Quasiclassical description of bremsstrahlung accompanying alpha decay   including quadrupole radiation
  We present a quasiclassical theory of alpha decay accompanied by bremsstrahlung with a special emphasis on the case of 210Po, with the aim of finding a unified description that incorporates both the radiation during the tunneling through the Coulomb wall and the finite energy E_gamma of the radiated photon up to E_gamma on the order of Q_alpha/sqrt(eta), where Q_alpha is the alpha-decay Q-value and eta is the Sommerfeld parameter. The corrections with respect to previous quasiclassical investigations are found to be substantial, and excellent agreement with a full quantum mechanical treatment is achieved. Furthermore, we find that a dipole-quadrupole interference significantly changes the alpha-gamma angular correlation. We obtain good agreement between our theoretical predictions and experimental results. 
U. D. Jentschura, A.I. Milstein, I.S. Terekhov, H. Boie, H. Scheit, D.   Schwalm