The backscattering factor for the Au N67VV Auger transition

The Au N₆₇VV Auger transition may take place after direct ionization of the N₆₇ subshells or after ionization of the N₄₅ subshells followed by the Coster-Kronig transitions N₄₅N₆₇V. The subshells N₆₇ and N₄₅ have much different ionization energies, by a factor of four, and this creates a problem in quantification of the N₆₇VV signal. Calculations of the backscattering factor from the analytical expressions require knowledge of a single value of the ionization energy. Furthermore, a single value of the ionization energy is needed in calculations of the ionizations cross section. An attempt is made here to decide which ionization energy should be used in calculations by comparison of the experimental energy and emission angle dependence of the AES signal intensity with this dependence determined from theory using different ionization energies. It has been found that the N₆₇VV signal intensity is strongly dominated by ionizations of the N₅ subshell. Furthermore, the ionization cross section for the N₅ subshell is well described by the Casnati et al. formula.     

Cascade Mi (i = 1–5) subshell X‐ray emission at incident photon energies across the Lj (j = 1–3) subshell absorption edges of 66Dy

The total M shell and the M_k (k = ξ, αβ, γ, m) X‐ray production cross sections for ₆₆Dy have been measured at incident photon energies across its L_j (j = 1–3) subshell absorption edge energies, ranging 7.8–9.2 keV. This study aims to investigate the evolution of the probability for cascade decay of L_j subshell vacancies as the tunable incident energy ionizes progressively different ₆₆Dy L_j subshells. The experimental X‐ray production cross sections have been compared with theoretical ones calculated using the nonrelativistic Hartree–Fock–Slater (HFS) model‐based photoionization cross sections; three sets of the X‐ray emission rates, fluorescence and Coster–Kronig yield based on the nonrelativistic Hartree–Slater (NRHS) model, Dirac–Hartree–Slater (DHS) model and Dirac–Fock (DF) model; the L_j (j = 1–3) subshell to the M_i (i = 1–5) subshell vacancy transfer probabilities evaluated in the present work. Presently measured total M shell and the M_αβ X‐ray production cross sections are found to be significantly lower than the theoretical ones evaluated using physical parameters based on the relativistic Dirac–Fock/Dirac–Hartree–Slater model calculations, whereas a much better agreement is observed with respect to the NRHS model‐based calculations; however, the measured X‐ray production cross sections are still systematically lower than the NRHS values.     

New screening coefficients for the hydrogenic ion model including l-splitting for fast calculations of atomic structure in plasmas

New screening coefficients are given for calculating the energy levels of many-electron atoms in the hydrogenic ion approximation including l-splitting. This model allows fast computation of various atomic parameters (one-electron energies, ionization potentials, etc.) for all ionization stages of any element with no restriction concerning the maximum nl subshell. Part of the screening coefficients have been obtained from numerical fits over a large data base containing ionization potentials and excitation energies of ions. The others have been extrapolated by means of regularities deduced from the adjustment procedure. The mean and root mean square errors are better than 5% and 16.2%, respectively, for the 15 636 data considered. Some properties of the new screened hydrogenic model are studied, such as the filling competitions between several subshells of the lanthanides. The meaning of one-electron energies available from the total ion energy is discussed and the status of the self-screening term in plasmas in local thermodynamic equilibrium is briefly addressed. These notions are of great importance for coherence between the statistical treatment of such media and the calculation of their spectral properties.     

Measurement of the X‐ray mass attenuation coefficients of silver in the 5–20 keV range

The X‐ray mass attenuation coefficients of silver were measured in the energy range 5–20 keV with an accuracy of 0.01–0.2% on a relative scale down to 5.3 keV, and of 0.09–1.22% on an absolute scale to 5.0 keV. This analysis confirms that with careful choice of foil thickness and careful correction for systematics, especially including harmonic contents at lower energies, the X‐ray attenuation of high‐Z elements can be measured with high accuracy even at low X‐ray energies (<6 keV). This is the first high‐accuracy measurement of X‐ray mass attenuation coefficients of silver in the low energy range, indicating the possibility of obtaining high‐accuracy X‐ray absorption fine structure down to the L₁ edge (3.8 keV) of silver. Comparison of results reported here with an earlier data set optimized for higher energies confirms accuracy to within one standard error of each data set collected and analysed using the principles of the X‐ray extended‐range technique (XERT). Comparison with theory shows a slow divergence towards lower energies in this region away from absorption edges. The methodology developed can be used for the XAFS analysis of compounds and solutions to investigate structural features, bonding and coordination chemistry.     

