Radiation detecting device insensitive to high magnetic fields

Abstract: There is disclosed a phototube (11) comprising a closed container having a light permeable face plate (12a) the outside surface of which is a light incident surface, a photocathode (13) so provided in the closed container that at least a part of a photo-electric surface is inclined to the light incident surface, and an anode (14) so provided in the closed container that an electron capturing surface is opposed to the photo-electric surface in parallelism therewith.

Description: Field of the Invention This invention relates to a phototube. More specifically the invention relates to a phototube which is operative even in a strong magnetic field, such as those which are encountered in the field of high energy physics. Related Background Art Conventionally the phototube of this kind has the structure of FIG. 1. A photocathode 2 is formed on the inside surface opposed to the light incident surface la of a glass container 1. A beam of light from the light incident surface la is converted into photoelectrons by the photocathode 2. The converted photoelectrons are attracted to an anode 3 opposed to the photocathode 2 by an electric field E to be captured by the anode 3. Some of the phototubes having the photoelectron multiplying function, i.e., including photoelectron multipliers, have the structure of FIG. 2. A photocathode 52 is formed on the inside surface opposed to the light incident surface 51a of a glass container 51. A beam of light from the light incident surface 5la is converted into photoelectrons by the photocathode 52. The converted photoelectrons are attracted to an electrode opposed to the photocathode 52 by an electric field E. A dynode 53 is made up with a plurality of electrodes 53a, b, ... and emits in secondary electrons the photoelectrons it received. The emitted secondary electrons are finally captured by an anode 54. But in the above-described conventional phototube 4, if a strong magnetic field B is present in the direction normal to the electric field E and in the vertical direction in the drawing, in other words, the direction parallel with the light incident surface la, although it depends on a voltage applied between the photocathode 2 and the anode 3, there will occur the phenomenon that the photoelectrons emitted by the photocathode 2 cannot be captured by the anode 3. That is, because of the strong magnetic field B, the photoelectrons emitted by the photocathode 2 have a cycloidal motion, a circular motion returning to the photocathode 2 as indicated by the arrow. Consequently the photodetecting efficiency is sometimes lowered because of the strong magnetic field B normal to the electric field E. This phenomenon is true also with the above-described conventional photoelectron multiplying tube 55. That is, if a strong magnetic field B is present in the direction parallel with the light incident surface 51a of the glass container 51, although it depends on a voltage applied between the photocathode 52 and the electrodes 53a, b, ... of the dynode 53, the photoelectrons emitted by the photocathode 52 cannot be captured by the dynode 53. In other words, similarly with the above-described phototube, the photoelectrons emitted by the photocathode 52 have a cycloidal motion, a circular motion returning to the photocathode 52 as indicated by the arrow. This phenomenon takes place also at the part of the dynode 53 which multiplies the electrons. Consequently the photodetecting efficiency of the photoelectron multiplying tube 55 is sometimes lowered because of the strong magnetic field B normal to the electric field E. FIG. 3 is a diagrammatic view of the cycloidal motion of photoelectrons in the above-described phototubes. The track of the photoelectrons is depicted by the dot line. For example, when a strength of the magnetic field B is 0.6 [T], an initial velocity of the emitted photoelectrons is 0 [eV], an applied voltage between the photocathode 2 and the anode 3 or between the photocathode 52 and the dynode 53a is 1000 [V], the photoelectrons are spaced by 0.177 [mm] at maximum (=y max ) from the photocathode 2 or 52 because of the cycloidal motion. Accordingly under these set conditions, if the photocathode 2 and the anode 3 or between the photocathode 52 and the dynode 53a are spaced from each other by more than 0.177 [mm], the photoelectrons emitted by the photocathode 2 or 52 cannot arrive at the anode 3 or the dynode 53a. In the photoelectron multiplying tube 55, such influence of the strong magnetic field B range not only between the photocathode 52 and the dynode 53a, but also to the electron multiplication of the dynode 53a. To solve this problem, the phototube 4 or the photoelectron multiplying tube 55 itself is so moved or turned in accordance with a direction of the magnetic field B known beforehand that the magnetic field B is normal to the light incident surface la or 51a. This is because when the electric field E and the magnetic field B are parallel with each other, the photoelectrons do not have a cycloidal