Gamma-ray array physics. (open access)

Gamma-ray array physics.

In this contribution I am going to discuss the development of large arrays of Compton Suppressed, High Purity Germanium (HpGe) detectors and the physics that has been, that is being, and that will be done with them. These arrays and their science have dominated low-energy nuclear structure research for the last twenty years and will continue to do so in the foreseeable future. John Sharpey Schafer played a visionary role in convincing a skeptical world that the development of these arrays would lead to a path of enlightenment. The extent to which he succeeded can be seen both through the world-wide propagation of ever more sophisticated devices, and through the world-wide propagation of his students. I, personally, would not be working in research if it were not for Johns inspirational leadership. I am eternally grateful to him. Many excellent reviews of array physics have been made in the past which can provide detailed background reading. The review by Paul Nolan, another ex-Sharpey Schafer student, is particularly comprehensive and clear.
Date: May 25, 1999
Creator: Lister, C. J.
Object Type: Article
System: The UNT Digital Library
Beam dynamics studies in a high-brightness photo-injector (open access)

Beam dynamics studies in a high-brightness photo-injector

A high-brightness photo-injector has been developed at Fermilab in collaboration with the TTF project at DESY. Two systems have been commissioned, one at DESY and one at Fermilab. The injector [1] consists of a 1.625-cell cavity RF gun, a superconducting niobium cavity (both 1.3 GHz), and a magnetic chicane. The gun is designed for an electric field of up to 50 MV/m on the cathode. Emittance compensation solenoids surround the gun to correct the linear space charge emittance growth. A high quantum efficiency Cs{sub 2}Te photocathode located in the first half-cell produces electrons when illuminated by 263 nm wavelength light (fourth harmonic of the Nd:YLF laser). The laser [2] was designed to produce a train of up to 800 equal amplitude, 10 {micro}J UV pulses spaced by 1 {micro}s at 1 Hz repetition rate. The laser pulse length is adjustable between 1 and 20 ps FWHM. The superconducting cavity is a 9-cell Nb structure fabricated by industry for TTF. It was tested with RF at DESY before being sent to Fermilab. At present, the cavity is operated at {approx}11 MeV/m. Beam measurements with the injector at Fermilab are in progress. Preliminary results for emittance and bunch length will be discussed …
Date: October 25, 1999
Creator: Carneiro, Jean-Paul
Object Type: Article
System: The UNT Digital Library
Questions of Identity (open access)

Questions of Identity

As an introduction to {nu}Fact '99, the ICFA/ECFA Workshop on Neutrino Factories Based on Muon Storage Rings, I place the issues of neutrino properties and neutrino oscillations in the broader context of fermion flavor.
Date: August 25, 1999
Creator: Quigg, Chris
Object Type: Article
System: The UNT Digital Library
Measurement of the light quark flavor asymmetry in the nucleon sea. (open access)

Measurement of the light quark flavor asymmetry in the nucleon sea.

Fermilab experiment E866 has performed a precision measurement of the ratio of Drell-Yan yields from 800 GeV/c protons incident on deuterium and hydrogen targets. The measurement is used to determine the ratio of down antiquarks({bar d}) to up antiquarks({bar u}) in the proton over a broad range in the fraction of the proton momentum carried by the antiquark, 0.02 < x < 0.345. For x < 0.15, the data is in reasonable agreement with pre-existing parton distributions while for x > 0.20 the data is much closer to unity than these parton functions had indicated. The light quark asymmetry provides valuable information on the relative role perturbative and non-perturbative mechanisms play in generating the nucleon sea. A proposal to extend the Drell-Yan measurement to higher values of x using 120 GeV protons from the Fermilab main injector will be discussed.
Date: June 25, 1999
Creator: Awes, T. C.; Beddo, M. E.; Brown, C. N.; Bush, J. D.; Collaboration, FNAL E866 /NuSea; Geesaman, D. F. et al.
Object Type: Article
System: The UNT Digital Library
The Physics of Fast Z Pinches (open access)

