JP2005241334A - Radiation detection instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation detection instrument enabling to reduce noises. <P>SOLUTION: A shield plate 11 is formed by a conductive material having a low shield factor against radiation such as conductive carbons and alminum plates, and the shield plate 11 is placed between a phototimer 12 which measures radiation dose (in this case, X-ray) and a radiation sensitive semiconductor thick film 1 over the whole area of a X-ray detection effective area A. The shield plate 11 is grounded. Due to the configuration, radiation noises from the phototimer 12 is shielded by the shield plate 11 and dissipated to the ground. Therefore, radiation noises affecting to the radiation detection instrument caused by the phototimer 12 can be decreased. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a radiation detection apparatus used in the medical field, the industrial field, and the nuclear field.

An X-ray detection apparatus will be described as an example. The X-ray detection apparatus includes an X-ray sensitive X-ray conversion layer (semiconductor layer). The X-ray conversion layer is converted into charge information by the incidence of X-rays, and the converted charge information is read out to read X Detect lines. A phototimer (radiation dose measuring means) for measuring the X-ray dose is disposed on the X-ray conversion side of the X-ray conversion layer. It is used to adjust the output of the line. As shown in FIG. 4, a shielding plate (shielding means) 103 that shields light and the like is disposed between the X-ray conversion layer 101 and the phototimer 102 (the voltage application electrode and the like are not shown). (Omitted). The shielding plate 103 is made of a material having a low shielding rate such as carbon or resin so as to minimize the attenuation of X-rays by the shielding plate. In addition, there is an X-ray detection apparatus in which a phototimer is disposed in an area (for example, a corner) other than the X-ray detection effective area (radiation detection effective surface) (see, for example, Patent Document 1).
JP 2002-90461 A (page 2-4, FIG. 1-3)

  However, the charges converted from the X-rays by the X-ray conversion layer are very small, and it is necessary to amplify the charges. In that case, since noise is amplified, it is necessary to reduce the noise in order to obtain an image with a good S / N (signal to noise) ratio. On the other hand, there is no need to reduce noise in the phototimer, and it is common to use a noisy power supply to drive the phototimer, and a general switching power supply is used for miniaturization and cost reduction. .

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the radiation detection apparatus which can reduce noise.

  As a result of intensive studies to solve the above problems, the inventors have obtained the following knowledge.

  That is, the inventors have conceived that noise caused by a phototimer has an influence on the X-ray detection apparatus. Therefore, it is conceivable to arrange the phototimer in an area other than the X-ray detection effective area as in Patent Document 1 described above, but in actuality, the noise is not reduced. In addition, it may be possible to shield noise by providing a shielding plate between the X-ray conversion layer and the phototimer only in the region where the phototimer is provided. It does n’t come. Therefore, noise is also generated from the switching power supply and driving circuit for driving the phototimer and the wiring connecting the phototimer to the phototimer, and the noise is radiated to affect the X-ray detection apparatus as radiation noise. I thought.

  A radiation detection apparatus includes a radiation-sensitive semiconductor layer typified by the above-described X-ray conversion layer and the like, a direct conversion type that directly converts radiation by the radiation-sensitive semiconductor layer, and a scintillator that converts radiation to light. And an indirect conversion type that includes a light-sensitive semiconductor layer and converts radiation into light and converts it into charge information. In particular, when the radiation detection apparatus is a direct conversion type, the semiconductor layer is formed of amorphous selenium (a-Se). The film thickness of amorphous selenium is thicker than that of the photosensitive semiconductor layer of the indirect conversion type radiation detection apparatus, and a high voltage (for example, about several hundred volts to several tens kV) must be applied with a bias voltage. In the case of such a direct conversion type radiation detection apparatus, it is particularly susceptible to radiation noise due to the application of a high bias voltage. Therefore, the knowledge that the shielding means represented by a shielding plate and the like is made of a grounded conductive material so as to shield radiation noise and the shielding means is disposed over the entire radiation detection effective surface is obtained. It was.

  The present invention based on such knowledge has the following configuration.

