An x-ray diffractometer is equipped with a position sensitive detector and a collimator preceding the detector. The lamellae of the collimator are radially aligned to the specimen, which is arranged in the center of a measurement circle along which the detector and collimator move during a measurement. Therefore, only the x-radiation scattered at the specimen contributes to the measured signal. An elliptically deformed multi-layer mirror is provided at the primary beam side, which deflects the source radiation in the direction of the specimen without great intensity loss and focuses it at a point lying on the measurement circle. Analysis of powdered specimens that are enclosed in glass capillaries can be undertaken. A low-background measurement of diffraction diagrams in an x-ray diffractometer given efficient use of the primary beam is achieved.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to an x-ray diffractometer for conducting 
a spectral analysis of a specimen. 
2. Description of the Prior Art 
X-ray spectrometers serve the purpose of non-destructive analysis of solid, 
powdered and liquid specimens. Powder x-ray diffractometers have achieved 
wide usage among devices of this type, because they have a relatively 
simple structure and are versatilely employable. With such a device, 
unknown substances and substance mixtures can be identified, their lattice 
structure can be defined and conclusions about their crystallization state 
can be made from the diffraction diagrams acquired (see, for example, 
Siemens Forschungs- und Entwicklungsberichte, Vol. 14 (1985) No. 4, pages 
167-176). 
Powder diffractometers predominately employ focusing beam arrangements that 
guarantee a high exploitation of the x-ray beam irradiating the specimen. 
In order to obtain a beneficial contrast of diffraction maxima relative to 
background, monochromator crystals are often utilized at the primary side 
or secondary side. The secondary monochromators are usually composed of 
bent graphite mosaic crystals and have the advantage that they are capable 
of separating the usable diffraction radiation from the fluorescent 
radiation which is unavoidably produced in the specimen. 
The mensuration technology of radiography was decisively enriched in the 
1980's by the employment of position sensitive detectors. These detectors 
act as a plurality of individual counters and thus allow significantly 
faster data collection. As a consequence of the increases in the measuring 
speed by more than a factor 100 accompanying this, advance "snapshots" of 
chronologically variable conditions (solid state reactions, phase 
conversions) are capable of being made in the specimen. 
Position sensitive detectors have especially proven useful in combination 
with monochromators on the primary side. Strictly focusing primary 
monochromators of high-perfection single crystals (germanium, silicon, 
quartz) are preferred in such combinations because these crystals are 
capable of resolving the K.alpha..sub.1 -K.alpha..sub.2 doublets that are 
problematical for the interpretation of the diffraction diagrams. Diagrams 
having only K.alpha..sub.1 reflexes are therefore obtained, whereby the 
intensity loss of the primary x-ray caused by the monochromator is more 
than compensated by the employment of the position sensitive detector. 
Compared to conventional methods of x-ray analysis, a technique referred to 
as total reflection x-ray fluorescence analysis (TXRF) has a high surface 
sensitivity, since the exciting radiation is incident on the specimen 
under examination at an extremely small angle .alpha.&lt;0.5.degree., and 
thus penetrates only a few nanometers into the specimen. The TXRF method 
is therefore particularly suited for the identification of the chemical 
composition of thin layers and surfaces. A TXRF measuring apparatus is 
described in European Application 0 456 897. Instead of having a 
monochromator of the primary side, this measuring instrument has a 
multi-layer mirror that deflects the radiation generated in an x-ray tube 
in the direction toward the specimen under examination without a greater 
loss in intensity. 
SUMMARY OF THE INVENTION 
It is an object of the invention is to provide an x-ray diffractometer 
wherein a low-background measurement of x-ray diffraction diagrams is 
possible. In particular, it should be guaranteed that only the x-radiation 
scattered by the specimen under examination proceeds to the detector. A 
reduction of the background in the diffraction diagrams is particularly 
desirable in the examination of specimens enclosed in glass capillaries. 
The above objects are achieved in accordance with the principles of the 
present invention in an x-ray diffractometer having a source of x-rays, a 
focusing reflector which deflects the x-rays in the direction of a 
specimen, a position sensitive detector which is displaceable along a 
measurement circle for angle-dependent detection of the x-rays scattered 
at the specimen, and a collimator preceding the detector having lamellae 
which are radially aligned onto the specimen, the specimen being disposed 
at the center of the measurement circle. 
The advantage obtainable with the invention is that the detection 
sensitivity is noticeably improved due to the efficient shielding of the 
background radiation by the collimator. It is therefore possible without 
further difficulty to arrange other experimentation devices, particularly 
a heating furnace, in the immediate proximity of the specimen without 
degrading the measurement quality.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As schematically shown in FIG. 1, the x-ray diffractometer of the invention 
includes an x-ray tube 1 which produces x-radiation 4 generated in a 
line-shaped electron beam focus 3 on the tube anode. A curved reflector 2 
deflects the x-radiation 4 in the direction of the specimen 6 mounted on a 
conventional goniometer head 5. At least a portion of the scattered 
radiation thereby produced proceeds to a position sensitive detector 7, 
having a collimator 8 that precedes the detector 7. Since the lamellae 9 
of the collimator 8 are radially aligned to the specimen 6, which is 
arranged in the center of a measurement circle 10, only the x-radiation 
scattered at the specimen 6 contributes to the measured signal. Other 
stray radiation is largely shielded by the collimator 8. It is therefore 
possible for the first time, for example, to arrange a cylindrical heating 
furnace 11 in the immediate proximity of the specimen 6 enclosed in a 
glass capillary (Mark tube) without the stray radiation emanating from the 
furnace walls and mounts, etc., having a disturbing effect as elevated 
background in the diffraction diagrams measured at various temperatures. 
