Radiant energy – Radiation controlling means
Reexamination Certificate
2000-07-21
2002-09-03
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Radiation controlling means
C378S149000, C378S150000
Reexamination Certificate
active
06444993
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus for radiation analysis of a sample to be examined, in which a radiation beam runs along an optical path from a radiation source to a radiation detector via the sample to be examined, in which optical path a collimator with collimating elements is present, which collimator, as a result of a movement through the radiation beam, exhibits a variable aperture angle for the radiation beam.
The invention likewise relates to a collimator to be used in such an apparatus.
2. Description of the Related Art
Such apparatus is known from “Patent Abstracts of Japan”, Application number 08208931, Publication number 10038823 A. In said document, the apparatus for radiation analysis is formed by a spectrometer for X-ray fluorescence. In the X-ray optical path of this known spectrometer, there are two collimators in the form of so-called Soller-slit collimators. Such collimators comprise a stack of mutually parallel plates of an X-ray-absorbing material which show certain spacings. A collimating element in such a collimator is thus formed by a spacing plus the adjacent plates. The aperture angle exhibited to the radiation beam by such an assembly of plates is equal to twice the ratio of the spacing to the length of the plates in the place of the X-ray beam passing the plates.
Apparatus for radiation analysis are often arranged for measuring a high-resolution spectrogram (for example, X-ray spectrometers) or diffraction pattern (for example, X-ray diffractometers). For certain rays in the radiation beam there are then deviations from the ideal radiation path, which have an adverse effect on the resolution of the measurements. To mitigate these deviations, it is known per se to install a collimator for bounding the radiation beam, more particularly bounding the aperture angle of the radiation beam, in the optical path of the apparatus.
A measurement with an X-ray spectrometer or an X-ray diffractometer often comprises making an angular scan, that is to say, the radiation intensity coming from the sample to be examined is measured for a large range of angular values around the sample. Said deviations from the ideal radiation path are then dependent on the angular value. To keep the measuring time with these apparatus shortest possible, the aperture angle (thus the total intensity) of the radiation beam is desirably not further confined than is necessary for the resolution. Therefore, during the measurement the aperture angle of the collimator is desirably made variable, that is, depending on the angular value.
In the X-ray spectrometer known from said document, this variable value of the aperture angle is achieved by arranging the Soller slit collimators shown there and comprising a stack of plates with equal mutual spacings, in such a way that the stack of plates comprises a plurality of sub-stacks exhibiting mutually different spacings between the plates. A different aperture angle may now be selected by displacing the respective Soller-slit collimator in a direction perpendicular to the surface of the plate, so that another sub-stack is inserted into the radiation beam.
Manufacturing a collimator in which the collimating elements have mutually different dimensions is inconvenient from the point of view of manufacturing. Besides, only some discrete values of the aperture angle can be realised in this known manner, or (with a continuously varying spacing) there are a plurality of spacings in the beam at the same time, so that the aperture angle is not defined well.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an apparatus for radiation analysis in which the aperture angle of the radiation beam is continuously variable and which can be manufactured in a relatively simple manner. For this purpose, the apparatus according to the invention is characterised in that the collimator can be moved through the radiation beam in such a way that the collimating element length exposed to the radiation beam allows of variation as a result. The invention is based on the recognition that the intended variation of the aperture angle can be obtained by a movement so that the dimensional differences, as they are often inherent in all sorts of equipment, are the cause of this variation in the aperture angle. However, it is not necessary for these inherent dimensional differences to be utilised; it is alternatively possible to apply dimensional differences that are easy to manufacture.
In an embodiment of the invention, in which inherent dimensional differences are utilised in a simple manner, the collimating elements have the form of mutually parallel plates, and said movement comprises a rotation around a shaft perpendicular to the plates. As a result of said rotation, the radiation beam will generally follow another path relative to the collimator, so that the beam encounters different dimensions.
In a further embodiment of the invention, in which inherent dimensional differences are utilised in a simple manner, the plates have a rectangular shape. This provides a high degree of simplicity in the manufacturing process with a shape that has already been of general use in this technique.
In another embodiment of the invention, the plates have, at least partly, an elliptical shape. In a strongly divergent radiation beam this measure makes it possible to reduce the difference in aperture angle for different trajectories in the beam.
In yet another embodiment of the invention, the collimating elements have the form of channels having a cross section closed in itself, which channels have mutually different lengths, and said movement comprises a displacement transverse to the longitudinal direction of the channels. The channels may be embodied as X-ray optical fibres, f.i. glass fibres. X-ray optical fibres are known per se for influencing the ray path in a radiation beam. Such fibres, however, are very thin, so that a collimator made of fibres comprises a very large number of fibres and cannot easily be manufactured in an arbitrary shape. However, it is highly possible indeed to make a stack of fibres so that this stack in side-elevation has the form of, for example, a triangle; by displacing the thus formed collimator transversely to the longitudinal axis of the fibbers, fibres of ever different lengths are fed into the beam.
REFERENCES:
patent: 4127398 (1978-11-01), Singer, Jr.
patent: 4205228 (1980-05-01), Tosswill
patent: 5165106 (1992-11-01), Barthelmes et al.
patent: 5192869 (1993-03-01), Kumakhov
Patent Abstracts of Japan, Application No. 08208931, Publication No. 10038823.
Koninklijke Philips Electronics , N.V.
Nguyen Kiet T.
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