JP7394039B2 - X-ray measurement device, X-ray measurement system, and X-ray measurement method - Google Patents

Description

The present invention relates to techniques for an X-ray measurement device, an X-ray measurement system, and an X-ray measurement method.

Methods for measuring radioactivity include methods described in Patent Document 1 and Patent Document 2.
Patent Document 1 states, ``The method modulates radiation from an external reference radiation source, causes the modulated radiation to pass through a non-measuring object, scans and measures the intensity of the passed radiation by changing the position continuously or intermittently, and A radioactivity distribution measuring method and apparatus are disclosed in which the radiation absorption coefficient distribution of the non-measuring body is determined from the difference between the maximum value and the minimum value, and the radiation count rate distribution of the non-measuring body itself is determined from the minimum value. (see summary).

Patent Document 2 states, "One or more radiation detectors and an external radiation source are arranged with a radioactive waste container in between, and the container is rotated relative to the radiation detector and the external radiation source. The radiation emitted from inside the container and the radiation emitted from an external radiation source and transmitted through the container are measured by the radiation detector while moving in the vertical direction, and the amount of radioactivity in the container is determined based on the results. In the desired method for measuring the amount of radioactivity in a radioactive waste container, radiation is emitted from an external source in a pulsed manner, and the radiation emitted from inside the container is measured one by one in pulse mode, and then emitted from the external source. A method for measuring the amount of radioactivity in a radioactive waste container is disclosed in which the radiation transmitted through the container is measured in current mode as a gross integral amount (see abstract).

Japanese Unexamined Patent Publication No. 61-204582 Japanese Patent Application Publication No. 1-65478

Here, the techniques described in Patent Document 1 and Patent Document 2 do not take pile-up of X-ray photons into consideration. Here, pileup is a phenomenon in which multiple X-ray photons are detected simultaneously and detection pulses overlap.

The technique described in Patent Document 1 takes the difference and removes γ-rays by providing a time when X-rays are not irradiated. However, with the technique described in Patent Document 1, the measurement time is more than twice as long as when no X-ray irradiation period is provided. Furthermore, although the number of incident γ-rays is smaller than the number of incident X-rays, it is affected by statistical variations, so the technique described in Patent Document 1 cannot completely eliminate errors.

Patent Document 2 assumes that X-ray photons are measured one by one, but this is to prevent the dead time that occurs when integrating and reading data in integral readout. . The removal of gamma rays and Therefore, it is not possible to separate X-rays and γ-rays by energy discrimination. Therefore, it is not possible to separate X-rays and γ-rays at the same time during X-ray irradiation.

The technique described in Patent Document 1 has the problem that the measurement time simply increases as described above. The technology described in Patent Document 2 aims to shorten the measurement time by using the time of non-X-ray irradiation for actual gamma-ray measurement, but the gamma-ray influence is particularly large and the number of transmitted X-ray photons is small. Sometimes it is unavoidable to extend the measurement time.

The present invention was made in view of this background, and an object of the present invention is to improve the accuracy of radiation measurement.

In order to solve the above-described problems, the present invention provides a detection section extending at least in the direction of the incident axis of X-rays, a first region that is a pile-up region, and a first region in the detection section that extends in the direction of the incident axis of X-rays; an X-ray photon number counting unit that counts the number of X-ray photons in the second region, and a second region that is a region of , an X-ray photon number estimation unit that estimates the number of X-ray photons in the first region; the number of X-ray photons detected in the second region; and the estimated number of X-ray photons in the first region; and a total X-ray photon number calculation unit that totals the total number of X-ray photons.
Other solutions will be described as appropriate in the embodiments.

According to the present invention, the accuracy of radiation measurement can be improved.

1 is a diagram showing the configuration of an X-ray measurement system according to a first embodiment. FIG. 2 is a diagram showing a detailed configuration of a data processing device. FIG. 2 is a diagram showing the hardware configuration of a data processing device. FIG. 3 is a diagram showing a channel configuration of a radiation detector in the first embodiment. FIG. 1 is a diagram showing the overall configuration of a radiation detector according to a first embodiment. FIG. 2 is a diagram showing the configuration of an analog signal processor used in the first embodiment. FIG. 2 is a diagram showing an example of a waveform (input waveform) of a signal input to a comparator. It is a figure which shows the output waveform of each comparator device. It is a flowchart which shows the procedure of the X-ray measurement process performed by the X-ray measurement system. This is the result of estimation processing of the number of detected X-ray photons displayed on the display monitor. FIG. 3 is a diagram showing a specific example of a radiation measuring device used for calculating a radiation absorption coefficient. It is a figure showing the composition of the X-ray measurement system in a 2nd embodiment. FIG. 2 is a diagram showing the configuration of a data processing device in a second embodiment. It is a flowchart which shows the procedure of X-ray measurement processing in a 2nd embodiment. It is a figure showing the composition of radiation detector 1 in a 3rd embodiment. It is a figure showing the channel composition in the radiation detector of a 3rd embodiment. It is a figure showing the composition of the radiation detector in a 4th embodiment.

Next, modes for carrying out the present invention (referred to as "embodiments") will be described in detail with reference to the drawings as appropriate. Furthermore, in this embodiment, radiation includes X-rays R1 (see FIG. 1) and γ-rays R2 (see FIG. 1).

[First embodiment]
<System configuration>
FIG. 1 is a diagram showing the configuration of an X-ray measurement system Z according to the first embodiment.
The X-ray measurement system Z includes an X-ray measurement device 1 and a radiation measurement device 2.
The X-ray measurement device 1 includes an X-ray generation device 110, an X-ray irradiation control device 120, a radiation detection device 130, a radiation signal processing device 140, a data processing device 150, and a control management device 160. Furthermore, radioactive waste 173 to be measured is stored in a waste container 172. This waste container 172 is placed on a sample stage 171. Further, a radiation measuring device 2 is provided separately from the X-ray measuring device 1. Note that the radioactive waste 173 stored in the waste container 172 is appropriately referred to as an X-ray source. Further, the detailed configuration of the data processing device 150 will be described later.

