  The Giant Dipole Resonance (GDR), which is conventionally described as due to
collective motion, is instead shown to be the result of a sudden increase in
level density at the 2h{\omega} shell closure. The energy of the GDR closely
follows the shell model harmonic oscillator energy model where h{\omega} =
39A^-1/3, for heavy nuclei. A better fit covering the entire mass range is
given by h{\omega} = 47:55(0:13)(A^-1/3 - A^-2/3). The GDR is shown to be
composed of a lower energy peak, E1, corresponding to the population of levels
with oblate deformation and a higher energy peak, E2 corresponding to the
population of levels with prolate deformation. The peak energy separation is
proportional to the \beta_2 deformation and given by E2-E1 =
11:03(0:22)|\beta_2|. The total photonuclear cross section, sigma = sigma1 +
sigma2, populating the GDR is proportional to the level density at the GDR and
is given by sigma = 0:483(0:006)A^4/3 where sigma1 = sigma2. The widths of the
two GDR peaks are consistent with Nilsson model predictions and found to be
Gamma1 = 7:41(0:15)A^-1/6 MeV and Gamma2 = 11:13(0:16)A^-1/6 respectively. The
Standard Lorentzian model parameters are fitt to high accuracy as a function of
mass and deformation and can be applied reliably to all nuclei. It is shown
that the energies of pygmy and spin flip resonances correspond to the E =
h{\omega} harmonic oscillator energy and that the giant quadrupole (GQR), giant
monopole (GMR), and giant octupole (GOR) resonances coincide with the E = 2-4
h{\omega} harmonic oscillator energies where the level density suddenly
increases at the shell gaps.

Nuclear Theory