JP2011145127A - Radiation measurement apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation measurement apparatus for simultaneously and independently calculating the film thicknesses of a plurality of layers by combining a single radiation source and different scintillators. <P>SOLUTION: In the radiation measurement apparatus for irradiating a measurement target with a radiation emitted from the same radiation source; transmitting it through the measurement target; and measuring the physical quantity of the measurement target from the quantity of the transmitted radiation, the transmitted radiation is detected by different types of detectors whose materials and thicknesses are different. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radiation measurement apparatus using radiation (for example, X-rays, beta rays, gamma rays, etc.), and uses a detector having a plurality of different scintillators for one radiation source, and particularly sufficiently receives high energy. The present invention relates to a radiation measurement apparatus that combines a crystal scintillator and a plastic scintillator that transmits most of the scintillator, and performs thickness measurement including energy discrimination from the ratio of the dose that passes through each scintillator.

  X-ray fluoroscopic analysis and inspection are images of X-ray transmission intensity, and X-ray intensity information is obtained by image processing. However, X-ray intensity information alone is only looking at the shadow of the substance, but there are limits to knowing the material and state in detail even if the shape inside the substance is known. On the other hand, since the human eye can capture not only the light intensity information but also the light wavelength (color) information, the material and state of the substance can be recognized in detail. In addition to capturing X-ray intensity information, if the energy (wavelength) information of X-rays can be captured, the internal material and state can be analyzed.

  FIG. 6 is a main part perspective view and a block configuration diagram showing an example of an apparatus for measuring the thickness (basis weight) of different materials using two types of X-ray and β-ray sources 1a and 1b. The object to be measured flows at a constant speed in the direction of arrow P, and the respective detectors (ionization chambers 2a and 2b) are arranged at the positions facing the radiation sources 1a and 1b. In different frames (11a: x-ray measuring device, 11b: β-ray measuring device) equipped with respective radiation sources 1a, 1b and detectors 2a, 2b, the x-ray source 1a includes a power supply circuit 11c and an x-ray drive circuit 11d. Accordingly, the β-ray source 1b is configured to be able to measure the same portion of the object to be measured (sheet) via the shutter drive circuit 1e. The measurement object 3 is, for example, a composite material in which different substances (magnetic materials) are thinly applied (deposited) on a thin base sheet with a magnetic film, and the amount of application (deposition) and the thickness of the base sheet can be measured respectively. Used for various purposes.

The absorption equation of the transmission measurement method can be expressed as I = I ₀ exp (−μx) where x is the measurement thickness, I ₀ is the detector output before transmission, and I is the detector output after transmission. . In the case of a β-ray source, the absorption coefficient μ is determined to be a constant value depending on its energy and is not affected by the DUT 3. Therefore, the type of the radiation source is selected according to the measurement thickness range.

For measurement of paper, plastic, etc., a weak energy β-ray source such as ⁸⁵ Kr or ¹⁴⁷ Pm is usually used.
In the case of X-rays, since the absorption coefficient varies depending on the object to be measured 3, it is necessary to optimally select the tube voltage in consideration of the measurement range. In the example of paper or sheet material, it varies depending on the type and thickness, and can be expressed as μ = a * x + b (a and b are constants determined by the type). In the example of 4.5 keV X-rays, the magnetic layer has an absorption coefficient about 5 times that of the base sheet of the magnetic film.

  The transmitted radiation with thickness information is detected by ionization chambers 2a and 2b containing a rare gas such as xenon. At this time, the air layer between the radiation sources 1a and 1b and the detectors (ionization chambers 2a and 2b) is also measured at the same time in both cases of X-rays and β-rays. . In order to eliminate this influence, the temperature of the air layer is detected by the temperature detectors 6a and 6b to compensate the temperature, and the minute detection current of the ionization chamber is amplified by the amplifier circuits 4a and 4b (preamplifier).