Precision X-ray optics for fundamental interactions in atomic physics,resolving discrepancies in the X-ray regime

Reliable knowledge of the complex X-ray form factor (Re(f) and f) is required for many fields including crystallography, medical diagnosis and XAFS studies. However, there are discrepancies between theory and theory, experiment and experiment and theory and experiment of 10% and more, over central X-ray energies. Discrepancies exist for most elements, despite claimed experimental accuracies of 1%. This paper summarises the current variation between experimental and theoretical results, and outlines key issues for obtaining experimental accuracies of 1% in critical wavelength ranges for selected elements to address these issues. This paper critically surveys available experimental data for attenuation coefficients and suggests a procedure for obtaining significantly higher accuracy measurements in the future.     

Determination of the primary dose component and primary linear attenuation coefficient in a 6 MV photon beam using a small attenuator

It is a common technique in radiotherapy treatment planning systems to simplify the calculations by splitting the radiation beam into two components: namely the primary and scattered components. The contributions of the two components are evaluated separately and then summed to give the dose at the point of interest.Usually the primary dose is obtained experimentally by extrapolating the ionization measured within the medium to zero-field size (Godden, 1983). This approach offers the opportunity to obtain the primary component of dose without the need for a non-linear extrapolation. It is based on a paper by Nizin and Kase from 1988.The primary dose can be obtained from four measurements of ionization in narrow beam geometry and two measurements of ionization in a large beam in a phantom. If these measurements are performed over a range of different depths, the primary linear attenuation coefficient can also be obtained.The value for the primary dose at d_max in a 10 cm × 10 cm field obtained in a 6 MV beam using this method is D_p(d_max, 10 cm × 10 cm) = 0.925 Gy/100 MU for a 1 cm thick lead attenuator and is D_p(d_max, 10 cm × 10 cm) = 0.941 Gy/100 MU for a 2 cm thick lead attenuator. The primary linear attenuation coefficient is μ₀ = 0.0445 ± 0.0007 cm^?1.The obtained values of the primary dose component compare well with the extrapolation of the phantom scatter correction factor to zero-field size from measurements done in the same beam and also to literature (Rice and Chin, 1990). One can thus conclude that this method has the potential to provide an independent measurable verification of calculations of primary dose.     

Measurement of angular distribution of M shell fluorescent X-rays excited by 5·95 keV photons in thorium

The differential cross-sections for the emission of M shell fluorescent X-rays from Th by 5·95 keV photons at eight angles ranging from 50° to 120° have been measured. The differential cross-section is found to decrease with increase in the emission angle showing anisotropic spatial distribution of M shell fluorescent X-rays. The present results contradict the predictions of the calculations of Cooper and Zare [1] that the atomic inner shell vacancy states produced in photoionization are not aligned but confirm those of Fluggeet al [2] and Scofield [3] that the vacancy states withJ > 1/2 are aligned. The integral M shell fluorescent emission cross sections have been determined from the measured angular distribution coefficients and compared with theoretical integral cross-sections calculated by using theoretical values of M subshell photoionization cross-sections, fluorescence yields and coster kronig transition probabilities available in literature. The experimental and theoretical values of integral crosssections show a reasonable agreement.     

Anisotropy of L X-rays of Uranium and Thorium

INTRODUCTION

The theoretical calculations by Flugge et a1 [l] have shown that the Xrays originating from the states corresponding to J=1/2(K shell and L_I, L_II, M_I, M_II subshell etc.) are emitted to be isotropic and those corresponding to state J=5/2(e.g. Mv subshell) are emitted to be anisotropic in their spatial distribution. There are many studies on L X-ray intensity ratios. But there is little reported on isotropy and anisotropy of L X-rays. Kahlon et a1 [2,3] investigated isotropy and anisotropy of L X-rays. We investigated the anisotropy of L shell X-rays in Au and Hg [4] and the angular dependence of differential cross-sections of L X-rays from Hg, T1 and Pb [5].     