motion, and resultantly the photodetecting efficiency of the phototube 4 and the photoelectron multiplying tube 55 is not lowered. But in the high energy particles (radiation) detecting devices using such phototube 4 or photoelectron multiplying tube 55, as described above it is generally difficult to optimumly change positions and directions of the phototube 4 or the photoelectron multiplying tube 55. That is, such radiation detecting device usually has a section of FIG. 4. A plurality of scintillators 5 of BaF 2 for detecting radiation are arranged so as to enclose the detecting portion for a light beam to pass through, and the photocathode 4 or the photoelectron multiplying tube for photoelectrically converting detected radiation is fixed to the back of each of the scintillators. Accordingly the position of the photocathode 4 or the photoelectron multiplying tube 55 itself is restricted by its connection to the output terminal of each of the scintillators 5 and cannot be optionally changed. Consequently to position the photocathode 4 or the photoelectron multiplying tube 55 so that the magnetic field B is normal to the light incident surface 1a or 51a of the glass container 1 or 51, it is not necessary to machine the scintillators 5 in a rod shape but to machine them 5 so that the output terminals form a required angle. Generally, however, it is difficult to machine scintillators. Consequently it is actually impossible to agree a direction of the electric field E generated between the photocathode 2 and the anode 3 or between the photocathode 52 and the dynode 53a with a direction of the magnetic field B. US-A-4623785 was cited by the European Patent Office during examination because it describes a radiation detector comprising a sealed container having a substantially planar light receiving surface, a photocathode and an anode. The photocathode is formed parallel to the light receiving surface. The anode is substantially conical in form and is placed within the container between the photocathode and a similarly conically formed dynode. Summary of the Invention The invention aims to solve the above-described problems. According to the invention there is provided a phototube comprising a sealed container having a substantially planar light-receiving surface, a photocathode and an anode, characterised in that said photocathode and anode are parallel to each other and are so oriented that the electric field (E) therebetween is inclined to the normal to said light-receiving surface. The invention extends to a radiation detecting device including such a phototube. A phototube according to an embodiment of the invention has a photoelectron multiplying function, and comprises a photocathode inclined to a light incident surface of a light permeable closed container, an electrode for emitting secondary electrons, and an anode opposed to the electrode. A phototube according to an embodiment of the invention has a photoelectron multiplying function, and comprises a solid-state semiconductor device, in place of the electrode for emitting secondary electrons, for internally multiplying photoelectrons emitted by a photocathode, and a photocathode inclined to a light incident surface of a closed container, the solid-state semiconductor device being opposed to the photocathode. A radiation detecting device according to an embodiment of the invention comprises a scintillator for emitting light upon detecting radiation, and any one of the above-described photocathodes for receiving the light emitted by the scintillator and emitting photoelectrons. In a phototube according to an embodiment of the invention, even if a magnetic field is applied in parallelism with the light incident surface of the light permeable closed container, the photoelectrons emitted by the photocathode move along a direction of the magnetic field to reach the anode because of a component of the electric field E along the direction of the magnetic field when the direction of the magnetic field forms an angle to the photo-electric surface with the photocathode formed on because the photocathode and the anode are inclined to the light incident surface. In the phototube having a function of secondarily multiplying photoelectrons, even if a magnetic field is applied in parallelism with the light incident surface of the light permeable closed container, the photoelectrons emitted by the photocathode move along a direction of the magnetic field because of a component of the electric field along the direction of the magnetic field to reach the electrons for emitting the secondary electrons when the direction of the magnetic field forms an angle to the photo-electric surface with the photocathode formed on, because the photocathode and the electrode for emitting the secondary electrons are inclined to the light incident surface. The secondary electrons as well move along the direction of the magnetic field to be captured by the anode opposed to the electrode. In the phototube for multiplying photoelectrons internally in the solid-state semiconductor device, even