JPS60181639A - Computer-tomography of industrial sample by radiation - Google Patents

Abstract

PURPOSE:To achieve a clearer image in the computer-tomography of the inside of metal for industrial application eliminating false images by forming a subject sample spherical to detect sections thereof with radiation being radiated from various angles. CONSTITUTION:For example, a sample 1 of a stainless steel formed spherical is irradiated with a radiation beam 5 from a radiation irradiator 3 to be scanned across the section 2. The attenuation of the radiation is detected with a detector 4 and the value obtained is converted 10 into digital from analog to be memorized into a buffer memory 12. Then, computation is performed with a CPU13 to make the section 2 of the sample 1 inversely projected. Subsequently, the sector 2 is turned on the sample 1 and inversely projected image is taken from another angle. Then, pixels taken are superposed with a main memory 14 to produce a tomographic image, which is displayed 19. Thus, the spherical formation of the sample can provide a clearer tomographic picture eliminating false images.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to radiation tomography for industrial applications.

(Prior art) Recently, the cross-sectional imaging method using radiation (for example, X-rays) [usually C, T, (Computerized 'J) o
(abbreviation of mography). ] was popular,
In particular, it has achieved great results in the medical field. This method makes it possible to observe the inside of the human body from the outside, which was previously impossible, and devices for the head and for the whole body are currently on the market.

On the other hand, in the field of general confectionery, transmission tests using radiation such as X-rays and γ-rays are widely used to detect internal defects in materials such as metals and metalized metal products. However, in this method, the radiation source is placed in front of the object to be imaged, as in human chest imaging.
Since the film is placed at the rear, it is not possible to obtain cross-sectional images.

It is also being considered to use the CT method for general industrial purposes, but the targets are metals, metal compounds, and other materials that emit low-energy radiation, such as those used in human body photography. (X
ffM), it is often not transparent, and no practical one has been developed yet. Recently, however, attempts have been made to apply the CT method to the general industrial field, as disclosed in, for example, Japanese Patent Laid-Open No. 57-67846 and Japanese Patent Laid-Open No. 57-76443. These methods are extremely useful because they allow observation and analysis of cross-sections of samples in a non-destructive and non-contact manner; The problem is that arch 7 act (usually called arch 7 act) appears and makes the tomographic image unclear. This false image is caused by the way the image is reconstructed in tomography, which will be described later.It often occurs in samples with many defective areas or in samples with many areas with excessively different radiolucencies, and they appear in CT photographs with a certain shape ( % 1θ, often linear). In addition, in the radiographic no-section imaging method, it is common to measure the degree of radiolucency as a CT value, which is expressed by the following equation.

Here, μS is the X-ray absorption coefficient of the target part of the sample, μW
is the absorption coefficient of water for X-rays, II-j is a constant.

Normally, tJ: 1000, the CT value of water is 0, and the CT value of air is -1O (10). However, the CT value is +1000, and it is rounded, and the protrusion Q is small.

In contrast, in the case of 7 industrial radiation tomography samples &'
, It: c't' value is high, iron) JA-it+ 7
000, and +2500 in the case of aluminum, and since there are many samples with protrusions such as angular shapes, false images are likely to occur.

(Object of the Invention) The object of the present invention is to eliminate false images in tomography of a sample of plum blossoms for use as a distraction.

(Structure and operation of the invention) The present invention is characterized in that a sample to be imaged is formed into a spherical shape, and tomography is performed by irradiating the sample with radiation.

For the purpose of industrial tomography using radiation, it is necessary to view the inside of a sample from all angles and obtain cross-sectional images to clarify the internal state. In that case, if there is an angular part, a false image will occur around the angular part, making the photograph unclear, so it is preferable to eliminate the C1 corner. For example, if the sample is formed into a cylindrical shape, no artifacts will appear when taking a horizontal tomogram, but when taking a longitudinal tomogram, angular parts will appear at the four corners of the screen. This can cause false images to occur.

Therefore, it is optimal to configure the sample in a spherical shape.

The samples used in the present invention can be easily prepared by using a cutting device equipped with a combinator.

In order to take a tomogram according to the present invention, a sample 1 is formed into a spherical shape as shown in FIG. The radiation beam 5 (!-heat irradiation) is performed from the radiation irradiation device 3, and the radiation dose transmitted through the sample 1 is detected by the radiation detector 4.

6 is a scanning plane of the radiation 5, and 7 is a scanning starting point. In addition, the radiation level is 140KV or more xm (by the way, medical use is 13
0 KV or less), rh such as 137 C, or 60 CO, and neutron beams such as CT can be used, and as radiation detectors, general cinnarration A tubes, GM (Geiger), etc. can be used. Millar) In addition to counting tubes, NGO
(A semiconductor detector such as BiGe (Jxide), a multi-scintillation detector, etc. can be used.

To further explain the details of tomography, as shown in FIGS. 1 and 2, radiation is irradiated so that the radiation beam 5 narrowed to a diameter of 0.5, for example, passes through the cross section 2 to be photographed. The apparatus 3 and the radiation detector 4 are moved together along the scanning surface 6, and the radiation dose a that has passed through the sample 1 during this movement is continuously detected. At this time, the radiation dose from the radiation paste irradiation device 3 is directly measured using a separately provided radiation detector 8. Detection value a of radiation detectors 4 and 8.

b is input to the buffer memory IJ l 2 of the arithmetic unit 11 via the amplifier 9 and the analog-to-digital converter lO,
The ratio of detected values a and b is the radiation detector 4 from the scanning starting point 7.
is stored in correspondence with the distance traveled.

