January 29, 2018, 12:00 PM, 112W
Alexandre Lepailleur (Rutgers University)
Transfer reactions with GODDESS (Gammasphere ORRUBA: Dual Detectors for Experimental Structure Studies) and nuclear astrophysics
The natural production of approximately half the elements heavier than iron (atomic number Z = 56) occurs through a process known as the rapid neutron capture process (r-process). It consists of a succession of neutron captures that happen so fast that it overcomes the radioactive decay of the nuclei produced duringthe process. For the r-process to take place, a very high density of free neutrons isrequired, a condition that can only be found in very specific systems such as neutron star mergers 1. Many uncertainties remain about the r-process. The study of direct neutron captures followed by gamma decays (n,gamma) on nuclei along the r-processpath is required to answer some of these outstanding questions. Unfortunately, the nuclei of interests are very neutron-rich and therefore highly unstable and short- lived. It is then impossible to create targets made out of these elements, or very complicated and limiting since such targets would produce high gamma-raybackground. Consequently, the development of indirect ways to study direct neutron captures are mandatory. The transfer of a neutron from a deuteron to a heavy radioactive ion followed by a gamma decay (d,p gamma) has been investigated as a possible surrogate for (n,gamma) 2. In this case, the nucleus of interest is used as the beam instead of the target (inverse kinematics), solving the issues mentioned previously.After the transfer of the neutron from the target, a proton is ejected and the reaction product decays by emitting a gamma ray. The experimental setup GODDESS (Gammasphere ORRUBA: Dual Detectors for Experimental Structure Studies) has been developed specifically to study such reactions and detect the reaction protons(with ORRUBA) in coincidence with the gamma rays (with Gammasphere) 3. The 134Xe(d,p gamma) reaction, used to commission the setup, was measured in inverse kinematics with stable beams from ATLAS impinged on C2D4 targets. An overview of GODDESS and preliminary results from the 134Xe(d,p gamma) study will be presented, aswell as prospects for measuring (d,p gamma) reactions with radioactive ion beams assurrogate for (n,gamma).
[1] Pian, E. et al, Nature 551, 67 (2017).
[2] Cizewski, J. A. et al. (2017).
[3] Pain, S. D. et al. Phys. Procedia 90, 455-462 (2017).

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