if a magnetic field is applied in parallelism with the light incident surface of the light permeable closed container, the photoelectrons emitted by the photocathode move along a direction of the magnetic field to reach the solid-state semiconductor device because of a component of the electric field along the direction of the magnetic field when the direction of the magnetic field forms an angle to the photo-electric surface with the photocathode formed on, because the photocathode and the solid-state semiconductor device are inclined to the light incident surface. Within the solid-state semiconductor device the incident photoelectrons are multiplied without any influence of the external magnetic field. When the magnetic field has no angle to the photoelectric surface, the photocathode itself is merely turned so that the direction of the magnetic field forms an angle to the photo-electric surface. Consequently, similarly with the above, the photoelectrons emitted by the photocathode move along the direction of the magnetic field because of a component of the electric field along the magnetic field to reach the anode, the electrode for emitting the secondary electrons or the solid-state semiconductor device. The present invention will become more fully understood from the detailed description of embodiments of the invention given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art form this detailed description. Brief Description of the Drawings FIG. 1 is a sectional view of the conventional phototube showing its structure; FIG. 2 is a sectional view of the conventional photoelectron multiplying tube showing its structure; FIG. 3 is a view of a cycloidal motion of the electrons in the conventional phototube and photoelectron multiplying tube; FIG. 4 is a view of the general structure of radiation detecting devices; FIGs. 5A and 5B are sectional views of the phototube according to a first embodiment of this invention showing its structure; FIGs. 6A and 6B are views of a track photoelectrons have when a magnetic field B is applied at an angle to the photo-electric surface of the phototube of FIG. 5; FIGs. 7A and 7B are views of a track photoelectrons have when a magnetic field B is applied without an angle to the photo-electric surface of the phototube of FIG. 5; FIGs. 8A and 8B are sectional views of the photoelectron multiplying tube according to a second embodiment of this invention showing its structure; FIGs. 9A and 9B are views of a track photoelectrons have when a magnetic field B is applied at an angle to the photo-electric surface of the photoelectron multiplying tube of FIG. 8; FIGs. 10A and 10B are a views of a track photoelectrons have when a magnetic field B is applied without an angle to the photo-electric surface of the photoelectron multiplying tube; FIG. 11 is a sectional view of the phototube according to a third embodiment of this invention showing its structure; FIG. 12 is a sectional view of the phototube according to a fourth embodiment of this invention showing its structure; FIG. 13 is a sectional view of the phototube according to a fifth embodiment of this invention; FIG. 14 is a sectional view of the photoelectron multiplying tube according to a sixth embodiment of this invention showing its structure; FIG. 15 is a sectional view of the photoelectron multiplying tube according to seventh embodiment of this invention; FIG. 16 is a sectional view of the photoelectron multiplying tube according to an eighth embodiment of this invention; FIG. 17 is a sectional view of a secondary electron multiplying portion of the photoelectron multiplying tube according to the sixth embodiment of FIG. 14 showing its structure in detail; FIG. 18 is a sectional view of the secondary electron multiplying portion of FIG. 17 with an external magnetic field B applied to; FIG. 19 is a graph of the photodetecting efficiency of the photoelectron multiplying tube according to the six embodiment of FIG. 14; and FIG. 20 is a sectional view of the photoelectron multiplying tube according to the ninth embodiment showing its structure. Detailed Description of the Embodiments FIG. 5A is a sectional view of the phototube according to a first embodiment of this invention, and FIG. 5B is a perspective view of this phototube. A phototube 11 is housed in a cylindrical glass bulb 12. The top surface and the bottom surface of the glass bulb are air-tightly closed and has the interior maintained vacuum. The glass bulb 12 is made of a transparent material, and the top surface, i.e., the outside of the top plate, i.e., the face plate of the bulb 12, is the light incident surface 12a. Thus a light permeable closed container is provided. The top plate, i,e., the face plate of this closed container must be light permeable, but the bottom plate and the side surfaces may be light shielding. In this glass bulb 12 there are provided a photocathode 13 for emitting photoelectrons upon receiving a beam of light, and an anode 14 for capturing the photoelectrons emitted by the photocathode 13. The photocathode 13 which constitutes the