Showing papers on "Synchrotron radiation published in 2007"

Imaging applications of synchrotron X-ray phase-contrast microtomography in biological morphology and biomaterials science. I. General aspects of the technique and its advantages in the analysis of millimetre-sized arthropod structure.

Abstract: Synchrotron-generated X-rays provide scientists with a multitude of investigative techniques well suited for the analysis of the composition and structure of all types of materials and specimens. Here, we describe the properties of synchrotron-generated X-rays and the advantages that they provide for qualitative morphological research of millimetre-sized biological organisms and biomaterials. Case studies of the anatomy of insect heads, of whole microarthropods and of the three-dimensional reconstruction of the cuticular tendons of jumping beetles, all performed at the beamline ID19 of the European Synchrotron Radiation Facility (ESRF), are presented to illustrate the techniques of phase-contrast tomography available for anatomical and structural investigations. Various sample preparation techniques are described and compared and experimental settings that we have found to be particularly successful are given. On comparing the strengths and weaknesses of the technique with traditional histological thin sectioning, we conclude that synchrotron radiation microtomography has a great potential in biological microanatomy.

X-ray Free-electron Lasers

Abstract: In a free-electron laser (FEL) the lasing medium is a high-energy beam of electrons flying with relativistic speed through a periodic magnetic field. The interaction between the synchrotron radiation that is produced and the electrons in the beam induces a periodic bunching of the electrons, greatly increasing the intensity of radiation produced at a particular wavelength. Depending only on a phase match between the electron energy and the magnetic period, the wavelength of the FEL radiation can be continuously tuned within a wide spectral range. The FEL concept can be adapted to produce radiation wavelengths from millimeters to Angstroms, and can in principle produce hard x-ray beams with unprecedented peak brightness, exceeding that of the brightest synchrotron source by ten orders of magnitude or more. This paper focuses on short-wavelength FELs. It reviews the physics and characteristic properties of single-pass FELs, as well as current technical developments aiming for fully coherent x-ray radiation pulses with pulse durations in the 100 fs to 100 as range. First experimental results at wavelengths around 100 nm and examples of scientific applications planned on the new, emerging x-ray FEL facilities are presented.

Analytical solutions for energy spectra of electrons accelerated by nonrelativistic shock-waves in shell type supernova remnants

Abstract: Context. Recent observations of hard X-rays and very high energy gamma-rays from a number of young shell type supernova remnants indicate the importance of detailed quantitative studies of energy spectra of relativistic electrons formed via diffusive shock acceleration accompanied by intense nonthermal emission through synchrotron radiation and inverse Compton scattering. Aims. The aim of this work was derivation of exact asymptotic solutions of the kinetic equation which describes the energy distribution of shock-accelerated electrons for an arbitrary energy-dependence of the diffusion coefficient. Methods. The asymptotic solutions at low and very high energy domains coupled with numerical calculations in the intermediate energy range allow analytical presentations of energy spectra of electrons for the entire energy region. Results. Under the assumption that the energy losses of electrons are dominated by synchrotron cooling, we derived the exact asymptotic spectra of electrons without any restriction on the diffusion coefficient. We also obtained simple analytical approximations which describe, with accuracy better than ten percent, the energy spectra of nonthermal emission of shock-accelerated electrons due to the synchrotron radiation and inverse Compton scattering. Conclusions. The results can be applied for interpretation of X-ray and gamma-ray observations of shell type supernova remnants, as well as other nonthermal high energy source populations like microquasars and large scale synchrotron jets of active galactic nuclei.

Soft X-ray spectromicroscopy beamline at the CLS: Commissioning results

Abstract: The soft X-ray spectromicroscopy beamline (SM) at the Canadian Light Source (CLS) is a dedicated spectromicroscopy facility, consisting of an elliptically polarized undulator (EPU), a beamline based on a collimated PGM optimized for 100–2000 eV range and two end stations: scanning transmission X-ray microscope (STXM) and roll-in X-ray photoemission electron microscope (X-PEEM, from Elmitec GmbH). The overall system has achieved its design parameters with an on-sample flux of ∼108 ph/s@R=3000, 0.5 A in STXM and ∼1012 ph/s@R=3000, 0.5 A in the PEEM, in each case at a spatial resolution exceeding 40 nm. It can also provide an energy resolving power above 10,000. A careful EPU calibration procedure enables advanced polarization measurements.

