X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
1999-10-26
2001-10-30
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
Reexamination Certificate
active
06310937
ABSTRACT:
The invention relates to an X-ray diffraction apparatus which includes a sample location for receiving a sample to be examined, an X-ray source for generating X-rays in the sample, a detector for detecting the X-rays emanating from the sample, and correction means for making a correction for a disturbing influencing of the X-rays in the X-ray optical path from the X-ray source to the detector.
An apparatus of this kind is known from the published international patent application WO 96/15442.
An analysis technique which is known as X-ray diffraction is available for X-ray analysis of materials. A sample to be examined is then generally irradiated by means of a monochromatic X-ray beam which is deflected (diffracted) only at given angles (whose value 2&thgr; is measured relative to the forward beam) because of the regularity of the crystal structure of the constituents of the sample. The diffraction angles provide information as regards the crystal structure of the constituents of the sample. The diffraction angles are measured by traversing a (art of) a circle around the sample by means of an X-ray detector while measuring the intensity of the X-rays diffracted by the sample. In a practical arrangement the diffraction angles are generally determined in two ways. According to a first measuring method, the sample to be examined is stationary and the X-ray source and the detector both rotate around the sample at the same speed; this method of measuring is known as a &thgr;—&thgr; scan. According to a second method of measuring, the X-ray source is stationary and the sample to be examined rotates at a given speed while the detector rotates around the sample at twice the speed; this measuring method is known as a &thgr;-2&thgr; scan.
This analysis technique, therefore, requires an X-ray source for generating X-rays in the sample and a detector for detecting the X-rays diffracted by the sample. The X-rays travel along an X-ray optical path which extends from the X-ray source to the detector via the sample. Other X-ray optical elements, such as paralleling collimators for paralleling the beam, beam-limiting diaphragms for limiting background radiation, and monochromator crystals for monochromatizing the X-ray beam, may also be present in said X-ray optical path.
For X-ray diffraction it is important to determine the intensity of the X-rays detected by the detector. It is then desirable to determine the content of a given chemical phase (for example, a compound) in the sample. A problem is then encountered in that these measurements often taken place in a given atmosphere which may vary in respect of a variety of parameters, such as pressure, temperature, humidity, composition, dust content etc. X-rays, notably soft X-rays (i.e. X-rays having a comparatively long wavelength of the order of 1 nm or more) are very sensitive to atmospheric absorption. Therefore, the intensity measured by the detector is dependent not only on the quantities to be measured, but also on the varying absorption which thus constitutes a disturbing influencing of the X-rays in the X-ray optical path from the X-ray source to the detector.
In order to counteract the problems stemming therefrom, the apparatus which is known from the cited international patent application is provided with correction means for correcting said disturbing influencing. The known correction means consist of a number of sensors, each of which picks up a parameter such as pressure, temperature, humidity etc., and a processor which calculates, on the basis of the parameters measured by the sensors and calculation formulas, correction coefficients for correcting the intensity measured by the detector and corrects the intensity on the basis thereof. This known method has the drawback that any disturbing effect must be known in advance and that a separate measuring channel must be available for this purpose, complete with associated formulas for calculating the correction coefficient associated with the relevant disturbing effect. Moreover, it is then assumed that each of the disturbing influences has its own effect on the intensity and that no additional effect occurs due to a combination of disturbing influences. It is difficult and in practice often impossible to correct the effect of the combination of disturbing influences in this known manner.
It is an object of the invention to provide an X-ray analysis apparatus of the kind set forth in which the measured intensity can be corrected for an arbitrary number of disturbing influences, even if these influences are not known in advance, and irrespective of the effect of a combination of the disturbing influences.
To this end, the apparatus according to the invention is characterized in that the correction means include reference means for forming a second X-ray optical path from the X-ray source, which second X-ray optical path extends at least partly separately from the former X-ray optical path and includes a detector for detecting the X-rays emanating from the source.
As a result of the formation of a second X-ray optical path which extends separately from the X-ray optical path intended for the measurements, it is possible to measure the variation of the attenuation of the radiation in the path intended for measurements. The intensity detected via the first path can be continuously or periodically compared with the intensity received via the second path, the intensity in the path intended for measurements being determined in standard circumstances. When the value of the intensity detected in the second path varies by a given factor during the actual measurements, the value of the intensity detected in the first path can be corrected by the same factor.
In an embodiment of the invention, the detector which forms part of the former X-ray optical path and the detector which forms part of the second X-ray optical path are formed by one and the same detector. In cases where it is not desired to monitor the variation of the disturbing influences continuously during the actual measurements but only to observe these influences, for example between the measurements, it suffices to use only one detector which is then used alternately for the actual measurements and for the intensity measurement in the second X-ray optical path in order to determine the variation of the disturbing influences therefrom. The use of only a single detector for the reference measurements as well as the actual measurements, moreover, offers the advantage that any differences between the detectors do not have an effect on the intensity measurements, so that no separate correction is required in this respect.
The second X-ray optical path in a further embodiment of the invention includes an X-ray mirror which is arranged in such a manner that when the sample to be examined is not present in the former X-ray optical path, this mirror reflects the X-rays from the source to the detector. During the actual measurements, the X-ray optical path intended for these measurements is used and the X-ray mirror does not receive radiation because in these circumstances it is situated, for example in the shade of the sample to be examined. During a change of sample, the sample is moved out of its original position, so that the radiation from the X-ray source can reach the mirror. The second X-ray optical path is then formed by the path extending from the source to the detector via the mirror. As long as the mirror receives radiation from the X-ray source, a reference measurement can be carried out so as to determine the disturbing influences. If desired, the period of time elapsing between the measurement of two samples can be slightly prolonged so as to allow for a better reference measurement.
A further embodiment of the apparatus according to the invention includes a parallel plate collimator in which there is provided a bore which forms part of the second X-ray optical path. This step advantageously utilizes the fact that in a parallel plate collimator (also referred to as a Soller slit unit) a major part of the X-rays generated by
Church Craig E.
U.S. Philips Corporation
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