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High-voltage-compatible, fully depleted CCDs

Description: We describe charge-coupled device (CCD) developmentactivities at the Lawrence Berkeley National Laboratory (LBNL).Back-illuminated CCDs fabricated on 200-300 mu m thick, fully depleted,high-resistivity silicon substrates are produced in partnership with acommercial CCD foundry.The CCDs are fully depleted by the application ofa substrate bias voltage. Spatial resolution considerations requireoperation of thick, fully depleted CCDs at high substrate bias voltages.We have developed CCDs that are compatible with substrate bias voltagesof at least 200V. This improves spatial resolution for a given thickness,and allows for full depletion of thicker CCDs than previously considered.We have demonstrated full depletion of 650-675 mu m thick CCDs, withpotential applications in direct x-ray detection. In this work we discussthe issues related to high-voltage operation of fully depleted CCDs, aswell as experimental results on high-voltage-compatible CCDs.
Date: May 15, 2006
Creator: Holland, Stephen E.; Bebek, Chris J.; Dawson, Kyle S.; Emes, JohnE.; Fabricius, Max H.; Fairfield, Jessaym A. et al.
Partner: UNT Libraries Government Documents Department

Technical Report on DOE project: X-ray physics of materials (proposal No.Z817)

Description: The SRI-CAT was able to order the construction of the First Optics Enclosure, the second enclosure housing the monochromator and the first user station, and various motors, controllers, and electronics for the control of the hard x-ray beamline components.
Date: January 1, 2001
Creator: Colella, Roberto & Durbin, Stephen
Partner: UNT Libraries Government Documents Department

The utility of diamond sensors for space flight

Description: Los Alamos National Laboratory has developed diamond sensors with interdigitated electrodes that operate in a photoconducting mode. The specific application for this work was for the Department of Energy`s instruments flown on the Global Positioning System satellites. Sensors have been fabricated and tested for their response to low-energy x-rays. These sensors can be operated to extremely high volumetric radiation doses. We find that the sensors are extremely useful for situations where the surface radiation dose is not excessive, but that this limit is exceeded for the GPS orbit. It is possible that further studies and special detector arrangements or auxiliary heating of the sensor may push this limit to higher values.
Date: March 1996
Creator: Higbie, P. R.; Han, S. S. & Wagner, R. S.
Partner: UNT Libraries Government Documents Department

New mechanism for lightning initiation

Description: This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). To distinguish radio-frequency (rf) signals generated by lightning from the electromagnetic pulse produced by a nuclear explosion, it is necessary to understand the fundamental nature of thunderstorm discharges. The recent debate surrounding the origin of transionospheric pulse pairs (TIPPs) detected by the BLACKBEARD experiment aboard the ALEXIS satellite illustrates this point. We have argued that TIPP events could originate from the upward propagating discharges recently identified by optical images taken from the ground, from airplanes, and from the space shuttle. In addition, the Gamma Ray Observatory (GRO) measurements of x-ray bursts originating from thunderstorms are almost certainly associated with these upward propagating discharges. When taken together, these three measurements point directly to the runaway electron mechanism as the source of the upward discharges. The primary goal of this research effort was to identify the specific role played by the runaway-air-breakdown mechanism in the general area of thunderstorm electricity and in so doing develop lightning models that predict the optical, rf, and x-ray emissions that are observable from space.
Date: October 1, 1996
Creator: Roussel-Dupre, R.; Buchwald, M. & Gurevich, A.
Partner: UNT Libraries Government Documents Department

