JPH0726919B2 - Element concentration distribution measuring method and apparatus - Google Patents

Description

The present invention relates to an element concentration distribution measuring method and apparatus capable of obtaining the concentration distribution of a specific element contained in a substance.

"Prior Art" Conventionally, in order to examine the homogeneity of a solidified body of a mixture, a method of cutting the solidified body itself and analyzing the concentration distribution of elements in the cross section has been adopted. However,
If the solidified body itself is cut, the product value may be impaired in some cases, and the cutting itself may be impossible. Therefore, it has been conventionally desired to realize nondestructive measurement of a solidified body. For example, regarding the measurement of concentration distribution of Pu (plutonium) and U (uranium) in mixed oxide fuel, non-destructive measurement of concentration distribution of elements such as measurement of concentration distribution of substances adhering to pipes of nuclear power plants There are many areas that need it.

“Problems to be Solved by the Invention” In the conventional measurement of such element concentration distribution, the substance cannot be inspected in a non-destructive state, and the measurement target is limited. There is also a problem that the measurement takes time.

On the other hand, as a device for measuring the concentration distribution of a substance, an emission CT or a transmission CT has been generally used. Among them, the former device measures the γ-rays emitted by the radioisotope present in the measurement sample and measures the two-dimensional distribution of the concentration of the radioisotope. Therefore, the element for which the concentration distribution is to be obtained needs to be (i) a radioisotope, and (ii) an element that emits a radiation having an intensity that can be sufficiently counted in measurement. is there.

FIG. 4 shows a device previously proposed as a device using a transmission CT. A gamma ray source 2 is housed in an external radiation source storage container 1 of this apparatus. The periphery of this γ-ray source 2 is covered with a γ-ray shield. A shutter 3 is arranged in a part of the γ-ray shield, and can be arbitrarily opened and closed by a shutter drive mechanism 4.

A radioactive solidified body 5 as a measurement sample is disposed in front of the shutter 3 of the external radiation source storage container 1. The radioactive solidified body 5 can be rotationally moved or linearly moved by the radioactive solidified body driving mechanism 6 in an arbitrary slice plane.

A collimator 7 is arranged on an extension line connecting the external radiation source storage container 1 and the radioactive solidified body 5. In front of the collimator window 7a of the collimator 7, a gamma ray detector 8 capable of discriminating energy, such as a Ge detector, is arranged. Collimator window
A γ-ray absorber 10 which can be inserted into the rear surface of the collimator window 7a by a γ-ray absorber driving mechanism 9 is arranged behind the 7a. The γ-ray absorber 10 shields the γ-rays emitted from the radioactive solidified body 5, while absorbing the γ-rays emitted from the γ-ray source 2 to the extent of being attenuated and transmitted.

A multiple wave height analyzer 12 is connected to the output terminal of the γ-ray detector 8 via an amplifier 11. Therefore, the detection signal of the γ-ray detected by the γ-ray detector 8 is amplified by the amplifier 11, and then the wave height analysis is performed by the multiple wave height analyzer 12. The electronic computer 13 reconstructs an image based on the data obtained as the analysis result.

With the device using this transmission CT, it is possible to obtain the two-dimensional distribution of the γ-ray absorption rate or the photon absorption rate at each position on the fault plane of the radioactive solidified body. It does not directly correspond to concentration.

Therefore, a device for nondestructively measuring the element concentration has been proposed.

FIG. 5 shows the proposed solution concentration measuring device.

In this device, the X-ray detector 21 is the irradiation X from the X-ray generator 22.
The transmission path of the line is arranged in the traveling direction of the line. With such an arrangement structure, the irradiation X-rays emitted from the X-ray generator 22 are transmitted through the sample container 23 and enter the X-ray detector 21. The detection data obtained by the X-ray detector 21 is
It is input to the processing computer 24 in which the measuring circuit is incorporated, and the concentration of the solute is obtained here. That is, this processing computer
24 is the X of two types of energy sandwiching the absorption edge energy of the element
The line intensity is analyzed to obtain the concentrations of several elements contained in the sample in the sample container 23.

In this solution concentration measuring device, the transmitted photon intensities on the low energy side and the high energy side of the absorption edge energy of the element to be obtained are measured, and the element concentration is calculated by this. Therefore, even with this apparatus, only the average element concentration in the measurement sample was measured, and the concentration distribution of the element could not be measured.

