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At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

Status of the Metrology Light Source

The Physikalisch-Technische Bundesanstalt (PTB), the German national metrology institute, has set up the low-energy electron storage ring Metrology Light Source (MLS) in close cooperation with the Helmholtz-Zentrum Berlin (HZB, formerly BESSY). This new storage ring has been in regular user operation since April 2008 and is dedicated to synchrotron-radiation-based metrology and technological developments in the far-IR/THz, IR, UV, VUV and EUV spectral range. The MLS has a double-bend-achromate lattice structure, injection is from a 105 MeV racetrack microtron. The electron energy can be ramped to any value from 105 MeV up to 630 MeV and the electron beam current covers the range from one stored electron (1 pA) up to 200 mA. The MLS is the first electron storage ring optimized for the generation of coherent synchrotron radiation, based on an electron bunch shortening mode. In this mode, MLS delivers coherent radiation in the far-IR/THz spectral range with enhanced intensity as compared to the normal mode of operation. Several beamlines are in operation or in construction, including one undulator beamline, bending magnet beamlines for the calibration of radiation sources and detectors and for reflectometry, an EUV metrology beamline and three IR/THz beamlines.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Terahertz free electron superradiation from mimicking surface plasmons-two electron beams interaction within a 3-mirror quasi-optical cavity

Interaction between mimicking surface plasmons and electron beams provides a good opportunity to develop terahertz (THz) radiation sources. In this paper, such an interaction in a special 3-mirror quasi-optical cavity is presented and explored. The 3-mirror quasi-optical cavity acts as a resonant tunable system, the resonance frequency of which can be tuned by adjusting the distance between mirrors. The study demonstrated THz free electron superradiation from the interaction of mimicking surface plasmons and two electron beams that formed a resonance within the structure, with the 3-mirror cavity enhancing the intensity of superradiation. Moreover, this system can work in the high-harmonic superradiation region with relatively high efficiency and low current density. This concept thus shows the application potential for electron-beam-driven terahertz sources.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Single Crystal Diamond Beam Position Monitors with Radiofrequency Electronic Readout

Over the energy range 5{approx}30 keV a suitably contacted, thin ({approx}100 {mu}m) diamond plate can be operated in situ as a continuous monitor of X-ray beam intensity and position as the diamond absorbs only a small percentage of the incident beam. Single crystal diamond is a completely homogeneous material showing fast (ns), spatially uniform signal response and negligible (<pA) leakage currents. Due to its unsurpassed thermal conductivity, it is the only semiconductor material that can be used in intense synchrotron white beams. We report on tests made at ESRF and DESY using diamond beam position monitors of simple quadrant electrode designs with metal contacts, operated using wideband electronic readout corresponding to the RF accelerator frequency. The instrumentation for these monitors must cover a large range of operating conditions: different beam sizes, fluxes, energies and time structure corresponding to the synchrotron fill patterns. Sophisticated new RF sampling electronics can satisfy most requirements: using a modified Libera Brilliance readout system, we measured the center of gravity position of a 25 {mu}m beam at the DORIS III F4 beam line at a rate of 130 Msample/s with narrowband filtering of a few MHz bandwidth. Digitally averaging the signal further provided a spatial resolution {approx}20 nm.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Site-Selective Determination of Magnetic Helices in BaTiCoFe{sub 10}O{sub 19} by Resonant Magnetic Scattering

