Abstract:
In this radiography device, the radiation conversion panel side of a scintillator is formed in a convex shape towards the radiation conversion panel, the end portions of columnar crystals are formed at said side, and the end portions of the columnar crystals can contact the radiation conversion panel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY CLAIM 
     This application is a Continuation of International Application No. PCT/JP2011/064398 filed on Jun. 23, 2011, which was published under PCT Article 21(2) in Japanese, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-194941 filed on Aug. 31, 2010, the contents all of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a radiographic image capturing apparatus (radiography device) having a scintillator for converting a radiation into a visible light and a radiation conversion panel for converting the visible light into an electric signal. 
     BACKGROUND ART 
     In the medical field, radiographic image capturing apparatuses have been widely used for detecting a radiation applied to a subject from a radiation source and passed through the subject to acquire a radiographic image of the subject. For example, the radiographic image capturing apparatus has an indirect conversion radiation detector containing a scintillator for converting the radiation transmitted through the subject into a visible light and a radiation conversion panel for converting the visible light into electric signals. 
     In a recently proposed radiation detector, the scintillator is formed by vapor-depositing columnar crystals of CsI or the like on a support board, the columnar crystals are approximately perpendicular to the support board, and the distal end portions of the columnar crystals are located on the radiation conversion panel with a protective layer interposed therebetween (see Japanese Laid-Open Patent Publication No. 2009-068888). 
     In a case where the radiation is converted into the visible light by the columnar crystals, the visible light passes through column portions of the columnar crystals, is transmitted from the distal end portions of the columnar crystals through the protective layer, and reaches the radiation conversion panel. Then, the incident visible light can be converted to the electric signal in the radiation conversion panel. 
     SUMMARY OF INVENTION 
     In Japanese Laid-Open Patent Publication No. 2009-068888, the radiographic image capturing apparatus, which has the radiation detector containing the scintillator, the protective layer, and the radiation conversion panel, is used while pressing the columnar crystals in the scintillator onto the radiation conversion panel via the protective layer. Thus, in Japanese Laid-Open Patent Publication No. 2009-068888, the scintillator and the radiation conversion panel cannot be frequently contacted with and separated from each other depending on the states of the radiographic image capturing apparatus. 
     For example, a doctor or a radiological technician may drop the radiographic image capturing apparatus by mistake during transport. In such a case, the radiographic image capturing apparatus is subjected to an external shock, and the columnar crystals are inadvertently subjected to a stress. Consequently, the columnar crystals may be broken (fractured) or cracked, resulting in deterioration in the performance of the radiographic image capturing apparatus such as radiographic image blurring, etc. In view of this problem, it is desirable that the scintillator and the radiation conversion panel can be separated from each other immediately before the external shock is applied to the radiographic image capturing apparatus (immediately before the inadvertent stress is applied to the columnar crystals). Furthermore, it is desirable that the radiographic image capturing apparatus is returned to the original state (the scintillator and the radiation conversion panel are brought into contact with each other) rapidly after a predetermined time has elapsed from the application of the external shock. The scintillator and the radiation conversion panel are desirably brought into contact with each other while avoiding the breakage (fracture) and cracking of the columnar crystals. 
     However, Japanese Laid-Open Patent Publication No. 2009-068888 describes no measures against the frequent contact and separation of the scintillator and the radiation conversion panel in the radiographic image capturing apparatus. 
     An object of the present invention is to prevent the cracking of the columnar crystals in the scintillator even if the scintillator and the radiation conversion panel are frequently contacted with and separated from each other in the radiographic image capturing apparatus. 
     In view of achieving the above object, according to the present invention, there is provided a radiographic image capturing apparatus comprising a radiation detector having a scintillator for converting a radiation into a visible light and a radiation conversion panel for converting the visible light into an electric signal, wherein the scintillator contains columnar crystals for converting the radiation into the visible light, the columnar crystals extend in non-parallel with the radiation conversion panel, the scintillator has a convex surface facing the radiation conversion panel, the distal end portions of the columnar crystals are disposed on the convex surface, and the distal end portions of the columnar crystals are capable of being brought into contact with the radiation conversion panel. 
     In the radiographic image capturing apparatus, the radiation detector preferably further has a buffer layer permeable to the visible light between the scintillator and the radiation conversion panel. It is desirable that the buffer layer has a first surface facing the scintillator and a second surface facing the radiation conversion panel, the first surface is capable of being brought into contact with the distal end portions of the columnar crystals, and the second surface is capable of being brought into contact with the radiation conversion panel. 
     In this case, the convex surface of the scintillator facing the radiation conversion panel may be convexly curved and protruded toward the radiation conversion panel. The first surface of the buffer layer may be curved along the convex surface of the scintillator and may be brought into contact with the distal end portions of the columnar crystals. 
     Alternatively, the convex surface of the scintillator facing the radiation conversion panel may be tapered toward the radiation conversion panel. The center of the convex surface may be approximately parallel to the radiation conversion panel, and the buffer layer may be brought into contact with the center of the convex surface. In this case, a light shielding layer may be disposed on a tapered portion of the convex surface of the scintillator to shield the visible light emitted from the distal end portions of the columnar crystals in the tapered portion. 
     The buffer layer is preferably a flexible plastic sheet, more specifically a transparent flexible plastic sheet permeable to the visible light such as a silicone rubber film, a polyimide film, a polyarylate film, a biaxially-oriented polystyrene film, or an aramid film. The thickness of the buffer layer is preferably less than 50 μm, more preferably less than 30 μm. 
     A surface of the radiation conversion panel, which is brought into contact with the second surface of the buffer layer, is preferably planarized using a tetrafluoroethylene resin film. 
     The columnar crystals are preferably cesium iodide crystals, and are preferably sealed by a protective moisture-proof material. 
     The bottoms of the columnar crystals may be disposed on a reflective film for reflecting the visible light (converted from the radiation by the columnar crystals) toward the buffer layer or a support board for supporting the scintillator and reflecting the visible light toward the buffer layer, the columnar crystals being vapor-deposited on the support board. In this case, the reflective film or the support board may act to seal the columnar crystals and may have a moisture-proof property. 
     In the invention, the radiation conversion panel may contain a flexible plastic sheet or a flexible thin glass sheet. 
     The radiographic image capturing apparatus preferably further has an image correction device for correcting a radiographic image corresponding to the electric signal read from the radiation conversion panel depending on the shape of the convex surface of the scintillator. 
     The radiographic image capturing apparatus may further have a contact mechanism for bringing the distal end portions of the columnar crystals into contact with the radiation conversion panel along the extending direction of the columnar crystals. 
     In this case, the contact mechanism may act to bring the distal end portions of the columnar crystals into contact with the radiation conversion panel at least when the radiation is emitted to the radiation detector. 
     The radiographic image capturing apparatus preferably further has a transfer detector and a contact control device. The transfer detector detects transfer of the radiographic image capturing apparatus. The contact control device controls the contact mechanism to bring the distal end portions of the columnar crystals into contact with the radiation conversion panel in a case where the radiation is emitted to the radiation detector. Furthermore, the contact control device controls the contact mechanism to stop the contact control between the distal end portions of the columnar crystals and the radiation conversion panel in a case where a physical quantity relevant to the transfer of the radiographic image capturing apparatus detected by the transfer detector becomes larger than a predetermined threshold value. 
     In this case, the contact control device controls the contact mechanism to bring the distal end portions of the columnar crystals into contact with the radiation conversion panel when a radiation source for emitting the radiation makes a preparation of the emission. 
     The contact mechanism is preferably an air-bag, which is inflated and deflated along the extending direction of the columnar crystals to control the contact between the distal end portions of the columnar crystals and the radiation conversion panel. The radiographic image capturing apparatus preferably further has an inflator for supplying an inert gas to the air-bag to inflate the air-bag along the extending direction of the columnar crystals. 
     As described above, in the present invention, the scintillator has the convex surface facing the radiation conversion panel. The distal end portions of the columnar crystals are located on the convex surface in the scintillator, and can be brought into contact with the radiation conversion panel. 
     Consequently, even if the scintillator containing the columnar crystals and the radiation conversion panel are frequently contacted with and separated from each other depending on the states of the radiographic image capturing apparatus, the columnar crystals can be prevented from being broken (fractured) and cracked. 
     In addition, since the scintillator has the convex surface facing the radiation conversion panel, even in a case where the scintillator and the radiation conversion panel are frequently contacted with and separated from each other, the columnar crystals can be prevented from being cracked in an end of the scintillator in the process of pressing the scintillator onto the radiation conversion panel. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view of a radiographic image capturing system having a radiographic image capturing apparatus (electronic cassette) according to an embodiment of the present invention; 
         FIG. 2  is a perspective view of the electronic cassette shown in  FIG. 1 ; 
         FIGS. 3A and 3B  are cross-sectional views of the electronic cassette taken along the line III-III of  FIG. 2 ; 
         FIGS. 4A and 4B  are cross-sectional views of an example of a principal part in the vicinity of a radiation detector in the electronic cassette of  FIG. 2 ; 
         FIGS. 5A and 5B  are cross-sectional views of another example of the principal part in the vicinity of the radiation detector in the electronic cassette of  FIG. 2 ; 
         FIGS. 6A and 6B  are cross-sectional views of a further example of the principal part in the vicinity of the radiation detector in the electronic cassette of  FIG. 2 ; 
         FIGS. 7A and 7B  are cross-sectional views of a still further example of the principal part in the vicinity of the radiation detector in the electronic cassette of  FIG. 2 ; 
         FIGS. 8A and 8B  are cross-sectional views of a still further example of the principal part in the vicinity of the radiation detector in the electronic cassette of  FIG. 2 ; 
         FIGS. 9A and 9B  are explanatory views for illustrating a problem arises in a case where a scintillator and a radiation conversion panel are bonded by an adhesive layer; 
         FIG. 10  is a schematic structural view of the electric structure of the electronic cassette of  FIG. 1 ; 
         FIG. 11  is a flowchart of the operation of the radiographic image capturing system of  FIG. 1 ; 
         FIG. 12  is a flowchart of the operation of the radiographic image capturing system of  FIG. 1  in a case where the electronic cassette is subjected to an external shock; 
         FIGS. 13A and 13B  are cross-sectional views of a principal part according to a first modification of the embodiment; 
         FIGS. 14A and 14B  are cross-sectional views of a principal part according to a second modification of the embodiment; 
         FIGS. 15A and 15B  are cross-sectional views of a principal part according to a third modification of the embodiment; and 
         FIG. 16A  is a schematic explanatory view of an inner structure of a cassette according to a fourth modification of the embodiment, and  FIG. 16B  is a schematic explanatory view of an example of a scintillator shown in  FIG. 16A . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A preferred embodiment of the radiographic image capturing apparatus of the present invention will be described in detail below with reference to  FIGS. 1 to 16B . 
     [Constitution of the Embodiment] 
       FIG. 1  is a schematic view of a radiographic image capturing system  10  having an electronic cassette  20  (radiographic image capturing apparatus) according to this embodiment. 
     The radiographic image capturing system  10  has a radiation output apparatus  18  for applying a radiation  16  to a subject  14  such as a patient lying on an image capturing base  12  such as a bed, the electronic cassette  20  for detecting the radiation  16  that has passed through the subject  14  and converting the detected radiation  16  into a radiographic image, a console  22  for controlling the entire radiographic image capturing system  10  and receiving operation input by a doctor or a radiological technician (hereinafter referred to simply as the doctor), and a display device  24  for displaying the captured radiographic image and the like. 
     The radiation output apparatus  18 , the electronic cassette  20 , the console  22 , and the display device  24  may send signals to and receive signals from each other via wireless communication using UWB (Ultra Wide Band), wireless LAN according to IEEE 802.11.a/b/g/n standard or the like, millimeter waves, etc. Alternatively, the components may send and receive signals via wired communication using cables. 
     The console  22  is connected to a radiology information system (RIS)  26 , which generally manages radiographic images and other information handled in the radiological department of a hospital. The RIS  26  is connected to a hospital information system (HIS)  28 , which generally manages medical information in the hospital. 
     The radiation output apparatus  18  has a radiation source  30  for emitting the radiation  16 , a radiation control unit  32  for controlling the radiation source  30 , and a radiation switch  34 . The radiation source  30  applies the radiation  16  to the electronic cassette  20 . The radiation  16  emitted from the radiation source  30  may be X-ray, α-ray, β-ray, γ-ray, electron beam, or the like. The radiation switch  34  is of a two stage stroke type. When the radiation switch  34  is pressed halfway by the doctor, the radiation control unit  32  makes a preparation to emit the radiation  16 . When the radiation switch  34  is pressed completely, the radiation  16  is emitted from the radiation source  30 . 
     As described above, the radiation output apparatus  18 , the electronic cassette  20 , the console  22 , and the display device  24  can send signals to and receive signals from each other. Therefore, when the radiation switch  34  is pressed halfway, the radiation output apparatus  18  may send a signal indicating the preparation for the emission to the console  22 , etc. Then, when the radiation switch  34  is pressed completely, the radiation output apparatus  18  may send a signal indicating the start of the emission of the radiation  16  to the console  22 , etc. 
       FIG. 2  is a perspective view of the electronic cassette  20  shown in  FIG. 1 , and  FIGS. 3A and 3B  are cross-sectional views of the electronic cassette  20  taken along the line III-III of  FIG. 2 . 
