Patent Publication Number: US-7902509-B2

Title: Photomultiplier tube and radiation detecting device

Description:
TECHNICAL FIELD 
     The present invention relates to a photomultiplier tube and a radiation detecting device. 
     BACKGROUND ART 
     A conventional photomultiplier tube includes a photocathode provided on an end of a vacuum vessel for emitting electrons, an electron multiplying section for multiplying the emitted electrons, and an electron detecting section for detecting the multiplied electrons. A electrode-layered unit including dynodes provided with a plurality of channel regions constitutes the electron multiplying section, and a plurality of anodes arranged in association with each channel region constitutes the electron detecting section (for example, refer to patent documents 1 and 2). In such a photomultiplier tube, a connecting section protrudes from each dynode constituting the electrode-layered unit, and each connecting section is individually connected to stem pins. The electrode-layered unit is supported above the electron detecting section by the stem pins in an electrically insulated state from the electron detecting section. 
     Further, another known photomultiplier tube is configured in such a manner that a shaft is provided for allowing the electron multiplying section to slidably move in parallel with an axis of the photomultiplier tube during manufacture of the photomultiplier tube, and that the electron multiplying section is fixed to the shaft when the manufacture is completed (for example, refer to patent document 3). 
     Also, there has been provided still another photomultiplier tube in which the electrode-layered unit is supported by, in addition to stem pins connected individually to each dynode, placing the electrode-layered unit on an insulating spacer that is disposed on the periphery of the electron detecting section. 
     Patent document 1: Japanese Patent Application Publication No. 2000-149860 (page 3, FIG. 2) 
     Patent document 2: Japanese Patent Application Publication No. HEI9-288992 (page 4, FIG. 2) 
     Patent document 3: Japanese Patent Application Publication No. SHO62-287560 (pages 4-5, FIG. 1) 
     DISCLOSURE OF THE INVENTION 
     Technical Problem 
     With the photomultiplier tubes described above, it is desired that anti-vibration performance be increased sufficiently to improve reliability, by enhancing fixation strength of an electrode-layered unit disposed above an electron detecting section formed by arranging a plurality of anodes. 
     In view of the foregoing, it is an object of the present invention to provide a photomultiplier tube and a radiation detecting device that realize high anti-vibration performance, and that preserve predetermined detection characteristics by increasing positioning accuracy between a photocathode and an electron multiplying section. 
     Technical Solution 
     In order to attain the above objects, the present invention provides a photomultiplier tube including: a vacuum vessel having a faceplate constituting one end and a stem constituting another end; a photocathode that converts incident light incident through the faceplate to electrons; an electron multiplying section that multiplies the electrons emitted from the photocathode; and an electron detecting section that transmits output signals in response to electrons from the electron multiplying section. The photocathode, the electron multiplying section, and the electron detecting section are provided within the vacuum vessel. The photomultiplier tube is characterized in that the electron multiplying section includes an electrode-layered unit in which electrodes including dynodes constituting a plurality of channels are stacked in a plurality of stages; the electron detecting section includes a plurality of anodes that is arranged spaced away from and in confrontation with a last stage electrode of the electrode-layered unit and that is arranged in association with the channels; and the stem is provided with supporting means for placing the last stage electrode thereon 
     With this configuration, the electron multiplying section is stably supported by the supporting means, and thus good anti-vibration performance is obtained. Also, because the position of the electron multiplying section can be defined with good precision, the distance from the photocathode to the electron multiplying section can be set accurately. Further, because no insulator exists between the anodes and the dynodes, it is possible to prevent an occurrence of leak current due to charging of an insulator, as well as emission of light that occurs when multiplied electrons collide on the insulator 
     At this time, preferably the plurality of stages of electrodes is stacked with an insulator interposed between two adjacent electrodes, and that the insulator and the supporting means are arranged coaxially. 
     Since the supporting means and the insulators are arranged coaxially in this way, sufficient pressure can be applied in a stacking direction to fix the electron multiplying section, thereby further improving the anti-vibration performance. 
     In any one of the above-described photomultiplier tubes, the last stage electrode of the electrode-layered unit may include a drawing electrode having an opening that allows the electrons emitted from the dynodes to reach the anodes. 
     With this configuration, the drawing electrode is provided between the last stage dynode and the electron detecting section, and is applied with an electric potential higher than the last stage dynode and lower than the electron detecting section. Hence, the electric field intensity between the last stage dynode and the electron detecting section uniformly increases. Accordingly, even when there are variations in the setting accuracy among each anode constituting the electron detecting section, electrons can be uniformly drawn from the last stage dynode. 
     It is preferable that the electron detecting section include either a plurality of multiple anodes arranged two-dimensionally or a plurality of linear anodes arranged one-dimensionally. 
     With this configuration, electrons can be detected by the plurality of anodes, and the incident position of the incident light that enters the photomultiplier tube can be measured. 
     Further, it is preferable that the supporting means be formed of an electrically-conductive material. 
     With this configuration, no light is emitted even when electrons collide on the supporting means, thereby preventing noise. 
     Further, it is preferable that the supporting means include a supporting section that extends from the stem in a stacking direction of the electrode-layered unit and a placing section on which the last stage electrode is placed, and that a cross-sectional area of the placing section in a plane perpendicular to the stacking direction be larger than a cross-sectional area of the supporting section in a plane perpendicular to the stacking direction. 
     With this configuration, the cross-sectional area of the placing section in the plane perpendicular to the stacking direction is larger than the cross-sectional area of the supporting section in the plane perpendicular to the stacking direction. Hence, the positioning accuracy of the electrode-layered unit in the stacking direction can be set reliably. In addition, the electrode-layered unit can be stably placed on the placing surface of the placing section. 
     Further, it is preferable that a first engaging section be formed on a surface of the placing section on which the last stage electrode is placed, that a second engaging section be formed on a surface of the last stage electrode that is placed on the placing section, and that the first engaging section and the second engaging section be engaged with each other when the last stage electrode is placed on the supporting means. 
     With this configuration, the positioning accuracy of the electrode-layered unit in the directions along the plane perpendicular to the stacking direction can be improved. 
