Measured X-ray Spectra Research Articles

A smoothing method for X-ray spectrum based on best beamforming

X-ray spectrum is widely used in the field of analysis and measurement. Due to the effect of electronic noise and statistical fluctuation of particle, the measurement spectrum is unsmoothed. In order to improve the signal-to-noise ratio of the spectrum, many smoothing methods were applied to process spectrum. The conventional smoothing algorithms regard the spectra as time series. In fact, X-ray spectrum is an angle series, and its essential is spatial spectrum. So the conventional smoothing algorithms are not fit for smoothing X-ray spectrum. In this paper, a new measuring model for X-ray spectrum is built up, and a new smoothing method based on best beam forming is proposed for X-ray spectrum. It regards the measured X-ray spectrum as the classic spectrum estimation result of array signal. The spatial spectrum is re-estimated to smooth the spectrum by best beam forming. The relationship between cross-correlation coefficient and number of array cell is applied to choose parameter q. The experimental results show that the method is effective to smooth X-ray spectrum with high resolution when q is larger than 200.

A new version of a portable polonium source for the non-destructive PIXE (particle induced X-ray emission) analysis in the cultural heritage field

A new version of the portable polonium source, named L-PIXE (large-particle induced X-ray emission), to be used for the non-destructive analysis in the Cultural Heritage field, was realised in the framework of a collaboration between the Italian LNS-INFN (Laboratori Nazionali del Sud-Istituto Nazionale di Fisica Nucleare) and IBAM-CNR (Istituto per i Beni Archeologici e Monumentali-Consiglio Nazionale delle Ricerche).The new source presents a compact geometry and it was designed to operate with large area SDD (silicon drift detector) detectors. In particular, the L-PIXE source was coupled to a 50mm² SDD detector and tested by measuring geochemical reference materials.Results evidenced a gain factor, in terms of counting statistics in the measured X-ray spectra, equal to 11–12 with respect to the previous versions of the source. A preliminary evaluation of the MDL (minimum detection limit) of the new experimental set-up evidenced the possibility of using the new L-PIXE source for identifying the presence of minor and, in some cases, trace elements composing samples under investigation.

Implementation of the elemental library stratified sampling technique on the GUI-based Monte Carlo library least squares (MCLLS) approach for EDXRF analysis

The Monte Carlo-based Energy Dispersive X-ray Fluorescence (MCXRF) elemental analyzer approach can be used to accurately calculate elemental weight fractions in rock formations or metal alloys, by least-squares regression of the measured X-ray spectrum with computer-generated elemental library spectra. The analog sampling scheme in a Monte Carlo simulation cannot generate satisfactory results for trace elements due to their low sampling probability. A stratified sampling variance-reduction technique is proposed and implemented to enable each element in the measured sample to have equal opportunity of being sampled with adjusted weights. Essentially, all computed elemental libraries have good statistical precision and improve the accuracy of the elemental analysis results.

Improved x-ray spectroscopy with room temperature CZT detectors

Compact, room temperature x-ray spectroscopy detectors are of interest in many areas including diagnostic x-ray imaging, radiation protection and dosimetry. Room temperature cadmium zinc telluride (CZT) semiconductor detectors are promising candidates for these applications. One of the major problems for CZT detectors is low-energy tailing of the energy spectrum due to hole trapping. Spectral post-correction methods to correct the tailing effect do not work well for a number of reasons; thus it is advisable to eliminate the hole trapping effect in CZT using physical methods rather than correcting an already deteriorated energy spectrum. One method is using a CZT detector with an electrode configuration which modifies the electric field in the CZT volume to decrease low-energy tailing. Another method is to irradiate the CZT surface at a tilted angle, which modifies depth of interaction to decrease low-energy tailing. Neither method alone, however, eliminates the tailing effect. In this work, we have investigated the combination of modified electric field and tilted angle irradiation in a single detector to further decrease spectral tailing. A planar CZT detector with 10 × 10 × 3 mm3 size and CZT detector with 5 × 5 × 5 mm3 size and cap-shaped electrode were used in this study. The cap-shaped electrode (referred to as CAPture technology) modifies the electric field distribution in the CZT volume and decreases the spectral tailing effect. The detectors were investigated at 90° (normal) and 30° (tilted angle) irradiation modes. Two isotope sources with 59.6 and 122 keV photon energies were used for gamma-ray spectroscopy experiments. X-ray spectroscopy was performed using collimated beams at 60, 80 and 120 kVp tube voltages, in both normal and tilted angle irradiation. Measured x-ray spectra were corrected for K x-ray escape fractions that were calculated using Monte Carlo methods. The x-ray spectra measured with tilted angle CAPture detector at 60, 80 and 120 kVp tube voltages were compared to corresponding theoretical spectra. The low-energy tailing was nearly completely eliminated from 59.6 and 122 keV isotope spectra, and 60, 80 and 120 kVp x-ray spectra, when CAPture detector was used with 30° tilted angle irradiation. It is concluded that using a CZT detector with modified electric field in tilted angle configuration resolves problem of the tailing effect in CZT detectors, opening promising possibilities in gamma-ray and x-ray spectroscopy applications.