     The electronic cassette  20  has a panel unit  42  and a control unit  48  disposed thereon. The panel unit  42  is thinner than the control unit  48 . 
     The panel unit  42  has a substantially rectangular casing  40  composed of a material permeable to the radiation  16 . The front surface (upper surface) of the panel unit  42  serves as an exposed surface  44  to be irradiated with the radiation  16 . The exposed surface  44  has guide lines  50  substantially at the center as a reference for the image capturing range and position of the subject  14 . The outer frame of the guide lines  50  corresponds to an image capturable area  52  indicative of an irradiation field of the radiation  16 . The central position of the guide lines  50  (the crisscross intersection between the guide lines  50 ) corresponds to the center of the image capturable area  52 . 
     A handle  54 , which the doctor can grip, is attached to the side surface of the casing  40  where the control unit  48  is disposed. The doctor can grip the handle  54  to transport the electronic cassette  20  to a desired place (e.g. the image capturing base  12 ). Thus, the electronic cassette  20  is a transportable radiographic image capturing apparatus. 
     A three-axis acceleration sensor  56  (transfer detector) for detecting an acceleration (the three-axis components thereof) of the electronic cassette  20  is disposed in the casing  40  in the vicinity of the handle  54 . The acceleration sensor  56  is located in the vicinity of the handle  54  in order that the acceleration sensor  56  can be prevented from being broken due to a drop impact in a case where the electronic cassette  20  is dropped by mistake. Furthermore, a three-axis pressure sensor  58  (transfer detector) for detecting an external pressure (the three-axis components thereof) applied to the electronic cassette  20  is disposed in the casing  40  in the vicinity of the center of the guide lines  50 . When the electronic cassette  20  is moved, the acceleration is produced. When the pressure is applied to the electronic cassette  20 , the electronic cassette  20  may be displaced. Therefore, the physical quantities are relevant to the transfer of the electronic cassette  20 . 
     A radiation detector  66  containing a scintillator panel  62  and a radiation conversion panel  64 , and further a drive circuit device  68  for driving the radiation conversion panel  64  are provided in the casing  40  (see  FIG. 10 ). 
     The scintillator panel  62  contains a scintillator  150  for converting the radiation  16  transmitted through the subject  14  into a visible fluorescent light (see  FIGS. 4A and 4B ). The radiation conversion panel  64  is an indirect conversion type panel, which can transmit the radiation  16  and can convert the fluorescence from the scintillator  150  into an electric signal. 
     The radiation detector  66  of  FIG. 3A  is a face side reading type, i.e. ISS (Irradiation Side Sampling) type radiation detector, wherein the radiation conversion panel  64  and the scintillator panel  62  are arranged in the casing  40  in this order from the exposed surface  44  to be irradiated with the radiation  16 . The radiation detector  66  of  FIG. 3B  is a reverse side reading type, i.e. PSS (Penetration Side Sampling) type radiation detector, wherein the scintillator panel  62  and the radiation conversion panel  64  are arranged in the casing  40  in this order from the exposed surface  44  to be irradiated with the radiation  16 . 
     The control unit  48  has a substantially rectangular casing  108  composed of a material impermeable to the radiation  16 . The casing  108  extends along one side of the exposed surface  44 , and the control unit  48  is located outside of the image capturable area  52  on the exposed surface  44 . In this case, the casing  108  contains a cassette control device  110  (contact control device, image correction device) for controlling the panel unit  42 , a buffer memory  112  for storing captured radiographic image data, a communication device  114  for sending signals to and receiving signals from the console  22  through a wireless communication link, and a power supply device  116  such as a battery (see  FIG. 10 ). The power supply device  116  supplies electric power to the components in the electronic cassette  20 . 
     A touch panel type display operation device  122  capable of displaying the captured radiographic image and the like, into which the doctor can input various information, and a speaker  124  for outputting a sound indicating various information to the doctor are disposed on the upper surface of the casing  108 . Furthermore, an AC adapter input terminal  126  for charging the power supply device  116  from an external power supply and a USB terminal  128  as an interface for sending information to and receiving information from an external device (such as the console  22 ) are disposed on a side surface of the casing  108 . 
       FIGS. 4A and 4B  are cross-sectional views of a principal part of the radiation detector  66  in the casing  40 . An example of the ISS type radiation detector  66  of  FIG. 3A  is shown in the drawings. In this case, the radiation detector  66  is located between a top plate  132  on the exposed surface  44  and a bottom plate  140  on the bottom surface of the casing  40 . 
     Specifically, an air-bag  240  (contact mechanism) is bonded to the bottom plate  140  by an adhesive layer  136 , and the scintillator panel  62  is bonded to the air-bag  240  by an adhesive layer  142 . The radiation conversion panel  64  is bonded to the top plate  132  (the surface facing the bottom plate  140 ) by the adhesive layer  130 . 
     The scintillator panel  62  contains the scintillator  150 . 
     The scintillator  150  is provided such that a thallium-doped cesium iodide (CsI:Tl) or the like is vacuum-deposited onto a surface of a support board (not shown) to form a strip-like columnar crystal structure  148 . A non-columnar crystal portion  146  is formed on the surface of the support board in the proximal end portion of the scintillator  150 . In the columnar crystal structure  148 , columns are arranged at a certain distance and extend in a direction non-parallel to the support board, ideally in a direction substantially perpendicular to the support board (the vertical direction at 90° of  FIGS. 4A and 4B ). The non-columnar crystal portion  146  in the scintillator  150  approximately flatly extends along the surface of the support board. The top of the columnar crystal structure  148  is convexly curved at the center. Thus, the thickness of the scintillator  150  varies with position. The columnar crystal structure  148  is insufficient in moisture resistance, and the non-columnar crystal portion  146  is significantly poor in moisture resistance. Therefore, the CsI scintillator  150  is sealed by a protective moisture-proof material  152 . 
     The scintillator panel  62  having the scintillator  150  is incorporated in the casing  40  as follows. 
     First, the scintillator  150  is separated from the support board. In this process, the substantially flat non-columnar crystal portion  146  is not covered with the protective moisture-proof material  152 . Therefore, a reflective film  260  composed of Al or the like is formed on the non-columnar crystal portion  146 . The reflective film  260  reflects a fluorescent light converted from the radiation  16  by the columnar crystal structure  148  toward the distal end portion of the columnar crystal structure  148 . The reflective film  260  has a fluorescent light reflective property and a moisture-proof property, and acts to seal the columnar crystal structure  148  and the non-columnar crystal portion  146  in cooperation with the protective moisture-proof material  152 . 
     A buffer layer  280  composed of a flexible plastic sheet is bonded by an adhesive layer  282  to the distal end portion of the columnar crystal structure  148  in the protective moisture-proof material  152 . 
     The buffer layer  280  is preferably a flexible transparent plastic sheet permeable to the fluorescent light, such as a silicone rubber film, a polyimide film, a polyarylate film, a biaxially-oriented polystyrene film, or an aramid film. In this case, the thickness of the buffer layer  280  is preferably less than 50 μm, more preferably less than 30 μm. 
     As shown in  FIG. 4A , the scintillator panel  62  having the above-described structure is incorporated in the casing  40  such that the reflective film  260  faces downward (the air-bag  240 ) and the buffer layer  280  faces upward (the radiation conversion panel  64 ). Therefore, in the scintillator panel  62 , the reflective film  260  is bonded to the air-bag  240  by the adhesive layer  142 . 
     The columnar crystal structure  148  is hard and brittle, and thereby is insufficient in resistance to external pressure or stress. Therefore, in a case where the electronic cassette  20  is dropped or subjected to an excessive external pressure, the columnar crystal structure  148  may be broken (fractured) or cracked. As a result, the image capturing performance and the sensitivity of the electronic cassette  20  may be deteriorated, resulting in radiographic image blurring, etc. 
     More specifically, in the columnar crystal structure  148  in the scintillator  150 , the columns have to be arranged at a certain distance (e.g. at a filling rate of 70% to 85%) to prevent the reduction of the fluorescent light and the crosstalk of the fluorescent lights between the columns. Thus, for example, in a case where the doctor drops the electronic cassette  20  by mistake during transport, the electronic cassette  20  is subjected to an external shock, and the columnar crystal structure  148  is inadvertently subjected to a stress, so that the columnar crystal structure  148  may be broken (fractured) or cracked to deteriorate the performance of the electronic cassette  20 , resulting in the radiographic image blurring, etc. Also in a case where the subject  14  comes into contact with the exposed surface  44  and applies an excessive pressure to the electronic cassette  20  through the exposed surface  44 , the columnar crystal structure  148  is inadvertently subjected to a stress, so that the columnar crystal structure  148  may be broken (fractured) or cracked. 
     The scintillator  150  and the radiation conversion panel  64  may be fixed (the columnar crystal structure  148  and the radiation conversion panel  64  may be pressed to each other) by using a protective layer, an adhesive layer, or the like. In this case, when the columnar crystal structure  148  is displaced on the radiation conversion panel  64  due to an external shock, the surface of the radiation conversion panel  64  may be scratched, and an image defect may be generated in the radiographic image by the scratch. 
     In general, as described in Japanese Laid-Open Patent Publication No. 2009-068888, the electronic cassette  20  is used while pressing the scintillator  150  onto the radiation conversion panel  64  through the protective layer. Therefore, the scintillator  150  and the radiation conversion panel  64  are not frequently contacted with and separated from each other depending on the states of the electronic cassette  20 . 
     Thus, it is desirable that the scintillator  150  and the radiation conversion panel  64  can be separated from each other immediately before the external shock is applied to the electronic cassette  20  (the inadvertent stress is applied to the columnar crystal structure  148 ). Furthermore, it is desirable that the electronic cassette  20  can be returned to the original state (the scintillator  150  and the radiation conversion panel  64  can be brought into contact with each other) rapidly after a predetermined time has elapsed from the application of the external shock. The scintillator  150  and the radiation conversion panel  64  are desirably brought into contact with each other while avoiding the breakage (fracture) and cracking of the columnar crystal structure  148 . 
     As described above, the columnar crystal structure  148  is hard and brittle, and thereby is insufficient in the resistance to external pressure or stress. Both sides of the scintillator  150  may be fixed by a support board  144  and the radiation conversion panel  64  using an adhesive agent (adhesive layer) or the like respectively. In this case, if the support board  144 , the scintillator  150 , and the radiation conversion panel  64  have different thermal expansion coefficients, as schematically shown in  FIGS. 9A and 9B , as in a bimetal, the entire radiation detector  66  is warped toward the support board  144  and the scintillator  150  or the radiation conversion panel  64  due to temperature change. 
     Assuming that the radiation conversion panel  64  is composed of a glass substrate (approximately 3 ppm/° C.) and the support board  144  is composed of aluminum (approximately 30 ppm/° C.), the shapes of the radiation conversion panel  64 , the scintillator  150 , and the support board  144  are changed due to the temperature change as schematically shown in  FIGS. 9A and 9B . At a relatively high temperature (for example, 50° C.) of  FIG. 9A  and a relatively low temperature (for example, −20° C.) of  FIG. 9B , the radiation conversion panel  64 , the scintillator  150 , and the support board  144  are significantly warped due to the extremely different thermal expansion coefficients. 
     The support board  144 , the scintillator  150 , and the radiation conversion panel  64  may have the same thermal expansion coefficient (may be composed of the same material) to prevent the warpage. However, in this case, the selection of the support board  144  is restricted. 
     In a case where the radiation conversion panel  64  and the scintillator  150  are bonded by the adhesive layer, the distance between the scintillator  150  and the radiation conversion panel  64  is increased due to the thickness of the adhesive layer. Therefore, the adhesive layer may lead to the radiographic image blur. 
     Furthermore, the adhesive layer may be deteriorated (the adhesive agent in the adhesive layer may be colored) by the radiation  16 , so that the light transmittance of the adhesive layer may be lowered. In this case, also the visible light sensitivity of the radiation conversion panel  64  is lowered. 
     In addition, both of the scintillator  150  having the columnar crystal structure  148  and the radiation conversion panel  64  are expensive components for the electronic cassette  20 . In the case where the scintillator  150  and the radiation conversion panel  64  are bonded by the adhesive layer, in a case where one of the components is broken or crashed, also the other component having the normal function is discarded. Thus, the bonding of the scintillator  150  and the radiation conversion panel  64  by the adhesive layer results in poor reworkability in view of reusing the normal component. 
     Accordingly, in this embodiment, the scintillator  150  having the columnar crystal structure  148  and the radiation conversion panel  64  can be frequently contacted and separated in the electronic cassette  20  while preventing the cracking of the columnar crystal structure  148 . The scintillator  150  and the radiation conversion panel  64  can be brought into contact with each other without using the adhesive agent (the adhesive layer). 
     Specifically, as shown in  FIGS. 4A and 4B , the air-bag  240  is bonded to the bottom plate  140  of the casing  40  by the adhesive layer  136 , and the scintillator panel  62  is bonded to the air-bag  240  by the adhesive layer  142 . The air-bag  240  is connected to an inflator  120  as shown in  FIG. 10 . The air-bag  240  and the inflator  120  have common structures for automotive air-bags and inflators. The top of the columnar crystal structure  148  is convexly curved at the center, and one surface (first surface) of the buffer layer  280  is bonded to the curved surface by the adhesive layer  282 . Therefore, the buffer layer  280  is convexly curved and protruded toward the radiation conversion panel  64 . The radiation conversion panel  64  preferably contains a flexible plastic substrate such as a polyimide film, a polyarylate film, a biaxially-oriented polystyrene film, or an aramid film. 
