285 Matching Results

Search Results

Advanced search parameters have been applied.

Wound-counting systems for the measurement and isolation of plutonium and americium

Description: Described are newly developed wound-counting systems which provide a high sensitivity for the detection and quantification of X-ray emissions from wounds contaminated with plutonium or americium; and for the location of deposition of radioactive material within a wound, as required by surgery. The systems are used in the medical facility at the Rocky Flats Plant. Work efforts over the past 20 years have concentrated on improving detection limits by reducing and stabilizing the background counting rate. The developments over the last three years have resulted in a family of instruments with excellent operational characteristics, complementary package design, easy maintenance, and reliable operation. A 13-stage photomultiplier tube system is used.
Date: April 16, 1977
Creator: Tyree, W. H.; Bell, T. H.; Lane, R. L. & Macaluso, J. B.
Partner: UNT Libraries Government Documents Department

Entrance windows in germanium low-energy x-ray detectors

Description: It was found experimentally that high-purity Ge low-energy X-ray detectors have a relatively thick entrance window which renders them practically useless below approximately 2.3 keV. A simple X-ray fluorescence experiment establishes clearly that the window is physically in the Ge material itself. Experiments with detectors made from different Ge crystals, and with Schottky barrier contacts of different metals indicate that the effect is due to a basic property of the transport of electrons near a surface. Theoretical considerations and a Monte Carlo calculation show that the window is caused by the escape of warm electrons which are the end product of a photo event. The mean free path of the electrons becomes longer as they lose energy by optical phonon collisions and they can be trapped at the surface before they are picked up by the electric field.
Date: October 1, 1976
Creator: Llacer, J.; Haller, E. E. & Cordi, R. C.
Partner: UNT Libraries Government Documents Department

Radioconductivity of insulators: their potential for ionographic imaging

Description: Measurements of the radioconductivity and thermocurrent properties of relatively pure insulating solids indicate charge collection yields which compare favorably to materials presently used for ionography. The radioconductivity varies with temperature giving rise to temperature windows of feasible use.
Date: January 1, 1975
Creator: DeWerd, L. A. & Moran, P. R.
Partner: UNT Libraries Government Documents Department

High-intensity, subkilovolt x-ray calibration facility. [Cockroft--Walton accelerator facility]

Description: A high-intensity subkilovolt x-ray calibration source utilizing proton-induced inner-shell atomic fluorescence of low-Z elements is described. The high photon yields and low bremsstrahlung background associated with this phenomenon are ideally suited to provide intense, nearly monoenergetic x-ray beams. The proton accelerator is a 3 mA, 300 kV Cockroft-Walton using a conventional rf hydrogen ion source. Seven remotely-selectable targets capable of heat dissipation of 5 kW/cm/sup 2/ are used to provide characteristic x-rays with energies between 100 and 1000 eV. Source strengths are of the order of 10/sup 13/ to 10/sup 14/ photons/sec. Methods of reducing spectral contamination due to hydrocarbon build-up on the target are discussed. Typical x-ray spectra (Cu-L, C-K and B-K) are shown.
Date: May 6, 1976
Creator: Kuckuck, R. W.; Gaines, J. L. & Ernst, R. D.
Partner: UNT Libraries Government Documents Department

Response of ultrafast scintillators

Description: Measurements of the properties of subnanosecond, quenched NE111 plastic scintillators with various concentrations of acetophenone and benzophenone are presented. These quenching agents have been found to very significantly decrease the NE111 decay time. Measurements are made using UV and laser produced x-ray radiations. The scintillations are detected using a visible streak camera with 10 ps resolution. The paper will include measurements of: (1) 10-90 percent rise time, (2) FWHM, (3) decay time, (4) relative scintillator efficiencies, (5) amplitudes vs. time measurements of the long decay component. All temporal measurements are obtained from a gold cathode ultrafast x-ray streak camera, and the detailed x-ray energy spectrum above 1 keV is also measured using an array of x-ray PIN diodes equipped with the appropriate K-edge filters. Details of the experimental measurements are discussed and anticipated applications are included.
Date: January 1, 1976
Creator: Cheng, J. C.; Lerche, R. A.; Tirsell, K. G. & Tripp, G. R.
Partner: UNT Libraries Government Documents Department

