The first measurement of the cross section of the quasifree pn→pn reaction has been carried out at the CELSIUS storage ring using a deuterium internal cluster jet target. The energy dependence of the cross section is extracted using a fixed incident proton energy of T p ϭ1350 MeV and exploiting the Fermi momentum of the struck neutron. The data cover a range of center-of-mass excess energies from 16 to 109 MeV. The shape of the excitation function is broadly similar to that of the pp→pp reaction, though with a cross section about a factor of 6.5 larger. ͓S0556-2813͑98͒02811-8͔

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Exclusive measurements of the production of η-mesons in the pp → ppη reaction have been carried out at excess energies of 16 and 37 MeV above threshold. The deviations from phase space are dominated by the proton-proton final state interaction and this influences particularly the energy distribution of the η meson. However, evidence is also presented at the higher energy for the existence of an anisotropy in the angular distributions of the η-meson and also of the final proton-proton pair, probably to be associated with D-waves in this system interfering with the dominant S-wave term. The sign of the η angular anisotropy suggests that ρ-exchange is important for this reaction.

The differential cross section for the pd→ 3 He reaction has been measured at four beam energies 930, 965, 1037, and 1100 MeV. The total cross section is nearly constant throughout the whole energy region, despite the c.m. angular distribution becoming more anisotropic with increasing energy. The data join smoothly onto the results of near-threshold measurements, which are dominated by the S-wave 3 He final state interaction. At all the energies the differential cross section is maximal for cos Ϸϩ0.5 and this may provide a clue to the reaction mechanism and, in particular, to two-step contributions.