A weak beta source and a high potential raise the helium atom of the @C00863@ to a @M03872@ state. All other substances having an @I03208@ lower than \(18\ \text{eV}\) are ionized, and the current that results is used to measure the components. The detector is usually employed to measure inorganic compounds at concentrations between \(0.1\) and \(10\ \text{ppmv}\). It has a @L03558@ of about \(10^{2}\) but is somewhat @U06569@ and requires great care to ensure the helium purity and to eliminate all leaks in the system.