     A radiation detecting device having the above-described effects can be obtained by disposing, outside of the faceplate of any one of the above-described photomultiplier tubes, a scintillator that converts radiation to light and that outputs the light 
     Advantageous Effects 
     According to the present invention, there is provided a photomultiplier tube and a radiation detecting device that have high anti-vibration performance and that preserve predetermined characteristics by increasing positioning accuracy between a photocathode and an electron multiplying section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of a radiation detecting device  1  according to an embodiment of the present invention; 
         FIG. 2  is a schematic cross-sectional view of a photomultiplier tube  10  taken along a line II-II of  FIG. 1 ; 
         FIG. 3  is a plan view showing an inner surface  29   a , a tubular member  31 , and an extending section  32  of a stem  29 ; 
         FIG. 4  is a cross-sectional view taken along a line IV-IV of  FIG. 3 ; 
         FIG. 5  is a partial enlarged view of  FIG. 2 ; 
         FIG. 6  is a partial enlarged view of  FIG. 4 ; 
         FIG. 7  is a partial enlarged view of  FIG. 1 ; 
         FIG. 8  is a schematic view of an anode  25  and its configuration at the lower side in z-axis, when viewed from the upper side in z-axis; 
         FIG. 9  is a partial enlarged view of  FIG. 8 ; 
         FIG. 10  is a schematic view of a dynode Dy 12  and its configuration at the lower side in z-axis, when viewed from the upper side in x-axis; 
         FIG. 11  is a partial enlarged view of  FIG. 10 ; 
         FIG. 12  is a schematic view of a focusing electrode  17  and its configuration at the lower side in z-axis, when viewed from the upper side in z-axis; 
         FIGS. 13  is a partial enlarged view of  FIG. 12 ; 
         FIG. 14  is a view showing electron trajectories from a photocathode  14  to a dynode Dy 1  projected on xy plane and on xz plane; 
         FIG. 15  is a view showing partition walls provided to a normal dynode; 
         FIG. 16  is a view showing partition walls provided to a predetermined dynode; 
         FIG. 17  is an overall view of a dynode provided with a large number of partition walls; 
         FIG. 18  is a cross-sectional view of  FIG. 17 ; 
         FIG. 19  is a cross-sectional view showing the configuration around an air discharging tube  40 ; 
         FIG. 20  is a view showing a method of manufacturing the air discharging tube  40  and the stem  29 ; 
         FIG. 21  is a view showing the method of manufacturing the air discharging tube  40  and the stem  29 ; 
         FIG. 22  is a view showing the method of manufacturing the air discharging tube  40  and the stem  29 ; 
         FIG. 23  is a perspective view showing an anode  125  according to a first modification; 
         FIG. 24  is a schematic cross-sectional view showing a radiation detecting device  100  according to a second modification; 
         FIG. 25  is a schematic cross-sectional view showing a radiation detecting device  200  according to a third modification; 
         FIG. 26  is a schematic cross-sectional view showing the radiation detecting device  100  according to a fourth modification; and 
         FIG. 27  is a plan view showing a modification of the shape of an opening part of the extending section  32 . 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1 : radiation detecting device 
           3 : scintillator 
           5 : incident surface 
           7 : output surface 
           10 : photomultiplier tube 
           13 : faceplate 
           14 : photocathode 
           15 : side tube 
           17 : focusing electrode 
           19 : drawing electrode 
           21 : supporting pin 
           23 : insulating member 
           25 : anode 
           27 : stem pin 
           29 : stem 
           31 : tubular member 
           32 :. extending section 
           33 : protuberant section 
           35 : shaft 
           47 : lead pin 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, an embodiment of the present invention will be described while referring to the accompanying drawings. 
       FIGS. 1 through 22  show a radiation detecting device including a photomultiplier tube according to the embodiment of the present invention. In each drawing, the substantially same parts are designated by the same reference numerals to avoid duplicating description. Note that, in the following description, the terms “upper”, “lower”, and the like are used based on a state shown in each drawing, for descriptive purposes. 
       FIG. 1  is a schematic cross-sectional view of a radiation detecting device  1  according to the present embodiment  FIG. 2  is a schematic cross-sectional-view of a photomultiplier tube  10  taken along a line II-II of  FIG. 1 . As shown in  FIGS. 1 and 2 , the radiation detecting device  1  includes a scintillator  3  that converts incident radiation to light and outputs the light, and the photomultiplier tube  10  that converts incident light to electrons, multiplies the electrons, and detects the electrons. The radiation detecting device  1  is a device that detects incident radiation and outputs signals. The photomultiplier tube  10  has a cylindrical shape with a substantially rectangular cross-section. The direction of the tube axis is defined as z-axis, the axis perpendicular to the drawing of  FIG. 1  is defined as x-axis, and the axis perpendicular to both z-axis and x-axis is defined as y-axis. 
     The scintillator  3  includes an incident surface  5  at one end in the z-axis direction and an output surface  7  at the other end, and has a substantially rectangular cross-section. Radiation is incident at the incident surface  5  side of the scintillator  3 , and the incident radiation is converted to light inside the scintillator  3 , and the light travels within the scintillator  3  and is outputted from the output surface  7  side. The photomultiplier tube  10  is in contact with the output surface  7  side of the scintillator  3 . The central axis of the scintillator  3  and the tube axis of the photomultiplier tube  10  are approximately coaxial. 
     The photomultiplier tube  10  is a vacuum vessel manufactured by hermetically connecting and fixing a faceplate  13  that constitutes one end section in the z-axis direction, a stem  29  that constitutes the other end section, a tubular member  31  provided at the periphery of the stem  29 , an air discharging tube  40  provided at an approximate center of the stem  29  in the xy plane, and a side tube  15  having a cylindrical shape. Within the vacuum vessel of the photomultiplier tube  10  arranged are a focusing electrode  17 , an electrode-layered unit including a plurality of dynodes Dy 1 -Dy 12 , an electron detecting section including a plurality of anodes  25  that detects electrons and outputs signals, and a drawing electrode  19  provided between the electrode-layered unit and the electron detecting section. 
     The faceplate  13  is formed of glass, for example, and has a substantially rectangular plate shape. A photocathode  14  for converting incident light to electrons is provided at the inner side of the faceplate  13 , that is, at the lower side in the z-axis direction. The photocathode  14  is formed by reaction of preliminary vapor-deposited antimony and alkali metal vapor, for example. The photocathode  14  is provided on an approximately entire surface of the inner side of the faceplate  13 . The photocathode  14  converts the light having been outputted from the scintillator  3  and incident through the faceplate  13  to electrons, and emits the electrons. The side tube  15  is formed of metal, for example, and has a cylindrical shape with a substantially rectangular cross-section. The side tube  15  constitutes side surfaces of the photomultiplier tube  10 . The faceplate  13  is hermetically fixed to one side of the side tube  15 , while the stem  29  is hermetically fixed to the other side of the side tube  15  via the tubular member  31 . Here, the photocathode  14  is electrically connected to the side tube  15 , and has the same electric potential as the side tube  15 . 
