Study of the liquid-methane ionization chamber

A liquid-methane ionization chamber has potential for high-efficiency neutron detection. As a preliminary study, we constructed a liquid-methane ionization chamber to examine the response to γ-rays, α particles and neutrons. The chamber consisted of three disk-shaped parallel-plate electrodes immersed in liquid methane. Pulse height distributions were obtained using a charge-sensitive preamplifier to detect γ-rays emitted from 60Co, 22Na and 137Cs sources. The concentration of oxygen, an impurity in the liquid methane, was evaluated using an inverse electric-field method that made use of the large collection characteristics of ionized electrons generated by γ-rays. The response of the liquid-methane chamber to γ-rays was analyzed by searching for the position of the Compton-edge in the pulse-height distributions obtained for γ-rays of 1275 and 662 keV emitted by 22Na and 137Cs, respectively. The full-energy peak appeared in the pulse-height distribution of the output signals for the detection of α particles emitted by 241Am. A continuous pulse-height distribution was observed for neutrons emitted from an Am-Be source.