  That is, the invention according to claim 1, comprising a semiconductor layer that converts the information of the radiation into charge information by the incidence of radiation, is a radiation detection device that detects radiation by reading the converted charge information, A radiation dose measuring means for measuring a dose of radiation; and a shielding means for shielding light, wherein the radiation dose measuring means is disposed on a radiation incident side, and the shielding means is a radiation dose measuring means and a semiconductor layer. The shielding means is formed of a conductive material which is disposed over the entire surface of the radiation detection effective surface and is grounded.

  [Operation / Effect] According to the invention described in claim 1, the shielding means is constituted by a grounded conductive substance, and the shielding means is disposed on the entire radiation detection effective surface between the radiation dose measuring means and the semiconductor layer. By disposing over, radiation noise from the radiation dose means can be shielded by the shielding means, and radiation noise can be released by grounding. As a result, it is possible to reduce the radiation noise from the radiation dose measuring means exerted on the radiation detection apparatus.

  The invention described above includes a phosphor (scintillator) that converts radiation information into light, and a light-sensitive semiconductor layer that converts radiation information into charge information indirectly, that is, converts the converted light into charge information. The present invention can also be applied to an indirect conversion type radiation detection apparatus provided and a direct conversion type radiation detection apparatus including a radiation sensitive semiconductor layer that directly converts radiation information into charge information. Invention described in 1.). In particular, in the case of the direct conversion type, conventionally, radiation noise from the radiation dose measuring means has been remarkable, which is particularly useful for reducing the radiation noise.

  According to the radiation detection apparatus of the present invention, the shielding means is constituted by the grounded conductive substance, and the shielding means is disposed over the entire radiation detection effective surface between the radiation dose measurement means and the semiconductor layer. Thus, since the shielding means shields the radiation noise from the radiation dose means and the radiation noise can be released by grounding, the radiation noise from the radiation dose measuring means exerted on the radiation detection apparatus can be reduced.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of a radiation detection apparatus according to an embodiment, and FIG. 2 is a plan view showing the configuration of the radiation detection apparatus. In this embodiment, a direct conversion type radiation detection apparatus will be described as an example.

  As shown in FIG. 1, the radiation detection apparatus according to the present embodiment is provided on a surface of the semiconductor thick film 1 and a radiation sensitive semiconductor thick film 1 in which carriers are generated when radiation such as X-rays enters. The applied voltage application electrode 2, the carrier collection electrode 3 provided on the back side opposite to the radiation incident side of the semiconductor thick film 1, and the charge storage capacitor Ca for collecting collected carriers to the carrier collection electrode 3. , And a thin film transistor (TFT) Tr that is a switching element for taking off charges that are normally OFF (blocked) for taking out the charges accumulated in the capacitor Ca. The semiconductor thick film 1 corresponds to the semiconductor layer in this invention.

  In addition, the radiation detection apparatus includes a data line 4 connected to the source of the thin film transistor Tr and a gate line 5 connected to the gate of the thin film transistor Tr. , Carrier collection electrode 3, capacitor Ca, thin film transistor Tr, data line 4, and gate line 5 are laminated on insulating substrate 6.

  As shown in FIGS. 1 and 2, for each of the carrier collection electrodes 3 formed in a large number (for example, 1024 × 1024) in a vertical / horizontal two-dimensional matrix arrangement, each capacitor Ca and thin film transistor Tr described above is provided. Are connected to each other, and the carrier collecting electrode 3, capacitor Ca, and thin film transistor Tr are separately formed as each detecting element DU. The voltage application electrode 2 is formed over the entire surface as a common electrode of all the detection elements DU. Further, as shown in FIG. 2, the data lines 4 described above are arranged in parallel in the horizontal (X) direction, and the gate lines 5 described above are arranged in the vertical (Y) direction as shown in FIG. The data lines 4 and the gate lines 5 are connected to the detection elements DU. The data line 4 is connected to the multiplexer 8 via the charge-voltage conversion group 7, and the gate line 5 is connected to the gate driver 9. Note that the number of detection elements DU arranged is not limited to the above-mentioned 1024 × 1024, but can be used by changing the number of arrangement according to the embodiment. Therefore, the form with only one detection element DU may be sufficient. The charge-voltage conversion group 7 includes an amplifier (not shown).