The Physics of Fast Z Pinches

The spectacular progress made during the last few years in reaching high energy densities in fast implosions of annular current sheaths (fast Z pinches) opens new possibilities for a broad spectrum of experiments, from x-ray generation to controlled thermonuclear fusion and astrophysics. Presently Z pinches are the most intense laboratory X ray sources (1.8 MJ in 5 ns from a volume 2 mm in diameter and 2 cm tall). Powers in excess of 200 TW have been obtained. This warrants summarizing the present knowledge of physics that governs the behavior of radiating current-carrying plasma in fast Z pinches. This survey covers essentially all aspects of the physics of fast Z pinches: initiation, instabilities of the early stage, magnetic Rayleigh-Taylor instability in the implosion phase, formation of a transient quasi-equilibrium near the stagnation point, and rebound. Considerable attention is paid to the analysis of hydrodynamic instabilities governing the implosion symmetry. Possible ways of mitigating these instabilities are discussed. Non-magnetohydrodynamic effects (anomalous resistivity, generation of particle beams, etc.) are summarized. Various applications of fast Z pinches are briefly described. Scaling laws governing development of more powerful Z pinches are presented. The survey contains 36 figures and more than 300 references.
Date: October 25, 1999
Creator: Ryutov, D. D.; Derzon, Mark S. & Matzen, M. Keith
Object Type: Article
System: The UNT Digital Library
Atmospheric test models and numerical experiments for the simulation of the global distribution of weather data transponders (open access)

Atmospheric test models and numerical experiments for the simulation of the global distribution of weather data transponders

A proposal has been made to establish a high density global network of atmospheric micro transponders to record time, temperature, and wind data with time resolution of {le} 1 minute, temperature accuracy of {+-} 1 K, spatial resolution no poorer than {approx}3km horizontally and {approx}0.1km vertically, and 2-D speed accuracy of {le} 1m/s. This data will be used in conjunction with advanced numerical weather prediction models to provide increases in the reliability of long range weather forecasts. Major advances in data collection technology will be required to provide the proposed high-resolution data collection network. Systems studies must be undertaken to determine insertion requirements, spacing, and evolution of the transponder ensemble, which will be used to collect the data. Numerical models which provide realistic global weather pattern simulations must be utilized in order to perform these studies. A global circulation model with a 3{sup o} horizontal resolution has been used for initial simulations of the generation and evolution of transponder distributions. These studies indicate that reasonable global coverage of transponders can be achieved by a launch scenario consisting of the sequential launch of transponders at specified heights from a globally distributed set of launch sites.
Date: August 25, 1999
Creator: Grossman, A & Molenkamp, C R
Object Type: Report
System: The UNT Digital Library
Reproducible measurements of MPI performance characteristics. (open access)

Reproducible measurements of MPI performance characteristics.

In this paper we describe the difficulties inherent in making accurate, reproducible measurements of message-passing performance. We describe some of the mistakes often made in attempting such measurements and the consequences of such mistakes. We describe mpptest, a suite of performance measurement programs developed at Argonne National Laboratory, that attempts to avoid such mistakes and obtain reproducible measures of MPI performance that can be useful to both MPI implementers and MPI application writers. We include a number of illustrative examples of its use.
Date: June 25, 1999
Creator: Gropp, W. & Lusk, E.
Object Type: Article
System: The UNT Digital Library
High Voltage GaN Schottky Rectifiers (open access)

High Voltage GaN Schottky Rectifiers

Mesa and planar GaN Schottky diode rectifiers with reverse breakdown voltages (V{sub RB}) up to 550V and >2000V, respectively, have been fabricated. The on-state resistance, R{sub ON}, was 6m{Omega}{center_dot} cm{sup 2} and 0.8{Omega}cm{sup 2}, respectively, producing figure-of-merit values for (V{sub RB}){sup 2}/R{sub ON} in the range 5-48 MW{center_dot}cm{sup -2}. At low biases the reverse leakage current was proportional to the size of the rectifying contact perimeter, while at high biases the current was proportional to the area of this contact. These results suggest that at low reverse biases, the leakage is dominated by the surface component, while at higher biases the bulk component dominates. On-state voltages were 3.5V for the 550V diodes and {ge}15 for the 2kV diodes. Reverse recovery times were <0.2{micro}sec for devices switched from a forward current density of {approx}500A{center_dot}cm{sup -2} to a reverse bias of 100V.
Date: October 25, 1999
Creator: Cao, X. A.; Cho, H.; Chu, S. N. G.; Chuo, C. C.; Chyi, J. I.; Dang, G. T. et al.
Object Type: Article
System: The UNT Digital Library
Atom-by-Atom and Concerted Hopping of Adatom Pairs on an Open Metal Surface (open access)

