Abstract:
Provided is an X-ray tube including an anode, a target on the anode, a cathode disposed separate from the target and the anode and comprising an emitter providing an electron beam to the target, and a side wall disposed between the cathode and the anode, and surrounding the target and the emitter. The side wall reflects a light generated by collision of the electron beam with the target to the cathode, and electrically insulates the cathode from the anode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 of Korean Patent Application No. 10-2014-0082554, filed on Jul. 2, 2014, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The present disclosure herein relates to an X-ray tube, and more particularly, to a photocathode coupled X-ray tube. 
     Since Roentgen discovered an X-ray, a manufacturing method of an X-ray tube has not been greatly changed. Today, an X-ray tube in a thermal electron emission scheme that heats a filament in a vacuum glass tube is most widely used. Recently, researches are being greatly performed which try to apply a photoelectron emission scheme or an electric field electron emission scheme to an X-ray tube. 
     Electron emission schemes are largely divided into the thermal electron emission, the field electron emission, and the photoelectron emission. 
     SUMMARY 
     The present disclosure provides an X-ray tube capable of maximizing electron emission. 
     The present disclosure also provides an X-ray tube capable of deriving electron beam emission by a photoelectric effect. 
     Embodiments of the inventive concept provide X-ray tubes, including: an anode; a target on the anode; a cathode disposed separate from the target and the anode and comprising an emitter providing an electron beam to the target; and a side wall disposed between the cathode and the anode, and surrounding the target and the emitter, wherein the side wall reflects a light generated by collision of the electron beam with the target to the cathode, and electrically insulates the cathode from the anode. 
     In some embodiments, the side wall may include an oxide. The oxide may include aluminum oxide. The oxide may include silicon oxide. 
     In other embodiments, the X-ray tube may further include reflection blocks protruding from an inner wall of the side wall and reflecting the light generated at the target to the emitter. The reflection blocks may include first reflection surfaces having slopes increased against the side wall along a direction from the anode to the cathode. The reflection blocks may have a scale shape. The reflection blocks may include a metal oxide or an insulating oxide. 
     In still other embodiments, the X-ray tube may further include a reflector focusing the light on the emitter from an inner wall of the side wall. The reflector may include a second reflection surface of which a radius is decreased along a direction from the anode to the cathode. The second reflection surface may have a “U”, parabola, bell, funnel, or trumpet shape. The reflector may include a metal oxide or an insulating oxide. 
     In even other embodiments, the X-ray tube may further include a gate disposed between the anode and the cathode and controlling the electron beam between the anode and the cathode. The side wall may include an upper side wall between the anode and the gate, and a lower side wall between the gate and the cathode. The X-ray tube may further include reflection blocks disposed on an inner wall of the upper side wall and reflecting the light generated in the target to the emitter. The reflection blocks may comprise first reflection surfaces having slopes increased against the side wall along a direction from the anode to the cathode. The reflection blocks have a scale shape. The side wall has a cylindrical tube shape, and the reflection blocks have a ring shape formed along an inner wall of the side wall. The X-ray tube may further include a reflector disposed on an inner wall of the upper wall and focusing the light on the emitter. The reflector may have a second reflection surface of which a radius is decreased along a direction from the anode to the cathode. The second reflection surface may have a “U”, parabola, bell, funnel, or trumpet shape. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the inventive concept, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the inventive concept and, together with the description, serve to explain principles of the inventive concept. In the drawings: 
         FIG. 1  illustrates an X-ray tube according to a first embodiment of the inventive concept; 
         FIG. 2  is a plan view of  FIG. 1 ; 
         FIG. 3  illustrates a first application example of the X-ray tube in  FIG. 1 ; 
         FIG. 4  illustrates a second application example of the X-ray tube in  FIG. 2 ; 
         FIG. 5  illustrates an X-ray tube according to a second embodiment of the inventive concept; 
         FIG. 6  illustrates a third application example of the X-ray tube in  FIG. 5 ; and 
         FIG. 7  illustrates a fourth application example of the X-ray tube in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Exemplary embodiments of the inventive concept will be described below in more detail with reference to the accompanying drawings. The inventive concept may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. Like reference numerals refer to like elements throughout. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated elements, steps, operations and/or components, but do not preclude the presence or addition of one or more other elements, steps, operations and/or components thereof. In addition, reference numerals shown according to an order of description are not limited to the order. 