Synchrotron radiation intensity measurements were made for single crystals of ferrimagnetic BaTiCoFe{sub 10}O{sub 19} at the BL-6C(3A) beamline of the Photon Factory. The resonant x-ray magnetic scattering (RXMS) method at the Fe K edge makes it possible to determine the magnetic crystal structure, having the magnetic helices for Fe ions in tetrahedral 4f{sub 1}, bipyramidal 2b, and octahedral 2a, 4f{sub 2} and 12k sites. Based on the information on x-ray magnetic circular dichroism (XMCD) and a resonant magnetic scattering factor f''{sub m} ( = 0.23) estimated from BaFe{sub 12}O{sub 19} at E = 7128.2 eV, the magnetic structures have been determined from an asymmetrical ratio {Delta}R (Y{sup +}-Y{sup -})/(Y{sup +}+Y{sup -}), where Y{sup +} and Y{sup -} are scattering intensities for left- and right-circular polarizations, respectively. Spin orientations were estimated in the least-squares procedure to minimize a residual factor of {Sigma}({Delta}R{sub obs}-{Delta}R{sub calc}){sup 2}. The canting angles estimated in this study are 180 deg., 19 deg., 118 deg., 180 deg. and 65 deg. for the magnetic moments of Fe ions in 4f{sub 1}, 2b, 2a, 4f{sub 2} and 12k sites, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Development of fast (sub-minute) micro-tomography

An x-ray fast micro-tomography system was developed at medical and imaging beamline BL20B2 in SPring-8. We attempted a 'continuous rotation method' whereby the sample keeps rotating in the beam during the measurement. The image acquisitions are synchronized with the trigger pulses branched from the stepper motor controller. An electron multiplier (EM)-CCD camera (C9100-02, 1000x1000 pixels, 30 fps, 8 {mu}m/pixel, Hamamatsu Photonics) and beam-monitor AA40P (Hamamatsu Photonics) were used as an image detector. The effective pixel size of the detector was 4.9 {mu}m/pixel and the spatial resolution was about 15 {mu}m. The total measurement time for 900 projections has been reduced to 36 s. The reconstruction time was also reduced using GPGPU and SSD system. Using these techniques, preliminary experiment for 4-D (time resolved 3-D) micro-imaging has also been performed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

X-ray Talbot-Lau interferometer for high-speed phase imaging and tomography using white synchrotron radiation

The Talbot interferometer using white synchrotron radiation has already been demonstrated for high-speed X-ray phase imaging and tomography as well as four-dimensional phase tomography for an observation of a dynamic specimen. In those previous experiments, the grating lines were oriented horizontally because the synchrotron radiation source size is large in the horizontal direction, and only the vertical spatial coherence satisfies the requirement for the operation of the Talbot interferometer given its distance from the source. For non-rigid samples, the horizontal axis of rotation causes unwanted motion of the sample due to gravity which results to artifact in the tomography reconstruction. For fluid samples, a vertical rotation axis is certainly necessary. While it is possible to orient the sample rotation axis perpendicular to the grating lines of the Talbot interferometer, solving the definite integral of the differential phase images to obtain the phase shift for x-ray phase tomography proves to be cumbersome when the sample extends outside the image and there is no null region for which the integration constant is known. In this work we aimed at increasing the spatial coherence of the x-rays along the horizontal so that the grating lines and the sample rotation axis could be oriented vertically. A Talbot-Lau interferometer was constructed by adding an absorption grating which acted as vertical line sources of horizontally spatially coherent white synchrotron radiation to the Talbot interferometer. An average of 20% moire fringe visibility was obtained. The set-up was demonstrated for highspeed phase tomography of a polymer sample.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

RCT: Module 2.08, Radiological Source Control, Course 8774

radioactive source is material used for its emitted radiation. Sources are sealed or unsealed and are classified as accountable or exempt. Radioactive sources are used for response checks, functional checks, and the calibration of instruments and monitors to traceable standards. To ensure the safety and welfare of all personnel, it is important to maintain control of radioactive sources to minimize the potential for the spread of contamination, unnecessary exposure to personnel, loss or theft, and improper disposal. This course will prepare the student with the skills necessary for RCT qualification by passing quizzes, tests, and the RCT Comprehensive Phase 1, Unit 2 Examination (TEST 27566) and will provide in-the-field skills.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
NASA NTRS2008