Experimental and Theoretical Evaluation of a High Resolution CMOS Based Detector Under X-Ray Imaging Conditions

Fundamental imaging performance in terms of Modulation Transfer Function (MTF), Noise Power Spectrum (NPS) and Detective Quantum Efficiency (DQE) was investigated for a high resolution CMOS based imaging sensor. The device consists of a 33.91 mg/cm2 Gd2O2S:Tb scintillator screen, placed in direct contact with a CMOS photodiode array. The CMOS photodiode array, featuring 1200×1600 pixels with a pixel pitch of 22.5 μm, was used as an optical photon detector. In addition to the conventional frequency dependent parameters characterizing image quality, image information content was assessed through the application of information capacity (IC). The MTF was measured using the slanted-edge method to avoid aliasing while the Normalized NPS (NNPS) was determined by two-dimensional (2D) Fourier transforming of uniformly exposed images. Both measurements were performed under the representative radiation quality (RQA) settings, RQA-5 (70 kVp digital-radiography) and RQA-M2 (28 kVp digital-mammography) recommended by the International Electrotechnical Commission Reports 62220-1 and 62220-1-2 respectively. The DQE was assessed from the measured MTF, NPS and the direct entrance surface air-Kerma (ESAK) obtained from X-ray spectra measurement with a portable cadmium telluride (CdTe) detector. The ESAK values ranged between 11-87 μGy for RQA-5 and 6-40 μGy for RQA-M2. Additionally the output electrons per X-ray photon of the detector and its signal transfer characteristics were assessed via an analytical model, within the framework of the linear cascaded systems (LCS) theory. It was found that the detector response function was linear for the exposure ranges under investigation. Additionally our results showed that for the same RQA quality the output electrons per X-ray photon, as well as the measured and analytically predicted MTF, were not significantly affected by ESAK. MTF and DQE where found better compared to previously published data for other CCD and CMOS sensors, while the NNPS appeared to be comparable in the frequency range under investigation (0-10 cycles/mm).

モリブデンターゲットＸ線管から放射されるＸ線スペクトルの推定計算式

A presumption calculating formula of the X-ray spectrum generated from a molybdenum target X-ray tube is presented. The calculation procedure is to add an amount of characteristic X-ray photons that corresponds to the ratio of characteristic photons and bremsstrahlung photons to the bremsstrahlung spectrum obtained using semiempirical calculation. The bremsstrahlung spectrum was calculated by using a corrected Tucker's formula. The corrected content was a formula for calculating the self-absorption length in the target that originated in the difference of the incident angle to the target of the electron and the mass stopping power data. The measured spectrum was separated into the bremsstrahlung component and the characteristic photon component, and the ratio of the characteristic photons and bremsstrahlung photons was obtained. The regression was derived from the function of the tube voltage. Based on this calculation procedure, computer software was constructed that can calculate an X-ray spectrum in arbitrary exposure conditions. The X-ray spectrum obtained from this presumption calculating formula and the measured X-ray spectrum corresponded well. This formula is very useful for analyzing various problems related to mammography by means of Monte Carlo simulations.

