Patent Application
20110095199
The present invention generally relates to an ionization chamber and, more particularly, to an ionization chamber having a guard electrode capable of collecting all signals produced in a chamber to avoid any signal loss and achieve more accurate measurement.
An ionization chamber is usually applied for testing and measuring an output of an irradiation device such as an X-ray machine, a cobalt 60 teletherapy apparatus, a linear accelerator and various radioactive measuring instruments to determine whether or not the irradiation device achieves the expected stability. To maximize the current output of an ionization chamber and minimize the space for a change of reaction, the ionization chamber is generally installed at the geometric center of the front of the irradiation device. Meanwhile, all possible factors causing interferences to the output of the device should be lowered to improve the accuracy of the measurement. To meet the aforementioned requirements, a good ionization chamber should be characterized in that:
1. The wall of the ionization chamber should be as thin as possible to reduce the possibility of output-blocking and spectrum changes. Furthermore, the ionization chamber should come with consistent beam emission ranges and thickness to prevent excessively large changes of the output homogeneity. Please refer to
2. The guard electrode 1313 has an effect of keeping an electric field vertical. However, the signals cannot be collected stably when an applied voltage source is changed to cause a change of the signals within an effective range of the electric field in the chamber 11.
3. Since the electric fields applied to the guard electrode 1313 and the inner electrode 1312 have the same electric potential, the installation of the guard electrode 1313 can prevent a current leakage. However, the second electrode plate 13 only has an inner electrode 1312 disposed at its upper layer, and its bottom 132 or its lateral side 133 is made of plastic without any graphite coating. Therefore, there is still a chance for the occurrence of current leakages that will affect the accuracy of collected signals.
In view of the description above, finding a way of overcoming the shortcomings of the conventional ionization chambers becomes an important subject for those skilled in the art, and an ionization chamber that can overcome the drawbacks of the prior art is needed.
It is one object of the invention to overcome the drawbacks of the prior art by providing an ionization chamber that can completely and effectively connect ionization signals in a chamber by a center electrode plate to avoid a signal loss and improve the accuracy of the test result of the ionization chamber.
It is another object of the present invention to provide an ionization chamber using a center electrode plate for maintaining a constant volume in the chamber and preventing a change of electric field that may cause a change to the effective volume in the chamber, so as to improve the stability of the test result of the ionization chamber.
It is still another object of the present invention to provide an ionization chamber that has a complete effective guard electrode for isolating any current leakage occurred between the center electrode plate and the outer electrodes and avoiding the possibility of having a current leakage.
In order to achieve the foregoing objectives, the present invention provides an ionization chamber comprising: a chamber, being a hollow body made of conductive metal and comprising a plurality of support pins and a signal pin protruded from an inner wall of said chamber; two outer electrode plates, fixed to upper and lower sides of said chamber respectively, and each having a first conductive portion disposed on one side of said two outer electrode plates and facing said chamber; and a center electrode plate, fixed in said chamber and comprising a second conductive portion, for collecting an ionization signal in said chamber.
The objects and spirits of the embodiments of the present invention will be readily understood by the accompanying drawings and detailed descriptions, wherein:
The present invention can be exemplified but not limited by various embodiments as described hereinafter.
Please refer to
The chamber 31 is a cylindrical hollow body made of conductive metal, which could be aluminum, copper, iron or one of combinations thereof. The chamber 31 has a plurality of support pins 311 and a signal pin 312 protruded from the inner wall of the chamber 31. The two outer electrode plates 32 are fixed respectively onto the upper and lower sides of the chamber 31 and made of a plastic material such as a polystyrene film. One side of the chamber 30 is coated with graphite to define a first conductive portion 321. The center electrode plate 33 is fixed in the chamber 31 for collecting ionization signals in the chamber 31 and made of a plastic material, and the whole surface of the center electrode plate 33 is coated with graphite to define a conductor of a second conductive portion 331.
The support pin 311 and the signal pin 312 respectively have an end fixed to the chamber 31, and another end having a slot 3111, 3121 for holding the center electrode plate 33. The support pin 311 comprises a guard electrode 3112, an electrode insulation pin 3113 and an outer insulation ring 3114. The guard electrode 3112 is made of metal such as aluminum, copper, iron, or combinations thereof. Both ends of the guard electrode 3112 are wrapped by the electrode insulation pin 3113 and the outer insulation ring 3114 to define an insulation shield for significantly reducing the current leakage from the guard electrode 3112. Furthermore, the signal pin 312 has a signal line 3122 electrically coupled to the center electrode plate 33 for outputting ionization signals in the chamber 31, and the external edge of the signal line is wrapped sequentially by an inner insulation ring 3123, a guard ring 3124 and an outer insulation ring 3125. These three layers of insulators can lower the possibility of current leakages.
Furthermore, the center electrode plate 33 is clamped by the slots 3111, 3121 of the support pin 311 and the signal pin 312 and fixed into the chamber 31 and disposed equidistantly from the two outer electrode plates 32. In other words, the center electrode plate 33 is installed at an interval of the same height and parallelly between the two outer electrode plates 32. The two outer electrode plates 32 are fixed respectively onto both upper and lower sides of the chamber 31 by screws, and the thickness of the two outer electrode plates is determined by the measured intensity of radiation, and factors such as blocking the output beams, changing the spectrum or losing the electron equilibrium should be taken into consideration. These factors are conventionally known, and thus will not be described herein.
Referring to
In view of the description above, the center electrode plate is installed in the chamber, and thus the ionization signals produced in the chamber can be collected completely by the center electrode plate. The invention does not only avoid signal loss, but also improves the accuracy of the test result of the ionization chamber. On the other hand, the center electrode plate can maintain a constant volume in the chamber and improve the stability of the test result of the ionization chamber by avoiding a change of the electric field and a change of the effective volume in the chamber. Furthermore, the protection electrode is wrapped by the electrode insulation pin and the outer insulation ring so that an insulation shield is formed between both ends of the protection electrode and the center electrode plate to siignificantly reduce the possibility of current leakages from the protection electrode. Such arrangement also improves the accuracy of the test result of the ionization chamber.
The present invention discloses an ionization chamber having a guard electrode capable of collecting all signals produced in a chamber to avoid any signal loss and achieve more accurate measurement. Therefore, the present invention is useful, novel and non-obvious.
Although this invention has been disclosed and illustrated with reference to particular embodiments, the principles involved are susceptible for use in numerous other embodiments that will be apparent to persons skilled in the art. This invention is, therefore, to be limited only as indicated by the scope of the appended claims.
