Signal processing method, signal processing device, and radiation detection device

Abstract

Provided are a signal processing method, a signal processing device, and a radiation detection device for accurately measuring the wave height of a response wave.　The signal processing method includes: generating a first shaped signal by shaping, through a first trapezoidal filter, an output signal outputted from a radiation detector; generating, through a CFD, a CFD wave by subtracting, from the first shaped signal, a signal obtained by delaying the first shaped signal by a prescribed delay time; determining, by using the first shaped signal, whether or not a response wave occurred in response to detection of radiation is included in the output signal; identifying a rise time point of the response wave on the basis of a zero-cross point of the CFD wave when it is determined that the response wave is included in the output signal; identifying, on the basis of the rise time point, a search time period including a signal value necessary for measuring the wave height of the response wave; and measuring the wave height of the response wave by using the search time period.

Description

Signal processing method, signal processing device, and radiation detection device

[0006] ,

[0005] ,

[0001] The present invention relates to a signal processing method, a signal processing device, and a radiation detection device for detecting radiation.

[0002] A radiation detection device that detects radiation such as X-rays includes a radiation detector and a signal processing device that processes a signal output by the radiation detector. The radiation detector outputs a stepped response wave each time radiation is detected. The signal processing device measures the peak height of the response wave included in the signal output by the radiation detector. The peak height of the response wave corresponds to the energy of the radiation. The signal processing device shapes the response wave into a trapezoidal wave, determines that the response wave has been obtained when the signal value included in the trapezoidal wave exceeds a predetermined threshold value, identifies the upper base portion of the trapezoidal wave, and measures the peak height of the response wave by detecting the height of the trapezoidal wave based on the value of the upper base portion. Alternatively, the signal processing device identifies the upper base portion of the trapezoidal wave using the rising threshold value and the falling threshold value of the trapezoidal wave, and measures the peak height of the response wave. Patent Document 1 discloses an example of a technique for measuring the peak height of a response wave.

[0003] International Publication No. 2022 / 162976

[0004] There is a certain time deviation from when the trapezoidal wave rises until it exceeds the threshold value. When the energy of the radiation to be detected is low, the time deviation becomes large, the position of the upper base portion of the trapezoidal wave becomes unclear, a wide search range is set to search for the value of the upper base portion, and the maximum value within the search range is used. Since the search range is wide, there is a risk of measuring the peak height higher than the actual value due to the influence of noise. In the form using the rising threshold value and the falling threshold value, there is a risk of misidentifying the position of the upper base portion and mismeasuring the peak height due to the influence of noise. Thus, when the energy of the radiation is low, it is difficult to accurately identify the position of the upper base portion of the trapezoidal wave, difficult to accurately measure the peak height of the response wave, and difficult to accurately detect the radiation.

[0005] An object of the present invention is to provide a signal processing method, a signal processing device, and a radiation detection device for accurately measuring the peak height of a response wave.

[0006] A signal processing method according to one embodiment of the present invention is characterized by generating a first shaped signal by shaping the output signal output from a radiation detector with a first trapezoidal filter, generating a CFD (Constant Fraction Discriminator) wave by subtracting a signal obtained by delaying the first shaped signal by a predetermined delay time from the first shaped signal, determining whether or not a response wave generated in response to the detection of radiation is included in the output signal using the first shaped signal, identifying the rising time of the response wave based on the zero-crossing point of the CFD wave if it is determined that the response wave is included in the output signal, identifying a search period that includes signal values ​​necessary to measure the wave height of the response wave based on the rising time, and measuring the wave height of the response wave using the search period.

[0007] In one embodiment of the present invention, the output signal from the radiation detector is shaped into a first shaped signal by a first trapezoidal filter, and the presence or absence of a response wave corresponding to the detection of radiation is determined using the first shaped signal. A CFD wave is generated from the first shaped signal, and the rising edge time of the response wave is determined based on the zero-crossing point of the CFD wave. Based on the rising edge time of the response wave, a search period for searching for the wave height of the response wave is determined, and the wave height of the response wave is measured using the search period. Since the zero-crossing point of the CFD wave can be accurately determined, the rising edge time of the response wave can be accurately determined from the zero-crossing point. Therefore, it is possible to accurately determine the search period and measure the wave height of the response wave with high precision.

[0008] A signal processing method according to one embodiment of the present invention is characterized in that the rising edge time is determined by going back a predetermined amount of time from the zero-crossing point of the CFD wave, according to the time constant of the first trapezoidal filter and the delay time.

[0009] In one embodiment of the present invention, the rising edge of the response wave is determined by the time point preceding the zero-crossing point of the CFD wave, depending on the time constant of the first trapezoidal filter and the delay time for generating the CFD wave. The rising edge of the response wave can be accurately determined based on a zero-crossing point that can be accurately identified.

[0010] In a signal processing method according to one embodiment of the present invention, the first trapezoidal filter is characterized in that the holding time, which is the period from when the first shaping signal rises until when it starts to fall, is defined as a time constant, and the delay time is the same length as the holding time of the first trapezoidal filter.

[0011] In one embodiment of the present invention, the delay time is the same length as the holding time of the first trapezoidal filter. Therefore, the rising edge of the response wave is determined by the time obtained by adding the peaking time and holding time of the first trapezoidal filter and moving back from the zero-crossing point of the CFD wave.

[0012] A signal processing method according to one embodiment of the present invention is characterized by generating a second shaped signal by shaping the output signal with a second trapezoidal filter having a longer time constant than the first trapezoidal filter, specifying the search period based on the rising edge time and the time constant of the second trapezoidal filter, and measuring the amplitude of the response wave according to the value of the second shaped signal within the search period.

