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Silicone-like SiOxCyHz polymeric thin films with different C/O atomic ratios have been studied by x-ray absorption spectroscopy and resonant Auger electron spectroscopy. The energy of the onset of the Si K absorption edge varies with the film composition from the value observed in SiC (i.e.,∼1840 eV) to that in SiO2 (i.e.,∼1844 eV). In the samples with a low C/O atomic ratio (i.e.,∼1),the main band of the Si K spectra depicts two well defined peaks that can be associated with the Si-C and Si-O bonds present in the samples. Their relative intensity can be used to assess the concentration of these two bond types. Resonant Si KLL Auger spectra of the polymeric thin film have been measured using photon energies across the Si K absorption edge. A first Auger peak appearing at a high kinetic energy was recorded for photon energies around the onset of the absorption edge and the first peak/shoulder of the Si K spectrum associated with the Si-C bonds. This resonant Si KLL Auger signal depicts the typical behavior of a resonant Auger process, i.e., its intensity increases when increasing the photon energy, passes through a maximum and then decreases to disappear. In parallel with the evolution of this resonant spectrum, a “normal” Si KLL Auger spectrum with a lower kinetic energy appeared for photon energies around the middle of the absorption curve. This spectrum is the only one prevailing at photon energies well above the absorption edge. An outstanding behavior of the Si KLL resonant Auger peaks in the polymers with a high C/O atomic ratio (i.e., >=4) is that they present a negative dispersion with photon energy, i.e., their kinetic energy decreases as the photon energy increases. This behavior is opposite to that generally found for resonant Auger peaks in most systems and particularly for SiO2. Although the origin of such behavior is still unclear, the study of the Si K absorption edge and the corresponding Si KLL resonant Auger spectra results helpful for the structural and electronic characterization of SiOxCyHz polymers. [ABSTRACT FROM AUTHOR]

The SwissFEL Aramis beamline, covering the photon energies between 1.77 keV and 12.7 keV, features a suite of online photon diagnostics tools to help both users and FEL operators in analysing data and optimizing experimental and beamline performance. Scientists will be able to obtain information about the flux, spectrum, position, pulse length, and arrival time jitter versus the experimental laser for every photon pulse, with further information about beam shape and size available through the use of destructive screens. This manuscript is an overview of the diagnostics tools available at SwissFEL and presents their design, working principles and capabilities. It also features new developments like the first implementation of a THz‐streaking based temporal diagnostics for a hard X‐ray FEL, capable of measuring pulse lengths to 5 fs r.m.s. or better. [ABSTRACT FROM AUTHOR]

Gamma and X-ray energy spectra measured with semiconductor detectors suffer from various distortions, one of them being so-called “tailing” caused by an incomplete charge collection. Using the Hecht equation, a response matrix of size 321 × 321 was constructed which was used to correct the effect of incomplete charge collection. The correction matrix was constructed analytically for an arbitrary energy bin and the size of the energy bin thus defines the width of the spectral window. The correction matrix can be applied separately from other possible spectral corrections or it can be incorporated into an already existing response matrix of the detector. The correction was tested and its adjustable parameters were optimized on the line spectra of 57 Co measured with a cadmium telluride (CdTe) detector in a spectral range from 0 up to 160 keV. The best results were obtained when the values of the free path of holes were spread over a range from 0.4 to 1.0 cm and weighted by a Gauss function. The model with the optimized parameter values was then used to correct the line spectra of 152 Eu in a spectral range from 0 up to 530 keV. An improvement in the energy resolution at full width at half maximum from 2.40 % ± 0.28 % to 0.96 % ± 0.28 % was achieved at 344.27 keV. Spectra of “narrow spectrum series” beams, N120, N150, N200, N250 and N300, generated with tube voltages of 120 kV, 150 kV, 200 kV, 250 kV and 300 kV respectively, and measured with the CdTe detector, were corrected in the spectral range from 0 to 160 keV (N120 and N150) and from 0 to 530 keV (N200, N250, N300). All the measured spectra correspond both qualitatively and quantitatively to the available reference data after the correction. To obtain better correspondence between N150, N200, N250 and N300 spectra and the reference data, lower values of the free paths of holes (range from 0.16 to 0.65 cm) were used for X-ray spectra correction, which suggests energy dependence of the phenomenon. [ABSTRACT FROM AUTHOR]

In this paper we analyse the response of two different Commercial Off The shelf CMOS image sensors as particle detectors. Sensors were irradiated using X-ray photons, gamma photons, beta particles and alpha particles from diverse sources. The amount of charge produced by different particles, and the size of the spot registered on the sensor are compared, and analysed by an algorithm to classify them. For a known incident energy spectrum, the employed sensors provide a dose resolution lower than microGray, showing their potentials in radioprotection, area monitoring, or medical applications. [ABSTRACT FROM AUTHOR]