  When creating a radiation detector formed of the semiconductor thick film 1 or the insulating substrate 6, the surface of the insulating substrate 6 is used by using a thin film forming technique by various vacuum deposition methods or a pattern technique by a photolithography method, The data line 4 and the gate line 5 are wired, and the thin film transistor Tr, the capacitor Ca, the carrier collection electrode 3, the semiconductor thick film 1, the voltage application electrode 2, and the like are sequentially stacked. The semiconductor for forming the semiconductor thick film 1 can be appropriately selected according to the application, withstand voltage, etc., as exemplified by amorphous semiconductors and polycrystalline semiconductors. Further, the substance forming the semiconductor thick film 1 is not particularly limited as exemplified by selenium (Se). In the present embodiment, since it is a direct conversion type radiation detector, the semiconductor thick film 1 is formed of amorphous selenium.

  The radiation detectors formed of the semiconductor thick film 1 and the insulating substrate 6 are accommodated in a housing (not shown), and a shielding plate 11 is disposed on the housing. A phototimer 12 for measuring the radiation dose is disposed on the radiation incident side of the shielding plate 11, and the shielding plate 11 is disposed over the entire X-ray detection effective area A shown in FIGS. ing. The size of the X-ray detection effective area A substantially matches the size of the voltage application electrode 2. When the shielding plate 11 and the phototimer 12 are separated from each other so that the shielding plate 11 and the phototimer 12 do not conduct, and the shielding plate 11 and the phototimer 12 are in physical contact, for example, an insulator or the like Intervene. Note that, if the shielding plate 11 and the phototimer 12 are too far apart, the measurement result from the phototimer 12 is not correctly reflected. Therefore, it is preferable to dispose the shielding plate 11 and the phototimer 12 close to each other. The shielding plate 11 corresponds to the shielding means in the present invention, and the phototimer 12 corresponds to the radiation dose measuring means in the present invention. The X-ray detection effective area A corresponds to the radiation detection effective surface in the present invention.

  The shielding plate 11 is formed of a material having a low radiation shielding rate such as conductive carbon or a thin aluminum (Al) plate. Since nickel (Ni) and copper (Cu) have a high radiation shielding rate and may shield only noise or even incident radiation, it is more preferable to form the conductive carbon or aluminum plate. Conductive carbon is carbon that has higher conductivity than normal carbon and that has a conductive filler (additive) added thereto. In addition, an aluminum plate or aluminum tape having a thickness of about 0.3 μm or several 100 μm may be used.

  The shielding plate 11 is grounded as shown in FIG. As a method of grounding, for example, it is connected to a conductive casing. In view of radiating radiation noise, which will be described later, due to grounding, it is more preferable to form the shielding plate 11 with a material having high conductivity, and it is better to form the shielding plate 11 with conductive carbon or aluminum plate than with normal carbon. More preferred.

Then, the effect | action of a present Example apparatus is demonstrated. In a state where a high voltage (for example, about several hundred V to several tens of kV) bias voltage V _A is applied to the voltage application electrode 2, radiation to be detected is incident.

  When radiation is incident, it passes through the phototimer 12 and the shielding plate 11. The phototimer 12 measures the dose of the incident radiation and sends the measurement result to an X-ray generation system (not shown). Since the shielding plate 11 is formed of a material having a low shielding rate, the radiation transmitted through the shielding plate 11 is transmitted without being attenuated, and only the radiation other than the light and the radiation to be detected is shielded by the shielding plate 11. Is done. Further, noise is also generated from the switching power supply and driving circuit for driving the phototimer 12 and the wiring connecting the phototimer to the phototimer 12, and the noise is radiated and stored in the shielding plate 11 or the casing as radiation noise. However, since the shielding plate 11 is grounded, radiation noise escapes to the ground side through the shielding plate 11.

