An X-ray fluorescence spectrometer comprising an X-ray source, a sample holder spaced from the X-ray source at a distance which ensures the illumination of the central portion of the sample not less than 0.3 ZU erg./s.cm.sup.2.w, where Z is the atomic weight of material of the X-ray anode and U is the voltage across the X-ray source, in kilovolts. The spectrometer further comprises a curved analyzing cristal for focusing the fluorescent radiation of the sample at an X-ray detector. The analyzing cristal and the detector are installed in an evacuated chamber. The X-ray source and the sample holder are positioned outside the evacuated chamber which has a window for passing X-ray radiation. The sample holder is positioned so that the average distance between the sample surface portion which produces radiation incident on the analyzing cristal and the window does not exceed the distance between said sample surface portion and the focus of the X-ray source.

FIELD OF THE INVENTION 
The present invention relates to spectrometers, and more particularly to 
X-ray fluorescence spectrometers. 
The present invention can be used for chemical analysis in metallurgy, 
geology, chemical industry, etc. 
BACKGROUND OF THE INVENTION 
In X-ray fluorescence spectrometers, the chemical composition of a 
substance is determined by irradiating the sample under test with X-rays 
and by recording the secondary X-ray fluorescent radiation emitted by the 
sample. Resolution of the sample fluorescence into its component 
wavelengths is achieved with the aid of an analyzing cristal which may be 
flat (as in Soller spectrometers) or curved (as in Johann or Johansson 
spectrometers). In the latter case the analyzing cristal provides focusing 
of the radiation reflected thereby at the focal circle defined by the 
curve of the planes of the analyzing cristal. 
In the X-ray spectrometers commonly used nowadays the sample is positioned 
at a considerable distance (from 20 to 40 mm) from the focus of the X-ray 
source (X-ray tube). Therefore, to ensure the required sensitivity, such 
spectrometers must employ powerful big-sized X-ray tubes. 
As is well known, soft X-ray radiation (having a relatively long 
wavelength) is strongly absorbed by air, which makes it impossible to 
determine the concentrations of light chemical elements in the test sample 
unless some special measures are taken to ensure a small degree of 
absorption of soft X-ray radiation. 
In the known X-ray fluorescence spectrometers this is achieved by 
installing the whole X-ray system, including the X-ray source and the 
sample-loading device, in a chamber which is evacuated or filled with a 
light gas (helium). Such spectrometers make possible determination of 
concentrations of both heavy and light chemical elements. 
However, spectrometers with such an evacuated chamber do not permit 
analysis of the samples susceptible to destruction by vacuum, such as 
solutions, powders, vegetable substances, etc. This substantially narrows 
the range of substances which can be analyzed. The employment of a 
helium-filled chamber makes the spectrometer very cumbersome in 
construction and use. 
Besides, in such spectrometers the sample is difficult of access, which 
increases the time required for analysis and therefore reduces the 
productivity of the spectrometer and makes the sample-loading device more 
complicated. 
Furthermore, breaking of vacuum occurring in such spectrometers when a 
sample is installed or removed necessitates restoration of vacuum each 
time a sample is installed. This also leads to increase in the time 
required by analysis and, besides, makes necessary the use of powerful 
vacuum pumps, which considerably increases the size and weight of the 
spectrometer. 
Known in the art is an X-ray spectrometer wherein the X-ray source is 
positioned fairly close to the surface of the sample. Such a spectrometer 
comprises an X-ray source, a sample holder positioned across the radiation 
path of the X-ray source and spaced from the X-ray source at a distance 
which ensures the illumination of the central portion of the sample 
surface not less than 0.3 ZU erg/s. cm.sup.2.w, where X is the atomic 
weight of material of the X-ray anode and U is the voltage across the 
X-ray source, in kilovolts, a curved analyzing cristal for focusing the 
fluorescent radiation of the sample, the curve of the planes of the 
analyzing cristal defining a focal circle, and a detector for recording 
the radiation reflected by the analyzing cristal, the sample holder being 
positioned so that the distance between the focal circle and the sample 
surface exposed to radiation does not exceed the product of the distance 
between the focus of the X-ray source and said sample surface by the ratio 
between the diameter of the focal circle and the length of the analyzing 
cristal (cf. U.S. Pat. No. 4,091,282). 
