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1. Machine learning enabled measurements of astrophysical ( $p,n$ ) reactions with the SECAR recoil separator

   https://doi.org/10.1103/PhysRevResearch.7.013074  

   Tsintari, P; Dimitrakopoulos, N; Garg, R; Hermansen, K; Marshall, C; Montes, F; Perdikakis, G; Schatz, H; Setoodehnia, K; Arora, H; et al (January 2025, Physical Review Research)

   The synthesis of heavy elements in supernovae is affected by low-energy $(n,p)$and $(p,n)$reactions on unstable nuclei, yet experimental data on such reaction rates are scarce. The SECAR (SEparator for CApture Reactions) recoil separator at FRIB (Facility for Rare Isotope Beams) was originally designed to measure astrophysical reactions that change the mass of a nucleus significantly. We used a novel approach that integrates machine learning with ion-optical simulations to find an ion-optical solution for the separator that enables the measurement of $(p,n)$reactions, despite the reaction leaving the mass of the nucleus nearly unchanged. A new measurement of the ${}^{58}\mathrm{Fe}(p,n){}^{58}\mathrm{Co}$reaction in inverse kinematics with a $3.66\pm 0.12$MeV/nucleon ${}^{58}\mathrm{Fe}$beam (corresponding to $3.69\pm 0.12$MeV proton energy in normal kinematics) yielded a cross-section of $20.3\pm 6.3$ mb and served as a proof of principle experiment for the new technique demonstrating its effectiveness in achieving the required performance criteria. This novel approach paves the way for studying astrophysically important $(p,n)$reactions on unstable nuclei produced at FRIB. Published by the American Physical Society2025 

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2. A technique for studying (n,p) reactions of astrophysical interest using radioactive beams with SECAR

   https://doi.org/10.1051/epjconf/202327913005  

   Tsintari, Pelagia; Berg, Georg P.; Blackmon, Jeff; Chipps, Kelly; Couder, Manoel; Deibel, Catherine; Dimitrakopoulos, Nikolaos; Garg, Ruchi; Greife, Uwe; Hermansen, Kirby; et al (January 2023, EPJ Web of Conferences)

   Freeman, S.; Lederer-Woods, C.; Manna, A.; Mengoni, A. (Ed.)

   The formation of nuclei in slightly proton-rich regions of the neutrino-driven wind of core-collapse supernovae could be attributed to the neutrino-p process (νp-process). As it proceeds via a sequence of (p,γ) and (n,p) reactions, it may produce elements in the range of Ni and Sn, considering adequate conditions. Recent studies identify a number of decisive (n,p) reactions that control the efficiency of the νp-process. The study of one such (n,p) reaction via the measurement of the reverse (p,n) in inverse kinematics was performed with SECAR at NSCL/FRIB. Proton-induced reaction measurements, especially at the mass region of interest, are notably difficult since the recoils have nearly identical masses as the unreacted projectiles. Such measurements are feasible with the adequate separation level achieved with SECAR, and the in-coincidence neutron detection. Adjustments of the SECAR system for the first (p,n) reaction measurement included the development of new ion beam optics, and the installation of the neutron detection system. The aforementioned developments along with a discussion on the preliminary results of the p( 58 Fe,n) 58 Co reaction measurement are presented. 

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3. First (p,n) reaction measurement in inverse kinematics with SECAR

   https://doi.org/10.1051/epjconf/202327502016  

   Tsintari, Pelagia; Berg, Georg; Blackmon, Jeff; Chipps, Kelly; Couder, Manoel; Deibel, Catherine; Dimitrakopoulos, Nikolaos; Garg, Ruchi; Greife, Uwe; Hermansen, Kirby; et al (January 2023, EPJ Web of Conferences)

   Lamia, L.; Pizzone, R.G.; Rapisarda, G.G.; Sergi, M.L. (Ed.)