Spatiotemporal Stability of a Femtosecond Hard-X-Ray Undulator Source Studied by Control of Coherent Optical Phonons

Abstract: We report on the temporal and spatial stability of the first tunable femtosecond undulator hard-x-ray source for ultrafast diffraction and absorption experiments. The 2.5-1 Angstrom output radiation is driven by an initial 50 fs laser pulse employing the laser-electron slicing technique. By using x-ray diffraction to probe laser-induced coherent optical phonons in bulk bismuth, we estimate an x-ray pulse duration of 140+/-30 fs FWHM with timing drifts below 30 fs rms measured over 5 days. Optical control of coherent lattice motion is demonstrated.

Simulating cosmic rays in clusters of galaxies - II. A unified scheme for radio halos and relics with predictions of the gamma-ray emission

Abstract: The thermal plasma of galaxy clusters lost most of its information on how structure formation proceeded as a result of dissipative processes. In contrast, non-equilibrium distributions of cosmic rays (CR) preserve the information about their injection and transport processes and provide thus a unique window of current and past structure formation processes. This information can be unveiled by observations of non-thermal radiative processes, including radio synchrotron, hard X-ray, and gamma-ray emission. To explore this, we use high-resolution simulations of a sample of galaxy clusters spanning a mass range of about two orders of magnitudes, and follow self-consistent CR physics on top of the radiative hydrodynamics. We model CR electrons that are accelerated at cosmological structure formation shocks and those that are produced in hadronic interactions of CRs with ambient gas protons. We find that CR protons trace the time integrated non-equilibrium activities of clusters while shock-accelerated CR electrons probe current accretion and merging shock waves. The resulting inhomogeneous synchrotron emission matches the properties of observed radio relics. We propose a unified model for the generation of radio halos. Giant radio halos are dominated in the centre by secondary synchrotron emission with a transition to the synchrotron radiation emitted from shock-accelerated electrons in the cluster periphery. This model is able to explain the observed correlation of mergers with radio halos, the larger peripheral variation of the spectral index, and the large scatter in the scaling relation between cluster mass and synchrotron emission. Future low-frequency radio telescopes (LOFAR, GMRT, MWA, LWA) are expected to probe the accretion shocks of clusters. [abridged]

Charge Ordering in α-(BEDT-TTF)2I3 by Synchrotron X-ray Diffraction

Abstract: The spatial charge arrangement of a typical quasi-two-dimensional organic conductor α-(BEDT-TTF) 2 I 3 is revealed by single crystal structure analysis using synchrotron radiation. The results show that the horizontal-stripe-type structure, which was suggested by the mean field theory, is established. We also find the charge disproportionation above the metal–insulator transition temperature and a significant change in the transfer integrals caused by the phase transition. Our result elucidates the insulating phase of this material as the 2 k F charge density localization.

Vacuum ultraviolet (VUV) photoionization of small water clusters.

Abstract: Tunable vacuum ultraviolet (VUV) photoionization studies of water clusters are performed using 10−14 eV synchrotron radiation and analyzed by reflectron time-of-flight (TOF) mass spectrometry. Phot...

Charge Ordering in alpha-(BEDT-TTF)2I3 by synchrotron x-ray diffraction

Abstract: The spatial charge arrangement of a typical quasi-two-dimensional organic conductor alpha-(BEDT-TTF)2I3 is revealed by single crystal structure analysis using synchrotron radiation. The results show that the horizontal stripe type structure, which was suggested by mean field theory, is established. We also find the charge disproportion above the metal-insulator transition temperature and a significant change in transfer integrals caused by the phase transition. Our result elucidates the insulating phase of this material as a 2k_F charge density localization.