X射线强度变化的测量实验

用X射线实验仪探测X射线强度的衰减规律,研究了X射线的衰减与不同厚度吸收体间的关系、X射线的衰减与样品原子序数的关系以及发射电流和管电压对X射线强度的影响。     

A combined experimental and theoretical approach to determine X‐ray atomic fundamental quantities of tin

The knowledge of atomic fundamental parameters, such as the mass attenuation coefficients or fluorescence yields with low uncertainties, is of decisive importance in elemental quantification involving X‐ray fluorescence analysis techniques. For example, several databases giving the mass attenuation coefficients are accessible and frequently used within a large community of users. These compilations are most often in good agreement for photon energies in the hard X‐ray ranges. However, they significantly differ for low photon energies and around the absorption edges of the elements. In the case of the fluorescence yields, some authors made a review of measured values found in the literature. However, reliable measurements are not so many illustrating the inherent difficulties. Mass attenuation coefficients of tin were determined experimentally in the photon energy range from 100 eV to 35 keV by using monochromatized synchrotron radiation at SOLEIL (France). The fluorescence yields of the 3 L‐subshells of tin were also determined using a reflection geometry setup and the X‐ray fluorescence setup of Physikalisch‐Technische Bundesanstalt. The Coster–Kronig factors for the tin L‐shells were also experimentally determined. The application of high‐accuracy experimental techniques resulted in low uncertainty mass attenuation coefficients and L‐subshell fluorescence yields that are directly compared with existing databases and with updated relativistic configuration mixing Dirac–Fock calculations including Quantum electrodynamics (QED) corrections.     

Forming metastable carbon-rich anions in planetary atmospheres: the case of diacetylene

Alignment of the L ₃ ? (J = 3 / 2) subshell vacancy states in the Au, Bi, Th and U elements following photoinisation have been investigated through angular distribution measurements of subsequently emitted L ₃ subshell X-rays. The 59.54 keV unpolarised γ-rays from the ²⁴¹Am radioactive point-source were used to ionize the target and the subsequently emitted L X-rays were measured using an HPGe detector. The improved experimental procedure along with correct evaluation scheme permits straight-forward method for investigating anisotropy in photo-excited L X-ray emission. The efficiency of the detector and the absorption correction for the emitted L X-rays in the target remain fairly constant as the target-detector assemblage remains undisturbed in the present measurements at various angles. Isotropically emitted L ₁ subshell (J = 1 / 2) X-rays measured simultaneously were used to normalize the L X-ray spectra taken at different emission angles. The present measurements clearly support small theoretical predicted values of the alignment parameter; however, it is difficult to infer regarding the predicted anisotropic trends. The angular distribution measurements for the L ₃ subshell X-ray emission were also performed by placing the target in magnetic field  ～ 0.6 T. The earlier reported large anisotropy in angular distribution of the emitted L ₃ subshell X-rays and significant effect of external magnetic field on the angular distribution are ruled out.     

Probabilities for radiative vacancy transfer from Li (i=1, 2, 3) sub-shells to the M, N and higher shells for elements with 77≤Z≤92

The probabilities for transfer of the L_i (i=1, 2, 3) subshell vacancy to the M, N and higher shells through radiative decay, ηLiJ(R), have been deduced for the elements with 77≤Z≤92 using the measured L X-ray production cross-sections at (i) the 59.54 keV γ-rays such that BL₁<Einc<BK and (ii) the K X-rays of a suitable secondary target chosen such that BL₃<EKα<BL₂ and BL₁/L₂<EKβ<BK; where BK/Li is the K shell/L_i subshell ionisation threshold of the target element. The deduced probabilities are compared with those calculated using the radiative and nonradiative transition rates based on the Dirac-Fock (DF) and the relativistic Dirac-Hartree-Slater (RDHS) calculations, respectively.     