     In the process of capturing the radiographic image of the subject  14 , the inflator  120  acts to ignite an ignition agent (not shown), generate an inert gas such as a nitrogen or helium gas, and send the generated inert gas to the air-bag  240 . When the inert gas is sent from the inflator  120 , the air-bag  240  is inflated toward the radiation conversion panel  64  due to the gas pressure. Thus, the scintillator panel  62  is shifted toward the radiation conversion panel  64 , and the other surface (second surface) of the buffer layer  280 , which is not bonded to the scintillator  150 , is pressed onto the radiation conversion panel  64  as shown in  FIG. 4B . Consequently, the relative positions of the scintillator  150  and the radiation conversion panel  64  are fixed in the casing  40 . 
     In this case, the top of the buffer layer  280  and the columnar crystal structure  148  is convexly curved and protruded toward the radiation conversion panel  64 , and the radiation conversion panel  64  is composed of the flexible plastic substrate. Therefore, in a case where the second surface of the buffer layer  280  is pressed onto the surface of the radiation conversion panel  64 , the surface of the radiation conversion panel  64  is slightly concaved along the second surface of the buffer layer  280 . Thus, the contact of the buffer layer  280  and the radiation conversion panel  64  can be improved. Consequently, the scintillator  150  and the radiation conversion panel  64  can be appropriately brought into (tight) contact with each other using the buffer layer  280  interposed therebetween without the adhesive agent. It is preferred that the inert gas is sent from the inflator  120  to gradually inflate the air-bag  240  from the viewpoint of not damaging the buffer layer  280  and the radiation conversion panel  64  in the contact step. 
     In a case where the radiation conversion panel  64  contains a thick glass substrate and is hardly to be deformed (is not flexible) as shown in  FIG. 4B , a silicone rubber may be used for the buffer layer  280 . In this case, when the scintillator  150  having the buffer layer  280  and the radiation conversion panel  64  are brought into contact with each other, the center of the buffer layer  280  is thinned, and the columnar crystal structure  148  and the radiation conversion panel  64  are appropriately tightly contacted at the center. Furthermore, since the center of the buffer layer  280  is thinned, the distance between the columnar crystal structure  148  and the radiation conversion panel  64  is reduced at the center, whereby the image blurring is reduced in the center of the image capturable area  52 , which is important for capturing the image of the subject  14 . The advantageous effects can be easily obtained by controlling the force to press the scintillator  150  onto the radiation conversion panel  64 . 
     The buffer layer  280  (the scintillator  150 ) and the radiation conversion panel  64  can be in (tight) contact with each other in this manner. In this state, when the radiation  16  is transmitted through the radiation conversion panel  64  and the buffer layer  280  and reaches the scintillator  150 , the radiation  16  is converted into the visible fluorescent light by the columnar crystal structure  148 , the converted fluorescent light is introduced from the columns in the columnar crystal structure  148  through the buffer layer  280  to the radiation conversion panel  64 , and thus the fluorescent light can be converted into the electric signal by the radiation conversion panel  64 . In this case, though part of the fluorescent light may be emitted toward the reflective film  260 , the part can be reflected by the reflective film  260  and the non-columnar crystal portion  146  toward the buffer layer  280  and may be introduced into the radiation conversion panel  64 . 
     The radiation conversion panel  64  is formed by stacking a pixel (photoelectric conversion element) for converting the fluorescent light into the electric signal on the above-described flexible plastic substrate (TFT substrate). The surface of the radiation conversion panel  64 , facing the support board  144 , is planarized with a tetrafluoroethylene resin film. In this case, the photoelectric conversion element may contain an organic photoconductor (OPC) for absorbing the fluorescent light and generating the electric charge. A part (TFT  72 ) for reading the electric charge from the photoelectric conversion element may contain an amorphous IGZO (a-IGZO). The photoelectric conversion element and the TFT  72  using the OPC and the a-IGZO can be formed on the plastic substrate at a relatively low temperature. 
     After the radiographic image is obtained, the supply of the inert gas from the inflator  120  to the air-bag  240  is stopped, and the inert gas in the air-bag  240  is discharged from a discharge hole (not shown). Thus, the buffer layer  280  and the radiation conversion panel  64  can be separated by deflating the air-bag  240 . 
     In this manner, at least when the radiation  16  is emitted without the external shock (drop or pressure shock), the buffer layer  280  and the radiation conversion panel  64  are pressed onto each other (brought into contact with each other) to fix the relative positions of the scintillator  150  and the radiation conversion panel  64  in the casing  40  (see  FIG. 4B ). Of course, the scintillator  150  and the radiation conversion panel  64  may be contacted even if the doctor transports the electronic cassette  20  without dropping. 
     In a case where the external shock is applied to the electronic cassette  20  while the buffer layer  280  and the radiation conversion panel  64  are in contact with each other (e.g., in a case where the doctor drops the electronic cassette  20  by mistake during transport, and the acceleration value detected by the acceleration sensor  56  becomes larger than a predetermined threshold value, or in a case where the subject  14  violently comes into contact with the exposed surface  44  in the step of positioning the subject  14  on the exposed surface  44  or the like, the excessive pressure is applied to the electronic cassette  20 , and the pressure value detected by the pressure sensor  58  becomes larger than a predetermined threshold value), the inadvertent stress is applied to the columnar crystal structure  148  due to the drop or pressure shock, whereby the columnar crystal structure  148  may be broken (fractured) or cracked, and the columnar crystal structure  148  may be displaced on the radiation conversion panel  64  to scratch the surface of the radiation conversion panel  64 . 
     In such a case, the inflator  120  stops the supply of the inert gas, and the inert gas in the air-bag  240  is discharged from the discharge hole. Thus, the air-bag  240  is deflated and shrunk in the thicknesswise direction of the casing  40  (toward the bottom plate  140 ), so that the buffer layer  280  and the scintillator  150  can be separated from the radiation conversion panel  64  as shown in  FIG. 4A . Consequently, even if the inadvertent stress is applied to the scintillator  150  due to the drop of the electronic cassette  20  or the application of the excessive pressure, the breakage (fracture) and cracking of the columnar crystal structure  148  and the surface scratching of the radiation conversion panel  64  can be prevented. 
     The above-described predetermined threshold value is an acceleration value smaller than a gravitational acceleration value observed when the doctor drops the electronic cassette  20  on a floor or the like by mistake during transport. Alternatively, the predetermined threshold value is a pressure value smaller than a measured pressure value leading to the breakage (fracture) and cracking of the columnar crystal structure  148  and the surface scratching of the radiation conversion panel  64  in the electronic cassette  20  subjected to the pressure. Thus, when the detected acceleration or pressure value becomes larger than the threshold value, the columnar crystal structure  148  may be broken or cracked, and the radiation conversion panel  64  may be scratched. Therefore, in this embodiment, immediately before that, the inflator  120  is stopped and the inert gas in the air-bag  240  is discharged, whereby the scintillator  150  and the buffer layer  280  is separated from the radiation conversion panel  64  to appropriately protect the scintillator  150  against the drop or pressure shock. 
     In this embodiment, the external pressure to be applied to the electronic cassette  20  may be predicted from the product of the acceleration of the electronic cassette  20  and the time. In a case where the electronic cassette  20  falls for a long time, even though the acceleration of the electronic cassette  20  does not reach the free fall acceleration (gravitational acceleration), the drop velocity of the electronic cassette  20  is increased. Therefore, the electronic cassette  20  is expected to be subjected to a remarkably high shock pressure. Specifically, in a case where the doctor grips the handle  54  and swings the electronic cassette  20  in an arc around the handle  54  (e.g. the doctor slides the electronic cassette  20  on the image capturing base  12  and separates the electronic cassette  20  from the image capturing base  12 ), the doctor may hit a part of the electronic cassette  20  against the image capturing base  12 , so that the electronic cassette  20  may be subjected to a large impact. In this embodiment, the scintillator  150  can be appropriately protected against such an impact. 
     In this embodiment, the shock to be applied to the electronic cassette  20  may be evaluated based on an image capturing procedure for the subject  14  (e.g. a procedure in the lying or standing position) and the acceleration of the electronic cassette  20 . For example, in a case where an image of the subject  14  in the lying position is captured using the electronic cassette  20  on the image capturing base  12 , and then the electronic cassette  20  is transferred from the image capturing base  12 , the user may drop the electronic cassette  20  from the image capturing base  12  onto the floor. In this case, the scintillator  150  and the buffer layer  280  may be separated from the radiation conversion panel  64  when the free fall acceleration is detected by the acceleration sensor  56  after the image capturing process. 
     In the process of capturing an image of the subject  14  in the standing position, an image capturing base (not shown) is located in a relatively high position, and the electronic cassette  20  is attached to the image capturing base. Therefore, the scintillator  150  and the buffer layer  280  may be separated from the radiation conversion panel  64  in a case where the electronic cassette  20  is removed from the image capturing base and the free fall acceleration is detected by the acceleration sensor  56  after the image capturing process. 
     In such an image capturing procedure that the electronic cassette  20  may be dropped before or after the image capturing process, the scintillator  150  and the buffer layer  280  may be preliminarily separated from the radiation conversion panel  64  by stopping the inflator  120  and the air-bag  240 . The scintillator  150  and the buffer layer  280  may be pressed onto the radiation conversion panel  64  in a case where the electronic cassette  20  is placed on the image capturing base  12  (or the non-illustrated image capturing base for the image capturing process in the standing position). 
     Though the scintillator  150  and the buffer layer  280  are completely separated from the radiation conversion panel  64  in the above description, this embodiment is not limited thereto. The scintillator  150  and the buffer layer  280  may be in contact with the radiation conversion panel  64  even if the air-bag  240  is stopped, as long as the contact pressure observed when the air-bag  240  is stopped is approximately zero or lower than the pressure observed when the scintillator  150  and the buffer layer  280  are pressed onto the radiation conversion panel  64 . Thus, in this embodiment, when the inflator  120  and the air-bag  240  are stopped, at least the contact control of the scintillator  150  and the buffer layer  280  with the radiation conversion panel  64  (the pressing of the scintillator  150  and the buffer layer  280  onto the radiation conversion panel  64 ) is stopped. 
       FIGS. 5A and 5B  are cross-sectional detail views of the PSS type radiation detector  66  shown in  FIG. 3B . Similarly to the ISS type radiation detector  66  of  FIGS. 4A and 4B , the PSS type radiation detector  66  is capable of inflating the air-bag  240  toward the radiation conversion panel  64  to bring the buffer layer  280  and the radiation conversion panel  64  into contact with each other. 
     In  FIGS. 6A and 6B , the distal end portion of the columnar crystal structure  148  in the protective moisture-proof material  152  is tapered toward the radiation conversion panel  64 , the center of the distal end portion is approximately parallel to the radiation conversion panel  64 , and the buffer layer  280  is bonded to the center by the adhesive layer  282 . In this case, the buffer layer  280  is approximately parallel to the radiation conversion panel  64 . Therefore, as shown in  FIG. 6B , the buffer layer  280  and the radiation conversion panel  64  can be brought into (tight) contact with each other without deforming the radiation conversion panel  64 . When the columnar crystal structure  148  and the buffer layer  280  are pressed onto the radiation conversion panel  64 , the periphery of the scintillator  150  (the tapered portion) is not pressed against the radiation conversion panel  64 . Therefore, the breakage and cracking can be prevented in the periphery. Furthermore, a light shielding layer  300  for preventing the visible light from leaking from the tapered portion of the distal end portion of the columnar crystal structure  148  is formed on the tapered portion of the protective moisture-proof material  152 . In the radiation conversion panel  64 , a portion facing to the light shielding layer  300  is preferably outside the radiographic image capturing range. 
     In this embodiment, the TFT substrate in the radiation conversion panel  64  is not limited to the above-described thin flexible plastic substrate, and may be a thin flexible glass substrate. The radiation conversion panel  64  containing the flexible thin glass substrate is shown in  FIGS. 7A and 7B . A sponge  284  is bonded to the top plate  132  by the adhesive layer  130 , and the radiation conversion panel  64  is bonded to the sponge  284  by an adhesive layer  286 . In this case, when the buffer layer  280  is pressed onto the radiation conversion panel  64 , the sponge  284  and the radiation conversion panel  64  are concaved to be brought into tight contact with the convexly curved surface of the buffer layer  280 . Therefore, the buffer layer  280  and the radiation conversion panel  64  can be appropriately brought into contact with each other (see  FIG. 7B ). In a case where the buffer layer  280  and the radiation conversion panel  64  are separated from each other, the radiation conversion panel  64  can be readily returned to the original shape by the sponge  284  as shown in  FIG. 7A . 
     In the above description, the scintillator  150  is separated from the support board to prepare the scintillator panel  62 . However, in this embodiment, as shown in  FIGS. 8A  and  8 B, the support board  144  of Al or the like having the vapor-deposited scintillator  150  may be used for the scintillator panel  62  without removing the support board  144  from the scintillator  150 . In this case, the support board  144  can act as the reflective film  260 , and the buffer layer  280  and the radiation conversion panel  64  can be contacted and separated similarly to those of  FIGS. 4A and 4B . 
