JP4984811B2 - Industrial X-ray CT system - Google Patents

Description

The present invention also relates to an X-ray CT equipment for the industry.

  Attempts have been made to produce a detector for an X-ray CT apparatus using a compound semiconductor CdTe having a density higher than that of Si. However, the sensitivity of CdTe semiconductor radiation detectors (hereinafter referred to as CdTe detectors) decreases with long imaging. Therefore, in Patent Document 1, the measurement sensitivity of X-ray detection is improved, and the improvement in image quality during long-time imaging is also considered. Non-Patent Document 1 discusses a structure that reduces the influence of leakage current that occurs when a high bias voltage is applied to a CdTe semiconductor.

JP 2006-10364 A K. Nakazawa, et. Al .: “Improvement of the CdTe Diode Detectors using a Guard-ring Electrode,” IEEE Transaction on Nuclear Science, vol. 51, No. 4, pp1881-1858, (2004).

  However, it is essential that the CdTe detectors used in the industrial X-ray CT apparatus be densely installed in order to improve the image resolution. Furthermore, the industrial X-ray CT apparatus is used for a long period of 5 to 10 years. In the background art, a method for preventing the sensitivity characteristic of the CdTe detector from being deteriorated by such long-term use has not been considered.

  Therefore, an object of the present invention is to suppress the deterioration of the sensitivity characteristics of the detector due to the use of an industrial X-ray CT apparatus for a long period of time.

The X-ray detector according to the present invention includes a first electrode provided on a surface parallel to the X-ray emission direction in the semiconductor crystal, a second electrode, a second electrode on a surface facing the first electrode, 3 and a fourth electrode, the third electrode is provided in the vicinity of a surface on which the X-rays are incident on the semiconductor crystal, and the fourth electrode is a surface on which the X-rays are incident on the semiconductor crystal. It is characterized by being provided in the vicinity of the opposite surface .

  According to this invention, this invention can suppress that the sensitivity characteristic of a detector deteriorates by using an industrial X-ray CT apparatus over a long period of time.

The industrial X-ray CT apparatus is a very useful nondestructive inspection apparatus for observing and measuring the internal shape of an object. For this reason, recently it has come to be used mainly by automobile companies for measuring the shape of developed products and measuring the distribution of casting nests. In order to take a tomographic image of a large-sized cast product or the like, an industrial X-ray CT apparatus using an accelerator that generates high-energy X-rays with high transmission power as an X-ray source has been developed. The background art shows an industrial X-ray CT apparatus using an electron linear accelerator as an X-ray source and a strip-shaped silicon semiconductor detector as an X-ray detector. This X-ray CT apparatus is a so-called third-generation CT apparatus that takes a tomographic image by rotating the device under test once around an axis perpendicular to the X-ray fan beam.

  In a semiconductor detector using silicon in an industrial X-ray CT apparatus, the detection efficiency of high energy X-rays of 1 to 10 MeV is about 20%. However, in order to improve the density resolution of the tomographic image, the higher the detection efficiency (sensitivity) of the detector, the better. In addition, it is preferable to use a CdTe semiconductor detector, which is expected to be twice as dense as silicon and capable of improving detection efficiency by about twice.

  For this reason, attempts have been made to use CdTe semiconductor detectors in industrial high-energy X-ray CT apparatuses. However, the CdTe detector has a problem that the output pulse height gradually decreases due to the polarization effect. Here, the polarization effect is a phenomenon in which electrons are trapped in the vicinity of an electrode, the electric field in the sensor is reduced, and the sensitivity of the sensor is lowered. The influence varies depending on the dose rate and the bias voltage. Therefore, even when used in an industrial high energy X-ray CT apparatus, there is a problem that the output current decreases in a few minutes to a few hours.

  In order to solve this problem, Patent Document 1 discloses a forward Schottky diode type CdTe detector using an In electrode as an anode (anode) and a Pt electrode as a cathode (cathode) with a small leakage current. Biased. The polarization effect is eliminated by using a semiconductor detector in a state where there is a large amount of leakage current. Further, in Non-Patent Document 1, a high bias voltage is applied to the CdTe detector in order to reduce the polarization effect, and a guard ring is arranged around the sensor in order to reduce the influence of the leakage current caused thereby.

