JPH01262453A - Method of reading diffracted x-ray intensity of x-ray diffraction device using accumulation type fluorescent plate - Google Patents

Abstract

PURPOSE:To minimize the influence of the fluctuation of a fluorescent reader by determining a calibration curve just prior to reading of an accumulation type fluorescent plate. CONSTITUTION:Several kinds of absorption plates, the transmittances of which to excitation rays to be cast to the accumulation type fluorescent plate are known, are first prepd. and the excitation rays are transmitted to these absorption plates. The intensities of the transmitted light rays thereof are measured by a fluorescent intensity measuring instrument. The calibration curve is then determined by corresponding the measured values of the transmitted light intensities and the transmittances of the absorption plates. On the other hand, the calibration curve of the accumulation type fluorescent plate on which the X-ray diffracted image from a sample to be measured is recorded as a latent image is determined and said plate is projected by the excitation rays right thereafter. The fluorescence generated from the accumulation type fluorescent plate is measured by the fluorescent intensity measuring instrument. The measured value of the fluorescent intensity is taken on the coordinate aces for the measured value of the fluorescent intensity in the calibration curve and the value of the transmittance corresponding there to is determined. This value is determined as the relative value of the diffracted X-ray intensity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for reading the intensity of diffracted X-rays in an X-ray diffraction apparatus using a stimulable fluorescent screen, and is characterized in 1b as a method for calibrating the reading rate. Regarding reading method.

[Prior Art 1] A stimulable phosphor screen has recently been in the spotlight as a two-dimensional X-ray detector that has more advanced characteristics than conventional X-ray films. Its features include sensitivity uniformity and positional resolution that are as good as those of X-ray film;
This is more than 10 times that of line film. therefore,
An X-ray diffraction device using this stimulable fluorescent screen has already been proposed (Japanese Patent Laid-Open No. 59-15843).

The diffraction image recorded on the stimulable fluorescent screen is read out as fluorescence generated by irradiation with laser light, and by measuring the intensity of this fluorescence, the intensity of the diffracted X-rays is determined. That is, the X-ray intensity recorded on the stimulable fluorescent screen can be determined from the ratio of the intensity of the irradiated laser light to the intensity of the generated fluorescence. A photomultiplier tube is usually used to measure fluorescence intensity.

When determining the intensity of diffracted X-rays using such a stimulable fluorescent screen, the relationship between the output of the fluorescence intensity measuring device and the X-ray intensity must be determined in advance as a calibration curve under predetermined conditions. I will keep it.

Using this calibration curve, X-ray intensity is excluded from the output of the fluorescence intensity measuring device.

[Problems to be Solved by the Invention] When determining the X-ray intensity in this way, if the conditions under which the calibration curve was obtained differ from the actual measurement conditions, a measurement error will naturally occur. For example, if the laser light intensity fluctuates, the fluorescence intensity will change even for the same X-ray intensity. Also, if the sensitivity of the photomultiplier tube changes,
Naturally, the output will differ even for the same fluorescence intensity.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for reading diffracted X-ray intensity in which the influence of fluctuations in a fluorescence reading device is minimized.

Means for Solving 1 Problem] In order to achieve the above object, the method for reading diffraction X-ray intensity according to the present invention has the following steps.

(a) Prepare multiple types of absorption plates with known transmittance for the excitation light irradiated onto the stimulable fluorescent screen, let the excitation light pass through these absorption plates, and measure the fluorescence intensity of the transmitted light. The stage of measuring with a device.

(b) determining a calibration curve by associating the measured value of the transmitted light intensity with the transmittance of the absorption plate;

(c) Immediately after determining the calibration curve, irradiating the excitation light beam onto a stimulable fluorescent screen that records the X-ray diffraction image from the sample to be measured as a latent image.

(d) measuring the fluorescence generated from the stimulable fluorescent screen with the fluorescence intensity measuring device;

(e) In the calibration curve, fit the measured fluorescence intensity value onto the coordinate axis of the measured transmitted light intensity value, find the corresponding transmittance value, and calculate this as the relative value of the diffracted X-ray intensity. stage.

When measuring the transmitted light intensity, it is convenient to reflect the excitation light beam with a reflection mirror placed close to the stimulable fluorescent screen. Thereafter, this excitation light beam is passed through the absorption plate and then made to enter the fluorescence intensity measuring device.

[If you want to find the effect calibration curve, pass the excitation light through an absorption plate,
The transmitted light is measured with a fluorescence intensity measuring device. This operation is performed for a plurality of absorption plates having different transmittances, and the relationship between the output of the fluorescence intensity measuring device and the transmittance is determined, and this is used as a calibration curve. Immediately after obtaining this calibration curve, the stimulable fluorescent screen is irradiated with excitation light and the generated fluorescence is measured using a fluorescence intensity measuring device. This output is applied to the coordinate axis of the transmitted light intensity measurement value in the previously determined calibration curve to determine the corresponding transmittance. This axis becomes the relative value of the X-ray intensity to be measured. Then, if the excitation light beam is scanned over the stimulable fluorescent screen, a diffraction pattern will be obtained.