photo-electric surface is provided on the inside surface (the inside of the face plate) of the glass bulb 12, which (the inside surface) is inclined at an angle to the light incident surface 12a thereof. The photo-electric surface with the photocathode 13 formed on is indicated by the dot line in the perspective view of FIG. 5B. The end a of this photo-electric surface is most distant from the light incident surface 12a, and the end b thereof is nearest to the light incident surface 12a. An anode 14 is provided in parallelism with the photocathode 13 and has a lead 14a electrically connected to the outside. The anode 14 is near enough to the photocathode 13 to necessitate no electrostatic focusing. In this structure, a beam of light from the light incident surface 12a impinges on the photocathode 13 and is converted there to photoelectrons. The emitted photoelectrons are attracted to the anode 14 because of the electric field E formed between the photocathode 13 and the anode 14 to finally impinge on the electron capturing surface of the anode 14 and captured by the anode 14. In the device of FIG. 5A, a scintillator 5 is provided opposed to and near (or on) the light incident surface 12a rotatably on the central axis A. In the phototube 11 according to this embodiment, even when an external magnetic field B is applied in parallelism with the light incident surface 12a, most of the photoelectrons emitted by the photocathode 13 are captured by the anode 14 because the photocathode 13 and the anode 14 are inclined to the light incident surface 12a. That is, as shown in FIGS. 6A and 6B, in the case that a direction of the magnetic field B has an angle to the photo-electric surface with the photocathode 13 formed on, the photoelectrons emitted by the photocathode 13 move along the direction of the magnetic field B, performing a cycloidal motion because of a component of the electric field E along the direction of the magnetic field, and finally arrive at the anode 14. The magnetic field B in FIG. 6A is directed from the left to the right as viewed in FIG. 6A, and that in FIG. 6B is directed from the right to the left as viewed in FIG. 6B. Irrespective of the direction of the magnetic field B, as long as the magnetic field B and the photo-electric surface form an angle to each other, the photoelectrons emitted by the photocathode 13 are guided to the anode 14. FIGS. 6A and 6B have common reference numerals with FIG. 1 for common members not to repeat their explanation. FIGs. 7A and 7B shows the case of the phototube according to the first embodiment that a direction of the external magnetic field B forms no angle to the photo-electric surface. FIGS. 7A and 7B have common reference numerals with FIG. 1 for common members not to repeat their explanation. In FIG. 7A, the direction of the magnetic field B is vertical as viewed in FIG. 7A and is perpendicular to the electric field E generated between the photocathode 13 and the anode 14. In this case, although the photo-electric surface provided by the photocathode 13 is inclined to a light incident surface 12a of the face plate, the photoelectrons emitted by the photocathode 13 take a track indicated by the arrow which returns to the photo-electric surface. In this case, the phototube 11 itself is turned on an axis normal to the light incident surface 12a, so that the photo-electric surface forms an angle to the magnetic field B. Consequently, similarly with the case of FIG. 6, the photoelectrons emitted by the photocathode 13 move along the direction of the magnetic field B because of a component of the electric field E along the direction of the magnetic field B to arrive at the anode 14. FIG. 7B is the case that the direction of the magnetic field B is parallel with the photoelectric surface and forms no angle to the photoelectric surface. A photoelectron emitted by the photo-electric surface, when a three dimensional coordinate system with the position where the photoelectron was emitted set at the origin of the coordinate system, have a cycloidal motion in the z-axis direction indicated by the arrow, and adversely returns to the photocathode 13. In this case, the phototube 11 itself is turned on the central axis so that the photo-electric surface has an angle to the direction of the magnetic field B. And the photoelectron can be guided to the anode 14. Thus, according to the above-described first embodiment, even when the magnetic field B is applied in parallelism with the light incident surface, most of the photoelectrons emitted by the photocathode 13 are captured by the anode 14. Consequently the photodetecting efficiency of the phototube 11 is not lowered by the influence of the external magnetic field B, as has been conventionally. In a radiation detecting device comprising the phototube 11 according to this embodiment and an scintillator, the phototube 11 is merely turned for the prevention of decreases of the radiation detecting efficiency. In other words, radiation detecting devices having good detecting efficiency can be prepared without machining the scintillator