The High-Intensity g-ray Source (HIgS) utilizing the intra-cavity back-scattering of free electron laser photons allows the production of a unique beam of high-flux g -rays with high polarization and selectable energy resolution which is ideal for low-energy (g -scattering experiments. Highly-sensitivity studies of E1 and M1 excitations have been performed at HIgS on nuclei close to a neutron or proton closed shell. A wide variety of nuclear structure phenomena have been investigated with the nuclear resonance fluorescence technique. Spectroscopic experiments on two-phonon excitations of even-even nuclei near closed shells revealed large magnetic dipole strengths in heavy deformed nuclei. The corres-ponding excitations have been associated with scissors-like oscillations of the deformed proton density distribution against the neutron distribution. This excitation mode is accordingly called the "scissors mode". Large electric dipole transitions to the ground states have been observed in spherical nuclei near Z = 50 and N = 82. These transitions are assumed to arise from the coupling of quadru-pole and octupole vibrational modes of the nucleus. In neutron rich nuclei, a so-called pygmy dipole resonance has been predicted as a clustering of states close to the neutron separation energies Ex ~ 5.5 - 8 MeV. The observations will be compared with calculations using quasiparticle random-phase approximations (QRPA) with multiphonon extension. The second part of the talk will summarize the experimental program at TUNL to measure (n,xng) excitation functions on actinides with the goal of improving the partial cross section database for the National Nuclear Security Administration's Stockpile Stewardship Program. The main experimental effort is devoted to the energy regime, 4 $\leq$ En $\leq$ 18 MeV, using monoenergetic and pulsed neutron beams. An example of this technique is the recent measurement of the 240Am (T$_(1/2)$ =50 h) production cross section using the 241Am(n,2n) reaction. Our recent results, as well as an overview of our future plans, will be presented.
Coffee & Cookies before the presentation at 3:50 pm, and refreshments after the presentation will both be served in Room 128.