JP3374114B2 - X-ray fluorescence analyzer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray fluorescence analyzer for performing X-ray fluorescence analysis of a sample, and more particularly to improving the rising characteristics of an X-ray tube.

[0002]

2. Description of the Related Art Generally, a fluorescent X-ray analyzer irradiates a sample with a primary X-ray generated by applying a high voltage to a target of an X-ray tube and detects the intensity of the fluorescent X-ray generated from the sample. Analyze the sample by measuring with the instrument. In this device, the primary X
When high voltage application is turned on to generate a line, most of the electric power is converted to heat and the target stores heat, and the target is cooled by a fan or the like.
The target expands due to thermal expansion, the distance between the target and the sample becomes shorter, and the X-ray intensity per unit area received by the sample increases in inverse proportion to the square of the distance. Therefore, it is necessary to wait for a long time (for example, 40 minutes) to measure the fluorescent X-ray intensity until the thermal expansion of the target becomes stable at the start-up of the X-ray tube for starting the measurement. Also,
Once high voltage application is turned off during sample replacement,
When the target was cooled and the thermal expansion up to that point was contracted and turned on again, it was necessary to wait until the thermal expansion of the target reached a stable state in the same manner.

[0003]

However, it is difficult to shorten the time until the start of measurement by waiting for the measurement until the thermal expansion of the target reaches a stable state as in the conventional case. Therefore, there is a demand for a device that can immediately perform measurement after the high voltage is applied to the target.

An object of the present invention is to solve the above-mentioned problems and to provide an X-ray fluorescence analyzer capable of shortening the time until the start of measurement when a high voltage is applied to a target. .

[0005]

In order to achieve the above object, an X-ray fluorescence analyzer according to claim 1 uses a sample of primary X-rays generated by applying a high voltage to a target of an X-ray tube. The intensity of fluorescent X-rays emitted from the sample is measured by a detector to analyze the sample, and the distance between the target and the sample corresponding to the expansion and contraction amount of the target due to thermal expansion is measured.
The intensity of the fluorescent X-ray changes according to the change in the standard state of the thermal expansion.
Fluorescence in correspondence to change in relative intensity of X-ray intensity of the reference of the fluorescent X-rays at the time of the measured at detector
Correction to match the fluorescent X-ray intensity at the time of the first condition
Correction means for changing the intensity of the fluorescent X-rays measured by the detector with respect to the time from the application of the high voltage, and of the fluorescent X-rays measured with the detector with respect to the time from the application of the high voltage OFF. Time obtained based on changes in intensity −
Storage means for storing an X-ray intensity correction curve, wherein the first correction means is based on the time-X-ray intensity correction curve stored in the storage means, and stores a time point measured by the detector. The X-ray fluorescence intensity is corrected.

According to the above structure, the distance between the target and the sample corresponding to the expansion and contraction amount of the target of the X-ray tube due to the thermal expansion.
Depending on the change in separation , based on the time-X-ray intensity correction curve,
Since the intensity of the fluorescent X-ray measured at the detector is corrected to the intensity of the fluorescent X-ray when the thermal expansion of the target is in the standard state, the measuring time from when the high voltage is applied to the target is ON.
At that time, the fluorescent X-ray intensity in the reference state was immediately obtained.
It

[0007]

An X-ray fluorescence analyzer according to a second aspect of the present invention irradiates a sample with primary X-rays generated by applying a high voltage to a target of an X-ray tube to measure the intensity of the fluorescent X-rays generated from the sample. This is to measure the sample with a detector and analyze the sample, and between the target and sample corresponding to the amount of expansion and contraction due to thermal expansion of the target.
Move the X-ray tube with respect to the sample according to the change in the
Target distance between the target and the sample at the measurement time Te
The second correction means is provided to perform correction so as to keep the same as in the reference state of thermal expansion .

According to the above construction, the distance between the target and the sample corresponding to the expansion and contraction amount of the target of the X-ray tube due to the thermal expansion.
In accordance with a change in distance, measured by moving the X-ray tube to the sample
The distance between the target and the sample at a constant time of the target heat
Since it is corrected so that it is kept the same as in the standard state of expansion ,
At the time of measurement from application of high voltage to the target ON
Immediately, the fluorescent X-ray intensity in the reference state is obtained .