in special forms. FIG. 8A is a sectional view of the photoelectron multiplying tube according to a second embodiment of this invention, and FIG. 8B is a perspective of the photoelectron multiplying device. A photoelectron multiplying tube 61 is housed in a cylindrical glass bulb 62. This glass bulb is air-tightly closed at the top surface and the bottom surface to maintain the interior vacuum. This glass bulb 62 is made of a transparent material, and the top surface is the light incident surface 62a. Thus a light permeable container is formed. On the inside surface of the glass bulb 62 there is formed a photocathode 63 for emitting photoelectrons when irradiated with a beam of light. A secondary electron multiplying portion 64, for emitting secondary electrons when the photoelectrons emitted by the photocathode 63 impinge thereon is opposed to and near the photocathode 63 in the glass bulb 62. The secondary electron multiplying portion may be, for example, a stacked electrode or a micro channel plate. Opposed to the secondary photoelectron multiplying portion 64 there is provided an anode 65 for capturing the emitted secondary electrons. The photocathode 63 is formed on an inside surface of the glass bulb 62 inclined at an angle to the light incident surface of the glass bulb 62. The photo-electric surface with the photocathode 63 formed on is indicated by the dot line in the perspective view of FIG. 8B. The end a of the photo-electric surface is most distant from the light incident surface 62a, and the end b thereof is nearest to the light incident surface of the incidence 62a. The secondary electron multiplying portion 64 and the anode 65 are parallel with the inclined photocathode 63, and a lead 65a is provided on the anode 65 and electrically connected to the outside of the glass bulb 62. The anode 65 and the photocathode 63 are sufficiently adjacent to each other to necessitate no electrostatic focusing. In this structure, the light from the light incident surface 62a is incident on the photocathode 63, and is converted there to photoelectrons. The emitted photoelectrons are attracted to the side of the secondary electron multiplying portion 6 because of the electric field E generated between the photocathode 63 and the secondary electron multiplying portion 64 to enter the inside electrode portion from the photoelectron incident surface and secondarily multiplied. Then the multiplied electrons are emitted from the secondary electron emitting part of the secondary electron multiplying portion 64 to enter the photoelectron capturing surface of the anode 65. Also in the photoelectron multiplying tube 61 according to this embodiment, even when an external magnetic field B is applied in parallelism with the light incident surface 62a, most photoelectrons emitted by the photocathode 63 are captured by the secondary electron multiplying portion 64 because the photocathode 63 and the secondary electron multiplying portion 64 are inclined to the light incident surface 62a. That is, as shown in FIGS. 9A and 9B, in the case that a direction of the magnetic field B has an angle to the photo-electric surface with the photocathode 63 formed on, the photoelectrons emitted by the photocathode 63 move along the direction of the magnetic field B in a cycloidal motion due to a component of the electric field E in the direction of the magnetic field finally to reach the secondary electron multiplying portion 64. In FIG. 9A, the magnetic field B is directed from the left to the right in the drawing, and in FIG. 9B the magnetic field B is directed from the right to the left in the drawing. Irrespective of a direction of the magnetic field B, as long as the magnetic field B and the photo-electric surface form an angle to each other, the photoelectrons emitted by the photocathode 63 are guided to the secondary electron multiplying portion 64. In the secondary electron multiplying portion 64 as well, the electrons secondarily emitted by the electrode move along the direction of the magnetic field B in a cycloidal motion finally to reach the anode 65. FIGs. 9A and 9B have reference numerals with FIGs. 7A and 7B for common members not to repeat their explanation. FIGs. 10A and 10B show the photoelectron multiplying tube 61 according the above-described second embodiment in which the external magnetic field B has no angle to the photo-electric surface, and have reference numerals common with FIG. 8 for common members not to repeat their explanation. In FIG. 10A, a direction of the magnetic field B is vertical in the drawing and is normal to the electric field E generated between the photocathode 63 and the secondary electron multiplying portion 64. In this case, because the direction of the magnetic field B has no angle to the photo-electric surface, the photoelectrons emitted b the photocathode 63 take the track back to the photo-electric surface indicated by the arrow. In this case, the photoelectron multiplying tube 61 itself is turned so that the photo-electric surface has an angle to the magnetic field B. Consequently, similarly