Purpose: Spectral information of the output of x-ray tubes in (dual source) computer tomography (CT) scanners can be used to improve the conversion of CT numbers to proton stopping power and can be used to advantage in CT scanner quality assurance. The purpose of this study is to design, validate, and apply a compact portable Compton spectrometer that was constructed to accurately measure x-ray spectra of CT scanners. Methods: In the design of the Compton spectrometer, the shielding materials were carefully chosen and positioned to reduce background by x-ray fluorescence from the materials used. The spectrum of Compton scattered x-rays alters from the original source spectrum due to various physical processes. Reconstruction of the original x-ray spectrum from the Compton scattered spectrum is based on Monte Carlo simulations of the processes involved. This reconstruction is validated by comparing directly and indirectly measured spectra of a mobile x-ray tube. The Compton spectrometer is assessed in a clinical setting by measuring x-ray spectra at various tube voltages of three different medical CT scanner x-ray tubes. Results: The directly and indirectly measured spectra are in good agreement (their ratio being 0.99) thereby validating the reconstruction method. The measured spectra of the medical CT scanners are consistent with theoretical spectra and spectra obtained from the x-ray tube manufacturer. Conclusions: A Compton spectrometer has been successfully designed, constructed, validated, and applied in the measurement of x-ray spectra of CT scanners. These measurements show that our compact Compton spectrometer can be rapidly set-up using the alignment lasers of the CT scanner, thereby enabling its use in commissioning, troubleshooting, and, e.g., annual performance check-ups of CT scanners. [ABSTRACT FROM AUTHOR]

X-ray polarimetry has great scientific potential and new experiments, such as X-Calibur, PoGOLite, XIPE, and GEMS, will not only be orders of magnitude more sensitive than previous missions, but also provide the capability to measure polarization over a wide energy range. However, the measured spectra depend on the collection area, detector responses, and, in case of balloon-borne experiments, the absorption of X-rays in the atmosphere, all of which are energy dependent. Combined with the typically steep source spectra, this leads to significant biases that need to be taken into account to correctly reconstruct energy-resolved polarization properties. In this paper, we present a method based on an iterative unfolding algorithm that makes it possible to simultaneously reconstruct the energy spectrum and the polarization properties as a function of true photon energy. We apply the method to a simulated X-Calibur data set and show that it is able to recover both the energy spectrum and the energy-dependent polarization fraction. [ABSTRACT FROM AUTHOR]

X-ray photon correlation spectroscopy (XPCS) of swollen rubber containing spherical silica nanoparticles is reported. It is shown that irradiation by intense X-rays leads to the breakdown of cross-links, thereby inducing the local rearrangement of silica nanoparticles. This rearrangement process depends on the cross-link density and is characterized by a compressed exponential relaxation with aging behaviour, which resembles a common feature of complex fluids observed with XPCS. [ABSTRACT FROM AUTHOR]

Single crystal scintilators are used in various radiation detectors applications. The efficiency of the crystal can be determined by the Detector Optical Gain (DOG) defined as the ratio of the emitted optical photon flux over the incident radiation photons flux. A parameter affecting DOG is the intrinsic conversion efficiency ( n) giving the percentage of the X-ray photon power converted to optical photon power. n is considered a constant value for X-ray energies in the order of keV although a non-proportional behavior has been reported. In this work an analytical model, has been utilized to single crystals scintillators GSO:Ce, LSO:Ce and LYSO:Ce to examine whether the intrinsic conversion efficiency shows non proportional behavior under X-ray excitation. DOG was theoretically calculated as a function of the incident X-ray spectrum, the X-ray absorption efficiency, the energy of the produced optical photons and the light transmission efficiency. The theoretical DOG values were compared with experimental data obtained by irradiating the crystals with X-rays at tube voltages from 50 to 140 kV and by measuring the light energy flux emitted from the irradiated screen. An initial value for n (calculated from literature data) was assumed for the X-ray tube voltage of 50 kV. For higher X-ray tube voltages the optical photon propagation phenomena was assumed constant and any deviations between experimental and theoretical data were associated with changes in the intrinsic conversion efficiency. The experimental errors were below 7% for each experimental setup. The behavior of n values for LSO:Ce and LYSO:Ce were found very similar, i.e., ranging with values from 0.089 at 50 kV to 0.015 at 140 kV, while for GSO:Ce, n demonstrated a peak at 80 kV. [ABSTRACT FROM AUTHOR]

It is shown that the accuracy of time-integrated measurements of pulsed X-ray emission from hot plasma with calibrated thermocouple calorimeters is mainly determined by two factors. The first and the most important factor is heating of the filter by the absorbed X-rays; as a result, the calorimeter measures the thermal radiation of the filter, which causes appreciable distortion of the temporal profile and amplitude of the recorded signal. The second factor is the dependence of the effective depth of X-ray absorption in the dielectric that covers the entrance window of the calorimeter on the energy of X-ray photons, i.e., on the recorded radiation spectrum. The results of model calculations of the calorimeter signal are compared with the experimental data. [ABSTRACT FROM AUTHOR]

Near-edge X-ray absorption spectroscopy (NEXAFS) is an essential analytical tool in material science. Combining NEXAFS with scanning transmission X-ray microscopy (STXM) adds spatial resolution and the possibility to study individual nanostructures. Here, we describe a full-field transmission X-ray microscope (TXM) that generates high-resolution, large-area NEXAFS data with a collection rate two orders of magnitude faster than is possible with STXM. The TXM optical design combines a spectral resolution of E/?E = 1 × 104 with a spatial resolution of 25 nm in a field of view of 15-20 µm and a data acquisition time of ?1 s. As an example, we present image stacks and polarization-dependent NEXAFS spectra from individual anisotropic sodium and protonated titanate nanoribbons. Our NEXAFS-TXM technique has the advantage that one image stack visualizes a large number of nanostructures and therefore already contains statistical information. This new high-resolution NEXAFS-TXM technique opens the way to advanced nanoscale science studies. [ABSTRACT FROM AUTHOR]

