Radiation from an @UT07492@ @L03447@ ionizes certain species in the @C00863@. A potential difference is applied and the resulting @I03183@ current is detected. The detector is only useful for substances with @I03183@ potentials below about \(11\ \text{eV}\). This makes it quite useful for detecting one component of a combined @E02040@ when the other component, for instance nitrogen, has a high @I03208@. The detector has a small linear dynamic range and is capable of detecting substances below \(1\ \text{ppmv}\).