X-ray or gamma ray systems or devices – Source
Reexamination Certificate
1995-11-20
2001-12-04
Church, Craig E. (Department: 2876)
X-ray or gamma ray systems or devices
Source
C378S122000
Reexamination Certificate
active
06327338
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns an x-ray source for radiography, more particularly a portable x-ray source and methods for conducting medical, biological and industrial x-ray radiography.
BACKGROUND OF THE INVENTION
The existing equipment used for medical (and dental) x-ray radiography contains high voltage vacuum tubes and produce x-rays as a result of the bombardment of a target by electrostatically accelerated electrons. The electrical supplies for such tubes are based on high voltage (~100 kilivolts) transformers. These transformers are very heavy, cumbersome, dangerous, and expensive pieces of equipment. Such conventional x-ray medical radiograph equipment is not portable and thus limits the use of the x-ray radiography in ambulances, distant areas, etc.
U.S. Pat. No. 5,323,442, filed Feb. 28, 1992, which is commonly assigned to the assignee of this patent document, the disclosure of which is incorporated herein by reference, describes an x-ray source that is based on an Electron Cyclotron Resonance (ECR) plasma. The ECR x-ray source is quite convenient to be used as a light, compact, safe and inexpensive low-voltage (but high enough photon energy and intensity) x-ray source. However, that ECR x-ray source has a large x-ray emitting surface which makes the resolution of the x-ray image poor and, without modification, not reasonably practicable for x-ray radiography, particularly in the medical field.
There remains a continuing need for better sources of x-rays for radiography. There also is a need for economical x-ray sources having sufficient intensity for radiography that are lightweight, portable, and may be operated from conventional energy supplies.
SUMMARY OF THE INVENTION
The present invention concerns an x-ray source based on an ECR plasma that, in contrast to the above ECR x-ray source of U.S. Pat. No. 5,323,442, possesses acceptable x-ray image resolution features for use as an exceptionally light, compact and safe portable x-ray radiograph. It also concerns an x-ray source which is free of the above deficiencies and provides nearly the same x-ray intensity and energy as the classical high voltage x-ray sources, although it has a drastically smaller volume, weight, electrical consumption and cost. In addition, the x-ray source of the present invention produces an x-ray intensity that is sufficient to produce high quality x-ray images on conventional x-ray sensitive films, with about the same exposure time as conventional high voltage x-ray sources.
Broadly, the invention is directed to apparatus and methods for producing x-ray radiation by providing a vacuumated chamber that is filled with a plasma support gas at low pressure and an x-ray emitter, and exposing the chamber to a resonant electrical field and perpendicular magnetic field to generate an Electron Cyclotron Resonance (ECR) plasma inside the chamber. The plasma support gas preferably is a heavy atomic weight gas. The chamber is configured and the magnetic field is established so that the ECR plasma forms a ring of hot electrons which bombard the x-ray emitter. This bombardment, in turn, produces an x-ray emission from the emitter generally directed at a target. As used herein, the term target includes any object to be irradiated. Where the context permits, it also includes a primary target or object which is being studied, and a secondary target or object such as x-ray sensitive film to record an image of the primary.
In one preferred embodiment, the chamber is within a microwave resonant cavity and between a pair of magnetic members that generate an axisymmetric magnetic mirror trap inside the cavity and chamber. This produces an ECR plasma occurring on an axisymmetric hyperboloid sheet with a ring of hot electrons in the central part of the magnetic mirror trap. The electron ring provides a steady (or controllable) electron current which is received by the x-ray emitter, and thus produces a continuous x-ray emission on the emitter surface. If both the position and orientation of the emitter surface are appropriately selected, the emission will be outgoing, perpendicular to the magnetic field lines. The emission is at a sufficient intensity to irradiate an object and expose an x-ray sensitive film using conventional exposure times as explained below.
Advantageously, because of its small size, low cost, and low power requirements, the x-ray source of the present invention is easily manipulated, can be used in a conventional manner, and can be made portable to make x-ray photographs virtually anywhere. For example, in the case of medical x-ray radiographs, the x-ray source of the present invention can be conventionally used, e.g., in a hospital, doctor's or dentist's office. A portable device can be used to obtain x-ray images of injuries at the injury site, before the patient is moved or transported to another location. Thus, civilian and military rescue vehicles, e.g., ambulances, helicopters, fire engines and the like, can be equipped with the portable x-ray source of the present invention for use during emergencies, whether on a city street, in a desert, or in space. Similarly, in the case of x-ray radiography of structures, welds and other physical things, a portable x-ray source in accordance with the present invention can be easily used at the site where the object to be examined is located, e.g., at any time during construction of a structure such as a submarine, nuclear power facility or spacecraft. The present invention also can be used for non-medical radiography, such as for fault analysis and identification of paintings and other works of art in museums and art galleries.
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Dugar-Zhabon Valeri D.
Golovanivsky Konstantin S.
Church Craig E.
Orrick Herrington & Sutcliffe
Ruxan Inc.
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