TeV light curve of PSR B1259–63/SS2883

Abstract: The inverse Compton (IC) scattering of ultrarelativistic electrons accelerated at the pulsar wind termination shock is generally believed to be responsible for TeV gamma-ray signal recently reported from the binary system PSR B1259-63/SS2883. While this process can explain the energy spectrum of the observed TeV emission, the gamma-ray fluxes detected by the Array of Imaging Atmospheric Cherenkov Telescopes (HESS) at different epochs do not agree with the published theoretical predictions of the TeV light curve. The main objective of this paper is to show that the HESS results can be explained, under certain reasonable assumptions concerning the cooling of relativistic electrons, by IC scenarios of gamma-ray production in PSR B1259-63. In this paper we study evolution of the energy spectra of relativistic electrons under different assumptions about the acceleration and energy-loss rates of electrons, and the impact of these processes on the light curve of IC gamma-rays. We demonstrate that the observed TeV light curve can be explained (i) by adiabatic losses which dominate over the entire trajectory of the pulsar with a significant increase towards the periastron or (ii) by the 'early' (sub-TeV) cut-offs in the energy spectra of electrons due to the enhanced rate of Compton losses close to the periastron. The first four data points obtained just after periastron comprise an exception - possibly due to interaction with the Be star disc, which introduces additional physics not included in the presented model. The calculated spectral and temporal characteristics of the TeV radiation provide conclusive tests to distinguish between these two working hypotheses. The Compton deceleration of the electron-positron pulsar wind contributes to the decrease of the non-thermal power released in the accelerated electrons after the wind termination, and thus to the reduction of the IC and synchrotron components of radiation close to the periastron. Although this effect alone cannot explain the observed TeV and X-ray light curves, the Comptonization of the cold ultrarelativistic wind leads to the formation of gamma-radiation with a specific line-type energy spectrum. While the HESS data already constrain the Lorentz factor of the wind, Γ ≤ 10 6 (for the most likely orbit inclination angle i = 35°, and assuming an isotropic pulsar wind), future observations of this object with GLAST should allow a deep probe of the wind Lorentz factor in the range between 10 4 and 10 6 .

Characteristics of focused soft X-ray free-electron laser beam determined by ablation of organic molecular solids.

Abstract: A linear accelerator based source of coherent radiation, FLASH (Free-electron LASer in Hamburg) provides ultra-intense femtosecond radiation pulses at wavelengths from the extreme ultraviolet (XUV; lambda< 100nm) to the soft X-ray (SXR; lambda<30nm) spectral regions. 25-fs pulses of 32-nm FLASH radiation were used to determine the ablation parameters of PMMA - poly ( methyl methacrylate). Under these irradiation conditions the attenuation length and ablation threshold were found to be (56.9 +/- 7.5) nm and similar to 2 mJ center dot cm(-2), respectively. For a second wavelength of 21.7 nm, the PMMA ablation was utilized to image the transverse intensity distribution within the focused beam at mu m resolution by a method developed here.

Biological small-angle X-ray scattering facility at the Stanford Synchrotron Radiation Laboratory

Abstract: Beamline 4-2 at the Stanford Synchrotron Radiation Laboratory is a small-angle X-ray scattering/diffraction facility dedicated to structural studies on mostly noncrystalline biological systems. The instrument consists of a pinhole camera, which covers the magnitude of the scattering vector Q in the range 0.004–1.3 A−1 [Q = (4π/λ)sin θ, where θ and λ are one half of the scattering angle and the X-ray wavelength, respectively], and a Bonse–Hart geometry ultra-small-angle X-ray scattering setup for the Q range an order of magnitude smaller. The pinhole camera allows quick automated distance and detector selection among any combination of five distances and three position-sensitive detectors. The double-crystal monochromator can have either Si 111 crystals or a pair of synthetic multilayer diffractive elements for higher flux applications. We have adopted a suite of software originally developed for macromolecular crystallography for integrated beamline control as well as static and slow time-resolved small-angle scattering data collection. This article outlines recent technological developments and specialized instrumentation for conducting noncrystalline scattering experiments in structural biology at improved time and spatial resolutions.

A Sino-German λ6 cm polarization survey of the Galactic plane - I. Survey strategy and results for the first survey region

Abstract: Aims. Polarization measurements of the Galactic plane at A6 cm probe the interstellar medium (ISM) to larger distances compared to measurements at longer wavelengths, enabling us to investigate properties of the Galactic magnetic fields and electron density. Methods. We are conducting a new λ6 cm continuum and polarization survey of the Galactic plane covering 10° < l < 230° and |b| ≤ 5°. Missing large-scale structures in the U and Q maps are restored based on extrapolated polarization K-band maps from the WMAP satellite. The λ6 cm data are analyzed together with maps in other bands. Results. We discuss some results for the first survey region, 7° x 10° in size, centered at (l, b) = (125°5,0°). Two new passive Faraday screens, G125.6-1.8 and G124.9+0.1, were detected. They cause significant rotation of background polarization angles but little depolarization. G124.9+0.1 was identified as a new faint HII region at a distance of 2.8 kpc. G125.6-1.8, with a size of about 46 pc, has neither a counterpart in enhanced Ha emission nor in total intensity. A model combining foreground and background polarization modulated by the Faraday screen was developed. Using this model, we estimated the strength of the ordered magnetic field along the line of sight to be 3.9 μG for G 124.9+0.1, and exceeding 6.4 pG for G125.6-1.8. We obtained an estimate of 2.5 and 6.3 mK kpc -1 for the average polarized and total synchrotron emissivity towards G124.9+0.1. The synchrotron emission beyond the Perseus arm is quite weak. A spectral curvature previously reported for SNR G126.2+1.6 is ruled out by our new data, which prove a straight spectrum. Conclusions. The new A6 cm survey will play an important role in improving the understanding of the properties of the magneto-ionic ISM. The magnetic fields in HII regions can be measured. Faraday screens with very low electron densities but large rotation measures were detected indicating strong and regular magnetic fields in the ISM. Information about the local synchrotron emissivity can he obtained.