with the case of FIGs. 9A and 9B, the photoelectrons emitted by the photocathode 63 move along the direction of the magnetic field B because of a component of the electric field E along the direction of the magnetic field to reach the secondary electron multiplying portion 64. Similarly, electrons secondarily emitted by the secondary electron multiplying portion 64 also move along the direction of the magnetic field B to reach the anode 65. FIG. 10B shows the case that a direction of the magnetic field B is parallel with the photo-electric surface and has no angle to the latter. In this case, a photoelectron emitted by the photo-electric surface, when a three-dimensional coordinate system is taken with the position where the photoelectron was emitted set at the coordinate origin, has a cycloidal motion directed in the z-axis direction indicated by the arrow and adversely returns to the photo-electric surface. In this case as well as the case described above, the photoelectron multiplying tube 61 itself is turned so that the photo-electric surface has an angle to the magnetic field B. Then the photoelectron is guided to the secondary electron multiplying portion 64, and the multiplied electrons are guided to the anode 65. Thus, according to the second embodiment, even when the magnetic field B is applied in parallelism with the light incident surface 62a, most of the photoelectrons emitted by the photocathode 63 are captured by the secondary electron multiplying portion 64, and the multiplied electrons are captured by the anode 65. Consequently the photodetecting efficiency of the photoelectron multiplying tube 61 is not lowered by the influence of an external magnetic field B, as has been conventionally. Also in the case that a radiation detecting device comprises the photoelectron multiplying tube 61 according to this embodiment and a scintillator, the photoelectron multiplying tube 61 is turned so that a direction of the magnetic field B has an angle to the photocathode 63, for the prevention of decreases of the radiation detecting efficiency. In each of the phototubes of FIGs. 11, 12 and 13, a photocathode 23, 32, 42 is inclined to the light incident surface 21a, 31a, 41a of the glass bulb. An anode 24, 33, 43 is opposed to the inclined photocathode. Consequently, even when a magnetic field B is applied in parallelism with the light incident surface 21a, 31a, 41a of the glass bulb, similarly with the above-described embodiments, the photoelectrons emitted by the photocathode 23, 32, 42 move along a direction of the magnetic field B because of a component of the electric field E in the direction of the magnetic field B and reach the anode 24, 33, 43. Accordingly these embodiments can achieve the same advantageous effect as the above-described embodiments and can be combined with scintillators to provide radiation detecting devices having improved radiation detecting efficiency. FIGs. 14, 15 and 16 are sectional views of photoelectron multiplying tubes according to a sixth, a seventh and an eighth embodiments of this invention. The photoelectron multiplying tube of FIG. 14 includes a light incident surface 71a on the inside surface of a glass bulb 71, and a separate inclined glass sheet 72. A photocathode 73 is formed on one side of the glass sheet 72 and is inclined to the light incident surface 71a. A secondary electron multiplying portion 74 is opposed to the photo-electric surface with the photocathode 73 formed on in parallelism therewith. An anode 75 is opposed to the secondary electron multiplying portion 74 in parallelism therewith. FIG. 17 is a sectional view of the secondary electron multiplying portion 74 detailing it structure. For the simplification of its explanation, the glass sheet 72 is omitted. FIG. 17 has reference numerals common with FIG. 14 for common members not to repeat their explanation. As shown in FIG. 17, the secondary electron multiplying portion 74 comprises three-stage dynodes 74a ∼ c which emit secondary electrons. Here it is assumed that a bore of the glass bulb 71 is L, and a thickness of the secondary electron multiplying portion 74 is h. FIG. 18 shows a state in which a strong magnetic field B is applied to the secondary electron multiplying portion 74 from the left to the right in the drawing. The photoelectrons emitted by the photocathode 73 on the glass sheet 72 not shown move because of the strong magnetic field B on the same principle as in FIG. 9 and impinge on the dynodes 74a. The dynodes 74a emit secondary electrons when the photoelectrons impinge thereon, and the secondary electrons secondarily emitted by the dynodes 74a are further secondarily multiplied by the dynodes 74b, 74c. The thus-multiplied electrons move along a direction of the strong magnetic field B in a cycloidal motion toward the side of the anode 75 to be finally captured by the anode 75. In such photoelectron multiplying tubes, it is preferable that the thickness h of the secondary electron multiplying portion 74 is sufficiently thin with respect to the bore L of the glass bulb 71. FIG. 19 is