Beam-foil-gas spectroscopy - A technique for studying steady-state non-equilibrium processes.

When a thin foil is inserted in the beam of a beam-gas experiment, the beam particle state populations are driven far from their beam-gas equilibrium values. Downstream from the foil, the 'new beam' and gas species interact to produce a new equilibrium, usually different from the beam-gas equilibrium. Experimental results are presented to demonstrate this effect and to show how relative cross-section measurements can be used to study the beam-foil interaction.