RU2642886C1 - Intensity modulation of x-ray beam - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: intensity modulation of the X-ray beam is carried out by changing the reflection conditions of X-ray reflection from a piezoelectric single crystal under the conditions of applying an electric field to it. The said change of conditions of X-ray reflection is made by changing the piezo deformation of said single crystal, resulting in a homogeneous change of interplain distance in crystal lattice of mentioned single crystal, accompanied by an angular offset of its diffraction reflection curve (DRC), under the influence of constant electric field, intensity E of which is change depending on the magnitude of the reflected X-rays (Iθ) according to a specified formula.

EFFECT: enabling optimal intensity modulation of the X-ray beam in the Bragg X-ray reflection mode from the piezoelectric single crystal with a small half-width of the original diffraction reflection curve in conditions of applying constant electric field to it.

2 cl, 2 tbl, 2 dwg

Description

The invention relates to technology for controlling X-ray radiation by changing the conditions of the Bragg diffraction of X-rays in piezocrystals under the influence of an electric field that creates the possibility of a given change (modulation) of the intensity of the X-ray beam, and can be used in the field of X-ray spectroscopy, X-ray diffraction analysis and experimental X-ray technology.

A known modulation of the intensity of the x-ray beam is that the x-ray beam is sent to a piezoelectric single crystal, which is installed in the reflective position or in the transmission mode and to which an alternating (pulsed) electric field is applied (see, for example, USSR copyright certificate No. 106058, G21K 3 / 00, G21K 1/06, 1957, US patent No. 3832562, G01N 23/2073, G01N 23/20, G21K 1/06, 1974 and USSR copyright certificate No. 728166, G21K 1/06, 1980) to create complicated and unstable conditions for changing the intensity of the x-ray beam due to periodic changes in the interplanar spacings of a selected family of atomic planes, leading to modulation of the angular position of the diffracted X-ray beam with the frequency of the ultrasonic vibrations of the resonator (see, for example, a report by A. Targonsky, A. A. Blagov and others. “X-ray acoustic diffractometry for electron component and materials. ”- Materials of the international scientific and technical conference. M., 2013, p. 32-35, on the Internet site: http://www.conf.mirea.ru/CD2013/pdf/p1/7.pdf).

The prior art in the field of X-ray control is characterized by the absence of information sources with information about the proposed modulation of the intensity of the X-ray beam, based on a change in the conditions for the reflection of X-ray from a piezoelectric single crystal under conditions of applying an electric field to it, which is carried out by changing the piezoelectric strain of the said single crystal, which leads to a uniform a change in interplanar spacing in the crystal lattice of the aforementioned onocrystal, accompanied by the angular displacement of its diffraction reflection curve (KDO), under the influence of an electric field, the intensity of which varies depending on the required intensity of the reflected x-ray radiation, which is the physical mechanism of the proposed modulation of the intensity of the x-ray beam, significantly different from the Bormann effect described above modulation (see, for example, US patent No. 3991309, G01N 23/20, 1976), in connection with which the selected option of drafting the claims (proposal Ai modulation method) without prototype.

The rationale for the chosen option for disclosing the essence of the proposed modulation method without a prototype is also known other physical mechanism (low-tech in implementation due to reduced controllability) of the X-ray beam intensity modulation by changing the Bragg diffraction of X-ray radiation as a result of inhomogeneous piezoelectric deformation of ADP crystals experimentally carried out and described in the article Trushina V.N. and others. "Features of x-ray diffraction on crystals of the KDP group in an electric field." - Reports of the Academy of Sciences. Technical Physics. 1993, t. 331, No. 3, p. 308-310, based on a decrease in the contribution of dynamic effects to the intensity of diffraction maxima and an increase in their intensity.

The technical result from the use of the present invention is the creation of an optimal method for modulating the intensity of an x-ray beam in the mode of Bragg reflection of x-ray radiation from a piezoelectric single crystal with a small (from 5 to 25 arc seconds) half-width of the original BWW under conditions of applying a constant (non-pulse) electric field to it, the intensity of which (as a result of using the possibility of changing the piezoelectric strain of the aforementioned single crystal, leading to a uniform change in the interplanar the bone distance in the crystal lattice of the aforementioned single crystal, accompanied by the angular displacement of its BWW, under the influence of an electric field) is changed depending on the required value of the intensity of the reflected x-ray radiation in accordance with the proposed formula.

The optimality of the proposed method of x-ray beam modulation is ensured by increasing the controllability of obtaining a stable desired change in the intensity of the reflected x-ray radiation with a change in the constant electric field applied to piezoelectric single crystals having a small half-width of BWW and a high value of the piezoelectric module.