[0013] In one embodiment of the present invention, a second shaping signal is generated from the output signal by a second trapezoidal filter having a longer time constant than the first trapezoidal filter. A search period is determined based on the time constant of the first trapezoidal filter, and the amplitude of the response wave is measured according to the value of the second shaping signal within the search period. By using the first shaping signal, whose signal value changes rapidly, the presence or absence of a response wave can be determined quickly. By using the second shaping signal, whose signal value changes slowly, it becomes possible to measure the amplitude of the response wave with high accuracy.

[0014] In a signal processing method according to one embodiment of the present invention, the second trapezoidal filter has a peaking time, which is the period during which the second shaping signal is raised, and a holding time, which is the period from when the second shaping signal rises until when it starts to fall, as time constants, and the search period is characterized in that it includes the time elapsed from the rising point to the time obtained by adding half the holding time of the second trapezoidal filter to the peaking time of the second trapezoidal filter.

[0015] In one embodiment of the present invention, the search period is the period that includes the time elapsed from the rise time when the peaking time of the second trapezoidal filter plus half of the holding time has elapsed. The amplitude of the response wave corresponds to the amplitude of the second shaping signal, and the amplitude of the second shaping signal is a value corresponding to the signal value of the upper base portion of the trapezoidal wave included in the second shaping signal. Since the signal value of the upper base portion is included in the defined search period, the amplitude of the response wave can be measured by obtaining a representative value of the signal value included in the search period.

[0016] A signal processing method according to one embodiment of the present invention is characterized in that, when the interval between the rising edges of two response waves determined to be included in the output signal is less than a predetermined period threshold, it is determined that a pileup of multiple response waves is occurring.

[0017] In one embodiment of the present invention, a pileup is determined to have occurred when the interval between the rising times of two response waves is short. When a pileup occurs, it becomes impossible to obtain the correct wave height. By determining whether a pileup has occurred, it is possible to prevent the measurement of an incorrect wave height caused by a pileup.

[0018] A signal processing device according to one embodiment of the present invention comprises: a first trapezoidal filter that shapes an output signal output from a radiation detector into a first shaped signal; a CFD that generates a CFD wave by subtracting a signal obtained by delaying the first shaped signal by a predetermined delay time from the first shaped signal; a determination unit that uses the first shaped signal to determine whether or not a response wave generated in response to the detection of radiation is included in the output signal; an information processing unit that, when the determination unit determines that the output signal includes the response wave, identifies the rising time of the response wave based on the zero-crossing point of the CFD wave, and identifies a search period that includes signal values ​​necessary to measure the wave height of the response wave based on the rising time; and a wave height measuring unit that uses the search period to measure the wave height of the response wave.

[0019] In one embodiment of the present invention, the signal processing device shapes the output signal from the radiation detector into a first shaped signal using a first trapezoidal filter, and determines the presence or absence of a response wave corresponding to the detection of radiation using the first shaped signal. The signal processing device generates a CFD wave from the first shaped signal and identifies the rising edge of the response wave based on the zero-crossing point of the CFD wave. Based on the rising edge of the response wave, the signal processing device identifies a search period for searching for the wave height of the response wave, and measures the wave height of the response wave using the search period. By using the zero-crossing point of the CFD wave, the signal processing device can accurately identify the rising edge of the response wave and accurately identify the search period. Furthermore, the signal processing device can accurately measure the wave height of the response wave using the identified search period.

[0020] A radiation detection device according to one embodiment of the present invention is characterized by comprising: a radiation detector that generates a response wave in response to incident radiation and outputs a signal including the response wave; a signal processing device according to one embodiment of the present invention; and a spectrum generation unit that generates the spectrum of the radiation based on the wave height of the response wave measured by the signal processing device.

[0021] In one embodiment of the present invention, the radiation detection device generates a spectrum of detected radiation based on the pulse height of the response wave measured by the signal processing device. Since the pulse height of the response wave is measured with high precision, the energy of the radiation can be obtained with high precision, and a high-precision radiation spectrum can be obtained.

[0022] The present invention offers excellent advantages, such as the ability to accurately measure the amplitude of the response wave output by a radiation detector.

[0023] This is a block diagram showing an example of the functional configuration of a radiation detection device. This is a block diagram showing the functional configuration of a radiation detector and a signal processing device. This is a schematic graph showing an example of an output signal including a response wave. This is a schematic graph showing an example of an output signal, a first shaping signal, and a second shaping signal. This is a schematic graph showing an example of a CFD wave. This is a schematic graph showing another example of a CFD wave. This is a schematic graph showing an example of a search period. This is a schematic graph showing another example of a search period. This is a schematic graph showing another example of a search period. This is a schematic graph showing another example of a search period. This is a schematic graph showing another example of a search period. This is a schematic graph showing another example of a search period. This is a schematic graph showing another example of a search period. This is a flowchart showing an example of the processing procedure performed by the signal processing device. This is a block diagram showing an example of the functional configuration of an information processing device according to Embodiment 2.

[0024] The present invention will be described in detail below based on the drawings illustrating its embodiments. <Embodiment 1> Figure 1 is a block diagram showing an example of the functional configuration of a radiation detection device 10. The radiation detection device 10 is, for example, a fluorescent X-ray analyzer. The radiation detection device 10 includes an irradiation unit 42 that irradiates a sample 52 with radiation such as an electron beam or X-rays, a sample stage 51 on which the sample 52 is placed, and a radiation detector 1. Radiation is irradiated from the irradiation unit 42 to the sample 52, and radiation such as fluorescent X-rays is generated in the sample 52, and the generated radiation is incident on the radiation detector 1. The radiation detector 1 detects the incident radiation. In the figure, radiation is indicated by arrows. Note that the radiation detection device 10 may also be configured to hold the sample 52 by a method other than placing it on the sample stage 51.

