JP3978389B2 - Radiation position detector and radiation position detection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radiation position detector or a radiation image detector capable of measuring an incident position of radiation such as X-rays, γ-rays, α-rays, and β-rays with high accuracy.
[0002]
[Prior art]
X-ray film has been most widely used as a technique for obtaining radiation images. X-ray film has been widely used in the medical field and industrial fields such as non-destructive inspection for a long time. Technology has been accumulated, the degree of perfection is high, and the resolution is good. The biggest drawback is not. Further, since the X-ray film is an integral detector, it is impossible to distinguish the energy of incident radiation, and it cannot be applied to a field that requires an image for each energy.
[0003]
In order to solve the problem of the X-ray film, there is conventionally a flat panel detector (see, for example, Patent Document 1) that obtains a radiation image in online and real time. In this flat panel detector, a large number of radiation detection elements are arranged in a two-dimensional direction to control a gate drive circuit and an analog multiplexer to obtain a radiation image. In addition, there is a gamma camera (for example, see Patent Document 2) that obtains an image of only the target energy online. In this gamma camera, a radiation image is obtained by using a fan beam collimator or a parallel beam collimator to limit the incident direction of radiation and using a scintillator and a number of photodetectors arranged in a two-dimensional direction. In any of the above cases, a large number of radiation position detectors are used to obtain a radiation image.
[0004]
In addition to a method using a large number of radiation position detectors, there is a silicon drift detector (see, for example, Non-Patent Document 1) that measures a radiation incident position in a single bulk. In this detector, an electrode pattern is formed on the surface of a thin silicon detector, an electric field is created in the element by the electrode pattern, and a carrier drift (movement) time is measured to detect the incident position of radiation.
[0005]
[Patent Document 1]
Japanese National Patent Publication No. 11-510313
[Patent Document 2]
JP 2001-324568 A
[Non-Patent Document 1]
IEEE Transaction on Nuclear Science Vol. 42, no. 5, pp 1497-1504 (1995) FIG.
[0006]
[Problems to be solved by the invention]
When a radiological image is obtained using a large number of elements with a small individual detection area, more elements are required to widen the detection area and increase the resolution, and the cost increases as the number of elements increases. Will increase. Further, as the number of elements increases, the number of signal processing circuits that process the output of each element increases, and costs associated with element mounting and microfabrication also increase. In addition, if the number of elements and processing circuits is large, the number of parts increases, and the failure rate inevitably increases. In addition, if a large number of detector elements are used, variations in characteristics occur, and measures such as sensitivity correction are required. As described above, a radiological image detector using a large number of elements is very expensive and needs to cope with an increase in failure rate.
[0007]
Further, in the silicon drift detector, a large number of electrodes must be formed on the surface of the silicon detector, which increases the manufacturing cost. Furthermore, in order to measure the carrier movement time with high accuracy, the electric field in the element needs to be constant. However, since the electric field is controlled from the side with respect to the carrier movement direction, the electric field strength is distorted. It tends to occur, and it becomes difficult to control the electric field, that is, to control the accuracy of carrier movement time. As described above, the silicon drift detector has a problem that the cost for measuring the incident position of radiation with high accuracy and the accuracy control become difficult.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide a radiation position detector that can greatly reduce the cost with a simple structure and can obtain a radiation incident position and a radiation image with high accuracy.
[0009]
[Means for Solving the Problems]
A radiation position detector according to the present invention has a rectangular parallelepiped shape, a semiconductor detection element having a pair of electrodes facing each other, and generating two types of charge carriers having different polarities upon incidence of radiation,
A charge-sensitive preamplifier connected to the semiconductor detection element;
Pulse rise time measuring means for measuring a pulse rise time at which the peak of the output waveform of the charge-sensitive preamplifier due to the two types of charge carriers generated by radiation incident on the semiconductor detection element reaches a peak;
An incident position calculating means for calculating an incident position of radiation from the pulse rise time;
It is characterized by providing.
[0010]
Instead of the pulse rise time measuring means, pulse waveform analyzing means for analyzing the output waveform and measuring the time when the slope of the output waveform changes may be used.
[0011]
The radiation position detection method according to the present invention is a radiation position detection method using a semiconductor detection element having a rectangular parallelepiped shape and having a pair of electrodes facing each other and generating two types of charge carriers having different polarities upon incidence of radiation. Because
The pulse rising time at which the peak of the output waveform due to the two types of charge carriers reaches a peak is measured, and the incident position of the radiation in the opposing direction of the pair of electrodes is measured from the rising time.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
A radiation position detector according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, substantially the same members are denoted by the same reference numerals.
