School of Physics - Research Publications

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    An algebraic solution of the multichannel problem applied to low energy nucleon-nucleus scattering
    Amos, K. ; Canton, L. ; Pisent, G. ; Svenne, J. P. ; van der Knijff, D. ( 2003)
    Compound resonances in nucleon-nucleus scattering are related to the discrete spectrum of the target. Such resonances can be studied in a unified and general framework by a scattering model that uses sturmian expansions of postulated multichannel interactions between the colliding nuclei. Associated with such expanded multichannel interactions are algebraic multichannel scattering matrices. The matrix structure of the inherent Green functions not only facilitates extraction of the sub-threshold (compound nucleus) bound state spin-parity values and energies but also readily gives the energies and widths of resonances in the scattering regime. We exploited also the ability of the sturmian-expansion method to deal with non-local interactions to take into account the strong non-local effects introduced by the Pauli principle. As an example, we have used the collective model (to second order) to define a multichannel potential matrix for low energy neutron-C12 scattering allowing coupling between the 0+ (ground), 2+ (4.4389 MeV), and 0+ (7.64 MeV) states. The algebraic S matrix for this system has been evaluated and the sub-threshold bound states as well as cross sections and polarizations as functions of energy are predicted. The results are reflected in the actual measured data, and are shown to be consistent with expectations as may be based upon a shell model description of the target and of the compound nucleus.
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    Diffraction-contrast imaging of cold atoms
    Turner, Lincoln D. ; Domen, Kenian E. F. M. ; Scholten, Robert E. ( 2005-01)
    We consider the inverse problem of in-line holography, applied to minimally-destructive imagingof cold atom clouds. Absorption imaging near resonance provides a simple, but destructive measurementof atom column density. Imaging off resonance greatly reduces heating, and sequential imagesmay be taken. Under the conditions required for off-resonant imaging, the generally-intractable inverseproblem may be linearized. A minimally-destructive, quantitative and high-resolution imageof the atom cloud column density is then retrieved from a single diffraction pattern.