[0025] The radiation detector 1 includes a radiation detection element 11 and a preamplifier 12. The radiation detector 1 is connected to a signal processing device 2 and a voltage application unit 43 that applies the voltage necessary for radiation detection to the radiation detection element 11. An analysis unit 3 is connected to the signal processing device 2. A display unit 44, such as a liquid crystal display or an EL display (Electroluminescent Display), is connected to the analysis unit 3. The signal processing device 2, the analysis unit 3, the voltage application unit 43, and the irradiation unit 42 are connected to a control unit 41. The control unit 41 controls the operation of the signal processing device 2, the analysis unit 3, the voltage application unit 43, and the irradiation unit 42. For example, the control unit 41 is configured using a computer having a calculation unit and memory. The control unit 41 may also be configured to receive user input and control each part of the radiation detection device 10 according to the received input.

[0026] Figure 2 is a block diagram showing the functional configuration of the radiation detector 1 and the signal processing device 2. In Figure 2, the signal flow is indicated by arrows. The radiation detection element 11 generates an electric charge corresponding to the energy of the radiation incident on the radiation detector 1 and outputs a current signal corresponding to the generated charge. For example, the radiation detection element 11 is a semiconductor radiation detection element such as a silicon drift type radiation detection element. The preamplifier 12 converts the current signal output by the radiation detection element 11 into a voltage signal and generates a response wave in response to the detection of radiation. In this embodiment, the response wave is a step wave in which the signal value increases in a step-like manner when radiation is detected. The radiation detector 1 outputs a signal that includes the response wave generated by the preamplifier 12. In this way, the radiation detector 1 detects the incident radiation. The signal output by the radiation detector 1 is called the output signal. The output signal is continuously output from the radiation detector 1, and the response wave is included in the output signal when radiation is detected.

[0027] Figure 3 is a schematic graph showing an example of an output signal including a response wave. In the figure, the horizontal axis represents time, and the vertical axis represents the signal value. Each time radiation is incident on the radiation detection element 11 and an event occurs in which radiation is detected, the radiation detector 1 outputs a response wave, which is a step wave in which the signal value increases in a step-by-step manner. One response wave is generated in response to one event, in which the signal value increases in a step-by-step manner. Although Figure 3 shows an example of a response wave in which the signal value increases instantaneously, in reality, a blunted response wave is obtained in which the increase in the signal value takes some time. If multiple events occur, an output signal containing multiple response waves is output. Each time an event occurs, the signal value of the output signal increases. The height of the step in which the signal value increases is defined as the wave height of the response wave. The wave height of the response wave corresponds to the energy of the radiation detected by the radiation detector 1. The radiation detection device 10 determines the energy of the radiation according to the wave height of the response wave.

[0028] The signal output by the radiation detector 1 is input to the signal processing device 2. The signal processing device 2 executes a signal processing method. As shown in Figure 2, the signal processing device 2 includes an A / D (analog / digital) conversion unit 21. The A / D conversion unit 21 receives the output signal from the radiation detector 1 and performs A / D conversion on the output signal. The A / D conversion unit 21 receives a continuous output signal, samples the output signal at predetermined time intervals, and performs A / D conversion on the values ​​obtained by the sampling to generate discrete signal values. The A / D conversion unit 21 generates the A / D converted output signal by sequentially generating signal values ​​at predetermined time intervals. The A / D converted output signal is a digital signal consisting of a plurality of discrete signal values.

[0029] The A / D conversion unit 21 is connected to a first trapezoidal filter 221 and a second trapezoidal filter 231. The first trapezoidal filter 221 and the second trapezoidal filter 231 receive the A / D converted output signal from the A / D conversion unit 21. Between the A / D conversion unit 21 and the first trapezoidal filter 221 and the second trapezoidal filter 231, a conversion unit that converts the signal to cancel out waveform distortion due to signal delay and a noise reduction unit that removes noise from the signal may also be connected.

[0030] The first trapezoidal filter 221 and the second trapezoidal filter 231 are digital filters that generate a shaped signal from the input signal by converting the step-like staircase wave contained in the input signal into a trapezoidal wave. That is, the response wave contained in the output signal is converted into a trapezoidal wave. The signal shaped by the first trapezoidal filter 221 is called the first shaped signal, and the signal shaped by the second trapezoidal filter 231 is called the second shaped signal. The first trapezoidal filter 221 and the second trapezoidal filter 231 have defined time constants: a peaking time (PT), which is the period during which the trapezoidal wave rises, and a holding time (HT), which is the period from when the trapezoidal wave rises until the falling edge begins. The PT and HT of the first trapezoidal filter 221 and the second trapezoidal filter 231 are different from each other.

[0031] Figure 4 is a schematic graph showing examples of the output signal, the first shaped signal, and the second shaped signal. The top row shows the output signal including the response wave, the middle row shows the first shaped signal, and the bottom row shows the second shaped signal. In the figure, the horizontal axis represents time, and the vertical axis represents the signal value. The first trapezoidal filter 221 and the second trapezoidal filter 231 shape the output signal by differentiating the output signal. The trapezoidal wave rises in accordance with the rising edge of the step-like response wave. The trapezoidal waves contained in the first shaped signal and the second shaped signal rise over time PT, maintain approximately the signal value over time HT, and fall over time PT.