Increased Accuracy of the Binding Energy of K- and L-Subshell Electrons in Krypton from Re-analysis of Experimental Data: Importance for Determination of the Neutrino Mass

Analyzing thoroughly K and L X-ray transition energies, results of the former L-shell photoabsorption study and M subshell binding energies from photoelectron and optical spectroscopy, we determined the following electron binding energies in gaseous krypton: 14 327.26(4) eV for the K-shell and 1 921.4(3), 1 731.91(3) and 1 679.21(3) eV for L₁-, L₂-, and L₃-subshells, respectively. These accurate values of electron binding energies are important for energy calibration of the next generation tritium -decay experiment KATRIN with sub-eV sensitivity for the electron-neutrino mass.     

Advances in the measurements of the mass attenuation coefficients

The knowledge of atomic fundamental parameters, such as mass attenuation coefficients or fluorescence yields with low uncertainties, is of decisive importance in elemental quantification involving X-ray fluorescence analysis techniques. Several databases providing the mass attenuation coefficients are accessible and frequently used within a large community of users. These compilations are most often in good agreement for photon energies in the hard X-ray ranges. However, they significantly differ for low photon energies and around the absorption edges of the elements. Mass attenuation coefficients of several elements were determined experimentally in the photon energy range from 100 eV to 35 keV by using monochromatized radiation at the SOLEIL synchrotron (France). The application of high-accuracy experimental techniques resulted in low uncertainty mass attenuation coefficients. The results are compared with tabulated data.     

H+ and He2 + induced W L X‐rays intensity ratios: part I,Si(Li) data and EDS high resolution insight

Recently, the authors have presented experimental evidences that for some energy windows, proton‐induced W L shell X‐rays intensity ratios of transitions to L₁ subshell depend on the ion beam energy and on the chemical species even after known matrix effects are subtracted. These results, which put in question the assumption of the invariance of the relative intensity of X‐ray transitions to the same atomic subshells, are further exploited in this work, where more data for three different W compounds (W, Li₂WO₄ and P₂O₅.24WO₃.xH₂O) are presented followed by a detailed study using an ultra‐pure (99.995%) W thick foil, used to avoid any possible target contamination interference on the results. Samples were irradiated by H⁺ beams in various conditions in the energy range between 0.25 and 2.38 MeV and by He^{2 +} beams having energies between 3.5 and 5.0 MeV. Spectra were collected using the Si(Li) detector at CTN 2.5 MV Van de Graaff standard Proton‐Induced X‐ray Emission (PIXE) set‐up as well as using the Energy Dispersive Spectrometry (EDS) high resolution X‐ray microcalorimeter spectrometer (XMS) at CTN 3.0 MV Tandetron accelerator high resolution high energy (HRHE) PIXE end station. Results were normalized to the theoretical intensity ratios and plotted as function of the ratio of collision characteristic times allowing the comparison of H⁺ and He^{2 +} results. W L X‐rays intensity ratio variations are presented and compared with theoretical expected results. Radiative Auger emission transitions observed in an EDS high resolution XMS spectra are shown to probably play a crucial role in the highly unexpected results obtained for intensity ratios of transitions to the same subshell. Copyright © 2013 John Wiley & Sons, Ltd.     

W44+ 离子双电子复合速率系数的理论研究

利用全相对论组态相互作用方法,详细研究了W44+ 离子从基组态3s23p63d104s2俘获一个电子形成双激发态(3s23p63d104s2)nln′l′(n = 4 ~ 6,n′= 4 ~7) 的双电子复合(DR) 过程。通过比较不同壳层电子激发的DR 速率系数,得知4s 电子激发和3d 电子激发的DR 速率系数分别在低温和中高温度时给出了主要贡献,得到了主要的电子激发DR通道。在1 eV~50 keV 温度范围内,计算了n = 4~18 的DR速率系数,并外推到了n= 100,得到总DR 速率系数。比较总DR 速率系数、三体复合(TBR) 以及辐射复合(RR) 速率系数,结果表明DR 速率系数在研究的温度范围内远大于TBR 和RR 速率系数,其将明显地影响ITER 等离子体的电离平衡和离化态布居。Based on the fully relativistic configuration interaction method, theoretical calculations are carried out to research the dielectronic recombination (DR) processes, in which W44+ ions in the ground state 3s23p63d104s2 trap an electron to form doubly excited states (3s23p63d104s2)nln’l’(n =4~6,n′= 4~7). The comparison of the DR rate coefficients of different shells shows that DR approach is as follow: the 4s subshell excitation dominates to DR at low temperature, but 3d subshell excitation attributes to DR at high temperature. Total DR rate coefficients from n=4~18 are evaluated directly, and the results are extrapolated up to n = 100 in the temperature range from 1 to 5×104 eV, and thus get the total DR rate coefficients. Compared total DR rate coefficients to three-body recombination (TBR) rate coefficients and radiative recombination (RR) rate coefficients, it showed that the total DR rate coefficients obviously significantly greater than other two recombination rate coefficients, and thus it obviously influence ionization equilibrium and ionization state population of ITER plasma.     