Abstract: The relative thermoluminescent (TL) response of LiF:Mg,Ti (TLD-100) for 50kVp X-rays relative to 60Co photons was investigated at doses of 0.1Gy and 10Gy using different maximum readout temperatures. Deconvolution was applied to the glow curves readout to a maximum temperature of 400°C in order to investigate the glow peak dependence of the relative TL response. Low-energy X-ray irradiation resulted in a larger over-response relative to 60Co photons for the high temperature glow peak groups (peaks 6–9) compared to low (peaks 2–4) and medium (peaks 5, 5b) temperature groups. The relative TL responses determined by the integral glow curve area obtained using different maximum readout temperatures did not show significant differences, due in part to the limits of system precision. [Copyright &y& Elsevier]

ABSTRACT Narrow-line Seyfert 1 (NLSy1) galaxies are a peculiar class of type 1 active galactic nuclei (broad-line Seyfert 1 galaxies, hereinafter BLSy1). The X-ray properties of individual objects belonging to this class are often extreme and associated with accretion at high Eddington ratios. Here, we present a study on a sample of 14 NLSy1 galaxies selected at hard X-rays (>20 keV) from the fourth INTEGRAL/IBIS catalogue. The 20-100 keV IBIS spectra show hard-X-ray photon indices flatly distributed (Γ20−100 keV ranging from ∼1.3 to ∼3.6) with an average value of 〈Γ20−100 keV〉= 2.3 ± 0.7, compatible with a sample of hard-X-ray BLSy1 average slopes. Instead, NLSy1 galaxies show steeper spectral indices with respect to BLSy1 galaxies when broad-band spectra are considered. Indeed, we combine XMM-Newton and Swift/XRT with INTEGRAL/IBIS data sets to obtain a wide energy spectral coverage (0.3-100 keV). A constraint on the high energy cut-off and on the reflection component is achieved only in one source, SWIFT J2127.4+5654 ( Ecut-off∼ 50 keV, R= 1.0+0.5− 0.4). Hard-X-ray-selected NLSy1 galaxies do not display particularly strong soft excess emission, while absorption fully or partially covering the continuum is often measured as well as Fe line emission features. Variability is a common trait in this sample, both at X-rays and at hard X-rays. The fraction of NLSy1 galaxies in the hard-X-ray sky is likely to be ∼15 per cent, in agreement with estimates derived in optically selected NLSy1 samples. We confirm the association of NLSy1 galaxies with small black hole masses with a peak at 107 M⊙ in the distribution; however, hard-X-ray NLSy1 galaxies seem to occupy the lower tail of the Eddington ratio distribution of classical NLSy1 galaxies. [ABSTRACT FROM AUTHOR]

Abstract: Radiative transfer equation in plane parallel geometry and Kompaneets equation is solved simultaneously to obtain theoretical spectrum of 1–125keV photon energy range. Diffuse radiation field are calculated using time-independent radiative transfer equation in plane parallel geometry, which is developed using discrete space theory (DST) of radiative transfer in a homogeneous medium for different optical depths. We assumed free-free emission and absorption and emission due to electron gas to be operating in the medium. The three terms n, n 2 and where n is photon phase density and , in Kompaneets equation and those due to free-free emission are utilized to calculate the change in the photon phase density in a hot electron gas. Two types of incident radiation are considered: (1) isotropic radiation with the modified black body radiation I MB and (2) anisotropic radiation which is angle dependent. The emergent radiation at and reflected radiation are calculated by using the diffuse radiation from the medium. The emergent and reflected radiation contain the free-free emission and emission from the hot electron gas. Kompaneets equation gives the changes in photon phase densities in different types of media. Although the initial spectrum is angle dependent, the Kompaneets equation gives a spectrum which is angle independent after several Compton scattering times. [Copyright &y& Elsevier]

Purpose: In diagnostic CT imaging, multiple important applications depend on the knowledge of the x-ray spectrum, including Monte Carlo dose calculations and dual-energy material decomposition analysis. Due to the high photon flux involved, it is difficult to directly measure spectra from the x-ray tube of a CT scanner. One potential method for indirect measurement involves estimating the spectrum from transmission measurements. The expectation maximization (EM) method is an accurate and robust method to solve this problem. In this article, this method was evaluated in a commercial CT scanner. Methods: Two step-wedges (polycarbonate and aluminum) were used to produce different attenuation levels. Transmission measurements were performed on the scanner and the measured data from the scanner were exported to an external computer to calculate the spectra. The EM method was applied to solve the equations that represent the attenuation processes of polychromatic x-ray photons. Estimated spectra were compared to the spectra simulated using a software provided by the manufacturer of the scanner. To test the accuracy of the spectra, a verification experiment was performed using a phantom containing different depths of water. The measured transmission data were compared to the transmission values calculated using the estimated spectra. Results: Spectra of 80, 100, 120, and 140 kVp from a dual-source CT scanner were estimated. The estimated and simulated spectra were well matched. The differences of mean energies were less than 1 keV. In the verification experiment, the measured and calculated transmission values were in excellent agreement. Conclusions: Spectrum estimation using transmission data and the EM method is a quantitatively accurate and robust technique to estimate the spectrum of a CT system. This method could benefit studies relying on accurate knowledge of the x-ray spectra from CT scanner. [ABSTRACT FROM AUTHOR]

