How did quantum tunneling help explain alpha decay?

In classical physics, an alpha particle trapped within a nucleus would be unable to escape if its energy were lower than the potential barrier surrounding it. However, quantum mechanics reveals that particles possess a nonvanishing probability of existing in regions of negative kinetic energy, allowing them to tunnel through these energetically forbidden barriers.12

In the context of alpha decay, the electrostatic repulsive potential between the alpha particle and the daughter nucleus creates a potential barrier. Even though the energy of the alpha particle is often significantly lower than the height of this barrier, the particle can "tunnel" through it and emerge from the nucleus.12

This theory, formulated independently by George Gamow, Ronald W. Gurney, and Edward Condon in 1928, successfully explained the wide range of observed half-lives for alpha emitters. It demonstrates that the probability of tunneling—and thus the decay rate—is extremely sensitive to the particle's energy, providing a robust theoretical basis for the empirical Geiger-Nuttall law.12