To achieve the indicated technical result, a method for modulating the intensity of an X-ray beam by changing the conditions for the reflection of X-ray radiation from a piezoelectric single crystal under conditions of applying an electric field to it is characterized in that the said change in the conditions for the reflection of X-ray radiation is carried out by changing the piezoelectric strain of said single crystal, which leads to a uniform change interplanar spacing in the crystal lattice of said mo of the nanocrystal, accompanied by the angular displacement of its BWW, under the influence of a constant electric field, the intensity E of which is changed depending on the required value of the intensity of the reflected x-ray radiation I (θ) in accordance with the formula:

where I _max is the maximum value of the intensity of the reflected x-ray radiation;

λ is the wavelength of x-ray radiation;

d _hkl is the interplanar distance for the hkl planes of the piezoelectric single crystal;

D ^(p) is the piezoelectric module of the piezoelectric single crystal in the direction of the z axis;

E is the constant electric field in the direction of the z axis;

β is the half-width of the initial BWW of the piezoelectric single crystal;

subject to the selection of a piezoelectric single crystal with a small half-width of the initial BWW β and a high value of the piezoelectric module D ^(p) and a change in the constant electric field E, leading to an angular displacement of the BWW in the range of changes in the intensity of the original BWW, which is close to linear.

In the particular case of the implementation of the proposed modulation method, a strontium-barium niobate single crystal (Sr _0.61 Ba _0.39 Nb ₂ O ₆ ) 0.5 mm thick with a half-width of the initial BWW of 20 arc seconds and a piezoelectric module D ^(p) = 140⋅10 ^{-12 is} used as a piezoelectric single crystal C / N, and a change in the intensity of the constant electric field E is performed within the range of its values 0 - 7.8 В10 ⁵ V / m with the angular displacement of the BWW of the indicated single crystal under the influence of a constant electric field with the indicated variable intensity in the interval e changes in the intensity of the initial BWW I (θ) of this single crystal 20-80% of the maximum intensity of the initial BWW I _max .

In FIG. 1 shows a perspective view of an apparatus for implementing the proposed modulation method; in FIG. 2 — two BWWs of a single crystal of strontium-barium niobate — the initial one and in the position of extreme angular displacement after the piezoelectric strain of the specified single crystal as a result of exposure to a constant electric field of 7.8 × 10 ⁵ V / m, showing the possibility of obtaining an operating range of modulation of the intensity of the x-ray beam in in accordance with the proposed modulation method.

The installation for implementing the proposed modulation method (see Fig. 1) contains an X-ray tube 1, slits 2 and 3, a crystal monochromator 4, a piezoelectric single crystal 5 (for which a single crystal of strontium-barium niobate Sr _0.61 Ba _0.39 Nb ₂ O ₆ s is selected a small half-width of the initial BWW - 20 arc seconds), electrodes 6, to which a constant voltage is applied, a high-voltage voltage converter (for example, XP-EMCO R12P) 7, to which a signal from a low-voltage source 8, an X-ray scintillation detector Nia 9, the pulse counter 10, the personal computer 11.

At a distance of 50 mm from the x-ray tube 1, a slot 2 with a width of 0.5 mm is supplied. The X-ray beam transmitted through it is reflected according to Bragg from the crystal-monochromator 4. On the path of the monochromatized beams — CuK _α1 and CuK _α2 , a slit 3 of 0.1 mm width is placed at a distance of 100 mm from the crystal-monochromator 4, with the help of which the CuK _α2 line is screened radiation.

Next, a monochromatized beam — CuK _{α1 — is} incident on a piezoelectric single crystal 5, after which diffraction is recorded using a scintillation detector 8, the signal from which passes through a pulse counter 9 to computer 10, where further processing is possible.

The proposed method for modulating x-ray radiation is based on the shift of the operating point by the BWW at its angular displacement caused by controlled piezoelectric deformation of the single crystal 5.

The change in the intensity of the diffracted X-ray beam I (θ), recorded by the pulse counter 9, occurs due to the shift of the Bragg angle of the diffraction maximum from the piezoelectric single crystal 5, at which the current operating point on the BWW (see Fig. 2) is shifted, changing the intensity value at this point in accordance with formula (1) depending on the magnitude of the electric field strength E in a predetermined range from R ₀ to R _1, when applying a variable DC voltage with vysokovoltnog converter 7 on the low-voltage source 8 contacts - electrodes 6.

To modulate the intensity of the reflected (diffracted) X-ray beam, single crystal 5 in the absence of an electric field is displayed in the Bragg reflective position, by angular rotation of this single crystal, a working point is selected on the left slope of the curve, at a height of about 0.2I _max (the beginning of the quasilinear section) corresponding to R ₀ in FIG. 2.

Depending on the magnitude of the intensity E of the constant electric field supplied to the single crystal 5, the operating point will shift in the interval from R ₀ to R ₁ corresponding to the maximum value of the intensity E of the constant electric field supplied to the specified single crystal.

The maximum value of the intensity E of the constant electric field that shifts the operating point by the BWW from position R ₀ to position R ₁ is calculated from the values of the piezoelectric module D ^{(p) of the} single crystal 5 and the half width β of its BWW. Intermediate values of the intensity of diffracted radiation I (θ) are calculated by the formula (1).

To calculate the intensity I (θ) according to formula (1), the input parameters of the strontium-barium niobate single crystal (Sr0.61Ba0.39Nb2O6), presented in Table 1, are used.