  In addition, improvement in the production method of CdTe crystals has progressed, and higher purity crystals have been obtained. For this reason, as shown in Patent Document 1, even in a CdTe detector in which an anode is an In electrode and a cathode is a Pt electrode, the time required to image one test object with an industrial X-ray CT apparatus (stereoscopic data is In order to obtain images for about 1 to 4 hours, it has become possible to shoot without lowering the output current.

  Here, the structure of a CdTe detector used in an industrial high energy X-ray CT apparatus is shown as a comparative example. FIG. 10 is an elevation view and a plan view showing the structure of the X-ray detector in the comparative example. A Pt electrode 51 and an In electrode 52 are deposited on the entire upper and lower surfaces of the CdTe crystal 50 to constitute an In / CdTe / Pt detector. The In / CdTe / Pt detector is bonded to the flexible substrate 53. The In electrode 52 on the flexible substrate 53 side is bonded to the printed wiring terminal 57 with a conductive adhesive. The upper Pt electrode 51 is coupled to the printed wiring terminal 56 by a bonding wire 55. The size of the CdTe crystal is 3 mm long × 40 mm wide × 0.5 mm high. The heavy metal substrate 54 is made of a tungsten alloy and plays a role of shielding X-ray scattering and counter-attacking electrons incident on the adjacent detector simultaneously with protection of the detector. The CdTe detector is installed in the CT apparatus so that X-rays are incident from the direction of the arrow in the figure. Since CdTe has a density about twice that of conventional Si, the absorption efficiency for incident X-rays, that is, the detection efficiency is about twice.

  However, an industrial X-ray CT apparatus is usually used for a long period of several to 10 years. It is desirable that the performance of the CdTe detector does not change during that period. However, when X-rays are irradiated to a CdTe detector that has been stored for a long time and the output is measured, it has been found that there are cases where the output decreases as the irradiation time elapses. FIG. 11 shows the relationship between the output reduction rate and the bias voltage when 4 hours have elapsed after X-ray irradiation to such a CdTe detector. A 1 MV electron linear accelerator was used as the X-ray source. There are two types of bias voltages, 100V and 200V. When the CdTe detector is directly irradiated with X-rays from the accelerator (without shielding), changes in output are measured under four conditions when acrylic, aluminum, or iron (SUS) 10 mm is placed in front of the detector. did.

Without shielding (data in this figure) 30% (bias 100V) or 10% in 4 hours
(200V) also decreases the output. On the other hand, if acrylic (□ data) or the like is installed in front of the detector, the output drop is greatly reduced under any bias condition, approaching zero.

  The X-ray energy from the 1MV linear accelerator is widely distributed from a maximum of 1 MeV to several tens of keV. However, the level of incident X-ray energy is merely related to the amount of generated charges (number of electron / hole pairs) in the CdTe crystal, and the charge collection mechanism is the same. However, the low energy of the X-rays incident on the CdTe crystal is almost absorbed near the front surface of the crystal when viewed from the incident surface in the incident direction. On the other hand, since the transmission ability is high at high energy, it reaches the back while being absorbed in the crystal.

From the test results shown in FIG. 11, it can be seen that the reduction effect of the output drop is almost the same between 10 mm acrylic and 10 mm iron. The energy of X-rays shielded by 10 mm of acrylic is several 10
It is up to about keV, and X-rays with higher energy are also shielded by high-density aluminum or iron. As described above, considering that the charge collection mechanism inside CdTe is the same regardless of the level of energy, the effect of reducing the output reduction due to the shielding is that the charge due to X-rays near the incident surface of the detector. It can be seen that it is expressed by a decrease in the generation amount.

  Further, the CdTe detector is processed into a detector by forming electrodes on both surfaces of a wafer cut into a plate shape and then cutting it into a strip shape (dicing). Therefore, the cut-out surfaces where the electrodes are not deposited (that is, the four surfaces sandwiched between the electrodes) are the surfaces that have been diced. Microscopically, such a surface has many defects and traps electrons and holes generated by X-rays or promotes recombination. In addition, there is a high possibility that defects will increase due to an increase in defects due to secular change, material change, penetration of hydrogen and oxygen atoms, and the like.

