RUI: Exploring the Origin of the Rarest Stable Isotopes via Photon-Induced Activation Studies at the Madison Accelerator Laboratory

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The question of how nuclear reactions in stars and stellar explosions have forged the elements out of hydrogen and helium leftover from the Big Bang is a longstanding but timely research topic in nuclear astrophysics. There is a fairly complete understanding of the production of the elements up to iron by nuclear fusion reactions in stars but important details concerning the production of the elements beyond iron remain puzzling. The proposed research aims to advance fundamental knowledge on a forefront topic in nuclear astrophysics - the synthesis of elements beyond Fe and of the rarest stable isotopes naturally occurring on Earth. The astrophysical phenomenon responsible for this synthesis is termed the p-process. Though simulating the p-process nucleosynthesis on a computer is a daunting task, significant progress can be made by performing key measurements which constrain the models that are used to calculate the unknown stellar reaction rates. Moreover, the proposed research will create an rich research experience for undergraduates in an accelerator-based environment at the newly opened Madison Accelerator Laboratory (MAL). MAL is a unique bremsstrahlung facility on the campus of James Madison University. The students will have an excellent opportunity for hands-on participation in an accelerator-based environment and they will be able to participate in cutting-edge research in nuclear astrophysics. This experience is an important part of their training as future researchers and will provide them with skills necessary to pursue STEM careers in Industry, at National Laboratories and Universities.The focus of this proposal's research program is to determine experimentally the ground state reaction rates for eight photo-neutron reactions which are to be investigated by photon-induced activation at MAL. The eight photo-neutron reactions are: 64Zn(gamma,n)63Zn, 70Ge(gamm,n)69Ge,74Se(gamma,n)73Se, 78,80Kr(gamma,n)77,79Kr, 84,86Sr(gamma,n)83,85Sr and 90Zr(gaamma,n)89Zr. The eight proton-rich stable nuclei of interest belong to the region A 124 which is notoriously under produced by the current stellar evolution models. In the laboratory one only has access to target nuclei in the ground state and so the stellar photodisintegration reaction rates, dominated by excited state contributions at the high temperature regime of the p-process, cannot be directly constrained experimentally. With the experiments at MAL, we can instead provide nuclear science input (through inverse reaction kinematics) to constrain crucial parameters of the nuclear reaction models, i.e. gamma ray strength function especially relevant for photo-neutron reactions. Considering the very large number of nuclear reactions involved in the production of even a single p-nucleus, any new measurement of photodisintegration reactions relevant to the p-process path will put the nucleosynthesis calculations on a firmer foundation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.