Atom-by-Atom and Concerted Hopping of Adatom Pairs on an Open Metal Surface

Atom-by-atom and concerted hopping of ad-dimers on the open (100) surface of fcc metals are studied by means of density-functional calculations. The adatom interaction is relatively short-ranged, and beyond next-nearest neighbors ad-dimers are effectively dissociated. Diffusion takes place by a simple shearing process, favored because it maximizes adatom coordination at the transition state This holds for Al, Au, and Rh, and is likely a general result because geometrical arguments dominate over details of the electronic structure.
Date: August 25, 1999
Creator: Bogicevic, A.; Ovesson, S.; Lundqvist, B. I. & Jennison, D. R.
Object Type: Article
System: The UNT Digital Library
Analysis of the ATW fuel cycle using the REBUS-3 code system. (open access)

Analysis of the ATW fuel cycle using the REBUS-3 code system.

Partitioning and transmutation strategies are under study in several countries as a means of reducing the long-term hazards of spent fuel and other high-level nuclear waste. Various reactor and accelerator-driven system concepts have been proposed to transmute the long-lived radioactive nuclei of waste into stable or short-lived species. Among these concepts, the accelerator-driven transmutation of waste (ATW) system has been proposed by LANL for rapid destruction of transuranic actinides and long-lived fission products ({sup 99}Tc and {sup 129}I).The current reference ATW concept employs a subcritical, liquid metal cooled, fast-spectrum nuclear subsystem. Because the discharged fuel is recycled, analysis of ATW nuclear performance requires modeling of the external cycle as well as the in-core fuel management. The fuel cycle analysis of ATW can be performed rigorously using Monte Carlo calculations coupled with detailed depletion calculations. However, the inefficiency of this approach makes it impractical, particularly in view of (a) the large number of fuel cycle calculations needed for design optimization and (b) the need to represent complex in-core and out-of-core fuel cycle operations. To meet the need for design-oriented capabilities, tools previously developed for fast reactor calculations are being adapted for application to ATW. Here we describe the extension and application …
Date: June 25, 1999
Creator: Khalil, H. S. & Yang, W. S.
Object Type: Article
System: The UNT Digital Library
Hard Exclusive and Processes in QCD (open access)

Hard Exclusive and Processes in QCD

Exclusive and semi-exclusive processes, the diffractive dissociation of hadrons into jets, and hard diffractive processes such as vector meson leptoproduction provide new testing grounds for QCD and essential information on the structure of light-cone wavefunctions of hadrons, particularly the pion distribution amplitude. I review the basic features of the leading-twist QCD predictions and the problems and challenges of studying QCD at the amplitude level. The application of the light-cone formalism to the exclusive semi-leptonic decay of heavy hadrons is also discussed.
Date: August 25, 1999
Creator: Brodsky, Stanley J.
Object Type: Report
System: The UNT Digital Library
New W mass results from CDF and D0 (open access)

New W mass results from CDF and D0

This article describes recent measurements of the W mass by the CDF and D0 Collabo-rations. CDF obtains a preliminary result of 80.473 ± 0.113 GeV for the W mass in the electron channel and D0 reports a preliminary result of 80.766 ± 0.234 GeV for electrons in the more forward (Endcap) rapidities. When combined with all previous measurements, the current average for the W mass measured at the Tevatron is 80.450 ± 0.063 GeV.
Date: October 25, 1999
Creator: Carithers, B.
Object Type: Article
System: The UNT Digital Library
New public information resources on salt caverns. (open access)

New public information resources on salt caverns.