   Nucleosynthesis in the ν p-process occurs in regions of slightly proton-rich nuclei in the neutrino-driven wind of core-collapse supernovae. The process proceeds via a sequence of (p, γ ) and (n,p) reactions, and depending on the conditions, may produce elements between Ni and Sn. Recent studies show that a few key (n,p) reactions regulate the efficiency of the neutrino-p process ( ν p-process). We performed a study of one of such (n,p) reactions via the measurement of the reverse (p,n) in inverse kinematics with SECAR at NSCL/FRIB.Such proton-induced reaction measurements are particularly challenging, as the recoils and the unreacted projectiles have nearly identical masses. An appropriate separation level can be achieved with SECAR, and along with the incoincidence detection of neutrons these measurements become attainable. The preparation of the SECAR system for accommodating its first (p,n) reaction measurement, including the development of alternative ion beam optics, and the setup of the in-coincidence neutron detection, along with discussion on preliminary results from the p( 58 Fe,n) 58 Co reaction measurement are presented and discussed. 

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4. Progress on nuclear reaction rates affecting the stellar production of ²⁶ Al

   https://doi.org/10.1088/1361-6471/ac9cf8  

   Laird, A M; Lugaro, M; Kankainen, A; Adsley, P; Bardayan, D W; Brinkman, H E; Côté, B; Deibel, C M; Diehl, R; Hammache, F; et al (January 2023, Journal of Physics G: Nuclear and Particle Physics)

   Abstract The radioisotope 26 Al is a key observable for nucleosynthesis in the Galaxy and the environment of the early Solar System. To properly interpret the large variety of astronomical and meteoritic data, it is crucial to understand both the nuclear reactions involved in the production of 26 Al in the relevant stellar sites and the physics of such sites. These range from the winds of low- and intermediate-mass asymptotic giant branch stars; to massive and very massive stars, both their Wolf–Rayet winds and their final core-collapse supernovae (CCSN); and the ejecta from novae, the explosions that occur on the surface of a white dwarf accreting material from a stellar companion. Several reactions affect the production of 26 Al in these astrophysical objects, including (but not limited to) 25 Mg( p , γ ) 26 Al, 26 Al( p , γ ) 27 Si, and 26 Al( n , p / α ). Extensive experimental effort has been spent during recent years to improve our understanding of such key reactions. Here we present a summary of the astrophysical motivation for the study of 26 Al, a review of its production in the different stellar sites, and a timely evaluation of the currently available nuclear data. We also provide recommendations for the nuclear input into stellar models and suggest relevant, future experimental work. 

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5. Prospects for Surrogate Neutron Capture Measurements with Radioactive Ion Beams and GODDESS

   https://doi.org/10.1007/978-3-030-58082-7  

   Jolie A. Cizewski, Andrew Ratkiewicz (February 2021, Compound-Nuclear Reactions, Springer Proceedings in Physics 254)

   null (Ed.)

   Neutron capture reactions are responsible for the synthesis of almost all of the elements heavier than iron through the slow s-process, that proceeds close to the line of stability, and the rapid r-process, with very neutron-rich waiting points. Uncertainties in (n,γ) rates in neutron rich nuclei, especially near closed neu- tron shells, can have significant impact [1] on the predictions of final abundances for different astrophysical scenarios for the r process. Understanding (n,γ) rates on neutron-rich fission fragments is also important for nuclear forensics and stockpile stewardship science. Ratkiewicz et al. [2 and references therein] has recently demonstrated that the (d,pγ) reaction is a valid surrogate for (n,γ), where the formation of the compound nu- cleus from the breakup of the deuteron has been calculated in a reaction model and the subsequent measured gamma-decay probabilities are reproduced with standard level density and strength functions in a Bayesian approach. In parallel to the surrogate validation efforts, we have demonstrated that the (d,pγ) reaction can be measured in inverse kinematics with Gammasphere ORRUBA: Dual Detectors for Experimental Structure Studies (GODDESS) [3] where the Gammasphere array of Compton-suppressed HPGe detectors is coupled to the Oak Ridge Rutgers University Barrel Array of position-sensitive silicon strip detectors. During the commis- sioning campaign we measured the (d,pγ) reaction with 134Xe and 95Mo beams, the latter to demonstrate the surrogate method in inverse kinematics. The present talk will present preliminary results from this campaign including γ-decay probabilities and prospects for surrogate (n,γ) measurements with 143Ba fission-fragment beams. 

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