An apparatus for measuring the energy and angular distribution of secondary electrons emitted from water vapor by fast heavy-ion impact

摘要

An apparatus has been built to measure the doubly differential cross-section of electron emission from water vapor with fast heavy-ion impact (6-25 MeV/u). Ejected electrons are detected by a Chevron-type microchannel plate assembly after being analyzed by a 45degrees inclined parallel-plate electrostatic spectrometer, which is rotatable from 200 to 1600 with respect to the incident-beam direction. The scattering chamber is made of iron, and both the electron spectrometer and the detector assembly are mounted in a p-metal housing in order to suppress the effects of stray magnetic fields (including that of Earth). Water vapor is emitted into the interaction region from a nozzle of 1 x 15 mm(2) aperture, and is instantly frozen and trapped as ice on a stainless-steel panel, which is cooled by liquid N-2. With this water-vapor generation and collection system, a stable water-vapor jet (10(-2)-10(-3) Torr) was obtained without deteriorating the pressure in the scattering chamber (similar to4 x 10(-7) Torr with a vapor flow of 40.0 cc/min). Using the present apparatus, we have successfully measured the energy and angular distribution (7-10,000 eV and 20-160degrees) of secondary electrons produced in the collision of a 6.0-MeV/u He2+ ion with water vapor; binary-encounter collision peaks were clearly observed at the several keV region for angles smaller than 90degrees, as well as the K-LL Auger peak of oxygen at similar to500 eV for all angles. (C) 2004 Elsevier B.V. All rights reserved.