X-ray or gamma ray systems or devices – Source – Electron tube
Reexamination Certificate
2000-08-04
2002-04-30
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Source
Electron tube
C378S138000, C378S140000
Reexamination Certificate
active
06381305
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to an x-ray tube for generating x-rays.
2. Related Background Art
X-rays are electromagnetic waves for which most of materials and objects exhibit favorable transmitting properties, and are often used for nondestructive
oncontact observation of internal structures of objects. Usually, an x-ray tube is used for generating x-rays, and electrons emitted from an electron gun are caused to collide against a target, so as to generate x-rays. In general, for this collision, the center axis of a tubular member accommodating the electron gun therein and the center axis of a tubular member accommodating the target therein are aligned with each other, or their center axes are set perpendicular to each other.
As such x-ray tubes, those described in U.S. Pat. (USP) Nos. 5,077,771 and 5,563,923 have been known.
FIG. 12
is a configurational view of an x-ray tube in which the center axis of a tubular member accommodating an electron gun therein and the center axis of a tubular member accommodating a target therein are substantially orthogonal to each other, the x-ray tube being disclosed in U.S. Pat. No. 5,077,771. As shown in
FIG. 12
, this x-ray tube comprises an electron gun portion
910
for generating/emitting electrons; and an x-ray generating portion
920
for receiving the electrons emitted from the electron gun portion
910
, in which the electrons collide against a target
921
, so as to generate x-rays.
Here, the electron gun portion
910
comprises a heater
911
for generating heat in response to an electric power supplied thereto from the outside; a cathode
912
for emitting electrons when heated by the heater
911
; a focus grid electrode
913
for accelerating/converging the electrons emitted from the cathode
912
; and a container
914
which accommodates the heater
911
, cathode
912
, and focus grid electrode
913
therein and has an electron passage port.
The x-ray generating portion
920
comprises the target
921
against which electrons emitted from the electron gun portion
910
collide, so as to generate x-rays; a hood electrode
922
formed like a flat tube enveloping the target
921
with its center axis being substantially orthogonal to the center axis of the electron gun portion
910
, while having an electron passage opening in a path through which the electrons emitted from the electron gun portion
910
reach the target
921
; a container
923
having an inner space for accommodating the target
921
and hood electrode
922
therein and having an opening for taking out the x-rays generated at the target
921
, the inner space being connected to the inner space of the container
914
by way of the electron passage port of the container
914
; and an x-ray takeout window
924
made of an x-ray transmitting member and disposed at the x-ray passage port of the container
923
. A positive high voltage is applied to the hood electrode
922
and target
921
with reference to the potential at the emitting port of the electron gun portion
910
.
In the x-ray tube of
FIG. 12
, the electrons emitted from the electron gun portion
910
are accelerated to a high speed by the electric field between the focus grid electrode
913
and the hood electrode
922
, so as to advance in a vertical direction (i.e., electric field direction) of an equipotential surface at each position of the electrons at a given time, thereby colliding against the target
921
after passing through the electron passage opening of the hood electrode. When the electrons collide against the target
921
, x-rays are generated, and the x-rays are outputted from the x-ray tube by way of the x-ray passage opening of the hood electrode
922
and x-ray passage window
924
in succession.
For quality control of parts and the like, x-ray tubes are used as an x-ray source in x-ray inspection apparatus for yielding magnified penetration images and the like. Also, capability of increasing the magnification rate is quite important in improving the accuracy of inspection.
FIG. 13
is a typical configurational view of such an x-ray inspection apparatus. In the x-ray inspection apparatus shown in
FIG. 13
, x-rays emitted from an x-ray tube
107
irradiate a sample on a sample dish
105
. The x-rays transmitted through the sample are detected by an x-ray/fluorescence multiplier (an image intensifier tube: I.I. tube)
102
, and a magnified penetration image is picked up by an image pickup tube
101
. The magnification rate of the penetration image in this apparatus is determined by the ratio between the distance (A) from the x-ray generating point (the focal position of the x-ray tube)
106
within the x-ray tube to the sample position and the distance (B) from the sample position to the x-ray entrance surface of the I.I. tube. That is, the magnification rate M is expressed by
M=(A+B)/A. (1)
Normally, A<<B, and therefore the expression (
1
) can be represented by
M=B/A. (2)
Namely, for yielding a greater magnification rate, decreasing A or increasing B may be considered. Increasing B, however, not only enhances the overall size of the x-ray inspection apparatus, but also remarkably increases its weight by requiring a greater amount of lead shield
103
for keeping the x-rays from leaking outside, and so forth. Therefore, it is desirable that A be as small as possible.
SUMMARY OF THE INVENTION
Hence, in view of the foregoing, it is an object of the present invention to provide an x-ray tube which can shorten the distance from the x-ray generating point to the x-ray emitting window.
The present invention provides an x-ray tube comprising an electron gun for emitting an electron; a target for receiving the electron emitted from the electron gun at a front end face and generating an x-ray; an x-ray emitting window, disposed in front of the front end face of the target, for emitting the x-ray; and a hood electrode, formed as a tubular body attached to a tip portion of the target, having a peripheral face provided with an electron passage port for passing the electron therethrough, the electron passage port widening more on a side opposite from the x-ray emitting window than on the x-ray emitting window side with respect to a position intersecting an extension of the electron gun in an electron emitting direction. Also, the present invention provides an x-ray tube in which, of the tip portion of the target, a part exposed from the electron passage port is cutoff. Further, the present invention provides an x-ray tube in which the electron is made incident onto a center axis of the front end face of the target.
According to these aspects of the invention, the electron emitted from the electron gun pass through the electron passage port of the hood electrode and are made incident on the front end face of the target. Here, since the electron passage port is formed wider on the opposite side in the x-ray emitting direction, the electron is bent toward the x-ray emitting direction, so as to be made incident at a position near the x-ray emitting window. As a consequence, the distance between the x-ray generating position and the x-ray emitting window can be shortened.
Also, the present invention provides an x-ray tube comprising an electron gun for emitting an electron; a target for receiving the electron emitted from the electron gun In at a front end face and generating an x-ray; an x-ray emitting window, disposed in front of the front end face of the target, for emitting the x-ray; and a hood electrode formed as an annular body attached to a tip portion of the target, the hood electrode being disposed closer to the x-ray emitting window than is a position where the electron is made incident on the front end face.
According to this aspect of the invention, the electron emitted from the electron gun passes behind the hood electrode and is made incident on the front end face of the target. Here, since the electric field in the area where the electron passes is tilted toward the x-ray emitting wi
Inazuru Tutomu
Ishihara Yoshitoshi
Ito Masuo
Nakamura Kimitsugu
Nakamura Tsutomu
Hamamatsu Photonics K.K.
Ho Allen C.
Kim Robert H.
Morgan & Lewis & Bockius, LLP
LandOfFree
X-ray tube having a hood electrode does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with X-ray tube having a hood electrode, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and X-ray tube having a hood electrode will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2823971