It is well known that the energy dependence of X-ray attenuation can be used to characterize materials. Yet, even with energy discriminating photon counting X-ray detectors, it is still unclear how to best form energy dependent measurements for spectral imaging. Common ideas include binning photon counts based on their energies and detectors with both photon counting and energy integrating electronics. These approaches can be generalized to energy weighted measurements, which we prove can form a sufficient statistic for spectral X-ray imaging if the weights used, which we term \mu-weights, are basis attenuation functions that can also be used for material decomposition. To study the performance of these different methods, we evaluate the Cramér-Rao lower bound (CRLB) of material estimates in the presence of quantum noise. We found that the choice of binning and weighting schemes can greatly affect the performance of material decomposition. Even with optimized thresholds, binning condenses information but incurs penalties to decomposition precision and is not robust to changes in the source spectrum or object size, although this can be mitigated by adding more bins or removing photons of certain energies from the spectrum. On the other hand, because \mu-weighted measurements form a sufficient statistic for spectral imaging, the CRLB of the material decomposition estimates is identical to the quantum noise limited performance of a system with complete energy information of all photons. Finally, we show that \mu-weights lead to increased conspicuity over other methods in a simulated calcium contrast experiment. [ABSTRACT FROM AUTHOR]

Purpose: Recently, novel CdTe photon counting x-ray detectors (PCXDs) with energy discrimination capabilities have been developed. When such detectors are operated under a high x-ray flux, however, coincident pulses distort the recorded energy spectrum. These distortions are called pulse pileup effects. It is essential to compensate for these effects on the recorded energy spectrum in order to take full advantage of spectral information PCXDs provide. Such compensation can be achieved by incorporating a pileup model into the image reconstruction process for computed tomography, that is, as a part of the forward imaging process, and iteratively estimating either the imaged object or the line integrals using, e.g., a maximum likelihood approach. The aim of this study was to develop a new analytical pulse pileup model for both peak and tail pileup effects for nonparalyzable detectors. Methods: The model takes into account the following factors: The bipolar shape of the pulse, the distribution function of time intervals between random events, and the input probability density function of photon energies. The authors used Monte Carlo simulations to evaluate the model. Results: The recorded spectra estimated by the model were in an excellent agreement with those obtained by Monte Carlo simulations for various levels of pulse pileup effects. The coefficients of variation (i.e., the root mean square difference divided by the mean of measurements) were 5.3%–10.0% for deadtime losses of 1%–50% with a polychromatic incident x-ray spectrum. Conclusions: The proposed pulse pileup model can predict recorded spectrum with relatively good accuracy. [ABSTRACT FROM AUTHOR]

We have developed a back-illuminated active pixel sensor (APS) which includes an SOI readout circuit and a silicon diode detector array implemented in a separate high-resistivity wafer. Both are connected together using a per-pixel 3-D integration technique developed at Lincoln Laboratory. The device was fabricated as part of a program to develop a photon-counting APS for imaging spectroscopy in the soft X-ray (0.3-10-keV) spectral band. Here, we report single-pixel X-ray response with spectral resolution of 181-eV full-width at half-maximum at 5.9 keV. The X-ray data allow us to characterize the responsivity and input-referred noise properties of the device. We measured interpixel crosstalk and found large left-right asymmetry explained by coupling of the sense node to the source follower output. We have measured noise parameters of the SOI transistors and determined factors which limit the device performance. [ABSTRACT FROM AUTHOR]

We report the measurement results of signal and noise characteristics induced by the direct x-rays in an indirect-conversion CMOS photodiode array detector. In order to isolate the signal and noise due to the direct x-rays from those due to the optical photons, we inserted a light-absorbing blackout material between a phosphor screen and the photodiode array. From the images irradiated with and without the blackout paper, the signal and noise characteristics due to the optical photons emitted from a phosphor screen were estimated. For the analysis of the measurements, we have developed a model describing the signal and noise transfers based on the cascaded linear-systems approach. The measured results show the direct x-ray is very harmful to the detector performances, such noise power spectrum (NPS) and signal-to-noise ratio (SNR). However, from the theoretical estimation, the degradation of NPS and SNR would not be due to the directly absorbed x-ray photons, but we believe that other sources, such as Compton and photoelectric scattered rays from a scintillator, a photodiode passivation layer or bulk substrate, are main causes. [ABSTRACT FROM AUTHOR]

