X-ray or gamma ray systems or devices – Specific application – Fluorescence
Reexamination Certificate
2000-03-31
2001-10-30
Porta, David P. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Fluorescence
C378S045000
Reexamination Certificate
active
06310935
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a fluorescent x-ray analyzer and more particularly to a fluorescent x-ray analyzer of the wavelength dispersion (WD) type.
A WD type fluorescent x-ray analyzer uses a dispersing crystal to disperse fluorescent x-rays generated by a sample irradiated by x-rays and to introduce diffracted x-rays having a specified wavelength into a detector. For the purpose of wavelength scan, the crystal and the detector are rotated while maintaining a specified angular relationship between them. Explained more in detail, the crystal and the detector are rotated so as to satisfy the Bragg condition given by:
2
d
sin &thgr;=
n&lgr;
(1)
where d is the lattice interval of the crystal, 2&thgr; is the angle of diffraction, &lgr; is the wavelength of the incident fluorescent x-rays and n is the order of diffraction. Since the wavelength of the x-rays entering the detector is gradually changed by such a scan, an x-ray spectrum can be generated by using the scanning angle 2&thgr; as the horizontal axis and the x-ray intensity as the vertical axis.
As can be understood from (1), however, it happens sometimes that the first-order diffraction beam of a certain element overlaps more or less at the same angular position of a diffracted x-ray beam of a higher order (that is, the second or higher order) corresponding to another element. In such a situation, since x-ray photons of these mutually overlapping beams have different energies, the detector may use a pulse height analyzer to differentiate between the wave heights of pulse signals by these x-ray photons such that only the pulse signals corresponding to the first-order diffraction beam are counted, thereby eliminating the effects of the higher-order beams and obtaining the x-ray intensity due only to the first-order beam.
Fluorescent x-rays emitted from a single element, however, usually include many characteristic rays having different wavelengths referred, for example, as K&agr; (more strictly speaking, K&agr;a and K&agr;2), K&bgr;1, K&bgr;2, K&bgr;3, L&agr;1, L2&agr;, etc., corresponding to the electron transitions related to the generation of fluorescent x-rays. Thus, when a sample containing a plurality of different elements is qualitatively or quantitatively analyzed on the basis of its x-ray spectrum, the analysis is carried out by determining which characteristic x-rays of which element are forming each of the peaks in the x-ray spectrum and obtaining the x-ray intensity from the top of the peak.
Although a range in pulse height for analysis is properly selected by means of a pulse height analyzer, however, a portion of the pulse signals due to higher-order x-rays of elements with high contents in the sample may fall within the range set by the pulse height analyzer for selecting the height of pulse signals due to the first-order beams. If the peaks are identified or the peak intensity of fluorescent x-rays is calculated by using an x-ray spectrum (hereinafter referred to as the “first-order beam profile”) produced on the basis of pulse signals selected by such a pulse height analyzer, peaks of higher-order beams of other elements may be near the scan angle of the first-order beam of an element of interest. In such a situation, it is not possible to determine from the obtained peak profile alone which element is represented by a given spectrum.
In view of the above, it has been known to obtain a first-order beam profile over a wide range covering almost all elements, to start the identification process from the peaks of elements with short wavelengths such that higher-order beam lines of the other elements are not likely to overlap, and to continue the process sequentially with peaks corresponding to elements with longer wavelengths on the basis of the data on the contained elements which have been identified, checking whether there is any overlapping between the first-order beam lines and higher-order beam lines. For analyzing an overlapping region between a peak corresponding to a first-order beam and peaks corresponding to higher-order beams, it has been known to preliminarily obtain the intensity ratio between them for a target element to be analyzed by making measurements on a standard sample and to carry out the analysis by referring to such ratio.
For preparing a first-order beam profile, use must be made of a crystal with lattice interval such that the condition 2d sin &thgr;=&lgr;≦2d is satisfied because n=1 in Formula (1) above. When a measurement is carried out over a large range of elements including both light and heavy elements, therefore, it is impossible to entirely cover such a wide range of wavelengths by using only one kind of crystal. Thus, it has been necessary to prepare a plurality of crystals having different lattice intervals corresponding to different spectral wavelength ranges and to keep replacing one by another of them as measurements are taken by scanning within specified angular ranges between the detector and the crystal. In other words, the apparatus had to be provided with a plurality of crystals and also with a device for exchanging these crystals. As a result, the apparatus could not be made small and its cost could not be reduced. Moreover, since the scanning must be repeated many times within a same range of angles, a long time was required for the measurement.
A further problem with the prior art technology has been that different experimental data are necessary for different elements for the analysis of the peaks. Even for the analysis of one element, different data are necessary, depending on the condition of the analysis such as the kind of the crystal and the slit. Even if measurement are taken under the same conditions, it is necessary to preliminarily prepare a huge amount of data in order to obtain an accurate result. This means that preparations become an extremely burdensome part of an analysis.
SUMMARY OF THE INVENTION
It is therefore an object of this invention, in view of these problems, to provide an improved fluorescent x-ray analyzer capable of correctly distinguish and evaluate the first-order peak of one element and a higher-order peak of another element which are overlapped such that the accuracy in qualitative and quantitative analyses can be improved.
It is another object of this invention to provide such a fluorescent x-ray analyzer capable of reducing the burden on its operator and improving the work efficiency by significantly reducing the amount of measurement data which are required to be preliminarily prepared for carrying out such an evaluation.
It is still another object of this invention to provide such a fluorescent x-ray analyzer capable of completing an analysis in a short time by using a crystal of one kind instead of using one after another of many kinds of crystals during an analysis such that the cost of the analyzer itself can be reduced.
A fluorescent x-ray analyzer embodying this invention may be characterized not only as comprising a light-dispersing crystal and a detector which are rotatable while maintaining a specified angular relationship therebetween such that fluorescent x-rays from a sample are scanned by this detector but also wherein a first-order profile and a higher-order profile showing x-ray intensities against scan angle from detection signals from the detector respectively within a specified lower and higher wave height analyzing range. Data related to ratios between preliminarily measured peak intensities of diffracted beams of first-order and higher-order obtained from a plurality of elements are stored and used to identify peaks in the first-order and higher-order profiles, if there is a possibility of a peak formed by a first-order spectrum of one element and a higher-order spectrum of another element overlapping each other and to determine the nature and extent of contributions to the peaks in the first-order and higher-order profiles from the first-order and higher-order spectra.
Explained more in detail, a prior art peak-identification routine is carried
Coudert Brothers
Porta David P.
Shimadzu Corporation
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