[0013]
Embodiment 1 FIG.
A radiation position detector according to the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing the configuration of the radiation position detector 10. This radiation position detector 10 includes a rectangular parallelepiped semiconductor detection element 1 and a DC power supply 6 that provides a potential difference between two electrodes 2a and 2b formed on a pair of opposing end faces of the detection element 1. A charge sensitive preamplifier (charge sensitive preamplifier) 5 connected to the electrode 2a, a pulse rise time measuring means 7 connected to the amplifier 5, and a pulse rise time measuring means 7 are connected. Incident position calculation means 8. The semiconductor detection element 1 is made of, for example, silicon and has a rectangular parallelepiped shape, and the pair of electrode surfaces 2a and 2b are formed to face the end surfaces in the longitudinal direction. Of the electrodes at both ends of the detection element 1, one electrode 2b is grounded, and the other electrode 2a is given a potential difference to the electrode 2b by a DC power source 6. Therefore, a uniform electric field is generated in the detection element 1 in the longitudinal direction.
[0014]
Next, an operation mechanism of radiation position detection in the radiation position detector 10 will be described. When ionizing radiation 3 such as X-rays, γ-rays, β-rays, and α-rays enters from the upper surface of the semiconductor detection element 1 and is given energy, a pair of electrons 4a and holes 4b as two different types of charge carriers. Is generated as The electrons 4 a and the holes 4 b move toward the electrodes 2 a and 2 b in opposite directions due to the electric field inside the semiconductor detection element 1, so that a current flows in the semiconductor detection element 1. In the charge-sensitive preamplifier 5 connected to the electrode 2a, the amount of electric charge that has flowed is converted into voltage and amplified, and the output waveform of the voltage pulse is output to the pulse rise time measuring means 7. The waveform of this voltage pulse greatly depends on the behavior of electrons 4a and holes 4b, which are charge carriers generated by radiation. The rising edge of the output waveform shows the time change of the amount of charge that has flowed. That is, the pulse rise time at which the wave height reaches a peak corresponds to the time from when charge is generated by the incidence of radiation until one charge carrier reaches the electrode. Further, the output of the pulse rise time measuring means 7 is outputted to the incident position calculating means 8, and the radiation incident position is calculated from the measured pulse rise time.
[0015]
FIG. 2A is a schematic diagram showing a pair of electrodes 2a and 2b facing each other at positions A, B, and C where radiation is incident in this radiation position detector, and FIG. ) Is a graph showing an output waveform of a voltage pulse for each radiation incident position. The horizontal axis of the graph is time, and the vertical axis is voltage. Graphs A, B, and C showing output waveforms in FIG. 2B correspond to the incident positions A, B, and C, respectively. TAe, tBe, and tCe are the time from the generation of charge carriers to the arrival of the electrons 4a among the charge carriers at the electrode 2a, and the charge carrier generation positions correspond to A, B, and C, respectively. Similarly, tAh, tBh, and tCh indicate the time required for the holes 4b to reach the electrode 2b after carriers are generated. The output waveform at this time is that the charge of both the electrons 4a and the holes 4b flows between the generation of carriers and the time when either the electrons 4a or the holes 4b reach the electrodes 2a and 2b. The slope of the waveform is steep. Thereafter, after one carrier reaches the electrode and until the other carrier reaches the electrode, only the charge of the other carrier flows, so the slope of the waveform becomes gentle. Furthermore, after the carriers of both electrons 4a and holes 4b reach the electrode, the total charge reaches the electrode, and no new charge flows anymore, so the wave height becomes a peak height corresponding to the charge q0 and is inclined. Becomes almost zero. Thereafter, the voltage of the output waveform decreases according to the decay time constant of the charge sensitive preamplifier 5. This decay time constant is normally sufficiently longer than the rise time. Therefore, as can be seen from FIG. 2, it can be seen that the rise time of the output waveform, that is, the time until the wave height reaches q0, differs depending on the incident position of the radiation 3. The rise time is obtained by dividing the longer one of the distances from the radiation incident position to the two electrodes 2a and 2b facing each other by the carrier moving speed. Therefore, the rise time of the output waveform can be measured by the pulse rise time measuring device 7, and the incident position of the radiation can be calculated by the incident position calculation means 8 using the charge carrier velocity. Further, since the intensity of incident radiation can be known by measuring the count rate of the voltage pulse to be measured, the position intensity distribution of radiation can also be measured. FIG. 2 shows a case where the velocity ve of the electrons 4a which are charge carriers in the semiconductor detection element 1 and the velocity vh of the holes 4b are substantially the same (ve≈vh).