The X-ray generator 110 generates X-rays R1 and irradiates the generated X-rays R1 toward the waste container 172. Further, the X-ray generator 110 includes an electron beam accelerator 111 and an X-ray generation target 112.
The electron beam accelerator 111 is a variable energy electron beam accelerator that generates an electron beam depending on the energy of the X-ray R1 required for measurement. Then, the X-ray generation target 112 is irradiated with the generated electron beam, thereby generating X-rays R1. The generated X-rays R1 are irradiated onto the waste container 172.
Note that the X-ray generator 110 includes a collimator for slice imaging and a neutron shielding body, as necessary.

The X-ray irradiation control device 120 controls the irradiation of X-rays R1. The electron beam accelerator 111 is controlled by an X-ray irradiation control device 120 so that a current or pulsed electron beam is emitted.

The radiation detection device 130 detects the X-rays R1 emitted from the X-ray generator 110 and transmitted through the waste container 172, and the γ-rays R2 emitted from inside the waste container 172. Furthermore, the radiation detection device 130 amplifies and shapes the electrical signals generated by the detected X-rays R1 and γ-rays R2, and then converts them into digital signals.
The radiation detection device 130 includes a radiation detector 131 and an analog signal processor 132.
As shown in FIGS. 3 and 4, the radiation detector 131 includes a scintillator element 301 that detects radiation and converts it into scintillator light, and an optical sensor 302 that amplifies the scintillator light and converts it into an electrical signal. The detailed configuration of the radiation detector 131 will be described later.
The analog signal processor 132 amplifies the electrical signal output from the radiation detector 131, extracts peak value information, converts it into a digital signal, and outputs it. The detailed configuration and operation of the analog signal processor 132 will be described later.

In addition to the X-rays R1 transmitted through the waste container 172, γ-rays R2 emitted from the radioactive waste 173 stored in the waste container 172 also enter the radiation detector 131. The X-rays R1 and γ-rays R2 are converted into light by the scintillator element 301 (see FIGS. 3 and 4) of the radiation detector 131, amplified by the optical sensor 302, and converted into electrical signals. This electrical signal is sent to analog signal processor 132 in pulse mode. The analog signal processor 132 amplifies and shapes the electrical signal output from the optical sensor 302, and then converts it into a digital signal.

The radiation signal processing device 140 converts the digital signal output from the radiation detection device 130 into measurement data that corresponds to the position where the X-ray was detected and the energy. The energy here is the energy of X-ray photons detected by the radiation detection device 130. Hereinafter, unless otherwise specified, energy refers to the energy of X-ray photons detected by the radiation detection device 130.
As mentioned above, the detailed configuration of the data processing device 150 will be described later.

The control management device 160 controls a series of processes. Further, the control management device 160 is connected to the X-ray irradiation control device 120, the data processing device 150, and the sample stage 171. Further, the control management device 160 is connected to a display monitor 161, a mouse 162, and a keyboard 163.
An operator inputs information regarding measurement and control via the mouse 162 and keyboard 163. Furthermore, information input by the operator and information calculated by the data processing device 150 are visualized on the display monitor 161. Further, the control management device 160 performs scanning control to rotate or translate the sample stage 171 or the X-ray generator 110 and the radiation detection device 130. Note that when the control management device 160 is connected to the sample stage 171, the control management device 160 performs scanning control by controlling the rotation and translational scanning of the sample stage 171. When the control management device 160 is not connected to the sample stage 171, the control management device 160 performs scanning control by rotating and translating the X-ray generator 110 and the radiation detection device 130 with respect to the sample stage 171. In addition, selection of the rotational scanning pitch, vertical scanning pitch, scanning range, X-ray irradiation time, X-ray energy to be irradiated to the waste container 172 (radioactive waste 173), X-ray The operator can instruct the control management device 160 to start and end irradiation.

The radiation measurement device 2 is a device provided separately from the X-ray measurement device 1, and measures radiation (γ-ray R2) emitted from the radioactive waste 173 based on the radiation absorption coefficient.

<Data processing device 150>
FIG. 2A is a diagram showing a detailed configuration of the data processing device 150.
The data processing device 150 performs various processes on the measurement data input from the radiation signal processing device 140. The data processing device 150 includes a radiation identification section 151, a pile-up detection section 152, an X-ray photon number distribution acquisition section 153, an X-ray photon number estimation section 154, an image reconstruction section 155, and a radiation absorption coefficient calculation section 156.
The radiation identification unit 151 identifies X-rays R1 and γ-rays R2, and removes events containing only γ-rays R2 and noise. The event will be described later.
The pile-up detection unit 152 determines the pile-up position based on the measurement data input from the radiation signal processing device 140.
The X-ray photon number distribution acquisition unit 153 acquires the number of X-ray photons that are not piled up, and acquires the X-ray photon number distribution at the detection position in the depth direction in each channel of the radiation detector 131. The channel will be explained later.
The X-ray photon number estimation unit 154 estimates the number of X-ray photons piled up from the number of X-ray photons at each detection position in the channel.
The image reconstruction unit 155 reconstructs an image of linear attenuation coefficients for each energy from the estimated number of X-ray photons.
The radiation absorption coefficient calculation unit 156 calculates the radiation absorption coefficient based on the measurement results of the radiation measurement device 2 provided separately from the X-ray measurement device 1.

<Hardware configuration>
FIG. 2B is a diagram showing the hardware configuration of the data processing device 150.
The data processing device 150 includes a CPU (Central Processing Unit) 701, a memory 702, and a storage device 703 such as an HD (Hard Disk).
A program stored in storage device 703 is loaded into memory 702. The loaded program is then executed by the CPU 701. As a result, each part 151 to 156 shown in FIG. 2A is realized.

Note that in this embodiment, a PC (Personal Computer) is used as the data processing device 150, but the data processing device 150 may be provided in a format such as a cloud. Furthermore, the storage device 150 may exist in the cloud.