CT multiscan: Using small area detectors to image large dense components

Description: The small size and dynamic range of the best two-dimensional X-Ray detectors are impediments in the use of three-dimensional X-Ray computed tomography (3D-XRCT) for 100% inspection of large ceramic components. The most common industrial 3D-XRCT systems use a ``rotate-only`` geometry in which the X-Ray source and the area detector remain stationary while the component placed between them is rotated through 360{degrees}. This configuration offes the highest inspection speed and the best utilization of X-Ray dose, but requires that the component be small enough to fit within the X-Ray/detector ``cone.`` Also, if the object is very dense, the ratio of an unattenuated X-Ray signal to that through the longest path in the component may exceed the dynamic range of the detector. To some extent, both of these disadvantages can be overcome by using ``Multi-scan CT,`` i.e. scanning small overlapping regions of a large component separately while maximizing the X-Ray dose to each. The overlapping scans can then be combined seamlessly into a single scan with optimal contrast.
Date: November 1, 1994
Creator: Sivers, E.A.; Ellingson, W.A.; Snyder, S.A. & Holloway, D.A.
Partner: UNT Libraries Government Documents Department

PIN diode array x-ray imaging. Final Technical report

Description: We have completed constructing an x-ray camera based on a solid state imaging device and have obtained images of Omega laser targets. A Si PIN diode array is used. Objective of this project is to investigate the use of a PIN diode array readout device for obtaining images of 1-20 keV x-ray emission from laser targets. The PIN array detector was successfully used for obtaining hard x-ray images in the high powered laser environment and real time images of the x-ray emission from laser targets.
Date: September 1, 1996
Creator: Jernigan, J.G.
Partner: UNT Libraries Government Documents Department

Monte Carlo Simulations of High-speed, Time-gated MCP-based X-ray Detectors: Saturation Effects in DC and Pulsed Modes and Detector Dynamic Range

Description: We present here results of continued efforts to understand the performance of microchannel plate (MCP)–based, high-speed, gated, x-ray detectors. This work involves the continued improvement of a Monte Carlo simulation code to describe MCP performance coupled with experimental efforts to better characterize such detectors. Our goal is a quantitative description of MCP saturation behavior in both static and pulsed modes. We have developed a new model of charge buildup on the walls of the MCP channels and measured its effect on MCP gain. The results are compared to experimental data obtained with a short-pulse, high-intensity ultraviolet laser; these results clearly demonstrate MCP saturation behavior in both DC and pulsed modes. The simulations compare favorably to the experimental results. The dynamic range of the detectors in pulsed operation is of particular interest when fielding an MCP–based camera. By adjusting the laser flux we study the linear range of the camera. These results, too, are compared to our simulations.
Date: October 31, 2008
Creator: Craig Kruschwitz, Ming Wu, Ken Moy, Greg Rochau
Partner: UNT Libraries Government Documents Department

Monte Carlo Simulations of High-Speed, Time-Gated MCP-based X-ray Detectors: Saturation Effects in DC Pulsed Modes and Detector Dynamic Range

Description: We present here results of continued efforts to understand the performance of microchannel plate (MCP)–based, high-speed, gated, x-ray detectors. This work involves the continued improvement of a Monte Carlo simulation code to describe MCP performance coupled with experimental efforts to better characterize such detectors. Our goal is a quantitative description of MCP saturation behavior in both static and pulsed modes. A new model of charge buildup on the walls of the MCP channels is briefly described. The simulation results agree favorably with experimental data obtained with a short-pulse, high-intensity ultraviolet (UV) laser. These results indicate that a weak saturation can change the exponent of gain with voltage and that a strong saturation lead to a gain plateau. These results also demonstrate that the dynamic range of an MCP in pulsed mode has a value of between 10^2 and 10^3.
Date: May 30, 2008
Creator: Craig Kruschwitz, Ming Wu, Ken Moy, Greg Rochau
Partner: UNT Libraries Government Documents Department

Achromatically filtered diamond photoconductive detectors for high power soft x-ray flux measurements

Description: A 1 mm square diamond photoconductive detector (PCD) has been installed on the LLNL Nova laser system, for use as a broad band soft x-ray power diagnostic. The PCD is installed behind an array of pinholes, which cast multiple, overlapping images of the source onto the diamond. This allows reduction of the x-ray intensity, to avoid saturation problems, while avoiding the spectral dependency of thin film filters. The diode current is read out on a 5 GHz bandwidth scope. The system is calibrated by comparison to an absolutely calibrated array of filtered vacuum x-ray photodiodes (XRD` s) (``dante``). The time response of the PCD and its bias electronics have been characterized using the 5th harmonic (210 nm) of a short pulse (< 1 ps) Ti:sapphire laser. The data show a fast rise, limited by the 5 GHz scope bandwidth, and a slower fall off, characterized by an RC time of order 200 ps.
Date: June 2, 1998
Creator: Turner, R. E.
Partner: UNT Libraries Government Documents Department