[0016]
FIG. 3 is a block diagram showing a preferred internal configuration of the pulse rise time measuring means 7. The pulse rise time measuring means 7 is preferably an analog type in order to perform measurement at high speed, but in order to measure with high accuracy, it is important how to reduce noise for measurement. Normally, noise is superimposed on the output waveform from the charge-sensitive preamplifier 5, and this noise becomes an obstacle to measuring timing. Therefore, the output from the charge-sensitive preamplifier 5 is branched into two. The noise component is removed by the inverting filter amplifier 12, that is, the inverting amplifier 12 having a bandpass filter that allows only the vicinity of the frequency of the target signal to pass, and then input to the constant fraction discriminator 16a. Get the start timing signal. Further, the other output from the charge-sensitive preamplifier 5 is input to the differential amplifier 14. Since the differential amplifier 14 differentiates the waveform, a bipolar signal that crosses zero is output when the rise of the output waveform of the charge-sensitive amplifier 5 is completed. By inputting this bipolar signal to the constant fraction discriminator 16b, a stop signal is obtained at the timing of zero crossing. Since the differential amplifier 14 also has a filtering function in the same manner as the inverting amplifier 12, a bipolar pulse from which noise has been removed is output, and as a result, a highly accurate timing signal can be obtained. The constant fraction discriminators 16a and 16b output the start timing and the stop timing, respectively. By measuring the time difference between the two by the time difference measuring device 18, the pulse rise time at the peak of the wave height can be increased at high speed and with high accuracy. Can be measured.
[0017]
Embodiment 2. FIG.
A radiation position detector according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 4 is a block diagram showing the configuration of the radiation position detector 20. The radiation position detector 20 is different from the radiation position detector according to the first embodiment in that a pulse waveform analysis unit 22 is provided instead of the pulse rise time measurement unit. As shown in FIG. 2, the output pulse from the semiconductor detection element 1 has inflection points tAe, tCh, tBe, tBh, tCe, and tAh at which the inclination changes in the output waveform. Therefore, the time to the inflection point on the waveform is obtained using the pulse waveform analysis means 22 for analyzing the output waveform. Next, the incident position calculation means 8 performs the incident position of the radiation between the pair of electrodes 2a and 2b facing each other using the charge carrier velocity in the same manner as the time difference measurement in the radiation position detector according to the first embodiment. Can be calculated. In this case, when two inflection points are shown, it is determined in advance which one is used. The pulse waveform analysis means 22 may be an analog method using a differentiation circuit or the like, or a method of digitally sampling the waveform and performing numerical analysis.
[0018]
Embodiment 3 FIG.
A radiation position detector according to Embodiment 3 of the present invention will be described with reference to FIG. FIG. 5A is a schematic diagram showing the position of the radiation 3 incident on the semiconductor detection element 1 of the radiation position detector, and FIG. 5B is an output waveform when the radiation position is detected by the radiation position detector. It is a graph which shows. This radiation position detector is different from the radiation position detector according to the first and second embodiments in that the charge carrier transport characteristic of the semiconductor detection element 1 differs depending on two types of charge carriers (electrons 4a and holes 4b). Is different. That is, this is a case where the moving speed of one charge carrier is sufficiently higher than the moving speed of the other charge carrier. For example, cadmium telluride, zinc cadmium telluride, zinc cadmium telluride, mercuric iodide, or the like is used as the semiconductor detection element 1 in which the moving speed ve of the electrons 4a is sufficiently higher than the moving speed vh of the holes 4b (ve >> vh). be able to. Here, the sufficiently high moving speed means that the moving speed of one charge carrier is approximately 10 times or more of the moving speed of the other charge carrier (ve> 10 × vh).
[0019]
In this semiconductor detection element 1, among the charge carriers generated by the incidence of radiation, the electrons 4a reach the electrode 2a in a short time, whereas the holes 4b take a long time to reach the electrode 2b or move. In the middle of, it is caught by the capture center and stops. As a result, as shown in FIG. 5, the resulting output waveform has a large slope while both the electrons 4a and the holes 4b are moving, whereas it has a small slope while only the holes 4b are moving. Virtually close to zero. Therefore, the rise time at which the wave height substantially peaks is tAe, tBe, and tCe, which are electron movement times, and these are proportional to the radiation incident position. Accordingly, since the incident position of the radiation 3 is proportional to the pulse rise time, data processing is simplified. Although the slope of these output waveforms also depends on the value of the applied voltage, the above-mentioned object can be achieved by adjusting the applied voltage to an optimum value so that the pulse rise substantially depends on the movement of the electrons 4a. Can be achieved.
