Measurement of L subshell fluorescence yield ratios of some high Z elements by selective excitation method

The L₁, L₂ and L₃ subshells of Hf, Ta and Re atoms have been excited selectively by using microprobe XRF beam line, Indus‐2, RRCAT, India. The consequent characteristic L X‐ray photons, emitted from the targets due to creations of vacancies in L subshells, are measured using silicon drift detector (X‐123) spectrometer. As the energy of synchrotron radiation increases, the contribution of characteristic L X‐ray intensity increases. The advantage of the increase in the intensity of the characteristic L X‐ray photons with an increase in the energy of synchrotron radiation has been used to determine the L subshell fluorescence yield ratios of Hf, Ta and Re atoms by adopting the selective excitation method. The measured ratios of L subshell fluorescence yield have been compared with theoretical and other experimental values.     

Monte Carlo Calculations of XRF Intensities in Annular Arrangements of Radioactive Source,Sample, Cylindrical Collimator and Detector

ABSTRACT

A Monte Carlo (MC) computer program for the calculation of the distribution of characteristic X-ray intensities as a function of the counting geometry is described. The program evaluates the contribution to the intensities of a fluorescent line from each point of the source, sample and detector. The main considerations of the calculation are based on the critical nature of the internal geometry of the main analyzer components within an energy dispersive X-ray fluorescence (EDXRF) spectrometer. The K XRF intensities for the inner and outer radius of the annular-sample and collimator radius were measured. An optimum geometry can be obtained by varying the collimator radius and the detector-sample distance. The results of the calculations show that the intensity distribution of the radioisotope excited fluorescent radiation through annular sample area is strongly dependent on the collimator radius, with a maximum intensity effect with a smaller sample area and with decreasing collimator radius. An investigation of the XRF intensities in the annular sample surface as a function of collimator radius is discussed.     

Fundamental parameter approach to XRF spectroscopy measurements of arsenic in polyester resin skin phantoms

A fundamental parameter (FP) approach that explicitly incorporates the energy‐broadening response of the detector was developed. The ratio between Kα fluorescence peak area and the sum of coherently and incoherently scattered peak areas was used as an indicator of trace element concentration. The peak ratio was theoretically calculated using the FP method. The energy‐broadening response curve of the Si(Li) detector was estimated by matching the theoretical and experimental values of this ratio. The method was implemented for the analysis of the K‐shell x‐ray fluorescence (K‐XRF) spectra of six polyester resin samples corresponding to six different arsenic concentrations. A ¹⁰⁹Cd radioactive source provided the excitation radiation for spectra acquisition. The predicted detector energy resolution expressed as full width at half‐maximum (FWHM) for Fe Kα fluorescence peak (208 ± 5 eV at 6.4 keV) and As Kα fluorescence peak (222 ± 5 eV at 10.5 keV) were in agreement with the experimental measurements. Copyright © 2008 John Wiley & Sons, Ltd.     

Methodology for the determination of minor and trace elements in petroleum cokes by wavelength‐dispersive X‐ray fluorescence (WD‐XRF)

This article describes a methodology for the analysis of minor and trace elements in petroleum cokes by wavelength‐dispersive X‐ray fluorescence (WD‐XRF) spectrometry. The methodology was developed in order to have a rapid and reliable control method of these elements, because they determine coke end uses. There are a number of standard methods of chemical analysis by WD‐XRF or inductively coupled plasma atomic emission spectrometry (ICP‐OES) techniques. However, the standards that use WD‐XRF measurement give detection limits (L_D) above 10 mg·kg^?1 and only analyse a few elements of interest, whereas the ICP‐OES method requires extensive sample handling and long sample preparation times, with the ensuing errors. In order to improve the method described in the standard ASTM D6376 and reach the L_D and quantification limits (L_Q) required, the different stages of the process, ranging from sample preparation to measurement conditions: analytical line, detector, crystal, tube power, use of primary beam filters, and measurement time, were optimised. The samples were prepared in the form of pressed pellets, under conditions of high cleanliness of the mills, crushers, presses, and dies, and of the laboratory itself. The following reference materials were used in measurement calibration and validation: SRM 1632c, SRM 2718, SRM 2719, SRM 2685b, AR 2771, AR 2772, SARM 18, SARM 19, and CLB‐1. In addition, a series of materials were analysed by WD‐XRF and ICP‐OES, and the results were compared. The developed methodology, which uses WD‐XRF, is rapid and accurate, and very low L_D and measurement uncertainties were obtained for the following elements: Al, Ba, Ca, Cr, Cu, Fe, Ge, K, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Se, Si, Sn, Sr, Ti, V, and Zn. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of in‐target Compton‐scattering in lanthanum fluorescence spectra