[0010] X-ray fluorescence analyzer according to claim 3, wherein
Item 1 or 2 further includes an estimation unit that estimates the expansion / contraction amount of the target due to thermal expansion from a parameter related to the thermal expansion of the target. Therefore, it is possible to estimate the expansion / contraction amount of the target, which is difficult to measure. The above parameters include high voltage power applied to the target, high voltage application time and dwell time, thermal conductivity to the cooling medium, temperature of the cooling medium, thermal expansion coefficient of the target, mechanical holding mechanism of the target. It includes dimensions and thermal conductivity, the initial value of the distance between the target and the sample, and so on.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of an X-ray fluorescence analyzer according to the first embodiment of the present invention. This device is a primary X
X-ray tube 2 for generating X-ray B1, detector 4 for measuring the intensity of fluorescent X-ray B2 generated from sample 3 irradiated with primary X-ray B1, X-ray spectrum based on the detection signal from detector 4. The multi-wave height analyzer 5 for obtaining the above is provided, and the fluorescent X-ray analysis of the sample 3 is performed. The X-ray tube 2, a part of the detector 4, and the sample 3 are placed in a vacuum container 6.

The X-ray tube 2 includes a target material 11 arranged so as to face the sample surface, a target support rod 12 attached to the inner wall 13 of the vacuum container 6 for supporting the target material 11, and a target surface. It is provided with a filament 15 which is provided around and serves as an electron source. The target 10 with the target material 11 and the target support rod 12
Is configured. The target 10 penetrates the insulating wall 21 and is drawn to the outside. When a high voltage is applied to the target 10 and the filament 15 is turned on, thermoelectrons generated from the filament 15 collide with the target surface. The primary X-ray B1 is generated by this collision. In this case, most of the electric power is converted to heat, and this heat is applied to the target support rod 1.
2 and the electrical insulator 14 to the outside. The target support rod 12 and the electrical insulator 14 are the fan 19
It is cooled by air.

This apparatus is characterized in that the change in the intensity of the fluorescent X-ray B2 measured by the detector 4 with respect to the time from the application of the high voltage and the fluorescence measured with the detector 4 with respect to the time from the application of the high voltage to OFF. Storage means 24 for storing the time-X-ray intensity correction curve obtained based on the change in the intensity of X-ray B2.
Then, based on the time-X-ray intensity correction curve stored in the storage means 24, the fluorescence X measured by the detector 4 according to the expansion / contraction amount of the target 10 (mainly the target support rod 12) due to thermal expansion. The first correction means 22 is provided to correct the intensity of the line B2 to the reference state, for example, the X-ray intensity in a state where the thermal expansion of the target 10 is stable.

FIG. 2 shows a typical metal such as copper metal .
An example of a time-X-ray intensity correction curve C1 obtained by an experiment in advance based on a change in the intensity of the fluorescent X-ray B2 measured by the detector 4 with respect to the time from application of the high voltage to ON using a metal sample Indicates. FIG. 3 shows an example of the time-X-ray intensity correction curve C2 obtained from the high voltage application OFF obtained in the same manner. The horizontal axis represents time (minutes), and the vertical axis represents the rate of change (%) in fluorescent X-ray intensity. 2 and 3, the rate of change of 0% indicates that the temperature rise reaches saturation and the fluorescent X-ray intensity reaches the saturation value (Ist). These time-X-ray intensity correction curves are described above.
It is stored in the storage means 24. This correction curve is
It is constant regardless of the size of the rate.

According to the present invention, the target 10 is sufficiently cooled.
Not only the time has passed since it was turned on in the
It can also be applied when it is turned on again before it is rejected. Figure 4
In such a case , the high voltage application to the target 10 is
It is an example of a model diagram showing a change in fluorescent X-ray intensity when the light is turned off and on. In this example, the target 10 is sufficiently cooled and then heated for a ta time by applying a high voltage when the X-ray tube 2 rises. At time point a (the fluorescent X-ray intensity at this time is Ia), a high voltage is applied, for example, to replace the sample for O.
It is FF'd and cooled for tb hours. Point b ( Firefly at this time
The optical X-ray intensity is Ib) and the high voltage application is turned on again, and
It is heated for c hours, and at time point c (the fluorescent X-ray intensity at this time is Ic
). In this case, the curve C1 from the fluorescent X-ray intensities I0 to Ia in FIG. 2 is used for ta time, and the curve C2 from the fluorescent X-ray intensities Ia to Ib in FIG. 3 is used at tb time. The curve C1 of the fluorescent X-ray intensities Ib to Ic in FIG. 2 is used for tc time. Based on this curve,
For example, the fluorescent X-ray intensity Ic measured by the detector 4 at time c
In such a manner that the thermal expansion of the target 10 is stable, that is, the fluorescent X-ray intensity Ist (0%) at the saturation value,
It is corrected by multiplying Ic by the ratio Ist / Ic. With this , immediately after the high voltage is applied to the target 10, the reference state is immediately obtained at the time point c measured without waiting for the measurement until the thermal expansion of the target 10 becomes stable.
The fluorescent X-ray intensity at is obtained .

