Radiant energy – Invisible radiant energy responsive electric signalling – Including a radiant energy responsive gas discharge device
Patent
1993-05-12
1994-09-13
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
Including a radiant energy responsive gas discharge device
H01J 4702
Patent
active
053471318
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a gas detector for ionizing radiation, such as .beta.-radiation.
The detection of ionizing radiation, such as .beta.-radiation emerging from surfaces of the body subjected to analysis, is currently produced by electron-avalanche multiplication in gases. Some detectors employ so-called multiwire chambers in which the amplification of the ionization electrons, generated by the ionizing radiation in the gaseous medium, is produced by virtue of an avalanche around a thin anode wire.
Other detectors use the amplification in the spaces between two parallel electrodes, consisting of metal wires, each forming an unmeshed network, and allow location of the avalanche produced by the multiplication of the ionization electrodes, or alternatively by optical methods by employing the light emitted by the avalanches. Such detectors function satisfactorily.
It will be noted, however, that the employment of this type of detector involves difficulties, inasmuch as the wires are successively assembled on a frame. The spacing between wires cannot at best be less than one millimeter, which consequently has the effect of limiting the spatial resolution of location of the avalanche front.
The object of the present invention is to overcome the aforementioned drawback.
Another object of the present invention is the implementation of a gas detector for ionizing radiation, of the .beta.-radiation type, making it possible to obtain a spatial resolution of detection of the avalanche front better than one hundred microns.
A further object of the present invention is the implementation of a gas ionizing-radiation detector in which, in the case of electrical discharge in the avalanche space, the electric current due to this discharge is very highly limited, which protects the electrodes or grids from corresponding damage.
A further object of the present invention is the implementation of a gas ionizing-radiation detector in which the mechanical deformations of the electrodes under the effect of the electrostatic forces applied to the latter, by virtue of their electrical polarization, are eliminated, without introducing any bracing or mechanical spacer into the avalanche space, in order to keep the inter-electrode distance constant.
The gas ionizing-radiation detector which forms the subject of the present invention comprises, in a sealed enclosure, a gas generating ionization electrons by the avalanche phenomenon, and at least two grids held at different electrical potentials and making it possible to accelerate the ionization electrons.
It is noteworthy in that at least one of the grids is formed in a first direction by a plurality of electrically insulating wires, acting as a support, and, in a second direction, distinct from the first, by a plurality of electrically conducting wires. These wires, directed respectively in the first and second directions, form a woven mesh.
The gas ionizing-radiation detector which forms the subject of the present invention is particularly well suited to detecting .beta.-rays, in particular high-intensity .beta.-radiation for which high counting rates are necessary.
The gas ionizing-radiation detector according to the invention will be described in more detail in the following description with reference to the drawings, in which:
FIG. 1a) the substructure of a gas ionizing-radiation detector which forms the subject of the present invention, in a viewing direction orthogonal to the direction of propagation of the avalanche Av, while FIGS. 1a' and 1a" show respective portions of grids G1 and G2 viewed in the direction of propagation; FIG. 1b) shows a view in section along the cutting planes 1b-1b or 1b'-1b' of FIG. 1a); and FIG. 1c) shows a view in section along the cutting plane 1c-1c of FIG. 1b);
FIG. 2 shows a view in section along the cutting plane 2-2 in FIG. 1b);
FIG. 3a shows a first variant embodiment of the detector according to the invention represented in FIG. 1a), in which the deformations of the electrodes or grids delimiting the avalanche-amplification space of the i
REFERENCES:
patent: 5025162 (1991-06-01), Charpak
patent: 5138168 (1992-08-01), Jeavons
Nuclear Instruments & Methods in Physics Research, vol. 216, No. 3, Nov. 1983 Amsterdam NL, pp. 393-397, De Palma, et al., "System of large multiwire proportional chambers . . . ".
William Frieze, Satish Dhawan, Adrian A. Disco, Lincoln Fajardo, Richard Majka, Jay N. Marx, Peter Nemethy, Jack Sandweiss and Anna J. Slaughter, "A High Resolution Multiwire Proportional Chamber System." Nuclear Instruments and Methods, vol. 136, No. 1 (Jul. 1, 1976) pp. 93-97 .COPYRGT.North-Holland Publishing Co.
J. M. Breare, K. A. Short, G. C. Smith and R. A. Cunningham, "A Sense Wire Support for Large Multiwire Proportional Chambers." Conference: 1973 International Conference on Instrumentation for High Energy Physics, Frascati, Italy (May 8-12, 1973) pp. 296-297.
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