X-ray Spectroscopy Applications Research Articles

Si wafers having one- and two-dimensionally curved (111) planes examined by X-ray diffraction

Si (111) wafers deformed at elevated temperatures into cylindrical or hemispherical shapes have been examined by X-ray diffraction. Well defined 333 peaks shifted with in-plane distance from the centre of the wafer as determined by ω scans. The shift of the peak position agreed with the curvature of the Si wafer, suggesting that the Si (111) lattice plane can be designed on an arbitrarily curved surface by this method. These crystals have potential for innovative applications in X-ray instrumentation, for both diffraction/scattering and spectroscopy.

A novel compact topology for high-resolution CMOS/BiCMOS spectroscopy amplifiers

In this work, we present the extensive analysis of a new class of current-mode shaping amplifiers that can be realized in CMOS or BiCMOS technology. They are suitable for high-resolution spectroscopy, as we have demonstrated in previous works. The proposed topology is suitable to design shaping amplifiers with a wide range of time constants (/spl sim/0.1-10 /spl mu/s) in a very compact scheme. In particular, we show the results of two fourth-order shapers characterized by 500- and 167-ns shaping time, respectively, realized in 0.8-/spl mu/m BiCMOS technology. The two prototypes were designed in view of the use with Silicon Drift Detectors for X-ray spectroscopy applications. The measured integral nonlinearity is below /spl plusmn/0.1% and the achieved energy resolution at the Mn K/spl alpha/ line (measured with the proposed spectroscopy amplifier with a 5 mm/sup 2/ Peltier-cooled Silicon Drift Detector) is 160 eV full width at half maximum (FWHM) with 500-ns shaping time, comparable to the one obtained with a commercial shaping amplifier with the same time constant.

A monolithic array of 77 silicon drift detectors for X-ray spectroscopy and gamma-ray imaging applications

Monolithic arrays of Silicon Drift Detectors (SDDs) have been employed successfully in X-ray spectroscopy and /spl gamma/-ray imaging applications. Thanks to the low electronics noise achieved at short shaping time, the SDD is an ideal device for high-resolution and high-rate X-ray spectroscopy experiments at synchrotron sources. Moreover, small monolithic arrays of SDDs have also been used as photodetector of the scintillation light in a first prototype of Anger Camera for /spl gamma/-ray imaging characterized by an intrinsic resolution better than 0.3 mm. In this work we present a new large-area monolithic array of Silicon Drift Detectors. It consists of a single chip composed by 77 single hexagonal units, each one with a front-end JFET integrated in its center, arranged in a honeycomb configuration. Each SDD unit has an active area of 8.7 mm/sup 2/, for a total active area of the device of 6.7 cm/sup 2/. The linear dimensions of the active area are approximately 29/spl times/26 mm/sup 2/. It represents the largest monolithic array of SDDs with on-chip JFETs produced up to now for X-ray and /spl gamma/-ray detection. The results achieved in the experimental characterization of a first prototype of the detector array are presented. They include also the preliminary X-ray spectroscopy characterization of the SDD's units. The energy resolution measured at 6 keV with the single unit of the array is of 142eV at -10/spl deg/C.

Planar LAAPDs: temperature dependence, performance, and application in low-energy X-ray spectroscopy

An experiment measuring the 2S Lamb shift in muonic hydrogen ( μ - p ) was performed at the Paul Scherrer Institute, Switzerland. It required small and compact detectors for 1.9 keV X-rays (2P–1S transition) with an energy resolution around 25% at 2 keV, a time resolution better than 100 ns, a large solid angle coverage, and insensitivity to a 5 T magnetic field. We chose Large Area Avalanche Photodiodes (LAAPDs) from Radiation Monitoring Devices as X-ray detectors, and they were used during the last data taking period in 2003. For X-ray spectroscopy applications, these LAAPDs have to be cooled in order to suppress the dark current noise; hence, a series of tests were performed to choose the optimal operation temperature. Specifically, the temperature dependence of gain, energy resolution, dark current, excess noise factor, and detector response linearity was studied. Finally, details of the LAAPDs application in the muonic hydrogen experiment as well as their response to α particles are presented.