If the above-mentioned calibration curve is obtained immediately before each reading of such a diffraction pattern from a stimulable fluorescent screen, it will be possible to calculate the
Measurement results will no longer be affected.

When measuring the above-mentioned transmitted light intensity, if the excitation light is reflected by a fouling mirror placed close to the stimulable fluorescence,
It's convenient. However, the excitation beam can be brought to this mirror by the excitation beam scanning mechanism.

[Example 1 Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view of a reading device used in an embodiment of the reading method of the present invention. The X stage 10 can move vertically along the stimulable fluorescent screen 13. Y stage 1
2 is on the X stage 10i: on the X stage 1
Can move horizontally relative to 0. The Y stage 12 includes a first reflection mirror 14 (formed by the inner surface of a prism).
The objective lens 16 is fixed. X stage 10
A second reversible mirror 18 is fixed to.

The laser beam generator 22 is arranged under the third reflecting mirror 2Q, and the emitted laser beam can pass through the hole 21 formed in the third reflecting mirror 20. This reading device is equipped with two photomultiplier tubes 24 and 26 as fluorescence intensity detection devices. The first photomultiplier tube 24 is arranged horizontally, and the second photomultiplier tube 26 is arranged vertically. The reason why the two photomultiplier tubes have 92 digits is as follows. The stimulable fluorescent screen has a dynamic range of 106 or more, and in order to make effective use of this dynamic range, this dynamic range is shared between two photomultiplier tubes. A half mirror 27 is connected between these photoelectron multipliers (8 tubes 24, 26 and the third anti-fouling mirror 20).
is located.

Absorption plates 28, 30, and 32 can be inserted between the half mirror 27 and the third reflecting mirror 20.

Although three absorption plates are shown in the drawing, this is the minimum necessary number, and in reality, it is preferable to use 5 to 10 absorption plates. The transmittance of these absorption plates for laser light is determined accurately, and their absorption rates are different from each other. In this embodiment, the three absorption plates 28, 30, and 32 are fixed to a rotating disk and can be used selectively. Moreover, this rotating disk can also be set at a position where no absorbing plate is present.

The absorption plate actually used was a 1 mm thick glass plate on which chromium was vapor-deposited in various thicknesses. To explain an example using five absorption plates, laser light (wavelength 63
The transmittance for 3 nm) is (1,110) to (1/
105) in 5 steps in 10 times increments.

A fourth reflective mirror 34 is arranged below and adjacent to the stimulable fluorescent screen 13. This mirror 34 is used to reflect the laser beam when determining the calibration curve. By placing the fourth reflection mirror 34I2 at this position, the laser beam can be brought to the position of the fourth reflection mirror 34 by using the laser beam scanning mechanism as is.

FIG. 2 is a block circuit diagram of this reading device. The output of the first photomultiplier tube 24 is connected to a computer 40 via an analog-to-digital converter 36; similarly, the output of the second photomultiplier tube 26 is connected to another analog The computer 4 via the digital converter 38
Connected to 0.

In the computer 40, the analog-to-digital converter 3
For the output of No. 6, only values greater than a predetermined digital value (hereinafter referred to as a boundary value) are accepted, and values less than that are cut. On the other hand, for the output of the analog-to-digital converter 38, only values below the above-mentioned boundary value are accepted, and values above this are cut off.

By doing this, inside the computer 40, there is a one-to-one correspondence between digital values and photomultiplier tubes.

This computer 40 is used to obtain a calibration curve, which will be described later, and is also used to calculate X-ray intensity based on this calibration curve. The output of the computer 40 is connected to a display 42, a printer 44, and a magnetic tape 46.

Next, a method of reading a stimulable fluorescent screen using this reading device will be explained. It is assumed that the stimulable fluorescent screen 13 has already stored the diffracted X-rays from the sample to be measured.

Before each reading operation, the reading device is calibrated. That is, a calibration curve representing the correspondence between the output of the reading device and the X-ray intensity is created.