A study was made of the continuum adjacent to the Kα₁ and Kα₂ peaks (the ‘shoulder’) in lanthanum fluorescence spectra. The fluorescence was induced by 59.537 keV γ‐rays from a ²⁴¹Am source. The spectra were observed with an La₂O₃‐loaded paraffin target (the ‘La target’). To limit the observations to the scattering in the target, a collimator was used in front of the germanium detector, which strongly reduced the near‐detector scattering. Changes in the shoulder spectra were observed on attaching additional mass to the La target and on changing its orientation with respect to the detector‐to‐target centre‐line. The measurements clearly show that the main cause of the shoulder spectra is the in‐target Compton scattering. A different distribution of mass in the vicinity of the fluorescing atoms with respect to the detector‐to‐target centre‐line results in different probabilities of the observed scattering at all angles. Since the energy of secondary Compton photons is directly related to the scattering angles, different distributions of mass cause changes in the shoulder spectra. Comparison of the calculated and measured shoulder spectra shows good agreement on an absolute scale. Copyright © 2006 John Wiley & Sons, Ltd.     

用于闪光照相的准直器设计及性能

为了实现高度准直同时较好地保留飞层界面信息,针对高能闪光照相实验中常用的准直技术,改进了设计方法,以法国实验客体(FTO)为例,利用蒙特卡罗程序对光子电子耦合输运过程进行数值模拟实验,验证了所提出的准直器的性能,对采用该准直器技术下的模拟照相结果进行了准直器光程扣除方法研究,结果表明:改进的准直器将客体芯部区域的散射照射量降低99.8%,接收平面处的客体信号动态范围降低99.7%,同时在图像中完整地保留了客体外界面信息;对准直器轴向分层照相的方法可以获得误差小于0.1的客体光程。     

Feasibility for chemometric energy dispersive X‐ray fluorescence and scattering (EDXRFS) spectroscopy method for rapid soil quality assessment

Soil quality assessment (SQA) is important for modulating agricultural productivity and thus requires simple and rapid analysis of soil (macro & micro) nutrients (here called soil quality indicators – SQIs). We report proof of concept of a chemometrics‐assisted energy dispersive X‐ray fluorescence and scattering (EDXRFS) spectroscopy technique for direct rapid analysis of SQIs. The EDXRFS method exploits, in addition to fluorescence, the X‐ray scatter peaks obtained non‐invasively from soils to develop a calibration strategy for quantitative analysis of SQIs in model clay soils doped with micronutrients (Fe, Cu, and Zn) and macronutrients (NO₃^?, SO₄^2?, and H₂PO₄^?). The soil samples and certified reference materials IAEA Soil‐7 and IAEA Soil‐1 (used to build spectral library for soil classification) were irradiated at various live times (to simulate different signal‐to‐noise ratios of analyte signals and analysis speed) in a teflon holder and were analyzed using a ¹⁰⁹Cd‐excited XRF spectrometer. Principal components analysis was used for spectral data compression and pattern recognition (including for those SQI spectral signatures without any visibly discernible characteristic X‐ray lines), whereas partial least squares regression and artificial neural networks were used to build a calibration and quantitative analysis strategy. The method furnishes soil micronutrient and macronutrient information simultaneously and rapidly (t = 200 s). To the best of the authors' knowledge, this is the first time that an XRF method has demonstrated spectroanalytical potential for quantitative macronutrients analysis in soils applicable to routine SQA. Coupling EDXRFS with multivariate chemometrics enables rapid and reliable assessment of chemical SQIs. Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental evaluation of effective atomic number of composite materials using back-scattering of gamma photons

A method has been presented for calculation of effective atomic number (Z_eff) of composite materials, by using back-scattering of 662?keV gamma photons obtained from a ¹³⁷Cs mono-energetic radioactive source. The present technique is a non-destructive approach, and is employed to evaluate Z_eff of different composite materials, by interacting gamma photons with semi-infinite material in a back-scattering geometry, using a 3^″?×?3^″ NaI(Tl) scintillation detector. The present work is undertaken to study the effect of target thickness on intensity distribution of gamma photons which are multiply back-scattered from targets (pure elements) and composites (mixtures of different elements). The intensity of multiply back-scattered events increases with increasing target thickness and finally saturates. The saturation thickness for multiply back-scattered events is used to assign a number (Z_eff) for multi-element materials. Response function of the 3^″?×?3^″ NaI(Tl) scintillation detector is applied on observed pulse-height distribution to include the contribution of partially absorbed photons. The reduced value of signal-to-noise ratio interprets the increase in multiply back-scattered data of a response corrected spectrum. Data obtained from Monte Carlo simulations and literature also support the present experimental results.     