X-ray absorption spectroscopy (XAS) has become an indispensable tool in catalysis research. The instrumentation at synchrotron radiation sources as well as analysis and calculation of XAS has reached such a high level that this technique is now attractive to a very large user community. Standard XAS, however, cannot answer all questions and complementary techniques that address the electronic structure in more detail and help to investigate low Z elements as ligand or absorber add to the repertoire of hard X-ray techniques. We discuss in this contribution how energy analysis of the scattered photons [1] in addition to control of the incident photon energy (cf. Figure 1) extends the range of applications of XAS and addresses some problems that XAS cannot solve [2]. [ABSTRACT FROM AUTHOR]

In this work, the general purpose Monte Carlo N-particle radiation transport computer code (MCNP-4C) was used for the simulation of X-ray spectra in diagnostic radiology. The electron's path in the target was followed until its energy was reduced to 10 keV. A user-friendly interface named 'diagnostic X-ray spectra by Monte Carlo simulation (DXRaySMCS)' was developed to facilitate the application of MCNP-4C code for diagnostic radiology spectrum prediction. The program provides a user-friendly interface for: (i) modifying the MCNP input file, (ii) launching the MCNP program to simulate electron and photon transport and (iii) processing the MCNP output file to yield a summary of the results (relative photon number per energy bin). In this article, the development and characteristics of DXRaySMCS are outlined. As part of the validation process, output spectra for 46 diagnostic radiology system settings produced by DXRaySMCS were compared with the corresponding IPEM78. Generally, there is a good agreement between the two sets of spectra. No statistically significant differences have been observed between IPEM78 reported spectra and the simulated spectra generated in this study. [ABSTRACT FROM AUTHOR]

Starting from a complete sample of type 1 active galactic nuclei (AGN) observed by INTEGRAL in the 20–40 keV band, we have selected a set of eight AGN which can be classified as radio-loud objects according to their 1.4 GHz power density, radio-to-hard X-ray flux density ratio and radio morphology. The sample contains six broad-line radio Galaxies and two candidate ones. Most of the objects in our sample display a double-lobe morphology, both on small and large scales. For all the objects, we present broad-band (1–110 keV) spectral analysis using INTEGRAL observations together with archival XMM–Newton, Chandra, Swift/XRT and Swift/BAT data. We constrain the primary continuum (photon index and cut-off energy), intrinsic absorption and reprocessing features (iron line and reflection) in most of the objects. The sources analysed here show remarkable similarities to radio-quiet type 1 AGN with respect to most of the parameters analysed; we only find marginal evidence for weaker reprocessing features in our objects compared to their radio-quiet counterparts. Similarly, we do not find any correlation between the spectral parameters studied and the source core dominance or radio to 20–100 keV flux density ratios, suggesting that what makes our objects radio loud has no effect on their high-energy characteristics. [ABSTRACT FROM AUTHOR]

The Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) X-ray data base (February 2002 – May 2006) has been searched to find solar flares with weak thermal components and flat photon spectra. Using a regularized inversion technique, we determine the mean electron flux distribution from count spectra for a selection of events with flat photon spectra in the 15 – 20 keV energy range. Such spectral behavior is expected for photon spectra either affected by photospheric albedo or produced by electron spectra with an absence of electrons in a given energy range ( e.g., a low-energy cutoff in the mean electron spectra of nonthemal particles). We have found 18 cases that exhibit a statistically significant local minimum (a dip) in the range of 13 – 19 keV. The positions and spectral indices of events with low-energy cutoff indicate that such features are likely to be the result of photospheric albedo. It is shown that if the isotropic albedo correction is applied, all low-energy cutoffs in the mean electron spectrum are removed, and hence the low-energy cutoffs in the mean electron spectrum of solar flares above ∼ 12 keV cannot be viewed as real features. If low-energy cutoffs exist in the mean electron spectra, their energies should be less than ∼ 12 keV. [ABSTRACT FROM AUTHOR]

X-ray photon correlation spectroscopy was used to probe the diffusive dynamics of colloidal particles in a shear flow. Combining X-ray techniques with microfluidics is an experimental strategy that reduces the risk of X-ray-induced beam damage and also allows time-resolved studies of processes taking place in flow cells. The experimental results and theoretical predictions presented here show that in the low shear limit for a 'transverse flow' scattering geometry (scattering wavevector q perpendicular to the direction of flow) the measured relaxation times are independent of the flow rate and determined only by the diffusive motion of the particles. This is not generally valid and, in particular, for a 'longitudinal flow' (q ǁ flow) scattering geometry the relaxation times are strongly affected by the flow-induced motion of the particles. The results here show that the Brownian diffusion of colloidal particles can be measured in a flowing sample and that, up to flux limitations, the experimental conditions under which this is possible are easier to achieve at higher values of q. [ABSTRACT FROM AUTHOR]

Abstract: Real-time measurement of the composition and spectroscopic characteristics of the radiation field inside the ATLAS detector and cavern will be carried out with MediPix2 devices. In view of this application, a calibration of the low energy threshold was performed by illuminating the devices with low energy photons, using 241Am sources and X-rays. A procedure was thereafter established for the calibration of all MediPix2 devices to be used in ATLAS. Using X-ray tubes with filters at the Czech Metrology Institute, photons of energies between 8 and 250keV were obtained and the detection efficiency of the MediPix devices to these radiations was determined. An exponential decrease of the photon intensity as a function of detector depth was observed, illuminating the detector with the beam almost parallel to the surface. The properties of the decrease of intensity were used to determine the exact incident angle of the beam. [Copyright &y& Elsevier]

