The 2H(n,p)2n reaction at 50 MeV and the neutron-neutron scattering length

The proton energy spectrum from the deuteron break-up induced by 50 MeV neutrons has been measured with a broad-range magnetic analyzer followed by a 200-proportionalcounter array and a plastic scintillation counter at the mean proton angle of 3.8° in the lab system. The measured spectrum was compared with the theoretical one calculated as a function of the neutron-neutron scattering length a_nn on the basis of the impulse approximation. From this comparison, a_nn = − 21.7 ± 1.2 fm was extracted at the effective range of 2.60 fm.