Seminarium Fizyki Jądra Atomowego

With a threshold against breakup into 7Be + p of just 137.5 keV, 8B is perhaps the most weaklybound β-stable nucleus known. Given this very low threshold one might expect two things: a large breakupcross section and an important influence of coupling to the breakup on the elastic scattering, at least forincident energies close to the Coulomb barrier. Unfortunately, 8B is also one of the most difficult radioactivebeams to produce at these energies, so that there is a lack of precision data. Nevertheless, it has beenestablished that while the first supposition is justified by the available evidence the second is not; models of8B assuming a 7Be + p structure predict large breakup cross sections consistent with available data but only amodest coupling influence on the elastic scattering. The effect of the very weak binding energy of 8B on itselastic scattering seems to be confined to what may be termed “static” effects. We examine this paradox andoffer some suggestions towards an explanation of the enigma.