<Radiation detector 131>
FIG. 3 is a diagram showing the channel configuration of the radiation detector 131 in the first embodiment.
As shown in FIG. 3, it is assumed that the X-ray R1 enters the radiation detector 131 from the left side of the paper (radiation incident direction D).
In the radiation detector 131, a plurality of radiation detection elements 304 each including a pair of scintillator elements 301 and an optical sensor 302 are arranged on the xy plane with respect to the radiation incident direction D. Among these, one row of radiation detection elements 304 arranged in the axial direction (x-axis direction) of the radiation incident direction D is called a channel. It has a configuration in which a plurality of channels shown in FIG. 3 are arranged in the y-axis direction. From the radiation incident direction D, γ-rays R2 emitted from the radioactive waste 173 are also incident along with the X-rays R1.

Although the radiation detector 131 shown in FIG. 3 has the radiation detection element 304 arranged on the xy plane, the radiation detection element 304 may also be arranged in the z-axis direction. Alternatively, the X-ray R1 in the z-axis direction may be scanned by moving the radiation detector 131 shown in FIG. 3 in the z-axis direction. Reference numerals 341 and 342 in FIG. 3 will be described later.

(Channel configuration)
FIG. 4 is a diagram showing the overall configuration of the radiation detector 131.
Note that in FIG. 4, the vertical direction (z-axis direction) is opposite to that in FIG. 3. As described above, in one channel, a plurality of radiation detection elements 304 are arranged in one row in the axial direction (x-axis direction) of the radiation incident direction D. That is, in one channel, the radiation detection element (detection section) 304 extends at least in the direction of the X-ray incident axis.

In this way, one channel has a multistage structure in which a plurality of radiation detection elements 304 of the same size are arranged in a direction parallel to the radiation incident direction D. Note that the number of radiation detection elements 304 does not matter. Further, the scintillator element 301 may be made of any material such as NaI, CsI, CeBr3, etc. Furthermore, as the scintillator element 301, semiconductors such as CZT, CdTe, and Ge can also be used as long as they have a positional resolution equivalent to that of NaI, CsI, and CeBr3. Furthermore, if neutrons can be generated from the sample, a phoswitch detection method that uses a neutron detection scintillator or the like can be employed. With such a configuration, it becomes possible to separate neutrons and other radiation. It is assumed that the optical sensor 302 uses a photomultiplier tube, a silicon photodiode, an avalanche photodiode, or the like. As shown in FIG. 4, a cover 303 that is a reflective material or a light shielding material is provided around the scintillator element 301. However, the cover 303 can be omitted. Further, in order to prevent saturation in the optical sensor 302, a light guide (not shown) may be provided between the scintillator element 301 and the optical sensor 302. By doing so, the light generated in the scintillator element 301 is dispersed, and the detection accuracy of the optical sensor 302 can be improved.

(Analog signal processor 132)
FIG. 5 is a diagram showing the configuration of the analog signal processor 132 used in the first embodiment.
The analog signal processor 132 shown in FIG. 5 is connected to each of the radiation detection elements 304 shown in FIGS. 3 and 4.
The signal sent from the optical sensor 302 is input to the preamplifier 401 of the analog signal processor 132 via the end 411 and amplified. The amplified signal is sent to waveform shaper 402. The waveform shaper 402 shapes the waveform of the signal according to a set time constant. The waveform-shaped signal is sent to each of a plurality of (five in the example of FIG. 5) comparators 403a to 403e (403) via the end portion 412. Different threshold values are set for each of the comparators 403a to 403e. Each comparator unit 403 outputs a digital signal of “1” when the voltage value of the signal input from the waveform shaper 402 is higher than the threshold value. Further, each comparator unit 403 outputs a digital signal of “0” when the voltage value of the signal input from the waveform shaper 402 is lower than the threshold value. Output signals are output from ends 413a to 413e. Note that it is possible to omit part of the analog signal processor 132 depending on the scintillator element 301, the gain of the optical sensor 302, and the noise level measured by the radiation detection device 130. Further, in the example of FIG. 5, five comparators 403 are provided, but the number of comparators 403 is not limited to five.

(input waveform and output waveform)
FIG. 6A is a diagram illustrating an example of the waveform (input waveform) of a signal input to the end portion 412 of FIG. 5. FIG.
FIG. 6A shows an example in which two X-rays R1 indicated by broken lines 502 and 503 are detected by the scintillator element 301. In such a case, the waveform (input waveform) of the signal input to the end portion 412 in FIG. 5 becomes a waveform shown by a solid line 501 on which broken lines 502 and 503 are superimposed. Furthermore, noise (represented by reference numeral 504) originating from γ-rays R2 and the like is superimposed on the input waveform shown by a solid line 501.

In FIG. 6A, dotted lines 511a to 511e are threshold values set in comparators 403a to 403e in FIG. 5. That is, the dotted line 511a is the threshold value installed in the comparator 403a in FIG. 5. Moreover, the dotted line 511b is the threshold value installed in the comparator device 403b of FIG. 5, and the dotted line 511c is the threshold value installed in the comparator device 403c of FIG. 5. Further, a dotted line 511d is a threshold value installed in the comparator 403d of FIG. 5, and a dotted line 511e is a threshold value installed in the comparator 403e of FIG.

FIG. 6B is a diagram showing the output waveform of each comparator 403. That is, each of the waveforms 512a to 512e shown in FIG. 6B represents the waveform of the signal output from each of the ends 413a to 413e shown in FIG. 5.
FIG. 6B shows an example in which the threshold values 511a to 511e shown in FIG. 6A are set for each of the comparators 403a to 403e shown in FIG. 5, and the input waveform 501 shown in FIG. 5 is input to each of the comparators 403a to 403e. It shows.
In FIG. 6B, waveform 512a is the output waveform of comparator 403a. That is, in the input waveform 501 in FIG. 6A, a voltage below the threshold 511a is output as "0", and a voltage above the threshold 511a is output as "1".
Similarly, waveform 512b is the output waveform of comparator 403b, and waveform 512c is the output waveform of comparator 403c. The waveform 512d is the output waveform of the comparator 403d, and the waveform 512e is the output waveform of the comparator 403e. Δtrise, Δtgap, and Δt will be described later.

