Processing device, system, X-ray measurement method, and recording medium

Abstract

The present invention provides a processing device, a system, an X-ray measurement method and a recording medium, which can reduce the influence of count omission even at a high count rate that cannot be covered by the existing method. The processing device comprises: a storage unit (220) that counts the pulse signal of the incident X-ray through a photon counting semiconductor detector and stores the read output value; and a calculation unit (230) that calculates the count value based on the read output value, and the calculation unit (230) uses a model in which the apparent time constant of the pulse signal decreases monotonically with respect to the increase of the pulse detection rate for exposure. In such a model, the corresponding apparent time constant can be obtained regardless of how high the count rate is. As a result, the influence of count omission can be reduced even at a high count rate that cannot be covered by the existing method.

Description

Technical Field

[0001] The present invention relates to a processing device, a system, an X-ray measuring method and a recording medium based on a photon counting type semiconductor detector. Background Art

[0002] Photon counting semiconductor detectors used in radiation measurement measure the intensity of X-rays by counting the number of times the intensity of pulse signals detected within a given time exceeds a threshold as the number of pulse signals. However, if the next pulse signal is generated when the intensity of a pulse signal exceeds the threshold, the pulse signal cannot be counted, resulting in missed counts. When the intensity of X-rays is too strong, missed counts occur frequently, and as a result, the measured X-ray intensity is estimated to be lower than the actual X-ray intensity.

[0003] As a method of reducing the influence of such count omissions, a method of correcting the measured count value is being studied (for example, Patent Document 1). In addition, a method of counting pulses during measurement so that the count value is close to the true count is also considered (for example, Patent Document 2).

[0004] Patent document 1 discloses a radiation measuring device, which includes a wave height discriminator 3 and a signal channel wave height analyzer 4 that output a digital pulse signal when an analog pulse signal output by a radiation detector 1 satisfies a given condition. The radiation measuring device described in Patent document 1 counts the digital pulse signals output from the first counter 5 and the second counter 6, respectively, and outputs count values ​​M and P. The operator 7 refers to the count omission correction tables 81 and 82 stored in the memory 8 for the count rates m and p obtained from the count values ​​M and P, and performs count omission correction and miscount correction. The correction table uses a virtual signal pulse generated experimentally to make double pulses close to obtain the decomposition time t1 of the accumulation and the approach time t2 that generates miscounts, and obtains the first correction count rate n and the second correction count rate (nq).

[0005] Patent document 2 discloses a method and apparatus for photon counting imaging with high ratio counting performance, wherein the high ratio counting performance is improved by using an immediate re-triggering capability with an adjustable dead time in the cells of the detector array. That is, the method and apparatus described in Patent document 2 counts the number of dead time intervals of a given amplitude contained in the time when the signal pulse exceeds the threshold only after the signal pulse initially exceeds the threshold, and regards it as the number of photons that arrived during the time when the signal pulse exceeds the threshold, thereby reducing the influence of missed counts.

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2012-013563

[0008] Patent Document 2: JP 2014-527162

[0009] However, in the radiation measuring device of Patent Document 1, the correction table uses the virtual signal pulse generated in the experiment to make the double pulses close to each other, and obtains the decomposition time t1 of the accumulation and the approach time t2 of the miscount, and performs correction. When the counting rate rises to the approach frequency of more than 3 pulses, the accuracy of the correction becomes insufficient. In addition, since the dead time of the method of Patent Document 2 is fixed with respect to the increase of the counting rate, the accuracy of the correction becomes insufficient with the increase of the counting rate. Summary of the invention

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a processing device, a system, an X-ray measurement method, and a program that can reduce the influence of count omissions even at high count rates that cannot be covered by conventional methods.

[0011] (1) In order to achieve the above-mentioned object, the processing device of the present invention is characterized by comprising: a storage unit that counts pulse signals of incident X-rays by means of a photon counting semiconductor detector and stores the read output value; and a calculation unit that calculates the count value based on the read output value.

[0012] The calculation unit uses a model in which an apparent time constant of the pulse signal decreases monotonically with an increase in a pulse detection rate for exposure.

[0013] In such a model where the apparent time constant of the pulse signal decreases monotonically with increasing pulse detection rate, the corresponding apparent time constant can be obtained regardless of how high the count rate is. As a result, the influence of missed counts can be reduced even at high count rates that cannot be covered by existing methods.

[0014] (2) In the processing device of the present invention, the pulse detection rate is equivalent to the ratio of the total time during which the pulse signal is detected for the exposure to the total time of the exposure. Thus, the pulse detection rate can be easily calculated in a short cycle using a detector that can perform exposure in a short unit time.

[0015] (3) In the processing device of the present invention, the apparent time constant is the original time constant when the pulse detection rate is zero. Therefore, when there is no repetition of pulses for exposure in the model, there is no influence on the count omission, and the model is in line with reality.