The output is A / D converted by the A / D converters 5a and 5b, sent to the signal processing units 7a and 7b included in the calculation unit 16 (microcomputer), and used for calculation. In the signal processing units 7a and 7b, by comparing with calibration data 8a and 8b of a calibration curve prepared by measurement of a sample having the same material as the object 3 to be measured and having a different basis weight in advance, The thickness of the desired material can be determined. This is performed for each of the radiation sources 1a and 1b used for measurement and stored in a storage unit (not shown). In particular, when determining the thickness of each of the laminated materials using the composite materials described above, the measured value obtained from each radiation source is the sum of the product of the absorption coefficient and thickness for each material. This can be calculated by solving it as simultaneous calculations in the comparison calculation processing section 9.
The thickness information is sent to the display unit and the production management server 10.

  The sensor units (the radiation sources 1a and 1b and the ionization chambers 2a and 2b) are configured to be mechanically scanned in the width direction of the object to be measured (sheet) and to measure the thickness distribution in the width direction. Both measurement points are synchronized so that the same location can be compared and calculated.

JP 2004-271333 A

By the way, in the conventional radiation measuring apparatus,
1) A system configuration in which two different radiation sources are installed and two measuring devices are arranged, resulting in an expensive system price and a space for two radiation sources and detectors.
2) It is necessary to provide independent control mechanisms for stable control (stable drive) of the two radiation sources. In particular, synchronous control for measuring the same position has become difficult due to the high speed of film formation. Further, when the same position cannot be accurately tracked (scanning positions of the radiation source and detector in the sheet width direction and the sheet flow direction), the measurement error is increased.
3) The measurement accuracy may be deteriorated depending on how the radiation source is corrected over time.
There was a problem.

  Therefore, the present invention can be realized by using an inexpensive and compact apparatus that can perform energy discrimination with high accuracy by combining different scintillators with one radiation source without using two radiation sources to measure the multilayer film thickness. It is intended to enable simultaneous and independent calculation of layer thickness.

In order to achieve such a problem, the invention of the radiation measuring apparatus according to claim 1 of the present invention is:
In a radiation measuring apparatus that measures the physical quantity of an object to be measured from the transmitted dose by irradiating the object to be measured with radiation irradiated from the same radiation source, the transmitted radiation is of different types including material or thickness. Detection is performed by a plurality of detectors.

In Claim 2, in the radiation measuring apparatus of Claim 1,
At least one of the plurality of detectors performs energy discrimination of the radiation.

In Claim 3, In the radiation measuring device of Claim 1 or 2,
At least one of the plurality of detectors uses a direct conversion semiconductor detector having different energy sensitivity to radiation.

In Claim 4, in the radiation measuring apparatus of Claims 1 thru | or 3,
At least one of the plurality of detectors is a detector capable of absorbing from a low energy region of several keV to a high energy region of about several MeV.

In Claim 5, in the radiation measuring apparatus of Claims 1 thru | or 3,
At least one of the plurality of detectors has a sensitivity characteristic from a low energy range of several keV to a high energy range of about several MeV, and in the high energy range, absorption is insufficient and transmission characteristics continuously. Is a scintillator or a direct conversion type semiconductor detector having a low absorptivity, which shows a decrease.

In Claim 6, in the radiation measuring apparatus of Claims 1 thru | or 4,
At least one of the plurality of detectors is a crystalline scintillator containing NaI (TI) (sodium iodide (thallium)) or CsI (Tl) (cesium iodide (thallium)), and has a high energy range. It is a detector having a thickness that sufficiently absorbs water.

In Claim 7, in the radiation measuring apparatus of Claims 1 thru | or 4,
At least one of the plurality of detectors includes at least PVT (polyvinyl toluene), GOS (Ce (Gd ₂ (SiO ₄ ) O: Ce)), and Gd ₂ O ₂ S: Tb (gadolinium oxysulfide). It is a fluorescent paper or plastic scintillator blended with one, and is characterized by insufficient absorption in a high energy range and a controlled thickness of transmission.