In vivo time‐resolved X‐ray fluorescence mapping measurements of Egeria densa immersed in Cr(VI) aqueous solution

In vivo time‐resolved Cr and Ca X‐ray fluorescence (XRF) mapping measurements were performed in a laboratory over a period of 69 days on a living common aquatic plant Egeria densa that was immersed in 5 mM K₂CrO₄ aqueous solution. The time and spatial resolution for each time‐resolved XRF map were ~1.6 days and 1 × 1 mm², respectively. The obtained XRF maps exhibited characteristic localized Cr and Ca areas where the XRF signals were especially strong (‘hot spots’), and this indicated the necessity of preliminary millimeter‐resolution surveying in XRF microscopy. Ca hot spots were detected prior to Cr(VI) immersion and nearly disappeared after immersion in deionized water for 2 weeks and the Cr(VI) solution for 1 week. After these immersions, a Cr hot spot was formed at approximately the same location of the missing Ca hot spot, which suggests that the original Ca‐accumulated regions were substituted for the isolation of Cr species when they were introduced. The sizes and intensity distributions of the Cr hot spots were sensitive to the Cr(VI) exposure approximately 1 week prior to each XRF measurement. This sensitivity suggests potential applications of E. densa as a Cr(VI) biomonitor in aquatic environments. Copyright © 2014 John Wiley & Sons, Ltd.     

Measurement of vacancy transfer probability from K to L shell using K-shell fluorescence yields

The vacancy transfer probabilities from K to L shell through radiative decay, η _KL, have been deduced for the elements in the range 19 ≤ Z ≤ 58 using K-shell fluorescence yields. The targets were irradiated with γ photons at 59.5 keV from a 75mCi ²⁴¹Am annular source. The K X-rays from different targets were detected with a high resolution Si(Li) detector. The measurement of vacancy transfer probabilities are least-squared fitted to second-order polynomials to obtain analytical relations that represent these probabilities as a function of atomic number. The obtained results agree with theoretical and fitted values.     

X-ray fluorescence intensity distribution in circular specimens

Summary The relative X-ray fluorescence (XRF) intensities for annular source and various annular specimen are measured with a Ge-Li detection system and calculated by the Monte Carlo numerical techniques (MCNT).Kα X-ray intensities of annular specimens with different radii prepared from a pure-molybdenum foil are measured and it is seen that the measured values are in good agreement with the values calculated by MCNT. The variation of the fluorescence intensity due to the collimator radius is also studied. The differences between the MCNT and experimental results are discussed in terms of the possible sources of errors.     

A new way of measuring the contribution of scattered photons to x‐ray fluorescence yields in secondary excitation mode

The characteristic K x‐rays from a secondary exciter in conjunction with an x‐ray tube or a radioisotope as primary source are frequently used for target excitation in x‐ray fluorescence measurements. In this experimental arrangement, the exciting photon spectrum consists of two parts: (i) characteristic K x‐rays of the secondary exciter and (ii) photons from the primary source, which are scattered from the secondary exciter. A new method is proposed for correcting the observed target x‐ray yield due to unwanted excitation by the scattered photons. This method involves measurement of x‐ray yield after replacing the secondary exciter by an equivalent exciter consisting of a low‐Z element foil with a high‐Z element backing. Copyright © 2004 John Wiley & Sons, Ltd.     

Measurement of K absorption edge energies of silver and tin targets using a weak beta source

K absorption edge energies of Ag and Sn elements have been determined by using a weak beta source. In this method, the beta particles from a ⁹⁰Sr? ⁹⁰Y beta source interact with an iron foil to produce the external bremsstrahlung (EB) photons. The spectrum of EB photons is passed through the elemental target and the spectrum of transmitted photons is recorded with a high resolution HPGe detector spectrometer coupled to 16K multichannel analyzer. The recorded transmitted EB spectrum shows a sharp decrease in intensity at the K shell binding energy of elemental target. Such a sharp decrease region, which is corrected for Kβ′₂ contribution, has been used to determine the K absorption edge energies of Ag and Sn elemental targets. The measured values have been compared with theoretical and experimental values. Copyright © 2010 John Wiley & Sons, Ltd.     

