Doped Lithium Fluoride Monochromator For X-Ray Analysis

Abstract

The invention relates to a crystalline lithium fluoride doped with at least 0.018 mol per kg of a divalent positive ion M present in the fluoride state, in particular of the single-crystal type. The ion may be Mg2+, Zn2+ or Co2+. This fluoride has a high reflectivity and intense radiation that can emanate therefrom may be effectively received by a fast light scintillator, especially of the rare-earth halide type. It is particularly useful as a monochromator for X-ray fluorescence radiation for the purpose of elemental analysis.

Description

EXAMPLES

Single crystals of pure LiF or those doped with Mg in fluoride form were prepared from a uniform blend of pure LiF and pure MgF² powders in various concentrations. The blend was placed in a platinum crucible and then melted by heating to 950° C. A crystallization operation was then carried out, resulting in a single crystal 2300 cm³ in volume.

The reflected X-radiation intensity was measured on single-crystal pieces cleaved along the (200) plane, with the molybdenum K_α line. The intensity varied little within an Mg concentration range between 0 and 400 ppm by weight. The intensity from the highly magnesium-doped Mg:LiF single crystals was expressed as a percentage of the intensity from the specimen containing 300 ppm Mg by weight. These results are given in Table 1. In this table, the specimen name contains the Mg content.

TABLE 1
	Mg content (in	Mg content	% intensity
Specimen	ppm by weight)	(mol/kg)	relative to LiF300
pure LiF	0	0	100%
LiF300	300	0.0123	100%
LiF501	501	0.0206	336%
LiF664	664	0.0273	476%
LiF765	765	0.0314	552%
LiF1063	1063	0.0437	589%

The effect of wavelength on the reflected intensity was also measured on specimens having a different Mg content. Table 2 gives the results. These results are expressed as a percentage of the reflected intensity for LiF₃₀₀. The reflected intensity increases very strongly when the wavelength decreases for specimens having a higher Mg content.

	TABLE 2
				λ =	λ =
	λ = 3.359 Å	λ = 2.750 Å	λ = 1.937 Å	1.542 Å	0.7107 Å
	Ca	Ti	Fe	Cu	Mo
LiF300	100%	100%	100%	100%	100%
LiF765	207%	252%	358%	410%	572%
LiF1063	238%	285%	404%	441%	595%

The increase in intensity, measured with a cleaved surface finish (on a (200) crystallographic plane), is maintained after plane plates have been curved. For example, at the iron wavelength (λ=1.937 Å), the intensity reflected by the cleaved plane LiF₆₆₄ was 2.8 times higher than that of cleaved plane LiF₃₀₀. The intensity reflected by curved LiF₆₆₄ plates, curved over a cylinder whose axis was parallel to the X-ray direction, remained higher than the intensity reflected by the curved LiF₃₀₀ plates, again curved over the same cylinder with its axis parallel to the direction of the X-rays. The intensity ratio of the plates curved over a cylinder of axis parallel to the X-ray beam remained the same (i.e. 2.8).

Claims

1-23. (canceled)

24: An analyzer, comprising a monochromator consisting of a single-crystal lithium fluoride doped with at east 0.018 mol per kg of a divalent positive ion M present in the fluorinated state.

25: The analyzer as claimed in claim 24, wherein the ionic radius of the divalent ion M ranges from 55 to 80 picometers.

26: The analyzer as claimed in claim 25, wherein M is present in the fluoride in an amount of at least 0.02 mol per kg.

27: The analyzer as claimed in claim 26, wherein M is present in the fluoride in an amount of at least 0.023 mol per kg.

28: The analyzer as claimed in claim 27, wherein M is present in the fluoride in an amount of at least 0.025 mol per kg.

29: The analyzer as claimed in claim 24, wherein M is present in the fluoride in an amount of at most 0.082 mol per kg.

30: The analyzer as claimed in claim 29, wherein M is present in the fluoride in an amount of at most 0.045 mol per kg.

31: The analyzer as claimed in claim 24, wherein M is Mg2+.

32: The analyzer as claimed in claim 24, wherein M is Co2+.

33: The analyzer as claimed in claim 24, wherein M is Zn2+.

34: The analyzer as claimed in claim 24, wherein M is a mixture of at least two ions chosen from Mg2+, Zn2+ and Co2+.

35: The analyzer as claimed in claim 24, wherein the fluoride is present in the form of a cube or a parallelepiped.

36: The analyzer as claimed in claim 24, wherein the volume of the fluoride ranges from 2·5×10−3 cm3 to 30 cm3.

37: The analyzer as claimed in claim 36, wherein the volume of the fluoride ranges from 0.01 to 20 cm3.

38: The analyzer as claimed in claim 24, wherein the fluoride has a cleaved surface,

39: The analyzer as claimed in claim 24, wherein the fluoride has a surface that is ground and then treated in an acid medium or polished,

40: The analyzer as claimed in claim 24, comprising at least one scintillator consisting of a rare-earth halide.

41: The analyzer as claimed in claim 40, wherein the rare-earth halide is CeCl3-doped LaCl3 or CeBr3-doped LaBr3.

42: A method of analyzing an element of a specimen by means of the analyzer as claimed in claim 24, wherein said analyzer comprises a detector consisting of a scintilator, said scintilator being set on a line having a wavelength of less than 3 Å.

43: The method as claimed in claim 42, wherein the scintilator is set on a line having a wavelength of less than 2 Å.

44: The method as claimed in claim 43, wherein the scintilator is set on a line having a wavelength of less than 1.5 Å.

45: A single-crystal lithium fluoride doped with 0.023 to 0.082 mol per kg of a divalent positive ion M present in the fluorinated state.

46: The fluoride as claimed in claim 45, wherein the ionic radius of the divalent ion M ranges from 55 to 80 picometers.

47: The fluoride as claimed in claim 46, wherein M is present in an amount of at least 0.025 mol per kg.

48: The fluoride as claimed in claim 47, wherein M is present in an amount of at most 0.045 mol per kg.

49: The fluoride as claimed in claim 45, wherein M is Mg2+.

50: The fluoride as claimed in claim 45, wherein M is Co2+.

51: The fluoride as claimed in claim 45, wherein M is Zn2+.

52: The fluoride as claimed in claim 45, wherein M is a mixture of at least two ions chosen from Mg2+, Zn2+ and Co2+.

53: The fluoride as claimed in claim 45, wherein said fluoride is present in the form of a cube or a parallelepiped.

54: The fluoride as claimed in claim 45, wherein the volume of said fluoride ranges from 2.5×10−3 cm to 30 cm3.

55: The fluoride as claimed in claim 54, wherein the volume ranges from 0.01 to 20 cm3.

56: The fluoride as claimed in claim 45, wherein said fluoride has a cleaved surface.

57: The fluoride as claimed in claim 45, wherein said fluoride has a surface that is ground and then treated in an acid medium or polished,

58: The use of a fluoride of claim 45 as monochromator.