ABSTRACT
The quadrupole potential involves the angle between the radius to the a-particle and the axis of the nucleus; it is a particular case of noncentral interactions for which the relative orbital angular momentum is not constant. The fact that certain of the naturally occurring radioactive elements emit α-particles was one of the first discoveries in the early days of modern physics; by 1908 E. Rutherford had conclusively demonstrated that α-particles are 4He nuclei. One of the first successful applications of quantum mechanics to a problem in nuclear physics was the theory of α-decay, presented in 1928 independently by G. Gamow and by E. U. Condon and R. W. Gurney. This chapter considers the simplest one-body form of the theory, in which the barrier is entirely Coulomb and the potential inside the barrier is constant, that is, the "traditional" potential. The angular distribution of a wave is closely related to the relative amplitudes of the constituent angular-momentum states.