       FIG. 3  is a plan view showing an inner surface  29   a  of the stem  29 , the tubular member  31 , and an extending section  32 . As shown in  FIGS. 1 through 3 , the stem  29  is formed of a Kovar glass, for example, and has a substantially rectangular plate shape. The stem  29  has the inner surface  29   a  at the inner side of the photomultiplier tube  10 , an outer surface  29   b , and a peripheral section  29   c  that connects those surfaces. Electrically-conductive stem pins  27  for supporting the anodes  25  are hermetically inserted in the stem  29 , the number of the stem pins  27  corresponding to the number of channels of the anodes  25  (64 in this example) 
     The tubular member  31  surrounding the peripheral section  29   c  is hermetically joined to the peripheral section  29   c  of the stem  29 . The tubular member  31  is formed of metal, for example, and has a tubular shape with a substantially rectangular cross-section. The tubular member  31  is also hermetically joined to the side tube  15 . The extending section  32  extends from the tubular member  31  to the inner side of the photomultiplier tube  10  along the inner surface  29   a  of the stem  29 . The extending section  32  is formed of metal, for example, and has a substantially rectangular tubular shape in a plan view. 
     A plurality of through-hole sections  22  and  48  is formed at both ends of the extending section  32  in the x-axis direction. Supporting pins  21  and/or lead pins  47  penetrate and are fixed to the plurality of through-hole sections  22  and  48  respectively. In addition, a focus pin  51  is erected in the extending section  32  at the left end thereof in the x-axis direction in  FIG. 3 . 
     The supporting pin  21  is formed of an electrically-conductive material. In the present embodiment, three supporting pins  21  are provided at each end in the x-axis direction (i.e., six supporting pins  21  in total). Note that  FIG. 2  shows a cross-section taken along a line V-V of  FIG. 3 . As shown in  FIG. 2 , the supporting pins  21  penetrate the stem  29  and extend upward in the z-axis direction for placing the drawing electrode  19  thereon. The supporting pins  21  have the same electrical potential as the drawing electrode  19 . 
     As shown in  FIG. 5 , the supporting pin  21  includes a supporting section  21   a  that penetrates the stem  29  and extends in the z-axis direction, and a placing section  21   b  provided to the upper end of the supporting section  21   a  in the z-axis direction for placing the electrode-layered unit thereon. Here, the placing section  21   b  is formed in such a manner that the cross-sectional area thereof in the xy plane is larger than that of the supporting section  21   a . The electrode-layered unit is supported on the supporting pins  21  in such a manner that the lower surface of the lowermost electrode (the drawing electrode  19  in the present embodiment) abuts on the upper surface (placing surface) of the placing section  21   b . Because the placing section  21   b  has a larger cross-sectional area in the xy plane than the supporting section  21   a ; the positioning accuracy of the electrode-layered unit in the z-axis direction is set reliably, and the electrode-layered unit can be placed stably on the placing surface of the placing section  21   b.    
     The lead pins  47  are formed of electrically-conductive material. In the present embodiment, a total of 35 lead pins  47  are provided at both ends in the x-axis direction.  FIG. 4  shows a cross-section taken along a line IV-IV of  FIG. 3 . As shown in  FIG. 4 , the lead pins  47  penetrate the stem  29  and extend upward in the z-axis direction. The lead pins  47  are connected to respective ones of the dynodes Dy 1 -Dy 12  and to the drawing electrode  19 , and supply predetermined electrical potentials thereto. Note that each of the lead pins  47  is formed in a length in accordance with the positions of the respective dynodes Dy 1 -Dy 12  to which the lead pins  47  are connected. The focus pin  51  is formed of electrically-conductive material. The focus pin  51  extends upward in the z-axis direction from the stem  29  and is connected to the focusing electrode  17 . The focusing electrode  17  is electrically connected to the side tube  15  via the focus pin  51  that is welded to the tubular member  31 . The focusing electrode  17  has the same electrical potential as the photocathode  14 . 
       FIG. 5  is a partial enlarged view of  FIG. 2 , that is, a cross-section taken along a line V-V of  FIG. 3 .  FIG. 6  is a partial enlarged view of  FIG. 4 , that is, a cross-section taken along a line IV-IV of  FIG. 3 . As shown in  FIGS. 5 and 6 , a protuberant section  33  raised from the stem  29  is formed at positions where the supporting pins  21  and the lead pins  47  in the through-hole sections  22  and  48  are connected to the inner surface  29   a  of the stem  29 . Here, a contact point between the protuberant section  33  and the supporting pin  21  or the lead pin  47  is referred to as a point P 1 . A virtual contact point between the inner surface  29   a  and the supporting pin  21  or the lead pin  47  is referred to as a point P 2 , when it is assumed that the protuberant section  33  does not exist. A contact point between the protuberant section  33  and the extending section  32  is referred to as a point P 3 . The distance between the point P 1  and the point P 3  is longer than the distance between the point P 3  and the point P 2 . Accordingly, in the present embodiment, the existence of the protuberant sections  33  ensures that the creepage distance between the supporting pin  21  or the lead pin  47  and the tubular member  31  is made long. 
     As shown in  FIGS. 1 and 2 , the focusing electrode  17  is arranged in confrontation with the photocathode  14  with a predetermined distance kept therebetween. The focusing electrode  17  is a thin electrode with a substantially rectangular shape, and includes a plurality of focus pieces  17   a  extending in the x-axis direction and a plurality of slit-shaped openings  17   b  formed by the plurality of focus pieces  17   a . The focusing electrode  17  serves to efficiently converge the electrons to electron multiplying openings  18   a  (see  FIG. 7 ) of the dynode Dy 1 l. The focusing electrode  17  is electrically connected to the side tube  15  via the focus pin  51  (see  FIG. 3 ) erected in the extending section  32 , and thus has the same electrical potential with the photocathode  14 . 
     The dynodes Dy 1 -Dy 12  are electrodes for multiplying electrons. The dynodes Dy 1 -Dy 12  are stacked below the focusing electrode  17  in the z-axis direction such that the dynodes are in confrontation with and in substantially parallel with each other.  FIG. 7  is a partial enlarged view of  FIG. 1 . As shown in  FIG. 7 , the dynodes Dy 1 -Dy 12  are thin-plate type electrodes having substantially rectangular shapes, in which electron multiplying pieces  18  are arranged in parallel with and spaced away from each other. The electron multiplying piece  18  has a cross-section with concavities and convexities in the yz plane. Thus, in the dynodes Dy 1 -Dy 12 , the slit-shaped electron multiplying openings  18   a  extending in the x-axis direction are formed between the adjacent electron multiplying pieces  18 . A predetermined number of the electron multiplying openings  18   a  correspond to each anode. Partition walls  71  (see  FIG. 15 ) extending in the y-axis direction are provided at positions corresponding to border sections in the x-axis direction of each channel of the anodes  25 . The partition walls  71  define borders in the y-axis direction of a plurality of channels of the dynodes Dy 1 -Dy 12 . Further, as shown in  FIGS. 2 and 5 , an insulating member  23  is arranged between adjacent two of the dynodes Dy 1 -Dy 12 . The dynodes Dy 1 -Dy 12  are applied with electric potentials by the lead pins  47 , where the electric potentials increase sequentially from the photocathode  14  side toward the stem  29  side. 