Reference-free total reflection X-ray fluorescence analysis of semiconductor surfaces with synchrotron radiation.

Abstract: Total reflection X-ray fluorescence (TXRF) analysis is a well-established method to monitor lowest level contamination on semiconductor surfaces. Even light elements on a wafer surface can be excited effectively when using high-flux synchrotron radiation in the soft X-ray range. To meet current industrial requirements in nondestructive semiconductor analysis, the Physikalisch-Technische Bundesanstalt (PTB) operates dedicated instrumentation for analyzing light element contamination on wafer pieces as well as on 200- and 300-mm silicon wafer surfaces. This instrumentation is also suited for grazing incidence X-ray fluorescence analysis and conventional energy-dispersive X-ray fluorescence analysis of buried and surface nanolayered structures, respectively. The most prominent features are a high-vacuum load-lock combined with an equipment front end module and a UHV irradiation chamber with an electrostatic chuck mounted on an eight-axis manipulator. Here, the entire surface of a 200- or a 300-mm wafer can be scanned by monochromatized radiation provided by the plane grating monochromator beamline for undulator radiation in the PTB laboratory at the electron storage ring BESSY II. This beamline provides high spectral purity and high photon flux in the range of 0.078-1.86 keV. In addition, absolutely calibrated photodiodes and Si(Li) detectors are used to monitor the exciting radiant power respectively the fluorescence radiation. Furthermore, the footprint of the excitation radiation at the wafer surface is well-known due to beam profile recordings by a CCD during special operation conditions at BESSY II that allow for drastically reduced electron beam currents. Thus, all the requirements of completely reference-free quantitation of TXRF analysis are fulfilled and are to be presented in the present work. The perspectives to arrange for reference-free quantitation using X-ray tube-based, table-top TXRF analysis are also addressed.

TOMCAT: A beamline for TOmographic Microscopy and Coherent rAdiology experimenTs

Abstract: Synchrotron‐based X‐ray Tomographic Microscopy (SRXTM) is nowadays a powerful technique for non‐destructive, high‐resolution investigations of a broad kind of materials. High‐brilliance and high‐coherence third generation synchrotron radiation facilities allow micrometer and sub‐micrometer, quantitative, three‐dimensional imaging within very short time and extend the traditional absorption imaging technique to edge‐enhanced and phase‐sensitive measurements. At the Swiss Light Source, a new, tomography dedicated beamline called TOMCAT has been built recently. The new beamline get photons from a 2.9 T superbend with a critical energy of 11.1 keV. This makes energies above 20 keV easily accessible. To guarantee the best beam quality (stability and homogeneity), the number of optical elements has been kept to a minimum. A Double Crystal Multilayer Monochromator (DCMM) covers an energy range between 8 and 45 keV with a bandwidth of a few percent down to 10−4. The beamline can also be operated in white‐beam mode, providing the ideal conditions for real‐time coherent radiology.

A re-visit of the phase-resolved X-ray and \gamma-ray spectra of the Crab pulsar

Abstract: We use a modified outer gap model to study the multi-frequency phase-resolved spectra of the Crab pulsar. The emissions from both poles contribute to the light curve and the phase-resolved spectra. Using the synchrotron self-Compton mechanism and by considering the incomplete conversion of curvature photons into secondary pairs, the observed phase-averaged spectrum from 100 eV - 10 GeV can be explained very well. The predicted phase-resolved spectra can match the observed data reasonably well, too. We find that the emission from the north pole mainly contributes to Leading Wing 1. The emissions in the remaining phases are mainly dominated by the south pole. The widening of the azimuthal extension of the outer gap explains Trailing Wing 2. The complicated phase-resolved spectra for the phases between the two peaks, namely Trailing Wing 1, Bridge and Leading Wing 2, strongly suggest that there are at least two well-separated emission regions with multiple emission mechanisms, i.e. synchrotron radiation, inverse Compton scattering and curvature radiation. Our best fit results indicate that there may exist some asymmetry between the south and the north poles. Our model predictions can be examined by GLAST.

