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The single-particle unit for alpha decay

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.