Alpha particle types: eventually named alpha, beta, and gamma by Rutherford, based on penetration of objects and deflection by a magnetic field. Alpha rays were defined by Rutherford as those having the lowest penetration of ordinary objects. Rutherford's work also included measurements of the ratio of an alpha particle's mass to its charge, which led him to the hypothesis that alpha particles were doubly charged helium ions (later shown to be bare helium nuclei). In 1907, Ernest Rutherford and Thomas Royds finally proved that alpha particles were indeed helium ions. To do this they allowed alpha particles to penetrate a very thin
Alpha decay done against electromagnetic repulsion to bring an alpha particle from infinity to a point near the nucleus just outside the range of the nuclear force's influence. An alpha particle can be thought of as being inside a potential barrier whose walls are 25 MeV. However, decay alpha particles only have kinetic energies of 4 MeV to about 9 MeV, far less than the energy needed to escape. Quantum mechanics, however, provides a ready explanation, via the mechanism of quantum tunnelling. The quantum tunnelling theory of alpha decay, independently developed by George Gamow and Ronald Wilfred Gurney and Edward Condon in