  The field of Diffraction Dissociation, which is the subject of this workshop,
began 50 years ago with the analysis of deuteron stripping in low energy
collisions with nuclei. We return to the subject in a modern context- deuteron
dissociation in $\sqrt{s_{NN}}= 200$ GeV d-Au collisions recorded during the
2003 RHIC run in the PHENIX experiment. At RHIC energy, d$\to$n+p proceeds
predominantly (90%) through Electromagnetic Dissociation and the remaining
fraction via the hadronic shadowing described by Glauber. Since the
dissociation cross section has a small theoretical error we adopt this process
to normalize other cross sections measured in RHIC.