[0016] (4) In the processing device of the present invention, the apparent time constant is the product of the actual time constant and a constant smaller than 1 when the pulse detection rate is 1. Thus, the count can be calculated for the maximum output value that can be measured on the model.

[0017] (5) In the processing device of the present invention, the storage unit stores the time constant of the pulse signal, and the calculation unit reads out and uses the stored time constant when using the model. Thus, the time constant can be read out and used when calculating the count value.

[0018] (6) In addition, the system of the present invention is characterized by comprising: the semiconductor detector; and the processing device described in any one of (1) to (5) above. Thus, the count value can be calculated in the processing device using the output value obtained from the semiconductor detector.

[0019] (7) In addition, in the system of the present invention, the semiconductor detector is exposed for a time shorter than the time constant of the pulse signal. This makes it possible to observe physical phenomena with high time resolution. In addition, more than three pulses are no longer detected in one exposure, which reduces the burden of readout. In addition, it is sufficient to read out the output value in a 2-bit mode, which can shorten the readout time.

[0020] (8) In addition, in the system of the present invention, it is characterized in that, in calculating the count value, the pulse signal is counted for a time obtained by adding a time constant of the pulse signal to a unit time of the exposure, and the count value is corrected, thereby obtaining a count value detected at a substantial exposure time.

[0021] (9) In addition, the X-ray measurement method of the present invention is characterized by comprising the steps of: counting pulse signals of incident X-rays by a photon counting semiconductor detector and reading out output values; and calculating count values ​​based on the read-out output values, wherein a model is used in which the apparent time constant of the pulse signal decreases monotonically with respect to an increase in the pulse detection rate for exposure in calculating the count values. Thus, the influence of count omissions can be reduced even at a high count rate.

[0022] (10) In addition, the recording medium of the present invention is a computer-readable, non-temporary recording medium having a program recorded thereon, wherein the program causes a computer to execute the following processing: counting pulse signals of incident X-rays by a photon counting semiconductor detector and reading out output values; and calculating count values ​​based on the read-out output values, wherein in the calculation of the count values, a model is used in which the apparent time constant of the pulse signal decreases monotonically with respect to an increase in the pulse detection rate for exposure. Thus, the influence of count omissions can be reduced even at a high count rate.

[0023] According to the present invention, the influence of count omissions can be reduced even for high count rates that cannot be covered by conventional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram showing an example of the configuration of the X-ray detection system of the present invention.

[0025] Figure 2 It is a schematic diagram showing the structure of an X-ray detector according to an embodiment.

[0026] Figure 3 It is a block diagram showing the functional structure of the processing device involved in the embodiment.

[0027] Figure 4 This is a schematic diagram showing the counting timing of the output value with respect to the pulse input in the X-ray measuring method of the present invention.

[0028] Figure 5 It is a graph showing the pulse height when pulses overlap.

[0029] Figure 6 This is a conceptual diagram showing the relationship between the exposure time δt and the time constant τ.

[0030] Figure 7 This is a diagram showing an example of a filling pattern in a storage ring.

[0031] Figure 8 This is a graph showing the detection current relative to time.

[0032] Fig. 9 It is a diagram showing the filling pattern in the storage ring and the exposure start position during the measurement of the time constant.

[0033] Fig.10 is a graph representing the number of times per unit time of each counted event for the exposure time.

[0034] Fig.11 This is a schematic diagram showing a method of counting rising edges.

[0035] Fig.12 This is a conceptual diagram showing the relationship among exposure time δt, time constant τ, and readout time.

[0036] Fig.13 is a graph representing the results of the simulation.

[0037] Fig.14 are graphs representing the results of experiments in a large radiation light facility.

[0038] Fig.15 It is a graph showing the results of an experiment based on the X-ray reflectivity method.

[0039] Explanation of symbols

[0040] 10 X-ray detection system, 20 X-ray source, S sample, 100 X-ray detector, 110 sensor, 120 readout circuit, 125 gate, 130 detection circuit, 140 counter, 150 memory, 160 forwarding circuit, 170 control circuit, 200 processing device, 210 measurement data management unit, 220 storage unit, 230 calculation unit, 240 correction unit, 300 input unit, 400 output unit, SB1 single bunch, TB1 train bunch DETAILED DESCRIPTION

[0041] Next, embodiments of the present invention will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components are denoted by the same reference numerals in the drawings, and repeated descriptions are omitted.

[0042] [Implementation Method]

[0043] (Structure of the detection system)

[0044] Figure 1 1 is a schematic diagram showing an example of the structure of the X-ray detection system 10. Figure 1 As shown, the X-ray detection system 10 includes an X-ray source 20 , a sample S, an X-ray detector 100 , and a processing device 200 .