For the past decade, interest has been growing in using underground salt caverns for disposing of wastes. The Railroad Commission of Texas has permitted a few caverns for disposal of nonhazardous oil field waste (NOW) and one cavern for disposal of naturally occurring radioactive materials (NORM) from oil field activities. Several salt caverns in Canada have also been permitted for disposal of NOW. In addition, oil and gas agencies in Louisiana and New Mexico are developing cavern disposal regulations. The US Department of Energy (DOE) has funded several studies to evaluate the technical feasibility, legality, economic viability, and risk of disposing of NOW and NORM in caverns. The results of these studies have been disseminated to the scientific and regulatory communities. However, as use of caverns for waste disposal increases, more government and industry representatives and members of the public will become aware of this practice and will need adequate information about how disposal caverns operate and the risks they pose. In anticipation of this need, DOE has fi.mded Argonne National Laboratory to develop a salt cavern public outreach program. Key components of this program are an informational brochure designed for nontechnical persons and a website that provides greater detail …
Date: August 25, 1999
Creator: Tomasko, D. & Veil, J. A.
Object Type: Article
System: The UNT Digital Library
Proton driver study at Fermilab (open access)

Proton driver study at Fermilab

Fermilab has started the design work of a high intensity proton source called the proton driver. It would provide a 4 MW proton beam to the target for muon production. This paper discusses the basic features of this machine and the associated accelerator physics and design issues.
Date: October 25, 1999
Creator: Chou, Weiren
Object Type: Article
System: The UNT Digital Library
FPIX1: An advanced pixel readout chip (open access)

FPIX1: An advanced pixel readout chip

At Fermilab, a pixel detector for BTeV is proposed for installation a few millimeters from the beam. Its information will be used in on-line track finding for the lowest level trigger system. This requires a high-speed readout and immediate data transfer from the pixel chip to the trigger processor. It is also believed that a 2-4 bits of analog information is required to achieve the targeted spatial resolution [1] with 50{micro} wide pixels. Our first prototype, FPIX0 [2], is now being used in a beam test to confirm physics simulations and to determine the required resolution of the analog ''information''. Our 2nd prototype, FPIX1, is a 160X18 pixel readout chip compatible with the ATLAS family of detectors. We have build and tested 4 FPIX1-detector assemblies. FPIX1 is realized in the HP 0.5{micro} process. The main features of FPIX1 are: 2bit flash ADC on each cell for maximum speed; Triggered or stand alone operation; and High speed sparse and time ordered Readout.
Date: October 25, 1999
Creator: al., A. Mekkaoui et
Object Type: Article
System: The UNT Digital Library
Approximate Near-Field Blast Theory: A Generalized Approach (open access)

Approximate Near-Field Blast Theory: A Generalized Approach

A method for analyzing strong shock waves in arbitrary one-dimensional geometry is presented. An approximation to classical Taylor-Sedov theory is extended to the near-field case where source mass is not negligible, accounting for differences in the chemical properties of the source mass and ambient medium. Results from example calculations are compared with previously published analytical formulae.
Date: October 25, 1999
Creator: Hutchens, G.J.
Object Type: Article
System: The UNT Digital Library
First results of the Fermilab high-brightness RF photoinjector (open access)

First results of the Fermilab high-brightness RF photoinjector

A collaboration has been formed between FNAL, UCLA, INFN Milano, the University of Rochester, and DESY to develop the technology of an RF photoinjector, followed by a superconducting cavity, to produce high bunch charge (8 nC) with low normalized emittance (< 20 mm {center_dot} mrad) in trains of 800 bunches separated by 1{micro}s. The activities of the collaboration fall into two categories: (1) the development of Injector II for the TeSLA/TTF accelerator [1]. This photoinjector (TTF RF Gun)was tested at Fermilab in September and October 1998 and installed at DESY in November 1998; (2) the installation at the A0 Hall of Fermilab of a modified version of the TTF photoinjector, for photoinjector R&D and to study novel applications of high-brightness, pulsed electrons beams. This photoinjector (A0 RF Gun) produced its first beam in March 1999. This paper presents a summary of the tests done at Fermilab on the TTF Injector II and the first results obtained on the new Fermilab photoinjector.
Date: October 25, 1999
Creator: Carneiro, Jean-Paul
Object Type: Article
System: The UNT Digital Library
Multilayer coated optics for an alpha-class extreme ultraviolet lithography system (open access)

