We discuss the role of environment in quantum measurement processes.
Solvable models can be used to show how interaction with environment
drives a quantum object to behave more classically. We analyze a quantum
system consisting of a particle travelling in a model-environment made up
of localized two-level subsystems. In this setting we discuss within a
nonperturbative approach a conjecture, made by N. F. Mott in 1929, on the
appearing of straight tracks in a tracking chamber.