NUKLEONIKA 2007, 52(1):7-12

INITIAL RECOMBINATION OF IONS IN IONIZATION CHAMBERS FILLED WITH HYDROCARBON GASES

Michał A. Gryziński1, Natalia Golnik2, Mieczysław Zielczyński3

1 Institute of Environmental Engineering Systems, Warsaw University of Technology, 20 Nowowiejska Str., 00-653 Warsaw, Poland
2 Institute of Precision and Biomedical Engineering, Warsaw University of Technology, 8 Saint A. Boboli Str., 02-525 Warsaw, Poland 3 Institute of Atomic Energy, 05-400 Otwock-Świerk, Poland


Data on the initial recombination of ions are needed for designing recombination chambers, used in mixed radiation dosimetry in order to obtain information about radiation quality. Nevertheless, experimental data for pressurized gases are scarce, whereas reliable theoretical models are absent.
The paper provides experimental data on the initial recombination in hydrocarbon gases (methane, ethane and propane) depending on gas pressure up to 1.8 MPa. The data were derived from the measurements of saturation curves of a tissue equivalent recombination chamber of an REM-2 type, in reference radiation fields of 137Cs and 239Pu-Be sources. Ion recombination due to volume recombination and back diffusion of ions was subtracted from the measured values of ion collection efficiency. The values of gas parameters needed for the subtraction procedure were determined by measurements of saturation curves of the chamber at several dose rates for each gas pressure. The important practical rule resulting from the experiments is that in the first approximation the initial recombination does not depend on the kind of the hydrocarbon gas but only on its density in the chamber.