Cathode shape dependence of gas ionization chamber on electron collection in ΔE − E telescope ERDA

Abstract

Our ΔE − E telescope elastic recoil detection analysis (ERDA) system employed a gas ionization chamber (GIC), which consisted of a U-shaped cathode, Frisch grid, and anode. The cathode shape was designed to downsize the electrodes. The difference of performance between the U-shaped and planar shaped cathodes, however, has not been studied well, yet. Therefore, we quantitatively evaluated the influence using the U-shaped cathode on ΔE − E telescope ERDA. The performances of U-shaped and planar shaped cathodes were compared from the viewpoint of a recoil counting loss due to the stagnation inducing a recombination of ion–electron pairs, and the electron uptake by the Frisch grid. No significant difference occurs between the two cathodes from the viewpoint of O recoil yields. The inhomogeneous electric field formed by the U-shaped cathode, however, induced the electron collection suppression, which leads to an attenuation of ΔE pulse heights. In our ERDA condition, the lateral straggling of recoils is suppressed due to their high energy, so that the attenuation of ΔE pulse heights is not severe and does not impair the reliability of ΔE − E telescope ERDA. These results show that the U-shaped cathode can also be used safely for ΔE − E telescope ERDA, and that GICs have a flexibility in the electrode shape, which is useful to make GICs more compact.