  A salient feature of quantum mechanics is the inherent property of collective
quantum motion, when apparent independent quasiparticles move in highly
correlated trajectories, resulting in strongly enhanced transition
probabilities. To assess the extend of a collective quantity requires an
appropriate definition of the uncorrelated average motion, often expressed by
single particle units. A well known example in nuclear physics is the Weisskopf
unit for electromagnetic transitions which reveals different aspects of
collective motion. In this paper we define the corresponding single particle
unit for alpha decay following Weisskopf's derivations. We evaluate the alpha
decay amplitude as induced by four uncorrelated/non-interacting protons and
neutrons and compare it with the one extracted from observed decay rates. Our
definition elucidates the collectivity in alpha decay and facilitates an
unified description of all alpha decay processes along the nuclear chart. Our
formalism is also applicable to other particle decay processes.