  From the above considerations, it is considered that the deterioration of characteristics in the vicinity of the X-ray incident surface (dicing surface) of the detector is a cause of a decrease in sensitivity of the entire detector (a decrease in output of the detector). The present invention is based on the above consideration and aims to prevent a change in performance even when a CdTe detector is used for a long period of time.

  FIG. 1 is an elevation view and a plan view of an embodiment of the present invention. This figure shows the structure of a CdTe detector 404 to which the present invention is applied. It should be noted that the present invention can be applied to members other than CdTe as long as the members deteriorate over time. A flexible substrate 104 is bonded to one side of the heavy metal substrate 105, and a CdTe crystal 100, which is a semiconductor crystal, is bonded thereon. Electrodes are deposited on the upper and lower surfaces of the CdTe crystal 100, which are two surfaces parallel to the X-ray emission direction. The CdTe crystal has a thickness of 0.5 mm, a width of 3 mm, and a depth of 40 mm. When the depth is 40 mm, it has sufficient sensitivity to X-rays from 400 keV to 12 MeV. In this embodiment, a Pt electrode is formed on the lower surface, and an In electrode 101 as the first electrode is formed on the upper surface. It operates as a radiation detector by applying a -bias voltage to the Pt electrode side or applying a + bias voltage to the In electrode side. In this embodiment, the In electrode is set to the ground potential, and a negative voltage is applied to the Pt electrode. Two Pt electrodes, a Pt pre-electrode 102 as a third electrode and a Pt main electrode 103 as a second electrode, are provided. The depth length of the Pt pre-electrode 102 is 0.2 mm, the gap between the Pt pre-electrode 102 and the Pt main electrode 103 is 0.05 mm, and the Pt pre-electrode 102 and the Pt main electrode 103 are electrically separated. . With such a configuration, the CdTe crystal 100 positioned between the Pt main electrode 103 and the In electrode 101 has no dicing surface on the X-ray incident direction side. The Pt pre-electrode 102 as the third electrode plays a role of removing leakage current.

The CdTe detector is installed in the CT apparatus in a state where X-rays are incident from the left side of the figure and the strip-shaped detector is set up. By doing in this way, the pitch between each detector becomes narrow and the detector can be densified. This increases the number of transmission data samplings and improves image resolution. In this embodiment, the pitch between the detectors is about 1.2 mm, and the data sampling pitch for reconstructing the image is less than 1 mm.

  The Pt pre-electrode 102 as the third electrode is provided in the vicinity of the surface (dicing surface) where X-rays enter the semiconductor crystal and the surface facing the In electrode 101. Since the Pt pre-electrode 102 is in the vicinity of a surface (dicing surface) on which X-rays are incident on the semiconductor crystal, only a degradation signal generated on the dicing surface can be extracted.

  In this CdTe detector, a negative bias voltage is applied to the Pt pre-electrode 102 and the Pt main electrode 103, and the In electrode is set to the ground potential. The output current of the Pt pre-electrode 102 is not normally measured, and the current flowing through the Pt main electrode 103 is amplified by a preamplifier and measured. Therefore, the CdTe detector having a stable performance for a long time is separated from the characteristic deterioration signal generated in the vicinity of the dicing surface, which is the X-ray incident surface of the detector, and the normal signal of the non-deteriorated portion generated in the Pt main electrode 103. realizable.

  The heavy metal substrate 105 is made of heavy metal such as tungsten. In order to shield scattered electrons and scattered X-rays from adjacent semiconductor detectors, the density should be higher and thicker, but this is determined in consideration of performance such as the resolution of the CT apparatus. In this embodiment, a tungsten alloy 0.5 mm thick shielding plate is used. When the energy of the X-ray source to be used is low, a slightly low density such as SUS or brass may be used.

  The signal extraction from the Pt pre-electrode 102 of the CdTe crystal 100 is connected to the wiring 113 on the flexible substrate 104 by the conductive bonding portion 114. The signal extraction of the Pt main electrode 103 is connected to the wiring 111 on the flexible substrate 104 by the conductive bonding portion 112. The In electrode 101 is bonded to the wiring 109 on the flexible substrate 106 by the conductive bonding portion 110. Then, the wiring 109 is bonded to the wiring 107 on the flexible substrate 104 by the conductive bonding portion 108. A flexible substrate with a thickness of 0.1 mm is used. The output current of the detector is small and the thickness is minimal, so it can be used without problems.