[0045] The X-ray source 20 generates X-rays by, for example, causing an electron beam emitted from a filament as a cathode to collide with a rotor target as a counter cathode. A metal such as Mo or Cu is provided on the outer peripheral surface of the rotor target. When the electrons collide with the Mo target, MoKα rays (wavelength 200 Å) as characteristic rays are radiated. When the electrons collide with the Cu target, they emit CuKα rays (wavelength ) X-rays. The X-rays radiated from the X-ray source 20 are so-called point-focused X-ray beams.

[0046] The sample S is supported by a sample support device. The X-ray detector 100 detects X-rays such as diffracted rays diffracted by the sample S. The processing device 200 processes the detected output value and calculates the count value. The details of the X-ray detector 100 and the processing device 200 will be described later. In addition, in the present invention, a characteristic step is to calculate the count value of a model that uses an apparent time constant of a pulse signal to monotonically decrease with an increase in the pulse detection rate for exposure. In the following description, the description is based on the premise that the step is basically performed in the processing device 200, but it can also be performed in the X-ray detector 100.

[0047] (Structure of X-ray Detector)

[0048] Figure 2 1 is a schematic diagram showing the structure of the X-ray detector 100. The X-ray detector 100 is a photon counting semiconductor detector having a two-dimensional data buffering function. The X-ray detector 100 detects X-rays and forwards the detection data to the outside in each frame. In addition, the X-ray detector 100 may be a one-dimensional detector or a zero-dimensional detector.

[0049] like Figure 2 As shown, the X-ray detector 100 includes a sensor 110, a readout circuit 120, a memory 150, a forwarding circuit 160, and a control circuit 170. Figure 2 For convenience, the configuration of one sensor 110 is shown, but the X-ray detector 100 basically includes a plurality of sensors. The readout circuit 120 has a function of reading out pulses, and includes a gate 125 , a detection circuit 130 , and a counter 140 .

[0050] The sensor 110 generates a pulse when detecting X-ray particles by exposure. The sensor 110 can detect the intensity of the X-ray beam incident on the light receiving surface as surface information.

[0051] The gate 125 allows the pulse to pass to the detection circuit 130 only during the gate open time. In this specification, the open time of the gate 125 is referred to as the exposure time δt. The opening and closing of the gate 125 is performed by an electronic shutter. If the exposure time δt is shortened, the time resolution is improved, and the measurement can be performed with better accuracy, so the shorter the exposure time δt, the better. For example, if the exposure time δt is shorter than the time constant τ of the pulse signal described later, more than three pulses will no longer be detected in one exposure, which reduces the burden of reading, and is therefore preferred. The lower limit of the exposure time δt is determined by the functional limit of the hardware, but the lower limit can be reduced by, for example, increasing the clock frequency, setting the command system of the gate control to a system different from other controls to issue commands with 1 bit, and making the clock n times (for example, 10 times) only for the gate control inside the CPU, etc.

[0052] The detection circuit 130 determines whether the pulse is higher than the threshold value. If it is high, it sends it as a voltage signal to the counter 140. The counter 140 can count the sent voltage signal as the number of pulses and output it as an output value. The memory 150 reads the output value counted in the counter 140 from the counter 140 and stores it. The timing of the readout can basically be just after the door 125 is closed, but it can also be read out with a waiting time. The memory 150 can transform the readout unarranged data into a real space configuration and forward the data to the next stage. In addition, the memory 150 stores the total exposure time or the number of exposures.

[0053] In addition, there may be multiple detection circuits for one sensor. When there are multiple detection circuits, each detection circuit has a counter. In addition, when there are multiple detection circuits, the threshold used in the determination of the pulse can be different in each detection circuit.

[0054] In addition, the memory may be a plurality of memories that can be switched for writing to one sensor. In the case of having a plurality of memories, since the door is opened during the period of reading from one memory, exposure can be performed, and thus the duty ratio can be increased. In the case of having a plurality of sensors, a plurality of memories may be independently provided for each sensor, or a plurality of memories may be shared. It is sufficient to provide only two memories for two sensors, and if these two memories can be switched for writing from each sensor.

[0055] The forwarding circuit 160 forwards the output value and the total exposure time or the number of exposures stored in the memory 150 to the processing device 200. The control circuit 170 stores the total exposure time or the number of exposures in the memory 150. In addition, the control circuit 170 controls the opening and closing of the gate 125, controls the reading and storage of the output value, and controls the forwarding of the stored output value and the total exposure time or the number of exposures to the processing device 200.

[0056] (Structure of Processing Device)

[0057] Figure 3 2 is a block diagram showing the structure of the processing device 200. The processing device 200 includes a measurement data management unit 210, a storage unit 220, a calculation unit 230, and a correction unit 240, and calculates a count value or a count rate based on an output value of X-rays detected by the X-ray detector 100 and a total exposure time or the number of exposures.

[0058] The measurement data management unit 210 manages the data handled by the storage unit 220, the calculation unit 230, and the correction unit 240. The measurement data management unit 210 receives the output value stored in the memory 150 of the X-ray detector 100 through the forwarding circuit 160, and the total exposure time or the number of exposures, and stores them in the storage unit 220.