Numeric simulation of the diffraction pattern of zigzag grating

The zigzag grating is one of the newly proposed optical dispersive elements which has an excellent diffraction characteristics and has important applications in the spectrum measurement and analysis. The simulation results of the diffraction pattern of the zigzag grating for X ray are presented using a new numerical method based on the convolution theorem, and comparison of its diffraction pattern with those of the traditional grating and sinusoidal grating are studied. It is seen from the results that all higher order diffractions of the zigzag grating are suppressed below the level of four orders of magnitude compared with the first order diffraction, which is superior to the traditional grating, being consistent with the theoretical expectations. Moreover, the impact caused by the absorber is analyzed, which eventually confirms that the zigzag grating has perfect practical application feasibility. The conclusions provide a potential alternative for the physical design of the zigzag gating, which is expected to replace the traditional transmission grating in applications to the soft X-ray spectrum measurement.

High‐rate x‐ray spectroscopy in mammography with a CdTe detector: A digital pulse processing approach

Direct measurement of mammographic x-ray spectra under clinical conditions is a difficult task due to the high fluence rate of the x-ray beams as well as the limits in the development of high resolution detection systems in a high counting rate environment. In this work we present a detection system, based on a CdTe detector and an innovative digital pulse processing (DPP) system, for high-rate x-ray spectroscopy in mammography. The DPP system performs a digital pile-up inspection and a digital pulse height analysis of the detector signals, digitized through a 14-bit, 100 MHz digitizer, for x-ray spectroscopy even at high photon counting rates. We investigated on the response of the digital detection system both at low (150 cps) and at high photon counting rates (up to 500 kcps) by using monoenergetic x-ray sources and a nonclinical molybdenum anode x-ray tube. Clinical molybdenum x-ray spectrum measurements were also performed by using a pinhole collimator and a custom alignment device. The detection system shows excellent performance up to 512 kcps with an energy resolution of 4.08% FWHM at 22.1 keV. Despite the high photon counting rate (up to 453 kcps), the molybdenum x-ray spectra, measured under clinical conditions, are characterized by a low number of pile-up events. The agreement between the attenuation curves and the half value layer values, obtained from the measured spectra, simulated spectra, and from the exposure values directly measured with an ionization chamber, also shows the accuracy of the measurements. These results make the proposed detection system a very attractive tool for both laboratory research and advanced quality controls in mammography.

Establishment of the mammographic radiation qualities in industrial equipment: spectra determination

Abstract In this work, a Si(Li) detector was used to analyze mammographic X-ray spectra produced by an industrial equipment with Molybdenum (Mo) target, operating at constant tube potentials between 20 and 35 kV. Filters of Mo and Al of suitable thickness were added to the tube exit, in order to reproduce the radiation qualities of an X-ray mammographic equipment, as recommended by the International Electrotechnical Commission (IEC 61267) and the Physikalisch-Technischen Bundesanstalt (PTB). A detailed evaluation of the detector response functions was made using Monte Carlo simulations. The validity of this method was tested through comparisons with the experimental spectra of radioactive sources. The results showed that the Si(Li) detector exhibits good response function in low energy (between 5 and 20 keV). The measured X-ray spectra for a Mo filtration (0.03 mm thickness), corrected using the response functions, show a good agreement with the reference clinical spectra. The results of this work also show that both the radiation qualities implemented and the spectra shape are consistent with that obtained for mammographic X-ray beams, and they can be applied to calibration of the mammography measurements instruments (e.g. ionization chambers and dosimeters).

First experiments with the Dresden EBIS-SC

The Dresden EBIS-SC is a new superconducting EBIS designed for applications in medicine, basic research and other fields. After mechanical construction and a longer installation period first experiments have been accomplished to understand the source behavior and to get a well-founded sense about the working characteristics of the ion source. In a first step electrical properties were investigated and it was shown that the source works stable over a period of several days with electron beam currents Ie of up to 500 mA at an electron beam transmission of better than 0.999 Ie. Actually using a cathode of 1.5 mm the source reaches electron beam currents up to 750 mA. All measurements were performed at magnetic fields of 6 T. First ion extraction experiments demonstrate that the H2+ output at a pulse repetition frequency of 330 Hz and an electron beam current of 300 mA is higher than 1 × 108 ions per pulse. This output is sufficient for medical applications, e.g. in so-called CYCLINACs. Furthermore, the corresponding DC beam was measured to about 1 eμA. The beam emittance of extracted carbon ions was determined to (7…25) mm mrad. Extracted ion pulses show pulse FWHM in the order of (4 …12) μs. In this paper first ion extraction spectra of highly charged carbon, argon and xenon ions are presented for different source operation regimes. Additionally energy-dispersive measured X-ray spectra from argon and xenon ions are shown and discussed.

