The favorable energy configurations of nuclei at magic numbers of N neutrons and Z protons are fundamental for understanding the evolution of nuclear structure. The Z = 50 (tin) isotopic chain is a frontier for such studies, with particular interest at and around the doubly magic 100Sn isotope, for which the mass is a topic of debate. Precise mass values for neutron-deficient isotopes provide necessary anchor points for mass models to test extrapolations near the proton drip line, where experimental studies remain out of reach. In this work, we report a Penning trap mass measurement of 101Sn. The determined mass excess of-59 889.89(96) keV for 101Sn represents a factor-of-300 improvement over the current precision and indicates that 101Sn is less bound than previously thought. Mass predictions from a recently developed Bayesian model combination framework employing statistical machine learning and nuclear masses computed within seven global models based on nuclear density functional theory agree within 1Q with experimental masses from the 48 Z 52 isotopic chains. The framework's resilience to new mass data gave confidence in the extrapolation of tin masses down to N = 46. Our calculations suggest that 96Sn is a two-proton drip line nucleus and predict a mass excess of-58 090(800) keV for 100Sn, showing a preference within 1Q for the mass of 100Sn derived from the 9-delayed Q value measured at GSI.

Understanding the evolution of nuclear size away from stability remains a central challenge in nuclear physics. In neutron-deficient systems, charge radii can be highly sensitive to the interplay between strong and electromagnetic interactions, and the effects of weak binding, giving rise to exotic nuclear phenomena. However, experimental data on these systems has been limited by short lifetimes and low production rates. Here we report the first laser-spectroscopy measurements of nuclear charge radii along the neutron-deficient aluminium isotopic chain, from ^25Al to the proton-drip-line nucleus ^22Al, using the Resonance Ionization Spectroscopy Experiment (RISE) at the Facility for Rare Isotope Beams (FRIB). Our measurements reveal a step-like increase in charge radius toward the drip line, with similar radii for ^22, 23Al. A comparison of our results with those of their mirror partners reveals an almost identical correlation with the calculated proton skins and is consistent with the systematic trend of well-bound nuclei. These results offer insight for understanding the evolution of nuclear size at the proton dripline and place important constraints on modern nuclear theory. They also demonstrate the unique combined capabilities of RISE and FRIB to probe the structures of previously inaccessible nuclei at the limits of existence.

As a step towards the ultimate goal of a high-precision mass measurement of doubly magic 100Sn, the mass of 103Sn was measured at the Low Energy Beam and Ion Trap (LEBIT) located at the Facility for Rare Isotope Beams (FRIB). Utilizing the time-of-flight ion cyclotron resonance technique, a mass uncertainty of 3.7 keV was achieved, an improvement by more than an order of magnitude compared to a recent measurement performed in 2023 at the Cooler Storage Ring (CSRe) in Lanzhou. Although the LEBIT and CSRe mass measurements of 103Sn are in agreement, they diverge from the experimental mass value reported in the 2016 version of the Atomic Mass Evaluation (AME2016), which was derived from the measured Q beta+ value and the mass of 103In. In AME2020, this indirectly measured 103Sn mass was classified as a "seriously irregular mass" and replaced with an extrapolated value, which aligns with the most recent measured values from CSRe and LEBIT. As such, the smoothness of the mass surface is confidently reestablished for 103Sn. Furthermore, LEBIT's mass measurement of 103Sn enabled a significant reduction in the mass uncertainties of five parent isotopes which are now dominated by uncertainties in their respective Q values.

This white paper is the result of a collaboration by those that attended a workshop at the Facility for Rare Isotope Beams (FRIB), organized by the FRIB Theory Alliance (FRIB-TA), on Theoretical Justifications and Motivations for Early High-Profile FRIB Experiments. It covers a wide range of topics related to the science that will be explored at FRIB. After a brief introduction, the sections address: (II) Overview of theoretical methods, (III) Experimental capabilities, (IV) Structure, (V) Near-threshold Physics, (VI) Reaction mechanisms, (VII) Nuclear equations of state, (VIII) Nuclear astrophysics, (IX) Fundamental symmetries, and (X) Experimental design and uncertainty quantification.

We report the first mass measurement of the proton-halo candidate ^{22}Al performed with the low energy beam ion trap facility's 9.4 T Penning trap mass spectrometer at facility for rare isotope beams. This measurement completes the mass information for the lightest remaining proton-dripline nucleus achievable with Penning traps. ^{22}Al has been the subject of recent interest regarding a possible halo structure from the observation of an exceptionally large isospin asymmetry [J. Lee et al., Large isospin asymmetry in Si22/O22 Mirror Gamow-Teller transitions reveals the halo structure of ^{22}Al, Phys. Rev. Lett. 125, 192503 (2020).PRLTAO0031-900710.1103/PhysRevLett.125.192503]. The measured mass excess value of ME=18 092.5(3)  keV, corresponding to an exceptionally small proton separation energy of S_{p}=100.4(8)  keV, is compatible with the suggested halo structure. Our result agrees well with predictions from sd-shell USD Hamiltonians. While USD Hamiltonians predict deformation in the ^{22}Al ground state with minimal 1s_{1/2} occupation in the proton shell, a particle-plus-rotor model in the continuum suggests that a proton halo could form at large quadrupole deformation. These results emphasize the need for a charge radius measurement to conclusively determine the halo nature.