     In this embodiment, the buffer layer  280  and the radiation conversion panel  64  can be contacted and separated. Therefore, even if the support board  144  and the scintillator  150  are integrated, the above-described shape change of the scintillator  150  due to the temperature change can be prevented. 
       FIG. 10  is a schematic structural view of the electric structure of the electronic cassette  20  shown in  FIG. 1 . 
     The electronic cassette  20  has the structure containing pixels  160  disposed on the TFTs  72  arranged in a matrix. The pixels  160  are arranged in a matrix and each have a photoelectric conversion element (not shown). The pixels  160 , which are supplied with a bias voltage from a bias supply  162  in the drive circuit device  68 , store electric charges generated by photoelectric conversion of the visible light (fluorescent light). The TFTs  72  are turned on sequentially column by column, whereby the electric charge signals (electric signals) can be read from signal lines  166  as analog pixel signal values. Though the pixels  160  and the TFTs  72  are arranged vertically and horizontally in a 4×4 matrix in  FIG. 10  for the sake of convenience, of course they may be arranged in a desired matrix. 
     The TFTs  72 , connected to the pixels  160 , are connected with gate lines  164  extending in the row direction and the signal lines  166  extending in the column direction. The gate lines  164  are connected to a gate drive part  168  in the drive circuit device  68 , and the signal lines  166  are connected to a multiplexer part  172  in the drive circuit device  68  through charge amplifiers  170 . The multiplexer part  172  is connected to an AD conversion part  174  for converting the analog electric signals into digital electric signals. The AD conversion part  174  outputs the converted digital electric signals (digital pixel signal values, hereinafter referred to also as digital values) to the cassette control device  110 . 
     The cassette control device  110  is for controlling the entire electronic cassette  20 . In this case, an information processor such as a computer can be used as the cassette control device  110  by installing a predetermined program thereinto. 
     In the cassette control device  110 , the electric signals (the digital pixel signal values) are read from the radiation conversion panel  64  by a readout control part  180 , and the radiographic image of the electric signals is corrected depending on the shape of the distal end portion of the columnar crystal structure  148  (protruded toward the radiation conversion panel  64 ). 
     The cassette control device  110  is connected with the memory  112  and the communication device  114 . The memory  112  stores the digital pixel signal values after the image correction processing in the cassette control device  110 , and the communication device  114  sends signals to and receives signals from the console  22 . The communication device  114  sends to the console  22  a packet of one image (one-frame image) containing the pixel values arranged in a matrix. The power supply device  116  supplies electric power to the cassette control device  110 , the memory  112 , the communication device  114 , etc. The electric power is transferred from the cassette control device  110  to the bias supply  162 , and is supplied to the pixels  160  by the bias supply  108 . 
     The cassette control device  110  has the readout control part  180 , a shock prediction judgment part  182 , a separation instruction part  184 , and a contact instruction part  186 . 
     The readout control part  180  controls the gate drive part  168 , the charge amplifiers  170 , the multiplexer part  172 , and the AD conversion part  174 , to read the electric signals stored in the pixels  160  sequentially row by row. 
     The shock prediction judgment part  182  judges whether or not the acceleration value detected by the acceleration sensor  56  or the pressure value detected by the pressure sensor  58  is larger or not than the predetermined threshold value. Thus, the shock prediction judgment part  182  acts to judge (predict), based on the result value detected by the acceleration sensor  56  or the pressure sensor  58 , whether or not the external shock to be applied to the electronic cassette  20  due to the crash (drop) of the electronic cassette  20  against the floor or the excessive pressure on the electronic cassette  20  causes the breakage (fracture) or cracking of the columnar crystal structure  148  or the surface scratch of the radiation conversion panel  64 . 
     In a case where the acceleration value detected by the acceleration sensor  56  or the pressure value detected by the pressure sensor  58  becomes larger than the threshold value, the shock prediction judgment part  182  sends a communication signal, which indicates that the external shock causing the breakage (fracture) or cracking of the columnar crystal structure  148  or the surface scratch of the radiation conversion panel  64  will be applied to the electronic cassette  20 , to the separation instruction part  184 . 
     The acceleration sensor  56  successively detects the acceleration and successively sends detection signals indicating the detected acceleration values to the cassette control device  110 . The pressure sensor  58  successively detects the pressure and successively sends detection signals indicating the detected pressure values to the cassette control device  110 . Thus, after the communication signal is sent to the separation instruction part  184 , the shock prediction judgment part  182  then judges whether the acceleration value detected by the acceleration sensor  56  or the pressure value detected by the pressure sensor  58  becomes smaller or not than the threshold value. In a case where the acceleration value and the pressure value are smaller than the threshold values, the shock prediction judgment part  182  sends a communication signal, which indicates that the external shock is no longer likely to be applied to the electronic cassette  20 , to the contact instruction part  186 . 
     In a case where m represents the total weight of the electronic cassette  20 , h represents the distance between the electronic cassette  20  and the floor at the start of the drop (the drop distance), g represents the gravitational acceleration, v represents the drop velocity of the electronic cassette  20  at the timing of the drop (crash) against the floor, and t represents the drop time from the drop start to the crash against the floor, the drop velocity v and the drop time t are obtained using the equations of v=(2×g×h) 1/2  and t=(2×h/g) 1/2  respectively. 
     Instead of predicting and judging the shock using the acceleration value, the shock prediction judgment part  182  uses a predetermined time shorter than the drop time t as a threshold value. In this case, the time when the acceleration value detected by the acceleration sensor  56  is increased from approximately 0 to a predetermined level value corresponding to the drop of the electronic cassette  20  is considered as the drop start. The shock prediction judgment part  182  sends the communication signal to the separation instruction part  184  when the predetermined time of the threshold value has elapsed from the drop start. Thus, the shock prediction judgment part  182  predicts the crash by measuring the elapsed time from the drop start based on the acceleration value detected by the acceleration sensor  56 . Therefore, also the measured elapsed time is the physical quantity relevant to the transfer of the electronic cassette  20 . 
     When the communication signal is input from the shock prediction judgment part  182 , the contact instruction part  186  sends, to the inflator  120 , an operation start instruction signal for driving the air-bag  240 . When the operation start instruction signal is entered, the inflator  120  ignites the ignition agent to generate the inert gas and sends the inert gas to the air-bag  240 . On the other hand, when the communication signal is input from the shock prediction judgment part  182 , the separation instruction part  184  sends, to the inflator  120 , an operation stop instruction signal for stopping the inflator  120 . When the operation stop instruction signal is entered, the inflator  120  stops the supply of the inert gas to the air-bag  240 . 
     As described above, when the radiation switch  34  is pressed halfway by the doctor, the radiation control unit  32  sends the signal indicating the preparation for the emission of the radiation  16  to the console  22  via the wireless communication. In this case, the console  22  sends, to the electronic cassette  20  via the wireless communication, a synchronization control signal for synchronizing with the emission of the radiation  16  from the radiation source  30 . When the electronic cassette  20  receives the synchronization control signal, the contact instruction part  186  sends the operation start instruction signal to the inflator  120  based on the synchronization control signal. Then, the inflator  120  starts to supply the inert gas to the air-bag  240  based on the operation start instruction signal. Consequently, the buffer layer  280  and the radiation conversion panel  64  are brought into contact with each other, so that the electronic cassette  20  becomes capable of detecting the radiation  16 . Also when the doctor operates the display operation device  122  and thereby instructs to bring the buffer layer  280  and the radiation conversion panel  64  into contact with each other in the preparation stage for the image capturing process, the contact instruction part  186  can send the operation start instruction signal to the inflator  120 . 
     On the other hand, when the doctor operates the display operation device  122  and thereby instructs to separate the buffer layer  280  and the radiation conversion panel  64  from each other after the radiographic image capturing process, the separation instruction part  184  can send the operation stop instruction signal to the inflator  120  to stop the inert gas supply from the inflator  120  to the air-bag  240 . 
     [Operations of the Embodiment] 
     The radiographic image capturing system  10 , which has the electronic cassette  20  of this embodiment, is basically constructed as described above. Operations of the radiographic image capturing system  10  will be described below with reference to the flowcharts of  FIGS. 11 and 12 . 
     The basic operation of the radiographic image capturing system  10  will be described first with reference to  FIG. 11 . 
     Then, the operation of the electronic cassette  20 , in the case where the electronic cassette  20  is subjected to the external shock, will be described with reference to  FIG. 12 . Specifically, the operation of the components (the inflator  120  and the air-bag  240 ) in the electronic cassette  20 , in the case where the doctor drops the electronic cassette  20  by mistake during transport or where the subject  14  violently comes into contact with the exposed surface  44  and applies the excessive pressure to the electronic cassette  20  in the step of positioning the subject  14 , will be described. 
     In step S 1  of  FIG. 11 , the doctor sets image capturing conditions for the subject  14  based on order information sent from the RIS  26  or the HIS  28  to the console  22 . The order information is prepared by the doctor in the RIS  26  or the HIS  28 . The order information may include subject information for identifying the subject  14  (such as the name, age, and sex of the subject  14 ), and may further include information of the radiation output apparatus  18  and the electronic cassette  20  to be used in the image capturing process, the imaging area of the subject  14 , the procedure of the image capturing process, etc. The image capturing conditions may include various conditions for emitting the radiation  16  to the imaging area of the subject  14  (such as the tube voltage and tube current of the radiation source  30  and the exposure time with the radiation  16 ). 
     In step S 2 , the doctor grips the handle  54  of the electronic cassette  20  stored in a certain storage and transports the electronic cassette  20  onto the image capturing base  12 . In step S 3 , the doctor lays the subject  14  on the image capturing base  12  and the electronic cassette  20  to locate the imaging area of the subject  14  in the image capturable area  52 . Thus, the positioning of the imaging area is carried out on the image capturable area  52 . 
     In this case, the power supply device  116  continuously supplies electric power to the cassette control device  110 , the communication device  114 , the acceleration sensor  56 , and the pressure sensor  58 . Therefore, the acceleration sensor  56  successively detects the acceleration of the electronic cassette  20  and successively sends the detection signals indicating the detected acceleration values to the cassette control device  110 . The pressure sensor  58  successively detects the external pressure applied to the electronic cassette  20  and successively sends the detection signals indicating the detected pressure values to the cassette control device  110 . 
     When the imaging area of the subject  14  is positioned in the image capturable area  52 , a pressure is applied by the subject  14  to the electronic cassette  20 . The pressure sensor  58  detects the pressure applied by the subject  14 , and sends the detection signal indicating the pressure to the cassette control device  110 . In a case where the pressure value of the detection signal is at a level appropriate for the subject  14  on the electronic cassette  20 , the shock prediction judgment part  182  judges that the electronic cassette  20  is in the process of positioning the subject  14 . 
     Based on the judgment by the shock prediction judgment part  182 , the cassette control device  110  acts to start the electric power supply from the power supply device  116  to the drive circuit device  68 , the display operation device  122 , and the speaker  124 . Thus, the bias supply  162  starts to supply the bias voltage to the pixels  160 , so that the pixels  160  become capable of storing the electric charges. Furthermore, the display operation device  122  displays various information and become capable of the input operation by the doctor, and the speaker  124  becomes capable of outputting sounds corresponding to signals from the cassette control device  110  to the outside. Consequently, the electronic cassette  20  is converted from the sleep state to the active state. 
     Based on the judgment by the shock prediction judgment part  182 , the cassette control device  110  further acts to send, to the console  22  via the wireless communication through the communication device  114 , a request signal for requesting to send the order information and the image capturing conditions. The console  22  receives the request signal, then sends the order information and the image capturing conditions to the electronic cassette  20  via the wireless communication, and sends the image capturing conditions to the radiation output apparatus  18  via the wireless communication. Consequently, in the radiation output apparatus  18 , the received image capturing conditions are registered in the radiation control unit  32 . Furthermore, in the electronic cassette  20 , the received order information and image capturing conditions are registered in the cassette control device  110 . When the cassette control device  110  receives the order information and the image capturing conditions, the cassette control device  110  may act to display them on the display operation device  122 . 
     In step S 4 , when the radiation switch  34  is pressed halfway by the doctor, the radiation control unit  32  makes a preparation to emit the radiation  16  and sends the signal indicating the emission preparation to the console  22  via the wireless communication. The console  22  sends, to the electronic cassette  20  via the wireless communication, a synchronization control signal for synchronizing with the emission of the radiation  16  from the radiation source  30 . In the electronic cassette  20 , the cassette control device  110  receives the synchronization control signal, and then may act to display information indicating the start of the emission preparation on the display operation device  122  and to output a sound corresponding to the information from the speaker  124  to the outside. 
     Based on the synchronization control signal, the contact instruction part  186  sends, to the inflator  120 , the operation start instruction signal for driving the air-bag  240 . When the operation start instruction signal is entered, the inflator  120  ignites the ignition agent to generate the inert gas and supplies the inert gas to the air-bag  240 . The air-bag  240  is inflated toward the radiation conversion panel  64  by the inert gas supplied from the inflator  120 , whereby the scintillator panel  62  is shifted toward the radiation conversion panel  64 , the second surface of the buffer layer  280  is brought into contact with the radiation conversion panel  64  as shown in  FIG. 4B , and the electronic cassette  20  becomes capable of detecting the radiation  16  (step S 5 ). 