     The drawing electrode  19  is arranged at the stem  29  side of the dynode Dy 12  so that the drawing electrode  19  is spaced away from the dynode Dy 12  via the insulating member  23  and is in confrontation with and in substantially parallel with the dynode Dy 12 . The drawing electrode  19  is a thin-plate type electrode formed of the same material as the dynodes Dy 1 -Dy 12 . The drawing electrode  19  includes a plurality of drawing pieces  19   a  extending in the x-axis direction and a plurality of slit-shaped openings  19   b  formed by the plurality of drawing pieces  19   a . The openings  19   b  serve to pass the electrons emitted from the dynode Dy 12  toward the anode  25 , and hence, are different from the electron multiplying openings  18   a  of the dynodes Dy 1 -Dy 12 . Hence, the openings  19   b  are designed so that the electrons emitted from the dynode Dy 12  can collide against the openings  19   b  as less as possible. The drawing electrode  19  is applied with a predetermined electric potential that is higher than the dynode Dy 12  and lower than the anode  25 , thereby producing a uniform electric field intensity on a secondary electron surface of the dynode Dy 12 . Here, the secondary electron surface indicates a portion formed at the electron multiplying openings  18   a  of each dynode Dy and contributing to multiplication of electrons. 
     If the drawing electrode  19  does not exist, an electric field for drawing electrons from the dynode Dy 12  depends on the potential difference between the dynode Dy 12  and the anode  25  and the distance therebetween. Hence, if each anode  25  is arranged in a somewhat slanted manner with respect to the xy plane, the distance between the dynode Dy 12  and the anode  25  is different depending on each position. Hence, the electric field intensity with respect to the dynode Dy 12  becomes nonuniform, and thus electrons cannot be drawn uniformly. However, in the present embodiment, because the drawing electrode  19  is arranged between the dynode Dy 12  and the anode  25 , the electric field with respect to the dynode Dy 12  is determined by the potential difference between the dynode Dy 12  and the drawing electrode  19  and the distance therebetween. Because the potential difference between the dynode Dy 12  and the drawing electrode  19  and the distance therebetween are uniform, the electric field intensity on the secondary electron surface of the dynode Dy 12  is kept uniform, thereby enabling electrons to be drawn from the dynode Dy 12  with a uniform force. Accordingly, even if each of the anodes  25  is arranged in a somewhat slanted manner with respect to the xy plane, electrons can be drawn from the dynode Dy 12  uniformly. 
     As described above, the peripheral section of the drawing electrode  19  is placed on the placing sections  21   b  of the supporting pins  21  made of a conductive material. As shown in  FIG. 5 , because the supporting pin  21  and the plurality of insulating members  23  are arranged coaxially on a z-axis direction axis  35 , it is possible to fix the focusing electrode  17 , the dynodes Dy 1 -Dy 12 , and the drawing electrode  19  by applying a high pressure downward in the z-axis direction. 
     The anode  25  is an electron detecting section that detects electrons and that outputs signals in response to the detected electrons to outside of the photomultiplier tube  10  via the stem pin  27 . The anode  25  is provided at the stem  29  side of the drawing electrode  19 , and arranged in substantially parallel with and in confrontation with the drawing electrode  19 . As shown in  FIGS. 1 and 2 , the anode  25  includes a plurality of thin-plate type electrodes provided in association with the plurality of channels of the dynodes Dy 1 -Dy 12 . Each anode  25  is welded to the corresponding stem pin  27 , and is applied with a predetermined electric potential that is higher than the electric potential of the drawing electrode  19  via the stem pins  27 . Further, the anode  25  is provided with a plurality of slits for diffusing alkali metal vapor that is introduced through the air discharging tube  40  during assembling. 
     Hereinafter, the configuration of the focusing electrode  17 , the dynodes Dy 1 -Dy 12 , the drawing electrode  19 , and the anodes  25  will be described in greater detail. 
       FIG. 8  is a schematic view of the electron multiplying section, when viewed from the upper side in z-axis, and FIG.  9  is a partial enlarged view of  FIG. 8 . As shown in  FIG. 8 , the electron multiplying section is configured by arranging a plurality of anodes  25  (64 anodes in the present embodiment) two-dimensionally. The anodes  25  are individually supported by respective ones of the stem pins  27 , and are electrically connected to a circuit (not shown) via the stem pins  27 . 
     Here, unit anodes are referred to as anode  25 ( 1 - 1 ),  25 ( 1 - 2 ), . . . ,  25 ( 8 - 8 ), beginning from the left top of  FIG. 8 , for descriptive purposes. With each anode  25 ( 1 - 1 ),  25 ( 1 - 2 ),  25 ( 8 - 8 ), concave sections  28  are formed between adjacent unit anodes in confrontation with each other. Bridge remaining sections  26  remain in the concave sections  28 . At the time of assembling, the anode  25  is formed as an integral anode plate where adjacent unit anodes are connected to each other by bridges, and each unit anode is welded and fixed to each stem pin  27  in an integral state. Thereafter, the bridges are cut off and the anodes  25 ( 1 - 1 ),  25 ( 1 - 2 ), . . . ,  25 ( 8 - 8 ) become independent from one another. The bridge remaining sections  26  are the remaining portions after the bridges are cut off. 
     Further, cutout portions  24  are formed in the anodes  25 ( 1 - 1 ),  25 ( 2 - 1 ), . . . ,  25 ( 8 - 1 ) and the anodes  25 ( 1 - 8 ),  25 ( 2 - 8 ),  25 ( 8 - 8 ) that correspond to the both end sections in the x-axis direction, except at corner sections  83  of the anodes  25 ( 1 - 1 ),  25 ( 1 - 8 ),  25 ( 8 - 1 ), and  25 ( 8 - 8 ). Hence, the cutout portions  24  serve to avoid contacts between the anodes  25  and each of the supporting pins  21 , the lead pins  47  and the focus pin  51 , and also to enlarge the effective area of the electron detecting section until the proximity of the side tube  15 . 
