  The present experiment exploits the interference between the Deeply Virtual
Compton Scattering (DVCS) and the Bethe-Heitler processes to extract the
imaginary part of DVCS amplitudes on the neutron and on the deuteron from the
helicity-dependent D$({\vec e},e'\gamma)X$ cross section measured at $Q^2$=1.9
GeV$^2$ and $x_B$=0.36. We extract a linear combination of generalized parton
distributions (GPDs) particularly sensitive to $E_q$, the least constrained
GPD. A model dependent constraint on the contribution of the up and down quarks
to the nucleon spin is deduced.