The calculation results of the initial and maximum biased BWW of the indicated single crystal are shown in table 2.

The rationale for the conclusion of the formula (1):

Consider the change in the peak intensity of BWW at its operating point.

BWW for planes (hkl) can be described by a Gaussian curve:

where: I _max - the maximum value of the intensity,

β is the half-width of the BWW,

θ _hkl - angular positions of MLC Center,

θ is the current value of the angle.

From the Wulf-Bragg equation it follows:

where θ _hkl is the Bragg angle for the (hkl) planes;

λ is the wavelength of x-ray radiation;

d _hkl - interplanar distance for planes (hkl).

Interplanar distance taking into account piezoelectric deformation:

d _hkl - initial interplanar distance,

Δd is the change in interplanar distance caused by piezoelectric deformation.

Relative deformations can be described by the expression:

In turn, small elastic strains arising in crystals as a result of the inverse piezoelectric effect are described by the expression:

- относительные пьезодеформации,Where

- relative piezoelectric deformations,

- матрица пьезоэлектрических модулей D^(p) рассматриваемого монокристалла,

- a matrix of piezoelectric modules D ^{(p) of} the single crystal under consideration,

E _i are the components of the constant electric field strength.

для плоскостей (hkl), при воздействии постоянного электрического поля на пьезоэлектрический монокристалл 5, зависит от напряженности E_i прикладываемого электрического поля:In general, the Bragg angle

for planes (hkl), when a constant electric field acts on the piezoelectric single crystal 5, it depends on the strength E _{i of the} applied electric field:

Thus, it follows from expressions (2) and (7) that the intensity value of the reflected x-ray radiation at the operating point on the Gaussian BWW curve will vary depending on the intensity of the applied constant electric field in accordance with formula (1).

In this case, the maximum value of the constant electric field strength E displacing the operating point by the BWW from position R ₀ to position R ₁ is calculated from the values of the piezoelectric module D ^{(p) of the} single crystal 5 and the half width β of its BWW. According to formulas (1) and (7), with an increase in the half-width β and a decrease in the modulus D ^(p), it will be necessary to increase the maximum value of the constant voltage applied to the single crystal 5; otherwise, the modulation depth determined by the interval of variation in the intensity of the initial BWW I (θ) of this single crystal, 20-80% of the maximum intensity of the initial BWW I _max will be less.

If we go beyond the quasilinear (close to linear) part of the BWW determined by the quasilinear dependence of the intensity change, then the maximum modulation depth determined by the interval of intensity change of 20-80% can be increased with a corresponding increase in the maximum value of the constant voltage applied to single crystal 5, or decrease half-width β and an increase in the value of the modulus D ^(p) .

Therefore, the non-fulfillment of the essential conditions of the proposed modulation method set forth in paragraph 1 of the utility model formula leads to modulation with a technologically disadvantageous deviation from the modulation optimality associated with increased energy costs and special requirements for the single crystal material 5, and indicates the materiality of the considered characteristics of the proposed modulation method set forth in paragraph 1 of the formula of the utility model.

Claims (10)

1. A method of modulating the intensity of an X-ray beam by changing the conditions for the reflection of X-ray radiation from a piezoelectric single crystal under conditions of applying an electric field to it, characterized in that said change in the conditions for the reflection of X-ray radiation is carried out by changing the piezoelectric strain of said single crystal, which leads to a uniform change in the interplanar distance in the crystalline lattice of said single crystal, followed by angular displacement of its diffraction curve action reflection (BWW), under the influence of a constant electric field, the intensity E of which is changed depending on the required value of the intensity of the reflected x-ray radiation I (θ) in accordance with the formula:

where I _max is the maximum value of the intensity of the reflected x-ray radiation; λ is the wavelength of x-ray radiation; d _hkl is the interplanar distance for the hkl planes; D ^(p) is the piezoelectric module of the piezoelectric single crystal in the direction of the z axis; E is the constant electric field in the direction of the z axis; β is the half-width of the initial BWW of the piezoelectric single crystal; subject to the selection of a piezoelectric single crystal with a small half-width of the initial BWW β and a high value of the piezoelectric module D ^(p) and a change in the constant electric field E, leading to an angular displacement of the BWW in the range of changes in the intensity of the original BWW, which is close to linear. 2. The modulation method according to claim 1, characterized in that a strontium-barium niobate single crystal (Sr _0.61 Ba _0.39 Nb ₂ O ₆ ) 0.5 mm thick with a half-width of the initial BWW β = 20 arc seconds and a piezoelectric module D ^{( p)} = 140 · 10 ^-12 C / N, and a change in the intensity of the constant electric field E is made within the range of its values 0-7.8 · 10 ⁵ V / m with the angular displacement of the BWW of the indicated single crystal under the influence of a constant electric field with the indicated variable intensity in Int interval The intensity of the initial BWW I (θ) of this single crystal is 20-80% of the maximum intensity of the initial BWW I _max .

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