  The use of gas expansions to generate atomic or molecular beams has become a
standard technique in nuclear and hadron physics for the production of
polarized ion beams and gas targets. A direct simulation Monte Carlo method was
used to understand the processes occurring in an expansion of highly
dissociated hydrogen or deuterium gas at low densities. The results were
verified in several measurements including time-of-flight and beam-profile
determinations which showed that the supersonic gas expansions can properly be
described by the Monte Carlo calculations. Additionally a new method of beam
formation, the hollow carrier jet, was tested under the conditions of the
atomic beam source operation.