[0032] The peak height (PT) of the first trapezoidal filter 221 is shorter than that of the second trapezoidal filter 231, and the peak height (HT) of the first trapezoidal filter 221 is also shorter than that of the second trapezoidal filter 231. Therefore, in response to the response wave, the first shaped signal rises and falls rapidly. In contrast, the second shaped signal rises and falls more slowly. Because the first shaped signal rises rapidly, it is suitable for determining the presence or absence of a response wave. Because the second shaped signal rises over a sufficient period of time in response to the response wave, it better reflects the characteristics of the response wave, and the amplitude of the second shaped signal is a value corresponding to the waveform of the response wave. Therefore, the signal processing device 2 measures the amplitude of the response wave by measuring the amplitude of the second shaped signal.

[0033] The wave height of the second shaping signal is the wave height of the trapezoidal wave contained in the second shaping signal, and the wave height of the trapezoidal wave is obtained from the signal value of the upper base portion of the trapezoidal wave. The upper base portion of the trapezoidal wave is the period from a point PT after the rising edge of the trapezoidal wave until HT has elapsed. The rising edge of the trapezoidal wave is equivalent to the rising edge of the response wave. If the rising edge of the response wave can be accurately determined, the upper base portion of the trapezoidal wave can be accurately determined using the rising edge as a reference and the PT and HT of the second trapezoidal filter 231. If the upper base portion of the trapezoidal wave can be accurately determined, the wave height of the response wave can be measured based on the signal value contained in the upper base portion.

[0034] The first trapezoidal filter 221 is connected to a determination unit 24 and a first delay unit 222. The first trapezoidal filter 221 inputs a first shaped signal, which is a shaped output signal, to the determination unit 24 and the first delay unit 222. The determination unit 24 uses the first shaped signal to determine whether or not a response wave is included in the output signal. More specifically, the determination unit 24 compares the first shaped signal with a predetermined threshold, and determines that a response wave is included in the output signal if the signal value of the first shaped signal exceeds the threshold. The determination unit 24 determines that a response wave is not included in the output signal if the signal value of the first shaped signal does not exceed the threshold. For example, the determination unit 24 is configured as an FPGA (Field Programmable Gate Array).

[0035] The first delay unit 222 delays the first shaping signal by a predetermined delay time. The delay time of the first delay unit 222 is, for example, HT of the first trapezoidal filter 221. The first delay unit 222 is configured using a delay circuit. A CFD (Constant Fraction Discriminator) 223 is connected to the first trapezoidal filter 221 and the first delay unit 222. The first trapezoidal filter 221 inputs the first shaping signal to the CFD 223, and the first delay unit 222 inputs the delayed first shaping signal to the CFD 223. The CFD 223 generates a CFD wave by subtracting the delayed first shaping signal from the first shaping signal.

[0036] Figure 5 is a schematic graph showing an example of a CFD wave. In the figure, the horizontal axis represents time, and the vertical axis represents the signal value. The first shaped signal is shown by a dashed line, the inverted signal obtained by reversing the sign of the delayed first shaped signal is shown by a dashed line, and the CFD wave is shown by a solid line. CFD 223 generates the inverted signal by multiplying the delayed first shaped signal by minus 1. Furthermore, CFD 223 generates the CFD wave by adding the first shaped signal and the inverted signal. Figure 5 shows an example where the delay time of the first delay unit 222 is HT of the first trapezoidal filter 221.

[0037] Figure 6 is a schematic graph showing other examples of CFD waves. The upper part of Figure 6 shows an example where the delay time of the first delay unit 222 is longer than the HT of the first trapezoidal filter 221. The CFD 223 may also be generated by multiplying the first shaping signal or inverted signal by a predetermined coefficient and then adding them together. The middle part of Figure 6 shows an example where the CFD wave is generated by multiplying the first shaping signal or inverted signal by a coefficient of "-1". The lower part of Figure 6 shows an example where the CFD wave is generated by multiplying the first shaping signal by a coefficient of "+1 / 2" and the inverted signal by a coefficient of "+2".

[0038] A zero-crossing point exists in the CFD wave because a delayed trapezoidal wave is subtracted from the trapezoidal wave contained in the first shaping signal. The zero-crossing point is the point in time when the signal value of the CFD wave becomes zero during the process of changing from a positive value to a negative value. The zero-crossing point may also be the point in time when the signal value of the CFD wave becomes zero during the process of changing from a negative value to a positive value. If there is a period during which the signal value remains zero, the zero-crossing point is defined as the midpoint of that period. The position of the zero-crossing point can be precisely determined based on the signal value of the CFD wave. Because the trapezoidal wave has a waveform corresponding to the PT and HT of the first trapezoidal filter 221, the rising edge of the first shaping signal is a predetermined time point backward from the zero-crossing point, corresponding to the time constant of the first trapezoidal filter 221 and the delay time of the first delay unit 222.

[0039] For example, in the example shown in Figure 5 and the upper example in Figure 6, the rising edge of the first shaping signal is the point where "delay time + (2PT + HT - delay time) / 2" is back from the zero-crossing point. The same applies to the example shown in the middle example in Figure 6. In the example shown in Figure 5, since the delay time is HT of the first trapezoidal filter 221, the rising edge of the first shaping signal is the point where "PT + HT" is back from the zero-crossing point. In the example shown in the lower example in Figure 6, the rising edge of the first shaping signal is the point where "delay time + (2PT + HT - delay time) / 5" is back from the zero-crossing point. The rising edge of the first shaping signal is equivalent to the rising edge of the response signal. Therefore, the rising edge of the response signal can be determined based on the zero-crossing point of the CFD wave. Since the zero-crossing point can be accurately determined, the rising edge of the response signal can be accurately determined.