Then, the objective of this invention is providing the element concentration distribution measuring method which can measure the element concentration distribution, and the element concentration distribution measuring device to which this is applied.

"Means for Solving Problems" In the element concentration distribution measuring method of the present invention, a measurement sample is irradiated with a photon source that generates photons of at least two types of energy sandwiching the absorption edge energy of the element to be obtained. Then, the operation for obtaining the intensity ratio between the photon having the energy lower than the absorption edge and the photon having the higher energy after passing through the measurement sample is performed from at least two directions on the surface to be measured of the measurement sample, and the photons collected by this are collected. The two-dimensional distribution of elements on the surface is obtained by processing the data on the intensity ratio. If a two-dimensional distribution is obtained for each of a number of surfaces, a three-dimensional distribution can be obtained using this result.

The element concentration distribution measuring apparatus of the present invention, which is an example of this measuring method, includes (i) a photon source that generates photons in an energy range from energy lower than the absorption edge energy of the element to be obtained to high energy; (Ii) a photon source collimator that limits the traveling range of photons generated from this photon source, and (iii) a sample mounting table on which a measurement sample irradiated with photons passing through this photon source collimator is placed. ,
(Iv) sample mounting table driving means for rotating or moving the sample mounting table in a predetermined direction so that photons are irradiated from at least two directions in an arbitrary cross section of the measurement sample; and (v) sandwiching the sample mounting table. The collimator for the detector, which is arranged so as to face the collimator for the photon source, (v
i) A photon detector that detects photons that have passed through this detector collimator; Concentration data calculating means for obtaining concentration data of the element based on the photon intensity data of the side, (vii
i) An element concentration distribution calculation means for calculating the concentration distribution of the element to be obtained in the above-mentioned cross section of the measurement sample by using the concentration data of the measurement sample for each displacement by the sample mounting table driving means.

Here, the sample mounting table driving means moves the sample mounting table so that photons are irradiated from at least two directions in an arbitrary cross section of the measurement sample, and the element concentration distribution calculating means calculates the concentration of the element to be obtained in the cross section. The distribution may be calculated. There may be a plurality of sets of detector collimators and photon detectors for detecting photons passing therethrough. In this case, these may be arranged centripetally with respect to one photon source. It is valid.

As described above, according to the present invention, a photon source is prepared, a photon is irradiated on a measurement sample, and concentration data of the element is obtained based on photon intensity data of the low energy side and high energy side of the absorption edge energy of the element. . Furthermore, since the sample mounting table on which the measurement sample is mounted can be rotated or moved in a predetermined direction by the sample mounting table driving means, the concentration data for each displacement of the measurement sample is supplied to the element concentration distribution calculating means for calculation. Thus, the element concentration distribution can be measured.

[Examples] The present invention will be described in detail below with reference to Examples.

FIG. 1 shows an outline of an element concentration distribution measuring apparatus according to an embodiment of the present invention. This element concentration distribution measuring device is equipped with an X-ray generating tube 31 as a photon generating means. The X-ray generation tube 31 has its control system 32 controlled to generate X-rays. The X-rays of the continuous energy spectrum generated from the X-ray generation tube 31 pass through the window of the photon source collimator 33. Then, the measurement sample 35 placed on the turntable 34 is irradiated. Turntable here
34 is set on the sample rotation / horizontal traveling mechanism 36,
The measurement sample 35 can be rotated and horizontally moved in the direction of arrow 38.

The X-rays that have passed through the measurement sample 35 pass through the window of the detector collimator 39 and enter the X-ray detector 41. As the X-ray detector 41, for example, a semiconductor detector is used. X-ray detector 41
The detection signal 42 obtained by the above is input to the measurement circuit system 43 having a multiple wave height analysis function. The measurement circuit system 43 performs the wave height analysis. The processing computer 44 sends and receives the data 45 to and from the measurement circuit system 43, and performs the arithmetic processing of projection data. At this time, the sample rotation / horizontal traveling mechanism 36 is driven to collect projection data of the measurement sample 35 from each direction. A drive control system 47 for driving the sample rotation / horizontal traveling mechanism 36 is also connected to the processing computer 44, and the measurement circuit system 43
Corresponding to the data obtained from.

Now, in this element concentration distribution measuring apparatus, the measurement sample 35 is irradiated with X-rays having a continuous energy spectrum as described above. Therefore, considering the vicinity of the absorption edge of the element of interest in the measurement sample 35, the energy spectrum before passing through the measurement sample 35 is smooth, but after passing through, a step is generated at this portion.