LETS: Lunar Environments Test System

The Environmental Effects Branch (EM50) at the Marshall Space Flight Center has developed a unique capability within the agency, namely the Lunar Environment Test System (LETS). LETS is a cryo-pumped vacuum chamber facility capable of high vacuum (10-7 Torr). LETS is a cylindrical chamber, 30 in. (0.8 m) diameter by 48 in. (1.2 m) long thermally controlled vacuum system. The chamber is equipped with a full array of radiation sources including vacuum ultraviolet, electron, and proton radiation. The unique feature of LETS is that it contains a large lunar simulant bed (18 in. x 40 in. x 6 in.) holding 75 kg of JSC-1a simulant while operating at a vacuum of 10-7 Torr. This facility allows three applications: 1) to study the charging, levitation and migration of dust particles, 2) to simulate the radiation environment on the lunar surface, and 3) to electrically charge the lunar simulant enhancing the attraction and adhesion of dust particles to test articles more closely simulating the lunar surface dust environment. LETS has numerous diagnostic instruments including TREK electrostatic probes, residual gas analyzer (RGA), temperature controlled quartz crystal microbalance (TQCM), and particle imaging velocimeter (PIV). Finally, LETS uses continuous Labview data acquisition for computer monitoring and system control.

Vaughn, Jason A.↗
DOE OSTI2011

Radiation burst from a single {gamma}-photon field

The radiation burst from a single {gamma}-photon field interacting with a dense resonant absorber is studied theoretically and experimentally. This effect was discovered for the fist time by P. Helisto et al.[Phys. Rev. Lett. 66, 2037 (1991)] and it was named the ''gamma echo''. The echo is generated by a 180 Degree-Sign phase shift of the incident radiation field, attained by an abrupt change of the position of the absorber with respect to the radiation source during the coherence time of the photon wave packet. Three distinguishing cases of the gamma echo are considered; i.e., the photon is in exact resonance with the absorber, close to resonance (on the slope of the absorption line), and far from resonance (on the far wings of the resonance line). In resonance the amplitude of the radiation burst is two times larger than the amplitude of the input radiation field just before its phase shift. This burst was explained by Helisto et al. as a result of constructive interference of the coherently scattered field with the phase-shifted input field, both having almost the same amplitude. We found that out of resonance the scattered radiation field acquires an additional component with almost the same amplitude as the amplitude of the incident radiation field. The phase of the additional field depends on the optical thickness of the absorber and resonant detuning. Far from resonance this field interferes destructively with the phase-shifted incident radiation field and radiation quenching is observed. Close to resonance the three fields interfere constructively and the amplitude of the radiation burst is three times larger than the amplitude of the input radiation field.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Formation of ECR Plasma in a Dielectric Plasma Guide under Self-Excitation of a Standing Ion-Acoustic Wave

The formation of a spatially localized plasma with a high brightness has been experimentally observed in a dielectric plasma guide under the electron cyclotron resonance discharge at the excitation of a standing ion-acoustic wave. The results obtained show the possibility of designing compact high-intensity radiation sources with a spectrum determined by the working gas or gas mixture type, high-intensity chemically active particle flow sources, and plasma thrusters for correcting orbits of light spacecraft.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Method for measuring the focal spot size of an x-ray tube using a coded aperture mask and a digital detector