The radiation signal processing device 140 outputs measurement data, to which energy information is added, to the data processing device 150 in response to signals input from the comparators 403 connected to the respective radiation detection elements 304. The energy information includes a channel number, a radiation detection element number, a comparator number, a time t when the digital signal rises from "0" to "1", and a time Δt during which the digital signal "1" is output. Further, the radiation detection element number is a number uniquely assigned to the radiation detection element 304 within a channel. Further, the comparator number is a number uniquely assigned to the comparator unit 403 in the analog signal processor 132.

(flowchart)
FIG. 7 is a flowchart showing the procedure of the X-ray measurement process performed by the X-ray measurement system Z.
First, the control management device 160 sets the X-ray irradiation position (S1). Setting of the X-ray irradiation position is performed by the control management device 160 rotating the sample stage 171, rotating the X-ray generator 110, or moving the X-ray generator 110 in the vertical direction.
Next, the radiation signal processing device 140 obtains output signals for each threshold value from each analog signal processor 132 (S2). Here, the radiation signal processing device 140 obtains output signals shown in waveforms 512a to 512e shown in FIG. 6B from the respective analog signal processors 132. As described above, the radiation signal processing device 140 outputs measurement data with energy information added to the signal acquired from the analog signal processor 132 to the data processing device 150.

Then, the radiation identification unit 151 removes γ-ray R2 and noise level events from the input measurement data (S3). Here, the event is measurement data in which the output signal of one of the comparators 403 among the signals output from the analog signal processor 132 is "1". That is, what corresponds to one of the input waveforms 501 in FIG. 6A is called an event.
Next, the pile-up detection unit 152 detects the pile-up detection position of the X-ray R1 in each channel (S4).

Here, the processing in steps S3 and S4 will be explained in detail with reference to FIGS. 5 to 6B.
First, the radiation identification unit 151 determines whether the time Δt during which the output signal from the comparator 403a having the lowest threshold value 511a rises is within a certain time (Δt _min <Δt<Δt _max ) based on the measurement data. Determine whether or not. Note that Δt _min is set to an appropriate value depending on the reciprocal of the clock frequency in digital signal processing or the noise situation. Further, Δt _max is set to an appropriate value in accordance with the time width when the maximum energy detectable in each channel is detected, or in accordance with the noise situation.

If the rising time Δt of the output signal from the comparator 403a to which the lowest threshold value 511a is set does not satisfy a certain period of time (Δt _min <Δt<Δt _max ), the output waveform may be caused by noise or not. Alternatively, it is assumed that there is a rise due to the γ-ray R2 or a pile-up of signals due to multiple radiation detections, so the radiation identification unit 151 eliminates that event. This process corresponds to step S3 in FIG.

That is, if Δt shown in the waveform 512a of FIG. 6B is less than or equal to a predetermined time, the radiation identification unit 151 determines that the event is caused by γ-ray R2 or other noise, and removes the event.

Note that if the lowest threshold value 511a is set to a level greater than the γ-ray R2 or noise, the process of step S3 can be omitted.

When Δt (see FIG. 6B) satisfies the condition within a certain period of time (Δt _min <Δt<Δt _max ), the pile-up detection unit 152 detects that the output signal from the comparator 403a to which the lowest threshold value 511a is set is The comparator unit 403 having the maximum threshold value that rises within a certain period of time (Δt _rise <Δt _{rise, max} ) from the time t at which it rises is detected. In the examples of FIGS. 5 to 6B, the comparator unit 403e having a threshold value 511e corresponds to the comparator unit 403e. Note that Δt _rise,max is a value that is set in consideration of the time constant of the waveform shaper 402.

In addition, from the relationship between the energy corresponding to the maximum threshold of the comparator unit 403 that detected the rise of the signal and the rise time t at the minimum threshold, a time width processing method (Time over Threshold method) is used to convert it into energy. , it is also possible to determine the energy of the X-ray photon. Thereby, the energy of the X-ray configuration can be determined with even higher precision.

Subsequently, the pile-up detection unit 152 detects an event in which the signal from the same comparator 403a changes from "0" to "1" once or more within Δt. In the example of FIG. 6B, the waveform 512c and the waveform 512d correspond. That is, when waveforms such as waveform 512c and waveform 512d are detected, the pileup detection unit 152 determines that a pileup is occurring as shown in FIG. 6A, and classifies such an event as a pileup event. Detected as.

Furthermore, the pile-up detection unit 152 detects that even in the event that the signal from the same comparator 403a changes from "0" to "1" twice or more within Δt, the signal from the same comparator 403a changes from "0" to "1" twice or more. An event in which the time difference between falling from "1" to "0" and rising from "0" to "1" is equal to or greater than a certain value (Δtgap>Δtgap, min) is detected. That is, when Δtgap in FIG. 6B is long, the pileup detection unit 152 considers each event to be independent and detects it as a non-pileup event.

The pile-up detection unit 152 detects an event in which the signal from the same comparator 403a does not change from "0" to "1" once or more within Δt as a non-pile-up event.

The pile-up detection unit 152 determines whether a pile-up event or a non-pile-up event is occurring for each radiation detection element 304.

The pile-up detection unit 152 detects, for one channel, a radiation detection element 304 in which a pile-up event has occurred and a radiation detection element 304 in which a non-pile-up event has occurred. Thereby, the pile-up detection unit 152 determines the position of the radiation detection element 304 that is piled up in the channel (step S4 in FIG. 7).

Here, among the radiation detection elements 304 in which a pile-up event has occurred in the channel, the position of the radiation detection element 304 that is farthest from the incident side of the X-ray R1 is defined as the X-ray R1 pile-up detection position. Furthermore, among the radiation detection elements 304 that are not piled up, the position of the radiation detection element 304 closest to the incident side of the X-ray R1 is defined as a non-pileup detection position. In this way, the pile-up position detection in step S4 in FIG. 7 is performed. The range of the radiation detection element 304 where pile-up occurs is defined as a pile-up region 341 (see FIG. 3). Furthermore, the range of the radiation detection element 304 in which no pile-up occurs is defined as a non-pile-up region 342 (see FIG. 3).