Multilayer coated optics for an alpha-class extreme ultraviolet lithography system

We present the results of coating the first set of optical elements for an alpha-class extreme-ultraviolet (EUV) lithography system, the Engineering Test Stand (ETS). The optics were coated with Mo/Si multilayer mirrors using an upgraded DC-magnetron sputtering system. Characterization of the near-normal incidence EUV reflectance was performed using synchrotron radiation from the Advanced Light Source at the Lawrence Berkeley National Laboratory. Stringent requirements were met for these multilayer coatings in terms of reflectance, wavelength matching among the different optics, and thickness control across the diameter of each individual optic. Reflectances above 65% were achieved at 13.35 nm at near-normal angles of incidence. The run-to-run reproducibility of the reflectance peak wavelength was maintained to within 0.4%, providing the required wavelength matching among the seven multilayer-coated optics. The thickness uniformity (or gradient) was controlled to within {+-}0.25% peak-to-valley (P-V) for the condenser optics and {+-}0.1% P-V for the four projection optics, exceeding the prescribed specification for the optics of the ETS.
Date: August 25, 1999
Creator: Folta, J. A.; Grabner, R. F.; Hudyma, R. M.; Montcalm, C.; Schmidt, M. A.; Spiller, E. et al.
Object Type: Article
System: The UNT Digital Library
Measurements of deep heating generated by ultra-intense laser-plasma interactions (open access)

Measurements of deep heating generated by ultra-intense laser-plasma interactions

We measure 300 eV thermal temperatures at near-solid densities by x-ray spectroscopy of tracer layers buried up to 30 pm inside CH slabs which are irradiated by a 0.5 kJ, 5 ps laser. X-ray imaging data suggest that collimated electron transport produces comparable temperatures as deep as 200 pm, and unexpectedly show the heated regions to be 50-120 pm-diameter rings. The data indicate that intense lasers can directionally heat solid matter to high temperatures over large distances; the results are relevant for fast-ignition inertial-confinement fusion and hot, dense plasma research
Date: August 25, 1999
Creator: Hatchett, S. P.; Key, M. H.; Koch, J. A.; Lee, R. W.; Pennington, D.; Stephens, R. B. et al.
Object Type: Article
System: The UNT Digital Library
Metrological Challenges of Synchrotron Radiation Optics (open access)

Metrological Challenges of Synchrotron Radiation Optics

Modern third generation storage rings, require state-of-the-art grazing incidence x-ray optics, in order to monochromate the Synchrotrons Radiation (SR) source photons, and focus them into the experimental stations. Slope error tolerances in the order of 0.5 {micro}Rad RMS, and surface roughness well below 5 {angstrom} RMS, are frequently specified for mirrors and gratings exceeding 300 mm in length. Non-contact scanning instruments were developed, in order to characterize SR optical surfaces, of spherical and aspherical shape. Among these, the Long Trace Profiler (LTP), a double pencil slope measuring interferometer, has proved to be particularly reliable, and was adopted by several SR optics metrology laboratories. The ELETTRA soft x-rays and optics metrology laboratory, has operated an LTP since 1992. We review the basic operating principles of this instrument, and some major instrumental and environmental improvements, that were developed in order to detect slope errors lower than 1 {micro}Rad RMS on optical surfaces up to one metre in length. A comparison among measurements made on the same reference flat, by different interferometers (most of them were LTPs) can give some helpful indications in order to optimize the quality of measurement.
Date: May 25, 1999
Creator: Sostero, G.
Object Type: Article
System: The UNT Digital Library
Lattice determinations of the strange quark mass (open access)