To provide the above-mentioned illumination of the sample surface, the 
X-ray source must be located very close to the sample. The distance 
between the focal circle and the sample in such a spectroueter is also 
small. Thanks to the small distance between the X-ray source and the 
sample, such a spectrometer provides considerable increase in the aperture 
ratio of the spectrometer and thus makes it possible to drastically 
(several tens of times) reduce the amount of power consumed by the X-ray 
tube, and hence its size and weight. 
However, in the absence of an evacuated chamber, such a spectrometer is not 
capable of determining the concentrations of light chemical elements, e.g. 
having atomic weight below 22, because of strong absorption of soft X-ray 
radiation by air. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an X-ray 
fluorescence spectrometer which is capable of determining the 
concentrations of light chemical elements in samples susceptible to 
destruction by vacuum. 
Another object of the present invention is to provide an X-ray fluorescence 
spectrometer which permits quick determination of the concentrations of 
light chemical elements in the test sample. 
Still another object of the present invention is to provide an X-ray 
fluorescence spectrometer capable of determining the concentrations of 
light chemical elements in the test sample and having a small size and 
weight. 
Still another object of the present invention is to provide an X-ray 
fluorescence spectrometer which permits determination of the 
concentrations of light chemical elements in the test sample without 
making the sample difficult of access. 
Still another object of the present invention is to provide an X-ray 
fluorescence spectrometer which permits determination of the 
concentrations of light chemical elements in the test sample without 
necessitating restoration of vacuum each time a sample is installed. 
With these and other objects in view there is proposed an X-ray 
fluorescence spectrometer comprising an X-ray source, a sample holder 
positioned across the radiation path of the X-ray source and spaced from 
the X-ray source at a distance which ensures the illumination of the 
central portion of the sample surface not less than 0.3 ZU 
erg/s.cm.sup.2.w, where Z is the atomic weight of material of the X-ray 
anode and U is the voltage across the X-ray source, in kilovolts, a curved 
analyzing cristal for focusing the fluorescent radiation of the sample, 
the curve of the planes of the analyzing cristal defining a focal circle, 
and a detector for recording the radiation reflected by the analyzing 
cristal, wherein, according to the invention, the detector and the 
analyzing cristal are installed in an evacuated chamber, the X-ray source 
and the sample holder being positioned outside the evacuated chamber which 
is provided with a window positioned on the focal circle across the path 
of the fluorescent radiation of the sample, the sample holder being 
positioned so that the average distance between the sample surface portion 
which produces fluorescent radiation incident on the analyzing cristal and 
the window does not exceed the distance between this sample surface and 
the focus of the X-ray source. 
The proposed spectrometer allows for determining the concentrations of 
light chemical elements in the test sample because, with the distances 
between the sample and the chamber window and between the X-ray source and 
the sample chosen as described above, these distances are so small to 
create little absorption of soft X-ray radiation. 
At the same time, the proposed spectrometer makes it possible to analyze a 
wide range of objects, including those susceptible to destruction by 
vacuum, provides an easy access to the test sample and eliminates the need 
for restoring vacuum each time a sample is installed, thanks to the 
arrangement of the sample holder and the X-ray source outside the 
evacuated chamber. Such an arrangement of the sample holder and the X-ray 
source can be easily accomplished inspite of the small distances between 
the sample and the source because the required sensitivity of the 
spectrometer is ensured in this case by using a small-power X-ray source 
having a small size. Thanks to the easy access to the sample and 
elimination of the need for restoring vacuum each time a sample is 
installed, the spectrometer is capable of performing a rapid analysis and 
has a small size and weight. 
Preferably, the window of the evacuated chamber is positioned at the top of 
a prism-shaped projection of the chamber, the projection of the protruding 
portion on the plane of the focal circle being bounded by two line 
segments converging at the focal circle at an angle to each other equal to 
the aperture angle of the analyzing cristal. 
The aforementioned and other objects and advantages of the present 
invention will become more apparent upon consideration of the following 
detailed description of its preferred embodiment taken in conjunction with 
the accompanying drawing.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawing, the X-ray fluorescence spectrometer comprises an 
X-ray source which is an X-ray tube 1 with a focal spot 2, and a sample 
holder 3 arranged across the radiation path of the tube 1. In the drawing, 
the spectrometer is shown with a sample 4 which is a pellet placed in the 
holder 3. The spectrometer further comprises a curved focusing analyzing 
cristal 5 defining by the curve of its planes the location of a focal 
circle 6, and a detector 7 for recording radiation reflected by the 
analyzing cristal 5. The detector 7 may be, for example, a proportional 
gaseous discharge counter. 