Corrosion resistance of stainless steel TP347H with aluminized layer

Corrosion resistance, structure, phase composition, and microhardness of aluminized layer on steel TP347H are studied. Aluminum saturation of the surface of stainless steel TP347H is performed from a solid-phase source in a chamber furnace at 900°C for 6 h. The properties of the aluminized layer are studied using the methods of light and scanning electron microscopy, energy dispersive x-ray spectrum analysis, x-ray diffractometry, and measurement of microhardness.

Performance of a digital CdTe X-ray spectrometer in low and high counting rate environment

The high performances of CdTe detectors for X-ray and gamma ray spectroscopy are already well known. Among the traditional semiconductor spectrometers, CdTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact detection systems. In this work, we investigated the performance of a CdTe detector coupled with a custom digital pulse processing (DPP) system for X-ray spectroscopy. The DPP method, implemented on a PC platform, performs a pile-up inspection and a pulse height analysis of the preamplifier output pulses, digitized by a 14-bit, 100MHz ADC. The spectroscopic results point out the excellent performance of the digital spectrometer both at low (150cps) and at high photon counting rate (up to 370kcps), confirming the high potentialities of CdTe detectors coupled with DPP systems. The detector and the DPP system were developed by our collaboration as a spectrometer prototype for direct measurement of diagnostic X-ray spectra in the 1–40keV energy range.

Measurement of radial and axial high energy x-ray spectra in electron cyclotron resonance ion source plasmas

Radial and axial x-ray measurements of electron cyclotron resonance ion sources operating at microwave frequencies of 6.4 and 14 GHz are presented. Results indicate a greater detected photon energy in the radial direction than the axial direction for both the 6.4 GHz source and the 14 GHz source. It is also seen that the 14 GHz source produces x-rays with higher energies, when compared to the 6.4 GHz source, in both radial and axial directions.

Probing neutron star physics using accreting neutron stars

We give an obervational overview of the accreting neutron stars systems as probes of neutron star physics. In particular we focus on the results obtained from the periodic timing of accreting millisecond X-ray pulsars in outburst and from the measurement of X-ray spectra of accreting neutron stars during quiescence. In the first part of this overview we show that the X-ray pulses are contaminated by a large amount of noise of uncertain origin, and that all these neutron stars do not show evidence of spin variations during the outburst. We present also some recent developments on the presence of intermittency in three accreting millisecond X-ray pulsars and investigate the reason why only a small number of accreting neutron stars show X-ray pulsations and why none of these pulsars shows sub-millisecond spin periods. In the second part of the overview we introduce the observational technique that allows the study of neutron star cooling in accreting systems as probes of neutron star internal composition and equation of state. We explain the phenomenon of the deep crustal heating and present some recent developments on several quasi persistent X-ray sources where a cooling neutron star has been observed.

X-ray astronomy in the laboratory with a miniature compact object produced by laser-driven implosion

Laboratory spectroscopy of non-thermal equilibrium plasmas photoionized by intense radiation is a key to understanding compact objects, such as black holes, based on astronomical observations. This paper describes an experiment to study photoionizing plasmas in laboratory under well-defined and genuine conditions. Photoionized plasma is here generated using a 0.5-keV Planckian x-ray source created by means of a laser-driven implosion. The measured x-ray spectrum from the photoionized silicon plasma resembles those observed from the binary stars Cygnus X-3 and Vela X-1 with the Chandra x-ray satellite. This demonstrates that an extreme radiation field was produced in the laboratory, however, the theoretical interpretation of the laboratory spectrum significantly contradicts the generally accepted explanations in x-ray astronomy. This model experiment offers a novel test bed for validation and verification of computational codes used in x-ray astronomy.