X‐ray fluorescence analysis of Co,Ni, Pd,Ag, and Au in the scrapped printed‐circuit‐board ash

A method for the quantitative analysis of Co, Ni, Pd, Ag, and Au in the scrapped printed‐circuit‐board ash by X‐ray fluorescence (XRF) spectrometry using loose powder was developed. The printed‐circuit‐board samples were converted to ash pyrolytically in porcelain crucibles by sequential heating using a gas burner and electric furnace, and then were ground with a ball mill. The calibrating standards were prepared by adding the appropriate amounts of NiO powder and aqueous standard solutions containing Co, Pd, Ag, and Au to the base mixtures of Al₂O₃ (5.0 mass%), SiO₂ (49 mass%), CaCO₃ (11 mass%), Fe₂O₃ (3.3 mass%), and CuO (30 mass%) as a matrix. Then, 10 g of the resulting mixtures were dried and homogenized for 90 min with a V‐type mixing machine. Specimens for XRF analysis were prepared from the so‐called loose‐powder method in which powder samples were compacted into a hole (12.0‐mm diameter and 5.0‐mm height) in an acrylic plate and covered with a 6‐µm thickness of polypropylene film. Matrix effects were corrected using the intensity value of Compton scattering for PdKα, AgKα, and AuLβ₂, and that of background scattering at 35.8° (2θ) for CoKα and NiKα. The detection limits corresponding to three times the standard deviation of the blank intensity were 2.5–45 µg g^?1. The proposed method was validated against the pressed‐powder‐pellet method by comparing the calibration curves. Moreover, the concentrations of Co, Ni, Pd, and Ag determined using the proposed XRF method were approximately the same as those resulting from an atomic‐absorption‐spectrometric analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of collimator size and absorber thickness on gamma ray attenuation measurements for bakelite and perspex

The mass attenuation coefficient (μ _m) of 662 keV gamma rays have been measured in the extended media of bakelite and perspex under different collimation conditions. The increase in attenuation coefficient is seen with increase in sample thickness as well as with collimator size due to the contribution of multiple scattered photons in the uncollided beam of 662 keV gamma rays.     

Photon distribution function in blinking fluorescence of individual molecules

A photon distribution function w_N(T) for blinking fluorescence with bright on- and dark off-intervals is derived. The function w_N(T) is expressed via few Poissonian functions each of which relates to corresponding exponential process in quantum dynamics of a given individual molecule. The distribution of photons is calculated for short, middle and long time intervals as compared to off-intervals. The distributions are much broader than Poissonian distribution and have rather complicated shape. If time resolution of an experiment does not permit us to see off-interval and, therefore, fluorescence looks like CW emission, the distribution of photons gives a signal about existence of hidden off- intervals in such CW fluorescence.     

Measurement of L subshell fluorescence yields of some rare earth elements using synchrotron radiation

The L subshell fluorescence yields ω₁, ω₂ and ω₃ of Gd, Tb and Ho have been measured using Indus‐2 synchrotron radiation. The L X‐ray photons generated in the elemental targets by 10 and 11 keV synchrotron radiation have been measured using silicon drift detector that has an energy resolution of 130 eV at 5.9 keV. The measured values of ω₁, ω₂ and ω₃ have been compared with theoretical values, semi‐empirical fitted values and other experimental values. Copyright © 2015 John Wiley & Sons, Ltd.     

A BaF2 crystal array for high energy γ-ray measurements

We shall discuss about the scientific motivation and construction of a 7×7 BaF₂ crystal array at Variable Energy Cyclotron Centre, Calcutta. This detector would be used to measure high energy γ-ray photons from GDR decay and proton-neutron bremsstrahlung reactions at the present 88″ cyclotron and upcoming superconducting cyclotron at VECC, Calcutta. This detector can also be used to measure photons from quark-gluon plasma at the relativistic heavy ion collider (RHIC) in USA.     

New experimental limits on the probabilities of pauli-forbidden transitions in the <Superscript>12</Superscript>C nucleus from data obtained with the borexino detector

The Pauli exclusion principle was tested for nucleons in the ¹²C nucleus by using data from the Borexino detector. The approach used consisted in seeking photons, neutrons, and protons, as well as electrons and positrons, emitted in the Pauli-forbidden transitions of nucleons from the 1P _3/2 shell to the filled 1S _1/2 shell. Owing to a uniquely low background level in the Borexino detector and its large mass, the currently most stringent experimental limits were obtained for the probabilities and relative intensities of Pauli-forbidden transitions for the electromagnetic, strong, and weak channels.     

Search for fermiophobic Higgs bosons in final states with photons at LEP 2

Higgs boson production with subsequent decay to photons was searched for in the data collected by the DELPHI detector at centre-of-mass energies between 183 GeV and 209 GeV, corresponding to a total integrated luminosity of nearly 650 pb^-1. No evidence for a signal was found, and limits were set on h ⁰ Z ⁰ and h ⁰ A ⁰ production with h ⁰ decay to photons. These results were used to exclude regions in the parameter space of fermiophobic scenarios of Two Higgs Doublet Models.