X-ray or gamma ray systems or devices – Source – Electron tube
Reexamination Certificate
1999-09-27
2001-12-25
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Source
Electron tube
Reexamination Certificate
active
06333967
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an X-ray generator usable as the X-ray source of an X-ray diffraction apparatus or the like, more particularly to an X-ray generator in which an X-ray beam emitted from the surface of a target bombarded with electrons is regulated beforehand within the main generator unit before passage to the exterior through an exit window.
2. Description of the Related Art
The prior-art X-ray generator produces an X-ray beam by bombarding a target with electrons emitted from an electron gun (cathode). The X-ray beam emitted from the surface of the target passes to the exterior through an exit window provided in a wall of the main generator unit.
The X-ray beam emitted from this type of X-ray generator is ordinarily regulated using an X-ray optical element to obtain a parallel beam, condensed beam, spectral or split beam or other beam with beam characteristics appropriate for the intended use.
FIG. 6
shows an example of the system layout of an X-ray diffraction apparatus utilizing this kind of X-ray generator as the X-ray source.
The X-ray diffraction apparatus has a sample base
3
, a divergence slit
4
, a receiving slit
5
and an X-ray detector
6
mounted on a goniometer
2
. X-ray diffraction analysis is effected by directing an X-ray beam emitted from an X-ray generator
1
onto a sample S attached to the sample base
3
.
An X-ray optical element
7
is provided in the path of the X-ray beam emitted from the X-ray generator
1
at a position upstream of the divergence slit
4
. The X-ray optical element
7
condenses the X-ray beam emitted from the X-ray generator
1
and directs the condensed X-ray beam onto the surface of the sample S.
The peak intensities of the diffracted X-rays produced by the irradiation of the sample S with the X-ray beam appear at diffraction angles dependent on the crystal structure etc. of the sample surface. These peak intensities are detected by the X-ray detector
6
. The diffraction angles (2&thgr;) at which the peak intensities appear are measured by the goniometer and used to analyze the sample crystal structure and the like.
The conventional X-ray generator described in the foregoing is only capable of producing an X-ray beam by bombarding a target with electrons from an electron gun and emitting the generated X-ray beam through an exit window. It is not capable of regulating the X-ray beam generated from the surface of the target.
Such regulation has therefore required an X-ray optical element to be disposed in the open air as a separate unit from the X-ray generator.
Since the X-ray optical element disposed in the air is susceptible to contamination by moisture, dust and the like contained in the air, its X-ray beam regulation performance rapidly deteriorates.
In addition, the X-ray beam encounters resistance from air molecules. The X-ray intensity therefore attenuates with increasing length of the X-ray beam path between the window of the X-ray generator and the point of irradiation (the surface of the sample on the X-ray diffraction apparatus). In the conventional mode of use, since the X-ray optical element has to be disposed in the air between the X-ray generator and the irradiation point, the length of the X-ray path is increased at least by the size of the X-ray optical element. Wasteful attenuation of the X-ray intensity is therefore unavoidable.
Since this requires a high-intensity X-ray beam to be generated from the target in order to make up for air attenuation, it causes a proportional increase in power consumption. It is therefore uneconomical from the point of operating cost.
SUMMARY OF THE INVENTION
This invention was accomplished to overcome these problems of this type of X-ray generator and the X-ray optical element used therewith and aims to provide an X-ray generator which, by incorporation of an X-ray optical element therein, improves the durability o the X-ray optical element and also enables the length of the X-ray path to the X-ray irradiation point to be shortened so as to suppress attenuation of the emitted X-ray beam by air resistance and thereby reduce power consumption.
The invention achieves this object by providing an X-ray generator which includes an electron gun and a target housed inside a hermetically sealed main generator housing which defines a main generator unit, bombards the target with electrons emitted from the electron gun and passes an X-ray beam emitted from a surface of the target owing to the bombardment to the exterior of the main generator unit through an exit window, the X-ray generator comprising at least one X-ray optical element provided inside the main generator unit on an output path of an X-ray beam emitted from the target for regulating the X-ray beam, the X-ray beam regulated by the X-ray optical element being passed to the exterior through the exit window.
Since the interior of the main generator unit is a hermetically sealed space, degradation of the X-ray optical element by moisture, dust and the like is suppressed. The X-ray beam emitted from the surface of the target is passed to the exterior through the exit window after being regulated by the X-ray optical element provided inside the main generator unit. The X-ray beam is therefore already converted into a parallel beam, condensed beam, spectral or split beam, or other beam state suitable for the purpose before exiting through the window. Since this makes it unnecessary to dispose an X-ray optical element in the open air, the length of the X-ray path between the exit window of the X-ray generator and the irradiation point can be shortened to the minimum required. The attenuation of the X-ray intensity in the air is therefore reduced and the power consumption required for X-ray generation decreases accordingly.
Since the target and the X-ray optical element are incorporated in the main generator unit, they can be located close to each other. Therefore, it is possible to enlarge a capture angle of an X-ray beam, emitted from the target, to the X-ray optical element.
By enlarging the capture angle as described above, a large amount of the X-ray emitted from the target can be captured into the X-ray optical element, whereby an amount of X-ray passed to the exterior through the exit window is increased. Therefore, the X-ray can be efficiently utilized.
Accordingly, the present invention with the above structure arrangement can accomplish not only a reduction of power consumption required for X-ray generation but a size reduction of the electron gun and the target. Further, since the reduction of the power consumption results in a decrease of heat value from the target, the circulating water for cooling the target can be saved. When the target is employed as a rotary target, the target can be driven at a low rotational speed, whereby vibrations caused by the rotation are remarkably lowered.
Further, even when the target with simple structure is employed as a fixed target, a large amount of the X-ray emitted from the target can be captured into the X-ray optical element. Thereby, it is possible to exit a sufficient amount of X-ray.
As explained above, the present invention can accomplish the effects in which power consumption is reduced, and the target for emitting a X-ray and others are simplified in structure and reduced in size, thereby bringing the satisfactory performance at low cost. Therefore, there are advantages to the users in using the present invention.
The optical element is selected among dispersive and reflective structures for regulating the X-ray beam emitted by the generator. For example, the optical element is a reflector having a reflective face of appropriate shape to regulate the X-ray beam as desired, for example a parabolic or cylindrical reflective surface or mirror, or a combination, for example, by assembly or juxtaposition, of such reflectors or mirrors to reflect and diverge the X-ray beam. Examples of such optical elements are given in U.S. Pat. No. 4,693,933 issued Sep. 15, 1987 in the form of multilayer Bragg reflectors used as cond
Hayashi Sei-ichi
Osaka Naohisa
Armstrong Westerman Hattori McLeland & Naughton LLP
Church Craig E.
Rigaku Corporation
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