48 research outputs found
Coupled-channel effective field theory and proton-Li scattering
We apply the renormalisation group (RG) to analyse scattering by short-range
forces in systems with coupled channels. For two S-wave channels, we find three
fixed points, corresponding to systems with zero, one or two bound or virtual
states at threshold. We use the RG to determine the power countings for the
resulting effective field theories. In the case of a single low-energy state,
the resulting theory takes the form of an effective-range expansion in the
strongly interacting channel. We also extend the analysis to include the
effects of the Coulomb interaction between charged particles. The approach is
then applied to the coupled Li and Be channels which couple to
a state of Be very close to the Be threshold. At
next-to-leading order, we are able to get a good description of the Li
phase shift and the Be(n,p)Li cross section using four parameters.
Fits at one order higher are similarly good but the available data are not
sufficient to determine all five parameters uniquely.Comment: 22 pages, 2 figures, RevTeX4, typos corrected, accepted for
publication in European Physical Journal
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Averaging sigma(n,. gamma. ) in the transition region E/sub n/ = 1-150 keV
The technique of determining a smooth average neutron capture cross section by least squares adjustment of strength functions is illustrated for /sup 179/Hf(n,..gamma..) high resolution data from ORELA. The s-, p- and d-wave neutron strength functions and GAMMA/sub ..gamma..// <D/sub l=0> found agree well with systematics, model calculations and other experimental information despite their strong correlation when determined solely from the capture data
Evaluation of the /sup 232/Th neutron capture cross section above 3 keV
This memo describes an evaluation of the /sup 232/Th neutron capture cross section in the neutron energy range from 3 keV to 20 MeV. Most existing differential measurements are reviewed, and some data are renormalized to current values of the standards. Several experimentally determined sets of average resonance parameters are also discussed. From 3 to 50 keV the evaluated cross section is described by a set of average statistical resonance parameters. Above 50 keV the evaluated capture cross section is a smooth curve which follows the trend of the most recent measurements. The evaluated capture cross section is compared with many measurements and uncertainty estimates are given