Polarization effects on multiple scattering gamma transport

La limite de detection minimum obtenue avec une excitation monochromatique est inferieure a 1 ppb ou 1 pg

Synchrotron radiation excited x-ray fluorescence analysis using total reflection of x-rays

The scattering of low energy X-rays by atoms is dominated by coherent (Rayleigh) and incoherent (many times known as “atomic Compton”) scattering. As electron synchrotron storage rings become more widely used as sources of intense, polarized X-rays, it is important to be able to properly calculate the scattering cross sections since the polarization of the X-rays can be utilized to reduce the X-ray scattering. This paper reviews the methods of calculating the Rayleigh and atomic Compton scattering cross sections of polarized X-rays and presents analytical integrations of the cross sections over solid angles of circular detectors from point sources into 90°. Special attention is paid to the effects the scattering has on the background of spectra collected with energy dispersive detectors. It is shown that the ratio of scattering to fluorescence does not approach zero for small values of rR (r = detector radius, R = distance to detector).

The calculation of scattering cross sections for polarized x-rays *

The X-ray external total reflection method was applied to the analysis of the concentration profile of As atoms near the Si surface. Si wafers were implanted with As ions and then annealed at a high temperature. The intensity of the As Kα fluorescence signal excited by monochromated synchrotron radiation was measured as a function of the glancing angle of the incident X-rays. The effect of annealing on the concentration profile was analyzed non-destructively. The results obtained are in good agreement with those using depth profiling by secondary ion mass spectrometry. The limit of detection by this method was estimated as 1013 As atoms/cm2.

Grazing incidence X-ray fluorescence analysis

A synchrotron X-ray producing device such as the National Synchrotron Light Source at Brookhaven National Laboratory will present the research worker in the field of archaeometry with a number of new possibilities. These derive from the fundamental characteristics of the extracted X-ray beam: (a) its extraordinary intensity, four to five orders of magnitude greater than that of bremsstrahlung produced by X-ray tubes, (b) its polarization in the plane of the synchrotron ring and, (c) its energy tunability. Among the archaeometric applications one may readily identify: (a) very fast, sensitive, bulk analyses of materials such as ceramic and stone, for provenance research, (b) spot (microprobe) analytical capability, for obtaining structural information on artifacts, (c) scanning applications leading to images of the distributions of particular elements and, (d) element speciation on a micro scale. There is every reason to believe that this instrument will quickly take a prominent place in archaeometric research.

Use of synchrotron radiation in archaeometry

Energy dispersive X-ray fluorescence measurements were made for trace elements using synchrotron radiation from a dedicated electron storage ring at the Photon Factory in Japan. Monochromatization of the excitation beam by a crystal monochromator is effective in improving the signal to background ratio, while the synchrotron continuum excitation attains an absolute detectability of better than pg. Trace elements in a thin sample down to 60 ppb are detected by monochromatic excitation when there is no line interference. The experimental geometry optimal for a high signal to background ratio is investigated experimentally. The practical advantages of monochromatic excitation for the selective excitation of a particular element are demonstrated; these include enhanced sensitivity, suppression of the effects of the matrix element, and removal of overlapping peaks. The effects of higher order reflections and the residual tail part of the diffraction curve are also discussed in connection with quantitative analysis.

Energy dispersive X-ray fluorescence analysis with synchrotron radiation

Wide band pass X-ray monochromators using reflection/transmission mirror and reflection mirror/absorber combinations were applied to the synchrotron radiation excited energy dispersive X-ray fluorescence analysis. Transmission mirrors were made from soap films or thin mylar films and were used as high pass filters. Characteristics of both films are described in detail. The width of band pass thus obtained was wider than 20%. Minimum detection limits in relative concentration and absolute amount are of the order of 0.1 ppm and less than 0.1 pg, respectively, when there is no line interference.

Synchrotron radiation excited X-ray fluorescence analysis using wide band pass monochromators

X-ray fluorescence experiments at the Photon Factory in Japan are described. An energy-dispersive X-ray fluorescence system was combined with various excitation modes, i.e., a continuum and a monochromatic excitation, which consist of a crystal monochromator or a wide band pass monochromator. These excitation modes provide a wide range of band width and photon flux of excitation beams. Minimum detection limits obtained for a thin sample were less than 0.1 ppm and 0.1 pg when there was no line interference. Advantages of using monochromatic excitation are discussed, with emphasis on the possibility of chemical state analysis. Grazing incidence X-ray fluorescence is a technique very appropriate to synchrotron radiation characteristics. Near-surface analysis and trace analysis of solution samples placed on a total reflection support were made. Future plans are discussed, including microbeam analysis, tomography, X-ray excited optical fluorescence, and applications of insertion devices (undulator and wiggler).

T. Matsushita

Papers

Energy dispersive X-ray fluorescence analysis with synchrotron radiation

Synchrotron radiation excited X-ray fluorescence analysis using wide band pass monochromators

X-ray fluorescence analysis using synchrotron radiation at the photon factory.