MINIMUM IN THE FORWARD ANGLE QUASI-ELASTIC (P,N) CROSS-SECTION - A MEANS OF DETECTING RAPID VARIATIONS IN THE FORWARD SCATTERING-AMPLITUDES

The zero degree (p,n) cross sections for a wide variety of targets and energies show an inverted angular shape for the differential cross se ction (the zero degree cross section has a minimum), which is correlat ed with the minimum observed in the neutron total cross section. Ramsa uer calculations do not reproduce this correlation without the additio n of a surface contribution. The existence of a zero degree (p,n) mini mum can be thought of as a Ramsauer effect in angular momentum space ( i.e., kR). We show that the existence of this inverted angular distrib ution also implies a rapid variation of the forward scattering amplitu de with energy. We conjecture that the detailed description of the for ward angle quasielastic (p,n) cross sections at these minima is extrem ely sensitive to the details of the nuclear surface.