Study of the neutron—neutron interaction from the n+d break-up process

Abstract

The resutts of the deuteron break-up d(n, nn) by 14 MeV neutrons, which show an n--n interaction in the final state, are analysed with the object of obtaining the n--n interaction parameters which cannot be obtained directly.The energy spectrum of the forward going protons in the inc0mplete experiments cannot easily gire the scattering length ann, for it is difficult to separate the effects of ann and of the two-body N--N potential. When the FADDEEV theory is not used, the incomplete experiments with three nucleons do not represent measnrements of ann, but must be considered as tests of final-state interaction theories, using ann ~ --17 fm asa parameter, By contrast, the shape of the n--n final state interaction peak in the complete experiments ought to gire ann more easily. The exact solution of the FADDEEV equations gives a shape which differs little (~ 109£ at Enn ~ 1 MeV) from that given by the simple MIGDAL--WATSON relation, and which varies then little with the two~body N--N interaction. The valnes ann ~ --17 fin obtained at Hamburg (M--W relation and without correction for momentum transfer dependence), and 1 ann I ~ 20 fin obtained at Grenoble (exact FADDEEV calculations, but with the YAMAGUCHI N--• potential) do not represent ah important disagreement.Finally, the magnitude of the n--n peak in the complete experiments depends noticeably on the choice of the N--N potential; the separable N--N potential of YAMAGUCHI ehosen for the exact calculations with the FADDEEV equations gives about two times measured value at Grenoble. The precise measurement of the magnitude of the n--n peak together with a better choice of the two-nucleon potential (hard core, tensor forces) for the solution of the FADDEEV equations, now seem necessary.