[0020]
Embodiment 4 FIG.
A radiation position detector 30 according to Embodiment 4 of the present invention will be described with reference to FIG. FIG. 6 is a block diagram showing the configuration of the radiation position detector 30. The radiation position detector 30 is different from the first embodiment in that a plurality of semiconductor detection elements 1a, 1b, 1c, and 1d are arranged in parallel to each other. The individual semiconductor detection elements 1a, 1b, 1c and 1d are connected in parallel with the charge sensitive preamplifiers 5a, 5b, 5c and 5d and the pulse rise time measuring means 7a, 7b, 7c and 7d, respectively. . Further, each pulse rise time measuring means 7 a, 7 b, 7 c, 7 d is connected to one incident position calculating means 8, and its output is stored in one memory 24. A voltage is applied to each of the semiconductor detection elements 1a, 1b, 1c, and 1d by a DC power source as in the case of FIG. 1, but is omitted in FIG. In addition, arrows X and Y in FIG. 6 indicate coordinate axes on a two-dimensional plane.
[0021]
Next, the radiation position detection operation in the radiation position detector 30 will be described. In this radiation position detection 30, the plurality of semiconductor detection elements 1a, 1b, 1c, and 1d are arranged in parallel in the y-axis direction so that the longitudinal direction is parallel to the x-axis direction. When radiation enters one semiconductor detection element 1a, the incident position calculation means 8 can measure the incident position of the radiation in the x-axis direction. On the other hand, information on the incident position in the y-axis direction can be obtained depending on which of the plurality of semiconductor detection elements 1a, 1b, 1c, and 1d arranged in the y-axis direction. This output is stored in the memory 24 in the memory relating to the position in the y-axis direction. Thus, since the radiation incident position on the two-dimensional plane corresponding to the X-axis direction and the Y-axis direction can be measured, a two-dimensional radiation position detector and a radiation image detector can be provided.
[0022]
Embodiment 5 FIG.
A radiation position detector 40 according to Embodiment 5 of the present invention will be described with reference to FIG. FIG. 7 is a block diagram showing the configuration of the radiation position detector 40. Compared with the radiation position detector according to the first embodiment, the radiation position detector 40 is divided into a plurality of divided electrodes 32a, 32b, 32c, and 32d among the opposed electrodes that are not grounded. Each of the divided electrodes 32a, 32b, 32c, 32d is individually connected to the charge sensitive preamplifiers 5a, 5b, 5c, 5d and the pulse rise time measuring means 7a, 7b, 7c, 7d. Is different. Further, in this radiation position detector 40, a single semiconductor detection element 1 having a constant area over the xy plane is used as compared with the radiation position detector according to the fourth embodiment, and one electrode is a plurality of divided electrodes. It is different in that it is divided into 32a, 32b, 32c, and 32d. The pulse rise time measuring means 7 a, 7 b, 7 c, 7 d are connected to one incident position calculating means 8, and the calculated incident positions are stored in one memory 24. Note that a voltage is applied to each of the divided electrodes 32a, 32b, 32c, and 32d by a DC power source as in FIG. 1, but the DC power source is not shown in FIG. In this case, the voltage values applied to the divided electrodes 32a, 32b, 32c, and 32d are all the same. In addition, arrows X and Y in FIG. 7 indicate coordinate axes on a two-dimensional plane.
[0023]
Next, the radiation position detection operation of the radiation position detector 40 will be described. When radiation is incident on the semiconductor detection element 31 having a certain area on the xy plane, electrons and holes are generated and move in opposite directions by the electric field applied in the element 31. The radiation incident position in the X-axis direction can be measured by the method described in the first embodiment. Further, the incident position of the radiation in the Y-axis direction can be measured by the following method. The semiconductor detection element 31 is a single element, but one electrode is divided into a plurality of divided electrodes, and the other electrode is the same as the ground electrode 34. Each region sandwiched between the divided electrodes 32a, 32b, 32c, and 32d and the opposing electrode 34 can operate as one element. Therefore, in the same manner as in the fourth embodiment, not only the incident position in the x-axis direction but also the incident position in the y-axis direction can be measured. In this case, a two-dimensional radiation incident position can be measured using a single element 31 without using a plurality of elements.
[0024]
Embodiment 6 FIG.