FIG. 2 shows the detection efficiency with respect to the energy of the X-ray of the CdTe detector of this embodiment. The horizontal axis represents X-ray energy, and the horizontal axis represents detection efficiency. The efficiency curve 301 shows the efficiency of the CdTe detector in the comparative example. The efficiency curve 302 of the CdTe detector of the present embodiment is less efficient than the efficiency curve 301 of the comparative example when the X-ray energy is 100 keV or less. However, when the X-ray energy is 100 keV or more, this example and the comparative example show the same detection efficiency. Further, compared with the detection efficiency curve 303 of the Si detector, the efficiency is about twice as high in a high energy region of 1 MeV.

  As an X-ray source using an electron linear accelerator used in an industrial high-energy X-ray CT apparatus, 1, 3, 6, 9, and 12 MeV accelerators are often used. The average energy of X-rays generated by the X-ray source is about 1/3 of the acceleration voltage. Therefore, in the region of 300 keV to 4 MeV, which is the average energy of X-rays, the CdTe detector in this example has a detection efficiency equivalent to that of the CdTe detector of the comparative example.

Note that industrial high-energy X-ray CT often images medium and large-sized aluminum castings and iron castings such as automobile parts. In addition, X-rays of 100 keV or less are almost absorbed by the subject at the time of imaging, and the amount incident on the detector is small. Therefore, the CdTe detector of this embodiment is 100
The low detection efficiency for X-rays below keV is not a problem at all in terms of application as an apparatus.

  Of course, the size of the CdTe detector is not limited to the above. The depth length of the Pt pre-electrode can be further shortened if there is no problem in electrode fabrication. Conversely, increasing the depth length further reduces the sensitivity of low-energy X-rays at the Pt main electrode, so it must be determined according to the application. In order to detect X-rays of 100 keV or higher, about 0.2 mm shown in this embodiment is appropriate.

FIG. 3 is a diagram showing a configuration of an industrial X-ray CT apparatus using a CdTe detector. The X-ray CT apparatus 700 is a means for emitting X-rays to a device under test. The X-ray CT apparatus 700 outputs an X-ray fan beam 402, that is, an electronic linear accelerator 401, a scanner 403 on which a device under test 414 is installed, In order to improve the S / N ratio of the X-ray detectors 404-1 to 404-512 that detect X-rays transmitted through the specimen 414 and the X-ray detector 404, the scattered X to the X-ray detector 404 is detected. A collimator 405 that serves to suppress the incidence of the line, a signal processing device 410 that amplifies the output signal of the detector and converts it into a digital signal, and a control that collects digital data from the signal processing device 410 and controls the entire device A device 406, an image reconstruction device 407 that performs image reconstruction, a display device 408 that displays an image created by image reconstruction and other information, and a control device 406. Electronic linear accelerator 401 by control command, a controller 409 for controlling the operation of the scanner 403, and a signal processing device 410.

  The X-ray CT apparatus 700 in the figure shows a third generation X-ray CT apparatus that rotates a test object and images one section. In addition to the rotation function, the scanner 403 has a function of moving up and down in order to take a cross-sectional image of each height of the DUT.

  The electronic linear accelerator 401 is connected to a controller 409 by a control cable 416, and generation / stop of the X-ray fan beam is controlled by the controller. Similarly, the scanner 403 is connected to the controller 409 via a control cable 415, and the rotation and vertical position of the scanner are adjusted.

As the X-ray detector 404, the CdTe detector or Si detector shown in FIG. 1 is used. And it arrange | positions in a line so that the generation | occurrence | production point of the fan beam 402 may be anticipated, and 512 pieces are installed in the present Example. The X-ray detector detects X-rays that have passed through the test object every time an X-ray pulse is output from the electronic linear accelerator 401 at a constant angle in synchronization with the rotation of the scanner. A signal corresponding to the X-ray dose output from the X-ray detector 404 is amplified and converted into a digital signal. Then, after the digital signal is transmitted to the control device 406 through the signal cable 417, it is sent to the image reconstruction device 407 and used for reconstruction of the CT image.

