Measurement of the gamma-anisotropy in (n)over-right-arrow+(p)over-right-arrow -> d+gamma

The study of the radiative neutron capture by protons, n + p --> d + gamma, provides valuable information about the nucleon-nucleon interaction. So fa r, no experimental value has existed for the gamma-anisotropy which may app ear if neutrons and protons both are polarised. A non-vanishing gamma-aniso tropy eta is a clear-cut signal for the existence of transitions S-3(1) --> (3)d(1) from the triplet initial state to the ground state of the deuteron . We report the first measurement of this observable. The result is eta = ( 1.0 +/- 2.5) x 10(-4) at 50.5% polarisation of neutrons and protons. (C) El sevier Science B.V. All rights reserved.