Symmetries and conservation laws lie at the foundation of the physical sciences and manifest themselves throughout the natural world. Within the atomic nucleus, an underlying symmetry exists due to the similarity between protons and neutrons. The strong short-range nuclear force that binds these particles together is found to be nearly independent of their electric charge. From the relative invariance of the nuclear interaction, a striking symmetry emerges in the quantum states of mirror nuclei whose proton and neutron numbers are exchanged. This fundamental property is an important predictor of nuclear structure and is described within the formalism of isobaric-spin symmetry, which has proved remarkably accurate since its inception in the early 1930's. Recently, we performed an experiment that has revealed, for the first time, a unique violation of mirror symmetry between the ground states of two mirror nuclei, 73Sr and 73Br. The experiment was conducted at the National Superconducting Cyclotron Laboratory (NSCL) and utilized the Beta-Counting Station (BCS) coupled to the Radio-Frequency Fragment Separator (RFFS) to investigate beta-delayed proton emission along the N=Z line. In this talk I will briefly review the concept of mirror symmetry in nuclei and discuss some of its consequences within nuclear physics. I will then describe details of our recent measurement and discuss our observation of ground-state mirror-symmetry breaking in atomic nuclei. This work is supported by the U.S. Department of Energy, Office of Nuclear Physics, under contract number DE-FG02-94ER40848 (UML).

"Vital Nuclear Processes in Core-collapse Supernovae" and "Measurements of alpha-processes relevant for the weak r-process", respectively

Core-collapse supernovae originate from the gravitational collapse of massive stars. These events are a source of neutrinos and a site of elements synthesis. They also play an important role in the evolution of galaxies. Despite being studied for decades, the explosion mechanism is still uncertain. This is in itself an important question, but it also affects the outcome (successful explosion or collapse to a black hole), the remnant left behind, and the detailed conditions under which explosive nucleosynthesis happens. In this talk, I will discuss the recent progress of my group in core-collapse supernova modeling.

In this talk I will present results from high energy density science and applied physics studies in the ATAP Division at Berkeley Lab (http://atap.lbl.gov/). We have recently expanded science at the BELLA petawatt laser from a focus on electron acceleration to include now also experiments on ion acceleration and laser-matter interactions with solid targets [1]. Here, a unique opportunity is warranted by the 1 Hz repetition rate of BELLA, which allows parametric explorations with thousands of shots. One example are nuclear reactions in plasmas and moderately hot targets where unreasonably high values of apparent electron screening potentials have been observed in studies of light ion fusion that can now be investigated with higher precision [2]. Pulsed ion beams provide access to the time domain of ion-solid interactions and they have been used to drive materials very far from equilibrium. I will report on our efforts to develop intense ion beams and on studies of color center qubit formation and damage accumulation in semiconductor devises with intense, pulsed ion beams [3, 4]. References: [1] J.-H. Bin, et al., Rev. Sci. Instr. 90, 053301 (2019) [2] T. Schenkel, et al., J. Appl. Phys. 126, 203302 (2019); C. P. Berlinguette, et al., Nature 570, 45 (2019) [3] J. Schwartz, et al., J. Appl. Phys. 116, 214107 (2014); J. J. Barnard, T. Schenkel, J. Appl. Phys. 122, 195901 (2017) [4] T Schenkel, et al., LLNL-CONF-758685; B. A. Ludewigt, et al., JRERE 36, 96 (2018) Acknowledgments: This work was supported by the Director, Office of Science, Offices of High Energy Physics and Fusion Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, by ARPA-E, and in part also by LDRD funding at Berkeley Lab, by Sandia National Laboratory, and by Google LLC under CRADA between LBNL and Google LLC.

Stardust grains, which are micrometer-sized particles found in meteorites, formed in the death throes of dying stars and recorded their parent stars nucleosynthetic fingerprint. Analyzing these bona fide stellar condensates allows us to obtain these fingerprints for various stellar events and - in combination with experimental physics, observations, and modeling - allows us to better constrain stellar nucleosynthesis and galactic chemical evolution. In this talk I will present recent isotopic measurements of stardust that inform our understanding of the origin of the elements that formed the solar system, and discuss recent advances and possibilities on exploring galactic chemical evolution. I will also discuss ongoing efforts to experimentally study determine the stellar sites of actinide nucleosynthesis, i.e., the rapid neutron capture process.

Coiled finned-tube heat exchangers, also called Collins type heat exchangers, are frequently used in small to medium scale cryogenic systems to improve design packaging (compactness) while maintaining high thermal effectiveness. A typical heat exchanger assembly of this kind consists of an inner cylindrical shell, called the mandrel, with helical finned-tube coils wrapped around it, and then enclosed by an outer shell. The two flow paths are through the helically wrapped tube, and the annular flow around the outside of the tubes. An accurate description of the shell-side thermal-hydraulic flow characteristics is a necessary part of the heat exchanger design. In this paper, these characteristics for cryogenic gaseous nitrogen, between 300 to 100 K, are numerically investigated. A computational fluid dynamics model of the shell-side geometry is developed and validated. Simulations are carried out for a wide range of flow conditions. Data obtained from the numerical simulations are used to form correlations between the shell-side Reynolds number (Re), Fanning friction factor (f), and Chilton-Colburn factor (j). In addition, the effect of geometrical variance on the correlation was investigated. The results from this study show reasonable agreement between the correlations developed numerically and experimental data.

Purifiers are crucial to support the cryogenic helium refrigeration systems used in superconducting particle accelerators, such as FRIB. Experimental systems, such as superconducting magnets, require low level purification (i.e., impurities in parts per million), due to inherent characteristics in their construction. Purifiers are also used for the commissioning of sub-systems, like the compressors, or cold boxes. Impurities in the helium used in the refrigerators can degrade performance and damage rotating equipment. From experience, traditionally used molecular sieves do not remove low-level impurities sufficiently and commercial freeze-out purifiers have short operating times (time between regeneration). A liquid-nitrogen assisted freeze-out purifier for helium has been designed, including a multi-pass, multi-stream heat exchanger and activated carbon adsorption bed. The design is expected to minimize liquid nitrogen usage and maximize the operating time. The goal of the design is to provide a simple to operate and efficient purifier system. An overview of the helium purification process will be provided, and some key mechanical design aspects will be discussed.