JP3059185B2 - X-ray detection method and apparatus therefor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting X-rays for measuring X-ray characteristics and the like.

[Related Art] Conventionally, an X-ray detector has been used to measure X-ray characteristics such as a tube voltage of an X-ray tube and an X-ray spectrum. As an example of the X-ray detecting device, an X-ray detecting unit composed of a combination of an X-ray absorbing plate (X-ray filter) and an X-ray detecting element is irradiated with X-rays, and the X-ray irradiation is performed based on the transmittance of the X-ray filter. An X-ray detection device (X-ray analyzer) for measuring an X-ray tube voltage, a spectrum, and the like of an X-ray is known. The X-ray detector of the X-ray analyzer includes a set of a scintillator that converts incident X-rays into fluorescence, an X-ray filter having a different thickness disposed on the front surface of the scintillator, and a photodetector disposed on the rear surface. It is configured to include a plurality of X-ray detectors that are combined. The X-rays radiated to the X-ray detector are detected independently for each X-ray detector, and the output signals of the respective photodetectors are subjected to a predetermined arithmetic processing so that a tube voltage of the irradiated X-rays is obtained. Information on desired X-rays such as spectrum and spectrum can be obtained (see JP-A-63-98583 and JP-A-63-135885).

[Problems to be Solved by the Invention] In the conventional X-ray analyzer as described above, although there is no problem in measuring the irradiation dose and irradiation time of the incident X-ray, the tube voltage and spectrum of the incident X-ray are not affected. For example, when measuring the distance between the X-ray detecting unit and the X-ray source, there is a problem that the measurement result may be different, and there is a problem that the accuracy is unstable in terms of accuracy, and improvement is desired. Was.

Therefore, the present invention has been made in view of the above-mentioned problems of the prior art, and
When measuring X-ray characteristics using a X-ray analyzer,
An object of the present invention is to provide a method and an apparatus for accurately measuring X-ray characteristics without depending on the distance between the X-ray detection unit and the X-ray source.

[Means for Solving the Problems] According to the present invention, a scintillator for converting incident X-rays into fluorescence and a photodetector arranged behind the scintillator for detecting the fluorescence are provided as objects for achieving the above object. And a plurality of X-ray detectors each having an X-ray filter having a different thickness disposed in front of the scintillator so that the X-ray incidence planes of the respective X-ray detectors are located substantially on the same plane. An X-ray detection unit arranged and
When detecting an X-ray using an X-ray detection device having an arithmetic processing unit for calculating the output of the X-ray detector to obtain the characteristic of the incident X-ray, the plurality of X-rays are detected by detecting the beam of the incident X-ray. X having the thickest X-ray filter in the vessel
An X-ray detection method, wherein the X-ray is incident so as to be perpendicular to the X-ray incidence surface of the X-ray detector.

According to the present invention, there is provided an X-ray detection apparatus used in the above-described X-ray detection method, which achieves the above object, and has the largest thickness among the plurality of X-ray detectors. An X-ray detector having an X-ray filter having the X-ray filter disposed at the most central position, further comprising: an X-ray detector used in the above-described X-ray detection method. An X-ray detection device, wherein a mark indicating the position of the X-ray detector having the thickest X-ray filter among the plurality of X-ray detectors is attached. , Are provided.

EXAMPLES Hereinafter, specific examples of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an X-ray analyzer used in the method of the present invention, and FIG.
It is a schematic diagram for explaining a line detection part.

As shown in FIG. 1, the X-ray analyzer includes an X-ray detector 1 for detecting incident X-rays, and an arithmetic processor 2 for converting an output signal from the X-ray detector into a desired X-ray characteristic value. And a display unit 6 for displaying the X-ray characteristic value. The arithmetic processing unit 2 further includes an amplification unit 3 that amplifies a signal from the X-ray detection unit 1;
Digitizing the analog information signal obtained by the amplifying unit
It comprises an AD conversion unit 4 and a calculation / storage unit 5 for calculating and storing the information signal digitized here.