[0040] The determination unit 24 and the CFD 223 are connected to an information processing unit 25. For example, the information processing unit 25 is configured as an FPGA. The information processing unit 25 may also be configured using a processor. When the determination unit 24 determines that the response wave is included in the output signal, it inputs information to the information processing unit 25 indicating that the response wave is included in the output signal. The CFD 223 inputs the CFD wave to the information processing unit 25.

[0041] The information processing unit 25 identifies the rising edge of the response wave when it receives information from the determination unit 24 indicating that the response wave is included in the output signal. The information processing unit 25 identifies the zero-crossing point of the CFD wave and sets the rising edge of the response wave to a point in time that is a predetermined amount of time backward from the zero-crossing point, corresponding to the time constant of the first trapezoidal filter 221 and the delay time of the first delay unit 222. If the absolute value of the coefficient used in the CFD 223 is "1" and the delay time of the first delay unit 222 is HT of the first trapezoidal filter 221, the information processing unit 25 sets the rising edge of the response wave to a point in time that is the sum of PT and HT of the first trapezoidal filter 221, from the zero-crossing point.

[0042] Furthermore, the information processing unit 25 identifies a search period for searching for the signal value necessary to measure the wave height of the response wave, based on the rising edge time of the response wave. The search period includes the signal value necessary to measure the wave height of the response wave. As mentioned above, the wave height of the response wave is obtained by measuring the wave height of the second shaping signal, and the wave height of the second shaping signal is a value corresponding to the signal value of the upper base portion of the trapezoidal wave included in the second shaping signal. For example, a representative value of the signal value included in the upper base portion of the trapezoidal wave can be used as the wave height of the second shaping signal. The representative value is the maximum value, average value, or median value. For example, the signal value located in the center of the upper base portion of the trapezoidal wave can be used as the wave height of the second shaping signal. The information processing unit 25 defines the search period as the period including the time corresponding to the center of the upper base portion of the trapezoidal wave. The period including the time corresponding to the center of the upper base portion of the trapezoidal wave is the period including the time elapsed from the rising edge time of the response wave to the time obtained by adding HT to PT of the second trapezoidal filter 231.

[0043] Figure 7 is a schematic graph showing an example of the search period. The search period is defined as the period from the rising edge to the time obtained by adding PT and HT of the second trapezoidal filter 231. The search period includes the time corresponding to the center of the upper base of the trapezoidal wave. Figures 8A, 8B, 8C, 9A, 9B, 9C, and 9D are schematic graphs showing other examples of the search period. The search period shown in Figure 8A is defined as the period from the rising edge to the time obtained by PT until HT has elapsed. The search period shown in Figure 8B is defined as the search period shown in Figure 7 extended by a predetermined time. The search period shown in Figure 8C is defined as the search period shown in Figure 8A, with the start time moved forward by a predetermined time and the end time extended by a predetermined time.

[0044] The search period shown in FIG. 9A is a period obtained by extending the search period shown in FIG. 8A by a predetermined time. The search period shown in FIG. 9B is a period obtained by advancing the end point of the search period shown in FIG. 7 by a predetermined time. The search period shown in FIG. 9C is a period in which the start point is delayed by a predetermined time and the end point is advanced by a predetermined time as compared with the search period shown in FIG. 8A. The predetermined time in the examples shown in FIGS. 9B and 9C is shorter than half of HT. The search period shown in FIG. 9D includes only the time point corresponding to the center of the upper base portion of the trapezoidal wave. Any search period includes the time point corresponding to the center of the upper base portion of the trapezoidal wave. Based on the rising time of the response wave and the time constant of the second trapezoidal filter 231, the position of the upper base portion of the trapezoidal wave can be accurately specified. Therefore, the search period including the time point corresponding to the center of the upper base portion of the trapezoidal wave can be accurately specified. The information processing unit 25 measures the wave height of the response wave by using the representative value of the signal values included in the specified search period as the wave height of the response wave.

[0045] Further, the information processing unit 25 determines whether or not a pile-up in which a plurality of response waves overlap occurs based on the rising time of the response wave. The information processing unit 25 stores the rising time of the specified response wave and calculates the interval between the rising time of the previous response wave and the rising time of the latest response wave. The information processing unit 25 determines that a pile-up has occurred when the calculated interval is less than a predetermined period threshold. The information processing unit 25 may determine that a pile-up has occurred when the calculated interval is less than or equal to a predetermined period threshold. When a pile-up occurs, the wave height of the response wave changes and the correct wave height cannot be obtained. The signal processing device 2 does not measure the wave height of the response wave when a pile-up occurs. For this reason, it is possible to prevent measuring an incorrect wave height due to a pile-up.

[0046] A second trapezoidal filter 231 is connected to a second delay unit 232. The second trapezoidal filter 231 inputs a second shaped signal obtained by shaping an output signal to the second delay unit 232. The second delay unit 232 delays the second shaped signal by a predetermined delay time. The delay time of the second delay unit 232 is a time exceeding the time required for the information processing unit 25 to specify the search period. The second delay unit 232 is configured using a delay circuit.