Industrial x-ray fluorescence analysis new applications and challenges for cryogenic detectors

Description: Cryogenic, high-resolution X-ray detectors have potential applications in industrial X-ray fluorescence (XRF) analysis. We discuss various XRF analysis techniques currently used in the semiconductor industry, problems encountered due to limitations of current detectors and the potential benefits of using cryogenic detectors in these applications. We give examples of demonstration experiments, compare the performance of current conventional and cryogenic X-ray spectrometers and present an outlook.
Date: August 1, 1997
Creator: Frank, M.
Partner: UNT Libraries Government Documents Department

Silicon photodiode characterization from 1 eV to 10 keV

Description: Silicon photodiodes offer a number of advantages over conventional photocathode type soft x-ray detectors in pulsed power experiments. These include a nominally flat response, insensitivity to surface contamination, low voltage biasing requirements, sensitivity to low energy photons, excellent detector to detector response reproducibility, and ability to operate in poor vacuum or gas backfilled experiments. Silicon photodiodes available from International Radiation Detectors (IRD), Torrance, California have been characterized for absolute photon response from 1 eV to 10 keV photon energy, time response, and signal saturation levels. The authors have assembled individually filtered photodiodes into an array designated the XUV-7. The XUV-7 provides seven photodiodes in a vacuum leak tight, electrically isolated, low noise, high bandwidth, x-ray filtered assembly in a compact package with a 3.7 cm outside diameter. In addition they have assembled the diodes in other custom configurations as detectors for spectrometers. Their calibration measurements show factor of ten deviations from the silicon photodiode theoretical flat response due to diode sensitivity outside the center `sensitive area`. Detector response reproducibility between diodes appears to be better than 5%. Time response measurements show a 10-90% rise time of about 0.1 nanoseconds and a fall time of about 0.5 nanoseconds. Silicon photodiodes have proven to be a versatile and useful complement to the standard photocathode detectors for soft x-ray measurement and are very competitive with diamond for a number of applications.
Date: October 1, 1997
Creator: Idzorek, G.C. & Bartlett, R.J.
Partner: UNT Libraries Government Documents Department

Wire number doubling in plasma-shell regime increases z-accelerator x-ray power

Description: Doubling the number of tungsten wires from 120 to 240, keeping the mass fixed, increased the radiated x-ray power relative to the electrical power at the insulator stack of the z accelerator by (40{+-}20)% for 8.75- and 20-mm-radii z-pinch wire arrays. Radiation-magneto-hydrodynamic calculations suggest that the arrays were operating in the {open_quotes}plasma shell{close_quotes} regime, where the plasmas generated by the individual wires merge prior to the inward implosion of the entire array.
Date: November 1, 1997
Creator: Sanford, T.W.L.; Spielman, R.B. & Chandler, G.A.
Partner: UNT Libraries Government Documents Department

Fielding and calibration issues for diamond photoconducting detectors

Description: Diamond photoconducting detectors are routinely fielded as soft x-ray diagnostics on Sandia`s Saturn facility. We have developed an improved detector mount that provides a 200-ps time response, is easily cleanable, and is very rugged. In addition, we have developed a new, fast insertion unit to apply bias voltage to the detectors. Absolute calibration of the PCDs is carried out either at the Brookhaven National Synchrotron Light Source or on Sandia`s laser calibration facility. We are now fielding diamond elements that have the dimensions 1x3x0.5 nun and 1x1xO.5 mm. We are neutron damaging some of the 1x1xO.5-mm detectors to reduce their sensitivity. We can tailor PCD sensitivity by adjusting element size and neutron damage level.
Date: December 1, 1996
Creator: Spielman, R.B.; Ruggles, L.E.; Pepping, R.E.; Breeze, S.F.; McGurn, J.S. & Struve, K.W.
Partner: UNT Libraries Government Documents Department