The analyzing cristal 5 and the detector 7 are installed in an evacuated 
chamber 8. The X-ray tube I and the sample holder 3 with the sample 4 are 
positioned outside the chamber 8. 
The chamber 8 has a protruding portion 9 shaped and positioned so that its 
projection on the plane of the focal circle 6 is bounded by two line 
segments converging at the focal circle 6 at an angle to each other equal 
to the aperture angle of the analyzing cristal 5. The chamber 8 is 
provided with a window 10 for passing X-ray radiation. The window 10 is 
positioned at the top of the prism-shaped projection 9 across the path of 
fluorescent radiation emitted by the simple 4, the analyzing cristal 5 
being positioned across the path of fluorescent radiation passing through 
the window 10. The window 10 is made of material permitting passage of 
X-ray radiation, such as polypropylene. 
The sample holder 3 is spaced from the X-ray tube I at a distance which 
ensures the illumination of the central portion of the sample surface not 
less than 0.3 ZU erg/s.cm.sup.2.w, where Z is the atomic weight of 
material of the X-ray anode and U is the voltage across the tube I, in 
kilovolts. The sample holder 3 is so positioned in relation to the window 
10 that the average distance "r" between the sample surface portion which 
produces radiation incident on the analyzing cristal 5 and the window 10 
does not exceed the distance "h" between this sample surface portion and 
the focal spot 2. 
The spectrometer operates as follows. 
The primary radiation of the X-ray tube I coming from the focal spot 2 
illuminates the sample 4 wherein a secondary X-ray fluorescent radiation 
is induced. The fluorescent radiation of the sample 4 passes through the 
window 10 into the evacuated chamber 8, is reflected from the analyzing 
cristal 5, focused on the detector 7 and recorded by the latter. 
With the illumination of the central portion of the sample surface not less 
than 0.3 ZU erg/s.cm.sup.2.w, the distance "h" between the focal spot 2 of 
the X-ray tube I and the sample surface will be small enough to create a 
relatively small weakening of the X-ray radiation leaving the tube I. This 
ensures a sufficiently effective excitation of light chemical elements 
present in the sample 4. Since the average distance "r" between the sample 
surface portion which produces radiation incident on the analyzing cristal 
5 and the window 10 does not exceed the distance "h", the distance "r" 
will be small enough to create, in the path between the sample 4 and the 
window 10, a relatively small weakening of the soft X-ray fluorescent 
radiation of the light chemical elements effective excitation of which is 
ensured at the chosen value of the distance "h". Thereupon, when the X-ray 
fluorescent radiation passes through the evacuated chamber 8, this 
radiation practically does not weaken. Therefore the intensity of the soft 
radiation produced by light chemical elements present in the sample 4 will 
be enough to allow determination of the concentrations of said elements in 
the sample 4. 
The arrangement of the window 10 at the top of the prism-shaped projection 
9 shaped and positioned as described above allows the window 10 to be 
brought as near to the sample 4 as possible, without causing any losses in 
the fluorescent radiation passing inside the portion 9, and thus provides 
the maximum reduction in the absorption of the fluorescent radiation of 
the sample 4 in the path between the sample 4 and the window 10. The 
positioning of the window 10 on the focal circle 6 provides the maximum 
reduction in the area of the window 10, and hence in the thickness of its 
material and in its ability to absorb the fluorescent radiation of the 
sample 4. 
According to this disclosure, the function of the dispersing element is 
performed by an analyzing cristal. Of course, this does not imply that the 
latter cannot be replaced by a technical equivalent, for example, a 
focusing diffraction grating. 
An X-ray fluorescence spectrometer has been built according to the 
arrangement shown in the drawing. This spectrometer employs an acute-focus 
5-watt 25-kilovolt X-ray tube having a silver anode, a Johansson analyzing 
cristal made of RbAP and having dimensions of 20.times.40 mm, and an argon 
proportional counter, with the distances "r" and "h" being 3 mm and the 
diameter of the focal circle being 150 mm. Such a spectrometer is capable 
of determining the concentrations of chemical elements having atomic 
weight from II (sodium) to 92 (titanium). The spectrometer has a small 
weight (about 15 kg) and size (about 400.times.400.times.150 mm). 
While the invention is described herein in the terms of the preferred 
embodiments, numerous modifications may be made without departure from the 
spirit and scope of the invention as defined in the appended claims.