A detailed study of the scintillation light pulse shape in CsI(Tl) at room temperature as a function of incoming photon energy in 6 ÷ 662 keV energy range is presented. Three samples of CsI(Tl) of different amount of TI dopant (0.01, 0.06 and 0.25 mol%) were used in measurements. A delayed coincidence single photon counting method was applied to measure the decay times in the microsecond range. Three-exponential function was fitted to the time spectra to describe the light pulse shape, which resulted in three components of τ1 = 730 ± 30 ns (fast), τ2 = 3.2 ± 0.3 µs (slow) and τ3 = 16 ± 2 µs (tail). The intensity of the second component was found to be sensibly independent of photon energy, whereas the intensities of the first and third ones varied with the energy of absorbed photon in low energy region. For a given crystal the most intense fast component was measured for 6-keV X-rays from 55Fe at the cost of decreasing intensity of the slowest one. Furthermore, the intensity of the fast component depends on TI concentration and reaches its maximum value for the 0.06 mol % doping, close to the well-know optimal concentration of 0.1 mol %. [ABSTRACT FROM AUTHOR]

Abstract: This article reviews the literature on X-ray fluctuation intensity spectroscopy or, as it is often called, X-ray photon correlation spectroscopy. It highlights measurements using different types of diffuse scattering. To cite this article: M. Sutton, C. R. Physique 9 (2008). [Copyright &y& Elsevier]

A prototype 64 pixel miniature camera has been designed and tested for the Simbol-X hard X-ray observatory to be flown on the joint CNES-ASI space mission in 2014. This device is called Caliste 64. It is a high performance spectro-imager with event time-tagging capability, able to detect photons between 2 keV and 250 keV. Caliste 64 is the assembly of a 1 or 2 mm thick CdTe detector mounted on top of a readout module. CdTe detectors equipped with Aluminum Schottky barrier contacts are used because of their very low dark current and excellent spectroscopic performance. Front-end electronics is a stack of four IDeF-X Vii ASICs, arranged perpendicular to the detection plane, to read out each pixel independently. The whole camera fits in a 10 × 10 × 20 mm3 volume and is juxtaposable on its four sides. This allows the device to be used as an elementary unit in a larger array of Caliste 64 cameras. Noise performance resulted in an ENC better than 60 electrons rms in average. The first prototype camera is tested at -10° C with a bias of -400 V. The spectrum summed across the 64 pixels results in a resolution of 697 eV FWHM at 13.9 keV and 808 eV FWHM at 59.54 keV. [ABSTRACT FROM AUTHOR]

Results are presented from experimental studies of the generation of hard X-ray (HXR) emission with photon energies above 20 keV during the implosion of wire arrays in the Angara-5-1 facility. An analysis of X-ray images of the Z-pinch shows that the dimensions and spatial structures of the emitting regions are different for hard and soft X rays. It is found that the HXR emission peak is delayed with respect to the soft X-ray (SXR) one. The dependence of the HXR power on the material, initial diameter, and mass (implosion time) of the wire array is determined. It is shown that the HXR intensity in the spectral range >50 keV is several orders higher than the emission intensity in the high-energy tail of the SXR spectrum (assuming that this spectrum is thermal). A comparison of the time evolution and spatial localization of the HXR and SXR sources during the implosion of wire arrays indicates the presence of a new superthermal phenomenon that differs qualitatively from the processes determining the peak power of the SXR pulse. Possible mechanisms that can be responsible for the generation of HXR pulses are considered. [ABSTRACT FROM AUTHOR]

We demonstrate sub-millijoule-energy, sub-4 fs-duration near-infrared laser pulses with a controlled waveform comprised of approximately 1.5 optical cycles within the full-width at half-maximum (FWHM) of their temporal intensity profile. We further demonstrate the utility of these pulses for producing high-order harmonic continua of unprecedented bandwidth at photon energies around 100 eV. Ultra-broadband coherent continua extending from 90 eV to more than 130 eV with smooth spectral intensity distributions that exhibit dramatic, never-before-observed sensitivity to the carrier-envelope offset (CEO) phase of the driver laser pulse were generated. These results suggest the feasibility of sub-100-attosecond XUV pulse generation for attosecond spectroscopy in the 100 eV range, and of a simple yet highly sensitive on-line CEO phase detector with sub-50-ms response time. [ABSTRACT FROM AUTHOR]

We present the results of the analysis of Rossi X-ray Timing Explorer ( RXTE) observations of the new X-ray transient, SWIFT J1753.5−0127, during its outburst in 2005 July. The source was caught at the peak of the burst with a flux of 7.19e-09 erg s−1cm−2 in the 3–25 keV energy range and observed until it decreased by about a factor of 10. The photon index of the power-law component, which is dominant during the entire outburst, decreases from ∼1.76 to 1.6. However, towards the end of the observations the photon index is found to increase, indicating a softening of the spectra. The presence of an ultrasoft thermal component, during the bright phases of the burst, is clear from the fits to the data. The temperature associated with this thermal component is 0.4 keV. We believe that this thermal component could be due to the presence of an accretion disc. Assuming a distance of 8.5 kpc, at the peak of the burst, for a black hole of mass . The source is found to be locked in the low/hard state during the entire outburst and likely falls in the category of the X-ray transients that are observed in the low/hard state throughout the outburst. We discuss the physical scenario of the low/hard state outburst for this source. [ABSTRACT FROM AUTHOR]

