SU940022A1 - X-ray spectrometer - Google Patents

Description

(54) X-RAY SPECTROMETER

one

The invention relates to X-ray spectral instruments for studying the quantitative and qualitative composition of a substance, in particular, to X-ray fluorescence spectrometers using a Johansson crystal analyzer, and 5 can be widely used in industrial laboratories and research institutes in analyzing various samples.

A fluorescent X-ray fluorescence spectrometer is known, containing a radiation source, a sample holder, an entrance and exit slit, an Johansson analyzer crystal, and an X-ray detector 1.

The closest technical solution to the present invention is an X-ray spectrometer containing a source of exciting radiation, located along the X-ray beam, the sample holder placed on the focal circle 2o entrance slit, Johansson analyzer and exit slit, as well as detector 2.

The edges of the entrance and exit slits of known spectrometers are located in planes perpendicular to the plane of the focal circle and to the middle beam, respectively, incident on the analyzer crystal, or reflected from it, and the width of the entrance slit S is selected from the ratio

S D S0sin05,

where D is the diameter of the focal circle;

60- mosaicity of the crystal analyzer; 6g- Bragg angle.

The disadvantage of these spectrometers is also low sensitivity.

The purpose of the invention is to increase the sensitivity of an X-ray spectrometer using a Johansson crystal analyzer.

This goal is achieved by the fact that in an X-ray spectrometer containing a source of excitation radiation, the sample holder located along the X-ray beam, the input slit, Johansson analyzer crystal and the output slit, as well as the detector, the input slit are located on the focal circle, so that edges

it is crossed by the latter, and the slit width S is chosen from the condition that the equality S D 66 is satisfied, where D is the diameter of the focal circle;

56- mosaic crystal analyzer.

FIG. 1 shows a functional diagram of the proposed spectrometer; in fig. 2 and 3 - the course of the rays, respectively, in the known spectrometer and the proposed one.

The X-ray spectrometer (Fig. 1) contains a source of excitation radiation 1, a holder with sample 2 located outside the focal circle 3, an entrance slit 4, an Johansson crystal analyzer 5 and an output slit 6 located on the focal circle, the radiation detector 7 located behind the exit slit 6. The edges of the entrance slit 4 are located on the focal circle 3, and the width is equal to the product of the diameter of the focal circle and the mosaicity of the crystal analyzer.

Known spectrometer works as follows (Fig. 2).

The SO beam falls on the crystal at the Bragg angle © B, the SO beam falls on the crystal at an angle -. The straight line NN (the line of intersection of the plane of the entrance slit with the plane of the focal circle) is perpendicular to the middle beam SO, and the segment SS is 1 / 2DX S0 sin6). From point S to point A of the crystal, the radiation falls under the Bragg angle, and the difference in the angle of incidence of the radiation at point A from point S exceeds (approximately equal to e) and the reflection efficiency for the beam bA is low. The difference between the angle of incidence of the rays at point A and the Bragg angle does not exceed only the section of the entrance slit (the beam passes through the same point of the focal circle as the beam SO).

A similar consideration for the right half of the crystal shows that the reflection conditions (the difference between the angle of incidence and Bragg less) are performed for a straight line section NN greater than 1 / 2D sin0B. Thus, when the entrance slit is perpendicular to the middle beam, losses of luminosity are proportional to the ratio - | d- for the left half of the crystal and the right half of the crystal. When building luminous schemes (using large crystals), the ratios reach 2-3.

The course of the rays in the proposed spectrometer is as follows (Fig. 3).

The rays SO and SO fall onto the crystal, respectively, at angles as they move. WB - The distance between points S and S is 1 / 2E 60. The difference between the angle of incidence and the Bragg angle is the same for all beams emanating from point S (for example, for beam SA) and equal to When the entrance slit is half-width SS –jD-69.

the crystal reflects 0.8 If (Y is the reflection coefficient) of monochromatic radiation incident on it.

The range of wavelengths reflected by the crystal is determined by the range of angles of incidence of the radiation on the crystal and is AX 2dcos6.

Comparison of the known and proposed spectrometers shows that the proposed spectrometer has a higher luminosity (approximately Щ-times) and

5 narrower bandwidth (approximately in times). When constructing high-aperture circuits with large-sized crystals, the gain is 2-3 times.

Thus, the proposed spectrometer with large crystal sizes makes it possible to obtain a significant gain in luminosity and contrast, and, consequently, in the threshold sensitivity. Due to this, the proposed spectrometer allows to expand the range of tasks solved

5 x-ray method.

Claims (2)

1.Afonin V.P., Gunicheva T.N. X-ray fluorescence analysis of rocks and minerals. Novosibirsk “Science, 1977 (Fig. 20). 2. Anisovich K. V., Buman A. I. X-ray spectrometer with a monochromator crystal for quantitative analysis. "Equipment and methods of x-ray analysis, L." Engineering, 1975, vol. 17, p. 82-86 (prototype).