     Hereinafter, exemplary embodiments of the inventive concept will be described in detail with reference to the accompanying drawings. 
       FIG. 1  illustrates an X-ray tube  70  according to a first embodiment of the inventive concept.  FIG. 2  is a plan view of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , the X-ray tube  70  according to the first embodiment of the inventive concept may include an anode  10 , a target  20 , a cathode  30 , and a side wall  40 . 
     The anode  10  may include a metal plate. For example, the anode  10  may include a copper plate. A positive DC voltage may be applied to the anode  10 . 
     The target  20  may be disposed between the anode  10  and the cathode  30 . According to an example, the target  20  may be coupled on the anode  10 . For example, the target  20  may include a metal such as copper, tungsten, or molybdenum, which is excellent in conductivity. 
     The cathode  20  may be separated from the anode  10  by a predetermined distance. The cathode  30  may be parallel with the anode  10  and the target  20 . The cathode  30  may include an emitter  32 . When a DC voltage is applied to the cathode  30 , an electron beam  12  may be emitted from the emitter  32 . The electron beam  12  may be collided with the target  20 . The target  20  may emit an X-ray  14 . The X-ray  14  may be transmitted through the anode  10  and the target  20  and proceed towards the same direction as that of the electron beam  12 . On the contrary, the target  20  may emit a light  16 . The light  16  may have lower energy and a longer wavelength than the X-ray  14 . For example, the light  16  may include an ultraviolet ray, a visible light, and an infrared ray. The light  16  may be provided to the emitter  32 . 
     The side wall  40  may be disposed between the anode  10  and the cathode  30 . The side wall  40  may fix each edge of the anode  10  and the cathode  30 . The side wall  40  may surround the target  20  and the emitter  32 . The side wall  40  may prevent electrical short-circuit between the anode  10  and the cathode  30 . According to an example, the side wall  40  may include an oxide insulator. The side wall  40  of the oxide insulator may include a metal oxide of ceramic (Al 2 O 3 ). The side wall  40  may have a cylindrical tube shape. 
     The side wall  40  may reflect the light  16  to the emitter  32 . The emitter  32  may absorb the light  16 . The emitter  32  may emit the electron beam due to the photoelectric effect. The electron beam emission effect may be maximized. 
       FIG. 3  shows a first application example of the X-ray tube in  FIG. 1 . The X-ray tube may include reflection blocks  50 . The reflection blocks  50  may be disposed on the side wall  40  between the anode  10  and the cathode  30 . The reflection blocks  50  may protrude internally from the side wall  40 . According to an example, the reflection blocks  50  may include an insulating oxide such as a ceramic metal oxide or silicon oxide. The reflection blocks  50  may have a ring shape formed along the inner wall of the side wall  40  of the cylindrical tube shape. The reflection blocks  50  may be inclined against the side wall  40 . The light  16  may be reflected by first reflection surfaces  58  of the reflection blocks  50 . The reflection blocks  50  may increase reflection efficiency of the light  16  on the side wall  40 . According to an embodiment, the reflection blocks  50  may include first to seventh reflection blocks  51  to  57 . The first reflection block  51  may disposed adjacent to the anode  10  and the target  20 . The seventh block  57  may be disposed adjacent to the cathode  30 . A slope of the first reflection surface  58  of the first reflection block  51  may be smaller than that of the first reflection surface  58  of the seventh reflection block  57 . The first to seventh reflection blocks  51  to  57  may have a scale shape on the side wall  40 . The light  16  may be reflected by the inclined surfaces of the first to seventh reflection blocks  51  to  57  and provided to the emitter  32 . An electron beam emission effect of the emitter  32  may be maximized by a photoelectric effect. 