As shown in FIG. 2, the X-ray detector 1 includes a reference X-ray detector 1s and a plurality of X-ray detectors 1a, 2a in a small chamber of an envelope 7 having a plurality of small chambers partitioned by partition walls. 1b is accommodated and configured. As shown, the X-ray detectors 1s, 1a, 1b are arranged in parallel. Reference X-ray detector 1s
Is a fluorescent plate 8s as a scintillator for converting incident X-rays L into an amount of fluorescent light proportional to the amount of incident light, and a photodetector provided on the surface opposite to the X-ray incident surface in close contact with the fluorescent plate and detecting the fluorescent light. 10s. The X-ray detectors 1a and 1b are respectively provided with fluorescent plates 8a and 8b serving as scintillators for converting incident X-rays L into fluorescent light in an amount proportional to the amount of incident light, and thicknesses provided in front of the X-ray incident surfaces of these fluorescent plates. X-ray filters 9a and 9b having different thicknesses (where t _a and t _b are respectively assumed to be t _a and t _b in this embodiment, t _a <t _b ) and the surface opposite to the X-ray incidence surface of the fluorescent plate. And photodetectors 10a and 10b for detecting the fluorescence.

In the present embodiment, three X-ray detectors including the reference X-ray detector 1s are provided. However, in order to improve the function and accuracy of the X-ray analyzer, they are provided in the X-ray detector 1. The greater the number of X-ray detectors, the better. In the present invention, it is necessary to provide at least two X-ray detectors, and in practice, it is preferable to provide three or more X-ray detectors. When measuring the tube voltage of an X-ray tube,
The reference X-ray detector 1s is not always necessary. Also,
The amplifying unit 3 and the AD converting unit 4 constituting the arithmetic processing unit 2 are independently provided for each of the X-ray detectors 1s, 1a, 1b arranged in the X-ray detecting unit 1.

The envelope 7 is for protecting each of the X-ray detectors 1s, 1a, 1b and for preventing invasion of external light and leakage of fluorescent light from other fluorescent screens. A material that does not transmit external light and fluorescence is selected, and for example, plastics such as a colored acrylic plate and a bakelite plate are used.

As the X-ray filters 9a and 9b, a material having a large X-ray absorption capacity and a large change in X-ray transmittance with respect to a change in thickness even if the thickness is several mm or less is preferable. For example, Cu, Al,
A metal plate such as Sn or Pb is preferably used.

As the fluorescent plates 8s, 8a, 8b, CaWO ₄ , Bi ₄ Ge ₃ O ₁₂ , ZnS: Ag, B
aFCl: Eu, LaOBr: Tm, (Zn, Cd) S: Ag, Y ₂ O ₂ S: Tb, Gd ₂ O ₂ S: Tb,
Gd ₂ O ₂ S: A phosphor coating solution made by dispersing an X-ray phosphor, such as Pr, which emits light with high efficiency by X-ray irradiation in a binder resin, is coated on a support such as paper or plastics. A phosphor layer obtained by forming a phosphor layer on a support by drying and drying, or a phosphor coating solution is applied to a substrate such as glass and dried, and the resulting phosphor layer is peeled off from the substrate. The obtained self-supporting fluorescent plate is used.

As the photodetectors 10s, 10a, and 10b, photoelectric conversion elements such as photodiodes and photomultiplier tubes that convert fluorescent light emitted from the fluorescent plates 8s, 8a, and 8b into electric signals are used. It is preferable to use a photodiode from the viewpoint that the capacity of the X-ray detection unit 1 can be reduced and the manufacturing cost can be reduced.

To detect X-rays for characteristic measurement using the above-described X-ray analyzer, the X-rays to be measured are irradiated on the X-ray detector 1 of the X-ray analyzer, and the X-rays are radially emitted from the X-ray tube. Therefore, depending on the distance between the X-ray tube and the X-ray detection unit 1 and the position of the X-ray detector in the X-ray irradiation field, the X-ray beam of the measured X-ray and the X-ray detection unit 1 are arranged. The angle between each of the X-ray detectors 1s, 1a, and 1b changes.