In the first embodiment, the fluorescent X-ray intensity is corrected based on the time-X-ray intensity correction curve stored in the storage means 24. However, the target estimated by the estimating means 34 described later is used. The fluorescent X-ray intensity may be corrected based on the expansion / contraction amount of 10.

FIG. 5 is a block diagram of an X-ray fluorescence analyzer according to the second embodiment of the present invention. This device is a primary X-ray B1.
X-ray tube 2 for generating X-ray, detector 4 for measuring the intensity of fluorescent X-ray B2 emitted from sample 3 irradiated with primary X-ray B1, and X-ray spectrum is obtained based on the detection signal from detector 4. The multi-wave height analyzer 5 is provided and the fluorescent X-ray analysis of the sample 3 is performed. Similar to the first embodiment, the X-ray tube 2, a part of the detector 4, and the sample 3 are placed in the vacuum container 6.

In this apparatus, the fixing base 16 for fixing the X-ray tube 2 and the inner wall 1 of the vacuum vessel 6 which are constructed in the same manner as in the first embodiment.
A moving means 18 such as a piezo element for changing the distance of the X-ray tube 2 to the sample 3 and a bellows 17 for vacuum sealing are provided between the three.

Further, the present apparatus uses the estimating means 34 for estimating the amount of expansion and contraction of the target 10 due to thermal expansion, and, for example, applying a predetermined voltage to the piezo element 18 based on the estimated amount of expansion and contraction of the target 10. And a control means 36 for controlling the amount of distortion. The moving means 18 and the control means 36 constitute the second correcting means 32. When the piezo element 18 extends, the position of the X-ray tube 2 withdraws with respect to the sample 3. When the piezo element 18 contracts, the position of the X-ray tube 2 advances with respect to the sample 3. The second correction unit 32 corrects the distance between the target 10 and the sample 3 so as to be constant according to the amount of expansion and contraction of the target 10 due to thermal expansion.

For example, before the thermal expansion of the target 10 (mainly the target support rod) stabilizes when the X-ray tube 2 rises, the distance between the target 10 and the sample 3 is increased according to the estimated expansion amount of the target 10. The X-ray tube 2 is moved so that is a constant value, for example, the value m in a state where the thermal expansion is saturated. As a result, the intensity of the primary X-ray B1 with which the sample 3 is irradiated, and thus the intensity of the fluorescent X-ray measured by the detector 4, is corrected to a state where the thermal expansion of the target 10 is stable, that is, a saturation value. Therefore, before the thermal expansion of the target 10 is stabilized, the high voltage is applied to the target 10 from ON,
The X-ray intensity can be measured immediately without waiting for the measurement until the thermal expansion of the target 10 becomes stable.

The estimating means 34 estimates the expansion amount ΔL of the target 10 from the parameters related to the thermal expansion of the target 10. The parameters include, for example, high voltage power applied to the target 10, high voltage application time and dwell time, thermal conductivity to a cooling medium (eg, an electrical insulator), temperature of the cooling medium, target 10
Thermal expansion coefficient (mainly target support rod), target 1
The dimensions of the mechanical holding mechanism of 0 and the thermal conductivity, the initial value of the distance between the target 10 and the sample 3, and the like are included. Therefore, the expansion / contraction amount ΔL of the target 10 can be estimated even when the high voltage applied to the target 10 is once turned off and then turned on again, or when the power of the applied high voltage is changed.

The operation of the estimating means 34 will be described below. FIG. 6 shows the target 1 due to the change in power of the applied high voltage.
It is a model figure which shows the temperature change of 0. Here, the saturation value of the temperature rise of I is Tq1 when the power of Q1 is applied from the completely cooled state. Regarding II, the saturation value of the temperature rise is Tq2 in the state where the temperature is switched from the temperature T1 to the electric power of Q2 after the state of I continues for t1 hours. III
Indicates that the saturation value of the temperature rise in the state where the temperature is switched from the temperature T2 to the electric power of Q3 after the state of II continues for t2 hours is Tq3. IV is the temperature T3 after the state of III continues for t3 hours.
The saturation value of the temperature rise when the power is switched from Q4 to Q4 is Tq4.