Soft x-ray imaging with a CCD area array

Description: To determine the feasibility of recovering data actively from x-ray imaging instruments used in the Lawrence Livermore Laboratory Laser Fusion Program, a commercial silicon video sensor was used to detect patterns of soft x-rays (1-8 keV). The sensor is a 2-dimensional frame transfer charge coupled device (CCD), modified to allow direct access of x-rays to the sensitive silicon. The x-ray sensitivity, linearity, and dynamic range of the CCD are discussed.
Date: October 4, 1976
Creator: Koppel, L. N. & Eckels, J. D.
Partner: UNT Libraries Government Documents Department

X-ray detector calibrations in the 183- to 932-eV energy range

Description: The absolute sensitivities of several different types of x-ray detectors were measured between 183 eV and 932 eV. The photons in this energy range were produced by bombarding thin, water-cooled, metal targets with protons from a Cockcroft-Walton ion accelerator. The detectors measured included a silicon-semiconductor detector, two photoelectric-diode detectors employing aluminum and gold photocathodes, and three detectors incorporating plastic scintillators and photodiodes.
Date: October 15, 1976
Creator: Gaines, J. L. & Ernst, R. D.
Partner: UNT Libraries Government Documents Department

X-ray detector calibrations in the 280-eV to 100-keV energy range

Description: The absolute sensitivity for several different types of radiation detectors has been measured using x-rays in the energy range of 280 eV to 100 keV. The photons in this energy range are produced using three separate x-ray-generating facilities. The detectors include a silicon semiconductor, two photoelectric diode detectors employing aluminum and gold photocathodes, and three detectors incorporating plastic scintillators and photodiodes. The plastic scintillators were MEL-150C, Pilot B, and NE102.
Date: April 21, 1976
Creator: Gaines, J. L.; Kuckuck, R. W. & Ernst, R. D.
Partner: UNT Libraries Government Documents Department

NOVEL INTEGRATING SOLID STATE DETECTOR WITH SEGMENTATION FOR SCANNING TRANSMISSION SOFT X-RAY MICROSCOPY.

Description: An integrating solid state detector with segmentation has been developed that addresses the needs in scanning transmission x-ray microscopy below 1 keV photon energy. The detector is not cooled and can be operated without an entrance window which leads to a total photon detection efficiency close to 100%. The chosen segmentation with 8 independent segments is matched to the geometry of the STXM to maximize image mode flexibility. In the bright field configuration for 1 ms integration time and 520 eV x-rays the rms noise is 8 photons per integration.
Date: July 29, 2001
Creator: FESER,M. JACOBSEN,C. REHAK,P. DE GERONIMO,G. HOLL,P. STUDER,L.
Partner: UNT Libraries Government Documents Department

High-purity germanium detection system for the in vivo measurement of americium and plutonium

Description: A high-purity germanium (HPGe) array, photon-counting system has been developed for the Rocky Flats Plant Body-Counter Medical Facility. The newly improved system provides exceptional resolutions of low-energy X-ray and gamma-ray spectra associated with the in vivo deposition of plutonium and americium. Described are the operational parameters of the system and some qualitative results illustrating detector performance for the photon emissions produced from the decay of plutonium and americium between energy ranges from 10 to 100 kiloelectron volts. Since large amounts of data are easily generated with the system, data storage, analysis, and computer software developments continue to be an essential ingredient for processing spectral data obtained from the detectors. Absence of quantitative data is intentional. The primary concern of the study was to evaluate the effects of the various physical and electronic operational parameters before adding those related entirely to a human subject.
Date: September 8, 1976
Creator: Tyree, W. H.; Falk, R. B.; Wood, C. B. & Liskey, R. W.
Partner: UNT Libraries Government Documents Department

A survey of nuclear-explosive prompt diagnostics

Description: Nuclear-explosive prompt diagnostics techniques and equipment are surveyed. These techniques and equipment have been developed to answer nuclear-explosive performance questions. The techniques and equipment must be selective in radiation sensitivity, linear in calibration, fast, insensitive to strong signals, wide in dynamic range, and reliable. Diagnostic techniques and equipment measure neutron, gamma-ray, and x-ray emissions, as well as aid in the determination of the physical location of the production of radiation through imaging. The high cost of nuclear experiments will continue to encourage the development of sophisticated techniques to gain as much information as possible from each experiment.
Date: March 25, 1986
Creator: Ebert, P. J.
Partner: UNT Libraries Government Documents Department

