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The X-ray FEL: An experimenter's dilemma
The specifications of presently proposed x-ray free electron lasers (FELs) are for machines that will provide x-ray pulses as short as 100 fs with a photon energy as high as 12.3 keV. Since the pulse will contain as much as 5 mJ of energy, these devices will present the experimenter with an opportunity to expose matter to an unprecedented x-ray energy density. This high concentration of energetic x-rays presents both a promising frontier in energy-matter interaction, as well as a technological crevasse to be crossed by the experimenter attempting to use the FEL beam. The authors shall look at three possible problems confronting the experimenter: (1) synchronization of a detector, laser pulse, etc., to the FEL pulse; (2) radiation damage to the target sample; and (3) the presence of an electromagnetic pulse that could damage sensitive electronics located in the experimental area.
Date:
July 5, 2000
Creator:
McPherson, A.
Object Type:
Article
System:
The UNT Digital Library
X-ray K-edge analysis of drain lines in Wilhelm Hall, Ames Laboratory
From August 12--27, 1998 X-ray K-edge measurements were made on drain lines in seven rooms in Wilhelm Hall, Ames Laboratory. The purpose of these measurements was to determine the extent of thorium (and other heavy metal) contamination inside these pipes. The K-edge method is a noninvasive inspection technique that can provide accurate quantification of heavy metal contamination interior to an object. Of the seven drain lines inspected, one was found to have no significant contamination, three showed significant thorium deposits, two showed mercury contamination, and one line was found to contain mercury, thorium and uranium. The K-edge measurements were found to be consistent with readings from hand-held survey meters, and provided much greater detail on the location and amount of heavy metal contamination.
Date:
January 5, 1999
Creator:
Jensen, T. & Whitmore, C.
Object Type:
Report
System:
The UNT Digital Library
Xenon and Samarium reactivity effects associated with coolant loss
In Hanford reactors the reactivity gain upon loss of coolant water is an important factor in the speed of control requirements. The reactivity gain in the cold, clean reactor is determined from experiments, but additional effects must be taken into account if the gain in the operating reactors is to be obtained. One of these effects is the change in Xenon and Samarium poisoning with neutron temperature, which is discussed here. Earlier work on the relationship of operating limits to the reactivity gain upon loss of coolant is given in Reference 1. Work on this problem is continuing by Reactor Physics, IPD, but the newer work is not yet documented. In earlier calculations, the neutron temperature could only be guessed. Recent measurements of neutron temperatures have indicated the magnitude of the neutron temperature change upon loss of water. This document interprets the data of Reference 2 in terms of the change in Xenon and Samarium poison to be expected on water loss under typical operating conditions.
Date:
April 5, 1960
Creator:
unknown
Object Type:
Report
System:
The UNT Digital Library
XMM-Newton Observations Reveal the X-ray Counterpart of the Very-high-energy gamma-ray Source HESS J1640-465
We present X-ray observations of the as of yet unidentified very high-energy (VHE) {gamma}-ray source HESS J1640-465 with the aim of establishing a counterpart of this source in the keV energy range, and identifying the mechanism responsible for the VHE emission. The 21.8 ksec XMM-Newton observation of HESS J1640-465 in September 2005 represents a significant improvement in sensitivity and angular resolution over previous ASCA studies in this region. These new data show a hard-spectrum X-ray emitting object at the centroid of the H.E.S.S. source, within the shell of the radio Supernova Remnant (SNR) G338.3-0.0. This object is consistent with the position and flux previously measured by both ASCA and Swift-XRT but is now shown to be significantly extended. We argue that this object is very likely the counterpart to HESS J1640-465 and that both objects may represent the Pulsar Wind Nebula of an as of yet undiscovered pulsar associated with G338.3-0.0.
Date:
March 5, 2007
Creator:
Funk, S.; Hinton, J. A.; Puhlhofer, G.; Aharonian, F. A.; Hofmann, W.; Reimer, O. et al.
Object Type:
Article
System:
The UNT Digital Library
Y-12 Uranium Exposure Study
Following the recent restart of operations at the Y-12 Plant, the Radiological Control Organization (RCO) observed that the enriched uranium exposures appeared to involve insoluble rather than soluble uranium that presumably characterized most earlier Y-12 operations. These observations necessitated changes in the bioassay program, particularly the need for routine fecal sampling. In addition, it was not reasonable to interpret the bioassay data using metabolic parameter values established during earlier Y-12 operations. Thus, the recent urinary and fecal bioassay data were interpreted using the default guidance in Publication 54 of the International Commission on Radiological Protection (ICRP); that is, inhalation of Class Y uranium with an activity median aerodynamic diameter (AMAD) of 1 {micro}m. Faced with apparently new workplace conditions, these actions were appropriate and ensured a cautionary approach to worker protection. As additional bioassay data were accumulated, it became apparent that the data were not consistent with Publication 54. Therefore, this study was undertaken to examine the situation.
Date:
August 5, 1999
Creator:
Eckerman, K. F. & Kerr, G. D.
Object Type:
Report
System:
The UNT Digital Library
YUCCA MOUNTAIN PROJECT - A BRIEFING --
This report has the following articles: Nuclear waste--a long-term national problem; Spent nuclear fuel; High-level radioactive waste; Radioactivity and the environment; Current storage methods; Disposal options; U.S. policy on nuclear waste; The focus on Yucca Mountain; The purpose and scope of the Yucca Mountain Project; The approach for permanently disposing of waste; The scientific studies at Yucca Mountain; The proposed design for a repository at Yucca Mountain; Natural and engineered barriers would work together to isolate waste; Meticulous science and technology to protect people and the environment; Licensing a repository; Transporting waste to a permanent repository; The Environmental Impact Statement for a repository; Current status of the Yucca Mountain Project; and Further information available on the Internet.