A radiation position detector 50 according to Embodiment 6 of the present invention will be described with reference to FIG. FIG. 8 is a block diagram showing the configuration of the radiation position detector 50. The radiation position detector 50 is different from the radiation position detector according to the first embodiment in that one of the opposed electrodes is a resistive electrode 42. One end of the resistive electrode 42 in the y-axis direction is connected to a pulse height measuring means 45a and a pulse rise time measuring means 46 via a charge sensitive preamplifier 44a. The other end of the resistive electrode in the y-axis direction is grounded. Further, pulse wave height measuring means 45b is connected to the other electrode 43 opposed to the resistive electrode 42 via a charge sensitive preamplifier 44b. Further, the two pulse wave height measuring means 45 a and 45 b are connected to the wave height dividing means 47. The output of the wave height dividing means 47 is input to the incident position calculating means 28b. The output of the pulse rise time measuring means 46 is input to the incident position calculating means 28a. Each output of the incident position calculation means 28 a and 28 b is input to the memory 48. Note that arrows X and Y in FIG. 8 indicate coordinate axes on a two-dimensional plane. Further, E is the energy imparted to the charge carrier by the incident radiation. Further, regarding the Y coordinate of the incident position of the radiation 3, the distance from one end of the resistive electrode 42 connected to the charge sensitive preamplifier 44a is defined as IY.
[0025]
Next, the radiation position detection operation by the radiation position detector 50 will be described. In the radiation position detector 50, when the radiation 3 is incident on the semiconductor detection element 41, electrons and holes are generated and move in opposite directions by the electric field applied in the element. The radiation incident position in the X-axis direction can be measured by the method described in the first embodiment, and for this, the rise time at which the peak of the output waveform of the charge-sensitive preamplifier 44a reaches a peak, Measurement is performed by the pulse rise time measuring means 46, and the radiation incident position in the x-axis direction can be obtained by the incident position calculating means 28a. On the other hand, the radiation incident position in the Y-axis direction can be measured as follows. In this case, since one end of the resistive electrode 42 is connected to the charge sensitive preamplifier 44a and the other end is grounded, the wave height of the output waveform of the charge sensitive preamplifier 44a is proportional to the distance IY. At the same time, it is proportional to the applied energy E. On the other hand, the output waveform of the charge-sensitive preamplifier 44b connected to the electrode 43 has a wave height proportional to the applied energy E only. Therefore, by dividing the output of the pulse height measuring means 45a by the output of the pulse height measuring means 45b by the wave height dividing means 47, a portion proportional to the applied energy can be removed, and only a portion proportional to the radiation incident position IY can be removed. Obtainable. Next, the radiation position in the y-axis direction can be calculated from the portion proportional to the incident position IY by the incident position calculator 28b. The incident position in the y-axis direction and the incident position in the x-axis direction calculated by the incident position calculating means 28a from the pulse rise time measuring means 46 are recorded in the memory 48. By the above, the incident position on a two-dimensional plane can be measured using the single semiconductor detection element 41, and a two-dimensional radiation incident position and a two-dimensional radiation image can be obtained.
[0026]
Embodiment 7 FIG.
A radiation position detector 60 according to Embodiment 7 of the present invention will be described with reference to FIG. FIG. 9 is a block diagram showing the configuration of the radiation position detector 60. The radiation position detector 60 is common in the circuit portion as compared with the radiation position detector according to the sixth embodiment, but is different in the electrode configuration provided in the semiconductor detection element 51. That is, the radiation position detector 60 is different in that a plurality of divided electrodes 52a, 52b, 52c, and 52d are provided in the y-axis direction in place of the resistive electrodes. Further, the divided electrodes 52a, 52b, 52c, and 52d are different from each other in that they are connected via external resistors 54a, 54b, and 54c, respectively. Further, a charge-sensitive preamplifier 44a is connected to the divided electrode 52d side, and the divided electrode 52a side is grounded. As a result, the divided electrodes 52a, 52b, 52c, 52d and the external resistors 54a, 54b, 54c play the same role as the resistive electrodes in the sixth embodiment. Note that arrows X and Y in FIG. 9 indicate coordinate axes on a two-dimensional plane. Further, E is the energy applied by the radiation 3. Further, regarding the Y coordinate of the incident position of the radiation 3, the distance from one end of the divided electrode 52d is IY. By the above, the incident position on a two-dimensional plane can be measured using the single semiconductor detection element 41, and a two-dimensional radiation incident position and a two-dimensional radiation image can be obtained.
[0027]
Embodiment 8 FIG.
