MODELING OF CHARGE TRANSPORT IN THE ACTIVE VOLUME OF THE IONIZATION FISSION CHAMBER IN CURRENT MODE
https://doi.org/10.29235/1561-2430-2018-54-1-97-109
Abstract
Charge transport in the active volume of the cylindrical ionization fission chamber (FC) in the current mode has been studied. The model is based on the continuity equations for ions and electrons, as well as on Poisson’s equation for the electric field. The source for the continuity equations is calculated taking into account a correct distribution of the initial ionization density in the active volume of the chamber and the charge, mass, and energy dependent distributions of the fission fragments. The distributions of the ion and electron density and electric fields inside the active volume are found for two types of chambers – miniature chambers and “large” chambers with the consideration of the space charge. The correct algorithm for calculation of the beginning of the plateau of the current-voltage characteristic – the minimum voltage on the FC to provide the stationary operation of the chamber is given. It is shown that the often used condition of the electric field absence at the anode E (ra ) = 0 to determine this value is incorrect, since it leads to complex values of the electric field inside the chamber active volume. Neglecting the processes of ion diffusion and recombination, the sensitivity and output current of the chamber in the stationary mode are calculated. Calculations have been carried out for miniature and “large” chambers. It has been shown that the use of the approximation for the generation density of ion pairs by the fission fragment along its track to be constant, often used in practice for “large” chambers, leads to significant errors when estimating the densities of ions, electrons and electric fields inside the FC; at that, the sensitivity may differ by an order of magnitude.
About the Authors
Le Thi Dieu Hien
Belarusian State University, Minsk
Belarus
Postgraduate Student
Belarus
Postgraduate Student
A. A. Khrutchinsky
Institute for Nuclear Problems of the Belarusian State University, Minsk
Belarus
Ph. D. (Physics and Mathematics), Head of the Laboratory, Institute for Nuclear Problems
Belarus
Ph. D. (Physics and Mathematics), Head of the Laboratory, Institute for Nuclear Problems
S. A. Kuten
Institute for Nuclear Problems of the Belarusian State University, Minsk
Belarus
Ph. D. (Physics and Mathematics), Leading Researcher
Belarus
Ph. D. (Physics and Mathematics), Leading Researcher
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