     In a case where the second surface of the buffer layer  280  is brought into contact with the radiation conversion panel  64 , the cassette control device  110  may act to display information indicating the contact on the display operation device  122  and to output a sound corresponding to the information from the speaker  124  to the outside. Consequently, the doctor can easily recognize that the electronic cassette  20  becomes capable of detecting the radiation  16 . 
     When the radiation switch  34  is completely pressed by the doctor in step S 6 , the radiation control unit  32  acts to emit the radiation  16  from the radiation source  30  to the imaging area of the subject  14  for a predetermined time included in the image capturing conditions (step S 7 ). In this step, at the start of the emission of the radiation  16 , the radiation control unit  32  may send, to the console  22  via the wireless communication, the signal indicating the start of the emission of the radiation  16 . The console  22  transfers the sent signal to the electronic cassette  20 . When the electronic cassette  20  receives the signal, the cassette control device  110  may act to display information indicating the emission on the display operation device  122  and to output a sound corresponding to the information from the speaker  124  to the outside. 
     In step S 8 , the radiation  16  is transmitted through the imaging area of the subject  14  and reaches the radiation detector  66  in the electronic cassette  20 . In a case where the radiation detector  66  is of the ISS type shown in  FIG. 4B , the radiation  16  is introduced through the radiation conversion panel  64  and the buffer layer  280  into the columnar crystal structure  148  in the scintillator  150 . 
     The columnar crystal structure  148  emits the visible light (the fluorescent light) with an intensity corresponding to the radiation  16 , and the fluorescent light is introduced from the columns in the columnar crystal structure  148  through the buffer layer  280  to the radiation conversion panel  64 . Though part of the fluorescent light may be transmitted toward the non-columnar crystal portion  146 , the part can be reflected by the reflective film  260  (or the support board  144 ) and the non-columnar crystal portion  146  toward the buffer layer  280  and may be introduced into the radiation conversion panel  64 . 
     The pixels  160  in the radiation conversion panel  64  converts the fluorescent light into the electric signals, and stores the electric signals as electric charges. Then, the electric charges corresponding to the radiographic image of the imaging area of the subject  14 , stored in the pixels  160 , are read out based on a drive signal sent from the readout control part  180  in the cassette control device  110  to the gate drive part  168 . 
     The gate drive part  168  selects the gate lines  164  in 0th to final rows sequentially, and outputs gate signals to the selected gate lines  164  sequentially. Then, the TFTs  72  are turned on by the gate signals sequentially, and the electric charges stored in the pixels  160  in the 0th to final rows are read out sequentially row by row. The electric charges, which are read out from the pixels  160  sequentially row by row, are sent through the signal lines  166  to the charge amplifiers  170  column by column, transferred through the multiplexer part  172  and the AD conversion part  174 , and stored as the digital electric signals in the memory  112  (step S 9 ). Thus, one-row image data are stored in the memory  112  sequentially row by row. 
     In this step, the cassette control device  110  acts to perform the image correction processing for correcting the digital pixel signal values in accordance with the shape of the distal end portion of the columnar crystal structure  148 . In a case where the distal end portion of the columnar crystal structure  148  is convexly curved as shown in  FIGS. 4B ,  5 B,  7 B, and  8 B or tapered as shown in  FIG. 6B  toward the radiation conversion panel  64 , the top shape may cause image distortion. Therefore, the digital pixel signal values are corrected depending on the distortion. Thus, the image data obtained by the image correction processing are stored in the memory  112  sequentially row by row. 
     The radiographic image, stored in the memory  112  after the image correction processing, is sent in combination with cassette ID information for identifying the electronic cassette  20  through the communication device  114  to the console  22  via the wireless communication. The console  22  acts to display the sent radiographic image and cassette ID information on the display device  24  (step S 10 ). The cassette control device  110  may act to display the radiographic image and the cassette ID information on the display operation device  122 . 
     The doctor visually recognizes the information on the display device  24  or the display operation device  122  and understands that the radiographic image is recorded. Then, the doctor operates the display operation device  122  to instruct to separate the buffer layer  280  from the radiation conversion panel  64 . The separation instruction part  184  sends the operation stop instruction signal to the inflator  120  based on the instruction by the doctor. The inflator  120  stops the inert gas supply to the air-bag  240  based on the operation stop instruction signal. Consequently, the inert gas in the air-bag  240  is discharged from the discharge hole (not shown) and the air-bag  240  is deflated, so that the buffer layer  280  (the scintillator panel  62 ) is separated from the radiation conversion panel  64  (step S 11 ). 
     The cassette control device  110  may act to display information indicating the separation of the buffer layer  280  from the radiation conversion panel  64  on the display operation device  122  and to output a sound corresponding to the information from the speaker  124  to the outside. Consequently, the doctor judges that the electronic cassette  20  can be transported without incident, and releases the subject  14  from the positioned state (step S 12 ). Also in this step, the pressure sensor  58  successively detects the external pressure applied to the electronic cassette  20  and successively sends the detection signals to the cassette control device  110 . When the pressure of the detection signal is lowered from the pressure of the subject  14  in the positioned state to approximately zero, the shock prediction judgment part  182  judges that the subject  14  is released from the positioned state. 
     Based on the judgment by the shock prediction judgment part  182 , the cassette control device  110  acts to stop the electric power supply from the power supply device  116  to the drive circuit device  68 , the display operation device  122 , and the speaker  124 . Thus, the bias voltage supply from the bias supply  162  to the pixels  160  is stopped, and also the display operation device  122  and the speaker  124  are stopped. Consequently, the electronic cassette  20  is converted from the active state into the sleep state. 
     In step S 13 , the doctor confirms that the image on the display operation device  122  is cleared and the electronic cassette  20  is converted into the sleep state. Then, the doctor grips the handle  54  of the electronic cassette  20 , and transports the electronic cassette  20  to the certain storage. 
     In  FIG. 11 , the buffer layer  280  and the radiation conversion panel  64  are brought into contact with each other in step S 5  and are separated from each other in step S 11 . This embodiment is not limited to  FIG. 11  as long as the buffer layer  280  and the radiation conversion panel  64  are in (tight) contact with each other at least during the emission of the radiation  16 . Alternatively, for example, the buffer layer  280  and the radiation conversion panel  64  may be brought into contact with each other in a case where the entire electronic cassette  20  is converted from the sleep state into the active state in step S 3 , and the buffer layer  280  and the radiation conversion panel  64  may be separated from each other in a case where the entire electronic cassette  20  is converted from the active state into the sleep state in step S 12 . 
     The operation of  FIG. 12  will be described below. 
     The acceleration sensor  56  successively detects the acceleration of the electronic cassette  20  and successively sends the detection signals indicating the detected acceleration values to the cassette control device  110 , while the pressure sensor  58  successively detects the external pressure applied to the electronic cassette  20  and successively sends the detection signals indicating the detected pressure values to the cassette control device  110  (step S 21 ). 
     In this case, whenever the detection signals are sent from the acceleration sensor  56  and the pressure sensor  58  into the cassette control device  110 , the shock prediction judgment part  182  judges whether or not the acceleration value corresponding to the detection signal from the acceleration sensor  56  is larger than the predetermined threshold value and whether or not the pressure value corresponding to the detection signal from the pressure sensor  58  is larger than the predetermined threshold value (acceptable value) (step S 22 ). 
     In a case where the value of the detected acceleration and the value of the detected pressure do not reach the predetermined threshold values in step S 22  (step S 22 : NO), the shock prediction judgment part  182  judges that the electronic cassette  20  is not subjected to a large shock causing the breakage (fracture) or cracking of the columnar crystal structure  148  or the surface scratch of the radiation conversion panel  64 , and is kept in the waiting state until the next detection signal is entered. 
     On the other hand, when the detected acceleration or pressure value is larger than the predetermined threshold value in step S 22  (step S 22 : YES), the shock prediction judgment part  182  judges that the breakage (fracture) or cracking of the columnar crystal structure  148  or the surface scratch of the radiation conversion panel  64  may be caused by the external shock (step S 23 ), and sends the communication signal, which indicates that the external shock will be applied to the electronic cassette  20 , to the separation instruction part  184 . 
     In step S 24 , the separation instruction part  184  sends the operation stop instruction signal to the inflator  120  based on the communication signal from the shock prediction judgment part  182 , and the inflator  120  stops the inert gas supply to the air-bag  240  based on the sent operation stop instruction signal. Then, the air-bag  240  discharges the inert gas from the discharge hole to be shrunk toward the bottom plate  140 . Consequently, the buffer layer  280  and the scintillator  150  are separated from the radiation conversion panel  64  as shown in  FIG. 4A . 
     Furthermore, when the communication signal is entered from the shock prediction judgment part  182 , the separation instruction part  184  sends, to the display operation device  122  and the speaker  124 , a warning signal indicating that the air-bag  240  will be deflated due to the external shock and that the buffer layer  280  and the scintillator  150  will be separated from the radiation conversion panel  64 . The display operation device  122  displays the information of the warning signal, and the speaker  124  outputs a sound corresponding to the warning signal to the outside (step S 25 ). The doctor can visually recognize the information on the display operation device  122  or hear the sound from the speaker  124  or both to understand that the air-bag  240  will be deflated due to the external shock and that the buffer layer  280  and the scintillator  150  will be separated from the radiation conversion panel  64 . 
     In this manner, the air-bag  240  is deflated, and the buffer layer  280  and the scintillator  150  are separated from the radiation conversion panel  64 . Therefore, even if practically the electronic cassette  20  is dropped onto the floor or the subject  14  violently contacts with the exposed surface  44 , whereby the electronic cassette  20  is subjected to the external shock causing the breakage (fracture) or cracking of the columnar crystal structure  148  or the surface scratch of the radiation conversion panel  64  (step S 26 ), the columnar crystal structure  148  can be appropriately protected. 
     Then, in a case where a predetermined time has elapsed from the deflation of the air-bag  240  (step S 27 : YES), the shock prediction judgment part  182  judges that the external shock is no longer likely to be applied to the electronic cassette  20 , and sends the communication signal to the contact instruction part  186 . In step S 28 , the contact instruction part  186  sends the operation start instruction signal to the inflator  120  based on the communication signal, and the inflator  120  restarts to supply the inert gas to the air-bag  240  based on the sent operation start instruction signal. Consequently, the air-bag  240  is inflated by the supplied inert gas, the buffer layer  280  and the scintillator  150  are brought into contact with the radiation conversion panel  64  again, and thus the electronic cassette  20  is returned (restored) to the original state. 
     Furthermore, the contact instruction part  186  acts to clear the warning on the display operation device  122  and to stop the warning sound from the speaker  124  based on the communication signal (step S 29 ). Consequently, the doctor can easily recognize that the buffer layer  280  and the scintillator  150  are brought into contact with the radiation conversion panel  64  again, and thus the electronic cassette  20  is returned to the original state. 
     Even during the deflation of the air-bag  240 , the acceleration sensor  56  can successively detect the acceleration of the electronic cassette  20  and can successively send the detection signals indicating the detected acceleration values to the cassette control device  110 , while the pressure sensor  58  can successively detect the external pressure applied to the electronic cassette  20  and can successively send the detection signals indicating the detected pressure values to the cassette control device  110 . Therefore, when the acceleration and pressure values become smaller than the predetermined threshold values after the deflation of the air-bag  240 , the shock prediction judgment part  182  can judge that the external shock is no longer likely to be applied to the electronic cassette  20 , and can send the communication signal to the contact instruction part  186 . Also in this case, the radiation conversion panel  64  and the scintillator  150  can be reliably returned to the original state. 
     The image on the display operation device  122  and the sound from the speaker  124  are used to give the warning in the above description. Alternatively, the separation instruction part  184  may send the warning signal through the communication device  114  to the console  22  via the wireless communication. In this case, the console  22  acts to display a warning corresponding to the warning signal on the display device  24 . The doctor can visually recognize the warning information on the display device  24  to understand that the air-bag  240  is deflated due to the external shock and that the buffer layer  280  and the scintillator  150  are separated from the radiation conversion panel  64 . Furthermore, the contact instruction part  186  may send a signal for clearing the displayed warning through the communication device  114  to the console  22  via the wireless communication. In this case, the console  22  acts to clear the warning on the display device  24  based on the sent signal. Consequently, the doctor can recognize that the buffer layer  280  and the scintillator  150  are brought into contact with the radiation conversion panel  64  again, and thus the electronic cassette  20  is returned to the original state. 
     [Advantageous Effects of the Embodiment] 
     As described above, in the electronic cassette  20  according to this embodiment, the distal end portion of the columnar crystal structure  148  is convexly curved and protruded toward the radiation conversion panel  64 , the first surface of the buffer layer  280  permeable to the visible light can be bonded to the curved distal end portion with the protective moisture-proof material  152  and the adhesive layer  282  interposed therebetween, and the second surface (opposite to the first surface) of the buffer layer  280  can be brought into contact with the radiation conversion panel  64 . Therefore, the top of the columnar crystal structure  148 , bonded to the first surface of the buffer layer  280 , can be brought into (tight) contact with the radiation conversion panel  64  via the second surface. 
     The electronic cassette  20  contains the scintillator  150  having the columnar crystal structure  148 , the buffer layer  280 , and the radiation conversion panel  64 . Even in a case where the scintillator  150  and the buffer layer  280  are frequently brought into contact with and separated from the radiation conversion panel  64  depending on the state of the electronic cassette  20 , the columnar crystal structure  148  can be prevented from being broken (fractured) or cracked in the process of pressing the scintillator  150  against the radiation conversion panel  64 . 