Design and testing of a compact X-ray diode. 1998 summer research program for high school juniors at the University of Rochester`s Laboratory for Laser Energetics: Student research reports

Description: Omega, the University of Rochester`s high powered laser dedicated to fusion research gives off x-rays with different energy levels. Measuring the number of x-rays and the energy of each is important in understanding what happens in the target chamber when Omega is fired. Existing x-ray detectors are expensive, big, and cumbersome. Imaging detectors such as x-ray pinhole cameras which record onto film, x-ray framing cameras which make videos, and most often, x-ray streak cameras which measure time dependences of x-rays. They require a lot of maintenance and are difficult to keep operational. Lawrence Livermore National Laboratory has developed the Dante Diode. The Dante diode array on Omega functions as a group of 12 diodes which take up a 24 inch port in the target chamber, making it space-consuming and difficult to move for alternate views. In designing a new detector, space was the main issue. The smallest possible functional diode, without losing accuracy was desired. Since the laser pulse only lasts a few nanoseconds it is important that the x-ray detector have a response time of a few tenths of a nanosecond. Other criteria include that it be easy to use for measuring the energy and number of x-ray photons and that cost be kept down. This report discusses the design process and testing of the new diode.
Date: March 1, 1999
Creator: Stern, A.
Partner: UNT Libraries Government Documents Department

Filtered x-ray diode diagnostics fielded on the Z-accelerator for source power measurements

Description: Filtered x-ray diode, (XRD), detectors are used as primary radiation flux diagnostics on Sandia`s Z-accelerator, which generates nominally a 200 TW, 2 MJ, x-ray pulse. Given such flux levels and XRD sensitivities the detectors are being fielded 23 meters from the source. The standard diagnostic setup and sensitivities are discussed. Vitreous carbon photocathodes are being used to reduce the effect of hydrocarbon contamination present in the Z-machine vacuum system. Nevertheless pre- and post-calibration data taken indicate spectrally dependent changes in the sensitivity of these detectors by up to factors up to 2 or 3.
Date: June 2, 1998
Creator: Chandler, G.A.; Deeney, C. & Cuneo, M.
Partner: UNT Libraries Government Documents Department

Non-equilibrium dynamics in superconducting tunnel junction detectors

Description: Superconducting tunnel junctions have the potential to serve as high-resolution, high-efficiency x-ray detectors for astrophysical and industrial applications. When irradiated by X rays, each X ray excites over 10{sup 6} charge carriers which cause the detector to generate a pulse of current. We present an analysis of pulse shapes from detectors we have constructed and operated. We fit the decay of the current pulse to a simple model that considers two classes of carrier loss. One model considers only the normal recombination of the charge carriers with themselves, the other included additional losses due to recombination sites in the within the detector medium. We found that both mechanisms most be taken into account. We also found a small variation in pulse shape depending on which layer of the tunnel junction absorbed the X ray. We expect that this analysis will be a useful tool in comparing different detector designs and operating conditions.
Date: December 9, 1994
Creator: Hiller, L. J.; Labov, S. E.; Mears, C. A.; Frank, M.; Bello, A. F. & Barfknecht, A. T.
Partner: UNT Libraries Government Documents Department

Gated monochromatic x-ray imager

Description: We have recently developed a gated monochromatic x-ray imaging diagnostic for the national Inertial-Confinement Fusion (ICF) program. This new imaging system will be one of the primary diagnostics to be utilized on University of Rochester`s Omega laser fusion facility. The new diagnostic is based upon a Kirkpatrick-Baez (KB) microscope dispersed by diffraction crystals, as first described by Marshall and Su. The dispersed images are gated by four individual proximity focused microchannel plates and recorded on film. Spectral coverage is tunable up to 8 keV, spectral resolution has been measured at 20 eV, temporal resolution is 80 ps, and spatial resolution is better than 10 {mu}m.
Date: September 1, 1995
Creator: Oertel, J.A.; Archuleta, T. & Clark, L.
Partner: UNT Libraries Government Documents Department