[0059] The storage unit 220 stores the received output value and the total exposure time or the number of exposures. In addition, the storage unit 220 stores the count value or the count rate calculated based on the output value and the total exposure time or the number of exposures. In addition, the storage unit 220 stores the total exposure time corrected by the correction unit 240. In addition, the storage unit 220 stores the time constant of the pulse signal.

[0060] The time constant is read from the storage unit 220 and used in calculating the count value and setting the exposure time. Since the time constant changes in value according to the set value such as the threshold value, if it is stored in advance in the form of a table, it can be adapted to any processing. In addition, the table can be stored on the X-ray detector 100 side, read out and used.

[0061] The calculation unit 230 calculates the count value or count rate based on the output value and the total exposure time. At this time, a model is used in which the apparent time constant of the pulse signal decreases monotonically with respect to the increase of the pulse detection rate for exposure. The model will be described in detail later. In addition, the pulse detection rate can be set to a value equivalent to the ratio of the total time of detecting the pulse signal for exposure to the total exposure time. The so-called equivalent value means that the total time of detecting the pulse signal for exposure can be replaced by the output value, which means that the total exposure time can be replaced by the number of exposures or the total exposure time after correction.

[0062] The correction unit 240 corrects the total exposure time. The correction of the total exposure time can be performed by, for example, setting the exposure time of one time to the time obtained by adding the time constant τ of the pulse signal and the unit time of exposure (exposure time δt) to calculate the total exposure time. In this way, the count value detected during the actual exposure time can be obtained.

[0063] The processing device 200 is, for example, a personal computer, which includes, for example, a CPU for operation control, a memory for storing data, system software stored in a predetermined area of ​​the memory, and application software stored in another predetermined area of ​​the memory.

[0064] A keyboard or the like is connected to the processing device 200 as an input unit 300 for receiving user input. An output unit 400 such as a display or a printer is also connected to the processing device 200. The output unit 400 outputs count values ​​or the like according to instructions from the processing device 200.

[0065] (X-ray measurement method)

[0066] Next, an outline of the X-ray measurement method from the detection of X-rays to the calculation of the count value is described. If the X-rays entering the detection surface are detected by the sensor, a pulse is generated. The pulse passes through the detection circuit during the period when the door is open due to exposure. The pulse is determined in the detection circuit to see if it is higher than each threshold value. If it is high, it is sent to the counter as a voltage signal. The pulse is counted in the counter. The output value of the counter is read out from the memory and forwarded to the processing device through the forwarding circuit. In the processing device, the count value is calculated based on the read output value. At this time, a model is used in which the apparent time constant of the pulse signal decreases monotonically with the increase of the pulse detection rate for exposure.

[0067] (Time constant of pulse signal)

[0068] The so-called time constant τ of a pulse signal refers to the time when the intensity of a single pulse signal exceeds a threshold value. In the case of a photon counting type semiconductor detector, it depends on the ROIC circuit. In the present invention, the original time constant τ of the pulse signal can be used in the setting of exposure conditions. In addition, it can also be used in the compensation formula used in the calculation of the count value. In addition, the method for measuring the time constant is described later as an example.

[0069] (Pulse signal counting method of the present invention)

[0070] Figure 4 This is a schematic diagram showing the counting timing of pulses in the X-ray measuring method of the present invention. Figure 4 t1 to t10 represent the exposure time δt when the gate is open. For each of these multiple exposure times δt, if the intensity of the pulse exceeds the threshold during that exposure time, the count is incremented by 1. This count is incremented by 1 regardless of whether it exceeds the threshold at the beginning or during the exposure time δt. In addition, during the exposure time δt, if the intensity of the pulse exceeding the threshold falls below the threshold once and then exceeds the threshold again, the count is incremented by 2. The same applies to the above cases. Figure 4 In the example of , t3, t6, t7, and t10 are not incremented, t1, t2, t5, t8, and t9 are incremented by 1, and t4 is incremented by 2, and the total count is 7. In addition, the intervals between exposure times may not be equal intervals.

[0071] In this counting method, it is preferred to set the exposure time δt to be shorter than the time constant τ. If the exposure time δt is shorter than the time constant τ, the phenomenon that the intensity of the pulse exceeding the threshold value once falls below the threshold value and then exceeds the threshold value again during the exposure time δt becomes less than 1 time. That is, the count during the exposure time δt becomes less than 2. In addition, if the exposure time δt is made sufficiently short, the V-shaped interval in the increase and decrease of the intensity of the pulse is no longer captured, so the count obtained during the exposure time δt becomes less than 1. Since the number of pulses counted per unit exposure time is reduced by shortening the exposure time δt, the number of false counts is reduced. If the exposure time δt is made shorter than the time constant τ of the pulse signal, the situation where more than 3 pulses are detected in one exposure will disappear, so the amount of forwarded information can be set to less than 2 bits. For this reason, the readout time can be shortened.