  X-rays are usually pulsed X-rays generated periodically due to the characteristics of the accelerator. As a general value, a powerful X-ray pulse (collection of X-ray photons) having a width of 5 μs is output in a period of 5 ms. In this embodiment, 1920 times of X-ray pulses are irradiated during one rotation of the test object, and data is measured. That is, the X-ray dose is measured every 0.1875 degrees. Since there are 512 detectors, the data for reconstructing one slice has a data amount of 512 × 1920.

FIG. 4 is a diagram showing the configuration of the signal processing device 410. The signal processing device 410 includes a bias power source 427 for supplying a bias voltage to all the X-ray detectors 404-1 to 404-512, and preamplifiers 421-1 to 421-for amplifying output current from each X-ray detector. 512, sampling and hold amplifiers (hereinafter referred to as S / H amplifiers) 422-1 to 422-512 for holding the outputs of the preamplifiers for AD conversion, AD converters 423-1 to 423 for AD conversion of the held signals 512, the digital data output from each AD converter via the bus 425 is read, and the output hold of the controller 426, S / H amplifier 422 that transfers the data to the control device 406 and the AD conversion start timing of the AD converter 423 are controlled. It consists of a timing controller 424.

FIG. 5 is a diagram showing the configuration of the preamplifier 421 and the connection between the CdTe detector 404.
The In electrode of the CdTe detector 404 is connected to the ground by the shield side of the coaxial cable 431. Further, the Pt main electrode is connected to the bias power source 427 via the resistor 434 by the core wire of the coaxial cable 431 and at the same time is coupled to the inverting input of the OP amplifier 456 via the capacitor 444. The output of the OP amplifier, the feedback resistor 457, and the feedback capacitor 458 are coupled to the inverting input. The output pulse current 460 output from the detector by the X-ray pulse passes through the capacitor 444 and is mostly supplied to the capacitor 458. Then, the output pulse current 460 is integrated in the capacitor 458 to be converted into current / voltage, and output from the preamplifier 421 as a voltage.

  Since the resistor 434 is a resistor for supplying a bias voltage, a high resistance of 1 to 10 MΩ is used. The capacitor 458 is determined so that the output of the OP amplifier does not exceed the maximum output voltage when the current from the detector is integrated. The values of the feedback resistor 457 and the capacitor 444 are set to appropriate values such that the preamplifier output becomes zero before the detector current by the next X-ray pulse is input. For example, when the capacitor 458 is 10 pF and the feedback resistance 457 is about 10 MΩ, the time constant is 100 μs, and the time constant is sufficient to integrate the output from the detector, which is a pulse current of 5 μs.

  The larger the capacitor 444 is, the better from the viewpoint of current integration. In this embodiment, it is set to 200 pF. Then, when the X-ray pulse continuously enters every 5 ms, the output of the DC component to the output of the OP amplifier 456 is prevented. When a differential circuit or a waveform shaping circuit is provided at the subsequent stage of the preamplifier 421, the capacitor 444 may have a larger value, such as 0.1 μF.

  On the other hand, the Pt pre-electrode 102 is connected to the bias power source 427 via the resistor 433 by the core wire of the coaxial cable 430. Since the resistor 433 is for bias supply, the same value as that of the resistor 434 is used. Capacitor 432 is 0.1 μF.

  When the X-ray pulse enters the detector, a current is generated between the Pt pre-electrode and the In electrode, and a current 461 flows through the coaxial cable 430. However, since the current 461 flows to the ground via the capacitor 432 provided before the resistor 433, the output of the preamplifier 421 is not affected. The coaxial cable may use a twisted pair wire as long as the influence of external noise can be ignored.

  Therefore, even if a defect occurs near the X-ray incident surface of the CdTe detector due to deterioration over time and the output current of that portion decreases, the deterioration signal and the normal signal are separated, so the measurement results are not affected. Absent. In addition, the detector performance and thus the image quality of the X-ray CT apparatus can be stably maintained for a long time.