The rapid development of new sources of coherent X-rays, such as third-generation synchrotrons, high-harmonic-generation lasers and X-ray free-electron lasers, has led to the emergence of the new field of X-ray coherent science. The extension of coherent methods to the X-ray regime makes possible methods such as coherent diffraction, X-ray photon-correlation spectroscopy, speckle interferometry and ultrafast probing at atomic resolution and femtosecond timescales. Despite rapid improvements in the resolution that conventional X-ray optics can achieve, new methods for manipulating X-rays are required to push this to the atomic scale. Here we demonstrate a coherent imaging technique that enables us to image the complex field at the focus of an X-ray zone plate without the need for conventional X-ray lenses. There are no fundamental limits on the resolution of this lensless imaging technique other than the wavelength of the X-rays themselves. The ability to characterize the beam with one measurement makes the method ideally suited to characterizing the fields generated by pulsed coherent X-ray sources. [ABSTRACT FROM AUTHOR]

A scanning dynamically focusing sagittal X-ray monochromator accepting 7 mrad of the fan from a 6 T wiggler is in routine use on beamline 16.5 (ultra-dilute spectroscopy) of the SRS at CCLRC Daresbury Laboratory, UK. The energy range covered is 7–27 keV, with a horizontal spot size of <1.1 mm FWHM. Measured monochromatic flux from a Si 220 crystal pair is 1 × 1011 photons s−1 (100 mA)−1 at 9 keV. This level of flux, usually associated with an insertion device on a third-generation source, permits collection of EXAFS data on concentrations at or below 10 ppm. [ABSTRACT FROM AUTHOR]

We study fractional variability as a function of energy from black hole X-ray binaries on time-scales from milliseconds to hundreds of seconds. We build a theoretical model of energy-dependent variability in which the X-ray energy spectrum varies in response to a changing physical parameter. We compare these models to rms spectra obtained from RXTE Proportional Counter Array (PCA) observations of black hole binaries XTE J1550–564 and XTE J1650–500. We show that two main variability models are consistent with the data: variable seed photon input in the hard state and variable power in the Comptonized component in the soft and very high states. The lack of clear reflection features in the rms spectra implies that the reflection and the X-ray continuum, when integrated over Fourier frequencies, are correlated and vary with similar fractional amplitudes. Our models predict two important features of rms spectra, not possible to be clearly seen by the PCA due sensitivity limits. At soft X-rays, ≲3 keV, we predict the presence of a break in the rms spectrum at energy directly related to the seed photon temperature. At higher energies, ∼20–30 keV, we predict a peak in the rms spectrum originating from the variability of the spectrum produced by a hybrid thermal/non-thermal electron distribution. If these features are confirmed by broad-band observations, they will impose important constraints on the origin of the seed photons for Comptonization and the electron distribution in the hot plasma. [ABSTRACT FROM AUTHOR]

We present results from a newXMM–Newtonobservation of the high-redshift quasar RX J1028.6– 0844 at a redshift of 4.276. The soft X-ray spectral flattening, as reported by a previous study withASCA, is confirmed to be present, with, however, a reduced column density when modelled by absorption. The inferred column density for absorption intrinsic to the quasar isfor cold matter, and higher for ionized gas. The spectral flattening shows remarkable similarity with that of two similar object, namely GB 1428+ 4217 and PMN J0525− 3343. The results improve upon those obtained from a previous short-exposure observation for RX J1028.6– 0844 withXMM–Newton. A comparative study of the twoXMM–Newtonobservations reveals a change in the power-law photon index fromto 1.5 on time-scales of about one year. A tentative excess emission feature in the rest-frame 5–10 keV band is suggested, which is similar to that marginally suggested for GB 1428+ 4217. [ABSTRACT FROM AUTHOR]

Abstract: In X-ray photon correlation spectroscopy (XPCS) the degree of coherence of the X-ray beam determines the contrast of the observed intensity correlation function. In this article, we present XPCS measurements of smectic liquid crystal membranes in a reflectivity geometry showing that both coherence and resolution can influence the time dependence of the correlation function. Variation of the pre-detector slits as well as of the projected coherence length on the membrane induce a time dependence of the intensity correlation function. We also treat several practical aspects and limitations we encountered during our XPCS studies. Finally the conditions for heterodyne detection at the specular ridge and homodyne detection at off-specular conditions are discussed. [Copyright &y& Elsevier]