Therefore, an X-ray detector having a thickest X-ray filter among a plurality of X-ray detectors disposed inside the X-ray irradiated surface of the X-ray detector 1 of the X-ray analyzer (hereinafter referred to as “X-ray detector”). This is called a "main X-ray detector": in the example of FIG. 2, the position where the X-ray detector 1b) is arranged is marked, and the X-ray detector 1 The X-ray detector 1 is set such that the surface of the portion marked with the mark (main X-ray detector position) is substantially perpendicular to the incident direction of the measured X-ray beam.

Instead of or in addition to the marking as described above, the main X-ray detector is arranged at the most central position, and the surface of the X-ray detector 1 is irradiated when the measured X-ray is irradiated. The X-ray detector 1 can be set so that the center of the X-ray is substantially orthogonal to the incident direction of the measured X-ray beam.

In this case, generally, X radiated from the X-ray source
Straight beam of X-ray (X-ray beam passing through the center of irradiation field)
Is set so as to be substantially perpendicularly incident on the main X-ray detector in the X-ray detection unit 1. However, even if the X-ray beam is other than the straight beam, it is detected by the main X-ray detection unit in the X-ray detection unit 1. What is necessary is just to set so that it may be made to enter a vessel almost perpendicularly.

The information signal of the measured X-ray detected by the X-ray detection unit 1 is amplified by the amplification unit 3 after light source conversion, digitized by the AD conversion unit 4, and temporarily stored in the calculation / storage unit 5. In addition, predetermined arithmetic processing is performed according to a procedure programmed in advance, and thus the X-ray to be measured, such as the tube voltage of the X-ray generator, the energy distribution of the X-ray to be measured, and the half-value layer, etc. Desired information regarding the information is obtained and displayed on the display unit 6.

There are many types of X-ray generators, such as a single-phase rectification system, a three-phase six-pulse rectification system, a smoothing system, and an inverter system, depending on the high-voltage generation system. The output waveforms (relationship between X-ray intensity and time) of X-rays generated from each device are different from each other. In the above-described measurement, for example, the tube voltage measurement in the X-ray generators having different high voltage generation methods, even if the same tube voltage is applied to the X-ray tube, the detected tube voltage measurement values of the X-ray tube are different. There is.

Therefore, in order to eliminate such adverse effects, when the light is detected by the photodetector of each X-ray detector, and this is photoelectrically converted and amplified by the amplifier 3, the light detection corresponding to the output waveform of the measured X-ray is performed. A process for removing a specific frequency component from the output waveform of the detector (the relationship between the photocurrent output from the photodetector and time) can be performed.

For this purpose, for example, as shown in FIG.
A low-pass filter circuit that cuts a specific high-frequency component is incorporated in the amplifier circuits 3a and 3b that amplify the respective output signals of 10a and 10b, and the capacitances Ca and Cb in the respective amplifier circuits 3a and 3b are included. By changing the ratio (Ca / Cb), regardless of the output waveform of the X-ray to be measured, by setting a specific Ca / Cb value such that the measured value of the tube voltage becomes constant, What is necessary is just to adjust the output frequency characteristic of each X-ray detector corresponding to the output waveform of the measured X-ray. At the time of this adjustment, an X-ray generator of a heterogeneous high voltage generation type whose tube voltage is known in advance is used.

FIG. 4 shows an X-ray filter made of a copper plate, a first X-ray detector (main X-ray detector) using a phosphor plate made of ZnS: Ag phosphor as a constituent member, and a phosphor plate made of ZnS: Ag phosphor. Using a X-ray analyzer having a second X-ray detector (without using an X-ray filter) using as a constituent member, the distance between the X-ray tube and the X-ray detector of the X-ray analyzer over a range of 40 cm to 150 cm 9 is a graph showing the results of measuring the tube voltage of an X-ray generator operating under the same conditions while changing the tube voltage. In FIG. 4, the curve of the group A and the curve of the group B are obtained when the setting of the tube voltage of the X-ray tube generating the measured X-ray is changed. The solid and dashed curves represent the case where the beam of the X-ray to be measured is vertically incident on the main X-ray detector of the X-ray detector and the case where the beam is incident at an angle of about 3 degrees.