FIG. 2 shows the change in principle before and after permeation of the measurement sample, focusing on an element. Here, the curve shown by the broken line represents a part of the energy spectrum before the measurement sample is transmitted, and the curve shown by the solid line is an example of the energy spectrum of the same part after the measurement sample is transmitted. The curve indicated by the alternate long and short dash line represents an example of the energy spectrum when the concentration of the element in the measurement sample containing the same element is higher than that shown by the solid line. It can be seen that the absorption edge energy E is unique to each element, and the degree of the step in the absorption edge energy E depends on the element concentration.

Now, it is assumed that the energy spectrum represented by the solid line in FIG. 2 is obtained in the state where the measurement sample 35 is arranged at a certain position. Here, the X-ray intensity T _L on the side of energy lower than the absorption edge energy and the X-ray intensity T _U on the side of high energy are respectively obtained from the X-ray spectra, and the following equation is calculated. Become.

Also, when a plurality of elements are mixed in the measurement sample, the concentration of each element can be obtained. Here, the case where two kinds of elements are present will be specifically described.

Now, it is assumed that uranium (U) and plutonium (Pu) are present in the measurement sample as two kinds of elements. If the energies (E (U) and E (Pu)) of the absorption edges of U and Pu are, for example, the outermost electron orbits of atoms, that is, the K-edge energy of the so-called K shell, E (U) = 115.6 KeV E (Pu) = 121.8 KeV.

At this time, similarly to FIG. 2, if these two elements are focused and the change before and after permeation of the measurement sample is expressed in principle,
It looks like Figure 6. In this figure, T _{L (U)} , T _{U (U)} ,
T _{L (Pu)} and T _{U (Pu)} are X on the low energy side of U and Pu, respectively.
The line intensity and the X-ray intensity on the high energy side are shown.

Since the energy at the absorption edge is unique to each element, even if two kinds of elements are mixed, each of them is independent of the X on the low energy side.
It is possible to measure the line intensity and the X-ray intensity on the high energy side.

When the same operation as (1) is performed on these, this becomes the data of the element of interest.

log (T _{L (U)} / T _{U (U)} ) …… (2) log (T _{L (Pu)} / T _{U (Pu)} ) …… (3) This projection data is used for the sample rotation / horizontal traveling mechanism. The sample is taken from each direction of the measurement sample 35 by driving 36, and the processing computer 44
If is calculated, the image of the two-dimensional distribution of the photon absorptance of the element of interest can be obtained. Here, the photon absorption rate of the element of interest and the concentration of the element are in a proportional relationship as described above. Therefore, by using the data relating to this proportional relationship, it is possible to obtain a two-dimensional distribution of the concentration of the element of interest.

Of course, the X-ray generation tube 31 or the photon source used to obtain the projection data needs to be capable of generating energy larger than the absorption edge energy of the element of interest in the measurement sample. is there. For example, it is assumed that the uranium concentration distribution in the measurement sample 35 is measured using the element concentration distribution measuring device of this embodiment. In this case, since the K absorption edge energy of uranium is 115.6 KeV, it is desirable to use an X-ray generating tube of 120 KeV or more, for example, an X-ray generating tube having a maximum energy of 140 KeV.

Next, the control contents of the processing computer in this embodiment will be described with reference to FIG. Although not shown, the processing computer 44 stores the control program in a storage medium such as a floppy disk, and the projection data of the measurement sample 35 in each direction is temporarily stored in these storage media. Based on, the element concentration distribution is obtained.

First, the processing computer sets the drive control system 47 to the initial state and sets the sample rotation / horizontal traveling mechanism 36 to the measurement start position. Then, the transmission X-ray spectrum is measured at the rotation angle position and the straight scanning position (step). Then the X-ray intensity before and after the absorption edge energy position from the measured spectrum (T _L, T _U) seek (step). Next, the processing computer 44 determines whether or not the straight-line scanning of a predetermined number (m times) has been completed (step). If it has not been completed (as a matter of course, the straight running scanning is not finished at the time when this first measurement is finished), the drive control system 47 is controlled to perform the straight running scanning by a predetermined amount (step). . Then, the X-ray spectrum is measured at the newly set position (step). In this way, the above control is repeated until the straight scan for m times is completed (steps-).