First, move the X stage 10 and Y stage 12,
The objective lens 16 is brought in front of the fourth reflecting mirror 34. Then, the laser beam generator 22 emits a laser beam.
′? Jru. The laser beam 23 is transmitted through the hole 2 of the third reflecting mirror 20.
1, the second reflecting mirror 18 and the first fouling mirror 1
4 and the objective lens 16, it reaches the fourth reflection mirror 34. This fourth reflecting mirror 341 is slightly inclined from perpendicular to the incident laser beam. Therefore, the reflected light travels back along a slightly different optical path than the incident laser light. The reflected laser beam returns to the third deflection mirror 20 via the objective lens 16, the first reflection mirror 14, and the second reflection mirror 18. At this point, the reflected laser beam does not enter the hole 21 and is reflected near the hole 121.
Proceed to absorption plate 2B. A portion of the reflected laser light is absorbed by the absorption plate 28, and the transmitted laser light advances to the half mirror 27. Here, the laser beam is split into two parts and enters the first photomultiplier tube 24 and the second photomultiplier tube 26.

The output of the first photomultiplier tube 24 (which is converted into a digital signal by the analog-to-digital converter 36 and inputted to the computer 40).Similarly, the output of the second photomultiplier tube 24 is also converted into an analog - It is converted into a digital signal by the digital converter 38 and inputted to the computer 40.By the way, since the two photomultiplier tubes have separate roles for the one with higher sensitivity and the one with lower sensitivity, either Therefore, as described above, the computer 40 compares the two digital outputs with a predetermined boundary value and selects the effective photomultiplier tube.

In the computer 40, a calibration curve is created based on the digital 1st shift obtained by q. FIG. 3 shows this calibration curve. First, the transmittance T1 of the absorption plate 28 in FIG. This transmittance T1 is known in advance for the laser beam used.

Here, the transmittance refers to the ratio of the intensity of the laser beam after passing through the absorption plate to the intensity of the laser beam before entering the absorption plate. The digital output when the intensity of the laser beam that has passed through the absorption plate 28 is detected by a photomultiplier tube is Dl.

This is plotted on the vertical axis.

If you do that, you will get 81 points.

Next, the absorption plate 28 is switched to 30: and the laser intensity is measured in the same manner. The transmittance of the absorption plate 30 is tW f'l
ll (taken, and the digital output D2 at that time is plotted on the vertical axis [
Then, P2 can be found. This transmittance Tz is selected so that the digital output D2 is just above the boundary value.

Furthermore, absorption 130 is switched to 32 and the laser intensity is measured in the same manner. If the transmittance T3 of the absorption plate 32 is plotted on the horizontal axis and the digital output D3 at that time is plotted on the vertical axis, then P
3 is found.

In this embodiment, three types of absorption plates are used, so one straight line is found for each of the two photomultiplier tubes. That is, a linear calibration curve 48a is obtained for the photomultiplier tube 24 with high sensitivity, and a linear calibration curve 48b is obtained for the photomultiplier tube 26 with low sensitivity. Of course, increasing the number of absorbing plates increases the number of points to be plotted, increasing the accuracy of the calibration curve, and can also represent deviations of the calibration curve from a straight line.

Incidentally, the procedure for determining the above-mentioned digital output D2 when determining the calibration curve 48 is actually a little more complicated.

This point will be explained using FIG. 4, which is an enlarged view of the central portion of FIG. First, only when measuring transmittance T2,
The operation of the computer 40 is slightly changed to eliminate the selection of photomultiplier tubes based on boundary values. Then, for this transmittance T2, a digital output D21 from the first photomultiplier tube 24 and a digital output D22 from the second photomultiplier tube 26 are determined. This allows P from T2 and D21.
21 points are found, and 222 points are found from T2 and D22.

A calibration curve 48a is obtained by connecting Pl in FIG. 3 and P21 in FIG. 4, and a calibration curve 48b is obtained by connecting P2 in FIG. 3 and P22 in FIG. As a result, correct calibration curves are determined for each of the two photomultiplier tubes.

Thereafter, inside the computer 40, the above-mentioned value of the digital output D21 is set as a new value of the boundary (iffl D z. In other words, below the boundary !11il value, the calibration curve 4
8b is used, and above the boundary value, the calibration curve 48a is used.

Hereinafter, the calibration curve as described is actually determined numerically by a controller (in the computer 40);
The results are stored within computer 40.

Immediately after obtaining the calibration curve in this manner, the reading operation of the stimulable fluorescent screen 13 begins. First, the three types of absorption plates 28, 30, and 32 are evacuated from the optical path and J><. Then, the X stage 10 and the Y stage 12 are moved to scan the laser beam over the entire surface of the stimulable fluorescent screen, and the fluorescence generated at this time is detected by the photomultiplier tubes 24 and 26. This output is converted into a digital value and inputted to the computer 40. If this digital value Da is smaller than the boundary value D2, the transmittance Taff14W is determined by the computer 40 based on the calibration curve 48bl for the photomultiplier tube 24 with low sensitivity. This transmittance D a corresponds to the X-ray intensity recorded on the stimulable fluorescent screen. The relationship between transmittance and X-ray intensity will be explained in detail below.