  Carriers are generated by the incidence of radiation, and the carriers are stored in the charge storage capacitor Ca as charge information. The gate line 5 is selected by the scanning signal for signal extraction of the gate driver 9, and the detection element DU connected to the selected gate line 5 is selected and designated. The electric charge accumulated in the capacitor Ca of the designated detection element DU is read out to the data line 4 via the thin film transistor Tr that has been turned on by the signal of the selected gate line 5.

  Also, the address (address) designation of each detection element DU is performed based on the scanning signal for signal extraction of the data line 4 and the gate line 5. When a scanning signal for signal extraction is sent to the multiplexer 8 and the gate driver 9, each detection element DU is selected according to the scanning signal in the longitudinal (Y) direction from the gate driver 9. Then, when the multiplexer 8 is switched in accordance with the scanning signal in the horizontal (X) direction, the charge accumulated in the capacitor Ca of the selected detection element DU is transferred via the data line 4 to the voltage-voltage conversion group 7 and the multiplexer. 8 is sequentially sent to the outside.

  With the above-described operation, for example, when this embodiment apparatus is used for detection of a fluoroscopic X-ray image of an X-ray fluoroscopic imaging apparatus, charge information read to the outside through the data line 4 is converted into image information, Output as a fluoroscopic image.

  According to the above-described apparatus of the present embodiment, the shielding plate 11 is formed of a grounded conductive material (for example, conductive carbon or aluminum plate), and the shielding plate 11 is interposed between the phototimer 12 and the semiconductor thick film 1. By disposing the X-ray detection effective area A over the entire surface, the shielding plate 11 shields the radiation noise from the phototimer 12, and the radiation noise can be released by grounding. As a result, the radiation noise from the phototimer 12 exerted on the radiation detection apparatus can be reduced.

  Further, as in this embodiment, in the case of a direct conversion type radiation detection apparatus, the semiconductor thick film is thicker than an indirect conversion type radiation detection apparatus, and since a high voltage bias voltage is applied in the related art, Since the radiation noise from the phototimer 12 is remarkable, it is particularly useful for reducing the radiation noise.

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In the above-described embodiment, the present invention is applied to the direct conversion type radiation detection apparatus in which incident radiation is directly converted into charge information by the semiconductor thick film 1 (semiconductor layer). The present invention may be applied to an indirect conversion type radiation detector that converts light into charge information by means of a semiconductor layer formed of a light sensitive substance.

  (2) In the above-described embodiments, the case of detecting X-rays has been described as an example. However, the present invention can also be applied to a detection device that detects γ-rays used in a nuclear medicine apparatus or the like.

  (3) In the above-described embodiment, the phototimer 12 (radiation dose measuring means) is disposed along with the shielding plate 11 over the entire X-ray detection effective area A (radiation detection effective surface), but as shown in FIG. In addition, the phototimer 12 may be disposed outside the area A, for example, at a corner. Even in this case, since the radiation noise from the phototimer 12 affects the detection device, for example, via the voltage application electrode 2, the X-ray detection effective area A regardless of the location of the phototimer 12 and the size of the phototimer 12. A shielding plate 11 is disposed over the entire surface.

It is a schematic sectional drawing of the radiation detection apparatus which concerns on an Example. It is a top view which shows the structure of the radiation detection apparatus which concerns on an Example. It is a schematic sectional drawing of the radiation detection apparatus which concerns on a modification. It is a schematic sectional drawing of the conventional radiation detection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor thick film 11 ... Shielding plate 12 ... Phototimer A ... X-ray detection effective area

Claims (2)

  A radiation detection apparatus comprising a semiconductor layer for converting radiation information into charge information upon incidence of radiation, and detecting radiation by reading the converted charge information, and a radiation dose measuring means for measuring radiation dose; A shielding means for shielding light, the radiation dose measuring means is disposed on the radiation incident side, and the shielding means is disposed over the entire radiation detection effective surface between the radiation dose measuring means and the semiconductor layer. A radiation detection apparatus comprising: a shielding means comprising a grounded conductive material. 2. The radiation detection apparatus according to claim 1, wherein the semiconductor layer is a radiation sensitive type that directly converts information of the radiation into charge information, and the detection apparatus includes the radiation sensitive semiconductor layer. A radiation detection apparatus characterized by being a direct conversion type.

Images