Date:
August 5, 2003
Creator:
unknown
Object Type:
Report
System:
The UNT Digital Library
Z-Contrast STEM Imaging and EELS of CdSe Nanocrystals: Towards the Analysis of Individual Nanocrystal Surfaces
We have applied Atomic Number Contract Scanning Transmission Electron Microscopy (Z-Contrast STEM) and STEM/EELS (Electron Energy Loss Spectroscopy) towards the study of colloidal CdSe semiconductor nanocrystals embedded in MEH-PPV polymer films. Unlike the case of conventional phase-contrast High Resolution TEM, Z-Contrast images are direct projections of the atomic structure. Hence they can be interpreted without the need for sophisticated image simulation and the image intensity is a direct measure of the thickness of a nanocrystal. Our thickness measurements are in agreement with the predicted faceted shape of these nanocrystals. Our unique 1.3A resolution STEM has successfully resolve3d the sublattice structure of these CdSe nanocrystals. In [010] projection (the polar axis in the image plane) we can distinguish Se atom columns from Cd columns. Consequently we can study the effects of lattice polarity on the nanocrystal morphology. Furthermore, since the STEM technique does not rely on diffraction, it is superbly suited to the study of non-periodic detail, such as the surface structure of the nanocrystals. EELS measurements on individual nanocrystals indicate a significant amount (equivalet to 0.5-1 surface monolayers) of oxygen on the nanocrystals, despite processing in an inert atmosphere. Spatially resolved measurements at 7A resolution suggest a surface oxide layer. …
Date:
April 5, 1999
Creator:
Erwin, M.; Kadavanich, A. V.; Kippeny, T.; Pennycook, S. J. & Rosenthal, S. J.
Object Type:
Article
System:
The UNT Digital Library
D-Zero Collider Detector Cryopump Design and Operation
The vacuum pumping of the CC Cryostat was anticipated to be dominated by a water vapor load. The Engineering Note 270, extrapolating from earlier experience, predicts the removal of water vapor will be the dominant pumping load and take ca. 45 days to remove at the pumping speed planned. Part of the planned pumping capability was a homemade, liquid nitrogen temperature, water vapor cryopump. This note describes the design, fabrication and performance experiences of the Cryopump described in the D0 assembly drawing 3740.514-ME-294693.
Date:
April 5, 1991
Creator:
Wu, J. & Mulholland, G. T.
Object Type:
Report
System:
The UNT Digital Library
D-Zero Collison Hall Ventilation Measurements
This engineering note documents air velocity measurements taken on September 5, 2002 for the D-Zero collision hall. These measurements were done after changes were made to the building dampers, DM-1, DM-2, and DM-14 such that the collision hall would be at a slight positive pressure. Measurements were made by Pete Simon and Mike Sarychev. They systematically took velocity measurements across the duct cross sections. Their raw measurements are included.
Date:
September 5, 2002
Creator:
Rucinski, Russell A.
Object Type:
Report
System:
The UNT Digital Library
D-Zero Nitrogen Dewar Failure Mode and Effects Analysis and "What-If" Analysis
All components related to the nitrogen storage dewar were included. Pipe failures were excluded. Instrument air valves and components were excluded. See the 'What if' analysis for consequences from loss of instrument air.
Date:
December 5, 1990
Creator:
Rucisnki, R.A.
Object Type:
Report
System:
The UNT Digital Library
Zinc surface complexes on birnessite: A density functional theory study
Biogeochemical cycling of zinc is strongly influenced by sorption on birnessite minerals (layer-type MnO2), which are found in diverse terrestrial and aquatic environments. Zinc has been observed to form both tetrahedral (Zn{sup IV}) and octahedral (Zn{sup VI}) triple-corner-sharing surface complexes (TCS) at Mn(IV) vacancy sites in hexagonal birnessite. The octahedral complex is expected to be similar to that of Zn in the Mn oxide mineral, chalcophanite (ZnMn{sub 3}O{sub 7} {center_dot} 3H{sub 2}O), but the reason for the occurrence of the four-coordinate Zn surface species remains unclear. We address this issue computationally using spin-polarized Density Functional Theory (DFT) to examine the Zn{sub IV}-TCS and Zn{sup VI}-TCS species. Structural parameters obtained by DFT geometry optimization were in excellent agreement with available experimental data on Zn-birnessites. Total energy, magnetic moments, and electron-overlap populations obtained by DFT for isolated Zn{sup IV}-TCS revealed that this species is stable in birnessite without a need for Mn(III) substitution in the octahedral sheet and that it is more effective in reducing undersaturation of surface O at a Mn vacancy than is Zn{sub VI}-TCS. Comparison between geometry-optimized ZnMn{sub 3}O{sub 7} {center_dot} 3H{sub 2}O (chalcophanite) and the hypothetical monohydrate mineral, ZnMn{sub 3}O{sub 7} {center_dot} H{sub 2}O, which contains only tetrahedral …
Date:
January 5, 2009
Creator:
Kwon, Kideok D.; Refson, Keith & Sposito, Garrison
Object Type:
Article
System:
The UNT Digital Library