Radiant energy – Invisible radiant energy responsive electric signalling – Including a radiant energy responsive gas discharge device
Patent
1990-12-28
1992-01-07
Westin, Edward P.
Radiant energy
Invisible radiant energy responsive electric signalling
Including a radiant energy responsive gas discharge device
2503851, G01T 1185
Patent
active
050794272
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a dosimeter for one- or two-dimensional dose measurement of ionizing radiation, said dosimeter comprising a flat box-shaped, gas-filled, gastight housing which encloses a measuring chamber and has at least two opposite walls which are transparent to the radiation to be measured, and electrode systems lying
opposite each other and between which an electric field prevails when in operation, at least one of the electrode systems being disposed on one of the opposite walls.
Such a dosimeter, which is specrally designed for use as a two-dimensional meter for X-rays passed through a body to be examined in a device for slit radiography, is described in the older Dutch Patent Application 8701122. Such a dosimeter, but designed for use as a one-dimensional meter, is also known from Dutch Patent Application 8503153. In the dosimeters described in the above-mentioned Dutch patent applications the measuring chamber is filled with a special gas or gas mixture such as, for example, xenon, or a mixture of argon and methane. The gas is at approximately atmospheric pressure.
In these dosimeters the problem arises that the opposite side walls, which are transparent to the radiation to be measured, have a tendency to bend when there are variations in the ambient pressure. This problem arises to a greater degree as the dimensions of the housing and in particular of the opposite walls increase. Since these walls carry the electrodes, the distance between individual electrodes lying opposite each other changes when there is a change in the ambient pressure. The bending is greatest in the center of the walls, so that the sensitivity of the meter no longer remains constant over the entire effective surface thereof when the walls bend. Another problem which occurs in the dosimeters according to Dutch Patent Application 8701122 and Dutch Patent Application 8503153 is that special measures are necessary to make these meters capable of withstanding low ambient pressures such as those which can occur, for example, in the hold of an aircraft.
There is therefore a need for a dosimeter for ionizing radiation which both electrically and mechanically is essentially insensitive to variations in the ambient pressure. The object of the invention is to meet this need.
To this end a dosimeter according to the invention is characterized by a pressure compensation element which with the measuring chamber forms a single gastight chamber, which pressure compensation element has at least partially walls of slack, substantially non-elastic and wrinkeable material, which walls of slack material are of such dimensions that said walls of slack material will not stretch tight under ambient pressure variations.
The invention will be explained in greater detail below with reference to the appended drawing.
FIG. 1 shows schematically in cross section a box-shaped dosimeter at low ambient pressure;
FIG. 2 shows schematically in perspective a first embodiment of a dosimeter according to the invention;
FIG. 3 shows schematically in cross section a second embodiment of a dosimeter according to the invention.
FIG. 1 shows schematically in cross section a box-shaped dosimeter 1 with a rectangular frame 2 which is clad with thin plates 3, 4 on either side. The plates are made of a material which transmits ionizing radiation, or at least attenuates it as little as possible. A suitable material is, for example, polymethyl methacrylate, normally known as perspex. The frame 2 can also be made of perspex or of another suitable material.
The frame 2 and the plates 3, 4 together enclose a gastight measuring chamber 5 in which a suitable gas or gas mixture, for example xenon or argon and methane, at approximately atmospheric pressure is present.
At least one of the plates has on the inside an electrode system which is schematically indicated at 6. In the example shown the plate 3 bearing the electrode system 6 extends along one edge beyond the frame 2, and the electrode system continues on the edge part 7 in question, so that the required operatin
REFERENCES:
patent: 2884537 (1959-04-01), Swift
patent: 3963924 (1976-06-01), Boag et al.
B.V. Optische Industrie "De Oude Delft"
Hanig Richard
Marn Louis E.
Westin Edward P.
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