Generally, the closer the radiation detection element 304 is to the incident side of the X-rays R1, the more X-rays R1 are incident thereon. As a result, the radiation detection element 304 closer to the incident side of the X-ray R1 has a higher probability of pile-up. Furthermore, the farther the radiation detection element 304 is from the incident side of the X-ray R1, the lower the probability of pile-up. The pile-up detection position changes depending on the irradiation intensity of X-ray R1, the distance between the X-ray source (radioactive waste) and the radiation detector 131, the radiation sensitivity of the radiation detector 131, the size and physical properties of the object to be measured, etc. .

Return to the process in FIG. 7.
After step S4, the X-ray photon number distribution acquisition unit 153 acquires the detected X-ray photon number distribution by energy in the non-pileup region 342 (S11). That is, the X-ray photon number distribution acquisition unit 153 acquires the number of X-ray photons for each radiation detection element 304 in the non-pile-up region 342 for each maximum threshold value (energy) at which a signal is detected. At this time, the X-ray photon number distribution acquisition unit 153 acquires the number of photons as the number of photons per unit time.
Then, the X-ray photon number distribution acquisition unit 153 calculates an X-ray photon number distribution with the horizontal axis representing the detection position of the X-ray photons and the vertical axis representing the number of X-ray photons that have not piled up. The X-ray photon detection position is the position of the radiation detection element 304 where the X-ray photon is detected. The X-ray photon number distribution will be described later.

Next, the X-ray photon number estimation unit 154 estimates the number of detected X-ray photons for each energy in the pile-up region 341 (S12). Here, the X-ray photon number estimating unit 154 acquires X-ray photon number distribution data in the radiation detector 131 that has been acquired in advance under a plurality of conditions different from step S11. Then, the X-ray photon number estimation unit 154 fits the X-ray photon number distribution data acquired in step S11 to the X-ray photon number distribution data.

Then, the X-ray photon number estimating unit 154 determines the condition closest to the X-ray photon number distribution acquired in step S11 from among the previously acquired X-ray photon distribution data. Furthermore, the X-ray photon number estimation unit 154 estimates the number of X-ray photons for each energy in the pile-up region 341. Since the structure of the radiation detector 131 is known, when determining the number of X-ray photons for each energy by simple analysis, the following equation (1) is used, for example.

I1 (Ek) = ΣI2 (n, Ek) + ΣI1 (n, Ek)
=ΣI2(0,Ek)(1-exp(-μ1(Ek)Δt))*(exp(-μ1(Ek)t)+ΣI1(n,Ek)
(1)

Here, I2 is the estimated number of X-ray photons in the pile-up region, and I1 is the number of X-ray photons in the non-pile-up region. Note that in the first and second lines of equation (1), the first term is the sum of the number of X-ray photons in the pile-up region 341 (0<n<n _pile ), and the second term is the sum of the number of X-ray photons in the non-pile-up region 342 (n _pile It shows the sum of the number of X-ray photons at <n<n _max ). Here, n _pile is the radiation detection element number at the pile-up position.

Furthermore, n is a radiation detection element number. Since the materials of the scintillator element 301 and the optical sensor 302 that constitute the radiation detector 131 are known, the linear attenuation coefficient μ(Ek) in the radiation detector 131 is known. Therefore, _{the X} -ray photon number estimation unit 154 calculates ΣI1 (0, Ek )(1-exp(-μ1(Ek)Δt))*(exp(-μ1(Ek)n). Then, the X-ray photon number estimation unit 154 calculates the pileup Calculate the number of X-ray photons ΣI2 (n, Ek) in the region 341 (0<n<n _pile ).In reality, more complex behavior of X-rays such as multiple scattering inside the radiation detector 131 is also possible. Therefore, detailed fitting can be performed using machine learning or deep learning.When performing machine learning or deep learning, the data that should be acquired in advance may be measured data or data from simulation. I do not care.

Then, the X-ray photon number estimation unit 154 calculates the total number of X-ray photons for each energy in the channel being processed (S13). That is, the X-ray photon number estimating unit 154 calculates the total value of the number of X-ray photons for each energy in the non-pile-up region 342 and the estimated number of X-ray photons for each energy in the pile-up region 341.

Here, details of the processing in steps S11 to S13 will be explained with reference to FIG.
FIG. 8 shows the processing results of steps S11 to S13 displayed on the display monitor 161.
Here, the processing screen 600 shown in FIG. 8 has a channel designation window 601, an energy designation window 602, and a photon number display area 610. In the energy specification window 602, the energy (maximum detection threshold) for which the number of X-ray photons is to be calculated is specified. For example, in the example of FIG. 8, an event having a maximum detection threshold corresponding to energy "100" is specified as a processing target.

The photon number display area 610 displays a graph having the X-ray photon detection position on the horizontal axis and the X-ray photon count rate (cps) on the vertical axis. The X-ray photon position corresponds to the number (element number) of the radiation detection element 304 that detected the X-ray. In this graph, the distribution of the number of detected X-ray photons by energy acquired in step S11 is plotted (numeral 611). That is, the distribution of the number of X-ray photon detections by energy acquired in step S11 corresponds to the plot indicated by reference numeral 611.

Then, the X-ray photon number estimation unit 154 applies a fitting curve to the plotted distribution of the detected number of X-ray photons (solid line 612, broken line 613). The fitting curves indicated by a solid line 612 and a broken line 613 are calculated based on X-ray photon number distribution data in the radiation detector 131 that has been obtained in advance under a plurality of conditions different from those in step S11.

Here, a solid line 612 indicates a fitting curve in the non-pileup region 342. Further, a broken line 613 indicates a fitting curve in the pile-up region 341. Thereby, the number of detected X-ray photons (in the example of FIG. 8, the counting rate) in the pile-up region 341 can be estimated. Calculation of the fitting curve shown by the solid line 612 and the broken line 613 corresponds to step S12 (estimation of the number of detected X-ray photons).

Then, the X-ray photon number estimating unit 154 calculates the detected Add up the number of line photons. Thereby, the number of X-ray photons for each energy detected in one channel is estimated (corresponding to step S13 (calculating the total number of X-ray photons for each energy)).
In the example of FIG. 8, the vertical axis is the count rate, but it may also be the count per measurement.