Lattice determinations of the strange quark mass

The importance of the strange quark mass, as a fundamental parameter of the Standard Model (SM) and as an input to many interesting quantities, has been highlighted in many reviews, eg in Ref [1]. A first principles calculation of m{sub s} is possible in lattice QCD but to date there has been a rather large spread in values from lattice calculations. This review aims to clarify the situation by explaining the particular systematic errors and their effects and illustrating the emerging consensus. In addition, a discussion of the strange quark mass is timely given the recent results from KTeV [2] and NA48 [3] for {epsilon}{prime}/{epsilon} which firmly establish direct CP-violation in the SM and when combined with previous measurements give a world average {epsilon}{prime}/{epsilon} (21:2 {+-} 2:8) x 10{sup {minus}4}. This is in stark disagreement with the theoretical predictions which favor a low {epsilon}{prime}/{epsilon} [4]. Although in principle {epsilon}{prime}/{epsilon} does not depend directly on m{sub s} in practice it has been an input in current phenomenological analyses. This dependence arises because the matrix elements of the gluonic, <Q{sub 6}>{sub 0}, and electroweak, <Q{sub 8}>{sub 2}, penguin operators are of the form <{pi}{pi}{vert_bar}Q{sub i}{vert_bar}K> and final state interactions make them notoriously …
Date: August 25, 1999
Creator: Ryan, Sinead
Object Type: Article
System: The UNT Digital Library
Tests of QCD using Heavy Flavors in e+e-->Z0 at SLD (open access)

Tests of QCD using Heavy Flavors in e+e-->Z0 at SLD

We present preliminary results on three SLD analyses: the gluon energy spectrum in 3-jet b{bar b}g events, the rate of g {r_arrow} b{bar b}, and the b fragmentation function in Z{sup 0} decays. The gluon energy spectrum, measured over the full kinematic range, is compared with perturbative QCD predictions. We set new 95% C.L. limits on the anomalous chromomagnetic coupling of the b quark: {minus}0.09 < {kappa} < 0.06. g{sub b{bar b}} is measured to be (3.07 {+-} 0.71 (stat) {+-} 0.66 (syst)) x 10{sup {minus}3}. The inclusive B hadron energy distribution is measured for the first time over the full kinematic range, using a novel B hadron energy reconstruction technique. Several models of b fragmentation including JETSET + Peterson are excluded by the data. The average scaled B hadron energy of the weakly decaying B hadron is measured to be x{sub B} = 0.713 {+-} 0.005 (stat) {+-} 0.007 (syst) {+-} 0.002 (model). All three measurements take advantage of the small and stable SLC interaction point as well as the excellent vertexing and tracking capabilities of the upgraded CCD-pixel vertex detector.
Date: May 25, 1999
Creator: Dong, Danning
Object Type: Report
System: The UNT Digital Library
Swing-Free Cranes via Input Shaping of Operator Commands (open access)

Swing-Free Cranes via Input Shaping of Operator Commands

This paper presents an open-loop control method for suppressing payload oscillation or swing caused by operator commanded maneuvers in rotary boom cranes and the method is experimentally verified on a one-sixteenth scale model of a Hagglunds shipboard crane. The crane configuration consists of a payload mass that swings like a spherical pendulum on the end of a lift-line which is attached to a boom capable of hub rotation (slewing) and elevation (luffing). Positioning of the payload is accomplished through the hub and boom angles and the load-line length. Since the configuration of the crane affects the excitation and response of the payload, the swing control scheme must account for the varying geometry of the system. Adaptive forward path command filters are employed to remove components of the command signal which induce payload swing.
Date: August 25, 1999
Creator: Groom, Kenneth N.; Parker, Gordon G.; Robinett, Rush D. & Leban, Frank
Object Type: Article
System: The UNT Digital Library
Imaging shocked sapphire at 200-460 KBAR: the effect of crystal orientation on optical emission (open access)

Imaging shocked sapphire at 200-460 KBAR: the effect of crystal orientation on optical emission

We have taken 12--50 ns exposure duration images of 200--460 kbar shock loaded, single crystal sapphire (Al{sub 2}O{sub 3}) windows of the c-cut (0001), r-cut (1,-1,0,2) and a-cut (1,1,-2,0) orientations. We find that the spectra of the emission are broad and relatively featureless, extending at least from 760 to 280 nm. Images of this emission at the lower end of the stress range (200--220 kbar) show that it is spatially very heterogeneous, coming from a few seemingly-randomly distributed locations within the crystal. This emission heterogeneity becomes more fine-grained with increasing shock stress. Finally, the r-cut orientation produces significantly less emission than the other two orientations at the same stress.
Date: August 25, 1999
Creator: Hare, D E; Holmes, N C & Webb, D J
Object Type: Article
System: The UNT Digital Library