[0072] In addition, when the X-ray count value is used in analysis, a count value that can ignore the influence of statistical fluctuations is required. For example, in order to obtain a relative standard deviation of 1%, a count of 10,000 counts is required. Since the number of counts of the pulse signal per exposure time δt is any one of 0, 1, and 2, it is preferable to set the exposure number so that the exposure is repeated with 10,000 to 30,000 counts as a rough target, so that the count of the pulse signal for the total time without exposure becomes a statistically significant value.

[0073] Regardless of the counting method, the high count region, for example, the region above 10 Mcps, is greatly affected by count omissions. In the subsequent processing, the influence of count omissions is corrected to make the number of pulses close to the original number.

[0074] It is preferred to use the result of counting using the pulse signal counting method of the above-mentioned present invention as the output value, but the result obtained by a method of counting rising edges (described later), a method of reapplying a time trigger to the detector circuit, etc. can also be used as the output value.

[0075] Specifically, the total time of detecting the pulse signal is read out as an output value, and the original pulse count value is calculated based on the read output value. In addition, the total time (output value) of detecting the pulse signal can be directly read out and used as the time when the pulse signal exceeds the threshold, or estimated based on the total count of the pulse signal. In calculating the count value, a model is used in which the apparent time constant of the pulse signal decreases monotonically with the increase of the pulse detection rate for exposure.

[0076] (Correction method based on a model in which the apparent time constant of a pulse signal decreases monotonically)

[0077] If X-rays continuously reach the sensor, pulse signals will overlap. If the height of the overlapping pulse signals exceeds the threshold, the time exceeding the threshold will be longer. However, the time exceeding the threshold is shorter than the value obtained by multiplying the number of pulses by the time constant τ by the amount of pulse overlap. For example, when two pulse signals overlap, the time exceeding the threshold is shorter than twice τ, and when three pulse signals overlap, it is shorter than three times τ.

[0078] In this specification, the value obtained by converting the time exceeding the threshold into the time per pulse signal is called the apparent time constant τa of the pulse signal. The relationship between the number of pulse signals and the apparent time constant τa is expressed by equation (1).

[0079]

[0080] Figure 5 is a graph showing pulse heights when pulses overlap. Figure 5 As shown in FIG. 1 , if the number (N) of pulse signals superimposed at each pulse detection time (Tup) increases, the apparent time constant τa gradually becomes shorter.

[0081] Such a tendency is related to the probability of pulse signal overlap. In addition, if the pulse detection rate (count rate) increases, the number of pulse signals (N) increases, and the probability of pulse signal overlap also increases. In other words, the apparent time constant τa can be calculated based on the probability without distinguishing how many signals overlap. The time of each pulse signal (apparent time constant τa) gradually becomes shorter than the time constant τ as the pulse detection rate (count rate) increases. In other words, the apparent time constant τa is represented by the product of the time constant τ and the monotonically decreasing function f of the count rate. As a result, the true count value (N) can be calculated based on the time Tup exceeding the threshold and the relationship between the apparent time constant τa and the pulse detection rate (count rate).

[0082] (Model conditions)

[0083] The model for calculating the above-mentioned count value and count rate needs to meet the following conditions. (1) The apparent time constant of the pulse signal decreases monotonically with the increase of the pulse detection rate. (2) When the pulse detection rate is 0, the apparent time constant of the pulse signal is consistent with the time constant τ. (3) When the pulse detection rate is 1, the apparent time constant of the pulse signal is smaller than the time constant τ. Preferably, when the pulse detection rate is close to 1, the apparent time constant of the pulse signal is close to 0. (4) The formula for calculating the count value created by the model is a dimensionless quantity. In addition, the result obtained by dividing the count value by the total exposure time is the count rate.

[0084] (Example of model)

[0085] As a model, the formula (2) for calculating the count value N as in the following example can be used. N represents the calculated count value, τ represents the time constant of the pulse signal, Tup represents the total time of the pulse signal detected for exposure, and Ttot represents the total time of exposure. In addition, τ·f(Tup, Ttot) represents the apparent time constant of the pulse signal. f(Tup, Ttot) becomes 1 when Tup is 0, and monotonically decreases when Tup / Ttot increases in the range of greater than 0 and less than 1. f(Tup, Ttot) is preferably close to 0 when Tup / Ttot is close to 1, but can also be a constant greater than 0 and less than 1.

[0086]

[0087]

[0088] By dividing the count value N shown in formula (1) by the total exposure time Ttot, the count rate n shown in formula (3) can be obtained. The function value f(Tup / Ttot) that always decreases with the increase of the independent variable Tup / Ttot is called monotonous decrease. f(Tup / Ttot) can be a monotonically decreasing function with such properties. f(Tup / Ttot) can be an n-order function or an exponential function, regardless of the type of function.