Returning to the explanation of FIG. 7.
After step S13, the control management device 160 determines whether the processing of steps S2 to S13 has been completed for all channels (S21).
If the processing in steps S2 to S13 has not been completed for all channels (S21→No), the control management device 160 returns the processing to step S2.
If the processing of steps S2 to S13 has been completed for all channels (S21→Yes), the control management device 160 determines whether the sample stage 171 has rotated once (S22). Here, one rotation means that the entire circumference of the waste container 172 (radioactive waste 173) is imaged by X-rays.
If the sample stage 171 has not rotated once (S22→No), the control management device 160 returns the process to step S2.

If the sample stage 171 has rotated once (S22→Yes), the image reconstruction unit 155 reconstructs an image of the linear attenuation coefficient for each energy from the number of X-ray photons estimated in step S13 (S23).

(Image reconstruction processing)
Here, image reconstruction processing will be explained.
When performing image reconstruction, the image reconstruction unit 155 calculates the number of X-ray photons I ₀ (E) incident on each channel and the total X detected in each channel when the radioactive waste 173 is not installed. The logarithm of the ratio of the number of line photons I(E) is determined for each energy. Thereby, the linear attenuation coefficient μ(Ek) for each energy in the channel is obtained using equation (4) obtained by converting equation (1).

μ(Ek) = ln(I ₀ (Ek)/I(Ek))...(4)

At this time, since the substance of each pixel in the reconstructed image is unknown, the linear attenuation coefficient is unknown. Note that an appropriate image filter is applied to the reconstructed image. Thereby, linear attenuation coefficients for each energy can be obtained for the measurement target.

The linear attenuation coefficient depends on the energy of the irradiated X-ray R1, the density of the substance, and the atomic number. Therefore, in conventional X-ray CT, a linear attenuation coefficient integrated up to the maximum energy of the irradiated X-ray R1 is obtained, but in this embodiment, a linear attenuation coefficient for each energy is obtained.

Returning to the explanation of FIG. 7.
Thereafter, the radiation absorption coefficient calculation unit 156 converts the radiation absorption coefficient based on the measurement results of the radiation measurement device 2 provided separately from the X-ray measurement device 1 (S24).

(Processing of radiation absorption coefficient calculation unit 156)
FIG. 9 is a diagram showing a specific example of the radiation measuring device 2 used for calculating the radiation absorption coefficient.
In the example of FIG. 9, it is assumed that measurement is performed using a radiation measuring device 2 provided separately from the X-ray measuring device 1. However, it is also possible to substitute the radiation measuring device 2 with the radiation detecting device 130 in the X-ray measuring device 1.
FIG. 9 shows an example in which a high energy resolution radiation detector is used as the radiation measuring device 2. In FIG. Such a radiation measuring device 2 has a collimator 21. With such a collimator 21, the radiation measuring device 2 allows only the incidence of γ-rays R2 from a specific direction. In order to determine the radioactivity Ai at the position i of the collimator 21, the radiation measuring device 2 measures the radiation while rotating the sample stage 171, and determines the radiation count rate Cj at the radiation detection position j in the collimator 21. Then, the radioactivity Ai at the position i of the collimator 21 is calculated by calculating the sum ΣRij of the radiation absorption coefficients Rij in the path taken until the γ-ray R2 is detected using the following equation (11). Note that ij of Rij is the coordinate in the radioactive waste 173.

Ai=Cj/ΣRij... (11)

Here, the radiation absorption coefficient Rij is calculated by the following equation (12).

Rij=1-exp(-ΣΣμ(Ek)xL)... (12)

Here, ΣΣ is the sum of the energy Ek and the path length xL that the γ-ray R2 passes. In this embodiment, it is possible to obtain the sum ΣRij of the radiation absorption coefficients Rij for each energy in a short time. This allows radioactivity to be determined with high accuracy. Although this embodiment can be applied regardless of the energy of the generated X-ray R1, for example, there is a possibility that various types of Co-60, Cs-137, etc. may enter the radioactive waste 173 that enters the waste container 172. be. Therefore, as an X-ray source, a higher energy than the radioactive waste 173 of 2 MeV or more is used.

According to the first embodiment, the data processing device 150 estimates the number of X-ray photons detected in the pile-up region 341 based on the number of X-ray photons detected in the non-pile-up region 342 of the radiation detector 131. do. By doing so, even if a pile-up of X-ray photons occurs, the coefficient accuracy of the number of X-ray photons detected in the channel can be improved. In other words, according to the first embodiment, it is possible to suppress a decrease in the separation ability and the occurrence of artifacts due to an error in the number of detected photons caused by pile-up.

Furthermore, one channel has a structure extending at least in the direction of the incident axis of the X-rays. With such a configuration, the non-pileup area 342 and the pileup area 341 can be easily distinguished.

Further, in the first embodiment, comparators 403 each having a different threshold value are provided. Then, signals originating from γ-rays R2 and the like are removed based on signals exceeding a predetermined threshold. Thereby, signals originating from γ-rays R2 and the like can be removed without prolonging the measurement time.

By setting the configuration of the radiation detector 131 as shown in FIGS. 3 and 4, the pile-up area 341 and the non-pile-up area 342 can be easily detected. Furthermore, by using the scintillator element 301 in the radiation detector 131, costs can be reduced.

An analog signal processor 132 is provided for each radiation detection element 304. This makes it possible to avoid pile-up and signal saturation in the scintillator element 301 and optical sensor 302.
Further, by making the analog signal processor 132 a multi-comparator circuit as shown in FIG. 5, the circuit scale of the analog signal processor 132 can be reduced. Moreover, power saving can be realized by using the analog signal processor 132 as a multi-comparator circuit as shown in FIG. Further, by using the analog signal processor 132 as a multi-comparator circuit as shown in FIG. 5, it is possible to easily identify the γ-ray R2 and determine whether or not there is a pile-up of the X-ray R1.

