1 Introduction to Modern Physics
1.25.1 Alpha Decay Tunneling
Alpha decay is considered a tunneling phenomenon in which α particles with
kinetic energies between 4 MeV and 9 MeV tunnel through a potential barrier
of the order of 30 MeV. The tunneling theory of the α decay was proposed
by George Gamow in 1928. Inside the parent nucleus (atomic number Z)
the α particle is free yet confined to the nuclear potential well by the strong
nuclear force. The dimension of the well is of the order of few fm; once the α
particle is beyond this distance from the center of the parent nucleus, it only
experiences Coulomb repulsion between its charge 2e and the charge of the
daughter nucleus (Z − 2)e.
A classical α particle with kinetic energy EK < 9 MeV cannot overcome
a potential barrier with EP > 30 MeV. On the other hand, a α particle with
wave-like attributes may tunnel through the potential barrier and escape the
parent nucleus through this purely quantum-mechanical phenomenon.
1.25.2