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

Abstract

The results of the deuteron break-upd(n, nn) by 14 MeV neutrons, which show ann−n interaction in the final state, are analysed with the object of obtaining then−n interaction parameters which cannot be obtained directly.

The energy spectrum of the forward going protons in the incomplete experiments cannot easily give the scattering lengtha _nn, for it is difficult to separate the effects ofa _n and of the two-bodyN−N potential. When theFaddeev theory is not used, the incomplete experiments with three nucleons do not represent measurements ofa _nn, but must be considered as tests of final-state interaction theories, usinga _nn≈−17 fm as a parameter.

By contrast, the shape of then−n final state interaction peak in the complete experiments ought to givea _nn more easily. The exact solution of theFaddeev equations gives a shape which differs little (≈ 10% atE _nn≈1 MeV) from that given by the simpleMigdal-Watson relation, and which varies then little with the two-bodyN−N interaction. The valuesa _nn≈−17fm obtained at hamburg (M-W relation and without correction for momentum transfer dependence), and |a _nn|≧20 fm obtained at Grenoble (exactFaddeev calculations, but with theYamaguchi N−N potential) do not represent an important disagreement.

Finally, the magnitude of then−n peak in the complete experiments depends noticeably on the choice of theN−N potential; the separableN−N potential ofYamaguchi chosen for the exact calculations with theFaddeev equations gives about two times measured value at grenoble. The precise measurement of the magnitude of then−n peak together with a better choice of the two-nucleon potential (hard core, tensor forces) for the solution of theFaddeev equations, now seem necessary.

Резюме

С целью получения параметров взаимодействия, которых непосредственно нельзя получить, рассматриваются результаты развала дейтерия под действием нейтронов с энер гией 14 Мэв, в конечном состоянии которого появляется взаимодействия типаn−n.