L subshell fluorescent X-ray measurements to study CK transitions in the 66<Emphasis Type="Italic">≤</Emphasis> <Emphasis Type="Italic">Z</Emphasis> <Emphasis Type="Italic">≤</Emphasis>83 region

L subshell fluorescent X-rays in Dy, Ho, Er, Lu, Ta, W, Pt, Au, Hg, Pb and Bi have been measured using synchrotron with selective creation of electron vacancies in individual subshells. Coster–Kronig (CK) yields were derived from the measured intensities. Present measurements have been made at photon energies above the edges where differences between measured and theoretical attenuation coefficients are almost negligible. Parametric trends for the results with Z were developed to cover all Zs in the range of 66–83. The trends predict the switching-off of L 1–L 2, N₁ transition at Z = 67. The extent of fall /rise of f_Lij values corresponding to off /on of certain transitions is found inversely proportional to the difference in binding energies of two consecutive subshells involved in the transition. For Zs above /below these rises /falls, f_L13 and f_L12 values are almost constants. f_L23 values involving no break at Zs follow the general photoionization behaviour that ionization probability is highest at the edge energy and decreases with photon energy. Yield measurements with synchrotron radiation for Dy, Ho, Lu, Hg and Bi and experimental values for f_L23, f_L12 in Lu and for f_L13 in Ta are being quoted for the first time.     

N‐shell ionization cross sections by proton impact in the BEA

The N‐subshell ionizations cross sections of heavy elements by proton impact have been calculated in the binary‐encounter approximation. The momentum distribution of target electrons is taken into account by the use of the nonrelativistic and relativistic hydrogenic models and the Hartree–Fock–Roothaan and the relativistic Hartree–Fock–Roothaan methods. The obtained subshell ionization cross sections are compared with the experimental data and other theoretical calculations. The electronic relativistic effect and the wave‐function effect on N‐shell ionization cross sections are discussed.     

光电离过程中Fe靶和V靶特征辐射的角相关研究

在发射角120°—170°的范围内,应用硅漂移探测器以10°为间隔对中心能量为13.1 keV的韧致辐射诱发Fe靶和V靶发射的典型K系X射线光谱进行了测量.得到特征X射线Kα和Kβ的特征谱线,考虑探测器对特征X射线的探测效率、靶对入射光子和出射光子吸收的校准及大气对特征X射线的吸收后,结果显示不同探测角度下Kβ与Kα的强度比为一常数.将本次实验探测角度为150°时的Kβ/Kα强度比值的实验值、理论计算值和Ertuğral的实验结果进行对比,发现实验结果与预期相符.对比不同探测角度下的强度比变化趋势推断特征X射线的角度依赖关系,分析认为Kα和Kβ在探测范围内是各向同性发射的.     

On the strong influence of inner shell resonances upon the outer shell photoionization of endohedral atoms

It is demonstrated by the example of the Xe atom stuffed inside the C₆₀ fullerene, i.e., the endohedral Xe@C₆₀, that the so-called confinement resonances in 4d subshell strongly affect the photoionization cross section of outer 5p and subvalent 5s electrons near the 4d ionization threshold. It is a surprise that these narrow inner 4d shell resonances are not smeared out in the outer shell photoionization cross section. On the contrary; the inner shell resonances affect the outer cross section by enhancing them enormously. Close to its own photoionization thresholds, 5p and 5s photoionization cross sections of Xe@C₆₀ are dominated by their own confinement resonances greatly affected by the amplification of the incoming radiation intensity due to polarization by it of the C₆₀ electron shell. Between 4d and 5p thresholds, the effect of 4d is becoming stronger while own resonances of 5p and 5s are becoming much less important.