Conventional X rays, i.e. X rays generating voltage between roughly 150 and 300 kV, are used in many radio-diagnostic procedures and also in radio-biological experiments. They release less energetic and, therefore, more densely ionising electrons than the high-energy gamma rays from 60Co or from the A bombs. Accordingly, they are considered to be somewhat more effective, especially at low doses. Various radiobiological studies, especially studies on chromosome aberrations have confirmed this assumption, but epidemiological investigations, e.g. the comparison of the excess relative risk for mammary cancer in the X-ray exposed patients and in the gamma-ray exposed A bomb survivors, have not demonstrated a similar difference. In view of the missing epidemiological evidence and largely for the reasons of practicality in radiation protection, the ICRP has recommended the radiation weighting factor unity equally for all photon radiations. However, in the discussion preceding the 2005 Recommendations of the ICRP, the issue remains controversial. In a recent paper, Harder et at argue—with reference to an assessment by the German Radiation Protection Commission (SSK)—that the use of the same weighting factor for different photon energies can be justified more directly. For high-energy incident photons, they present the degraded photon spectra at different depths in a phantom, and they conclude that much of the difference between high-energy gamma rays and conventional X rays disappears in a large phantom. The present assessment, which is more direct, compares the spectra of electrons released (through pair production, Compton effect and photo effect) in a small and in a very large receptor for the incident photons of 150 keV, 1 MeV and 6 MeV. For the 1 Mev and 6 MeV photons, there is a substantial shift towards smaller electron energies in the large receptor, but the electron spectra remain much harder than those from the 150 keV incident photons. Furthermore, it is seen—in agreement with earlier conclusions by Straume—that for the broad gamma-ray spectrum from the A bombs there is no shift at all to lower energies within the body, but rather some degree of hardening of the radiation. The assumption that distinct differences between high-energy gamma rays and conventional X rays are restricted to small samples must, thus, be rejected. The attribution of the same effective quality factor or radiation weighting factor to all photon energies remains, therefore, an issue that is based on the considerations beyond dosimetry. [ABSTRACT FROM AUTHOR]

In the nonrelativistic approximation, the absolute values and the forms of the differential cross sections of the anomalous elastic scattering of a linearly polarized x-ray photon by manganese and copper atoms in the energy region of the ionization threshold of the 1s shell are calculated for the wave functions of one-electron states. We take into account the multiparticle effects of relaxation of atomic shells in the field of core vacancies, multiplet splitting, the configuration interaction, and Auger and radiative decays of vacancies, as well as the processes of double excitation/ionization of the ground state of the atom. The calculation results are in good agreement with the synchrotron experiment. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

A new, fast x-ray detector system is presented for high-throughput, high-sensitivity, time-resolved, x-ray scattering and imaging experiments, most especially x-ray photon correlation spectroscopy (XPCS). After a review of the architectures of different CCD chips and a critical examination of their suitability for use in a fast x-ray detector, the new detector hardware is described. In brief, its principal component is an inexpensive, commercial camera—the SMD1M60—originally designed for optical applications, and modified for use as a direct-illumination x-ray detector. The remainder of the system consists of two Coreco Imaging PC-DIG frame grabber boards, located inside a Dell Power-edge 6400 server. Each frame grabber sits on its own PCI bus and handles data from 2 of the CCD’s 4 taps. The SMD1M60 is based on a fast, frame-transfer, 4-tap CCD chip, read out at12-bit resolution at frame rates of up to 62 Hz for full frame readout and up to 500 Hz for one-sixteenth frame readout. Experiments to characterize the camera’s suitability for XPCS and small-angle x-ray scattering (SAXS) are presented. These experiments show that single photon events are readily identified, and localized to within a pixel index or so. This is a sufficiently fine spatial resolution to maintain the speckle contrast at an acceptable value for XPCS measurements. The detective quantum efficiency of the SMD1M60 is 49% for directly-detected 6.3 keV x rays. The effects of data acquisition strategies that permit near-real-time data compression are also determined and discussed. Overall, the SMD1M60 detector system represents a major improvement in the technology for time-resolved x-ray experiments, that require an area detector with time-resolutions in few-milliseconds-to-few-seconds range, and it should have wide applications, extending beyond XPCS. [ABSTRACT FROM AUTHOR]

Since the Medipix system is a photon counting system with selectable threshold, it is possible to use it as a spectroscopic device, which is sensitive to the energy of the incoming photons. One feature of the Medipix system is the possibility to adjust the threshold for each pixel by a three-bit mask. A simple method for creating threshold equalisation masks for different threshold settings including both detector and channel stability influences is proposed. The method is suitable for systems using X-ray sources with a wide energy range, since the threshold adjustment is energy dependent. This is an alternative to the well-known method for correction of non-uniformity, which uses mono energetic sources.The proposed method is based on the analysis of histograms of series of images. The model for the histograms was created assuming a standard dental X-ray source, which allows mask-creating parameters such as threshold range to be found. This procedure can be performed for each of the energies of interest. Based on these arrays, mask files that narrowed the threshold distribution close to the theoretical limit, were prepared. The limit of the spectroscopic resolution for the system was measured by analysing histograms for a series of flat images under identical conditions. [Copyright &y& Elsevier]

Linear systems theory is used for the numerical assessment of the detective quantum efficiency (DQE) of the hybrid semiconductor pixel detector DIXI. The Monte Carlo based code GEANT is used to simulate the photon transport in the sensor, charge transport modeling is treated analytically and the readout chip is simulated using PSPICE. The DQE for two differently shaped X-ray spectra of the same quality and for different operational conditions of the readout chip regarding the discrimination level are computed in order to validate the model. The model described in this paper can be adopted for optimizing the detector. [ABSTRACT FROM AUTHOR]