Polarization of High-Energy Emission from the Crab Pulsar

Abstract: We investigate the polarization of the high-energy emission from the Crab pulsar within the framework of the outer gap accelerator, following previous studies by Cheng and coworkers. A recent version of the outer gap, in which the gap extends from inside the null charge surface to the light cylinder, is used to examine the synchrotron radiation from the secondary and tertiary pairs that are produced outside the gap. We are able to simultaneously reproduce the light curve, the spectrum, and the polarization characteristics by taking into account the gyration of the particles. The polarization position angle curve and the degree of polarization are calculated and compared with the Crab optical data. We demonstrate that the radiation from inside the null charge surface produces the outer wing and off-pulse portions of the light curve and that the tertiary pairs contribute to the bridge emission. The emission from the secondary pairs explains the main features of the observed light curve and spectrum. On the other hand, the emissions both from inside the null charge surface and from the tertiary pairs are required in order to explain the optical polarization behavior of the Crab pulsar. The energy dependence of the polarization features is predicted by the model. The polarization position angle curve indicates that our viewing angle as measured from the pulsar's rotational axis is greater than 90°.

Direct measurement of the kinetics of geopolymerisation by in-situ energy dispersive X-ray diffractometry

Abstract: In-situ energy dispersive X-ray diffractometry (EDXRD) using synchrotron radiation has been used to directly observe the kinetics of formation of a geopolymeric gel from a metakaolin precursor. The use of a purpose-built hydrothermal cell with polychromatic radiation from a wiggler source enables collection of a full diffraction pattern approximately every 150 s. This provides sufficient time resolution to observe the collapse of the metakaolin structure as it dissolves in the activating solution, accompanied by the reprecipitation of the geopolymeric gel binder phase from the now-supersaturated solution. Measurements taken on a limited set of samples of different composition (Si/Al ratio) show a clear trend in the rate of reaction with composition, and also a distinctly different mechanism of reaction in the most highly alkaline systems compared to those containing higher levels of dissolved silica in the activating solution. This corresponds to the results of previous microscopic observations showing significantly different microstructures in these systems, and confirms the value of this technique in analysis of the kinetics of geopolymerisation.

Gamma-ray emission from massive young stellar objects

Abstract: Context. Massive stars form in dense and massive molecular cores. The exact formation mechanism is unclear, but it is possible that some massive stars are formed by processes similar to those that produce the low-mass stars, with accretion/ejection phenomena occurring at some point of the evolution of the protostar. This picture seems to be supported by the detection of a collimated stellar wind emanating from the massive protostar IRAS 16547 4247. A triple radio source is associated with the protostar: a compact core and two radio lobes. The emission of the southern lobe is clearly non-thermal. Such emission is interpreted as synchrotron radiation produced by relativistic electrons locally accelerated at the termination point of a thermal jet. Since the ambient medium is determined by the properties of the molecular cloud in which the whole system is embedded, we can expect high densities of particles and infrared photons. Because of the confirmed presence of relativistic electrons, inverse Compton and relativistic Bremsstrahlung interactions are unavoidable. Aims. We aim at making quantitative predictions of the spectral energy distribution of the non-thermal spots generated by massive young stellar objects, with emphasis on the particular case of IRAS 16547 4247. Methods. We study the high-energy emission generated by the relativistic electrons that produce the non-thermal radio source in IRAS 16547 4247. We also study the result of proton acceleration at the terminal shock of the thermal jet and make estimates of the secondary gamma-rays and electron-positron pairs produced by pion decay. Results. We present spectral energy distributions for the southern lobe of IRAS 16547 4247, for a variety of conditions. We show that high-energy emission might be detectable from this object in the gamma-ray domain. The source may also be detectable at X-rays through long exposures with current X-ray instruments. Conclusions. Gamma-ray telescopes like GLAST, and even ground-based Cherenkov arrays of new generation can be used to study non-thermal processes occurring during the formation of massive stars.

