Radiant energy – Invisible radiant energy responsive electric signalling – Including a radiant energy responsive gas discharge device
Patent
1995-09-18
1998-08-18
Tokar, Michael J.
Radiant energy
Invisible radiant energy responsive electric signalling
Including a radiant energy responsive gas discharge device
25034002, G01T 1185
Patent
active
057961107
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a device of gas ionization array detectors for high energy X or .gamma.-ray radiography which pertains to the area of nuclear technical applications.
BACKGROUND OF THE INVENTION
In the known prior art, China Patent No. 86,108,035 disclosed a device of gas discharge array detectors which primarily utilizes secondary electrons generated by the interaction of a solid state plate converter made of high atomic number material (e.g. Ta) and at a small approach angle (1.degree. or less) to the incident X or .gamma. photons with the rays to cause gas discharge to output a signal. Such device of detectors employs thin anode wires arranged in an array to obtain X or .gamma.-ray intensity signals at different positions. Each (or each pair) of the anode wires forms a pixel, the discharge signal of which represents the X or .gamma.-ray intensity at its position. The working gas is usually supplied by gas-flow system, keeping the pressure around one atmosphere. This patent also mentioned that it is also possible to use working gas of pressure less than 10.sup.6 pascals and placed in a sealed case, such as to eliminate the gas-flow systems. However, gas-flow systems supplied by steel gas bottles are still used in actual products. The container inspecting system ("Sycoscan" system) using such device of array detectors manufactured by the Schlumberger Inc. has been marketed.
The dynamic range of the signals of such detecting device is large (10.sup.5), as well as their detecting efficiency and sensitivity are high, satisfying the basic requirements of detecting systems. However, the following drawbacks still exist therein:
(1) The secondary electrons generated by the incident X or .gamma.-photons can not be prevented from passing through between the pixels due to only gas existing between the pixels constituted by the respective anode wires and without any other isolators. Thus, the X or .gamma. photon incident upon any one of the pixels not only causes the respective pixel but also its neighboring pixels to output signals. Therefore, the output signal of each (or each pair) of the anode wires not only reflects the incident of X or .gamma.-ray intensity on the spot, but also reflects the influences of the X or .gamma. rays incident upon other positions, this will make the image "fuzzy". In order to overcome this disadvantageous factor, special computer software and high speed hardware system must be configured to carry out large amount of anti-convolution calculation processing, this significantly increases the difficulty of image processing, and hence the cost.
(2) Each of anode wires is very thin (tens of .mu.m), and has a length of 200-300 mm, thereby noise can be easily produced due to vibration.
(3) The gas-flow working mode currently used needs to configure a gas supply system with bulky pressurized steel gas bottle. In addition, the steel gas bottle should be renewed every period of time (for example every three months).
(4) Gas discharging requires a working voltage of several thousands volts which should be well regulated. Otherwise, it will result in the fluctuation of the gas amplification ratio.
(5) The multi-atom molecule gases (e.g. CH.sub.4) that should be mixed into the working gas may be decomposed during gas discharge and produce sediments. Furthermore, the discharging process itself may damage the surface of the anode wires, therefore, the life of such detecting device is rather short.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved device of gas ionization array detectors for high energy X or .gamma.-ray radiography, which utilizes the ionization effect of the secondary electrons generated by the interaction of the high energy X or .gamma.-ray with the special pressurized high atomic number working gas to output signals, achieving the aims of imaging detection. This detecting device primarily makes use of the drift motions of the ions and electrons under the effect of electrical field to out
REFERENCES:
patent: 4394578 (1983-07-01), Houston et al.
patent: 4583020 (1986-04-01), Cliquet et al.
patent: 5025376 (1991-06-01), Bova et al.
An Jigang
Wu Haifeng
Hanig Richard
Tokar Michael J.
Tsinghua University
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