[0089] Since the apparent time constant τa (=τ·f) is the product of the time constant τ and the monotonically decreasing function, in other words, the apparent time constant τa also decreases monotonically as the pulse detection rate (Tup / Ttot) increases.

[0090] In the following embodiments, the following formula (4) is used as a monotonically decreasing function f(Tup, Ttot). This function becomes a monotonically decreasing function by determining k in the range of 0<k≤1. For example, by conducting experiments and simulations, the optimal constant m is further determined according to the range of the counting rate and the system, and theoretically, correction can be performed until the counting rate is infinite. The counting rate n in this case is as shown in formula (5).

[0091]

[0092]

[0093] In the above-mentioned compensation formula, the time constant τ changes in value according to the setting value of the detection circuit and the pixel. For this reason, it is preferably updated according to the corresponding detector and the measurement conditions. For example, the time constant τ is measured by changing the conditions, and the value in the form of a table corresponding to the setting value of the pixel is read out and used.

[0094] In the detector described in the embodiment, since it is difficult to directly read the time when the pulse signal is detected, that is, the time when the pulse signal exceeds the threshold, the total time Tup when the pulse signal is detected for exposure can be estimated and used as the output value.

[0095] For example, in a method in which a time trigger is reapplied in hardware on a circuit to make the count close to the true count as in the technique described in Reference 2, since the time constant τ is constant, the value obtained by multiplying the time constant τ by the number of dead time can be estimated as Tup.

[0096] In the counting method of the present invention, the value obtained by multiplying the total number of counts of the pulse signal by the exposure time δt is set to Tup. The total exposure time Ttot becomes the value obtained by multiplying the exposure time δt by the number of exposures. In addition, the detection rate of the pulse (Tup / Ttot) is equivalent to the ratio of the total number of counts of the pulse signal to the number of exposures.

[0097] The total time Tup of the pulse signal detected for exposure is represented by the product of the exposure time δt and the number of counts, and the total exposure time Ttot is represented by the product of the exposure time δt and the number of exposures (number of frames). Therefore, the detection rate of the pulse is Tup / Ttot=number of counts / number of exposures. For this reason, by processing the total number of counts of the pulse signal and the number of exposures as output values, the numerical values ​​to be processed are simplified and the processing burden is reduced.

[0098] (Relationship between exposure time and time constant)

[0099] When the exposure time δt is shorter than the time constant τ, it is preferable to use a value obtained by multiplying the sum of the exposure time δt and the time constant τ by the number of exposure times as the total exposure time Ttot. Figure 6 This is a conceptual diagram showing the relationship between exposure time δt and time constant τ. The phenomenon of counting within exposure time δt is as follows Figure 6 As shown, it is from the pulse generated before the exposure time δt by the time constant τ to the pulse generated when the exposure time δt is about to end. In this way, the phenomenon counted within the exposure time δt is a phenomenon that occurs during (exposure time δt) + (time constant τ). Therefore, when accumulating and outputting multiple captured images, it is necessary to take this effect into consideration and make corrections.

[0100] (Summary)

[0101] As described above, instead of counting at the timing when the pulse breaks through the threshold upward, the exposure is repeated multiple times, and the count value is calculated based on the output value and pulse detection rate obtained from the results of a large number of samplings, using a model in which the apparent time constant of the pulse signal decreases monotonically with respect to the increase of the pulse detection rate for exposure. During sampling, it is determined whether the pulse exceeds the threshold during the exposure time δt shorter than the time constant τ until a statistically significant number is reached. In this way, the influence of missed counts can be reduced even for high count rates that cannot be covered by correction using existing methods.

[0102] [Example]

[0103] (Determination of the time constant τ in large-scale radiation light facilities)

[0104] The time constant τ of the X-ray detector of the embodiment was measured using the Spring-8 cluster, which has an accelerator group for accelerating and storing electrons, experimental facilities for using the generated radiation, and various auxiliary facilities. The X-ray detector was incorporated as part of the radiation detection device of Spring-8, and the following measurement was performed.

[0105] For example, in Spring-8, the electron beam generated by the electron gun is accelerated to 1 GeV by a linear accelerator, and then introduced into a synchrotron to be accelerated to 8 GeV. The electron beam is introduced into the storage ring, and while maintaining the energy of 8 GeV, the radiation light is generated by deflecting electromagnets and inserting light sources. The generated radiation light is guided to the experimental center located inside and outside the storage ring building through the beam line. In addition, the electron beam basically does not exist continuously in the ring, but exists as a block called a bunch.

[0106] Figure 7 is a diagram showing an example of a filling pattern in a storage ring. Figure 8 This is a graph showing the detected current of the bunch with respect to time. Specifically, it shows the filling pattern of each bunch operation mode (E mode) of Spring-8 2018A (early 2018). Figure 7 In the filling mode shown, a single bunch SB1 of electrons in the form of dots and a string bunch TB1 of electrons in the form of lines are shown. The flying interval of the bunches in this operation mode is 165.2 nsec. Figure 8 As shown, the trapezoidal bunches and the spike-shaped single bunches are characterized at the above-mentioned time intervals.

