Multidetection (e,2e) electron spectrometer

Abstract

An electron-pair coincidence spectrometer, using only a single electrostatic toroidal analyzer, has been developed for the study of final-state electron pairs following ionization by electron impact. The system allows the angular and energy distribution of electron pairs emitted in a selected plane to be detected by a single planar microchannel plate stack followed by two position-sensitive semicircular wedge-and-strip anodes. The output signals are decoded into energy, angle and nanosecond coincidence timing information from which relative energy and angular triple differential ionization cross sections are determined. The performance of the instrument is indicated by He I photoionization of krypton and the first measurements of differential cross sections for electron-impact ionization of the P3∕22 and P1∕22 states of krypton. For perpendicular-plane scattering and an excess energy of 10 eV for the P3∕22 state and 0.67 eV less for the P1∕22 state, these cross sections are significantly different for the two states and indicate the importance of the final state of the ion in the scattering process.