The present invention has the following effects.
According to claims 1 to 7,
1. Since only one radiation source is required, the system price is kept low, and the measurement frame for two units is not required, which is advantageous for the footprint and contributes to shortening the installation space of the production line.
2. Since stable control (stable drive) of the radiation source may be performed for one radiation source, only one control mechanism is required.
3. Transmission characteristics can also be calibrated from a single source, making it easy to obtain calibration data in advance.
4). Even if the correction of the aging of the radiation source is not highly accurate, the energy discrimination accuracy does not deteriorate because each detector depends on one radiation source in synchronization.
5. Even if the penetration dose is the same for a thin object to be measured with a large density (with a large atomic number) and a thick object with a small density (with a small atomic number), the material (substance) can be distinguished. .

FIG. 2 is a perspective view of a main part showing an example of an embodiment of the present invention, and a block diagram of a main part (b). It is a figure which shows the absorption characteristic of the scintillator with respect to the energy level of NaI (TI). It is a figure which shows the absorption characteristic of the scintillator with respect to the energy level of PVT. It is explanatory drawing about the process of a calculating part. FIG. 5A is a diagram schematically showing the output level of the detection element with respect to the output of the detector, and FIG. It is a principal part perspective view (a) and a block block diagram (b) which show an example of the conventional radiation measuring device.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 (a, b) shows a configuration diagram of the present invention. FIG. 1A is a perspective view of a main part, and FIG. 1B is a block diagram of the main part. In these figures, the same elements as those in the conventional example shown in FIG.

  A first detector (line sensor... Camera) 22a having a first scintillator and a second detector (line) having a second scintillator at a position facing the radiation source 21 such as X-ray, β-ray or γ-ray. Sensor) 22b is provided close to the sensor and 22b so as to be perpendicular to the conveyance direction P of the measurement object. Further, a collimator 23, an irradiation tube (not shown), and the like are provided so that excess radiation does not leak.

  The first detector 22a and the second detector 22b are aligned so that the upper surfaces thereof are substantially coincident with each other, and the object to be measured (sheet-like sample) 3 passes over the respective sensors, and the detection portions of the respective sensors. The first detector 22a and the second detector 22b are configured so that the same measurement location can be calculated in synchronization with the distance between them and the conveyance speed of the object to be measured.

  In each detector, a minute detection current corresponding to the transmitted dose is converted into a voltage using a high-precision high resistance in the preamplifier units 4a and 4b, and A / D converted by the A / D converters 5a and 5b. It is sent to the arithmetic processing units 7a and 7b. On the other hand, in order to eliminate the influence of the temperature change of the air layer, the temperature of the air layer, the detector temperature, and the source temperature are detected and temperature compensation is performed, and the arithmetic processing units 7a and 7b are used to correct the data Perform calibration and calibration curve calculations.

The first scintillator has an absorption characteristic from a low energy range (several KeV) to a high energy range (several MeV), for example, NaI (TI) (sodium iodide (thallium)) or CsI (Tl) (cesium iodide). Crystalline scintillators such as (thallium)) are used.
FIG. 2 is a diagram showing the absorption characteristics of the scintillator with respect to the energy level of NaI (TI). The horizontal axis represents radiation energy and the vertical axis represents absorption (%).

On the other hand, the second scintillator is a plastic scintillator represented by PVT (polyvinyltoluene), GOS (Ce (Gd ₂ (SiO ₄ ) O: Ce)) and Gd ₂ O ₂ S: Tb (gadolinium oxysulfide). It is an inexpensive and easy-to-use scintillator with a detection energy range of about 10-100 KeV, and in the higher energy range, it is not absorbed by the scintillator and is transmitted and exhibits a characteristic that does not contribute much to phosphorescence.