The position sensitive detector 7 may be a linear proportional counter. 
This is arranged such that its counter wire 12 tangentially touches the 
measurement circle 10. As a consequence of its limited expansion, the 
detector 7 can simultaneously acquire the x-radiation scattered at the 
specimen 6 only within an angular range of, for example, 10.degree. 
through 20.degree.. It is therefore necessary for registering the entire 
diffraction diagram to displace the unit consisting of the detector 7 and 
the collimator along the measurement circle 10 with a stepping motor 19. 
Data acquisition thereby preferably ensures by employing the measuring 
method disclosed in German Patentschrift 26 37 945. It is thereby also 
assured that no shadowing effects caused by the collimator 8 occur in the 
diffraction diagram (also see FIG. 3). 
As already mentioned, crystal monochromators of the primary side have a 
low, integral reflectivity. Considerable intensity losses also occur with 
the employment of a broad band monochromator composed of a combination of 
reflection and transmission mirrors, since the transmission mirrors are 
highly absorbent. Additionally, a complicated mechanics is needed in order 
to align the individual components relative to one another as well as 
relative to the x-ray source and relative to the specimen. In order to 
guarantee a better utilization of the intensity of the primary x-ray beam 
4, the x-ray diffractometer of the invention employs a multi-layer mirror 
2 arranged in a housing 13 as a reflector. This multi-layer mirror has a 
high reflectivity (reflectivity above 80%) and is elliptically or 
circularly deformed with the assistance of a bending means composed of a 
set screw 14 and a lever element 15 such that it focuses the x-radiation 4 
deflected in the direction of the specimen 6 in a point 16 lying on the 
measurement circle 10. The diaphragms 17 and 18 present at or in the 
housing 13 serve the purpose of limiting the beam cross section in the 
horizontal and vertical directions. 
The multi-layer mirror schematically shown in FIG. 2 is composed of a 
periodically repeating sequence of layers of materials A and B having 
different refractive indices n.sub.A and n.sub.B, whereby the plurality N 
of the layers within a period satisfies the condition N.gtoreq.2. This 
layer sequence is preferably produced by sputtering, vapor-deposition or 
by growing the corresponding materials A or B on a silicon substrate. The 
layers themselves can be amorphous or crystalline. For example, one of the 
following combinations of the materials A/B may be used for a mirror 
composed of a periodic sequence of two layers: Mo/B.sub.4 C, Re/Si, Re/C, 
W/Si, W/C, Ta/Si, W/Be, Mo/Be, Mo/Si, Mo/C, Ni/C, Au/C, AuPd/C, ReW/B, 
ReW/C, Al/Be or V/C. The periodicity length d=d.sub.A +d.sub.B (d.sub.A 
=thickness of the layer A, d.sub.B =thickness of layer B), as well as the 
layer thickness ratio d.sub.A :d.sub.B of layers having a high and low 
refractive index n.sub.A or n.sub.B, are freely prescribable. Therefore, 
the properties of the reflector 2 can be well-matched to the respective 
experimental conditions. 
The diffraction diagram shown in FIG. 3 was registered with the x-ray 
diffractometer of the invention using the measurement method disclosed in 
German Patentschrift 26 37 945. A silicon powder that was charged with 
Cu-K-Alpha radiation and was enclosed in a 0.5 mm thick quartz capillary 
served as the specimen (tube parameter: 35 kV/28 mA). The intensity 
(counting rate per channel, measured in the position sensitive 
proportional counter 7 is entered dependent on the angle of deflection. 
Since the detector 7 moved on the measurement circle during the 
measurement with a speed of 30.degree./minute, only approximately 3 
minutes were required for registering the diffraction diagram in the 
angular range between 0.degree. and 95.degree.. The angular range between 
95.degree. and 110.degree. was registered with a stationary detector. One 
can clearly see the shadowing effect caused by the collimator 8 that does 
not appear in the remaining diffraction diagram. 
The invention, of course, is not limited to the exemplary embodiment that 
has been set forth. Thus, it is possible without further difficulty to 
replace the multi-layer mirror with a total reflection mirror and to 
corresponding deform the latter. As in the case of the multi-layer mirror, 
the deformation can be elliptical, circular or parabolic (focus in the 
infinite, parallel primary beam). Detectors known as "Curved PSPC" (Curved 
Position Sensitive Proportional Counter) and other wide-angled detectors, 
of course, may be used as the position sensitive detector. Further, the 
specimen need not necessarily be in powdered form. Rod-shaped 
preparations, planar specimens and single crystals are likewise suitable 
for investigation in the x-ray diffractometer of the invention. 
Although modifications and changes may be suggested by those skilled in the 
art, it is the intention of the inventor to embody within the patent 
warranted hereon all changes and modifications as reasonably and properly 
come within the scope of his contribution to the art.