Resource Type

Evaluation of production samples of the scintillators LaBr3:Ce and LaCl3:Ce (open access)

Evaluation of production samples of the scintillators LaBr3:Ce and LaCl3:Ce

We report on the evaluation of the performance of two recently developed scintillator materials, LaCl{sub 3}:Ce and LaBr{sub 3}:Ce, at the task of gamma ray spectroscopy. Their performance is compared to a standard scintillator used for gamma ray spectroscopy--a 25 mm diameter 25 mm tall cylinder of NaI:Tl. We measure the pulse height, energy resolution, and full-energy efficiency of production LaBr{sub 3}:Ce and LaCl{sub 3}:Ce scintillation crystals of different sizes and geometries for a variety of gamma-ray energies. Using production rather than specially selected crystals will establish whether immediate large-scale use is feasible. The crystal is excited by gamma rays from one of six isotopic sources ({sup 125}I, {sup 241}Am, {sup 57}Co, {sup 22}Na, {sup 137}Cs, and {sup 60}Co) placed 15 cm away from the scintillator. Our measurements show that both LaCl{sub 3} and LaBr{sub 3} outperform NaI:Tl in almost all cases. They outperform NaI:Tl at all energies for the photopeak fraction and counting rate measurements, and for energy resolution at higher energies (above 200 keV for LaCl{sub 3} and 75 keV for LaBr{sub 3}). The performance of production crystals is excellent and these scintillators should be considered for immediate use in systems where stopping power and energy resolution are …
Date: September 15, 2005
Creator: Choong, Woon-Seng; Derenzo, Stephen E. & Moses, William W.
System: The UNT Digital Library
Laser-beam propagation in high temperature hohlraum plasmas (open access)

Laser-beam propagation in high temperature hohlraum plasmas

The authors have developed a new target platform to study propagation and backscatter of a frequency-doubled (2{omega}) laser beam through large-scale length plasmas at ignition-design densities, intensities and temperatures above 3 keV. The plasma is created by heating a gas filled hohlraum target with 37 heater beams that deliver a total energy of up to 15 kJ in a 1 ns square pulse. They measure a factor of two higher temperatures than in open geometry gasbag targets investigated earlier. This new temperature regime with a measured beam transmission of up to 80% suggests we can expect good laser coupling into ignition hohlraums at the National Ignition Facility (NIF) using 2{omega} light.
Date: September 15, 2005
Creator: Niemann, C.; Froula, D.; Divol, L.; Meezan, N.; Jones, O.; Ross, R. et al.
System: The UNT Digital Library
X-ray diffraction characterization of suspended structures for MEMS applications (open access)

X-ray diffraction characterization of suspended structures for MEMS applications

Mechanical stress control is becoming one of the major challenges for the future of micro and nanotechnologies. Micro scanning X-ray diffraction is one of the promising techniques that allows stress characterization in such complex structures at sub micron scales. Two types of MEMS structure have been studied: a bilayer cantilever composed of a gold film deposited on poly-silicon and a boron doped silicon bridge. X-ray diffraction results are discussed in view of numerical simulation experiments.
Date: September 15, 2005
Creator: Goudeau, P.; Tamura, N.; Lavelle, B.; Rigo, S.; Masri, T.; Bosseboeuf, A. et al.
System: The UNT Digital Library
2004 Molecular Basis of Microbial One-Carbon Metabolism Gordon Conference - August 1-6, 2004 (open access)

2004 Molecular Basis of Microbial One-Carbon Metabolism Gordon Conference - August 1-6, 2004

The Gordon Research Conference (GRC) on 2004 Molecular Basis of Microbial One-Carbon Metabolism Gordon Conference - August 1-6, 2004 was held at Mount Holyoke College, South Hadley, MA from August 1-6, 2004. The Conference was well-attended with 117 participants (attendees list attached). The attendees represented the spectrum of endeavor in this field coming from academia, industry, and government laboratories, both U.S. and foreign scientists, senior researchers, young investigators, and students. In designing the formal speakers program, emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate lively discussion about the key issues in the field today. Time for formal presentations was limited in the interest of group discussions. In order that more scientists could communicate their most recent results, poster presentation time was scheduled. Attached is a copy of the formal schedule and speaker program and the poster program. In addition to these formal interactions, 'free time' was scheduled to allow informal discussions. Such discussions are fostering new collaborations and joint efforts in the field.
Date: September 15, 2005
Creator: Krzycki, Joseph A.
System: The UNT Digital Library
Probing small x parton densities in ultraperipheral AA and pAcollisions at the LHC (open access)

Probing small x parton densities in ultraperipheral AA and pAcollisions at the LHC

We calculate photoproduction rates for several hard processes in ultraperipheral proton-lead and lead-lead collisions at the LHC with {radical}s{sub NN} = 8.8 and 5.5 TeV respectively which could be triggered in the large LHC detectors. We use ATLAS as an example. The lead ion is treated as a source of (coherently produced) photons with energies and intensities greater than those of equivalent ep collisions at HERA.We find very large rates for both inclusive and diffractive production which will extend the HERA x range by nearly an order of magnitude for similar virtualities. We demonstrate that it is possible to reach the kinematic regime where nonlinear effects are larger than at HERA.
Date: September 15, 2005
Creator: Strikman, Mark; Vogt, Ramona & White, Sebastian
System: The UNT Digital Library
Physical Property Modeling of Concentrated Cesium Eluate Solutions, Part I - Derivation of Models (open access)

Physical Property Modeling of Concentrated Cesium Eluate Solutions, Part I - Derivation of Models

Major analytes projected to be present in the Hanford Waste Treatment Plant cesium ion-exchange eluate solutions were identified from the available analytical data collected during radioactive bench-scale runs, and a test matrix of cesium eluate solutions was designed within the bounding concentrations of those analytes. A computer model simulating the semi-batch evaporation of cesium eluate solutions was run in conjunction with a multi-electrolyte aqueous system database to calculate the physical properties of each test matrix solution concentrated to the target endpoints of 80% and 100% saturation. The calculated physical properties were analyzed statistically and fitted into mathematical expressions for the bulk solubility, density, viscosity, heat capacity and volume reduction factor as a function of temperature and concentration of each major analyte in the eluate feed. The R{sup 2} of the resulting physical property models ranged from 0.89 to 0.99.
Date: September 15, 2005
Creator: Choi, A.S.; Pierce, R. A.; Edwards, T. B. & Calloway, T. B.
System: The UNT Digital Library
Structure, Stability and Elm Dynamics of the H-Mode Pedestal in DIII-D (open access)

Structure, Stability and Elm Dynamics of the H-Mode Pedestal in DIII-D

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Date: September 15, 2005
Creator: Fenstermacher, M. E.; Osborne, T. H.; Leonard, A. W.; Snyder, P. B.; Thomas, D. M.; Boedo, J. A. et al.
System: The UNT Digital Library