Measurement of electron energy distribution from X-rays diagnostics - foil techniques used with the hard X-ray camera on PBX-M

Description: A half-screen foil technique is used with the Hard X-ray Camera on the PBX-M tokamak to determine the energy distribution of the suprathermal electrons generated during lower hybrid current drive. The ratio of perpendicular to parallel temperature of the suprathermal electrons is deduced from the anisotropy of the bremsstrahlung emission utilizing Abel inversion techniques. Results from lower hybrid current drive discharges are discussed.
Date: December 31, 1995
Creator: Goeler, S. von; Bell, R.; Bernabei, S.; Davis, W. & Ignat, D.
Partner: UNT Libraries Government Documents Department

Performance of MBE grown CdTe photoconductor arrays for hard x-ray detection

Description: Photoconductor linear array detectors for hard x-ray photon detection were fabricated using Molecular Beam Epitaxially (MBD) grown (111)B CdTe layers on (100) orientation Si substrates. Since the Si substrates used for the MBE growth are semiconducting, the CdTe epitaxial layers were removed from the substrates using chemical etching of Si and mounted on insulating ceramic substrates. Linear array detectors were then fabricated on the resulting CdTe layers. The response current uniformity of 64 element photoconductor array was measured at 300 K and 230 K. The ohmic contact to the highly resistive CdTe is excellent to provide the linear response to the x-ray photon counts. The response current was linearly increased in the energies from 7 to 19 KeV. Stability of the detectors are very satisfactory and they were tested for over an extended period of time without any noticeable degradations. The performance of the photoconductor was greatly improved when the detector was cooled by a thermoelectric cooler. Due to its reduced noise at these temperatures, the dynamic range of the detector response increases to nearly four decades at 230 K.
Date: July 1, 1995
Creator: Yoo, S.S.; Montano, P.A.; Rodricks, B.; Faurie, J.P. & Sivanathan, S.
Partner: UNT Libraries Government Documents Department

A High-Speed Detector System for X-ray Fluorescence Microprobes.

Description: We have developed a high-speed system for collecting x-ray fluorescence microprobe data, based on ASICs developed at BNL and high-speed processors developed by CSIRO. The system can collect fluorescence data in a continuous raster scan mode, and present elemental images in real time using Ryan's Dynamic Analysis algorithm. We will present results from a 32-element prototype array illustrating the concept. The final instrument will have 384 elements arranged in a square array around a central hole.
Date: October 29, 2006
Creator: Siddons,P.D.; Dragone, A.; De Geronimo, g.; Kuczewski, A.; Kuczewski, J. & O
Partner: UNT Libraries Government Documents Department

Electron Energy Distributions at Relativistic Shock Sites: Observational Constraints from the Cygnus A Hotspots

Description: We report new detections of the hotspots in Cygnus A at 4.5 and 8.0 microns with the Spitzer Space Telescope. Together with detailed published radio observations and synchrotron self-Compton modeling of previous X-ray detections, we reconstruct the underlying electron energy spectra of the two brightest hotspots (A and D). The low-energy portion of the electron distributions have flat power-law slopes (s {approx} 1.5) up to the break energy which corresponds almost exactly to the mass ratio between protons and electrons; we argue that these features are most likely intrinsic rather than due to absorption effects. Beyond the break, the electron spectra continue to higher energies with very steep slopes s&gt;3. Thus, there is no evidence for the 'canonical' s=2 slope expected in 1st order Fermi-type shocks within the whole observable electron energy range. We discuss the significance of these observations and the insight offered into high-energy particle acceleration processes in mildly relativistic shocks.
Date: October 15, 2007
Creator: Cheung, C.C.Teddy; Stawarz, L.; Harris, D.E. & Ostrowski, M.
Partner: UNT Libraries Government Documents Department