Letting t be the time from the change of each state and τr the time constant of the temperature change, the temperature T in each state is calculated as follows: I: T = Tq1-Tq1 · Exp (-t / τr) II : T = Tq2- (Tq2-T1) * Exp (-t /
τr) III: T = Tq3- (Tq3-T2) .Exp (-t /
τr) IV: T = Tq4− (Tq4−T3) · Exp (−t /
τr) The time constant τr is the heat conduction to the cooling medium, the temperature of the cooling medium,
It is set by the dimensions of the mechanical holding mechanism of the target 10 and the coefficient of thermal conductivity.

Estimating the general formula, T = Tst- (Tst-Te) .Exp (-t / .tau.r) (1) where Tst is the saturation temperature in a predetermined state and Te is the temperature at the start of the predetermined state. However, it is set to 0 in the completely cooled state. Since Tst is considered to be proportional to the supplied power Q, p is taken as its proportional constant, and Tst = pQ (2) Therefore, T = pQ- (pQ-Te) * Exp (-t / τr)

Now, the distance from the fixed point to the target surface is L (see FIG. 1), the temperature rise due to high voltage, that is, the expansion amount of the target due to thermal expansion is ΔL, the saturation expansion amount is ΔLst, and the predetermined state is Letting ΔLe be the amount of elongation at the beginning, the following relationships exist between these and T, Tst, and Te. ΔL = k · L · T, ΔLst = k · L · Tst, ΔLe = k
・ L ・ Te where k is the coefficient of thermal expansion of the target support rod.

Therefore, from equation (1),   ΔL = kL · (Tst− (Tst−Te) · Exp (−t / τr))       = ΔLst− (ΔLst−ΔLe) · Exp (−t / τr) Also, from equation (2),   ΔL = kLpQ- (kLpQ-kLTe) · Exp (-t / τr) (3)

Assuming that the distance between the target 10 and the sample is m 0 (initial value in a completely cooled state) (see FIG. 1), the primary X-ray intensity Ir from the X-ray tube 2 in the sample 3 is
Is, Ir = I0 (m0 / ( m0 - △ L)) is ^{2 ≒ I0 (1 + 2 △} L / m0) I0 is the primary X-ray intensity in the absence of △ L = 0, that is, the temperature rise. Therefore, Ir / I0 = 1 + (2 / m) * ([Delta] Lst-([Delta] Lst- [Delta] Le) * Exp (-t / [tau] r)) = 1 + A * (hQ- (hQ- [Delta] Le) * Exp (-t) / Τr)) (4) ΔL = hQ- (hQ-ΔLe) · Exp (-t / τr) (5) where kLp = h. Here, the proportional constant h and the constant A can be obtained as follows. When the supply power Q is applied from a sufficiently cooled state and the amount of change in the X-ray intensity when reaching the saturated state is ΔV, then X is corresponding to this amount of change.
Letting ΔU be the amount of movement when the wire tube 2 is moved by a minute distance, h = ΔU / Q and A = ΔV / ΔU The constants h and A above and the time constant of the temperature change in a predetermined state. τr can be obtained from experiments. Further, the initial value of the elongation amount ΔLe when the predetermined state starts is 0. Therefore, ΔL can be estimated from the supplied power Q and the time t from the start of the predetermined state by using the above equation (5).

Next, considering the parameter of W = ΔL / h, the equation (4) is transformed as follows. Ir / I0 = 1 + B. (Q- (Q-We) .Exp (-t / .tau.r)) (6) W = Q- (Q-We) .Exp (-t / .tau.r) (7) Constant B is B = ΔV / Q (= Ah), which can be obtained by an experiment similar to the above. The W can be considered as a variable proportional to the amount of heat accumulated in the target 10.

The equation (6) shows that the X-ray intensity can be managed as a variable of W, and the constant B and the time constant τr of the temperature change in a predetermined state are measured in advance to determine the supply power Q. It is shown that the X-ray intensity in the rising (when Q changes to the larger side) or the falling (when Q changes to the smaller side) state can also be estimated. That is, as described above, the estimating unit 34 can be used instead of the storing unit 24 (FIG. 1) of the device according to the first embodiment.

In each of the above-described embodiments, when the thermal expansion of the target is saturated is used as the reference state, and the X-ray intensity at this time is corrected. However, when the target does not have thermal expansion, the reference state is used for correction. You may

In the present invention, the heat generated in the target 10 is transferred to the target support rod 12 and the electric insulator 14.
Although it is used for the indirect cooling type device which diffuses through the through, it may be used for the direct cooling type device which introduces the cooling medium (for example, cooling water) directly under the target material 11.

The present invention is applied to the so-called energy dispersive X-ray fluorescence analyzer in which the fluorescent X-rays generated from the sample are directly detected by the detector and the spectrum is separated by the multiple wave height analyzer in each of the above embodiments. However, it may be applied to a so-called wavelength dispersive X-ray fluorescence analyzer in which fluorescent X-rays generated from a sample are dispersed by a dispersive crystal using a goniometer and detected by a detector.

