Standard measurement of processing level gamma ray dose rates with a parallel-plate ionization chamber
AbstractAbstract
[en] An accurate and practical method of measuring the processing level exposure rates of 60Co gamma rays with an ionization chamber was studied to develop standardization of a dosimetry system with wide and flexible applicability for current gamma ray irradiation facilities. A parallel-plate, free-air cavity ionization chamber was designed with an aluminium wall and an electrode gap of 1 mm having some geometries for accurate measurement of high exposure rates. The active collection volume of the chamber was estimated within an accuracy of +-1%. As a result of experiments, the polarity effect on the saturation current was observed without beam collimation, and was found to have its origin in extraneous current generated in the signal cable, the chamber stem and the connector outside the ionization volume of the chamber. The net collection current can be evaluated by reversing polarity and taking the mean value of the measured currents. Other influences such as the saturation characteristics of the ionization chamber, gamma ray dose attenuation in the chamber wall, a scattered gamma ray and a temperature rise of the cavity gas during irradiation were also examined. For the standard 60Co gamma ray radiation field of the order of 0.258 C.kg-1.h-1(1 kR.h-1), the exposure rate values absolutely measured with the chamber agree with the standard values within an accuracy of +-1%; these agreements have also been maintained for as long as six years. In comparing high exposure rate measurements with different ionization chambers, good agreement (within +-2%) was obtained over the range from 5.16 C.kg-1.h-1(20 kR.h-1) to 516 C.kg-1.h-1(2 MR.h-1). It was proved experimentally that the parallel-plate cavity ionization chamber absolutely calibrated in the standardization field (even of the order of 0.258 C.kg-1.h-1(1 kR/h)) can be applied with good reliability for processing level radiation fields up to 774 C.kg-1.h-1(3 MR/h), even with broad beam geometry and an appreciable amount of scattered gamma rays. (author)
Secondary Subject
Source
International Atomic Energy Agency, Vienna (Austria); Proceedings series; 449 p; ISBN 92-0-010085-6;
; 1985; p. 203-220; IAEA; Vienna (Austria); International symposium on high-dose dosimetry; Vienna (Austria); 8-12 Oct 1984; IAEA-SM--272/17

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Book
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Conference; Numerical Data
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Descriptors (DEC)
BETA DECAY RADIOISOTOPES, BETA-MINUS DECAY RADIOISOTOPES, COBALT ISOTOPES, CURRENTS, DATA, DOSIMETRY, INFORMATION, INTERMEDIATE MASS NUCLEI, ISOMERIC TRANSITION ISOTOPES, ISOTOPES, MEASURING INSTRUMENTS, MINUTES LIVING RADIOISOTOPES, NUCLEI, NUMERICAL DATA, ODD-ODD NUCLEI, RADIATION DETECTORS, RADIOISOTOPES, YEARS LIVING RADIOISOTOPES
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