When the fluorescence intensity incident on the photomultiplier tube is L, and the digital conversion value of the output of the photomultiplier tube is D, the sensitivity S of the photomultiplier tube is expressed as S-D/L (1). be done.

On the other hand, the relative X-ray intensity (2) recorded on the stimulable fluorescent screen is the ratio of the generated fluorescence intensity to the incident laser light intensity R, so that I=L/R (2). Reading a stimulable fluorescent screen means measuring the digital value and knowing the X-ray intensity I, so it is sufficient if the relationship between I and D is clear.

Therefore, from equations (1) and (2), D=(R-3)I...(3) is (q).

On the other hand, since the transmittance T of the absorption plate is the ratio of the intensity Rt of the transmitted laser beam to the intensity R of the incident laser beam, T=Rt/R (4). Comparing equations (2) and (4), the denominator laser light intensity R is the same, and the X-ray intensity I and absorption plate transmission S$1- can be expressed on the same coordinate axis. can. Therefore, in order to create a calibration curve for the X-ray intensity I, an absorption plate with a known transmittance can be used.

By the way, according to the above equation (3), the relationship between the digital value and the X-ray intensity I is J′3 depending on R-3,
This relationship becomes the calibration curve. That is, the calibration curve depends on the laser light intensity R and the sensitivity of the photomultiplier tube, 1 uS. In the present invention, this calibration curve is obtained each time immediately before the reading operation of the stimulable fluorescent screen, so that the fluctuations in the laser light intensity R and the fluctuations in the sensitivity S of the photomultiplier tube are already reflected in the calibration curve. is incorporated within. therefore,
Determination of X-ray intensity is performed with high precision.

To explain the fluctuation in laser light intensity, this example uses a He-Ne laser, and this laser has the following characteristics:
It is known that the intensity fluctuates over a long period of time. for example,
A decrease in strength of about 10% is observed in 24 hours. On the other hand, it is known that the sensitivity of photomultiplier tubes changes depending on the ambient temperature. In any case, in the present invention, even if there is such a variation, the X-ray intensity can be determined with almost no influence thereof.

To explain the time required for reading in this example, the reading time is 200 m.
A stimulable fluorescent screen with dimensions of m x 200 mm and a pixel count of 2000.
It takes about 5 minutes to read with x2000.

And it only takes 1 to 2 minutes to create a calibration curve just before that. In the end, one cycle of reading is completed within 10 minutes.

[Effects of the Invention] As explained above, in the present invention, the calibration curve is obtained immediately before reading the stimulable fluorescent screen, so the effects of fluctuations in the intensity of the excitation light beam and fluctuations in the sensitivity of the fluorescence intensity measuring device can be avoided. X-ray intensity can be determined with almost no radiation.

In addition, when determining the calibration curve, if the excitation beam is reflected by a reflective mirror placed close to the stimulable phosphor screen, a conventional scanning mechanism for the excitation beam can be used to direct the laser beam to the reflective mirror. You can bring it to.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a reading device for carrying out the method of the present invention, FIG. 2 is a block circuit diagram of this reading device, FIG. 3 is a graph showing a calibration curve, and FIG. 4 is a graph showing a calibration curve. This is a partially enlarged graph. 13...Stormative fluorescent plate 23...Laser light as an excitation beam 24.26...Photomultiplier tube 28 as a fluorescence intensity measuring device 30.32...Absorption plate 34...Calibration curve Reflection mirror 48 for finding...
・Calibration curve

Claims (2)

[Claims] (1) In an X-ray diffraction device using a stimulable fluorescent screen,
A method for reading diffraction X-ray intensity, which has the following steps. (a) Prepare multiple types of absorption plates with known transmittance for the excitation light irradiated onto the stimulable fluorescent screen, let the excitation light pass through these absorption plates, and measure the fluorescence intensity of the transmitted light. The stage of measuring with a device. (b) determining a calibration curve by associating the measured value of the transmitted light intensity with the transmittance of the absorption plate; (c) Immediately after determining the calibration curve, irradiating the excitation light beam onto a stimulable fluorescent screen that records the X-ray diffraction image from the sample to be measured as a latent image. (d) measuring the fluorescence generated from the stimulable fluorescent screen with the fluorescence intensity measuring device; (e) In the calibration curve, take the fluorescence intensity measurement value on the coordinate axis of the transmitted light intensity measurement value, find the corresponding transmittance value, and calculate this as the relative value of the diffracted X-ray intensity. stage. (2) When measuring the intensity of the transmitted light, the excitation light beam is reflected by a reflection mirror placed close to the stimulable fluorescent plate, and then the excitation light beam is passed through the absorption plate, and then the fluorescence 2. The reading method according to claim 1, further comprising making the light incident on an intensity measuring device.