[0047] A wave height measurement unit 26 is connected to the information processing unit 25 and the second delay unit 232. For example, the wave height measurement unit 26 is configured by an FPGA. The information processing unit 25 inputs the specified search period to the wave height measurement unit 26. The second delay unit 232 inputs the delayed second shaped signal to the wave height measurement unit 26. The wave height measurement unit 26 measures the wave height of the response wave by measuring the wave height of the second shaped signal using the search period. The wave height measurement unit 26 acquires a representative value of the signal values of the second shaped signal within the search period, and uses the acquired value as the value of the wave height of the response wave. For example, the wave height measurement unit 26 acquires the maximum value of the signal values of the second shaped signal within the search period as the representative value, and uses the acquired value as the value of the wave height of the response wave. For example, the wave height measurement unit 26 calculates the average value or the median value of the signal values of the second shaped signal within the search period as the representative value, and uses the calculated value as the value of the wave height of the response wave.

[0048] When the information processing unit 25 determines that pile-up has occurred, it does not input the specified search period to the wave height measurement unit 26. Alternatively, when the information processing unit 25 determines that pile-up has occurred, it inputs information indicating that pile-up has occurred to the wave height measurement unit 26. The wave height measurement unit 26 cannot measure the wave height of the response wave when the search period is not input. Alternatively, the wave height measurement unit 26 aborts the measurement of the wave height of the response wave when information indicating that pile-up has occurred is input. In this way, the signal processing device 2 does not measure the wave height of the response wave when pile-up occurs.

[0049] A counting unit 27 is connected to the wave height measurement unit 26. For example, the counting unit 27 is a multi-channel analyzer. The wave height measurement unit 26 inputs the measured wave height of the response wave to the counting unit 27. The counting unit 27 counts the response waves for each wave height. Specifically, each time the wave height of a response wave is input to the counting unit 27, it increments the count number associated with the input wave height by 1. The counting unit 27 may be configured to count the response waves for all wave heights, or it may be configured to count the response waves only for specific wave heights. In this way, the response waves are counted for each wave height.

[0050] The signal processing unit 2 outputs data showing the relationship between the wave height of the response wave and the count number counted by the counting unit 27. The count number corresponds to the number of times the radiation detector 1 detected radiation having energy corresponding to the wave height of the response wave. The analysis unit 3 receives the data output by the signal processing unit 2 as input. The analysis unit 3 is configured using a computer having a calculation unit and memory. The analysis unit 3 and the control unit 41 may be configured using the same computer.

[0051] The analysis unit 3 performs a process to generate a spectrum of radiation detected by the radiation detector 1 based on the relationship between the wave height and count of the response wave. The analysis unit 3 corresponds to the spectrum generation unit. The spectrum represents the relationship between the energy of the radiation corresponding to the wave height and the count. The analysis unit 3 may further perform further processing, such as elemental analysis of the sample 52, based on the generated radiation spectrum. For example, the radiation detector 1 detects fluorescent X-rays, and the analysis unit 3 performs qualitative or quantitative analysis of the elements contained in the sample 52 based on the fluorescent X-ray spectrum. The display unit 44 displays the spectrum generated by the analysis unit 3 and the analysis results performed by the analysis unit 3.

[0052] The following describes the processing flow performed by the radiation detection device 10. Figure 10 is a flowchart showing an example of the processing procedure performed by the signal processing device 2. Hereinafter, steps will be abbreviated as S. When radiation is incident on the radiation detection element 11, the radiation detector 1 generates a response wave having a wave height corresponding to the energy of the radiation and outputs an output signal including the response wave. The radiation detector 1 also outputs an output signal even when no radiation is incident on the radiation detection element 11. The signal processing device 2 receives the output signal from the radiation detector 1 (S1). The A / D conversion unit 21 performs A / D conversion on the input output signal (S2). The A / D converted output signal consists of a plurality of discrete signal values. The A / D conversion unit 21 inputs the A / D converted output signal to the first trapezoidal filter 221 and the second trapezoidal filter 231.

[0053] The first trapezoidal filter 221 shapes the output signal into a first shaped signal and inputs the first shaped signal to the determination unit 24, the first delay unit 222, and the CFD 223. The first delay unit 222 inputs the delayed first shaped signal to the CFD 223. The CFD 223 generates a CFD wave (S3). The CFD 223 inputs the CFD wave to the information processing unit 25.

[0054] The determination unit 24 uses the first shaping signal to determine whether or not the response wave is included in the output signal (S4). S3 and S4 may be executed in parallel. If the response wave is not included in the output signal (S4: NO), the signal processing device 2 terminates processing without counting the response wave. If the determination unit 24 determines that the response wave is included in the output signal (S4: YES), it inputs information indicating that the response wave is included in the output signal to the information processing device 25.

[0055] The information processing unit 25 identifies the zero-crossing point of the CFD wave (S5) and, based on the zero-crossing point, identifies the rising edge time of the response wave (S6). Next, the information processing unit 25 identifies a search period for searching the wave height of the response wave based on the rising edge time of the response wave (S7). The information processing unit 25 determines, based on the interval between the rising edge times of the response waves, whether or not a pileup of multiple response waves is occurring (S8). If the information processing unit 25 determines that a pileup has occurred (S8: YES), the signal processing unit 2 terminates processing without counting the response waves. At this time, the signal processing unit 2 either inputs information indicating that a pileup has occurred to the wave height measurement unit 26, or does not input the identified search period to the wave height measurement unit 26. The information processing unit 25 may execute S8 before S7.

[0056] If no pile-up occurs (S8: NO), the information processing unit 25 inputs the specified search period to the wave height measurement unit 26, and the wave height measurement unit 26 uses the search period to measure the wave height of the response wave (S9). The second trapezoidal filter 231 shapes the output signal into a second shaped signal, inputs the second shaped signal to the second delay unit 232, and the second delay unit 232 inputs the delayed second shaped signal to the wave height measurement unit 26. The wave height measurement unit 26 measures the wave height of the response wave by measuring the wave height of the second shaped signal using the search period. The wave height measurement unit 26 inputs the measured wave height of the response wave to the count unit 27. The count unit 27 counts the response waves by wave height (S10). After S10 is completed, the signal processing device 2 terminates processing.

