Online Bayesian Optimization for a Recoil Mass Separator

The SEparator for CApture Reactions (SECAR) is a next-generation recoil separator system at the Facility for Rare Isotope Beams (FRIB) designed for the direct measurement of capture reactions on unstable nuclei in inverse kinematics. To maximize the performance of this system, stringent requirements on the beam alignment to the central beam axis and on the ion-optical settings need to be achieved. These can be difficult to attain through manual tuning by human operators without potentially leaving the system in a sub-optimal and irreproducible state. In this work, we present the first development of online Bayesian optimization with a Gaussian process model to tune an ion beam through a nuclear astrophysics recoil separator. We show that this method achieves small incoming angular deviations (\textless 1 mrad) in an efficient and reproducible manner that is at least three times faster than standard hand-tuning. Additionally, we present a Bayesian method for experimental optimization of the ion optics, and show that it validates the nominal theoretical ion-optical settings of the device, and improves the mass separation by 32\% for some beams

Catching Element Formation In The Act ; The Case for a New MeV Gamma-Ray Mission: Radionuclide Astronomy in the 2020s

High Energy Astrophysic

Experimental study of

40K is one of the main isotopes responsible for the radiogenic heating of the mantle in Earth-like exoplanets [1] and hence, plays a very important role in the internal geophysical dynamics of a planet. The abundance of 40K in the mantle and the core of such planets is not always possible to be determined by astrophysical observations, although constraining the nuclear reaction rates of 40K during stellar evolution can also lead to constraining the present amount of 40K in these planets, which will improve our understanding on the habitability potential of Earth-like exoplanets. This study aims to constrain the 40K(n,α)37Cl reaction rate, one of the two major destruction paths of 40K in stellar nucleosynthesis,by measuring the reverse reaction 37Cl(α,n)40K and applying the principle of detailed balance as we have done before for the 40K (40K(n,p)40Ar reaction rate) [2]. During the first set of measurements we performed differential cross-section measurements of the 37Cl(α,n1γ)40K, 37Cl(α,n2γ)40K and 37Cl(α,n3γ)40K reaction channels, for six different center of mass energies in the range between 5.1 and 5.4 MeV. The experiment took place at the Edwards Accelerator Laboratory of Ohio University. The gamma rays from the reaction channels mentioned above were detected by two LaBr3 scintillators. Using the swinger facility to change the angle of the beam-target system with respect to the detection system, we were able to take measurements for the differential cross-section at six different angles between 20° and 120° in the lab system

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

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(58Fe,n)58Co reaction measurement are presented