libraries Government Documents Department

Calculated distance distributions of energy transfer events in irradiated liquid water

Description: Histories from a Monte Carlo electron transport calculation in liquid water are analyzed to obtain the distance distribution functions, t(x) and T(x), of energy transfer events. These functions, which give the average energy transferred within a distance x from an arbitrary transfer event, are presented for irradiation by monoenergetic electrons of several energies between 500 eV and 1 MeV, for monoenergetic photons of 10, 50, and 200 keV energy and for 65 kVp and 200 kVp x rays and /sup 60/Co..gamma.. rays. The dose average lineal energy in spherical sites as a function of site radius is also presented for these same photon spectra.
Date: January 1, 1980
Creator: Hamm, R.N.; Turner, J.E.; Wright, H.A. & Ritchie, R.H.
Partner: UNT Libraries Government Documents Department

Differential cross sections for electron emission in heavy ion-atom collisions

Description: The systematics of differential ionization cross sections are explored for incident charged particles which possess atomic structure. Although little has been published regarding outer shell ionization by structured projectiles, sufficient data are becoming available to provide some insight into the collision process. This discussion concentrates on systematics of emission cross sections for the intermediate and high energy projectiles where the applicability of high energy approximations can be tested and the dramatic changes in emission spectra observed as the projectile energies decrease. Since heavy ion interactions are important in many research fields, it is particularly useful to determine where simple methods of cross section scaling may be appropriate.
Date: January 1, 1978
Creator: Toburen, L. H.
Partner: UNT Libraries Government Documents Department

Fusion reactivity graphs and tables for charged particle reactions

Description: Graphs and tables are presented on 31 light isotope fusion reaction parameters (<sigma v>, n<sigma v>, <sigma v>Q/sub +/, n<sigma v>Q/sub +/ (for n = 10/sup 20/ fuel ion species/m/sup 3/ and Q/sub +/ = energy release in charged particles)) in the kinetic temperature range 1 to 1000 keV.
Date: August 1, 1979
Creator: McNally, J.R. Jr.; Rothe, K.E. & Sharp, R.D.
Partner: UNT Libraries Government Documents Department

Multiple scattering enhancement of x rays

Description: A Monte Carlo calculation is described for the determination of the contribution of multiple scattering to x rays scattered at 90 deg in various thicknesses of beryllium and carbon plates. The plates are inclined at an angle of 45 deg to the incident radiation. The photon energy range considered is 1 keV to 100 keV. Scatterer thicknesses range from 0.0046 g/cm/sup 2/ to 1.204 g/ cm/sup 2/. Two sets of results are given: one from a formulation neglecting the polarization, the other including polarization. Results are presented in the form of an enhancement factor defined as the ratio of the number of scattered photons escaping from the scatterer at 90 deg to the number escaping at 90 deg after scattering only once. Enhancement factors are given in both tabular and graphical form. (auth)
Date: February 1, 1974
Creator: Bennett, E.W.
Partner: UNT Libraries Government Documents Department