       FIG. 10  is a schematic view of the dynode Dy 12 , when viewed from the upper side in z-axis, and  FIG. 11  is a partial enlarged view of  FIG. 10 . Note that, in  FIGS. 10 and 11 , the openings  18   a  and  19   b  of the electron multiplying pieces  18  and the drawing electrode  19  are omitted. As shown in  FIG. 11 , the dynode Dy 12  and the drawing electrode  19  have outer shapes substantially identical to the shape of the anode  25  in the xy plane. That is, the dynode Dy 12  and the drawing electrode  19  are formed with cutout portions  49  at the both end sections in the x-axis direction for avoiding the supporting pins  21 , the lead pins  47 , and the like. The cutout portions  49  of the drawing electrode  19  are formed with protruding portions  55 . The supporting pins  21  support the entire drawing electrode  19  by placing the protruding portions  55  on the supporting pins  21 . Similarly, the dynode Dy 12  also has the protruding portions  53 . In case of the dynode Dy 12 , since the dynode is connected to lead pins  47 A and  47 B and is applied with a predetermined electric potential, protruding portions  53  are formed around the lead pins  47 A and  47 B. Further, the electrode is formed to the proximity of the inner wall surface of the side tube  15  at the both end sections in the y-axis direction. Especially, corner sections  85  protrude at the four corner sections. Note that dynodes Dy 1 -Dy 11  have substantially the same configuration as the dynode Dy 12 . Each lead pin  47  extends in the z-axis direction and is connected to a predetermined dynode Dy. 
       FIG. 12  is a schematic view of the focusing electrode  17 , when viewed from the upper side in z-axis, and  FIG. 13  is a partial enlarged view of  FIG. 12 . Note that, in  FIGS. 12 and 13 , the focus pieces  17   a  and the openings  17   b  shown in  FIGS. 1 and 2  are omitted. As shown in  FIGS. 12 and 13 , the focusing electrode  17  is provided to the peripheral sections in the x-axis direction so that the focusing electrode  17  can cover the cutout portions  24  of the anodes  25  and the cutout portions  49  of the dynodes Dy 1 -Dy 12  and the drawing electrode  19 . Note that portions of the focusing electrode  17  that cover the cutout portions  24  or the cutout portions  49  constitute flat-plate electrode sections  16  with no slits formed thereon. The four corner sections of the focusing electrode  17  constitute corner sections  87  having slits. 
     The outer shapes in the xy plane of the above-described focusing electrode  17 , the dynodes Dy 1 -Dy 12 , the drawing electrode  19 , and the anode  25  have effects on electron trajectories inside the photomultiplier tube  10 . The effects will be described hereinafter.  FIG. 14  is a view showing the electron trajectories from the photocathode  14  to the dynode Dy 1  projected on the xy plane and on the xz plane. As shown in  FIG. 14 , an electron emitted from the peripheral section of the photocathode  14  in the x-axis direction is converged to an electron multiplying hole opening  89  by the flat-plate electrode section  16  provided with the focusing electrode  17  for covering the cutout portions  24  and  49 , and enters the dynode Dy 1  as indicated by a trajectory  61 . Further, an electron emitted from a region of the photocathode  14  that confronts the corner section  87  is converged by the corner section  87  of the focusing electrode  17 , and enters the corner section  85  of the dynode Dy 1  as indicated by a trajectory  63 . In this way, because the corner sections  87  and  85  of the focusing electrode  17  and the dynode Dy 1  are provided, electrons emitted from the peripheral sections of the photocathode  14  enter the dynode Dy 1  efficiently. 
     Incidentally, if the travel distances of electrons from the photocathode  14  to the dynode Dy 1  differ, the output signals have timing difference. For example, an electron emitted from a position closer to the center of the photocathode  14  enters the dynode Dy 1  as indicated by a trajectory  65 . Although the trajectory  61  and the trajectory  65  enter approximately the same part of the dynode Dy 1 , their travel distances of electrons from the photocathode  14  to the dynode Dy 1  are different, thereby generating time base difference in output signals. Additionally, an electron emitted from a region of the photocathode  14  that confronts the corner section  87  enters the center side of the dynode Dy in the x-axis direction in a slanted direction in the trajectory  63 . Accordingly, if the corner sections  83 ,  85 , and  87  are not provided to each electrode, that is, if the corner sections of each electrode are not effective areas, electrons emitted from the region of the photocathode  14  that confronts the corner section  87  need to be converged widely in order to make the electrons enter the dynode Dy 1 . Thus, the difference in travel distance between this trajectory and the trajectory  61  with respect to the trajectory  65  becomes even larger. However, in the present embodiment, the cutout portions  24  and  49  are provided for the dynodes Dy 1 -Dy 12 , the drawing electrode  19 , and the anode  25 , and the corner sections  83 ,  85 , and  87  are configured to become effective areas for multiplying and detecting electrons. Hence, electrons are converged so that the difference in travel distance of electrons emitted from the regions of the photocathode  14  in opposition to the corner sections  83 ,  85 , and  87  becomes shorter. Accordingly, timing difference of electrons that enter the dynode Dy 1  in each trajectory  61 ,  63 , and  65  can be suppressed to minimum. 
     Next, the configuration of partition walls provided to the dynodes Dy 1 -Dy 12  will be described.  FIG. 15  is a view showing partition walls provided to a normal dynode,  FIG. 16  is a view showing partition walls provided to a predetermined dynode,  FIG. 17  is an overall view of a dynode provided with a large number of partition walls, and  FIG. 18  is a cross-sectional view of  FIG. 17 . Note that the electron multiplying pieces  18  are omitted in  FIGS. 15 and 16 . 
     As described above, the dynodes Dy 1 -Dy 12  in the present embodiment have slits formed in the x-axis direction. As shown in  FIG. 15 , the dynodes Dy 1 -Dy 12  are provided with partition walls  71  in the y-axis direction, the partition walls  71  corresponding to the border sections in the y-axis direction of a plurality of channels of the anode  25 . In the photomultiplier tube  10 , in order to broaden the effective area of the faceplate  13 , photoelectrons emitted from the peripheral sections of the photocathode  14  are converged toward the center of the xy plane in response to light incident on the proximity of the peripheral sections of the faceplate  13 . Some of the electrons from the peripheral sections have been lost when converged. Consequently, uniformity of an electron multiplying ratio at t h e peripheral sections tends to decrease. Thus, as shown in  FIGS. 16 and 17 , partition walls  73  extending in the y-axis direction are provided in the dynode Dy except in the peripheral sections in the y-axis direction, thereby adjusting the electron multiplying ratio. With this configuration, in the A-A cross-section of  FIG. 17 , the electron multiplying pieces  18  exist in the entire electrode-layered unit. as shown in  FIG. 7 . In contrast, in the B-B cross-section, as shown in  FIG. 18 , the dynode Dy 5  has the partition wall  73  except in the peripheral sections in the y-axis direction. The electron multiplying openings  18   a  are not formed in the partition walls  73 , and thus electrons entering the partition walls  73  do not contribute to multiplication. Hence, electron multiplication is suppressed at the central portion in the xy plane, thereby enabling a uniform electron multiplying ratio to be produced 
     Next, the configuration of the air discharging tube  40  will be described.  FIG. 19  is a cross-sectional view showing the configuration around the air discharging tube  40 . The air discharging tube  40  is hermetically joined to the central portion of the stem  29 . The air discharging tube  40  has a double-tube structure of an inner side tube  43  and an outer side tube  41 . The outer side tube  41  is formed of Kovar metal, for example, having good adhesion with glass and the same thermal expansion coefficient, for tightly connecting to the stem  29 . The outer side tube  41  has, for example, a thickness of 0.5 mm, an outer diameter of 5 mm, and a length of 5 mm. Note that a thickness of the stem  29  can be 4 mm, for example. In this case, the outer side tube  41  protrudes from the outer surface  29   b  of the stem  29  outward by 1 mm. Because the outer side tube  41  protrudes outward from the outer surface  29   b , it is prevented that the stem  29  goes beyond the outer side tube  41  and enters between the inner side tube  43  and the outer side tube  41 . Further, in order to facilitate sealing (pressure welding), the air discharging tube  40  is configured in such a manner that the inner side tube  43  protrudes from the lower end of the outer side tube  41  even after sealing is completed. 