As can be seen from FIG. 4, regardless of the tube voltage applied to the X-ray tube, if the beam of the measured X-ray is obliquely incident on the main X-ray detector of the X-ray detection unit (indicated by a broken line). Curve shown) When the distance between the X-ray tube and the X-ray detector of the X-ray analyzer changes, the measured value of the tube voltage changes, whereas the beam of the X-ray to be measured is changed to the main X-ray of the X-ray detector. When the light is perpendicularly incident on the X-ray detector (the curve shown by the solid line), the measured value of the tube voltage does not change even if the distance between the X-ray tube and the X-ray detector of the X-ray analyzer changes.

Although not shown, the same tendency was observed when the tube voltage was further varied.

In addition to measuring the X-ray tube voltage using an X-ray analyzer, in addition to measuring the spectral distribution of the X-ray to be measured and the half-value layer, the X-ray beam to be measured is also used as the main X-ray detector of the X-ray detector. When the measurement was carried out so as to be perpendicular to the X-ray, it was recognized that the change in the measured value was small even if the distance between the X-ray tube and the X-ray detector of the X-ray analyzer was changed.

The present invention also includes a case where one of the plurality of X-ray detectors has a thickness of the X-ray filter of 0, that is, no X-ray filter.

[Effects of the Invention] As described above, according to the present invention, an X-ray having an X-ray detection unit having a plurality of combinations of an X-ray filter and an X-ray detection element is provided.
When measuring X-ray characteristics using a X-ray analyzer,
The X-ray characteristics can be measured with good accuracy without depending on the distance between the X-ray detection unit and the X-ray source.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an X-ray analyzer used in the method of the present invention, and FIG. 2 is a schematic diagram for explaining an X-ray detecting section of the apparatus. FIG. 3 is a diagram showing an example of a circuit configuration of the X-ray detection device of the present invention. FIG. 4 is a graph showing a change in the tube voltage of the X-ray generator with respect to a change in the distance between the X-ray tube and the X-ray detector of the X-ray analyzer. 1s, 1a, 1b: X-ray detection unit, 2: Operation processing unit, 3s, 3a, 3b: amplification circuit, 8s, 8a, 8b: fluorescent plate, 9a, 9b: X-ray filter, 10s, 10a, 10b: light detection vessel.

Claims (3)

(57) [Claims] 1. A scintillator for converting incident X-rays into fluorescence, a photodetector disposed behind the scintillator for detecting the fluorescence, and an X-ray filter having a different thickness disposed in front of the scintillator. Xs with
X-ray detectors in which the X-ray detectors are arranged in parallel so that the X-ray incidence surfaces of the X-ray detectors are located on substantially the same plane, and the outputs from the X-ray detectors are calculated. When detecting X-rays using an X-ray detection device having an arithmetic processing unit for calculating characteristics of incident X-rays, the beam of the incident X-rays is converted into an X-ray having the largest thickness among the plurality of X-ray detectors. An X-ray detection method, wherein the X-ray is incident so as to be perpendicular to the X-ray incidence surface of an X-ray detector having a line filter. 2. An X-ray detection device used in the X-ray detection method according to claim 1, wherein the X-ray detection device has an X-ray filter having the largest thickness among the plurality of X-ray detectors. X is characterized in that the vessel is arranged most centrally,
Line detector. 3. An X-ray detection device used in the X-ray detection method according to claim 1, wherein the X-ray detection device has an X-ray filter having the largest thickness among the plurality of X-ray detectors. Characterized by a mark indicating the position of the container,
X-ray detector.