[0057] The signal processing device 2 repeatedly executes the processes S1 to S10. The signal processing device 2 outputs data showing the relationship between the wave height of the response wave and the count number counted by the counting unit 27. The analysis unit 3 receives the data output by the signal processing device 2 as input and generates the spectrum of the radiation detected by the radiation detector 1 based on the input data.

[0058] As described in detail above, the signal processing device 2 shapes the output signal from the radiation detector 1 into a first shaped signal using the first trapezoidal filter 221, generates a CFD wave from the first shaped signal, identifies the zero-crossing point of the CFD wave, and identifies the rising edge time of the response wave based on the zero-crossing point. The signal processing device 2 also identifies a search period for searching the wave height of the response wave based on the rising edge time of the response wave, measures the wave height of the response wave using the search period, and counts the response waves according to their respective wave heights. Since the zero-crossing point of the CFD wave can be accurately identified, the rising edge time of the response wave can be accurately identified from the zero-crossing point using the delay time obtained by delaying the first shaped signal to generate the CFD wave and the PT of the first trapezoidal filter 221.

[0059] In this embodiment, the rising edge of the response wave is determined without using a signal threshold. Compared to conventional techniques that utilize a signal threshold, the rising edge of the response wave is determined more accurately. Because the rising edge of the response wave is accurate, it is possible to accurately determine the position of the upper base portion of the trapezoidal wave included in the second shaping signal. Therefore, the search period can be accurately determined so that the time corresponding to the center of the upper base portion of the trapezoidal wave is reliably included. For example, the search period can be set narrower than in conventional techniques while still including the time corresponding to the center of the upper base portion of the trapezoidal wave. Because the search period is accurate, it is possible to measure the wave height of the response wave with high precision, and the energy of the radiation detected by the radiation detector 1 can be measured with high precision. By measuring the energy of the radiation with high precision, a high-precision radiation spectrum can be obtained.

[0060] Since the rising edge of the response wave can be determined without using a signal threshold, it is possible to accurately measure the wave height of the response wave even when the radiation energy is low. Therefore, the radiation detection device 10 can accurately measure the wave height of the response wave and accurately measure the energy of the detected radiation, even when the energy of the radiation to be detected is low. Consequently, the radiation detection device 10 can accurately detect low-energy radiation.

[0061] The signal processing device 2 uses a first trapezoidal filter 221 with short PT and HT, and a second trapezoidal filter 231 with long PT and HT. The signal processing device 2 uses the first shaping signal generated by the first trapezoidal filter 221 to determine whether or not a response wave is included in the output signal and to specify the search period. The signal processing device 2 also uses the second shaping signal generated by the second trapezoidal filter 231 to measure the amplitude of the response wave. Since the signal value of the first shaping signal changes rapidly, it is possible to quickly determine the presence or absence of a response wave by using the first shaping signal. Since the signal value of the second shaping signal changes slowly, the amplitude of the second shaping signal corresponds to the amplitude of the response wave. Therefore, by measuring the amplitude of the second shaping signal and using that as the amplitude of the response wave, it is possible to accurately measure the amplitude of the response wave.

[0062] In Embodiment 1, a configuration using a first trapezoidal filter 221 and a second trapezoidal filter 231 was shown, but the signal processing device 2 may also use a configuration using only one type of trapezoidal filter. For example, the signal processing device 2 does not include a second trapezoidal filter 231 and a second delay unit 232, and the information processing unit 25 specifies a search period corresponding to the PT and HT of the first trapezoidal filter 221, and the wave height measurement unit 26 measures the wave height of the response wave by measuring the wave height of the first shaping signal. Even in this configuration, the signal processing device 2 can specify the search period more accurately than in the conventional configuration and measure the wave height of the response wave.

[0063] <Embodiment 2> In Embodiment 2, the information processing unit 25 executes processing using a computer program. Figure 11 is a block diagram showing an example of the functional configuration of the information processing unit 25 according to Embodiment 2. The information processing unit 25 has an arithmetic unit 251 and a memory 252. The arithmetic unit 251 is a processor and is configured using, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or a multi-core CPU. The arithmetic unit 251 may be configured using a quantum computer. The memory 252 is a non-volatile memory. The memory 252 stores a computer program 253. The computer program 253 is read from a recording medium 250 such as an optical disc or portable memory that stores the computer program 253 by a recording device (not shown) and written to the memory 252, thereby being stored in the memory 252. The arithmetic unit 251 executes the necessary processing in the information processing unit 25 according to the computer program 253. The computer program 253 may be a computer program product. The memory 252 may store data necessary for processing.

[0064] The arithmetic unit 251 performs the necessary processing for the information processing unit 25 in Embodiment 1 by executing information processing according to the computer program 253. In this way, the information processing unit 25 is realized. The configuration and functions of the parts of the radiation detection device 10 other than the signal processing unit 2 are the same as in Embodiment 1. The configuration and functions of the parts of the signal processing unit 2 other than the information processing unit 25 are the same as in Embodiment 1. The signal processing unit 2 and the radiation detection device 10 perform the same processing as in Embodiment 1.