RadSensor: Xray Detection by Direct Modulation of an Optical Probe Beam

Description: We present a new x-ray detection technique based on optical measurement of the effects of x-ray absorption and electron hole pair creation in a direct band-gap semiconductor. The electron-hole pairs create a frequency dependent shift in optical refractive index and absorption. This is sensed by simultaneously directing an optical carrier beam through the same volume of semiconducting medium that has experienced an xray induced modulation in the electron-hole population. If the operating wavelength of the optical carrier beam is chosen to be close to the semiconductor band-edge, the optical carrier will be modulated significantly in phase and amplitude. This approach should be simultaneously capable of very high sensitivity and excellent temporal response, even in the difficult high-energy xray regime. At xray photon energies near 10 keV and higher, we believe that sub-picosecond temporal responses are possible with near single xray photon sensitivity. The approach also allows for the convenient and EMI robust transport of high-bandwidth information via fiber optics. Furthermore, the technology can be scaled to imaging applications. The basic physics of the detector, implementation considerations, and preliminary experimental data are presented and discussed.
Date: August 1, 2003
Creator: Lowry, M E; Bennett, C V; Vernon, S P; Bond, T; Welty, R; Behymer, E et al.
Partner: UNT Libraries Government Documents Department

Sub-nanosecond plastic scintillator time response studies using laser produced x-ray pulsed excitation

Description: The light emission time response of quenched NElll plastic scintillators has been measured using a streak camera (20 ps resolution) and 100 to 180 ps, 1.06 ..mu..m, laser-produced, pulsed, low energy x-ray excitation. Each light output pulse was obtained by deconvolution from the film data using the x-ray temporal response measured with an x-ray sensitive streak camera (10 ps resolution). Time response parameters are presented for benzophenone and acetophenone, quenching agents which most effectively reduce the decay time of the singlet component. Full width-half-maximums less than or equal to 260 ps were observed for NElll samples quenched with greater than or equal to 2 percent benzophenone. Results are given for unquenched samples consisting of different concentrations of butyl-PBD in PVT and for the phosphor ZnO doped with Ga.
Date: November 17, 1976
Creator: Tirsell, K. G.; Tripp, G. R.; Lent, E. M.; Lerche, R. A.; Cheng, J. C.; Hocker, L. et al.
Partner: UNT Libraries Government Documents Department

X-ray studies of microstructures in semiconductors and superconducting materials

Description: Objective is to use synchrotron x rays to probe short-range-order (SRO) structures in these materials. These SRO structures, with a scale of a few angstroms, include these around interfaces in multilayers, strain and local environs around impurity or constituent atoms, as well as lattice mismatch, intermixing of atoms across interfaces, annealing, etc. A new soft x-ray detector has been built and was used to measure x-ray fluorescence from O and F in bulk materials. The research on microstructure in both semiconductors and high-T{sub c} superconductors is being continued with emphasis on multilayer materials. X-ray absorption fine structure spectroscopy is being used in many of the studies, as is grazing incidence x-ray fluorescence and scattering. Total electron yield is used with fluorescence to probe surfaces and interfaces. Effects of doping on superconducting properties, especially these related to microstructures around impurities or constituent atoms, were studied. Resulting papers are listed.
Date: April 1, 1992
Creator: Kao, Y. H.
Partner: UNT Libraries Government Documents Department

Experimental applications for the MARK-1 and MARK-1A pulsed ionizing radiation detection systems. Volume 3

Description: This report is the third volume in a three volume set describing the MARK series of pulsed ionizing radiation detection systems. This volume describes the MARK-1A detection system, compares it with the MARK-1 system, and describes the experimental testing of the detection systems. Volume 1 of this set presents the technical specifications for the MARK-1 detection system. Volume 2 is an operations manual specifically for the MARK-1 system, but it generally applies to the MARK-1A system as well. These detection systems operate remotely and detect photon radiation from a single or a multiple pulsed source. They contain multiple detector (eight in the MARK-1 and ten in the MARK-1A) for determination of does and incident photon effective energy. The multiple detector arrangement, having different detector sizes and shield thicknesses, provides the capability of determining the effective photon energy of the radiation spectrum. Dose measurements using these units are consistent with TLD measurements. The detection range is from 3 nanorads to 90 microrads per source burst; the response is linear over that range. Three units were built and are ready for field deployment.
Date: December 1, 1993
Creator: Harker, Y. D.; Lawrence, R. S.; Yoon, W. Y. & Lones, J. L.
Partner: UNT Libraries Government Documents Department