  FIG. 6 is a diagram showing temporal changes in the X-ray pulse incident on the CdTe detector, the output currents of the main and pre-electrodes of the detector, the pre-amplifier output voltage, and the output voltage of the S / H amplifier in the next stage. . As described above, the X-ray pulse width Tp (= t1-t0) is 5 μS. The generation interval (t3-t0) of the X-ray pulse is constant and is controlled by the controller 9. In this embodiment, it is 5 ms. Regardless of the presence or absence of an X-ray pulse, a constant minute leakage current flows through the detector output current, and the output current resulting from the X-ray increases only while the X-ray is incident on the detector. In the preamplifier described with reference to FIG. 5, only the main electrode output current by X-rays passes through the capacitor 444 and is integrated into the capacitor 458. Therefore, only the output current from the main electrode contributes to the preamplifier output voltage.

  The preamplifier output voltage is 0 V before X-ray pulse generation. Then, while the X-ray pulse is incident on the X-ray detector (from time t0 to t1), the preamplifier output voltage increases by integrating the current (in the negative direction because it is an inverting circuit). When X-ray generation is eliminated, the preamplifier output voltage attenuates with a constant time constant and returns to zero. Since the S / H amplifier holds the output at time t1 under the control of the timing controller 424, it can be converted into a digital value by the AD converter during the hold period (from time t1 to t2).

  FIG. 7 shows a configuration diagram of a preamplifier 521 in which a deterioration diagnosis function of the CdTe detector is added to the X-ray CT apparatus. The preamplifier 521 is used instead of the preamplifier 421 shown in FIG. The difference in the circuit is that a switch 560 for switching two signals of the Pt pre-electrode and the Pt main electrode and its control signal 561 are provided. The switch 560 takes two states depending on the state of the control signal. The control signal 561 is output from the controller 409 (FIG. 3). In FIG. 7, similarly to the preamplifier 421, the output current of the Pt pre-electrode flows to the capacitor 432, and the output current of the Pt main electrode is input to the OP amplifier 456.

When the switch 560 is switched, the output current of the Pt main electrode flows to the capacitor 432, and the output current of the Pt pre-electrode is input to the OP amplifier 456. By measuring the X-ray pulse in this state, it is possible to measure the output current in the vicinity of the X-ray incident surface where the output changes due to secular change. Therefore, by comparing the measured data with the initial CT operation start time, CdTe
The replacement time of the detector can be determined.

  Of course, the values of the capacitors and resistors in the above-described embodiments are not limited to these values.

  As described above, the combination of the CdTe detector of the present invention and the AC coupling (AC coupling) current / voltage conversion preamplifier combined with the X-ray detector increases the preamplifier output due to the high sensitivity of the CdTe detector. In addition to being obtained, it is possible to eliminate the influence due to aging such as characteristic deterioration near the X-ray incident surface of the detector. Therefore, it is possible to provide an industrial X-ray CT apparatus that increases the measurement sensitivity of X-ray CT and does not deteriorate the quality of a reconstructed image even when used for a long time.

FIG. 8 is a structural diagram of the CdTe detector in the second embodiment. As in the first embodiment, the flexible substrate 104 is bonded to one side of the heavy metal substrate 105, and the CdTe crystal 100 is bonded thereon. Electrodes are deposited on the upper and lower surfaces of the CdTe crystal 100, respectively. The CdTe crystal has a thickness of 0.5 mm, a width of 4 mm, and a depth of 41.5 mm. Unlike the first embodiment, the electrode is provided with not only the Pt pre-electrode 102 on the dicing surface on which X-rays enter but also a Pt rear electrode 702 that is a fourth electrode behind the Pt main electrode 103. The fourth electrode is provided in the vicinity of the surface opposite to the dicing surface on which X-rays enter the semiconductor crystal. The depth of the electrode is 0.2 mm for both the Pt pre-electrode 102 and the Pt rear electrode 702. The In electrode 101 is wired by the flexible substrate 106. The electrode wiring method and biasing method are the same as in the first embodiment. The CdTe detector of the present embodiment can be applied to an industrial high energy X-ray CT apparatus in the same manner as the detector of the first embodiment.

  If the method of the present embodiment is applied, in addition to the effects of the first embodiment, it is possible to prevent the deterioration of the detector characteristics due to the aging deterioration phenomenon (defect increase, interface state increase) occurring on the rear dicing surface. .