[Second embodiment]
Next, a second embodiment of this embodiment will be described with reference to FIGS. 10 to 12.
In the second embodiment, the X-ray measurement device 1 is used as a nondestructive inspection device for identifying and quantifying substances constituting a measurement target. That is, in the second embodiment, the X-ray measuring device 1 is applied to non-destructive testing.

<System configuration>
FIG. 10 is a diagram showing the configuration of an X-ray measurement system Za in the second embodiment. Further, FIG. 11 is a diagram showing the configuration of the data processing device 115a in the second embodiment.
In FIGS. 10 and 11, the same components as those in FIGS. 1 and 2A are denoted by the same reference numerals, and the description thereof will be omitted. Furthermore, since the hardware configuration of the data processing device 150a is the same as that shown in FIG. 3, illustration and description thereof will be omitted here.
10 and 11 differ from FIGS. 1 and 2A in the following points.
(A1) As shown in FIG. 10, instead of the waste container 172 containing the radioactive waste 173 in FIG. 1, a nondestructive test object that does not emit γ-rays R2 is placed on the sample stage 171. Note that since the measurement target is no longer the radioactive waste 173 stored in the waste container 172, the gamma rays R2 from the radioactive waste 173 are no longer mixed. Therefore, in the X-ray measurement system Za shown in FIG. 10, the radiation measurement device 2 shown in FIG. 1 is omitted.
(A2) The radiation detection device 130 detects only the X-ray R1 irradiated from the X-ray generator 110. However, the configuration itself of the radiation detection device 130 has the same configuration as the radiation detection device 130 shown in FIG.

(A3) As shown in FIG. 11, the data processing device 150a is provided with a substance identification unit 158 for identifying substances, instead of the radiation absorption coefficient calculation unit 156 in the data processing device 150 of FIG. .

<Flowchart>
FIG. 12 is a flowchart showing the procedure of X-ray measurement processing in the second embodiment.
In FIG. 12, the same steps as those in FIG. 7 are given the same step numbers, and the description thereof will be omitted.
The flowchart shown in FIG. 12 differs from the flowchart shown in FIG. 7 in the following points.
(B1) Step S3 of removing the γ-ray R2 and the noise level event in FIG. 7 is omitted.
(B2) Step S24 of converting the radiation absorption coefficient and Step S25 of converting the radioactivity from the radiation absorption coefficient constitute a substance identification process (S31) for identifying the substance of the non-destructive inspection measurement target.
The other processing is the same as that in FIG.

In the substance identification process in step S31, the linear attenuation coefficient μ(Ek) for each energy determined by equation (1) has a value that differs for each substance more than the linear attenuation coefficient for the total energy. Therefore, the second embodiment not only simply improves material identification compared to previous techniques, but also obtains the linear attenuation coefficient for each interaction of X-ray R1 by inverse analysis, which improves the The accuracy can be improved.

[Third embodiment]
Next, the configuration of the radiation detector 131a will be shown with reference to FIGS. 13 and 14.
In FIGS. 13 and 14, as in FIGS. 3 and 4, it is assumed that the X-ray R1 is incident from the left side of the page.
First, similar to FIGS. 3 and 4, the vertical direction (z-axis direction) in FIGS. 13 and 14 is opposite to each other.
The radiation detector 131a shown in FIGS. 13 and 14 has a scintillator element 301a in the shape of a continuous rectangular parallelepiped with respect to the radiation incident direction D. That is, in FIGS. 13 and 14, one scintillator element 301a is provided for one channel. The scintillator element 301a is provided with an optical sensor 302 having the same configuration as in FIGS. 3 and 4. X-rays R1 incident on the scintillator element 301a from the radiation incident direction D proceed in the x-axis direction of the drawing while reacting with the scintillator element 301a. The optical sensor 302 detects light emission generated when the X-ray R1 and the scintillator element 301a react.

According to the third embodiment, energy loss between scintillator elements 301 can be reduced.

[Fourth embodiment]
FIG. 15 is a diagram showing the configuration of a radiation detector 131b in the fourth embodiment.
The radiation detector 131b shown in FIG. 15 has a configuration in which the semiconductor detector 321 extends in the lateral direction (xy plane) of the paper with respect to the radiation incident direction D. Plate-shaped electrodes 322a and 322b are provided above and below the semiconductor detector 321 in the drawing. Here, with respect to the semiconductor detector 321, an electrode 322a provided on the paper surface is provided in a direction parallel to the radiation incident direction D. Further, with respect to the semiconductor detector 321, an electrode 322b provided downward in the plane of the drawing is provided in a direction perpendicular to the radiation incident direction D (y-axis direction). That is, the electrode 322a and the electrode 322b are provided so as to be orthogonal to each other. As shown in FIG. 15, when the semiconductor detector 321 is used, the cover 303 shown in FIGS. 3 and 4 does not need to be installed.

X-rays R1 incident from the radiation incident direction D react with the semiconductor detector 321. The semiconductor detector 321 that has reacted with the X-ray R1 emits electrons, and the electrodes 322a and 322b receive the emitted electrons, thereby generating current in the electrodes 322a and 322b. Here, if a current is detected between a certain electrode 322a and a certain electrode 322b, the X-ray R1 and the semiconductor detector 321 react at the intersection of the electrode 322a and the electrode 322b where the current was detected. It can be determined that

According to the radiation detector 131b as shown in FIG. 15, the detection accuracy of X-rays R1 can be improved.

As shown in FIGS. 3, 4, and 13 to 15, if the structure is such that the position (coordinates) where an X-ray photon is detected within one channel can be specified, ~A structure other than the structure shown in FIG. 15 may be used.

Furthermore, by expanding the radiation detectors 131, 131a, and 131b shown in FIGS. 3, 4, and 13 to 15 and stacking them in the vertical direction, it is also possible to image a plane perpendicular to the radiation incident direction D. . That is, the X-ray R1 images in the yz plane shown in FIGS. 3, 4, and 13 to 15 can be obtained. Further, this structure can also be used by being installed in a direction parallel to the radiation incident direction D.
Further, this structure can also be used by rotating it by 90 degrees with respect to the X-ray irradiation direction, or by rotating it by 90 degrees and arranging a plurality of them in a direction parallel to the X-ray irradiation direction.
Further, the analog-to-digital converter in the analog signal processor 132 may use a flash type or Wilkinson type ADC instead of using the plurality of comparators 403 as shown in FIG. In that case, the processing explained in the first embodiment can be applied to the processing in the radiation signal processing device 140 and the data processing device 150. With such a configuration, the γ-ray R2 can be removed even from a signal in which the γ-ray R2 has piled up.