A space fiber-optic x-ray burst detector

Description: We describe a novel, lightweight x-ray burst detector that can be embedded in a satellite structure, thus forming a ``smart skin,`` which has minimal impact on the host satellite. The design is based on two types of optical fibers coupled to photodiodes. The first is a scintillating fiber, which gives a fast signal for timing. The second is a germanium-doped silica fiber, which darkens for a few milliseconds when irradiated with a burst of x rays. The resulting slow signal is used to discriminate against electrostatic discharges. The coincidence of a fast signal from the scintillating fiber with a slow signal from the darkening fiber is the signature of an x-ray burst. The response is linear at low doses and becomes nonlinear at high doses. We have two techniques to test the instrument in a space experiment scheduled for 1994. First, a small, space-qualified flash x-ray unit can illuminate the fibers. Second, we can detect space background radiation. The cumulative dose will be monitored by RADFET dosimeters. Future work on embedding the fibers and the electronics as Application Specific Integrated Circuits (ASICs) in the spacecraft skin could lead to use of these detectors on many satellites.
Date: October 1, 1993
Creator: Moss, C. E.; Casperson, D. E.; Echave, M. A.; Edwards, B. C.; Miller, J. R.; Saylor, W. W. et al.
Partner: UNT Libraries Government Documents Department

Spectral distribution of the two-photon decay of He-like krypton

Description: We report Progress on a measurement of the spectral distribution of photons from the two-photon decay of the 2{sup 1}S{sub 0} level in heliumlike krypton. A measurement of the exact shape of the continuum singles spectrum of the two-photon decay in heliumlike ions provides a sensitive probe of the calculation of the transition probability. In our experiment a beam of Kr{sup 34+} ions is excited using a thin carbon foil and the subsequent decays are observed in an array of four x-ray detectors.
Date: October 1, 1994
Creator: Ali, R.; Ahmad, I. & Berry, H. G.
Partner: UNT Libraries Government Documents Department

A VXI-based high speed x-ray CCD detector

Description: For time-resolved x-ray scattering, one ideally wants a high speed detector that also is capable of giving position sensitive information. Charge Coupled Devices (CCDS) have been used successfully as x-ray detectors. Unfortunately, they are inherently slow because of the serial readout EEV has developed a CCD that has eight channels of parallel readout, thus increasing the speed eight fold. Using state-of-the-art VXI electronics, we have developed a readout system that could read the entire array in 2.5 ms using a 20-MHz readout clock. For testing and characterization the device was clocked at a significantly slower speed of 30 kHz. The data is preamplified and all eight channels of output are simultaneously digitized to 12 bits and stored in buffer memory. The system is controlled by a 486-based PC through an MXI bus and VXI controller using commercially available software. The system is also capable of real-time image display and manipulation.
Date: October 1, 1993
Creator: Huang, Qiang; Hopf, R. & Rodricks, B.
Partner: UNT Libraries Government Documents Department

A large area detector for x-ray applications

Description: A large area detector for x-ray synchrotron applications has been developed. The front end of this device consist of a scintillator coupled to a fiber-optic taper. The fiber-optic taper is comprised of 4 smaller (70 mm x 70 mm) tapers fused together in a square matrix giving an active area of 140 mm x 140 mm. Each taper has a demagnification of 5.5 resulting in four small ends that are 12 mm diagonally across. The small ends of each taper are coupled to four microchannel-plate-based image intensifiers. The output from each image intensifier is focused onto a Charge Coupled Device (CCD) detector. The four CCDs are read out in parallel and are independently controlled. The image intensifiers also act as fast (20 ns) electronic shutters. The system is capable of displaying images in real time. Additionally, with independent control on the readout of each row of data from the CCD, the system is capable of performing high speed imaging through novel readout manipulation.
Date: October 1, 1993
Creator: Rodricks, B.; Huang, Qiang; Hopf, R. & Wang, Kemei
Partner: UNT Libraries Government Documents Department