Study on response function of CdTe detector

So far the origin of the mechanism of light emission in the sonoluminescence has not elucidated whether it is due to blackbody radiation or bremsstrahlung. The final goal of our study is measuring X-ray energy spectrum using high-sensitivity cadmium telluride (CdTe) detector in order to obtain information for understanding sonoluminescence phenomena. However, the scope of this report is the measurement of X-ray spectrum using a high-resolution CdTe detector and determination of CdTe detector response function to obtain the corrected spectrum from measured soft X-ray source spectrum. In general, the measured spectrum was distorted by the characteristics of CdTe detector. Monte Carlo simulation code, MCNP, was used to obtain the reference response function of the CdTe detector. The X-ray spectra of 57Co, 133Ba, and 241Am were obtained by a 4×4×1.0(t) mm 3 CdTe detector at room temperature.

A PHOTOIONIZED NEBULA SURROUNDING AND VARIABLE OPTICAL CONTINUUM EMISSION FROM THE ULTRALUMINOUS X-RAY SOURCE IN NGC 5408

We obtained optical spectra of the counterpart of the ultraluminous X-ray source NGC 5408 X-1 using the FORS spectrograph on the VLT. The spectra show strong high excitation emission lines, He{\sc ii} $\lambda$4686 and [Ne{\sc V}] $\lambda$3426, indicative of X-ray photoionization. Using the measured X-ray spectrum as input to a photoionization model, we calculated the relation between the He{\sc ii} and X-ray luminosities and found that the He{\sc ii} flux implies a lower bound on the X-ray luminosity of $3 \times 10^{39} \rm erg s^{-1}$. The [Ne{\sc v}] flux requires a similar X-ray luminosity. After subtraction of the nebular emission, the continuum appears to have a power-law form with a spectral slope of $-2.0^{+0.1}_{-0.2}$. This is similar to low-mass X-ray binaries where the optical spectra are dominated by reprocessing of X-rays in the outer accretion disk. In one observation, the continuum, He{\sc ii} $\lambda$4686, and [Ne{\sc V}] $\lambda$3426 fluxes are about 30% lower than in the other five observations. This implies that part of the line emission originates within one light-day of the compact object. Fitting the optical continuum emission and archival X-ray data to an irradiated disk model, we find that $(6.5 \pm 0.7) \times 10^{-3}$ of the total bolometric luminosity is thermalized in the outer accretion disk. This is consistent with values found for stellar-mass X-ray binaries and larger than expected in models of super-Eddington accretion flows. We find no evidence for absorption lines that would permit measurement of the radial velocity of the companion star.

Double K-shell photoionization of low-Z atoms and He-like ions

We report on the investigation of the photon energy dependence of double 1s photoionization of light atoms and compare the cross sections for hollow atom and He-like ion production. Measurements of the Kα hypersatellite x-ray spectra of Mg, Al, and Si were carried out using the Fribourg high-resolution x-ray spectrometer installed at the ID21 and ID26 beam lines at the ESRF. The double-to-single photoionization cross section ratios were derived as a function of the incident photon beam energy and compared to convergent close-coupling (CCC) calculations for He-like ions. The dynamical electron-electron scattering contribution to the DPI cross-sections was found to be more important for neutral atoms than for the He isoelectronic series.

Physical Mechanisms and Scaling Laws ofK-Shell Double Photoionization

We report on the photon energy dependence of the K-shell double photoionization (DPI) of Mg, Al, and Si. The DPI cross sections were derived from high-resolution measurements of x-ray spectra following the radiative decay of the K-shell double vacancy states. Our data evince the relative importance of the final-state electron-electron interaction to the DPI. By comparing the double-to-single K-shell photoionization cross-section ratios for neutral atoms with convergent close-coupling calculations for He-like ions, the effect of outer shell electrons on the K-shell DPI process is assessed. Universal scaling of the DPI cross sections with the effective nuclear charge for neutral atoms is revealed.

Surface coating of microparticles with tungsten carbide by using the barrel sputtering system

We studied the coating of microparticles with tungsten carbide using a sputtering system with barrel-type powder sample holder (the barrel sputtering system). In order to find suitable sputtering conditions using the system, tungsten carbide was coated on a glass plate under various desired methane fractions, total pressures and RF powers. According to the XRD analysis on the fabricated films, the desired parameter is attained at a methane fraction of 5%, a total pressure of 1.5 Pa, and an RF power of 100 W. Surface coating of polymer microparticles with a WC layer was performed under this condition. Scanning electron microscope and energy-dispersion X-ray spectrum measurement show that the surface of the microparticle is uniformly coated with a thin WC layer.