The present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to having all the configurations described. Furthermore, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace some of the configurations of each embodiment with other configurations.

Further, a part or all of the above-described configurations, functions, units 151 to 156, 158, storage device 703, etc. may be realized in hardware by designing, for example, an integrated circuit. Further, as shown in FIG. 2B, each of the above-described configurations, functions, etc. may be realized by software by a processor such as the CPU 701 interpreting and executing a program for realizing each function. Information such as programs, tables, files, etc. that realize each function can be stored in memory, storage devices such as SSD (Solid State Drive), or IC (Integrated Circuit) cards, in addition to being stored on HD (Hard Disk). , an SD (Secure Digital) card, a DVD (Digital Versatile Disc), or the like.
Furthermore, in each embodiment, control lines and information lines are shown that are considered necessary for explanation, and not all control lines and information lines are necessarily shown in terms of the product. In reality, almost all configurations can be considered interconnected.

1, 1a X-ray measurement device 2 Radiation measurement device 130 Radiation detection device (detection unit)
131 Radiation detector (detection unit)
132 Analog signal processor (signal processing section)
151 Radiation identification section (noise removal section)
153 X-ray photon number distribution acquisition unit (X-ray photon number counting unit)
154 X-ray photon number estimation unit (total X-ray photon number calculation unit)
301 scintillator element 302 optical sensor 321 semiconductor detector 322a electrode (first electrode)
322b electrode (second electrode)
341 Pileup area (first area)
342 Non-pileup area (second area)
403 Comparator device S11 Obtaining the distribution of the number of detected X-ray photons (X-ray photon number counting step)
S12 Estimating the number of X-ray photons detected (X-ray photon number estimation step)
S13 Calculation of total number of X-ray photons by energy (total number of X-ray photons calculation step)
R1 X-rays R2 γ-rays (radiation other than X-rays)
Z,Za X-ray measurement system

Claims (12)

a detection unit extending at least in the direction of the incident axis of the X-ray;
The detection unit distinguishes between a first region that is a pile-up region and a second region that is another region, and counts the number of X-ray photons in the second region. a number counting section;
an X-ray photon number estimation unit that estimates the number of X-ray photons in the first region based on the number of X-ray photons detected in the second region;
a total X-ray photon number calculation unit that totals the number of X-ray photons detected in the second region and the estimated number of X-ray photons in the first region;
An X-ray measuring device comprising: a signal processing unit in which a plurality of threshold values are set and outputs a signal indicating whether or not each of the threshold values has been exceeded for the signal output from the detection unit;
a noise removal unit that removes noise caused by factors other than X-rays based on the signal output from the signal processing unit;
The X-ray measuring device according to claim 1, comprising: The detection unit includes a scintillator element and a light sensor,
The X-ray measuring device according to claim 1, wherein a plurality of the optical sensors are provided on the scintillator element in the direction of the incident axis of the X-rays. The detection unit includes:
The X-ray measurement according to claim 3, wherein a plurality of detection elements, each of which corresponds to one of the scintillator elements, is arranged in the direction of the X-ray incident axis for one of the optical sensors. Device. a signal processing unit in which a plurality of threshold values are set and outputs a signal indicating whether or not each of the threshold values has been exceeded for the signal output from the detection unit;
a noise removal unit that removes noise caused by factors other than X-rays based on the signal output from the signal processing unit;
has
The signal processing section includes:
The X-ray measurement device according to claim 4, wherein the X-ray measurement device is provided for each of the detection elements. The signal processing section includes:
The X-ray measuring device according to claim 5, comprising comparators each having a different threshold value. The detection unit includes:
The X-ray measuring device according to claim 3, wherein one scintillator element is provided with a plurality of the optical sensors. The detection unit includes a semiconductor detector and a plurality of electrodes,
Each of the plurality of electrodes has a length;
A plurality of first electrodes among the plurality of electrodes are provided on one surface of the semiconductor detector so as to be parallel to each other,
Of the surfaces of the semiconductor detector, a second electrode, which is an electrode different from the first electrode, is arranged on a surface opposite to the surface on which the first electrode is provided. The X-ray measuring device according to claim 1, wherein a plurality of second electrodes are provided in different directions, and each of the second electrodes is provided parallel to each other. The X-ray measurement according to claim 1, further comprising a substance identification unit that identifies the substance of the object to be irradiated with the X-rays based on the number of X-ray photons totaled by the total X-ray photon number calculation unit. Device. a detection unit extending at least in the direction of the incident axis of the X-ray;
The detection unit distinguishes between a first region that is a pile-up region and a second region that is another region, and counts the number of X-ray photons in the second region. a number counting section;
an X-ray photon number estimation unit that estimates the number of X-ray photons in the first region based on the number of X-ray photons detected in the second region;
a total X-ray photon number calculation unit that totals the number of X-ray photons detected in the second region and the estimated number of X-ray photons in the first region;
An X-ray measurement system comprising: an X-ray measurement device. Separately from the X-ray measurement device, a radiation measurement device that measures radiation emitted from a radioactive substance is provided,
The X-ray measurement system according to claim 10, further comprising a radiation absorption coefficient calculation unit that calculates a radiation absorption coefficient based on the radiation measured by the radiation measurement device. An X-ray measurement device having a detection section extending at least in the direction of the incident axis of the X-rays,
The detection unit distinguishes between a first region that is a pile-up region and a second region that is another region, and counts the number of X-ray photons in the second region. a number counting step;
estimating the number of X-ray photons in the first region based on the number of X-ray photons detected in the second region;
a step of calculating a total number of X-ray photons, summing the number of X-ray photons detected in the second region and the estimated number of X-ray photons in the first region;
An X-ray measurement method characterized by performing the following.

Images