[0107] In this measurement of the time constant τ, a bunch of H-mode bunch structures was used. In the experiment based on the H-mode bunch structure, there are intervals where the bunches do not fly. Fig. 9As shown in the figure, if the measurement is started from the position where the bunch flies, the X-rays do not fly before the first 40nsec of the door opening, so the time constant τ is measured based on this. Exposure is performed from the string point part, and the exposure time is extended from 40ns to 800ns in units of 4ns. 10,000 detections are performed respectively, and the number of events per unit time is calculated, thereby confirming the circuit operation time inside the ROIC.

[0108] Fig.10 The curves p1, p2, and p3 represent the number of events per unit time of 1 count, 2 counts, and 3 counts, respectively. That is, 10,000 times are measured at 40ns, and the number of times of 1 count, 2 counts, and 3 counts is counted, and the number of times per unit time is calculated and plotted. Then the same measurement is repeated at 44ns.

[0109] like Fig.10 As shown in FIG. 1 , if the exposure time is gradually increased, the curve of p2 rises, and an event of 2 counts occurs. In this measurement, when the exposure is performed for a time shorter than the time constant τ, the second count does not occur, so the position where the 2 counts begin to appear represents the time constant τ. Fig.10 It can be seen that the time constant τ of the X-ray detector of the embodiment is about 100 ns because the graph of 2 counts falls toward 0 at about 100 ns. In addition, the measurement of the time constant τ is not limited to the above method, and can be estimated by, for example, changing the count rate and reading the counts.

[0110] (Example 1)

[0111] The X-ray measurement method of the present invention is suitable for use in the X-ray reflectivity method. In the X-ray reflectivity method, there are parts with high intensity and parts with low intensity of reflected X-rays. Therefore, it is preferable to use the method of the present invention for parts with high intensity and to use the existing method for parts with low intensity. For example, if 100 exposures of 40nsec are introduced for measurement, and separately from this, 1 exposure of 1msec is introduced for measurement, then even if there is a distribution of intensity within the surface, data can be obtained for weak parts by 1msec exposure, and data can be obtained for strong parts by 40nsec exposure.

[0112] A method for measuring by introducing an attenuator into X-rays with a high count rate, for example, attenuating the X-ray intensity to 1 / 10. In contrast, in the present invention, measurement can be performed without installing an attenuator. Therefore, there is no need to install or remove the attenuator, making the overall structure of the system simple. In addition, in the case of switching as described above, it is preferred that the switching action be performed by software.

[0113] (Example 2)

[0114] The X-ray measurement method of the present invention is suitable for use in a large-scale radiation light facility such as Spring-8. In this case, data obtained from a general X-ray detector attached to a radiation light detection device of the large-scale radiation light facility is processed using the X-ray measurement method, processing device, or recording medium of the present invention.

[0115] (Other Embodiments)

[0116] In addition to the above, total reflection of metal complex samples among single crystal X-ray diffraction methods, small angle X-ray scattering methods, etc. are suitable for use in the X-ray measurement method of the present invention because the intensity of X-rays to be measured increases.

[0117] [simulation]

[0118] The comparison between the X-ray determination method of the present invention and the method of counting rising edges was simulated by computer experiments. Fig.11 is a schematic diagram showing a method for counting rising edges. Fig.11 The position of the black dot on the graph shown, i.e., the timing when the pulse breaks through the threshold upward, is counted, and the observed count rate per unit time is obtained from here. The count rates obtained using the following methods are calculated respectively: a method in which a pulse is randomly generated in a computer for each input count rate of several count rates greater than 0Mcps and less than 20Mcps, and the rising edge is counted; a method in which a simple count omission correction is performed on the count rate obtained from the output value; and the X-ray measurement method of the present invention. In the method in which a simple count omission correction is performed on the count rate obtained from the output value, the following formula (6) is used to calculate the count rate n. In addition, I represents the count rate obtained by measurement. Fig.12 This is a conceptual diagram showing the relationship among exposure time δt, time constant τ, and readout time.

[0119]

[0120] In the X-ray measurement method of the present invention, the count rate n is calculated using the above-mentioned formula (4). The exposure time δt and the time constant τ are the same as those in the above-mentioned embodiment, and the count rate n is corrected in consideration of the influence of the time constant τ. Fig.13 is a graph representing the results.

[0121] like Fig.13As represented, in the method of counting rising edges, if the count rate of the input pulse exceeds 2Mcps, the deviation of the obtained count rate from linearity gradually increases, and if it exceeds 6Mcps, the obtained count rate decreases. This is because if the count rate of the input pulse is expressed, the overlap of pulses occurs frequently, and it becomes difficult to produce the phenomenon that the pulse breaks through the threshold upward. In the method of correcting the count omission of the result of rising edge counting, although the obtained count rate is slightly closer to linearity than the existing method, since the extruded value set as the correction is the value counted by the existing method, there is no change in the fact that the count rate obtained decreases when the count rate of the input pulse increases.