  FIG. 3 is a graph showing the absorption characteristics of the scintillator with respect to the energy level of PVT. The horizontal axis represents radiation energy and the vertical axis represents absorption (%).

FIG. 4 is an explanatory diagram for the processing of the calculation unit. An example is shown in which a crystal scintillator (first scintillator) and a plastic scintillator (second scintillator) are combined, the basis weight of an object to be measured is calculated by the first scintillator, and energy discrimination is performed by the second scintillator.
In the process 1 shown in FIG. 4, the A / D converted voltage output from the first detector 22a is taken into the computing unit 6, and the output from the first detection is normalized in step S1. Almost simultaneously, in step S2, the temperature of the first detector 22a and the ambient temperature of the first detector 22a are also taken into the computing unit 6 as necessary. The calculation unit 6 normalizes the voltage value according to the dose, the sensitivity of the detector, and the like. Further, the temperature characteristic is corrected to obtain the output of the first detector 22a.

  In step S3, the calibration curve stored in the storage device of the calculation unit 6 is read and compared with the output value. The calibration curve is prepared in advance by measuring a plurality of calibration reference plates having different plate thicknesses using the first detector 22a in advance. FIG. 4a ′ is a diagram schematically showing a state in which the basis weight (b) is obtained by tracing the calibration curve from the output value (A) using the calibration curve.

  Next, the A / D converted voltage output from the second detector 22b is taken into the calculation unit 6, and the output from the second detection is normalized in step S1 '. Almost at the same time, in step S2 ', the temperature of the second detector 22b and the ambient temperature of the second detector 22b are taken into the calculation unit 6 as required. The calculation unit normalizes the voltage value according to the dose and the sensitivity of the detector. Further, the temperature characteristic is corrected to obtain the output of the second detector 22b.

In step S3 ′, the output characteristics after transmission with respect to the energy stored in the storage device of the calculation unit are read into the calculation unit and compared with the output value. It is assumed that the characteristic diagram is calculated in advance by using a second detector 22b to measure the output of the radiation source from a low frequency to a wide frequency.
FIG. 4a '' is a diagram schematically showing a state in which the energy value (d) is obtained by tracing the characteristic diagram from the output value (c) using the characteristic diagram.
If the processing to find the basis weight is processing 1, and the processing to discriminate energy is processing 2, in the explanation of the calculation unit in FIG. 4, it has been described as processing 1 → processing 2, but the order is also changed to processing 2 → processing 1. good. Further, parallel processing may be performed depending on the configuration of the calculation unit.

  Here, it is assumed that the penetrating dose of the object to be measured (sample) 2 coated with two different substances is obtained. Assume that the transmitted dose of the two objects to be measured is the same value. In that case, the two substances cannot be distinguished from each other even if the imaging is based on only the transmitted dose as in the past. Furthermore, when energy discrimination was obtained, different results were obtained for the two measured objects.

  FIG. 4 b is a graph showing the relationship between the intensity (kev) of radiation energy and the output of the second detector after passing through the sample 2. As shown in FIG. 4b, it is assumed that one substance 1 has an output A after transmission. In this case, the energy is B as shown in FIG. The other substance 2 has the output C of the detector after transmission and the energy D. From the above results, it can be seen that the substance 1 is a thick substance having a small density (small atomic number). On the other hand, substance 2 can be identified as a thin substance having a large density (a large atomic number).

Actually, detection is performed by a one-dimensional detection element of several hundred to several thousand pixels, and is calculated in a time series to form a two-dimensional image, and the thickness and the composition ratio of the substance are grasped.
FIG. 5a schematically shows the output level of the detection element with respect to the output of the first detector 22a. This is a case where the detection element mounted on the scintillator is a 16-dimensional one-dimensional sensor.
According to the output, level 1, level 2, and level 3 are categorized from the highest level.

  FIG. 5b shows the image divided for each layered pixel. If each classified image is displayed with a contrast that matches the transmitted dose output of the first detector 22a, the thickness (basis weight) of the same substance can be compared. If the images are displayed with different monochromatic light for each layered image, the image can be distinguished even if the images are superimposed.

