This award facilitates the initiation of a U.S.-led experimental program and international collaboration in nuclear astrophysics at Japan's RIKEN Radioactive Ion Beam Factory (RIBF), regarded as the most outstanding radioactive ion beam facility in the world. The origin of the elements remains one of the largest unanswered questions in nuclear physics. In particular, nucleosynthesis processes involving nuclei far from stability (the rp- and r-processes) remain largely untested. The experiment in this U.S.-Japan collaboration will measure the masses of atomic nuclei relevant to the astrophysical rp-process, the nuclear process thought to fuel x-ray bursts. These masses will be measured using the TOF-technique; that is, the time-of-flight of nuclei of known momentum in the beam will be measured between two points in the beamline. Knowing these nuclear masses will allow a better understanding of the light emission profile in an x-ray burst. Primary collaborators in Japan include Toshiyuki Kubo of the RIBF, Shigeru Kubono of the University of Tokyo, and Toshitaka Kajino of the University of Tokyo. Four U.S. graduate students and one post-doctoral researcher will participate in the project, which is jointly funded by the Office of International Science & Engineering and the Division of Physics. The award also supports planning for the next stage of a longer-term international collaboration between scientists in the United States and Japan.
