抄録
A homemade airflow pulse ionization chamber system was inexpensively made for the measurement of alpha-radioactivity in atmosphere. The signal electrode of the ionization chamber was divided into two for the reduction of common-mode noises, and pulse signals from each electrode were treated with electronic circuits based on a field programmable gate array (FPGA). Multichannel pulse-height analyzers, multichannel scalers and other related electronic modules were constructed for the analysis of alpha-radioactivity in the FPGA. The symmetrical structure of the electrodes of the ionization chamber was effective in the cancellation of common-mode noises induced by commercial electricity, mechanical vibration and others. An alpha-ray source (241Am) was set inside the ionization chamber for the monitoring of air conditions. It was confirmed from an experiment with a mantle containing thorium ore that radon alpha-radioactivity in air could be well measured with this system.