When the m-th straight scanning is completed (step: Y), it is determined whether or not a predetermined number (n times) of rotational movement is completed (step). When the rotational movement of the turntable 34 is not completed (N), the drive control system 47 is controlled and the turntable 34 is rotated by a predetermined angle (step). Then, the transmission X-ray spectrum is measured at the position after this rotation (step). At this time, the straight scan is performed at this rotational position, and the respective transmission spectra are obtained (steps-).

When the measurement at the rotation position is completed in this way, the turntable 34 is moved to the next measurement position (step). Then, the same work is performed by changing the rotational position m times (steps-).

When the above measurement work is completed (step: Y), image reconstruction processing is performed based on the obtained m × n data, that is, the data obtained by the equation (1) (step). Then, a two-dimensional distribution of the reconstructed element concentration is obtained (step). The obtained results are stored in the above-mentioned floppy disk or the like, and displayed on a CRT (not shown) or a hard copy is output by a printer as needed. Since the technique of processing data two-dimensionally is not different from the technique in the field of CT (Computed Tomography) in particular, its explanation is omitted.

In the embodiment, one set of the detector collimator and the photon detector is arranged, but a plurality of sets of these may be centripetally arranged in one photon source. This makes it possible to shorten one measuring time. Although the position of the measurement sample is moved in the embodiment, the measurement sample may be fixed and the positions of the photon source and the detector may be moved on the contrary.

[Advantages of the Invention] As described above, according to the present invention, it is possible to obtain a two-dimensional distribution of the concentration of an element, which can be utilized as completely new information that has never existed before. For example, the distribution of substances adhering to the inside of the pipe can be measured without destroying the object to be measured, and can be widely used not only in the industrial field but also in other fields for analysis of phenomena.

[Brief description of drawings]

1 to 3 are for explaining an element concentration distribution measuring apparatus in one embodiment of the present invention, in which FIG. 1 is a schematic configuration diagram of the element concentration distribution measuring apparatus, and FIG. Fig. 3 is an explanatory view showing the measurement principle, Fig. 3 is a flow chart showing the control of the processing computer, and Fig. 4 is a transmission CT.
FIG. 5 is a schematic configuration diagram of a related device using the related art, FIG. 5 is a schematic configuration diagram of a conventionally proposed solution concentration measuring device, and FIG. 6 shows a measurement principle when two kinds of elements to be measured are present in the present invention. FIG. 31 …… X-ray generator, 33 …… Photon source collimator, 34 ……
Turntable, 35 …… Measurement sample, 36 …… Sample rotation / horizontal traveling mechanism, 39 …… Detector collimator, 41 …… X-ray detector, 43 …… Measuring circuit system, 44 …… Processing computer, 47 …… Drive control system.

Claims (3)

[Claims] 1. A measurement sample is irradiated with a photon source that generates photons of at least two types of energy sandwiching the absorption edge energy of the element to be obtained, and the energy of the energy lower than the absorption edge after passing through the measurement sample is measured. The operation for obtaining the intensity ratio between the photons and the photons of high energy is performed from at least two directions on the surface to be measured of the measurement sample, and the data about the photon intensity ratio collected by the operation is calculated to perform the operation. A method for measuring an element concentration distribution, which comprises obtaining a two-dimensional distribution of elements. 2. A photon source for generating photons in an energy range from an energy lower than the absorption edge energy of the element to be sought to a high energy, and a photon for limiting a traveling range of photons generated from the photon source. Source collimator, a sample mounting table on which a measurement sample to be irradiated with photons passing through the photon source collimator is mounted, and this sample so that the photons are irradiated from at least two directions in arbitrary cross sections of the measurement sample. Sample mounting table driving means for rotating the mounting table or moving it in a predetermined direction, a collimator for a detector arranged to face the photon source collimator so as to sandwich the sample mounting table, and a photon passing through the collimator for the detector. And a photon detector for detecting the absorption edge energy of the element to be obtained in the measurement sample by inputting the output of the photon detector. Concentration data calculation means for obtaining the concentration data of the element based on the photon intensity data of the energy side and the high energy side, and the concentration data in the measurement sample for each displacement by the sample mounting table drive means, in the cross section of the measurement sample An element concentration distribution measuring device, comprising: an element concentration distribution calculating means for calculating a concentration distribution of an element to be obtained. 3. A plurality of sets of a collimator for a detector and a photon detector for detecting photons passing through the collimator are present.
The element concentration distribution measuring device according to claim 2, wherein the element concentration distribution measuring device is arranged centripetally with respect to one photon source.