  FIG. 9 is a structural diagram of the CdTe detector according to the third embodiment. As in the first embodiment, the flexible substrate 604 is bonded to one side of the heavy metal substrate 605, and the CdTe crystal 600 is bonded thereon. Electrodes are deposited on the upper and lower surfaces of the CdTe crystal 600, respectively. The CdTe crystal has a thickness of 0.5 mm, a width of 4 mm, and a depth of 41.5 mm. Unlike the first and second embodiments, the Pt pre-electrode 602 is disposed on the lower part of four surfaces including not only the dicing surface on which X-rays enter but also the remaining dicing surface, and is disposed on the ring. The width of the ring is 0.2 mm. A ring-shaped Pt pre-electrode 602 is provided on the outer peripheral side of the Pt main electrode 603. The Pt pre-electrode 602 is provided in the vicinity of the four dicing surfaces formed in the semiconductor crystal. The In electrode 601 is wired by the flexible substrate 606.

  The electrode wiring method and biasing method are the same as in the first embodiment. The CdTe detector of the present embodiment can be applied to an industrial high energy X-ray CT apparatus in the same manner as the detector of the first embodiment.

  If the method of the present embodiment is applied, in addition to the effects of the first embodiment, an aging deterioration phenomenon that occurs on a dicing surface other than the X-ray incident surface (side surface of the CdTe crystal 600 sandwiched between the Pt electrode and the In electrode). This also has an effect of preventing the deterioration of the detector characteristics due to (defect increase, interface state increase).

  In all of Examples 1 to 3, it is also possible to provide a plurality of In electrodes and one Pt electrode. However, since the In electrode surface has a Schottky diode structure that reduces the leakage current, it is possible that the characteristics deteriorate and the leakage current increases, so care should be taken.

  Furthermore, it is also possible to apply the present invention by using both electrodes as Pt electrodes. However, in this case, the leakage current increases.

  The present invention can be used for an X-ray detection unit of an industrial X-ray CT apparatus, and can be used for inspection of a cast hole of a cast product, three-dimensional shape data acquisition, density distribution measurement, and the like.

It is a figure which shows the structure of one Example of this invention. It is the detection efficiency with respect to the X-ray energy of the detector of one Example of this invention. It is a block diagram of the industrial X-ray CT apparatus using one Example of this invention. It is a block diagram of the signal processing apparatus of the industrial X-ray CT apparatus of one Example of this invention. It is a figure which shows the structure of the preamplifier of the industrial X-ray CT apparatus of one Example of this invention, and the connection of a CdTe detector. It is the figure which showed the time change of the CdTe detector output of one Example of this invention, a preamplifier output, and the output of S / H amplifier. It is a block diagram of the preamplifier for adding the deterioration diagnostic function of a CdTe detector to the X-ray CT apparatus of one Example of this invention. It is a figure which shows the structure of the 2nd Example of this invention. It is a figure which shows the structure of the 3rd Example of this invention. It is a figure which shows the structure of a comparative example. It is a figure which shows the relationship between an output fall rate and a bias voltage when 4 hours have passed since X-ray irradiation of the conventional CdTe detector.

Explanation of symbols

100 CdTe crystal 101 In electrode 102 Pt pre-electrode 103 Pt main electrode 104, 106 Flexible substrate 105 Heavy metal substrate 401 Electronic linear accelerator 403 Scanner 404-1 to 404-512 X-ray detector 405 Collimator 406 Controller 407 Image reconstruction device
408 Display device 409 Controller 410 Signal processing device 421,521 Preamplifier

Claims (1)

An industrial X-ray CT apparatus comprising means for emitting X-rays to a device under test and an X-ray detector for detecting X-rays transmitted through the device under test with a semiconductor crystal,
The X-ray detector includes a first electrode provided on a plane parallel to the X-ray emission direction in the semiconductor crystal;
On the surface facing the first electrode, a second electrode, a third electrode, and a fourth electrode are provided,
The third electrode is provided in the vicinity of a surface where X-rays are incident on the semiconductor crystal;
The industrial X-ray CT apparatus, wherein the fourth electrode is provided in the vicinity of a surface opposite to a surface on which X-rays are incident on the semiconductor crystal.

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