Abstract
Angular distributions for elastic scattering of 100 MeV and 140 MeV alpha particles by heavy nuclei are characterized by strong damping of the Fraunhofer diffraction oscillations at large angles. This effect is attributed to refraction by the real part of the alphanucleus potential. It is shown that this can be accounted for through a technical modification of Frahn's closed formalism for strong absorption scattering together with a suitable parameterization of the nuclear scattering coefficients. The result exhibits not only the characteristic filling in of the Fraunhofer minima at large angles, but also a subtle interplay of Coulomb and nuclear effects which produce a characteristic dip and hump in the lower Fraunhofer envelope at smaller angles. It is shown that less structured 180 MeV proton-nucleus elastic angular distributions can also be accounted for. Finally, it is suggested that the refractive damping of the Fraunhofer oscillations does not appear at lower energies because of the masking of refraction by quantal surface reflection from the complex nuclear potential, and it is shown how this effect can be included in the formalism.
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I wish to acknowledge the guidance of W.E. Frahn, from whom I learned the physics of heavy ion elastic scattering. The special features of high-energy alpha angular distributions were pointed out to me by G.F. Burdzik. I am indebted to T.F. Hill for motivating me to critically re-examine partial-wave summation techniques.
Financial support in the form of a University of Cape Town Research Fellowship is gratefully acknowledged.
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Kauffmann, S.K. Refractive damping of Fraunhofer diffraction in light ion-nucleus elastic scattering at high energy. Z Physik A 282, 163–171 (1977). https://doi.org/10.1007/BF01408160
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DOI: https://doi.org/10.1007/BF01408160