Impactite from Henbury, Australia

Impactite was formed in several small, closely spaced craters by the impact of iron meteorites on sandstone at Henbury, central Australia. Through application of energy dispersive X-ray spectroscopy, convergent-beam electron diffraction, and selected-area electron diffraction, chemical compositions and space groups were determined for multiple crystalline phases in the impactite. Based on this chemical and structural information, sub-micrometer fayalite (approximately 40% of the total volume of crystalline phases), magnetite (25%), α-quartz (20%), hercynite (10%), diamond (3%), and a Nisulfide phase (2%) were identified, in addition to abundant glass. Compared with the pre-shock rock, the Henbury impactite was subjected to dramatic phase transformation and chemical redistribution and fractionation processes during the impact event. The newly formed dendritic crystalline phases such as fayalite, magnetite, and hercynite, as well as the surrounding glass, may represent metastable eutectic crystallization that occurred between approximately 1600 °C (liquidus temperature of hercynite) and 850 °C (75% of the liquidus temperature of fayalite) on a time scale of seconds. Generally, the composition of glass surrounding magnetite, fayalite, and hercynite is close to SiO 2 , plus small amounts of Fe (about 10%), but the glass around magnetite can also be considerably more enriched in Fe. The distribution of magnetite and fayalite is probably related to the Fe 3+ /Fe 2+ ratio in the original melt as altered by the local oxygen fugacity, and the formation of hercynite is governed by both the Fe 3+ /Fe 2+ ratio and the distribution of Al in the sample. Alpha quartz probably formed from Fe-depleted silica in the autoannealing period, at low pressure and relatively low temperatures. Diamond crystals in the impactite are euhedral and may have formed through chemical vapor deposition (CVD) at very high temperatures. Nickel sulfide probably crystallized directly from sulfide vapor or quenched sulfide melts, under supercooled and reduced conditions. The impactite is chemically very heterogeneous, presumably due to the limited diffusion time available for mixing of Fe and silica during the rapid cooling history. Iron, Ni, and Mg tend to concentrate in fayalite, magnetite, and hercynite, whereas K and Si are enriched in glass. Hercynite contains more Al, and other crystalline phases less Al, than the glass. In general, the Henbury impactite reflects a chaotic mixture of equilibrium, metastable, and non-equilibrium domains produced at high temperatures in a very short time, and most crystallization appears to have occurred in the post-shock period.

Dynamic behavior of the charge-to-voltage conversion in Si-drift detectors with integrated JFETs

We report on the transient behavior of the charge-to-voltage conversion of a silicon drift detector with an integrated JFET in a source follower configuration, suitable for X-ray spectroscopy and imaging applications. The experimental results are based on the measurements of the JFET's source voltage in the time domain. The dependence on count rate up to 600 kcts/s and on photon energy up to 15.7 keV are presented at operating temperatures around 20/spl deg/C. The charge collecting capacitance shunting the gate of the JFET is discharged by a continuous reset current, which is attributed to the I-V characteristic of the JFET's gate-to-channel junction. Its influence on the signal amplitude is discussed with respect to the voltage dependence of the charge-collecting capacitance. A set of analytical equations and an equivalent circuit fully describes the dependence of the mean source voltage, of the discharging current, and of the signal amplitude as a function of count rate and photon energy. The simulated responses show a good quantitative agreement with the measured characteristics.

Theoretical comparison between two different filtering techniques suitable for the VLSI spectroscopic amplifier ROTOR

The development of new detection systems based on arrays of Silicon Drift Detectors (SDD) used for new X-ray spectroscopy applications, like X-ray Holography and EXAFS experiments, requires the realization of suitable integrated low-noise electronics for the readout of the detector signals. Recently, a new VLSI time-variant signal processor called ROTOR has been developed. Despite its time-variant nature ROTOR is capable of correctly processing events randomly distributed along the time axis, thanks to the employment of the Concurrent Wheel Technique (CWT). Two different possible solutions for the ROTOR chip have been developed, both suitable for the CWT working mechanism. A theoretical comparison between the noise performances of the two filtering methods has been carried out and is presented in this work.