A radiation position detector according to Embodiment 8 of the present invention will be described with reference to FIGS. FIG. 10 is a block diagram showing the configuration of this radiation position detector. Compared with the radiation position detector according to the first embodiment, the radiation position detector 70 has a pair of electrodes 53b and 53d opposed in the y-axis direction in addition to the pair of electrodes 53a and 53c opposed in the x-axis direction. It differs in that it is provided. Of the electrodes opposed in the x-axis direction, one electrode 53a is connected to a pulse waveform measuring means 55a via a charge sensitive preamplifier 44a. Further, of the electrodes facing in the y-axis direction, the pulse waveform measuring means 55b is connected to one electrode 53b via a charge sensitive preamplifier 44b. The two pulse waveform measuring means 55a and 55b are connected to the incident position calculating means 28a and 28b, respectively. The outputs of the incident position calculation means 28 a and 28 b are stored in the memory 48. The electrodes 53a, 53b, 53c, and 53d are individually connected to the DC power sources 56a, 56b, 56c, and 56d, and an electric field is applied to the element 61. In addition, arrows X and Y in FIG. 10 indicate coordinate axes on a two-dimensional plane.
[0028]
Next, the radiation position detection operation by the radiation position detector 70 will be described with reference to FIG. FIG. 11 is a schematic plan view of the semiconductor detection element 61 viewed from the z-axis direction perpendicular to the xy plane. The charge carriers generated at the position 57 by the radiation incident on the detection element 61 move according to the electric field in the element 61. For example, when the charge carrier is an electron, it moves in the direction of an electric field vector 58 having an electric field component 58a in the x-axis direction and an electric field component 58b in the y-axis direction. At this time, the charge-sensitive preamplifier 44a outputs a waveform corresponding to the electric field component 58a in the X-axis direction. On the other hand, the charge-sensitive preamplifier 44b outputs a waveform corresponding to the electric field component 58b in the Y-axis direction. The incident position in the x-axis direction and the y-axis direction can be measured from the rise time at which the peak of the output waveform becomes a peak and the slope of the rise portion. Therefore, the incident position in the X-axis direction is output by the pulse waveform measuring means 55a shown in FIG. 10, and the incident position in the Y-axis direction is output by the pulse waveform measuring means 55b. The memory 48 stores a radiation incident position on a two-dimensional plane or a radiation image. The pulse waveform measuring means may be either an analog system using a differential circuit or a system that performs digital sampling and performs numerical analysis. As described above, according to the radiation position detector 70, it is possible to measure the incident position and radiation image of radiation on a two-dimensional plane using the single semiconductor detection element 61.
[0029]
The direction and density of the electric field applied to the element, that is, the lines of electric force, determine the direction and speed of movement of the charge carriers. The measurement accuracy and position resolution when measuring the incident position of radiation, and the distortion of the measurement image are determined. It is an important parameter to decide. In order to measure with high accuracy, it is desirable that the direction and intensity of the electric field applied in the element are constant.
[0030]
In the semiconductor detection element, the potential at an arbitrary position may be adjusted. For example, FIG. 12 is a schematic plan view of the case where the potential is adjusted by a pair of ridge lines corresponding to diagonal lines of a rectangular parallelepiped semiconductor detection element (b (v) ≈c (v)). FIG. 13 shows a case where potentials are adjusted at a plurality of locations inside a rectangular parallelepiped detection element (b (v) ≈c (v), d (v) ≈e (v) ≈f (v), g (v) It is a schematic plan view of ≈h (v)). FIG. 14 is a schematic cross-sectional view in the case where a plurality of potential adjusting electrodes 64 perpendicular to the diagonal line connecting the pair of ridge lines a and o are provided inside the rectangular parallelepiped detection element. As described above, by providing the portion for adjusting the potential inside the detection element or the like and the potential adjustment electrode 64, the electric field in the detection element can be made uniform. Therefore, it is possible to measure the movement of the charge carrier with high accuracy and to detect the incident position with high accuracy. In addition, since data processing can be facilitated, the circuit configuration can be simplified.
[0031]
Embodiment 9 FIG.
A radiation position detector 80 according to Embodiment 9 of the present invention will be described with reference to FIG. FIG. 15 is a block diagram showing the configuration of the radiation position detector 80. Compared with the radiation position detector according to the eighth embodiment, the radiation position detector 80 is provided with a ground electrode 66 at the center of the semiconductor detection element 71, has the same center, is similar, and has a side length. Are different from each other in that rectangular adjustment electrodes 68 having different rectangular shapes are provided. Further, four systems for measuring the output waveform are provided for each of the electrodes 53a, 53b, 53c and 53d, and a comparator 67a for comparing the outputs of the pulse waveform measuring means 55a and 55c, and a pulse waveform measuring means. It is also different in that a comparator 67b for comparing the outputs of 55b and 55d is provided. Further, the outputs of the comparators 67a and 67b are connected to the incident position calculation means 28a and 28b, respectively. Note that arrows X and Y in FIG. 15 indicate coordinate axes on a two-dimensional plane.