     The buffer layer  280  is disposed on the distal end portion of the columnar crystal structure  148 , and the columnar crystal structure  148  is pressed onto the radiation conversion panel  64  with the buffer layer  280  interposed therebetween. Therefore, the columnar crystal structure  148  can be reliably prevented from being broken (fractured) or cracked. In addition, even if the distal end portion of the columnar crystal structure  148  (the protective moisture-proof material  152 ) is slightly uneven, the second surface of the buffer layer  280  can be a curved or flat surface without the unevenness. Consequently, if the buffer layer  280  is brought into contact with the radiation conversion panel  64 , the surface of the radiation conversion panel  64  is not scratched. 
     In this embodiment, the distal end portion of the columnar crystal structure  148  is convexly curved and protruded toward the radiation conversion panel  64 , and the first surface of the buffer layer  280  is bonded to and curved along the convexly curved distal end portion of the columnar crystal structure  148  (see  FIGS. 4A to 5B  and  7 A to  8 B). Alternatively, the distal end portion of the columnar crystal structure  148  in the protective moisture-proof material  152  is tapered toward the radiation conversion panel  64 , the center of the distal end portion is approximately parallel to the radiation conversion panel  64 , and the buffer layer  280  is bonded to the center of the distal end portion (see  FIGS. 6A and 6B ). Consequently, the contact between the buffer layer  280  and the radiation conversion panel  64  can be improved in the process of pressing the buffer layer  280  onto the radiation conversion panel  64 . 
     In the cassette control device  110 , the digital pixel signal values (the radiographic image) read from the radiation conversion panel  64  are corrected depending on the shape of the distal end portion of the columnar crystal structure  148 . Therefore, the radiographic image can be appropriately acquired regardless of the shape of the distal end portion. 
     In this embodiment, the scintillator  150  (the columnar crystal structure  148  formed therein) and the radiation conversion panel  64  are brought into contact with each other without using the adhesive agent. Therefore, the problem of the light detection deterioration, caused by the adhesive agent deteriorated under the radiation  16 , can be prevented. Consequently, the ISS type radiation detector  66  can exhibit an improved light detection function. 
     In a case where the buffer layer  280  is the flexible transparent plastic sheet permeable to the fluorescent light (such as the silicone rubber film, the polyimide film, the polyarylate film, the biaxially-oriented polystyrene film, or the aramid film) and has a thickness of less than 50 μm (more preferably less than 30 μm), the buffer layer  280  is substantially not warped or is only slightly warped due to the temperature change of the electronic cassette  20 . Thus, in a case where the buffer layer  280  is the thin, flexible, light transmittable, plastic sheet, the columnar crystal structure  148  can be prevented from being broken and cracked in the process of pressing the buffer layer  280  onto the radiation conversion panel  64 . Furthermore, since the distance between the scintillator  150  and the radiation conversion panel  64  is not large, the resultant radiographic image is not blurred. 
     The surface of the radiation conversion panel  64 , which is brought into contact with the second surface of the buffer layer  280 , is planarized by using the tetrafluoroethylene resin film. Therefore, when the buffer layer  280  is pressed against the radiation conversion panel  64 , the second surface of the buffer layer  280  can be brought into tight contact with the surface of the radiation conversion panel  64 , whereby the fluorescent light can be efficiently introduced from the scintillator  150  into the radiation conversion panel  64 . In addition, the scratch or the like on the radiation conversion panel  64  can be prevented in the process of pressing the buffer layer  280  onto the radiation conversion panel  64 . 
     The scintillator  150  having the columnar crystal structure  148  of the CsI is sealed by the protective moisture-proof material  152 , and the reflective film  260  is disposed on the non-columnar crystal portion  146 . Therefore, the scintillator  150  can be appropriately protected against moisture. Furthermore, the fluorescent light emitted toward the non-columnar crystal portion  146  is reflected by the reflective film  260  and the non-columnar crystal portion  146  toward the buffer layer  280 . Therefore, the quantity of the fluorescent light introduced into the radiation conversion panel  64  can be increased. 
     The scintillator  150  may be vapor-deposited on the support board  144 , and the scintillator  150  and the support board  144  may be used in the scintillator panel  62  without removing the support board  144 . In this case, it is not necessary to separate the scintillator  150  from the support board  144 . Therefore, the electronic cassette  20  can be efficiently produced. 
     The scintillator  150  is pressed against the radiation conversion panel  64  with the buffer layer  280  interposed therebetween as described above. Therefore, even if the thickness of the scintillator  150  varies with the position, the buffer layer  280  and the radiation conversion panel  64  can be appropriately brought into tight contact with each other. In addition, the scintillator  150  is not vapor-deposited on the radiation conversion panel  64 . Therefore, in a case where the scintillator  150  is unsuccessfully vapor-deposited on the support board  144 , the radiation conversion panel  64  can be reused. 
     The scintillator  150  and the radiation conversion panel  64  are independent from each other. Therefore, in a case where one of the components is broken or crashed, the other component can be reused. Thus, the electronic cassette  20  is excellent in reworkability. 
     In a case where the buffer layer  280  and the radiation conversion panel  64  are repeatedly contacted and separated, the buffer layer  280  may be damaged. Therefore, the buffer layer  280  is preferably a replaceable member. 
     In this embodiment, the distal end portion of the columnar crystal structure  148  has the convexly curved shape. The support board  144  may be convexly curved toward the radiation conversion panel  64 . In this case, the distal end portion of the columnar crystal structure  148  can be protruded along the shape of the support board  144  by forming the scintillator  150  with a uniform thickness. 
     This embodiment achieves a further effect as follows. At least while the radiation  16  is emitted to the radiation detector  66 , the scintillator  150  and the radiation conversion panel  64  are brought into contact with each other with the buffer layer  280  interposed therebetween. When the acceleration value detected by the acceleration sensor  56 , the pressure value detected by the pressure sensor  58 , or the drop time of the electronic cassette  20  based on the acceleration becomes larger than the predetermined threshold value, the buffer layer  280  and the scintillator  150  are separated from the radiation conversion panel  64  (the contact control of the scintillator  150  with the radiation conversion panel  64  is stopped). Therefore, in a case where the electronic cassette  20  is subjected to the external shock, the scintillator  150  (the columnar crystal structure  148  therein) can be appropriately protected against the shock, and the columnar crystal structure  148  can be reliably prevented from being broken (fractured) or cracked by the shock. Furthermore, even in a case where the columnar crystal structure  148  is displaced by the shock, the surface of the radiation conversion panel  64  can be reliably prevented from being scratched due to the displacement. In addition, in a case where the electronic cassette  20  is likely to be subjected to the external shock, the columnar crystal structure  148  can be reliably protected against the shock. Therefore, the electronic cassette  20  can maintain excellent image capturing performance regardless of the shock. 
     When the inert gas supply from the inflator  120  to the air-bag  240  is stopped and the inert gas in the air-bag  240  is discharged, the air-bag  240  is shrunk in the thicknesswise direction of the casing  40 , whereby the buffer layer  280  and the scintillator  150  are separated from the radiation conversion panel  64 . Therefore, the buffer layer  280  and the scintillator  150  can be rapidly separated from the radiation conversion panel  64  in preparation for the external shock. The buffer layer  280  and the scintillator  150  can be brought again into contact with the radiation conversion panel  64  by restarting the inert gas supply from the inflator  120  to inflate the air-bag  240 . Therefore, the buffer layer  280  and the scintillator  150  can be temporarily separated from the radiation conversion panel  64 , and can be readily returned (restored) to the original state. 
     As described above, when the radiation switch  34  is pressed halfway by the doctor, the radiation control unit  32  sends the signal indicating the preparation for the emission of the radiation  16  to the console  22  via the wireless communication, and the console  22  sends the synchronization control signal to the electronic cassette  20  via the wireless communication. 
     In this embodiment, the inflator  120  and the air-bag  240  may be stopped to separate the scintillator  150  and the buffer layer  280  from the radiation conversion panel  64  in time periods the electronic cassette  20  is likely to be subjected to the external shock before the preparation for the emission of the radiation  16  and after the completion of the emission of the radiation  16 . Meanwhile, the inflator  120  and the air-bag  240  may be driven to bring the buffer layer  280  and the scintillator  150  into contact with the radiation conversion panel  64  after the electronic cassette  20  receives the synchronization control signal until the emission of the radiation  16  is completed. For example, in the step of positioning the subject  14 , the excessive load (pressure) may be applied by the subject  14  to the electronic cassette  20 , so that the columnar crystal structure  148  may be broken or cracked, and the surface of the radiation conversion panel  64  may be scratched. Therefore, the scintillator  150  and the buffer layer  280  are separated from the radiation conversion panel  64  while the electronic cassette  20  is likely to be subjected to such a shock. 
     The electronic cassette  20  is less likely to be subjected to the external shock during the emission of the radiation  16 , and the buffer layer  280  and the scintillator  150  are brought into contact with the radiation conversion panel  64  only during the emission of the radiation  16  in this embodiment. Therefore, the scintillator  150  can be appropriately protected against the shock, the electronic cassette  20  can be prevented from being deteriorated in the image capturing performance, and the radiographic image can be appropriately acquired. Thus, in the electronic cassette  20 , based on the registered order information, the scintillator  150  and the buffer layer  280  can be brought into contact with the radiation conversion panel  64  before the emission of the radiation  16  to the subject  14 , and the scintillator  150  and the buffer layer  280  can be separated from the radiation conversion panel  64  after the emission of the radiation  16 . 
     [Modifications of the Embodiment] 
     First to fourth modifications of this embodiment will be described below with reference to  FIGS. 13A to 16B . 
     Components of the modifications, which are identical to those of  FIGS. 1 to 12 , are denoted by identical reference numbers, and detailed explanations thereof are omitted. 
     In the first modification, as shown in  FIGS. 13A and 13B , an air-bag  274  (contact mechanism) is interposed between the top plate  132  and the radiation conversion panel  64 . 
     In this case, the air-bag  274  is bonded to the top plate  132  by an adhesive layer  272 , and the radiation conversion panel  64  is bonded to the air-bag  274  by an adhesive layer  276 . The reflective film  260  is bonded to the bottom plate  140  by an adhesive layer  270 . 
     When the air-bag  274  is inflated in the thicknesswise direction of the casing  40  by the inert gas from the inflator  120  as shown in  FIG. 13B , the buffer layer  280  and the radiation conversion panel  64  are brought into contact with each other and become capable of capturing the radiographic image. 
     When the shock prediction judgment part  182  judges that the electronic cassette  20  will be subjected to the external shock, the separation instruction part  184  acts to stop the inert gas supply from the inflator  120  based on the communication signal from the shock prediction judgment part  182 . Then, the inert gas in the air-bag  274  is discharged from a discharge hole (not shown), whereby the air-bag  274  is shrunk in the thicknesswise direction of the casing  40  (toward the top plate  132 ). Consequently, the buffer layer  280  and the radiation conversion panel  64  can be separated from each other as shown in  FIG. 13A . 
     In a case where the electronic cassette  20  is not likely to be subjected to the external shock, the contact instruction part  186  acts to activate the inflator  120  again. Then, the inert gas supply to the air-bag  274  is restarted, whereby the radiation conversion panel  64  is brought into contact with the buffer layer  280  and the scintillator  150  again as shown in  FIG. 13B . 
     Thus, also in the first modification, the radiation conversion panel  64  can be contacted with and separated from the buffer layer  280  and the scintillator  150  (the contact control of the radiation conversion panel  64  with the buffer layer  280  and the scintillator  150  can be executed and stopped) by using the air-bag  274  and the inflator  120 . Consequently, the first modification can achieve the same effects as the above embodiment. 
     In the second modification, as shown in  FIGS. 14A and 14B , the second surface of the buffer layer  280  is coated with a weak adhesive layer  290 . In this case, a sticking or adhesive agent in the adhesive layer  282  has a sticking or adhesive power larger than at least that of the weak adhesive layer  290 . Therefore, in a case where the buffer layer  280  and the radiation conversion panel  64  are brought into contact with each other with the weak adhesive layer  290  interposed therebetween as shown in  FIG. 14B , the tight contact between the buffer layer  280  and the radiation conversion panel  64  can be further improved. Furthermore, the buffer layer  280  and the radiation conversion panel  64  can be easily separated from each other due to the weak adhesive layer  290  as shown in  FIG. 14A . Also the second modification can achieve the same effects as the above embodiment. 
     In the third modification, as shown in  FIGS. 15A and 15B , the buffer layer  280  is bonded to the radiation conversion panel  64  by an adhesive layer  292 . Therefore, the distal end portion of the columnar crystal structure  148  in the scintillator panel  62  does not have the buffer layer  280 . In a case where the distal end portion of the columnar crystal structure  148  is pressed onto the radiation conversion panel  64  as shown in  FIG. 15B , regardless of the unevenness of the distal end portion of the columnar crystal structure  148 , the buffer layer  280  can prevent the penetration of the distal end portion into the protective moisture-proof material  152 . Also the third modification can achieve the same effects as the above embodiment. 
     The radiation detector  66  may have a structure shown in  FIGS. 16A and 16B  (the fourth modification). In the fourth modification, a specific structure of the radiation detector  66 , which contains the CsI scintillator used in the above embodiment, will be described in detail below. 