a graph of the relationship between ratios h/L (on the horizontal axis) of bores L to thicknesses h, and the photodetecting efficiency (on the vertical axis: %). As seen from the graph, the higher the photodetecting efficiency is, the smaller the ratio is. The photoelectron multiplying tube of FIG. 15 has the inside surface of a light incident surface 81a of a glass bulb 81 of triangular section with the light incident surface 81a as the bottom side. A photocathode 82 is formed on the sides other than the bottom side. A secondary electron multiplying portion 82 is opposed to the photo-electric surface with the photocathode 82 formed on in a V-shape contour to the triangular section. An anode 84 is opposed to the secondary electron multiplying portion 83. The photoelectron multiplying tube of FIG. 16 has the inside surface of the light incident surface 91a of a glass bulb 92 of substantially semi-circular section. A photocathode 92 is formed on the periphery of the light incident surface of substantially semi-circular section. A secondary electron multiplying portion 93 and an anode 94 are opposed to the periphery of substantially semi-circle contour to the section. In each of the phototubes of FIGs. 14 to 16, the photocathode 73, 82, 92 is inclined to the light incident surface 71a, 81a, 91a of the glass bulb. The secondary electron multiplying portion 74, 83, 93 is opposed and near to the photocathode 73, 82, 92. Consequently when a magnetic field B is applied in parallelism with the light incident surface 71a, 81a, 91a of the glass bulb, the photoelectrons emitted by the photocathode 73, 82, 92 move along a direction of the magnetic field B because of a component of the electric field E in the direction of the magnetic field B on the same principle as in FIGs. 9A and 9B to reach the secondary electron multiplying portion 74, 83, 93. Similarly the secondarily multiplied electrons also move in the direction of the magnetic field B to reach the anode 75, 84, 94. These embodiments can achieve the same advantageous effect as the above-described embodiments, and are combined with scintillators to provide radiation detecting devices having improved radiation detecting efficiency. FIG. 20 is a sectional view of the photoelectron multiplying tube according to a ninth embodiment of this invention. The photoelectron multiplying tube is accommodated in a glass bulb 101. In the interior of the glass bulb maintained vacuum there is provided a silicon photodiode 102, a solid-state semiconductor device. Inside the glass bulb 101 a photocathode 103 for emitting photoelectrons when irradiated with a beam of light is inclined to a light incident surface 101a. The silicon photodiode 102 is opposed to the photocathode 103 near and in parallelism with the same. The photocathode 103 is supplied with a negative high voltage -H[V] through a lead 104, and the photoelectron incident surface of the silicon photodiode 102 is grounded at the earth voltage. A positive high voltage +H[V] is applied to the rear side of the silicon photodiode 102 through a lead 106. This lead 106 is a lead (OUT) for taking out a signal. In this structure, a beam of light from the light incident surface 101a collide against the photocathode 103, and is converted into photoelectrons at the photocathode 103. The emitted photoelectrons are attracted to the side of the photodiode 102 because of the electric field E generated between the photocathode 103 and the silicon photodiode 102. Then the photoelectrons enter at the electron incident surface to be captured by the same. The photoelectrons which have entered the photodiode 102 are electron-multiplied there and are taken outside as a photoelectric current through the lead 106. Also in the photoelectron multiplying tube according to this embodiment, even when an external magnetic field B is applied in parallelism with the light incident surface 101a, most of the photoelectrons emitted by the photocathode 103 enter the photodiode 102 because the photocathode 103 and the photodiode 102 are inclined to the light incident surface 101a. Accordingly this embodiment can produce the same advantageous effect as the above-described embodiments. Furthermore in this embodiment, the influence of the external magnetic field does not range to the interior of the photodiode 102, and the influence of the external magnetic field is limited between the photocathode 103 and the exterior of the photodiode 102. The photoelectrons in this space are led to the pohotodiode 102 as described above. Consequently a photoelectron multiplying tube which is operative even in strong magnetic fields can be provided. Similarly with the above-described embodiments, this embodiment can be combined with a scintillator to provide a radiation detecting device having good radiation detecting efficiency. As described above, in the phototube according to this invention, even when a magnetic field is applied in parallelism with the light incident surface of the light permeable closed container, the photoelectrons emitted by the photocathode move along a