[0032]
Next, the radiation position detection operation by the radiation position detector 80 will be described. When radiation enters the semiconductor detection element 71, charge carriers are generated, and the charge carriers move according to the direction of the electric field applied in the detection element 71. In this case, a ground electrode 66 is provided at the center of the detection element 71, and a similar rectangular potential adjusting electrode 68 having the same center is provided. The potential is adjusted so as to increase toward the surrounding electrodes. Therefore, among the generated charge carriers, for example, electrons are generated on the electrode 53a when the generation position is on the right side, on the electrode 53b when on the upper side, on the electrode 53c when on the left side, and on the electrode 53c when on the lower side. Each moves toward 53d. At this time, considering the case where electrons move to the electrode 53a on the right side, the output waveform of the charge-sensitive preamplifier 44a reflects X1 which is the X-direction component of the electron generation position, that is, the radiation incident position. Has a pulse rise time. The output waveform from the charge-sensitive preamplifier 44b has a pulse rise time that reflects Y1, which is the Y-direction component of the radiation incident position. The output waveform of the charge-sensitive preamplifier 44c has a pulse rise time that reflects X2 which is the X-direction component of the radiation incident position. The output waveform of the charge-sensitive preamplifier 44d has a pulse rise time that reflects Y2 which is the Y-direction component of the incident position of radiation. The output waveform of each charge-sensitive preamplifier is input to pulse waveform measuring means 55a, 55b, 55c, and 55d, and the waveform is measured. The outputs of the pulse waveform measuring means 55a and 55c are compared with X1 and X2 by the comparator 67a, and the X coordinate on the element is obtained by the incident position calculating means 28a from the comparison result. Similarly, the outputs of the pulse waveform measuring means 55b and 55d are compared with Y1 and Y2 by the comparator 67b, and the Y coordinate on the element is obtained from the comparison result by the incident position calculating means 28b. Each output of the incident position calculation means 28 a and 28 b is stored in the memory 48. As described above, since the positions in the X-axis direction and the Y-axis direction can be known according to the electron generation position, the incident position of the incident radiation on the two-dimensional plane using the single radiation position detection element 71 and Radiation images can be measured.
[0033]
In addition, although the rectangular parallelepiped-shaped semiconductor detection element 71 is used here and the ground electrode is provided at the center and the electrodes are provided on the four sides, the present invention is not limited to the rectangular parallelepiped shape. For example, an element having a polygonal planar shape may be used, and an electrode may be provided on each side. Further, a plurality of arc-shaped electrodes may be provided by using an element having a circular planar shape.
[0034]
Embodiment 10 FIG.
A radiation position detector according to Embodiment 10 of the present invention will be described with reference to FIG. FIG. 16 is a block diagram showing the configuration of the radiation position detector 90. As compared with the radiation position detector according to the sixth embodiment, the radiation position detector 90 uses a resistive electrode 42 and has a circuit configuration using pulse height measuring means 45a and 45b for measuring the height of the output waveform. Common in terms of preparation. On the other hand, the pulse wave height measuring means 45 b and the memory 48 are connected, and the difference is that the output of the pulse wave height measuring means can be stored in the memory 48. That is, in this radiation position detector 90, the radiation incident position can be measured on a two-dimensional plane by the single semiconductor detection element 81, as in the radiation position detector according to the sixth embodiment, and the pulse height measuring means 45b. A component proportional to the energy value E obtained in step (1) can be recorded in the memory 48. Thereby, in addition to the obtained two-dimensional radiation incident position, information on the energy E of the incident radiation can be obtained, and therefore, a radiation incident position or a radiation image discriminated for each energy can be obtained.
[0035]
In this case, the radiation position detector 90 is not limited to discriminating the incident radiation for each energy and measuring the incident position of the radiation within a predetermined energy range. For example, the incident radiation in any of the radiation position detectors of other embodiments 1 to 9 may be discriminated for each energy. Further, if a radiation image for each energy is obtained, an image of only radiation of a specific energy emitted from the object can be obtained, and application to a medical radiation image detector can be expected. Furthermore, the contrast of the radiographic image can be improved according to the elemental composition of the object, and conversely, applications such as estimating the elemental composition of the object by analyzing the energy distribution of the obtained radiographic image are expected. it can.