Supertrack Monte Carlo variance reduction experience for non-Boltzmann tallies

Description: This paper applies a recently developed variance reduction technique to the first-principles calculations of photon detector responses. This technique makes possible the direct comparison of pulse height calculations with measurements without the need for unfolding techniques. Comparisons are made between several experiments and the calculations to demonstrate the utility of the supertrack Monte Carlo technique for reproducing and interpreting experimental count rate spectra.
Date: October 1, 1994
Creator: Estes, G. P. & Booth, T. E.
Partner: UNT Libraries Government Documents Department

Neutron detector for fusion reaction-rate measurements

Description: We have developed a fast, sensitive neutron detector for recording the fusion reaction-rate history of inertial-confinement fusion (ICF) experiments. The detector is based on the fast rise-time of a commercial plastic scintillator (BC-422) and has a response < 25-ps FWHM. A thin piece of scintillator material acts as a neutron-to- light converter. A zoom lens images light from the scintillator surface to a high-speed (15 ps) optical streak camera for recording. The zoom lens allows the scintillator to be positioned between 1 and 50 cm from a target. The camera simulaneously records an optical fiducial pulse which allows the camera time base to be calibrated relative to the incident laser power. Bursts of x rays formed by focusing 20-ps, 2.5-TW laser pulses onto gold disk targets demonstrate the detector resolution to be < 25 ps. We have recorded burn histories for deuterium/tritium-filled targets producing as few as 3 {times} 10{sup 7} neutrons.
Date: September 3, 1993
Creator: Lerche, R. A.; Phillion, D. W. & Tietbohl, G. L.
Partner: UNT Libraries Government Documents Department

Gain uniformity, linearity, saturation and depletion in gated microchannel-plate x-ray framing cameras

Description: The pulsed characteristics of gated, stripline configuration microchannel-plate (MCP) detectors used in X-ray framing cameras deployed on laser plasma experiments worldwide are examined in greater detail. The detectors are calibrated using short (20 ps) and long (500 ps) pulse X-ray irradiation and 3--60 ps, deep UV (202 and 213 nm), spatially-smoothed laser irradiation. Two-dimensional unsaturated gain profiles show < 5% percent long-range transverse variations but up to 3 dB/cm drop in gain parallel to the pulse propagation direction. Up to 50% gain enhancements due to voltage reflection from the bends of a meander stripline geometry and from the ends of conventional straight striplines are also observed. Reproducible gate profiles are obtained with either picosecond X-ray or UV bursts and FWHM extracted with 3 picosecond accuracy. A novel single-shot method for measuring local gate propagation speeds using a tilted MCP is also demonstrated. Detailed output versus input studies indicate a linear dynamic range of 300. At higher irradiances, the gradual transition from linear behavior to hard saturation is gathered over a range of 10{sup 5} in irradiation and fitted using a discrete dynode model. Finally, a pump-probe experiment quantifying for the first time long-suspected gain depletion by strong localized irradiation was performed. The mechanism for the extra voltage and hence gain degradation is shown to be associated with intense MCP irradiation in the presence of the voltage pulse, at a fluence at least an order of magnitude above that necessary for saturation. Results obtained for both constant pump area and constant pump fluence are presented. The data are well modeled by calculating the instantaneous electrical energy loss due to the intense charge extraction at the pump site and then recalculating the gain downstream at the probe site given the pump-dependent degradation in voltage amplitude.
Date: July 20, 1994
Creator: Landen, O. L.; Bell, P. M.; Satariano, J. J.; Oertel, J. A. & Bradley, D. K.
Partner: UNT Libraries Government Documents Department

Characteristics of an ultrafast x-ray streak camera

Description: The detection and temporal dispersion of the x-rays using x-ray streak cameras has been limited to a resolution of 2 ps, primarily due to the transit time dispersion of the electrons between the photocathode and the acceleration grid. The transit time spread of the electrons traveling from the photocathode to the acceleration grid is inversely proportional to the accelerating field. By increasing the field by a factor of 7, we have minimized the effects of transit time dispersion in the photocathode/accelerating grid region and produce an x-ray streak camera with sub-picosecond temporal resolution ({approximately}900 fs). The streak camera has been calibrated using a Michelson interferometer and 100 fs, 400 nm laser light. Time resolved x-ray data is shown from an aluminum target heated at 10{sup 18} W/cm{sup 2} with a 100 fs, 400 nm laser .
Date: June 1, 1994
Creator: Shepherd, R.; Booth, R. & Price, D.
Partner: UNT Libraries Government Documents Department