In the above energy dispersive X-ray fluorescence analyzer, the primary X-rays from the X-ray tube may be dispersed by a dispersive crystal to be monochromatic. In this case, in the first embodiment for correcting the X-ray intensity, the movement of the target of the X-ray tube has a large effect on the deterioration of the spectral characteristics, and it is difficult to estimate the correction amount. The second embodiment is applied in which the target position is kept stable.

[0034]

As described above, according to one configuration of the present invention, the expansion and contraction amount of the target of the X-ray tube due to the thermal expansion can be dealt with.
Depending on the change in the distance between the target and the sample , time-X
Based on the line strength correction curve, the intensity of the fluorescent <br/> light X-ray at the time measured by the detector, the thermal expansion of the target is corrected to the fluorescent X-ray intensity at the reference state, the high to the target Immediately after the voltage application is turned on , the reference condition
The fluorescent X-ray intensity is obtained .

According to another structure of the present invention, the target corresponding to the expansion and contraction amount of the target of the X-ray tube due to the thermal expansion.
The X-ray tube is moved with respect to the sample according to the change in the distance between the target and the sample, and the distance between the target and the sample at the time of measurement is measured.
Since corrected so as to maintain the same as for the standard state of the thermal expansion of the target, measuring the applied ON the high voltage to the target
Immediately at a fixed time, the fluorescent X-ray intensity in the reference state
Is obtained .

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a fluorescent X-ray analysis apparatus according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing an example of a time-X-ray intensity correction curve from high voltage application ON.

FIG. 3 is a characteristic diagram showing an example of a time-X-ray intensity correction curve from high voltage application OFF.

FIG. 4 is a model diagram showing changes in X-ray intensity due to ON and OFF of high voltage application.

FIG. 5 is a configuration diagram showing a fluorescent X-ray analysis apparatus according to a second embodiment of the present invention.

FIG. 6 is a model diagram showing a temperature change of a target due to a power change of an applied high voltage.

[Explanation of symbols]

2 ... X-ray tube, 3 ... Sample, 4 ... Detector, 5 ... Multiwave height analyzer, 10 ... Target, 11 ... Target material, 12 ... Target support rod, 18 ... Moving means, 22 ... First correcting means, 24 ... storage means, 32 ... second correction means, 34 ... estimation means, 36 ... control means.

Continuation of front page (56) Reference JP-A-11-174007 (JP, A) JP-A-10-185844 (JP, A) JP-A-7-286977 (JP, A) JP-A-8-255695 (JP , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 23/223 H05G 1/02 H05G 1/26

Claims (3)

(57) [Claims] 1. A sample is analyzed by irradiating a sample with primary X-rays generated by applying a high voltage to a target of an X-ray tube and measuring the intensity of fluorescent X-rays generated from the sample with a detector. A fluorescent X-ray analyzer, the target corresponding to the amount of expansion and contraction due to thermal expansion of the target
And the intensity of the fluorescent X-ray changes depending on the change in the distance between the sample and the sample.
It changes with the intensity of fluorescent X-rays in the standard state of expansion
Corresponding to the above, the intensity of the fluorescent X-ray measured at the detector should be matched with the fluorescent X-ray intensity at the reference state.
A first correction means for correcting as described above, a change in the intensity of the fluorescent X-ray measured by the detector with respect to the time from ON of application of the high voltage, and a change with the detector with respect to the time from OFF of application of the high voltage. And a storage unit that stores an X-ray intensity correction curve, wherein the first correction unit stores the time stored in the storage unit.
Based on the X-ray intensity correction curve, measured at the detector
An X-ray fluorescence analyzer that corrects the X-ray fluorescence intensity at the time point . 2. A sample is analyzed by irradiating a sample with primary X-rays generated by applying a high voltage to a target of an X-ray tube and measuring the intensity of fluorescent X-rays generated from the sample with a detector. A fluorescent X-ray analyzer, the target corresponding to the amount of expansion and contraction due to thermal expansion of the target
The X-ray tube to the sample according to the change in the distance between the sample and
Move it to set the distance between the target and sample at the time of measurement .
An X-ray fluorescence analyzer provided with a second correction means for correcting the thermal expansion of the target so as to keep the same as in the standard state . 3. The X-ray fluorescence analyzer according to claim 1 , further comprising an estimation unit that estimates the expansion / contraction amount of the target due to thermal expansion from a parameter related to the thermal expansion of the target.