       FIG. 4  illustrates a second application example of the X-ray tube  70  in  FIG. 1 . The X-ray tube  70  may include a reflector  60 . The reflector  60  may have a second reflection surface  62  reflecting the light  16  to the emitter  32 . According to an embodiment, the reflection surface  62  may have a “U”, parabola, bell, funnel, or trumpet shape. The emitter  32  may be disposed at the center of the reflector  60 . The light  16  may be focused on the emitter  32  at the center of the reflector  60 . 
       FIG. 5  illustrates the X-ray tube  170  according to a second embodiment of the inventive concept. The X-ray tube  170  according to the second embodiment of the inventive concept may include an anode  110 , a target  120 , a cathode  130 , a side wall  140 , and a gate  148 . 
     The anode  110  and the cathode  130  may be separated from each other. The side wall  140  may fix the anode  110  and the cathode  130 . The anode  10  may fix the target  120  to be inclined against the cathode  130 . The target  120  may be disposed on the reflection surface  111  of the anode  110 . An emitter  132  of the cathode  130  may provide an electron beam  112  to the target  120 . The target  120  may be disposed between the anode  110  and the cathode  130 . The electron beam  112  may allow an X-ray  114  and a light  116  to be emitted from the target  120 . 
     The X-ray  114  may proceed towards a different direction from the electron beam  112 . The X-ray  114  may be provided to the side wall  140  in the inclined direction of the anode  110 . Since the X-ray  114  has higher energy than the light  116 , the X-ray  114  may be transmitted through the side wall  140  and emitted externally. On the contrary, the light  116  may be reflected by the side wall  140 . The side wall  140  may reflect the light  116  to the emitter  132  of the cathode  130 . The emitter  132  may be disposed at the center of the cathode  130 . 
     The gate  148  may be fixed on the side wall  140  between the cathode  130  and the anode  110 . The gate  148  and the cathode  130  may be parallel. The gate  148  may receive a DC supply voltage for controlling the electron beam  112 . 
     The side wall  140  may include an insulating oxide such as a metal oxide like ceramic or silicon oxide. The side wall  140  may include a lower side wall  142   b  and an upper side wall  142   a . The lower side wall  142   b  may be disposed between the gate  148  and the cathode  130 . The upper side wall  142   a  may be disposed between the gate  148  and the anode  110 . 
       FIG. 6  illustrates a third application example of the X-ray tube in  FIG. 5 . The X-ray tube  170  may include reflection blocks  150 . The reflection blocks  150  may be disposed on an upper side wall  144  between the anode  110  and the gate  148 . According to an embodiment, the reflection blocks  150  may have first reflection surfaces  158  reflecting the light  116  to the emitter  132 . The reflection blocks  150  may include first to seventh reflection blocks  151  to  157 . The first reflection block  151  may be disposed adjacent to the anode  110 . The seventh reflection block  157  may be adjacent to the gate  148 . The first reflection surface  158  of the first reflection block  151  may have a smaller slope than the first reflection surface  158  of the seventh reflection block  157 . The first to seventh reflection blocks  151  to  157  may have a scale shape on the upper side wall  144 . 
       FIG. 7  illustrates a fourth application example of the X-ray tube in  FIG. 6 . The X-ray tube  170  may include a reflector  160 . The reflector  160  may be disposed on an inner wall of the upper side wall  144 . The reflector  160  may have a second reflection surface  162  reflecting the light  116 . According to an embodiment, the second reflection surface  162  may have a “U”, parabola, bell, funnel, or trumpet shape. The emitter  132  may be disposed at the center of the reflector  160 . The light  116  may be focused on the emitter  132 . 
     According to embodiments of the inventive concept, an X-ray tube can include a side wall insulating an anode from a cathode and reflecting a light emitted from a target on the anode to an emitter of the cathode. The emitter can emit electron beams due to a photoelectric effect. The electron beam emission from the emitter can be maximized. 
     The above-disclosed subject matter is to be considered illustrative and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the inventive concept. Thus, to the maximum extent allowed by law, the scope of the inventive concept is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.