XPEEM valence state imaging of mineral micro-intergrowths with a spatial resolution of 100 nm

The crystal chemistry and textural relationships of minerals hold a vast amount of information relating to the formation, history and stability of natural materials. The application of soft X-ray spectroscopy to mineralogical material has revealed that 2p (L2,3 spectra provide a sensitive fingerprint of the electronic states of 3d metals. In bulk powdered samples much of the textural and microstructural information is lost, but the area-selectivity capability of X-ray Photo-Emission Electron Microscopy (XPEEM) provides the ability to obtain valence state information from mineral intergrowths with a submicron spatial resolution. Using the state-of-the-art PEEM2 facility on beamline 7.3.1.1 at the Advanced Light Source, Berkeley, USA, a range of minerals, mineral intergrowths and mineralogical textures have been studied for a broad suite of geological, planetary and environmental science materials. High-quality, multi-element valence images have been obtained showing the distribution/variation of the metal valence states across single grains or mineral intergrowths/textures at the l00 nm scale and quantitative valence state ratios can be obtained from areas of ~0.01 .

Ultimate performance of a superconducting quantum detector

We analyze the ultimate performance of a superconducting quantum detector in order to meet requirements for applications in near-infrared astronomy and X-ray spectroscopy. The detector exploits a combined detection mechanism, in which avalanche quasiparticle multiplication and the supercurrent jointly produce a voltage response to a single absorbed photon via successive formation of a photon-induced and a current-induced normal hotspot in a narrow superconducting strip. The response time of the detector should increase with the photon energy providing energy resolution. Depending on the superconducting material and operation conditions, the cut-off wavelength for the single-photon detection regime varies from infrared waves to visible light. We simulated the performance of the background-limited infrared direct detector and X-ray photon counter utilizing the above mechanism. Low dark count rate and intrinsic low-frequency cut-off allow for realizing a background limited noise equivalent power of 10 −20 W Hz −1/2 for a far-infrared direct detector exposed to 4-K background radiation. At low temperatures, the intrinsic response time of the counter is rather determined by diffusion of nonequilibrium electrons than by the rate of energy transfer to phonons. Therefore, thermal fluctuations do not hamper energy resolution of the X-ray photon counter that should be better than 10 −3 for 6-keV photons. Comparison of new data obtained with a Nb based detector and previously reported results on NbN quantum detectors support our estimates of ultimate detector performance.

PIN diode-preamplifier set for the measurement of low-energy γ- and X-rays

Abstract A detector–preamplifier set for X-ray spectroscopy applications in the energy range of 5–60 keV, for use in research laboratories, industry and in school experiments is presented. The main contribution of this work is the demonstration of an easy-to-implement, low-cost detector–preamplifier set that can be built with an inexpensive PIN diode and a low-noise preamplifier of the charge-sensitive type. A junction field-effect transistors in the front end and extremely low feedback capacitance are used in the preamplifier. The set was built and characterized experimentally. High conversion gain and good linearity over the whole energy range were obtained; the set provides an acceptable equivalent noise charge, on the order of 120 electrons r.m.s. Spectra from different X-ray radioactive sources were obtained by using the PIN detector at room temperature together with the preamplifier that is described.

An 8/spl times/8 pixel IC for X-ray spectroscopy

An integrated circuit (IC) providing 64 channels of low-noise signal processing electronics in an 8/spl times/8 pixel arrangement has been developed as part of an integrated silicon detector array for high count-rate X-ray spectroscopy applications. Each pixel features low-noise charge integration, programmable peaking time and gain, and an output driver. The 8/spl times/8 pixel IC builds upon our previous development of the XPS chip, a 1-dimensional (1-D) preamplifier-shaper IC for linear silicon detector arrays. The new pixel design features significant improvements to the shaper and output driver stages, including digital peaking time and gain selection, and a low-power charge driver/receiver design. When operated with a cooled, low-capacitance silicon detector, an energy resolution of /spl sim/210 eV FWHM was obtained for 5.89 keV X-rays. The power dissipation is /spl sim/6 mW per pixel at a supply voltage of 3.3 V.