[0036]
【The invention's effect】
According to the radiation position detector of the present invention, the radiation incident position in the longitudinal direction between a pair of opposed electrodes of a rectangular parallelepiped semiconductor detection element is measured by measuring the rise time at which the peak of the output waveform becomes a peak. It can be measured with a single sensing element. As a result, the cost can be reduced with a simple structure, and the radiation incident position can be measured with high accuracy.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a radiation position detector according to Embodiment 1 of the present invention.
FIG. 2 is a graph showing an example of an output waveform of the radiation position detector according to the first embodiment of the present invention.
FIG. 3 is a block diagram showing an internal configuration of a pulse rise time measuring means constituting the radiation position detector according to the first embodiment of the present invention.
FIG. 4 is a block diagram showing a configuration of a radiation position detector according to Embodiment 2 of the present invention.
FIG. 5 is a graph showing an example of an output waveform of the radiation position detector according to the third embodiment of the present invention.
FIG. 6 is a block diagram showing a configuration of a radiation position detector according to a fourth embodiment of the present invention.
FIG. 7 is a block diagram showing a configuration of a radiation position detector according to a fifth embodiment of the present invention.
FIG. 8 is a block diagram showing a configuration of a radiation position detector according to a sixth embodiment of the present invention.
FIG. 9 is a block diagram showing a configuration of a radiation position detector according to a seventh embodiment of the present invention.
FIG. 10 is a block diagram showing a configuration of a radiation position detector according to an eighth embodiment of the present invention.
FIG. 11 is a schematic plan view of a semiconductor detection element constituting a radiation position detector according to an eighth embodiment of the present invention.
FIG. 12 is a schematic diagram showing an example of potential adjustment of a semiconductor detection element of a radiation position detector according to an eighth embodiment of the present invention.
FIG. 13 is a schematic diagram showing an example of potential adjustment of a semiconductor detection element in a radiation position detector according to Embodiment 8 of the present invention.
FIG. 14 is a diagram showing an example of potential adjustment of a semiconductor detection element in a radiation position detector according to an eighth embodiment of the present invention.
FIG. 15 is a block diagram showing a configuration of a radiation position detector according to the ninth embodiment of the present invention.
FIG. 16 is a block diagram showing a configuration of a radiation position detector according to the tenth embodiment of the present invention.
[Explanation of symbols]
1, 1a, 1b, 1c, 1d Semiconductor detection element, 2a, 2b electrode, 3 radiation, 4a charge carrier (electron), 4b charge carrier (hole), 5, 5a, 5b, 5c, 5d before charge sensitive type Preamplifier, 6 DC power supply, 7, 7a, 7b, 7c, 7d Pulse rise time measuring means, 8, 28a, 28b Incident position calculating means 10, 20, 30, 40, 50, 60, 70, 80, 90 Radiation Position detector, 12 Inversion filter amplifier, 14: Differential amplifier, 16a, 16b Constant fraction discriminator, 18 Time difference measuring device, 22 Pulse waveform analysis means, 24 Memory, 31, 41, 51, 61, 71, 81 Semiconductor detection element, 32a, 32b, 32c, 32d Split electrode, 34 electrode, 42 Resistive electrode, 43 Conductive electrode, 44a, 44b Charged Type preamplifier, 45a, 45b Pulse height measurement means, 46 Pulse rise time measurement means, 47 Wave height division means, 48 Memory, 52a, 52b, 52c, 52d Split electrode, 53 Conductive electrode, 54a, 54b, 54c Electrical resistance 55a, 55b, 55c, 55d Pulse waveform measuring means, 56a, 56b, 56c, 56d DC power supply, 57 radiation incident position (charge carrier generation position), 58 traveling direction, 58a X component, 58b Y component, 62 electric field lines 64, 68 Potential adjustment electrode, 66 Ground electrode, 67a, 67b Comparator

Claims (1)

It has a rectangular parallelepiped shape and has a first pair of electrodes facing each other and a second pair of electrodes facing each other in a direction orthogonal to the facing direction of the first pair of electrodes. A semiconductor detection element that generates two types of charge carriers of different polarities;
A charge-sensitive preamplifier connected to the semiconductor detection element;
Pulse rise time measuring means for measuring a pulse rise time at which the peak of the output waveform of the charge-sensitive preamplifier due to the two types of charge carriers generated by radiation incident on the semiconductor detection element reaches a peak;
An incident position calculating means for calculating an incident position of radiation from the pulse rise time,
A radiation position detector, wherein the semiconductor detection element includes a potential adjustment electrode for adjusting a potential in the detection element in the middle of the lines of electric force .

Images