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

恒星中的核反应和恒星爆炸如何从大爆炸残留的氢和氦中锻造出元素的问题是核天体物理学中一个长期但及时的研究课题。人们对恒星核聚变反应产生铁等元素的过程有了相当全面的了解，但关于铁以外元素的产生的重要细节仍然令人困惑。这项研究旨在推进核天体物理学前沿课题的基础知识-铁以外的元素和地球上自然存在的最稀有的稳定同位素的合成。负责这种合成的天体物理现象被称为p过程。虽然在计算机上模拟p-过程核合成是一项艰巨的任务，但通过进行关键测量可以取得重大进展，这些测量限制了用于计算未知恒星反应速率的模型。此外，拟议中的研究将在新开放的麦迪逊加速器实验室（MAL）的基于加速器的环境中为本科生创造丰富的研究经验。 MAL是詹姆斯麦迪逊大学校园内一个独特的韧致辐射设施。学生将有一个很好的机会在基于加速器的环境中动手参与，他们将能够参与核天体物理学的前沿研究。这一经验是他们作为未来研究人员的培训的重要组成部分，并将为他们提供在国家实验室和大学从事工业STEM职业所需的技能。该提案的研究计划的重点是通过实验确定八个光中子反应的基态反应速率，这些反应将在MAL通过光子诱导活化进行研究。64 Zn（γ，n）63 Zn，70 Ge（γ，n）69 Ge，74 Se（γ，n）73 Se，78，80 Kr（γ，n）77，79 Kr，84，86 Sr（γ，n）83，85 Sr和90 Zr（γ，n）89 Zr。八个富质子稳定核属于A124区，这是众所周知的根据目前的恒星演化模型产生的。 在实验室中，人们只能接触到处于基态的目标核，因此在p过程的高温区，由激发态贡献主导的恒星光致蜕变反应速率不能直接通过实验来约束。通过MAL的实验，我们可以提供核科学输入（通过逆反应运动学）来约束核反应模型的关键参数，即与光中子反应特别相关的伽马射线强度函数。考虑到即使是单个p核的产生也涉及大量的核反应，任何与p过程路径相关的光致衰变反应的新测量都将使核合成计算建立在更坚实的基础上。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.