That is, this buffer memo IJ 12 stores the intensity distribution of transmitted X-rays along the scanning direction. The signals stored in the buffer memory 12 are processed in the central processing unit 13 so as to be back-projected onto the cross section 2 of the sample 1. For example, as shown in FIG. 3(,), the detected strength is uniformly distributed on the cross section S along the direction perpendicular to the fixed meal direction S in proportion to the strength. The distributed values represent the shading of the image when the image is reconstructed, and are displayed on the display device 19.

When the first scan of the cross section 2 is completed in this way, the pair of radiation irradiation device 3 and radiation detector 4 is disconnected +Mi
2 around the sample 1, and performs the same scan as the first time from a different direction. Repeat this operation by changing the direction.
Figure 3 (a), (b), (e)...
A back projection image 7il- as shown in . . . is obtained. This image is composed of, for example, 512 x 512 pixels, and is displayed in gray scale in proportion to the amount of transmitted radiation. Furthermore, this back-projected image is combined by arithmetic processing in the medium heat processing device 1ia, and pixels corresponding to each strip are stored in the two-dimensionally arranged strips in the back memory 14. Note that one pixel and the sample For example, the correspondence with the cross section of is 0.1 t+I
m X O, 1 m (this superimposed and reconstructed one image is schematically shown in Figure 4). At this time, if a component F having different radiation #, :ll & radiation exists on the scanned surface of the sample 1, another component I#G is generated at that position. It should be noted that the number of times the radiation is applied is at least three times, and preferably 30 times or more in order to obtain a clear image. The image stored in the memo IJ 14 is read out by the reading device 15, converted into a digital analog 1H by the digital-to-analog converter 17, and sent to the display device 19 via the amplifier 18. , a cross-sectional image is displayed. Note that each of the above-mentioned arithmetic processes in the arithmetic unit 11 is executed according to a program read out from the program store 16.

To observe and analyze the tomography of sample 1, the image displayed on the display device 19 is photographed, and the image is put into a known image analysis device to classify the amount of radiation transmitted by each pixel into levels, and to analyze the sample. Ma) This is done by dividing the pixels into pixels with a radiation-transparent lid corresponding to the Rix and pixels with a radiation-transparent lid corresponding to the target component, and counting each pixel.

Incidentally, false images appear to a greater or lesser degree in connection with the pixel reconstruction method shown in FIGS. 3 and 4, and in principle it is extremely difficult to completely eliminate them. FIG. 5 shows an example of a false image when a cross section of cubic pure iron is observed using high-voltage X-rays (420 KV, 3 mA). As is clear from this figure, numerous false formations appear from the four corners, obstructing internal observation. When measuring a sample with an angular shape as in this example, there are areas where the CT value is significantly higher than the surrounding area. If there is, the number of false images will increase. However, in the case of the present invention, since the sample is formed into a spherical shape, the occurrence of false images is generally reduced no matter which direction tomography is performed.

(Example) Next, the implementation of the present invention will be shown.

Three-dimensional observation of porosity in stainless steel samples was conducted. Austenitic stainless steel (SLI830
A spherical sample (diameter: 46) collected from the bloom of 4) was used, and the sample was collected so that the center of the sample was higher than the center of the sphere, tJI11 (as shown in Figure 6). High-pressure X-ray irradiation system [(420KV, 3mA) and detector (f3G
0), rotate the sample in 6° increments to increase the slice width +1.
311 measurements were made at 5 m. Time required: 10 minutes, display device pixel count: 240 x 240, spatial resolution: 0.2
It was my throat. The obtained image is analyzed by an image analysis device, and the amount of transmitted X-ray glands (calculated value) for each tube pixel is calculated as 1, with black being large and white being small.
The display was divided into 6 stages, with the stainless steel matrix being the 8th stage to the 16th stage, and the porosity being the others. Figure 7 ()
(b) Shown in (C). Since the sample was formed into a spherical shape, the shape of the cross section sliced by the radiation was always circular, and a clear cross-sectional photograph could be obtained without the appearance of artifacts as shown in FIG. Note that when the area ratio indicating porosity in the sample is calculated, the results are as shown in Table 1.

Table 1 (Effects of the Invention) As explained above, the present invention makes it possible for the first time to perform three-dimensional observation of porosity in a metal sample, as well as rapid and accurate quantification7 without the influence of artifacts. is extremely large.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the misfire ψJ method, FIG. 2 is an explanatory diagram showing an example of the method of the present invention, FIG. 3 is an explanatory diagram showing an example of the image reconstruction method in the method of the present invention, and FIG. Fig. 3 is an explanatory diagram showing the principle of image construction by the reconstruction method, Fig. 5 is an explanatory diagram schematically showing a false image when tomographically photographing a cubic iron sample, and Fig. 6 is an explanatory diagram showing the method of the present invention. FIG. 7 is a perspective view showing a sample used in the present invention, and FIG. 7 is a diagram showing three-dimensional measurement results of defects in a stainless steel sample obtained by the method of the present invention. 1: Sample, 2: Cross section, 3: Radiation irradiation device, 4: Radiation tester, 5: Radiation beam, 6: Scanning surface, 7:
Scanning start point, 8: Radiation detector, 9 Two amplifiers, 10: Analog-digital conversion all: Arithmetic unit, 12: Buffer memory, 13: Central processing unit, 14: Main memory, 15
: reading device, 16: program store, 17: digital/analog converter, 18: amplifier, 19: display device. Figure 1 Figure 2 Figure 8 Figure 5 Figure 6

Claims (1)

[Claims] A method for tomography of an industrial sample using radiation, which is characterized in that the target sample is configured in a spherical shape and the sample is irradiated with radiation.