X-ray or gamma ray systems or devices – Accessory – Testing or calibration
Reexamination Certificate
1999-08-13
2002-04-02
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Accessory
Testing or calibration
C378S044000
Reexamination Certificate
active
06364528
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a specimen part and to a method for the determination of the intensity data of a measuring spot in X-ray fluorescence analysis.
BACKGROUND OF THE INVENTION
If a substance is irradiated with hard, i.e. shortwave and therefore high energy X-radiation, electrons are ionized in the atoms of this substance, particularly the inner shells and as a consequence the vacancy is filled by electrons from the outer shells. The so-called X-ray fluorescent radiation (secondary radiation) is emitted and is softer, i.e. of a longer wave nature and therefore lower energy nature than the incident primary radiation. The emitted secondary radiation is characteristic for each atoms of the periodic system. Each X-ray fluorescent spectrum emitted by an atom comprises only a few characteristic lines, by means of which it is clearly identifiable. For quantitative analysis, apart from the wavelength, also the intensity, i.e. the amplitude of the emitted radiation is measured and this constitutes a measure of the content of the corresponding atomic species in the specimen, the coating thickness and the concentration of the corresponding atomic species.
X-ray fluorescence analysis is inter alia used as a method for non-destructive material testing for the analysis of coating thicknesses and compositions of coated and solid specimens, where it is of major importance, particularly when analyzing very small and/or structured specimens, such as conducting tracks, solder or bond faces, as well as other contact faces, such as electrolytic coatings.
In X-ray fluorescence analysis, the specimen to be investigated is excited to emit fluorescent radiation with the hard, polychromatic radiation of a X-ray tube. The primary beam incident on the specimen material is focussed either by means of collimators made from metal or glass or with focussing elements, such as glass capillaries. The analytical area of the specimen material excited by the primary beam or the surface of the primary radiation striking the specimen is known as the measuring spot. The size of the measuring spot of the X-ray fluorescence analysis of small test specimens is approximately 10 to 100 &mgr;m. The X-ray fluorescent radiation emitted by the specimen material is detected by means of suitable detectors, such as proportional counter tubes or semiconductor detectors.
Particularly when analyzing small specimens it is necessary not only to adequately define the geometrical dimensions of the measuring spot, but also to visibly represent the same in order to accurately position the specimen. For the representation of the measuring spot it is on the one hand necessary to determine the beam centre of the primary beam striking the specimen and on the other the spatial extension or the contour of the measuring spot.
For determining the beam centre it is e.g. known to displace over the width of the measuring spot the planar interface of a fluorescent material and also a non-fluorescent material in the case of an identical excitation and the emitted fluorescent radiation of the fluorescent material is measured for different relative positions with respect to the primary beam. If the interface is in the beam centre, the intensity of said fluorescent radiation is precisely half as large as if the entire surface of the fluorescent material was excited by the primary beam. This position with half the intensity is then used for the setting or adjustment of e.g. a cross-line or reticle of an observation instrument, such as a video camera.
A disadvantage of the described method is that, due to the mutually influencing, differing materials in the vicinity of their interfaces, it suffers from errors, particularly with small measuring spots. The reason for the errors is that the primary beam penetrates relatively deeply into the specimen and consequently fluorescent radiation not only occurs on the specimen surface, but also in deeper areas, so that the attenuation of the fluorescent radiation produced in the specimen material is important for the measured intensity. This follows the known attenuation law
I=I
0
. e
−&mgr;x
(1)
in which I
0
is the intensity of the X-ray fluorescent radiation emitted directly at an excited atom and I is the radiation intensity after traversing the path x of a material with the linear attenuation coefficient &mgr;, which is dependent on the material.
For the determination of the geometrical dimensions (contour) of the measuring spot, it is known to estimate the same as a function of the cross-section of the collimator used or as a function of the distances between the radiation source, collimator and specimen. The shape and size of the actual measuring spot can diverge from the thus interpreted shape, because the fundamental assumptions only approximately correspond to reality, because the actual size and position of the projected spot of the radiation source are not precisely known. The primary beam axis also changes with respect to the optical axis due to thermal influences. Account is also not taken of the incomplete absorption of the primary radiation on the collimator edges. A divergence from the actual conditions (spot size, maladjustment of the beam centre) is not noticed.
It is also known for the determination of the measuring spot contour, to expose in place of a specimen a film material which is sensitive to X-radiation and whose wavelength is in the primary radiation range. Although this method provides a realistic image of the measuring spot, the film material must be removed for development and the beam centre information is lost.
Whilst avoiding the aforementioned disadvantages, the problem of the invention is to propose a specimen part and a method for determining both the intensity centre and also the intensity distribution of a measuring spot, i.e. the intensity data of an X-ray striking a surface in the case of X-ray fluorescence analysis.
SUMMARY OF THE INVENTION
According to the invention, the problem is solved with a specimen part for the determination of intensity data of a measuring spot in X-ray fluorescence analysis, in that the specimen part has a probe with a clearly defined contour surrounded by a surrounding material, said surrounding material and the probe material having the same linear attenuation coefficients for the emitted X-ray fluorescent radiation.
For the determination of the intensity centre of the measuring spot, the specimen part according to the invention is moved over the width of the measuring spot, so that either the probe or surrounding material or both the probe and the surrounding material are excited with primary radiation. As the probe and surrounding material differ, the characteristic fluorescence spectra can differ. Since, according to the invention, the probe material and the surrounding material have the same linear attenuation coefficients for the emitted fluorescent radiation, the intensities (amplitudes) of the fluorescent radiation emitted in different depths of the probe and the surrounding material of the specimen part are attenuated or absorbed in the same way, so that at the boundary between the probe and the surrounding material there is no mutual influencing of the segments and the intensities of the fluorescence spectra emitted by the probe and surrounding material are comparable. A secondary beam e.g. emitted in a lower plane of the probe, consequently undergoes the same attenuation in the surrounding material after passing out of the probe material.
The specimen part according to the invention can e.g. be firmly connected to a programmable specimen table, with which it is possible to perform clearly defined positional displacements relative to the fixed primary beam.
The specimen part comprising the probe and the surrounding material preferably has a planar surface, so that the probe is aligned with the surronding material and no absorption and scattering effects take place on projecting edges.
According to a preferred embodiment, the probe and the surrounding material are saturation-tight in th
Church Craig E.
Immobiliengesellschaft Helmut Fischer GmbH & Co. KG
McGlew and Tutle, P.C.
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