Surface X-ray absorption spectroscopy principles and some examples of applications

The application of X-ray spectroscopy to surface problems has started almost at the same time as that in materials science. While the theoretical bases are obviously the same, SEXAFS has some experimental peculiarities which are reviewed here. Some examples of this technique will then be given.

A novel multicell silicon drift detector module for X-ray spectroscopy and imaging applications

A novel 61-cell silicon drift detector module is proposed for high-counting rates and high-resolution X-ray spectroscopy and imaging applications at energies up to about 30 keV. Its hexagonal geometry with sloped sidewalls allows a buckyball arrangement. Up to 1860 cells of an active area of 5 mm/sup 2/ each can he reached at an average distance to the specimen of only 4.3 cm. An optimized electrical connection concept offers a vertical integration of a sensor array and signal processing electronics. Worst-case crosstalk of 0.3% (-50 dB) and signal loss of 7% (-24 dB) were derived from electrical field analysis. A sandwich of metal foils between the X-ray sensor and electronics reduces the dose of radiation at the electronics by more than eight orders of magnitude. Module-induced background fluorescence reaches its maximum at an incident energy of 13 keV, but remains below 10/sup -4/ of the incoming photon flux at all energies. Three-dimensional (3-D) simulations on thermal module behavior show that the use of graphite as housing material allows an operation with spatial inhomogeneities of <1/spl deg/C on the sensor's active area. Empirically, we found that the difference between the temperatures of the sensor and the heat sink depends linearly on the power dissipated by the electronics and sensor chip. The corresponding thermal resistances are 4.3 and 0.8 K/W.

Characterization of Large-Area Silicon Drift Detectors at High Count Rates

Abstract Silicon Drift Detectors (SDD) are being developed for analytical x-ray spectrometry having large active area, high-energy resolution and capability of operating at high counting rates. The development derives from the charged coupled device (CCD) for light-signal imaging, utilizing the extremely low capacitance of the detector and readout electronics and subsequent developments of silicon drift detectors for high-energy physics applications and more recently, x-ray spectroscopy applications. The now well-known advantage of the drift detector design is that, unlike traditional planar detectors, it allows for relatively large active area while still maintaining a very low anode capacitance (60 fF). This low value of detector capacitance results in a lowering of the series-noise component and hence the overall inherent electronic noise. Additionally, the reduction of the series noise leads to faster optimal shaping time, and as a consequence this provides for extremely high count rates.

Semiconductor drift detectors: applications and new devices

Recent technological developments and new topology designs have made semiconductor drift detectors ideal devices for high-resolution x-ray spectrometry. In this paper the basic topology of a semiconductor drift detector with on-chip electronics specially designed for x-ray spectrometry is reviewed. These devices have been used for the first time in x-ray and γ-ray spectroscopy applications. In particular, the results obtained in non-destructive analyses by using a EDXRF spectrometer based on a Peltier cooled semiconductor drift detector and in photodetection of scintillation light are reported. The working principle and the first experimental results for a novel position-sensitive x-ray detector with spectroscopic capability are presented. Copyright © 1999 John Wiley & Sons, Ltd.

New high-power laser facility PALS—prospects for laser–plasma research

In this paper, we report on a new laser facility called PALS (Prague Asterix Laser System), which is currently under construction, and which will house the high-power iodine laser Asterix IV. Upon its completion in late 1999, the PALS facility will be capable of providing single- or multiple-pulse irradiation with a variable pulse duration ranging from 100 to 500 ps. Wavelengths available will be 1.315 μm, 658 nm, and 438 nm. The system will provide one main beam with energy up to 1200 J and two smaller auxiliary beams with a combined energy of up to 100 J. A wide variety of geometries and variable pulse timings is available. We assess PALS' potential for investigating the physics of laser plasmas in inertial confinement fusion, the development and applications of X-ray lasers, X-ray spectroscopy, and radiation transport, using multiple-pulse and extended beam capability.