     The inner side tube  43  is formed of Kovar metal or copper, for example. The inner side tube  43  has, for example, an outer diameter of 3.8 mm and a length prior to cutting of 30 mm. The inner side tube  43  is coaxially arranged with the outer side tube  41 . One end section of the inner side tube  43  at the inner surface  29   a  side of the stem  29  is hermetically joined to the outer side tube  41 . Further, because the other end section of the inner side tube  43  is hermetically sealed at the end of manufacture of the photomultiplier tube  10 , it is preferable that the thickness of the inner side tube  43  be as thin as possible and be 0.15 mm, for example. A connecting section  41   a  that is connected to the stem  29  is arranged so that the connecting section  41   a  protrudes upward in the z-axis direction by 0.1 mm, for example, in order to prevent material of the stem  29  from entering inside of the air discharging tube  40 . 
     Next, the method of manufacturing the photomultiplier tube  10  will be described.  FIGS. 20 through 22  are diagrams showing the method of manufacturing the air discharging tube  40  and the stem  29 . As shown in  FIG. 20 , first, the outer side tube  41  and the inner side tube  43  are prepared. Subsequently, the inner side tube  43  is arranged coaxially inside the outer side tube  41 . At this time, the positions of one end of the inner side tube  43  and one end of the outer side tube  41  are aligned with each other, and the connecting section  41   a  is joined by laser-welding. After joined, an oxide film is formed on the outer surface of the outer side tube  41  for facilitating fusion bonding with the stem  29  Further, the tubular member  31  and the extending section  32  are prepared, on which oxide films are formed for facilitating fusion bonding with the stem  29 . As shown in  FIG. 21 , a predetermined number of through-holes  38  for mounting the supporting pins  21 , a predetermined number of through-holes  30  for mounting the stem pins  27  and the like, and one though-hole  34  for mounting the air discharging tube  40  are formed in the stem  29 . 
     As shown in  FIG. 22 , the air discharging tube  40 , the tubular member  31 , the extending section  32 , the stem  29 , the supporting pins  21 , the stem pins  27 , the lead pins  47 , and the like are arranged at the positions indicated by the drawing, respectively, and are placed on a carbon jig (not shown). The stem  29  is then sintered while the inner surface  29   a  side and the outer surface  29   b  side of the stem  29  are pinched and pressed by the jig, thereby allowing glass and each metal to be hermetically fusion bonded. At this time, the material of the stem  29  is pushed out to the connection section where the supporting pins  21  and the lead pins  47  inserted in the through-hole sections  22  and  48  of the extending section  32  are connected to the stem  29 , thereby forming the protuberant section  33 . After fusion bonding, the jig is removed, and removal of the oxide films and cleaning are performed. In this way, the stem section is completed. 
     Subsequently, the integrally-formed anode  25  is placed on the stem pins  27  and fixed. After fixing, the bridges are cut off so that the anode  25  can become independent as the anodes  25 ( 1 - 1 ),  25 ( 1 - 2 ), . . . ,  25 ( 8 - 8 ). The drawing electrode  19  is placed on the supporting pins  21  such that the drawing electrode  19  can be substantially parallel to and spaced away from the anodes  25 . Further, the electrode-layered unit is placed on the drawing electrode  19 . In the electrode-layered unit, dynodes Dy 12 -Dy 1  and the focusing electrode  17  are sequentially arranged in confrontation with each other, while spaced away from each other via the insulating members  23 . At this time, the lead pins  47  corresponding to respective ones of the dynodes Dy 1 -Dy 12  are connected to the protruding portions  53 , the focusing electrode  17  is connected to the focus pin  51 , and pressure is applied downward in the z-axis direction for fixation. Thereafter, the end section of the side tube  15  which has been fixed to the faceplate  13  at the other end thereof is welded to the tubular member  31 , assembling the photomultiplier tube. 
     Next, after air inside of the photomultiplier tube  10  is discharged through the air discharging tube  40  by a vacuum pump or the like, alkali vapor is introduced thereinto to activate the photocathode  14  and the secondary electron surface. After air inside of the photomultiplier tube  10  is discharged again and evacuated, the inner side tube  43  constituting the air discharging tube  40  is cut to a predetermined length and the distal end thereof is sealed. At this time, it is preferable that the inner side tube  43  be cut short to such a degree that the bond between the stem  29  and the connecting section  41   a  can not be harmed, so that the inner side tube  43  may not become impediment when the radiation detecting device  1  is placed on a circuit board. Throughout the above-described processes, the photomultiplier tube  10  is obtained. 
     In the radiation detecting device  1  according to the present embodiment having the above-described configuration, when radiation is incident on the incident surface  5  of the scintillator  3 , light is outputted from the output surface  7  side in response to the radiation. When light outputted by the scintillator  3  is incident on the faceplate  13  of the photomultiplier tube  10 , the photocathode  14  emits electrons in response to the incident light. The focusing electrode  17  provided in confrontation with the photocathode  14  converges the electrons emitted from the photocathode  14  to enter the dynode Dy 1 . The dynode Dy 1  multiplies the incident electrons and emits secondary electrons to the dynode Dy 2  located at the below stage. In this way, the electrons multiplied sequentially by the dynodes Dy 1 -Dy 12  reach the anode  25  via the drawing electrode  19 . The anode  25  detects the reached electrons and outputs signals to outside through the stem pins  27 . 