     In the fourth modification, as shown in  FIGS. 16A and 16B , the radiation detector  66  has a scintillator  500  for converting the radiation  16  transmitted through the subject  14  into the visible light (absorbing the radiation  16  and emitting the visible light), and further has a radiation detection part  502  for converting the visible light from the scintillator  500  into the electric signals (the electric charges) corresponding to the radiographic image. The scintillator  500  corresponds to the above scintillator  150 , and the radiation detection part  502  corresponds to the radiation conversion panel  64 . The protective moisture-proof material  152  is omitted in  FIGS. 16A and 16B . 
     As described above, the radiation detector  66  may be the ISS type radiation detector (wherein the radiation detection part  502  and the scintillator  500  are arranged in this order from the exposed surface  44  to be irradiated with the radiation  16  as shown in  FIGS. 16A and 16B ) or the PSS type radiation detector (wherein the scintillator  500  and the radiation detection part  502  are arranged in this order from the exposed surface  44 ). 
     The scintillator  500  emits the light more intensely at the side closer to the exposed surface  44 , which is irradiated with the radiation  16 . In the ISS type radiation detector  66 , the light emitting portion of the scintillator  500  is closer to the radiation detection part  502 . Therefore, as compared with the PSS type radiation detector  66 , the ISS type radiation detector  66  exhibits a higher resolution of the radiographic image in the image capturing process and a larger visible light quantity received in the radiation detection part  502 . Thus, the ISS type radiation detector  66  exhibits a sensitivity higher than that of the PSS type radiation detector  66  (in the electronic cassette  20 ). 
     The scintillator  500  may be composed of a material such as CsI:Tl, CsI:Na (sodium-activated cesium iodide), GOS(Gd 2 O 2 S:Tb), or the like. 
     An example of the scintillator  500  having a columnar crystal region, which is produced by vapor-depositing a material containing CsI on an evaporation board  504  corresponding to the above support board  144 , is shown in  FIG. 16B . Thus, the scintillator panel  62  contains the evaporation board  504  and the scintillator  500  (see  FIG. 16A ). 
     More specifically, in the scintillator  500  shown in  FIG. 16B , the columnar crystal region containing columnar crystals  500   a  is formed closer to the exposed surface  44  to be irradiated with the radiation  16  (the radiation detection part  502 ), and a non-columnar crystal region containing non-columnar crystals  500   b  is formed remotely from the exposed surface  44 . The columnar crystals  500   a  correspond to the columnar crystal structure  148  (see  FIGS. 4A ,  4 B,  6 A to  8 B, and  13 A to  15 B), and the non-columnar crystals  500   b  correspond to the non-columnar crystal portion  146 . The evaporation board  504  is preferably composed of a highly heat-resistant material such as low-cost aluminum (Al). The columnar crystals  500   a  in the scintillator  500  have a substantially uniform average diameter along the longitudinal direction of the columnar crystals  500   a.    
     As described above, the scintillator  500  includes the columnar crystal region (the columnar crystals  500   a ) and the non-columnar crystal region (the non-columnar crystals  500   b ). The columnar crystal region of the columnar crystals  500   a , which are capable of highly efficient light emission, is disposed in close proximity to the radiation detection part  502 . Therefore, the visible light generated in the scintillator  500  travels through the columnar crystals  500   a  to the radiation detection part  502 . As a result, the diffusion of the visible light emitted toward the radiation detection part  502  can be prevented, so that the radiographic image detected by the electronic cassette  20  can be prevented from blurring. In addition, the visible light that reaches the deep region (the non-columnar crystal region) of the scintillator  500  is reflected by the non-columnar crystals  500   b  toward the radiation detection part  502 . Therefore, the amount of the visible light introduced into the radiation detection part  502  (the efficiency of detecting the visible light from the scintillator  500 ) can be improved. 
     In this embodiment, the top of the columnar crystal structure  148  corresponding to the columnar crystals  500   a  may be convexly curved at the center, and the thickness of the scintillator  150  corresponding to the scintillator  500  may vary with the position (see  FIGS. 4A to 5B ,  7 A to  8 B, and  13 A to  15 B). In the scintillator  500 , in a case where the columnar crystal region closer to the exposed surface  44  has a thickness t 1  and the non-columnar crystal region closer to the evaporation board  504  has a thickness t 2 , the thicknesses t 1  and t 2  preferably satisfy the relationship 0.01≦(t 2 /t 1 )≦0.25 at least around the center of the scintillator  500 . 
     In a case where the thickness t 1  of the columnar crystal region and the thickness t 2  of the non-columnar crystal region satisfy the above relationship, the ratio in the thicknesswise direction of the scintillator  500  between the columnar crystal region having a high light emission efficiency and a visible light diffusion preventing capability and the non-columnar crystal region capable of reflecting the visible light can be within an appropriate range, to improve the light emission efficiency of the scintillator  500 , the efficiency of detecting the visible light emitted from the scintillator  500 , and the resolution of the radiographic image. 
     In a case where the thickness t 2  of the non-columnar crystal region is too large, the region with the low light emission efficiency is increased to lower the sensitivity of the electronic cassette  20 . Therefore, the ratio (t 2 /t 1 ) is more preferably within a range of 0.02 to 0.1. 
     In the above example, the columnar crystal region and the non-columnar crystal region are arranged adjacent to each other in the scintillator  500 . Alternatively, for example, a light reflecting layer made of Al or the like may be used instead of the non-columnar crystal region, and the scintillator  500  may have only the columnar crystal region. The scintillator  500  may have a structure different from these examples. 
     The radiation detection part  502  serves to detect the visible light emitted from the light emitting side (the columnar crystals  500   a ) of the scintillator  500 . In the side elevation of  FIG. 16A , an insulative substrate  508 , a TFT layer  510 , and photoelectric transducers  512  are stacked in this order from the exposed surface  44  along the direction of incident radiation  16 . The photoelectric transducers  512  are covered with a planarization layer  514  formed on the bottom surface of the TFT layer  510 . 
     The radiation detection part  502  is a TFT active matrix board containing the insulative substrate  508  and thereon a plurality of pixels  520  arranged in a matrix as viewed in plan (hereinafter referred to as a TFT board). Each of the pixels  520  includes the photoelectric transducer  512  such as a photodiode (PD), a storage capacitor  516 , and a TFT  518 . 
     The TFTs  518  correspond to the aforementioned TFTs  72  (see  FIG. 10 ), and the photoelectric transducers  512  and the storage capacitors  516  correspond to the pixels  160 . 
     The photoelectric transducer  512  is formed by disposing a photoelectric conversion film  512   c  between a lower electrode  512   a  in close proximity to the scintillator  500  and an upper electrode  512   b  in close proximity to the TFT layer  510 . The photoelectric conversion film  512   c  absorbs the visible light emitted from the scintillator  500  and generates the electric charge corresponding to the absorbed visible light. 
     The lower electrode  512   a  is preferably composed of an electrically conductive material transparent at least to the emission wavelength of the scintillator  500  to inject the visible light emitted from the scintillator  500  into the photoelectric conversion film  512   c . Specifically, the lower electrode  512   a  preferably contains a transparent conducting oxide (TCO) having a high visible light transmittance and a small resistance value. 
     The lower electrode  512   a  may be a thin film of a metal such as Au. However, the thin metal film with a light transmittance of 90% or more tends to exhibit a high resistance, and thus the TCO is preferred. For example, the lower electrode  512   a  preferably contains ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), AZO (Aluminum-doped Zinc Oxide), FTO (Fluorine-doped Tin Oxide), SnO 2 , TiO 2 , ZnO 2 , or the like. Among these oxides, the ITO is most preferable in view of processing simplicity, low resistance, and transparency. The lower electrode  512   a  may be in the form of a single film, which is shared by all of the pixels  520 . Alternatively, the lower electrode  512   a  may be divided for each of the pixels  520 . 
     The photoelectric conversion film  512   c  may be composed of a material capable of absorbing the visible light to generate the electric charge, and may contain for example an amorphous silicon (a-Si), an organic photoconductor (OPC), etc. The photoelectric conversion film  512   c  containing the amorphous silicon can absorb the visible light emitted from the scintillator  500  within a wide wavelength range. However, in the case of forming the photoelectric conversion film  512   c  containing the amorphous silicon, it is necessary to carry out a vapor deposition process. Therefore, in a case where the insulative substrate  508  is composed of a synthetic resin, the heat resistance of the insulative substrate  508  has to be taken into account. 
     On the other hand, the photoelectric conversion film  512   c  composed of a material containing the organic photoconductor can exhibit an absorption spectrum with high absorption mainly in the visible range. Therefore, the photoelectric conversion film  512   c  hardly absorbs electromagnetic waves other than the visible light from the scintillator  500 . Thus, the photoelectric conversion film  512   c  can be prevented from absorbing the radiation  16  such as the X-ray or γ-ray, thereby preventing noise from being generated. 
     The photoelectric conversion film  512   c  composed of the organic photoconductor can be formed by depositing the organic photoconductor on a target using a liquid discharge head such as an ink-jet head. Therefore, the target is not required to be heat-resistant. In fourth modification, the photoelectric conversion film  512   c  is composed of the organic photoconductor for this reason. 
     The photoelectric conversion film  512   c  composed of the organic photoconductor hardly absorbs the radiation  16 . Therefore, in the ISS type radiation detector  66  (wherein the radiation  16  is transmitted through the radiation detection part  502 ), attenuation of the radiation  16  in the radiation detection part  502  can be reduced, and deterioration in sensitivity of the radiation  16  can be prevented. Thus, the photoelectric conversion film  512   c  composed of the organic photoconductor is preferred particularly in the ISS type radiation detector  66 . 
     The organic photoconductor in the photoelectric conversion film  512   c  preferably has an absorption peak wavelength closer to the emission peak wavelength of the scintillator  500  to absorb the visible light from the scintillator  500  more efficiently. It is ideal that the absorption peak wavelength of the organic photoconductor is equal to the emission peak wavelength of the scintillator  500 . In a case where the difference between the peak wavelengths is small enough, the organic photoconductor can satisfactorily absorb the visible light from the scintillator  500 . Specifically, the difference between the absorption peak wavelength of the organic photoconductor and the emission peak wavelength of the scintillator  500  under the radiation  16  is preferably 10 nm or less, more preferably 5 nm or less. 
     Such organic photoconductors satisfying the above requirement include quinacridone-based organic compounds and phthalocyanine-based organic compounds. For example, quinacridone has an absorption peak wavelength of 560 nm in the visible range. Therefore, in a case where the quinacridone is used as the organic photoconductor and CsI:Tl is used as the material of the scintillator  500 , the difference between the above peak wavelengths can be 5 nm or less, whereby the amount of the electric charges generated in the photoelectric conversion film  512   c  can be substantially maximized. 
     The photoelectric conversion film  512   c  applicable to the radiation detector  66  will be described more specifically below. 
     In the radiation detector  66 , an electromagnetic wave absorption/photoelectric conversion region may be formed by the upper and lower electrodes  512   b  and  512   a  and an organic layer containing the photoelectric conversion film  512   c  sandwiched between the upper and lower electrodes  512   b  and  512   a . Specifically, the organic layer may be formed by stacking or combining an electromagnetic wave absorption component, a photoelectric conversion component, an electron transport component, a hole transport component, an electron blocking component, a hole blocking component, a crystallization preventing component, an electrode, an interlayer contact improving component, etc. 
     The organic layer preferably contains an organic p-type or n-type compound. The organic p-type semiconductor (compound) is an organic donor semiconductor (compound) typified by an organic hole transport compound, which has an electron donating property. More specifically, in a case where two organic compounds are used in contact with each other, the organic donor compound is one compound having a lower ionization potential. Thus, any organic compounds having the electron donating property can be used as the organic donor compound. The organic n-type semiconductor (compound) is an organic acceptor semiconductor (compound) typified by an organic electron transport compound, which has an electron accepting property. More specifically, in a case where two organic compounds are used in contact with each other, the organic acceptor compound is one compound having a higher electron affinity. Thus, any organic compounds having the electron accepting property can be used as the organic acceptor compound. 
     Compounds usable as the organic p-type and n-type semiconductors and the structure of the photoelectric conversion film  512   c  are described in detail in Japanese Laid-Open Patent Publication No. 2009-032854, and therefore explanations thereof are omitted. 
     Each of the photoelectric transducers  512  contains at least the upper electrode  512   b , the lower electrode  512   a , and the photoelectric conversion film  512   c . Further, the photoelectric transducer  512  preferably contains at least one of an electron blocking film and a hole blocking film, and more preferably contains the both, to prevent dark current increase. 
     The electron blocking film may be disposed between the upper electrode  512   b  and the photoelectric conversion film  512   c . In a case where a bias voltage is applied between the upper and lower electrodes  512   b  and  512   a , the electron blocking film can prevent electron injection from the upper electrode  512   b  into the photoelectric conversion film  512   c , and thus can prevent the dark current increase. The electron blocking film may be composed of an organic electron donating material. The material of the electron blocking film may be practically selected depending on the material of the adjacent electrode and the material of photoelectric conversion film  512   c , etc. It is preferred that the material of the electron blocking film has an electron affinity (Ea) larger by 1.3 eV or more than the work function (Wf) of the material of the adjacent electrode and has an ionization potential (Ip) equal to or smaller than that of the material of the adjacent photoelectric conversion film  512   c . Materials usable as the organic electron donating material are described in detail in Japanese Laid-Open Patent Publication No. 2009-032854, and therefore such materials will not be described in detail below. 