[0065] In Embodiment 2, the signal processing device 2 repeatedly executes the processes S1 to S10. The signal processing device 2 outputs data showing the relationship between the wave height of the response wave and the count, and the analysis unit 3 receives the data output by the signal processing device 2 as input and generates the spectrum of the radiation detected by the radiation detector 1 based on the input data. In Embodiment 2, as well, the signal processing device 2 can accurately identify the rising time of the response wave included in the output signal from the radiation detector 1 by utilizing the zero-crossing point of the CFD wave. Therefore, similar to Embodiment 1, the signal processing device 2 can accurately identify the search period for searching for the wave height of the response wave and measure the wave height of the response wave with high accuracy. Thus, in Embodiment 2 as well, the radiation detection device 10 can accurately detect low-energy radiation.

[0066] In addition to embodiments 1 and 2, the radiation detection device 10 may be configured such that some or all of the functions of the signal processing device 2 described in embodiments 1 and 2 are implemented by a computer that performs processing according to a computer program. For example, the radiation detection device 10 may be configured such that some or all of the processing performed by the signal processing device 2 in embodiments 1 and 2 is performed by an analysis unit 3 configured by a computer. For example, the signal processing device 2 may not have a counting unit 27, and the analysis unit 3 may perform the processing of counting response waves by wave height.

[0067] In the embodiments described above, a configuration was shown in which radiation is irradiated onto the sample 52 and radiation generated from the sample 52 is detected. However, the radiation detection device 10 may also be configured to detect radiation that has been transmitted through or reflected by the sample 52. The radiation detection device 10 may also be configured to scan the sample 52 with radiation by changing the direction of the radiation. The radiation detection device 10 may also be configured to irradiate a moving sample 52 with radiation. The radiation detection device 10 may also be configured without an irradiation unit 42, a sample stage 51, or a display unit 44. In the embodiments described above, a configuration in which the radiation detection element 11 is a semiconductor radiation detection element was shown. However, the radiation detection element 11 may be an element other than a semiconductor radiation detection element, as long as it is possible to output a response wave having a pulse height corresponding to the energy of the radiation.

[0068] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. That is, embodiments obtained by combining technical means that have been appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

[0069] The matters described in each embodiment can be combined with each other. Furthermore, the independent and dependent claims described in the claims can be combined with each other in any combination, regardless of the form of reference. Moreover, although the claims use a form in which claims referencing two or more other claims (multi-claim form), they are not limited to this. A form in which multi-claims referencing at least one multi-claim (multi-multi-claim) may also be used.

[0070] 1 Radiation detector 10 Radiation detection device 11 Radiation detection element 2 Signal processing device 221 First trapezoidal filter 223 CFD 24 Judgment unit 25 Information processing unit 26 Wave height measurement unit 27 Counting unit 231 Second trapezoidal filter 3 Analysis unit (spectrum generation unit) 42 Irradiation unit 52 Sample

Claims

1. A signal processing method characterized by: generating a first shaped signal by shaping the output signal output from a radiation detector with a first trapezoidal filter; generating a CFD (Constant Fraction Discriminator) wave by subtracting a signal obtained by delaying the first shaped signal by a predetermined delay time from the first shaped signal; determining whether or not a response wave generated in response to the detection of radiation is included in the output signal using the first shaped signal; identifying the rising time of the response wave based on the zero-crossing point of the CFD wave if it is determined that the response wave is included in the output signal; identifying a search period that includes signal values ​​necessary to measure the wave height of the response wave based on the rising time; and measuring the wave height of the response wave using the search period.

2. The signal processing method according to claim 1, characterized in that the rising edge time is identified as the point in time obtained by going back a predetermined amount of time from the zero-crossing point of the CFD wave according to the time constant of the first trapezoidal filter and the delay time.

3. The signal processing method according to claim 1 or 2, characterized in that the first trapezoidal filter has a time constant defined as a holding time, which is the period from when the first shaping signal rises until when it starts to fall, and the delay time is the same length as the holding time of the first trapezoidal filter.

4. A signal processing method according to any one of claims 1 to 3, characterized in that a second shaped signal is generated by shaping the output signal with a second trapezoidal filter having a longer time constant than the first trapezoidal filter; the search period is determined based on the rising time and the time constant of the second trapezoidal filter; and the amplitude of the response wave is measured according to the value of the second shaped signal within the search period.

5. The signal processing method according to claim 4, characterized in that the second trapezoidal filter has a peaking time which is the period during which the second shaping signal is raised, and a holding time which is the period from when the second shaping signal rises until the falling edge begins, and the search period is the period that includes the time elapsed from the rising edge to the peaking time of the second trapezoidal filter plus half of the holding time of the second trapezoidal filter.

6. The signal processing method according to any one of claims 1 to 5, characterized in that it is determined that a pileup of multiple response waves is occurring when the interval between the rising edges of two response waves determined to be included in the output signal is less than a predetermined period threshold.

7. A signal processing device comprising: a first trapezoidal filter that shapes an output signal output from a radiation detector into a first shaped signal; a CFD that generates a CFD wave by subtracting a signal obtained by delaying the first shaped signal by a predetermined delay time from the first shaped signal; a determination unit that uses the first shaped signal to determine whether or not a response wave generated in response to the detection of radiation is included in the output signal; an information processing unit that, when the determination unit determines that the output signal includes the response wave, identifies the rising time of the response wave based on the zero-crossing point of the CFD wave, and identifies a search period that includes signal values ​​necessary to measure the wave height of the response wave based on the rising time; and a wave height measuring unit that uses the search period to measure the wave height of the response wave.

8. A radiation detection device comprising: a radiation detector that generates a response wave in response to incident radiation and outputs a signal including the response wave; a signal processing device according to claim 7; and a spectrum generation unit that generates a spectrum of radiation based on the wave height of the response wave measured by the signal processing device.

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