     As shown in  FIG. 5 , the photomultiplier tube  10  includes the supporting pins  21  for placing the electrode-layered unit thereon. Because of the configuration that the electrode-layered unit is placed on the placing surfaces of the placing sections  21   b  constituting the supporting pins  21 , large pressure can be applied from the upper side of the electrode-layered unit in the z-axis direction for fixation. Hence, the fixing strength of the electrode-layered unit increases and the anti-vibration performance improves. In addition, the positioning accuracy of the electrode-layered unit (each electrode constituting the electrode-layered unit) in the z-axis direction increases. Further, the drawing electrode  19 , which is the lowest stage electrode of the electrode-layered unit, is placed on and supported by the placing sections  21   b  of the supporting pins  21 , and there is no insulator between the drawing electrode  19  and the anode  25 . Hence, it. can be prevented that electrons collide on an insulator and emit light. Accordingly, generation of noise in the signals outputted from the anode  25  can also be prevented. Additionally, because the supporting pins  21  are formed of an electrically-conductive material, the supporting pins  21  do not emit light even if electrons collide on the supporting pins  21 , thereby further preventing noise from being generated. 
     The focusing electrode  17 , the dynodes Dy 1 -Dy 12 , and the drawing electrode  19  are stacked in confrontation with and separated away from each other via the insulating members  23  that are coaxially arranged with the supporting pins  21 . Thus, because higher pressure can be applied in the z-axis direction to fix the focusing electrode  17 , the dynodes Dy 1 -Dy 12 , and the drawing electrode  19 , the anti-vibration performance further improves. Further, accurate positioning of each electrode in the xy plane can be realized, by stacking the focusing electrode  17 , the dynodes Dy 1 -Dy 12 , and the drawing electrode  19  via the insulating members  23 . 
     Because the focusing electrode  17  is provided at the photocathode  14  side of the dynodes Dy 1 -Dy 12 , electrons emitted from the photocathode  14  can be incident on the dynode Dy 1  efficiently. 
     As shown in  FIGS. 8 and 10 , the dynodes Dy 1 -Dy 12 , the drawing electrode  19 , and the anode  25  are provided with the cutout portions  49  and  24 , and the supporting pins  21  and the lead pins  47  are arranged in the cutout portions  49  and  24 . Thus, the effective area of each electrode can be sufficiently preserved, and fluctuations in signals due to the difference in traveling time of electrons or the like can be minimized. Additionally, the lead pins  47  extend in the z-axis direction, and the cutout portions  49  and  24  formed in the dynodes Dy 1 -Dy 12 , the drawing electrode  19 , and the anode  25  overlap in the z-axis direction. Therefore, the effective areas can further be preserved. 
     Further, as shown in  FIG. 12 , because the focusing electrode  17  is provided to the peripheral sections in the xy plane for covering the cutout portions  49  of the dynodes Dy 1 -Dy 12 , it is possible to converge electrons to the effective area of the dynode Dy 1 , the electrons being emitted from the regions of the photocathode  14  corresponding to the cutout portions  49  and  24  formed in the dynodes Dy 1 -Dy 12 , the drawing electrode  19 , and the anode  25 . Thus, it is ensured that the photomultiplier tube  10  can have a large effective area for detecting light. At the same time, it is prevented that collision of electrons on the lead pins  47  may decrease the multiplying ratio. 
     Further, as shown in  FIG. 14 , the openings  17   b  of the focusing electrode  17  extend in the x-axis direction, that is, the direction perpendicular to the peripheral sections where the cutout portions  49  and  24  of the drawing electrode  19  and the anode  25  are formed. Although it is preferable that as many electrons as possible enter the openings  17   b,  the electrons that impinge against the focus pieces  17   a  do not enter the openings  17   b . Accordingly, it is preferable that the trajectories of electrons be controlled to avoid the focus pieces  17   a . Especially, it is preferable that the trajectories of electrons that enter from a part of the photocathode  14  in confrontation with the flat-plate electrode section  16  be controlled to avoid the flat-plate electrode section  16  as well. At that time, the electrons that enter from the part in confrontation with the flat-plate electrode section  16  travel in the x-axis direction as indicated by the trajectory  61 . However, the control in the x-axis direction, that is, the direction in which the electrons originally travel is more difficult than the control in the y-axis direction. Accordingly, in the present embodiment, the openings  17   b  extend in the x-axis direction, that is, the direction perpendicular to the peripheral sections where the cutout portions  49  and  24  of the drawing electrode  19  and the anode  25  are formed. Hence, electrons can be made to enter the openings  17   b  efficiently, by performing the control in the y-axis direction which is relatively easy. 
     Further, as shown in  FIG. 5 , since the drawing electrode  19  is provided between the last stage dynode Dy 12  and the anode  25 , the electric field intensity at the lower side of the dynode Dy 12  in the z-axis direction can be made uniform. Hence, the electron emitting characteristics of the dynode Dy 12  is made uniform. Accordingly, for example, even if each unit anode is slanted after the bridges are cut off and the distances between each of the anodes  25  and the drawing electrode  19  vary, electrons can be drawn from the dynode Dy 12  uniformly for each channel region. 
     In addition, as shown in  FIGS. 16 and 18 , the partition walls  73  are provided to the dynode Dy located at a predetermined stage to adjust an opening ratio, thereby reducing variations of the electron multiplying ratio in the xy plane. 
     The anode  25  is integrally formed, and the unit anode  25  is made independent by cutting off the bridges after each anode is fixed to the corresponding stem pin  27 . Hence, the step of placing the anode  25  on the stem pins  27  can be simplified, and the positioning accuracy of setting each anode  25  increases. Further, as shown in  FIGS. 8 and 9 , because the bridges are provided within the concave portions  28 , the effective areas of the anode  25  can be sufficiently preserved. Further, because the bridge remaining sections  26  are disposed within the concave portions  28 , electric discharge between the bridge remaining sections  26  can be prevented. In addition, because the multiple anodes arranged two-dimensionally in this way are used, the incident positions of light in the xy plane can be detected. 
     As shown in  FIG. 3 , the stem  29  is formed of glass. The tubular member  31  is provided at the peripheral section  29   c  of the stem  29 , and the extending section  32  is provided on the inner surface  29   a  of the stem  29 . The supporting pins  21  and the lead pins  47  penetrate in the extending section  32 , and the focus pin  51  is erected in the extending section  32 . Hence, each pin can be provided near the side tube  15 , and thus the effective area of each electrode can be sufficiently preserve. 
     Additionally, as shown in  FIG. 6 , since the protuberant section  33  is formed at the connection section where the stem  29  is connected to the supporting pins  21  and the lead pins  47 , the creepage distance between the tubular member  31  and each pin can be made long. This configuration can prevent occurrence of creeping discharge as well as occurrence of noises due to emission of light generated when multiplied electrons collide on an insulating object. Additionally, because the through-hole sections  22  and  48  are provided at the extending section  32 , the through-hole sections  22  and  48  function as an adjustive part for glass material during manufacture of the stem  29 , thereby facilitating adjustment of the thickness of the stem  29 . Further, because the thickness of the stem  29  can be controlled in this way, the positioning accuracy of the outer surface  29   b  of the stem  29  relative to the faceplate  13  increases. Consequently, the dimensional accuracy of the overall length of the photomultiplier tube  10  improves. Hence, for example, when the photomultiplier tube  10  is surface-mounted on a circuit board or the like for use, the distance between a light source and the faceplate  13  of the photomultiplier tube  10  becomes constant, enabling detection of light with less error. 
