Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1995-06-01
1996-10-29
Cain, Edward J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
2503361, 2504721, 524495, C08K 300
Patent
active
055696996
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a polymer composition, equivalent to the biological tissue and having a very high resistivity. The invention also relates to the use of this polymer composition in the production of the cathode of a proportional counter equivalent to the biological tissue, as well as proportional counters equivalent to the biological tissue incorporating a cathode made with the aid of the aforementioned polymer composition.
Any person working in a nuclear power station or in the vicinity of a radioactive source must permanently carry a dosimeter or a radioactivity measurement counter. These apparatuses make it possible on the one hand to establish whether or not said person has been exposed to radiation and on the other to quantify the absorbed dose and the dose equivalent. These counters are of two types, the first or "passive" type only making it possible to record the radiation quantity received, but requiring a subsequent development treatment in order to obtain results and the second or "active" type combined with a display makes it possible to obtain the absorbed radiation dose in real time.
Among the active counters, there are biological tissue-equivalent proportional counters, i.e. counters intended to simulate a biological tissue volume of a few micrometers. The term biological tissue has a number of meanings and here refers exclusively to the biological tissue reproducing human striated muscles. In general terms, this type of counter comprises an enclosure defined by a sheath forming a cathode. This sheath is made from a biological tissue-equivalent material. The enclosure is filled with a gaseous mixture, which must have biological tissue-equivalent properties, so that the interactions taking place in said counter are identical to those occurring in the human tissue. Finally, an anode is provided in the centre of said enclosure. This anode is connected to means for amplifying the electrical signal supplied by said anode.
In order that a material is equivalent to the biological tissue, it is necessary for its composition to be as close as possible to that of the biological tissue standard defined by the ICRU (International Commission on Radiation Units and Measurements), 1964.
The theoretical mass atomic composition of a biological tissue-equivalent material is as follows:
______________________________________ hydrogen: 10.20% magnesium: 0.02%
carbon: 12.30% phosphorus:
0.20%
nitrogen: 3.50% sulphur: 0.50%
oxygen: 72.90% potassium: 0.30%
sodium: 0.08% calcium: 0.07%.
______________________________________
Among these constituents, hydrogen and nitrogen are particularly important with respect to the interactions of neutrons with the biological tissue-equivalent material. Therefore priority is given to the respecting of their weights. The mean atomic number of the material obtained is also respected, so as to obtain a good equivalence to the biological tissue of the material during its interaction with photons. Thus, photons mainly interact with electrons. The interaction number is in an initial approximation proportional to the number of electrons contained in the material. The mean atomic number is calculated according to the formula Z=(.SIGMA..sub.i n.sub.i z.sub.i)/(.SIGMA..sub.i n.sub.i), n.sub.i representing the number of atoms of the constituent i per unit of mass and z.sub.i the atomic number of the constituent i. This mean atomic number corresponds to the average number of electrons "attached" to an atom. It is therefore an overall quantitative indicator of the interaction of the photons with the material.
The prior art also discloses a biological tissue-equivalent material used at present for producing certain components of biological tissue-equivalent proportional counters. This material is a conductive polymer known under the name A150 (registered trademark), developed by F. Shonka. It is in particular described in an article by James B. Smather and Victor A. Ohe, "Composition of A-150 tissue equivalent plastic", Medical Physics, vol. 4, No. 1, Jan.-Feb.
Barthe Jean
Bordy Jean-Marc
Cain Edward J.
Commissariat a l''Energie Atomique
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