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Nuclear Structure Studies at HI g S

Nuclear Structure Studies at HI g S. Henry R. Weller The HI g S Nuclear Physics Program. The energy spread and the intensity have major impacts on nuclear structure experiments.

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Nuclear Structure Studies at HI g S

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  1. Nuclear Structure Studies at HIgS Henry R. Weller The HIgS Nuclear Physics Program HIGS2 Workshop June 3-4, 2013

  2. The energy spread and the intensity have major impacts on nuclear structure experiments • Increased intensities will allow for much greater speed in obtaining results in NRF studies, especially in coincidence experiments. This will have a great impact on studies of decay patterns of low lying collective modes such as the M1 Scissors Mode and the Pygmy Dipole Resonance. • Reducing the present energy spread of ~3% to a value of 0.5% (or less?) will have a major impact on NRF studies. • Will provide precision measurements of the polarizabilities of light nuclei via Compton Scattering. HIGS2 Workshop June 3-4, 2013

  3. The g3 CampaignSetup installed at HIgS in summer of 2012.Four 60% HPGe, four 3”x 3” LaBr3 and four 1.5” x 1.5” LaBr3 HIGS2 Workshop June 3-4, 2013

  4. The g3 Campaign The combination of NRF with g-g coincidence spectroscopy is the ideal method for investigating the decay pattern of the Scissors M1 mode and the Pygmy Dipole Resonance. Recent experiments have shown that a major part of the dipole-excited states decay through cascades instead of direct transitions to the ground state. But the detailed decay pattern is unknown. This should reveal new information on the detailed structure of the M1 and E1 excited states. This is the main intention of the experimental campaign using the new g3installation. This work has begun at HIgS but is clearly limited by the beam intensities and the energy resolution of the beams. HIGS2 Workshop June 3-4, 2013

  5. Example of coincidence spectra HIGS2 Workshop June 3-4, 2013

  6. Compton scattering at very low energies to determine the polarizabilities of6Li (running right now) and 4He (to be proposed on Wednesday) Polarizabilities of light nuclei Polarizabilities have been measured for d and 3He, but only the sum rule result exists for 4He. These are fundamental constants of these nuclei. Predictions based on modern two and three nucleon potential models exist and need to be tested. These quantities are also important for high precision tests of quantum electrodynamics and for accurate determination of the nuclear charge radius from spectroscopic measurements in helium atoms where they amount to 28(3) kHz for the 1S-2S transition in 4He+, for example. HIGS2 Workshop June 3-4, 2013

  7. Projected results for running at 3 energies (3, 9 and 15 MeV) for a total of 365 hours. HIGS2 Workshop June 3-4, 2013

  8. The double-humped potential model could not fit the new data in a consistent manner.The triple-humped barrier parameters were adjusted to best describe the photofission data and the (g,n) data using the EMPIRE-3.1 code. The hyperdeformed third potential minimum, when adjusted to reproduce the 5.5 MeV resonance, predicts an additional resonance at 4.55 MeV. HIGS2 Workshop June 3-4, 2013

  9. Impact on Photofission Studies • An increase in the beam intensity from the present ~100 g/eV s to 106 g/eV s with a decrease in energy resolution to ~0.5% or better will make it possible to identify sub-barrier transmission resonances in the fission channel having integrated cross sections 10 times smaller than presently possible. (Gs ~0.1 eV b instead of 10 eV b). • The narrow energy bandwidth will lead to a significant reduction in the background from non-resonant processes. • This will allow for preferential population and identification of vibrational resonances in the photofission cross section. • The present model for 238U predicts a resonance at E = 4.55 MeV. This could be confirmed using the HIgS2 beams. HIGS2 Workshop June 3-4, 2013

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