     Further, as shown in  FIG. 19 , the air discharging tube  40  provided to the stem  29  has a double-tube structure, where the outer side tube  41  is thickly formed of a material having good adhesiveness with the stem  29 , and the inner side tube  43  is thinly formed of a soft material With such a double-tube structure, generation of a pinhole and the like during laser welding can be prevented owing to the thickness of the outer side tube  41 . Further, the inner side tube  43  can be connected to the outer side tube  41  only at the end section at the inner surface  29   a  side of the stem  29 . The inner side tube  43  can be cut short and sealed to a degree that the connection section is not. damaged and the length does not become an impediment when placed on a circuit board, while the outer side tube  41  ensures close contact with the stem  29 . Also, the inner side tube  43  may be made of a material having good sealing characteristics for easy sealing. Further, the tube diameter of the air discharging tube  40  may be made large. When alkali metal vapor is introduced, the processing time can be shortened and the uniformity of the introduced vapor improves. 
     Further, as shown in  FIG. 1 , because the scintillator  3  is provided at the faceplate  13  side of the photomultiplier tube  10 , it is possible to detect radiation and to output signals. 
     Next, a first modification will be described while referring to  FIG. 23 .  FIG. 23  is a perspective view showing an electron detecting section according to the modification. Although the anode  25  constituting the electron detecting section is multiple anodes arranged two-dimensionally in the above-described embodiment, linear anodes  125  are arranged one-dimensionally in the first modification. The border sections of the linear anodes  125  are provided at positions corresponding to the partition walls  71  of the dynodes Dy 1 -Dy 12 . Each linear anode  125  is connected to and supported by a stem pin  127  that penetrates the stem  29 , and applied with a predetermined electric potential and outputs signals in response to detected electrons. It is preferable that the linear anode  125  be also provided with concave portions (not shown) having bridges at parts that confront the adjacent unit anodes, and that the bridges be cut off after the entire linear anode  125  is fixed on the stem pins  127 . 
     Next, a second modification will be described while referring to  FIG. 24 .  FIG. 24  is a schematic cross-sectional view showing a radiation detecting device  100  according to the modification of the scintillator. Instead of the scintillator  3  according to the above-described embodiment, a plurality of scintillators  103  having a size corresponding to the channel region of the photomultiplier tube  10  is arranged one-dimensionally in the radiation detecting device  100 . The other configurations are identical to the first modification. According to this configuration, the incident positions of radiation in the xy plane can be detected. 
     Next, a third modification will be described while referring to  FIG. 25 .  FIG. 25  is a schematic cross-sectional view showing a radiation detecting device  200  according to another modification of the scintillator. Instead of the scintillator  103  according to the second modification, a plurality of scintillators  203  having a size smaller than the anode  125 , for example, corresponding to one half of the anode  125  is arranged one-dimensionally in the radiation detecting device  200 . The other configurations are identical to the second modification. According to this configuration, the incident positions of radiation in the xy plane can be detected more accurately. 
     Next, a fourth modification will be described while referring to  FIG. 26   FIG. 26  is an explanatory diagram of the shapes of the placing section  21   b  and the drawing electrode  19  according to the modification. A convex portion  21   c  is formed on the surface of the placing section  21   b  for placing the drawing electrode  19  thereon. A concave portion  19   c  is formed on the surface of the drawing electrode  19  that is placed on the placing section  21   b . When the drawing electrode  19  is placed on the supporting pin  21 , the convex portion  21   c  and the concave portion  19   c  are engaged with each other. According to this configuration, the positioning accuracy of the electrode-layered unit including the focusing electrode  17  and the plurality of dynodes Dy 1 -Dy 12  in the xy plane can improve. Note that, if the drawing electrode  19  is not provided, a concave portion may be formed in the last stage dynode Dy 12 . Alternatively, a concave portion may be formed in the placing section  21   b , and a convex portion may be formed in the drawing electrode  19 . 
     It would be apparent that the photomultiplier tube and the radiation detecting device according to the present invention are not limited to the above-described embodiments, and that various changes and modifications may be made therein without departing from the spirit of the present invention. 
     For example, although the extending section  32  of the tubular member  31  extends at the inner surface  29   a  side of the stem  29 , the extending section  32  may be provided at the outer surface  29   b  side. In that case, the electric potential of the photocathode  14  is exposed to the periphery of the extending section  32  and to the lead pins  47  penetrating the extending section  32 . A circuit board is often arranged closely at the outside of the stem  29 . Hence, if the electric potential of the photocathode  14 , which has the largest potential difference relative to the anode  25 , is exposed, there is a possibility that a problem in terms of withstand voltage may arise. Accordingly, the extending section  32  is preferably located internally. 
     In the manufacturing method, the air discharging tube  40  is connected to the stem  29  after the outer side tube  41  and the inner side tube  43  are connected. There is also a method in which only the outer side tube  41  is first oxidized and is connected to the stem  29 , and an oxide film is subsequently removed. The inner side tube  43  is then connected to the outer side tube  41 . 
     Although the cross-sections of the photomultiplier tube and each electrode have substantially rectangular shapes, the cross-sections may have circular or other shapes. In this case, it is preferable that the shape of the scintillator be modified depending on the shape of the photomultiplier tube. 
     The partition walls  73  are provided to the fifth stage dynode Dy 5  in the. above-described example. However, the partition walls  73  may be provided to another stage, or may be provided to a plurality of stages of dynodes. 
     The openings l 9   b  of the drawing electrode  19  are not limited to a linear shape, but may be a meshed shape. 
     As shown in  FIG. 27 , instead of the through-hole sections  22  and  48 , a plurality of openings  122  and  148  may be formed with a comb-like shape at the both peripheral sections of the extending section  32  in the x-axis direction. With the plurality of openings  122  and  148  formed with the comb-like shape, the degree of improvement in strength of the stem  29  by the extending section  32  becomes slightly low compared to the through-hole sections  22  and  48 . In addition, because the adjustive part for the material of the stem  29  from the open portions becomes larger, forming the protuberant section  33  is slightly harder. However, in this case as well, the effective area of the electron multiplying section and the electron beam detecting section can be preserved efficiently. 
     INDUSTRIAL APPLICABILITY 
     The radiation detecting device of the present invention is applicable to an image diagnostic apparatus in medical devices and the like.