     The thickness of the electron blocking film is preferably 10 to 200 nm, more preferably 30 to 150 nm, particularly preferably 50 to 100 nm, from the viewpoints of reliably achieving the dark current reducing effect and preventing the photoelectric conversion efficiency of the photoelectric transducer  512  from being reduced. 
     The hole blocking film may be disposed between the photoelectric conversion film  512   c  and the lower electrode  512   a . In a case where the bias voltage is applied between the upper and lower electrodes  512   b  and  512   a , the hole blocking film can prevent hole injection from the lower electrode  512   a  into the photoelectric conversion film  512   c , and thus can prevent the dark current increase. The hole blocking film may be composed of an organic electron accepting material. The material of the hole blocking film may be practically selected depending on the material of the adjacent electrode and the material of the adjacent photoelectric conversion film  512   c , etc. It is preferred that the material of the hole blocking film has an ionization potential (Ip) larger by 1.3 eV or more than the work function (Wf) of the material of the adjacent electrode and has an electron affinity (Ea) equal to or larger than that of the material of the adjacent photoelectric conversion film  512   c . Materials usable as the organic electron accepting material are described in detail in Japanese Laid-Open Patent Publication No. 2009-032854, and therefore such materials will not be described in detail below. 
     The thickness of the hole blocking film is preferably 10 to 200 nm, more preferably 30 to 150 nm, particularly preferably 50 to 100 nm, from the viewpoints of reliably achieving the dark current reducing effect and preventing the photoelectric conversion efficiency of the photoelectric transducer  512  from being reduced. 
     In a case where the bias voltage is provided such that, among the electric charges generated in the photoelectric conversion film  512   c , the holes are transferred to the lower electrode  512   a  and the electrons are transferred to the upper electrode  512   b , the positions of the electron blocking film and the hole blocking film may be reversed. It is not essential to form both of the electron blocking film and the hole blocking film. A certain level the dark current reducing effect can be achieved by forming one of the films. 
     The TFT  518  in the TFT layer  510  contains a stack of a gate electrode, a gate insulating film, and an active layer (channel layer). A source electrode and a drain electrode are disposed on the active layer at a predetermined distance. The active layer may be composed of an amorphous silicon, an amorphous oxide, an organic semiconductor material, a carbon nanotube, or the like, although the material of the active layer is not limited thereto. 
     For example, the amorphous oxide for the active layer is preferably an oxide containing at least one of In, Ga, and Zn (such as In—O oxide), more preferably an oxide containing at least two of In, Ga, and Zn (such as In—Zn—O, In—Ga—O, or Ga—Zn—O oxide), particularly preferably an oxide containing all of In, Ga, and Zn. The amorphous In—Ga—Zn—O oxide is preferably an amorphous oxide having a composition of InGaO 3 (ZnO) m  (wherein m is a natural number of less than 6) in a crystalline state, particularly preferably InGaZnO 4 . It should be noted that the amorphous oxide for the active layer is not limited to such oxides. 
     The organic semiconductor materials for the active layer include, but not limited to, phthalocyanine compounds, pentacene, and vanadyl phthalocyanine. The structures of the phthalocyanine compounds are described in detail in Japanese Laid-Open Patent Publication No. 2009-212389, and therefore the structures will not be described below. 
     In a case where the active layer of the TFT  518  is composed of one of the amorphous oxides, the organic semiconductor materials, the carbon nanotubes, and the like, the active layer does not absorb the radiation  16  such as X-ray or absorbs only an extremely small amount of the radiation  16 , and thereby can effectively reduce noise generation in the radiation detection part  502 . 
     In a case where the active layer is composed of the carbon nanotube, the TFT  518  can have a high switching speed and a lowered visible light absorption. However, in a case where the active layer is composed of the carbon nanotube, the performance of the TFT  518  could be degraded significantly by trace metal impurities mixed with the active layer. Therefore, the carbon nanotube for the active layer has to be isolated and extracted by centrifugal separation or the like to have a high purity. 
     Both of the organic photoconductor and the organic semiconductor material can be used for forming a flexible film. Therefore, in the case of using the combination of the photoelectric conversion film  512   c  composed of the organic photoconductor and the TFT  518  containing the active layer composed of the organic semiconductor material, it is not necessary to increase the rigidity of the radiation detection part  502 , to which a load is applied due to the body weight of the subject  14 . 
     The insulative substrate  508  may be made of a material having a light transmittability and a low absorbability with respect to the radiation  16 . Both of the amorphous oxide for the active layer in the TFT  518  and the organic photoconductor for the photoelectric conversion film  512   c  in the photoelectric transducer  512  can be formed into a film at low temperature. Therefore, the insulative substrate  508  is not limited to a highly heat-resistant substrate such as a semiconductor substrate, a quartz substrate, or a glass substrate, and may contain a flexible synthetic resin, an aramid, or a bionanofiber. Specifically, the insulative substrate  508  may be a flexible substrate of a polyester (such as a polyethylene terephthalate, a polybutylene phthalate, or a polyethylene naphthalate), a polystyrene, a polycarbonate, a polyethersulfone, a polyarylate, a polyimide, a polycycloolefin, a norbornene resin, a poly(chlorotrifluoroethylene), or the like. In the case of using the flexible synthetic resin substrate, the radiation detector  66  can be made lighter and easier to carry around. The insulative substrate  508  may have an insulating layer for maintaining the insulation property, a gas barrier layer for preventing penetration of moisture and oxygen, an undercoat layer for improving the flatness or the adhesion to the electrode, etc. 
     The aramid can undergo a process at a high temperature of 200° C. or higher. Therefore, in the case of using the aramid, a transparent electrode material can be hardened at a high temperature to lower the resistance, and a driver IC can be automatically mounted using a solder reflow process. Furthermore, the aramid has a thermal expansion coefficient close to those of ITO and glass, whereby the insulative substrate  508  containing the aramid is less liable to warp and crack after fabrication thereof. In addition, the insulative substrate  508  of the aramid can be made thinner as compared with glass substrates and the like. The insulative substrate  508  may be formed by stacking the aramid on an ultrathin glass substrate. 
     The bionanofiber is prepared by combining a transparent resin with a cellulose microfibril bundle (bacteria cellulose) produced by bacteria (acetic acid bacteria, Acetobacter Xylinum). The cellulose microfibril bundle has a width of 50 nm, which is 1/10 of the visible light wavelength, and exhibits a high strength, a high elasticity, and a low thermal expansion. The bionanofiber can be produced with a light transmittance of about 90% at a wavelength of 500 nm even at a fibril content of 60% to 70% by impregnating the bacteria cellulose with the transparent resin such as an acrylic resin or an epoxy resin and then hardening the resin. The bionanofiber has a low thermal expansion coefficient (3 to 7 ppm) comparable to a silicon crystal, a high strength (460 MPa) comparable to a steel, a high elasticity (30 GPa), and a high flexibility, whereby the insulative substrate  508  of the bionanofiber can be made thinner as compared with glass substrates and the like. 
     In a case where a glass substrate is used as the insulative substrate  508 , the entire radiation detection part  502  (TFT substrate) has a thickness of e.g. about 0.7 mm. In the fourth modification, the thin light-transmittable substrate composed of the synthetic resin is used as the insulative substrate  508  to make the electronic cassette  20  thinner. Therefore, the entire radiation detection part  502  can have a small thickness of e.g. about 0.1 mm and can be flexible. In a case where the radiation detection part  502  is flexible, the electronic cassette  20  can exhibit an improved impact resistance and can be prevented from being broken due to the external shock. In a case where the insulative substrate  508  is composed of the material having the low radiation  16  absorbability (such as the plastic resin, the aramid, or the bionanofiber), the insulative substrate  508  absorbs only a small amount of the radiation  16 . Therefore, even if the radiation  16  is transmitted through the radiation detection part  502  in the ISS type structure, the deterioration of the radiation  16  sensitivity can be prevented. 
     It is not essential to use the synthetic resin substrate as the insulative substrate  508  in the electronic cassette  20 . The insulative substrate  508  may be composed of another material such as a glass although the other material may make the electronic cassette  20  thicker. 
     In the radiation detection part  502  (TFT substrate), the planarization layer  514  for planarizing the radiation detection part  502  is disposed remotely from the source of the radiation  16  (close to the scintillator  500 ). 
     In the fourth modification, the radiation detector  66  may be as follows. 
     (1) The photoelectric transducers  512  including the PDs may contain the organic photoconductor, and the TFT layer  510  may contain CMOS sensors. In this case, since only the PDs are made of an organic material, the TFT layer  510  containing the CMOS sensors may be inflexible. The photoelectric transducers  512  containing the organic photoconductor and the CMOS sensors are described in detail in Japanese Laid-Open Patent Publication No. 2009-212377, and therefore explanations thereof are herein omitted. 
     (2) The photoelectric transducers  512  including the PDs may contain the organic photoconductor, and the TFT layer  510  may be a flexible layer using CMOS circuits with TFTs composed of an organic material. In this case, the CMOS circuits may contain pentacene as an organic p-type semiconductor material, and may contain fluorinated copper phthalocyanine (F 16 CuPc) as an organic n-type semiconductor material. In this manner, the TFT layer  510  can be a flexible layer having a smaller bend radius, and the gate insulating film can be significantly thinned to lower the drive voltage. Furthermore, the gate insulating film, the semiconductor, and the electrodes can be fabricated at a room temperature or a temperature of 100° C. or lower. In addition, the CMOS circuits can be fabricated directly on the flexible insulative substrate  508 . The TFTs composed of the organic material can be microfabricated using a fabrication process according to a scaling law. The insulative substrate  508  can be produced as a flat substrate by spin-coating a thin polyimide substrate with a polyimide precursor and then heating the applied polyimide precursor to convert the same into polyimide. 
     (3) The PDs and the TFTs may contain crystalline Si and may be disposed on the insulative substrate  508  containing a resin by a fluidic self-assembly process. In the fluidic self-assembly process, a plurality of device blocks on the order of microns are placed at designated positions on a substrate. In this case, the PDs and the TFTs (corresponding to the device blocks on the order of microns) are prefabricated on another substrate, separated from the substrate, and statistically spread and positioned in a liquid on the insulative substrate  508  (corresponding to a target substrate). The insulative substrate  508  is preliminarily processed to adapt itself to the device blocks, so that the device blocks can be selectively placed on the insulative substrate  508 . Accordingly, the optimum device blocks (the PDs and the TFTs) composed of the optimum material can be integrated on the optimum substrate (the insulative substrate  508 ). Thus, it is possible to integrate the PDs and the TFTs into the non-crystalline insulative substrate  508  (the resin substrate). 
     [Other Constitution Examples of the Embodiment] 
     The electronic cassette  20  of this embodiment is not limited to the above descriptions, and may have the following features. The following features may be used in combination with the above structures. 
     The air-bags  240  and  274  are described above as a specific example of the contact mechanism for contacting and separating the scintillator  150  and the radiation conversion panel  64 . The contact mechanism is not limited to the specific example, and may have any structure as long as the scintillator  150  and the radiation conversion panel  64  can be dynamically brought into contact with and separated from each other by using the mechanism. 
     In the above embodiment and the first to third modifications, the inert gas generated in the inflator  120  is supplied to the air-bag  240  or  274 , whereby the air-bag  240  or  274  is inflated. Alternatively, an air gas cylinder for externally supplying air may be mounted on or connected to the electronic cassette  20 . In this case, a valve of the air gas cylinder is opened and closed, and the air is supplied from the air gas cylinder to the air-bag  240  or  274 , whereby the air-bag  240  or  274  is inflated. Alternatively, a compressed air may be supplied from an air pump (compressor) to the air-bag  240  or  274 , to inflate the air-bag  240  or  274 . In the examples, in the step of deflating the air-bag  240  or  274 , the air in the air-bag  240  or  274  may be discharged from a hole (not shown) or evacuated using an air pump. 
     In the drawings according to the above embodiment and the first to third modifications, the scintillator  150  and the radiation conversion panel  64  are completely separated from each other (in the non-contact states). The above embodiment and the first to third modifications are not limited to the drawings. The scintillator  150  and the radiation conversion panel  64  may be in contact with each other even if the contact control by the above-described contact mechanism is stopped, as long as the contact pressure is approximately zero or lower than the pressure observed in the process of pressing the scintillator  150  and the radiation conversion panel  64  against each other. In this case, though the scintillator  150  and the radiation conversion panel  64  cannot be completely separated from each other, the above-described effects can be achieved by stopping the contact control of the contact mechanism. 
     In the above embodiment and the first to third modifications, before the process of capturing the image of the subject  14 , the scintillator  150  and the radiation conversion panel  64  may be brought into contact with (pressed against) each other by the contact mechanism based on the order information. After the process of capturing the image of the subject  14 , the scintillator  150  and the radiation conversion panel  64  may be separated from each other, or the contact pressure between the scintillator  150  and the radiation conversion panel  64  may be lowered. Thus, the scintillator  150  and the radiation conversion panel  64  may be pressed against each other only in the image capturing process, in which the electronic cassette  20  is not likely to be subjected to the external shock. Therefore, also in this case, the above-described effects relevant to the contact control can be achieved. 
     It is to be understood that the present invention is not limited to the above embodiment, and various changes and modifications may be made therein without departing from the scope of the invention.