Radiant energy – Invisible radiant energy responsive electric signalling – Including a radiant energy responsive gas discharge device
Reexamination Certificate
1999-11-19
2002-07-02
Epps, Georgia (Department: 2873)
Radiant energy
Invisible radiant energy responsive electric signalling
Including a radiant energy responsive gas discharge device
C250S385200, C250S374000, C250S375000
Reexamination Certificate
active
06414317
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a detector for detection of ionizing radiation, to an apparatus for use in planar beam radiography and to a method for detecting ionizing radiation.
BACKGROUND OF THE INVENTION AND RELATED ART
A detector and an apparatus of the kind mentioned above are described in the copending PCT-application PCT/SE98/01873, which is incorporated herein by reference. The detector described therein includes a gaseous parallel plate avalanche chamber. The detector provides good resolution, high X-ray detection efficiency, and possibility to count every photon absorbed in the detector. This provides a huge number of possibilities when processing the detection signals, such as energy detection, discriminating detection signals from photons in certain energy ranges or from photons incident at certain distance ranges from the anode or the cathode.
When using a detector of this kind in planar beam X-ray radiography, e.g. slit or scan radiography, an apparatus which provides that an object to be imaged only needs to be irradiated with a low dose of X-ray photons is achieved, while an image of high quality is obtained.
Another detector and apparatus of the kind mentioned above, in the section field of the invention, is disclosed in EP-A1-0 810 631.
For gaseous parallel plate avalanche chambers it has been regarded as necessary that the avalanche anode and cathode plates are parallel, and much effort has been made to achieve high parallelism between the plates. However, the critical point is that the distance where the electrons are subjected to avalanche amplification, i.e. the length of the electron avalanches, do not differ at different locations in the gaseous parallel plate avalanche chamber. The reason for this is that the amplification is strongly dependent on the distance from the starting point to the end point of the avalanche. However, avalanche anodes and cathodes have large dimensions, in the planes they extend, compared with the distance between them. Therefore, it has been very complicated and costly to obtain a sufficient uniformity of those distances or gaps.
SUMMARY OF THE INVENTION
The present invention is directed to a one-dimensional detector for detection of ionizing radiation, which employs avalanche amplification, and provides well defined avalanches, and which can be manufactured in a simple and cost effective way.
This and other objects are attained by a detector having a chamber filled with an ionizable gas and a radiation entrance, the detector comprising first and second electrode arrangements located within the chamber, spaced apart such that a portion of the space therebetween acts as a conversion and drift volume, wherein the radiation entrance permits radiation, including electrons, to enter the conversion and drift volume, an electron avalanche amplification unit including at least one avalanche cathode and the at least one avalanche anode, between which a voltage can be applied to create an electric field in the vicinity of each of a plurality of avalanche regions formed by an arrangement of the at least one avalanche cathode and at least one avalanche anode, and at least one arrangement of read-out elements for detecting electron avalanches in the plurality of avalanche regions.
The above detector can be given a length, in the direction of the incoming radiation, for achieving a desired stopping power, which makes it possible to detect a major portion of the incoming radiation.
In the detector electrons are released by interactions between photons and gas atoms and can be extracted in a direction essentially perpendicular to the incident radiation to obtain a very high position resolution.
The above detector also can provide good resolution, high X-ray detection efficiency, and count a major portion of the photons incident in the detector.
A detector which provides good energy resolution for X-rays is also obtained.
The above detector can also operate at high X-ray fluxes without performance degradation and has a long lifetime.
The above detector can also be used for effective detection of any kind of radiation, including electromagnetic radiation as well as incident particles, including elementary particles. The present invention is directed to an apparatus for use in planar beam radiography, comprising at least one one-dimensional detector for detection of ionizing radiation, which employs avalanche amplification, provides well defined avalanches, and can be manufactured in a simple and cost effective way.
This and other objects are attained by an apparatus for use in planar beam radiography, comprising an X-ray source, means for forming an essentially planar X-ray beam positioned between said X-ray source and an object to be imaged, wherein it further comprises a detector as described above.
The above apparatus can be used in planar beam radiography, e.g. slit or scan radiography, such that an object to be imaged only needs to be irradiated with a low dose of X-ray photons, to obtain a high quality image.
The above apparatus can also be used in planar beam radiography, in which a major fraction of the X-ray photons incident on the detector can be detected, for further counting or integration in order to obtain a value for each pixel of the image.
The above apparatus can also be used in planar beam radiography, in which image noise caused by radiation scattered in an object to be examined is strongly reduced.
The above apparatus can also be used in planar beam radiography, in which image noise caused by the spread of X-ray energy spectrum is reduced.
The above apparatus can also be used in planar beam radiography, including a simple and inexpensive detector that can operate with high X-ray detection efficiency and with good energy resolution for X-rays.
The above apparatus can also be used in planar beam radiography, including a detector which can operate at high X-ray fluxes without a performance degradation and has a long lifetime.
The present invention is also directed to a method for detection of ionizing radiation, which employs avalanche amplification, provides well defined avalanches, and can be implemented in a simple and cost effective way.
This and other objects are attained by a method for detecting ionizing radiation, wherein the radiation interacts with gas atoms in a gas filled conversion and drift volume, for creation of released electrons, wherein the electrons are subjected to a first electric field in the conversion and drift volume, said first electric field being substantially perpendicular to the direction of the radiation, in each of a plurality of regions a concentrated electric field for causing electron avalanches is formed, said first electric field forcing the electrons to enter one of said plurality of regions with a concentrated electric field, and said electron avalanches being detected by means of read-out elements.
The above method makes it possible to detect a major portion of the incoming radiation.
In the above method electrons released by interactions between photons and gas atoms are extracted in a direction perpendicular to the incident radiation, to thereby obtain a very high position resolution.
The above method can be used at high X-ray fluxes.
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 preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
REFERENCES:
patent: 5347131 (1994-09-01), Charpak
patent: 5959302 (1999-09-01), Charpak
patent: 0810631 (1997-12-01), None
pa
Francke Tom
Peskov Vladimir
Birch & Stewart Kolasch & Birch, LLP
Epps Georgia
Hasan M.
Xcounter AG
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