Purpose: The goal of this study is to evaluate a new method based on a coded aperture mask combined with a digital x-ray imaging detector for measurements of the focal spot sizes of diagnostic x-ray tubes. Common techniques for focal spot size measurements employ a pinhole camera, a slit camera, or a star resolution pattern. The coded aperture mask is a radiation collimator consisting of a large number of apertures disposed on a predetermined grid in an array, through which the radiation source is imaged onto a digital x-ray detector. The method of the coded mask camera allows one to obtain a one-shot accurate and direct measurement of the two dimensions of the focal spot (like that for a pinhole camera) but at a low tube loading (like that for a slit camera). A large number of small apertures in the coded mask operate as a ''multipinhole'' with greater efficiency than a single pinhole, but keeping the resolution of a single pinhole. Methods: X-ray images result from the multiplexed output on the detector image plane of such a multiple aperture array, and the image of the source is digitally reconstructed with a deconvolution algorithm. Images of the focal spot of a laboratory x-ray tube (W anode: 35-80 kVp; focal spot size of 0.04 mm) were acquired at different geometrical magnifications with two different types of digital detector (a photon counting hybrid silicon pixel detector with 0.055 mm pitch and a flat panel CMOS digital detector with 0.05 mm pitch) using a high resolution coded mask (type no-two-holes-touching modified uniformly redundant array) with 480 0.07 mm apertures, designed for imaging at energies below 35 keV. Measurements with a slit camera were performed for comparison. A test with a pinhole camera and with the coded mask on a computed radiography mammography unit with 0.3 mm focal spot was also carried out. Results: The full width at half maximum focal spot sizes were obtained from the line profiles of the decoded images, showing a focal spot of 0.120 mmx0.105 mm at 35 kVp and M=6.1, with a detector entrance exposure as low as 1.82 mR (0.125 mA s tube load). The slit camera indicated a focal spot of 0.112 mmx0.104 mm at 35 kVp and M=3.15, with an exposure at the detector of 72 mR. Focal spot measurements with the coded mask could be performed up to 80 kVp. Tolerance to angular misalignment with the reference beam up to 7 deg. in in-plane rotations and 1 deg. deg in out-of-plane rotations was observed. The axial distance of the focal spot from the coded mask could also be determined. It is possible to determine the beam intensity via measurement of the intensity of the decoded image of the focal spot and via a calibration procedure. Conclusions: Coded aperture masks coupled to a digital area detector produce precise determinations of the focal spot of an x-ray tube with reduced tube loading and measurement time, coupled to a large tolerance in the alignment of the mask.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Generation of high-power tunable terahertz-radiation by nonrelativistic beam-echo harmonic effect

A new type of terahertz radiation source based on the nonrelativistic electron beam-wave interaction is proposed. Here, the beam echo harmonic effect is applied to a traveling wave tube like device. The scheme is configured as a combination of a frequency multiplier and amplifier with, for instance, W-band (millimeter wave) input signals and terahertz output power. A one-dimensional model of this device shows that a 10th order harmonic-wave can be generated while other harmonic waves are suppressed. The device only requires a readily available input source (W-band), and the output frequency can be tuned continuously over a wide band.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Scanning spectrometer/monochromator for a wavelength range of 50 – 330 Å

A flat-field scanning spectrometer/monochromator of the Hettrick – Underwood type is implemented for a wavelength range λ ≈ 50 – 330 Å. The optical arrangement of the spectrograph comprises a focusing spherical (R = 6000 mm) mirror, mounted at a grazing angle of 8.34 °, and a grazing-incidence plane varied line-space (VLS) grating operating for a constant deflection angle of 16.68 °. The entrance and output slits of the instrument are immobile, and the focal distance varies only slightly over its operating spectral range. The short-wavelength boundary of the operating range is determined by the spectral source brightness and the reflection coefficients of the grating and the mirror rather than by defocusing. Laser-produced plasma spectra excited by a focused laser beam (0.5 J, 8 ns, 1.06 μm) are recorded. A spectral resolving power λ/δλ = 1300 is demonstrated at a wavelength of 182 Å. The configuration of the instrument of this type is suited to soft X-ray reflectometry and metrology with the use of laser-plasma and synchrotron radiation sources, and is perfectly compatible with modern CCD detectors. (x-ray spectrometer)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2010

Submicrometer Single Crystal Diffractometry for Highly Accurate Structure Determination

Submicrometer single crystal diffractometry for highly accurate structure determination was developed using the extremely stable and highly brilliant synchrotron radiation from SPring-8. This was achieved using a microbeam focusing system and the submicrometer precision low-eccentric goniometer system. We demonstrated the structure analyses with 2x2x2 {mu}m{sup 3} cytidine, 600x600x300 nm{sup 3} BaTiO{sub 3}, and 1x1x1 {mu}m{sup 3} silicon. The observed structure factors of the silicon crystal were in agreement with the structure factors determined by the Pendelloesung method and do not require absorption and extinction corrections.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2010