  The above description merely shows a specific preferred embodiment for the purpose of explanation and illustration of the present invention. In the embodiment, two detectors such as line sensors having different scintillators are arranged side by side. However, a TDI (Time Delay Integration) line sensor may be used.

  Some TDI line sensors are arranged in multiple rows (for example, 4 rows, 8 rows,..., 128 rows) instead of one row. When reading the CCD charge, it is incident on the CCD surface and the transfer timing. By matching the timing of moving the target image, the exposure is performed for the number of vertical stages of the CCD. Different scintillators are installed in such a plurality of rows of detection units, and the integration range is limited for each type of scintillator, or two detection results are obtained from one sensor by taking out each independently without integration. You may do it.

  Further, although the one-dimensional line sensor is used in the embodiment, it may be a two-dimensional area sensor or a combination of two or more single sensors. Further, the radiation source is not necessarily one radiation source but may be plural.

Further, in the case where any one of the film thickness variations is small with respect to the multi-layer sample, the cost may be reduced by appropriately reducing the number of elements of one scintillator detector and obtaining a representative value. Furthermore, when the film thickness variation is extremely small or when there is a strong demand for cost reduction, one detection element may be used, or an ionization chamber may be used instead of the scintillator.
Therefore, the present invention is not limited to the above-described embodiments, and includes many changes and modifications without departing from the essence thereof.

1,21 Radiation source 2 Ionization chamber 3 Object to be measured (sample)
4 Preamplifier 5 A / D Converter 6 Temperature Detector 7 Signal Processing Unit 8 Calibration Data 9 Comparison Operation Processing Unit 10 Display Unit, Production Management Server 11a X-ray Measurement Device 11b β-ray Measurement Device 11c Power Supply Circuit 11d X-ray Drive Circuit 16 Calculation unit (microcomputer)
22a first detector 22b second detector

Claims (7)

  In a radiation measuring apparatus that measures the physical quantity of an object to be measured from the transmitted dose by irradiating the object to be measured with radiation irradiated from the same radiation source, the transmitted radiation is of different types including material or thickness. A radiation measurement apparatus, wherein detection is performed by a plurality of detectors.   The radiation measuring apparatus according to claim 1, wherein at least one of the plurality of detectors performs energy discrimination of the radiation.   The radiation measurement apparatus according to claim 1, wherein at least one of the plurality of detectors uses a direct conversion semiconductor detector having energy sensitivity different from that of radiation.   4. The radiation according to claim 1, wherein at least one of the plurality of detectors is a detector capable of absorbing from a low energy region of several keV to a high energy region of about several MeV. 5. measuring device.   At least one of the plurality of detectors has a sensitivity characteristic from a low energy region of several keV to a high energy region of about several MeV, and the absorption is insufficient in the high energy region and continuously. 4. The radiation measuring apparatus according to claim 1, wherein the radiation measuring apparatus is a scintillator or a direct conversion type semiconductor detector having a low absorption characteristic and showing a decrease in transmission characteristics.   At least one of the plurality of detectors is a crystalline scintillator containing NaI (TI) (sodium iodide (thallium)) or CsI (Tl) (cesium iodide (thallium)), and has a high energy range. The radiation measuring apparatus according to claim 1, wherein the radiation measuring apparatus is a detector having a thickness that sufficiently absorbs water. At least one of the plurality of detectors includes at least PVT (polyvinyl toluene), GOS (Ce (Gd ₂ (SiO ₄ ) O: Ce)), and Gd ₂ O ₂ S: Tb (gadolinium oxysulfide). The radiation measurement according to any one of claims 1 to 5, wherein the thickness is a fluorescent paper or plastic scintillator blended with one, and has a thickness with insufficient absorption in a high energy range and a controlled transmission rate. apparatus.