Time-Resolved Synchrotron Radiation Excited Optical Luminescence: Light-Emission Properties of Silicon-Based Nanostructures

Abstract: The recent advances in the study of light emission from matter induced by synchrotron radiation: X-ray excited optical luminescence (XEOL) in the energy domain and time-resolved X-ray excited optical luminescence (TRXEOL) are described. The development of these element (absorption edge) selective, synchrotron X-ray photons in, optical photons out techniques with time gating coincide with advances in third-generation, insertion device based, synchrotron light sources. Electron bunches circulating in a storage ring emit very bright, widely energy tunable, short light pulses (<100 ps), which are used as the excitation source for investigation of light-emitting materials. Luminescence from silicon nanostructures (porous silicon, silicon nanowires, and Si-CdSe heterostructures) is used to illustrate the applicability of these techniques and their great potential in future applications.

Resonant two-photon absorption of extreme-ultraviolet free-electron-laser radiation in helium

Abstract: We have investigated the nonlinear response of helium to intense extreme-ultraviolet radiation from the free-electron laser in Hamburg (FLASH). We observe a spectral feature between 24 and $26\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ electron kinetic energy in photoemission which shows a quadratic fluence dependence. The feature is explained as a result of subsequent processes involving a resonant two-photon absorption process into doubly excited levels of even parity ($N=5$ and 6), radiative decay to the doubly excited states in the vicinity of the ${\mathrm{He}}^{+}$ $(N=2)$ ionization threshold and finally the photoionization of the inner electron by the radiation of the next microbunches. This observation suggests that even-parity states, which have been elusive to be measured with the low pulse energy of synchrotron radiation sources, can be investigated with the intense radiation of FLASH. This also demonstrates a first step to bring nonlinear spectroscopy into the xuv and soft-x-ray regime.

BiFeO3: Synchrotron radiation structure refinement and magnetoelectric geometry

Abstract: Presently BiFeO{sub 3} focuses attention due to its multiferroic nature. This phase shows a highly distorted perovskite crystal structure, with R3c crystal symmetry. Details of the crystallographic structure are required input for a detailed explanation of its remarkable magnetoelectric properties. Present report contributes a high-resolution synchrotron radiation diffraction analysis of the BiFeO{sub 3} crystal structure. Single-phased sample was obtained by conventional solid-state reaction under bismuth atmosphere. XRD experiment was performed on beamline 2-1, Stanford Synchrotron Radiation Laboratory, with 12 keV X-rays. For data Rietveld processing, Fullprof software package was applied. Obtained cell parameters (in {angstrom}, hexagonal system description) were a = 5.57414(4); c = 13.85882(12). Group-theoretical analysis of BiFeO{sub 3} linear magnetoelectric tensor is presented. Only transverse effect is allowed by symmetry. Axial-symmetry polycrystal ceramics cannot show linear magnetoelectric coupling.

Non-invasive measurement of X-ray beam heating on a surrogate crystal sample.

Abstract: Cryocooling is a technique routinely used to mitigate the effects of secondary radiation damage on macromolecules during X-ray data collection. Energy from the X-ray beam absorbed by the sample raises the temperature of the sample. How large is the temperature increase and does this reduce the effectiveness of cryocooling? Sample heating by the X-ray beam has been measured non-invasively for the first time by means of thermal imaging. Specifically, the temperature rise of 1 mm and 2 mm glass spheres (sample surrogates) exposed to an intense synchrotron X-ray beam and cooled in a laminar flow of nitrogen gas is experimentally measured. For the typical sample sizes, photon energies, fluxes, flux densities and exposure times used for macromolecular crystallographic data collection at third-generation synchrotron radiation sources and with the sample accurately centered in the cryostream, the heating by the X-ray beam is only a few degrees. This is not sufficient to raise the sample above the amorphous-ice/crystalline-ice transition temperature and, if the cryostream cools the sample to 100 K, not even enough to significantly enhance radiation damage from secondary effects.

High-resolution X-ray mapping of CdZnTe detectors

Abstract: Recently the use of micro-characterization techniques employing synchrotron radiation permitted identification of the deteriorating effects associated with tellurium (Te)-rich secondary phases existing in CdZnTe (CZT) radiation detectors. These randomly distributed microscopic defects behave as trapping regions, where an unpredictable number of charges are lost leading to significant fluctuations in the total collected charge. Consequently, they adversely affect the efficiency and energy resolution of CZT devices, and are found to be the dominant cause of performance degradation in thick detectors. Mapping of the detector response with synchrotron radiation can reveal the details of transport properties and charge collection efficiency in semiconductor detectors on a spatial scale never before realized. A new dedicated beam-line has been recently established at BNL's National Synchrotron Light Source (NSLS) for detector characterization; it will assist with systematic studies focused on improvement of detectors and crystal-growth techniques.