Radiant energy – Invisible radiant energy responsive electric signalling – Including a radiant energy responsive gas discharge device
Patent
1991-04-26
1992-02-11
Fields, Carolyn E.
Radiant energy
Invisible radiant energy responsive electric signalling
Including a radiant energy responsive gas discharge device
250374, 25039001, 25039002, G01T 1185, G01T 300
Patent
active
050878212
DESCRIPTION:
BRIEF SUMMARY
The present invention relates in particular to a device for detecting and locating particles in a flux of neutral particles emitted by a source, the device comprising:
a substantially plane solid converter suitable for producing electrical charges under the impact of said neutral charges, the converter comprising conversion elements which are electrically independent from one another;
anode wires for raising to an electric potential different from that of the converter to cause an electric field to appear, and for amplifying charges by ionizing a surrounding gas under stimulation from said electric field;
charge collecting means comprising conductor elements that are electrically independent from one another, with at least some of them constituting conversion elements; and
an enclosure permeable to the neutral particles and containing the converter, the anode wires, the charge collecting means, and the gas.
A device of this type is described in the European patent application published under the number 0 000 271.
Although this prior art device makes it possible to obtain two-dimensional images directly, its design is based on an attempt at optimizing efficiency in certain particular applications to the detriment of optimizing resolution.
In contrast, an aim of the present invention is to make it possible to provide images of higher resolution, and also to obtain high contrast, where possible, even under conditions that are a priori unfavorable for irradiating the object to be examined, and more particularly in the event of poor conversion rates and/or in the presence of an incident particle flux of low intensity.
To this end, the apparatus of the invention is essentially characterized in that said conversion elements also suitable for collecting charge are constituted by cells distributed over a plane two-dimensional matrix disposed on the opposite side of the anode wires to the source.
By virtue of this disposition, the images obtained by the device of the invention have higher resolution than the images obtained using the prior art device described in the patent EP 0 000 271, in which the two-dimensional matrix is made up of tow parallel planes of linear components which are parallel to one another in each plane, while the components in the two different planes cross one another.
Because of the spacing between the two planes which together form the two-dimensional matrix, and because of the parallax error resulting therefrom, this prior art disposition gives rise to different deformations in the partial images collected on the two planes for any radiation that is not perpendicular to the matrix, and this significantly degrades resolution.
In an advantageous embodiment of the invention, the converter comprises an insulating plate having one face carrying said cells, said plate including, for each cell, a through hole putting said cell into electrical contact with a conductor leading to the other face of said plate.
In a disposition which is known per se, it is preferable in the invention for the anode wires to be disposed in at least one plane substantially parallel to the plane of the converter, and for them to be substantially parallel to one another.
Given the disposition adopted in the invention, in order to obtain good efficiency, it is preferable for the cells to include a conversion material selected from the group comprising: gadolinium, boron, and lithou, in the event that the neutral particles used are neutrons; and for the cells to include a conversion material selected from the group comprising: iron, and silver, in the event that the neutral particles used are X-rays, in particular soft X-rays.
In the event of the counting rate being particularly low, for whatever reason, it is advantageous for the gas to contain a quencher constituting not less than 25% of the gas and for the ratio of the distance "S" between two adjacent anode wires to the distance "G" between these wires and the converter to be not less than 1.
These characteristics enable the device to operate in a mode known to the perso
REFERENCES:
patent: 4816683 (1989-03-01), Marsden
Bateman et al., "A Hybrid MWPC Gamma Ray Detecting System for Applications in Nuclear Medicine", Nuc. Instru. and Methods, 156, 1978, pp. 27-31.
Dorion et al., "A Novel Unidimensional Position Sensitive Multiwire Detector", IEEE Trans Nucl. Sci, NS-34 (1), Feb. 1, 1987, pp. 442-443.
Anderson et al., "A Versatile Helium-Filled Detector Using Thin Foils for Converting Low Energy Gamma Rays to Electrons", Nucl. Instru. and Methods, 167, 1979, 351-354.
Dorion Irene
Maitrejean Serge
Ruscev Mario
Asman Sanford J.
Fields Carolyn E.
Schlumberger Industries
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