[0122] In contrast, it can be seen that in the X-ray measurement method of the present invention, the deviation from linearity does not increase until the count rate of the input pulse reaches about 12Mcps. In addition, if it exceeds 12Mcps, although the deviation from linearity increases to some extent, the obtained count rate does not decrease. The range of the count rate that can be relied on in the X-ray measurement method of the present invention varies according to each model and formula, but theoretically it can be calculated to infinity.

[0123] [experiment]

[0124] (Experiments in large radiation light facilities)

[0125] ThScan was performed on 10keV X-rays using a Spring-8 bunch with exposure times of 40ns and 1600ns to confirm the difference in contour shape. ThScan is a method of measuring X-ray intensity while changing the threshold set during measurement. The change in intensity relative to the threshold can be measured under the same exposure conditions for the optical system.

[0126] Fig.14 is a graph that represents the results. Fig.14 As shown in the figure, a significantly different profile is obtained. From this chart, it can be confirmed that the effectiveness of counting with an exposure time set to less than the time constant can be confirmed. In addition, when the exposure time is 40ns, the actual exposure time is extended by the time constant, so the figure is a chart of the value obtained by dividing the exposure time extension amount when the threshold value is 5keV by 2.5. The so-called extension amount of the exposure time refers to using the sum of the exposure time and the time constant as the total exposure time.

[0127] (Experiment based on X-ray reflectivity method)

[0128] As an experiment based on the X-ray reflectivity method, the reflected X-rays of the zinc oxide film (ZnO) on the glass substrate were measured. Fig.15This is a graph showing the results. In the graph of 40ns exposure and adding the calculated results for 25,000 sheets, since the time constant τ of the X-ray detector is 100ns, the actual total exposure time is 3.5ms. In contrast, in the method of performing 1, 2, 3, and 4ms exposure, there is generally no need to correct the exposure time. In the case of 40ns exposure, although it is actually 3.5ms exposure, the count rate becomes higher than that of the 4ms graph. It can be seen that by repeating short exposures, the impact of count omissions can be reduced more than when performing long exposures.

Claims

1. A processing device, characterized in that: have: a storage unit that stores an output value obtained by counting pulse signals of incident X-rays by a photon counting type semiconductor detector; and a calculation unit that calculates a count value based on the output value, The calculation unit uses a model in which an apparent time constant of the pulse signal decreases monotonically with an increase in the pulse detection rate for exposure. The pulse detection rate corresponds to a ratio of a total time during which the pulse signal is detected for the exposure to a total time during which the exposure occurs. The apparent time constant is a value obtained by converting the time for detecting a pulse signal into the time per one pulse signal.

2. The processing device according to claim 1, characterized in that The apparent time constant is an actual time constant when the pulse detection rate is zero.

3. The processing device according to claim 1, characterized in that The apparent time constant is the product of the actual time constant and a constant smaller than 1 when the pulse detection rate is 1.

4. The processing device according to claim 1, characterized in that The storage unit stores the time constant of the pulse signal. When using the model, the calculation unit reads out and uses the stored time constant.

5. A system, characterized in that: have: said semiconductor detector; and The processing device as claimed in claim 1.

6. The system according to claim 5, characterized in that The semiconductor detector is exposed for a time shorter than a time constant of the pulse signal.

7. The system according to claim 6, characterized in that In calculating the count value, the pulse signal is counted for a time obtained by adding a time constant of the pulse signal and a unit time of the exposure, and the count value is corrected.

8. An X-ray measurement method, characterized in that: The steps include: storing an output value obtained by counting pulse signals of incident X-rays by a photon counting type semiconductor detector; and calculating a count value based on the output value, In calculating the count value, a model is used in which the apparent time constant of the pulse signal decreases monotonically with increasing pulse detection rate for exposure. The pulse detection rate corresponds to a ratio of a total time during which the pulse signal is detected for the exposure to a total time during which the exposure occurs. The apparent time constant is a value obtained by converting the time for detecting a pulse signal into the time per one pulse signal.

9. A recording medium, which is a computer-readable, non-temporary recording medium, having a program recorded thereon, characterized in that: The program causes the computer to execute the following processing: storing an output value obtained by counting pulse signals of incident X-rays by a photon counting type semiconductor detector; and calculating a count value based on the output value, In the calculation process of the count value, a model is used in which the apparent time constant of the pulse signal decreases monotonically with an increase in the pulse detection rate for exposure. The pulse detection rate corresponds to a ratio of a total time during which the pulse signal is detected for the exposure to a total time during which the exposure occurs. The apparent time constant is a value obtained by converting the time for detecting a pulse signal into the time per one pulse signal.

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