A CMOS detector leakage current self-adaptable continuous reset system: Theoretical analysis

A continuous reset system for the discharge of the feedback capacitance of integrated charge preamplifiers is presented. The system, based on the use of a FET operating in the saturation region, is self-adaptable with respect to a wide range of detector leakage currents. A circuit which provides compensation of the signal from the charge amplifier is also proposed. The noise analysis, which takes into account both the stationary and non-stationary noise contributions and the effect of the rate, shows that the system, when carefully designed, can offer good signal/noise performance for applications in γ-ray and high-energy X-ray spectroscopy. Practical layout considerations are also made.

Flat and Spherically Bent Muscovite (Mica) Crystals for X-ray Spectroscopy

Essential parameters for the application of crystals toquantitative X-ray spectroscopy are the upper wavelength limit and thequantitative reflection properties (intrinsic resolving power,luminosity) of the crystal. Due to the large lattice constant,muscovite, a mica group mineral, can be used in the wavelength rangeup to about 2nm. Muscovite crystals can be bent to small radii ofcurvature due to their favourable cleavage and elastic properties.Characteristic reflection properties at reflections 002 – 00 24were investigated theoretically and experimentally. The integratedreflectivity was calculated for various reflections of perfect flat aswell as spherically bent muscovite crystals with curvature radii R = 100 and R = 186mm. It was measured for flat crystalsin the reflections 00 10 – 00 26 using CuKα- andMoKα-radiation from X-ray tubes and compared with calculationsfor both perfect and mosaic crystals. Available high-quality muscovitecrystals have a mosaic structure with a mosaic spread of about 1arcmin. This mosaic spread limits the spectral resolving power forhigh reflection orders.

Erosion behavior and surface characterization of beryllium under high-flux deuterium plasma bombardment

The erosion of beryllium subject to a high-flux deuterium plasma is studied, including post-bombardment surface characterization. Simulating divertor plasma conditions of the ITER tokamak, the PISCES-B steady-state plasma facility at U.C., San Diego is used to bombard beryllium specimens. The measured sputtering yield is compared with theoretical Monte Carlo calculations using the TRIM.SP code, and with experimental values obtained by others using an ion beam facility. It is found that at elevated specimen temperatures (250° C ≤ T ≤ 720° C), low atomic number impurities of the plasma, such as carbon, nitrogen, and oxygen, form an impurity layer on the beryllium surface. This layer is not eroded away by extended plasma exposure but appears to be continuously regenerated. The presence of this film reduces the apparent sputtering yield of beryllium by up to two orders of magnitude. An in-situ emission spectroscopy technique is used to confirm the effect of deposited contaminants. Depth-profile Auger electron spectroscopy (AES) data shows that relative concentration of carbon, nitrogen, and oxygen in the thin film is each in the range, 10 to 20%. X-ray photoelectron spectroscopy (XPS) data indicates the formation of BeO and a small amount of Be 2C on the surface. X-ray diffraction (XRD) patterns obtained with a small angle of incidence show no evidence for crystalline Be 2C and suggest that the impurity layer may have a disordered or amorphous structure. Importantly, no impurity deposition is observed when the specimen is maintained at room temperature (∼ 40° C). Application of energy dispersive X-ray spectroscopy (EDX) confirms that the low temperature surface is free of impurities except for a trace amount of oxygen. The sputtering yield measured at room temperature agrees with theoretical values within a factor of two.

Comparison of HgI 2, CdTe and Si (p-i-n) X-ray detectors

This paper presents a comparison of HgI 2, CdTe and Si (p-i-n) detector technologies for use in X-ray spectroscopy applications in terms of the basic material properties, the detector fabrication techniques and the spectral responses achieved. The requirements imposed on the detector technologies by the design and construction of portable, hand-held instrumentation are discussed. A number of new spectral results are shown. For example, the energy resolution of 596 eV FWHM at 59.5 keV obtained with CdTe (p-i-n) detectors and the energy resolution of 415 eV FWHM at 22 keV measured with HgI 2 structures are reported. A discussion of the various practical applications with the above detector technologies is presented.