---

In the original formulation of Quantum Mechanics the existence of a precise border between a microscopic world, governed by Quantum Mechanics, and a macroscopic world, described by Classical Mechanics was assumed. Modern theoretical and experimental physics moved that border several times, carefully investigating its definition and making available to observation larger and larger quantum systems. The book examines a paradigmatic case of transition from quantum to classical behavior: a quantum particle is revealed in a tracking chamber as a trajectory obeying the laws of Classical Mechanics. The authors attempt to give a purely quantum-mechanical description of such a behavior.

---

Preface.- Tracks in the cloud chamber.- A time-dependent analysis of Mott´s model.- Modeling atoms as multi-channel point interactions.- Concluding remarks.- Appendix.

---