direction of the magnetic field because of a component of the electric field along the direction of the magnetic field when the direction of the magnetic field has an angle to the photo-electric surface with the photocathode formed on. This is due to that the photocathode and the anode are inclined to the light incident surface. Also in the phototube in which photoelectrons are secondarily multiplied, and the phototube in which photoelectrons are multiplied internally in the solid-state semiconductor device, even when a magnetic field is applied in parallelism with the light incident surface of the light permeable closed container, the photoelectrons emitted by the photocathode move along a direction of the magnetic field because of a component of the electric field in the direction of the magnetic field to reach the electrode and the solid-state semiconductor device for emitting the secondary electrons. Consequently in each of the above described phototubes, the photoelectrons emitted by the photocathode can be captured by the anode, and the electrode and the solid-state semiconductor device for emitting secondary electrons, and the photodetecting efficiency of the phototubes are maintained good. The electrons secondarily emitted also move along the direction of the external magnetic field to be captured by the anode opposed to the electrode. Consequently the photoelectrons can be secondarily multiplied without the influence of the external strong magnetic field, and a sufficient number of electrons can captured by the anode. In the interior of the solid-state semiconductor device, the photoelectrons which have entered the same can be multiplied without the influence of the external magnetic field. Consequently the photoelectron multiplying tube can perform electron multiplication without the influence of the external magnetic field. Furthermore, the phototubes, and the photoelectron multiplying tube can be applied to radiation detecting devices, and such radiation detecting devices have good radiation detecting efficiency. From the invention thus described, it will be obvious that the invention may be varied in many ways.

Claims: A phototube comprising a sealed container (12,21, 31,41,62,71,81,91,101) having a substantially planar light-receiving surface (12a,21a,31a,41a,62a,71a,81a, 91a,101a), aphotocathode (13,23,32,42,63,73,82,92,103) and an anode (14,24,33,43,65,75,84,94), characterised in that said photocathode and anode are parallel to each other and are so oriented that the electric field (E) therebetween is inclined to the normal to said light-receiving surface. A phototube according to claim 1 or 2, wherein in the light-receiving surface (62a) comprises the outer surface of a light permeable face plate which has an inside surface formed inclined to the light-receiving surface; and the photocathode (13,32,42,65,82,92) is formed on the inside surface of the face plate. A phototube as claimed in claim 3, wherein the inside surface is formed as a substantially conical surface. A phototube as claimed in claim 3, wherein the inside surface is formed as a curved surface. A phototube according to claim 1 or 2, further comprising between the light-receiving surface and the anode a light permeable plate (22,72) which is inclined to the light-receiving surface; and wherein the photocathode (23,73) is formed on the light permeable plate. A phototube according to any preceding claim, further comprising secondary electron multiplying means (64,74,83,93) provided in parallel to the photocathode. A phototube according to claim 7, wherein an electrode portion of the secondary electron emitting means has a thickness (h) smaller than a diameter (L) of the sealed container. A phototube as claimed in any preceding claim, further comprising a solid-state semiconductor device (102) having an electron incident surface, the semiconductor device being so provided in the sealed container that the electron incident surface is substantially opposed to and parallel to the photocathode (103). A phototube according to claim 9, wherein the solid-state semiconductor device (102) is arranged to multiply internally the photoelectrons incident thereon. A radiation detecting device comprising: a phototube according to any preceding claim; and a scintillator (5) provided on or adjacent to the light-receiving surface, the scintillator emitting light when exposed to radiation. A radiation detecting device according to claim 11, wherein the scintillator (5) is rotatable on an axial line which is perpendicular to the light-receiving surface and passes the center of the light-receiving surface.

Inventors: ITO MASUO, NAKAMURA KIMITSUGU, SUZUKI SEIJI, WATASE YASUSHI, ITO, MASUO, NAKAMURA, KIMITSUGU, SUZUKI, SEIJI, WATASE, YASUSHI, Ito, Masuo, c/o Hamamatsu Photonics K.K., NAKAMURA, KIMITSUGU, C/O HAMAMATSU PHOTONICS K.K., Suzuki, Seiji, c/o Hamamatsu Photonics K.K., Watase, Yasushi, c/o Hamamatsu Photonics K.K.
Applicants: HAMAMATSU PHOTONICS KK, HAMAMATSU PHOTONICS K.K.
Application year: 1992
Main classification: H01J43
IPC codes: H01J40, H01J43