Improvement in Stability of SPring-8 Standard X-Ray Monochromators with Water-Cooled Crystals

SPring-8 standard double-crystal monochromators containing water-cooled crystals were stabilized to a sufficient level to function as a part of optics components to supply stable microfocused x-ray beams, by determining causes of the instability and then removing them. The instability was caused by two factors--thermal deformation of fine stepper stages in the monochromator, which resulted in reduction in beam intensity with time, and vibrations of coolant supply units and vacuum pumps, which resulted in fluctuation in beam intensity. We remodeled the crystal holders to maintain the stage temperatures constant with water, attached x-ray and electron shields to the stages in order to prevent their warming up, introduced accumulators in the water circuits to absorb pressure pulsation, used polyurethane tubes to stabilize water flow, and placed rubber cushions under scroll vacuum pumps. As a result, the intensity reduction rate of the beam decreased from 26% to 1% per hour and the intensity fluctuation from 13% to 1%. The monochromators were also modified to prevent radiation damage to the crystals, materials used as a water seal, and motor cables.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

High-Precision Time Delay Control with Continuous Phase Shifter for Pump-Probe Experiments Using Synchrotron Radiation Pulses

Brilliant pulsed x-ray synchrotron radiation (SR) is useful for pump-probe experiment such as time-resolved x-ray diffraction, x-ray absorption fine structure, and x-ray spectroscopy. For laser pump-SR x-ray probe experiments, short pulsed lasers are generally synchronized to the SR master oscillator controlling the voltage for acceleration of electron bunches in an accelerator, and the interval between the laser and the SR pulses is changed around the time scale of target phenomenon. Ideal delay control produces any time delay as keeping the time-precision and pointing-stability of optical pulses at a sample position. We constructed the time delay control module using a continuous phase shifter of radio frequency signal and a frequency divider, which can produce the delayed trigger pulses to the laser without degradation of the time precision and the pointing stability. A picoseconds time-resolved x-ray diffraction experiment was demonstrated at SPring-8 storage ring for fast lattice response by femtosecond pulsed laser irradiation, and suggested the possibility of accurate sound velocity measurement. A delay control unit operating with subpicosecond precision has also been designed for femtosecond pump-probe experiments using a free electron laser at SPring-8 campus.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Poster — Thur Eve — 38: Feasibility of a Table-Top Total Body Irradiation Technique using Robotic Couch Motion

Purpose: To develop and test the feasibility of a table-top implementation for total body irradiation (TBI) via robotic couch motion and coordinated monitor unit modulation on a standard C-arm linac geometry. Methods: To allow for collision free delivery and to maximize the effective field size, the couch was rotated to 270° IEC and dropped to 150 cm from the vertical radiation source. The robotic delivery was programmed using the TrueBeam STx Developer Mode using custom XML scripting. To assess the dosimetry of a sliding 30×20 cm{sup 2} field, irradiation on a solid water phantom of varying thickness was analyzed using EDR2 radiographic film and OSLDs. Beam modulation was achieved by dividing the couch path into multiple segments of varying dose rates and couch speeds in order to deliver 120 cGy to the midline. Results: The programmed irradiation in conjunction with coordinated couch motion was successfully delivered on a TrueBeam linac. When no beam modulation was employed, the dose difference between two different phantom sections was 17.0%. With simple beam modulation via changing dose rates and couch speeds, the desired prescription dose can be achieved at the centre of each phantom section within 1.9%. However, dose deviation at the junction was 9.2% due to the nonphysical change in the phantom thickness. Conclusions: The feasibility of robotic table-top TBI on a C-arm linac geometry was experimentally demonstrated. To achieve a more uniform dose distribution, inverse-planning allowing for a combination of dose rate modulation, jaw tracking and MLC motion is under investigation.

07 ISOTOPE AND RADIATION SOURCES↗