Conductivity Pulses Induced in Insulating Liquids by Ionizing Radiations

Abstract

Conductivity pulses due to electron collection have been observed in liquid and solid argon exposed to $\ensuremath{\alpha}$- or $\ensuremath{\gamma}$-radiation. The maximum pulse sizes, ${P}_{M}$, for $\ensuremath{\alpha}$-particles depend only on the field strength, $E$, and not on the electrode spacing, proving that the pulse limiting effect is columnar recombination and not electron trapping by impurities. The maximum pulse sizes obey the equation $(\frac{{P}_{M}}{{P}_{0}})=1\ensuremath{-}\mathrm{exp}(\ensuremath{-}A{E}^{\frac{1}{2}})$, where ${P}_{0}$ is the $\ensuremath{\alpha}$-pulse size in an argon gas counter. The counting efficiency for $\ensuremath{\alpha}$-particles is close to 100 percent, but there is some variation in pulse size due to variation of columnar recombination with angle of emission. No $\ensuremath{\alpha}$- or $\ensuremath{\gamma}$-pulses were observed in liquid nitrogen or heptane, but weak $\ensuremath{\alpha}$-induced pulses were observed in liquid methane.The effects of nitrogen and oxygen in solution in liquid argon in decreasing the pulse sizes are interpreted as being due to electron capture by these molecules.