The Reaccelerator (ReA) of the Facility for Rare-Isotope Beams (FRIB) at Michigan State University uses a Beam Cooler/Buncher (BCB) and an Electron-Beam Ion Trap (EBIT) as a charge-breeding injector system. The rare isotopes produced by In-flight Separation are selected by the Advanced Rare Isotope Separator (ARIS) and stopped in a helium gas cell. Long-lived and stable-isotope beams can also be extracted from a Batch-Mode Ion Source (BMIS). The continuous beams transported at low energy to ReA are injected into the BCB. The pulsed beams are then injected into the EBIT, charge bred, ejected, and accelerated by ReA's LINAC. The EBIT electron current (300 - 600 mA) is a factor that limits its capacity to similar to 2 x 10(10) elementary charges, which restricts the maximum EBIT-extracted rates to less than 2 x 10(10) particles per second for light ions. An upgrade of the EBIT electron gun is expected to provide 2 A in current. In parallel, a High-Current Electron-Beam Ion Source (HCEBIS) is being commissioned. The HCEBIS can presently provide an electron current of 2 A. An upgrade will increase the current to 4 A. The implementation of these two upgrades is expected to allow for maximum rates to be similar to 10(11) pps, compatible with FRIB projected rates and user demands. We review the high-current capabilities and upgrades of ReA's charge-breeding system.

We present a novel technique to probe electroweak nuclear properties by measuring parity violation (PV) in single molecular ions in a Penning trap. The trap's strong magnetic field Zeeman shifts opposite-parity rotational and hyperfine molecular states into near degeneracy. The weak interaction-induced mixing between these degenerate states can be larger than in atoms by more than twelve orders of magnitude, thereby vastly amplifying PV effects. The single molecule sensitivity would be suitable for applications to nuclei across the nuclear chart, including rare and unstable nuclei.

We report the first direct measurement of the nuclear electron-capture (EC) decay Q value of 7Be -> 7Li via high-precision Penning trap mass spectrometry (PTMS). This was performed using the LEBIT Penning trap located at the National Superconducting Cyclotron Laboratory/Facility for Rare Isotope Beams (NSCL/FRIB) using the newly commissioned Batch-Mode Ion-Source (BMIS) to deliver the unstable 7Be+ samples. With a measured value of QEC = 861.963(23) keV, this result is three times more precise than any previous determination of this quantity. This improved precision and accuracy of the 7Be EC decay Q value is critical for ongoing experiments that measure the recoiling nucleus in this system as a signature to search for beyond the Standard Model (BSM) neutrino physics using 7Be-doped superconducting sensors. This experiment has extended LEBIT capabilities, using the first low-energy beam delivered by BMIS at FRIB for PTMS, as well as measuring the lightest-mass isotopes so far with LEBIT.

Background: Light curves are the primary observable of type-I x-ray bursts. Computational x-ray burst models must match simulations to observed light curves. Most of the error in simulated curves comes from uncertainties in r p process reaction rates, which can be reduced via precision mass measurements of neutron-deficient isotopes in the r p process path. Purpose: Perform a precise atomic mass measurement of 27P. Use this new measurement to calculate r p process reaction rates and input these rates into an x-ray burst model to reduce simulated light curve uncertainty. Use the mass measurement of 27P to validate the isobaric multiplet mass equation (IMME) for the A = 27 T = 3 2 isospin quartet which 27P belongs to. Method: High-precision Penning trap mass spectrometry utilizing the time-of-flight ion cyclotron resonance technique was used to determine the atomic mass of 27P. The MESA code (Modules for Experiments in Stellar Astrophysics) was then used to simulate x-ray bursts using a one-dimensional multizone model to produce updated light curves. Results: The mass excess of 27P was measured to be -670.7(6) keV, a 14-fold precision increase over the mass reported in the 2020 Atomic Mass Evaluation (AME2020). The 26Si(p, gamma ) 27P - 27P(gamma , p) 26Si rate equilibrium has been determined to a higher precision based on the precision mass measurement of 27P. x-ray burst light curves were produced with the MESA code using the new reaction rates. Changes in the mass of 27P seem to have minimal effect on light curves, even in burster systems tailored to maximize impact. Conclusion: The mass of 27P does not play a significant role in x-ray burst light curves. It is important to understand that more advanced models do not just provide more precise results, but often qualitatively different ones. This result brings us a step closer to being able to extract stellar parameters from individual x-ray burst observations. In addition, the IMME has been validated for the A = 27, T = 3/2 quartet. The normal quadratic form of the IMME using the latest data yields a reduced chi 2 of 2.9. The cubic term required to generate an exact fit to the latest data matches theoretical attempts to predict this term.

The Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap (St. Benedict) is currently under construction at the University of Notre Dame Nuclear Science Laboratory. It is designed to measure the beta-neutrino angular correlation parameter in superallowed mixed beta-decay transitions between mirror nuclei in order to extract the Fermi-to-Gamow Teller mixing ratio and test theoretical corrections entering in the determination of the Vud element of the Cabibbo–Kobayashi–Maskawa quark mixing matrix. St. Benedict includes a large volume gas catcher to thermalize the radioactive ion beam from TwinSol, a differentially-pumped extraction system, a radiofrequency quadrupole ion cooler and buncher, and a Paul trap for the observation and detection of the β decay products. The status of each of these components will be presented.

The Facility for Rare Isotope Beams (FRIB) at Michigan State University (MSU) consists of a newly constructed linear accelerator and fragment separator that are designed for enhanced production rates of rare isotopes for use in research and other societal applications. Recent activities through to August 2022 took place to commission the Advanced Rare Isotope Separator (ARIS) and carry out the first experiments. This followed commissioning of the newly constructed linac that is designed to provide orders of magnitude higher beam power than the previously coupled cyclotrons. This required that more advanced target, beam dump, and collimation systems of the new separator be designed and constructed to sustain unprecedented conditions by heavy ion beams. Commissioning with ∼1 kW beams began recently and results from activities that began in late 2021 are reported here. Comparisons between the previous and current facilities are provided.

The dynamics of ions in an electrostatic ion beam trap in the presence of an external time-dependent field is studied with a recently developed particle-in-cell simulation technique. The simulation technique, capable of accounting for space-charge effects, has reproduced all the experimental results on the bunch dynamics in the radio frequency mode. With simulation, the motion of ions is visualized in phase space and it is shown that the ion-ion interaction strongly affects the distribution of ions in phase space in the presence of an rf driving voltage.

The Facility for Rare Isotope Beams (FRIB) at Michigan State University provides a wide range of beams and energies for science with fast, stopped and reaccelerated rare-isotope beams. FRIB was commissioned in 2022 with the science program beginning in May 2022. The combination of fast beams followed by gas stopping of rare-isotope beams together with reacceleration is unique to FRIB. Stopping techniques and beam manipulation at very-low energies are important to slow down fast beams for use in either stopped-beam experimental devices, or subsequent injection in the reaccelerator for experiments at energies ranging from 0.3 MeV/u to 12 MeV/u, depending on the Q/A of the ion. Innovative stopped-beam techniques to optimize the stopping and extraction efficiencies across a wide range of atomic numbers, as well as to reduce contamination and increase extraction speed, were developed. Reacceleration of those beams involve cooling, bunching, charge breeding and acceleration by a state-of-the-art superconducting reaccelerator, ReA. In this contribution we present the latest results of various gas stoppers and techniques to eliminate contaminants after reacceleration by the ReA.

We demonstrate both experimentally and using a numerical simulation that, under special conditions, the repulsive Coulomb interaction helps to suppress the emittance growth of an rf-driven bunch of ions in an electrostatic ion beam trap. The underlying mechanisms can be explained by the synchronization of ion motion when nonlinear interactions are present. The surprising effect can help in improving the phase space manipulation of ions and the beam control in storage rings and accelerators and may be applied to other systems with many-body interactions in a periodic potential.

Mainly because of its long half-life and despite its scientific relevance, spectroscopic measurements of $^{176}$Lu forbidden $\beta$-decays are very limited and lack formulation of shape factors. A direct precise measurement of its $Q$ value is also presently unreported. In addition, the description of forbidden decays provides interesting challenges for nuclear theory. The comparison of precise experimental results with theoretical calculations for these decays can help to test underlying models and can aid the interpretation of data from other experiments.

Light curves are the primary observable of type-I x-ray bursts. Computational x-ray burst models must match simulations to observed light curves. Most of the error in simulated curves comes from uncertainties in $rp$ process reaction rates, which can be reduced via precision mass measurements of neutron-deficient isotopes in the $rp$ process path. We perform a precise Penning trap mass measurement of $^{27}$P utilizing the ToF-ICR technique. We use this measurement to calculate $rp$ process reaction rates and input these rates into an x-ray burst model to reduce simulated light curve uncertainty. We also use the mass measurement of $^{27}$P to validate the Isobaric Multiplet Mass Equation (IMME) for the A=27 T=$\frac{3}{2}$ isospin quartet which $^{27}$P belongs to. The mass excess of $^{27}$P was measured to be -670.7(6) keV, a fourteen-fold precision increase over the mass reported in the 2020 Atomic Mass Evaluation (AME2020). X-ray burst light curves were produced with the MESA (Modules for Experiments in Stellar Astrophysics) code using the new mass and associated reaction rates. Changes in the mass of $^{27}$P seem to have minimal effect on light curves, even in burster systems tailored to maximize impact. The mass of $^{27}$P does not play a significant role in x-ray burst light curves. It is important to understand that more advanced models do not just provide more precise results, but often qualitatively different ones. This result brings us a step closer to extracting stellar parameters from individual x-ray burst observations. The IMME has been validated for the $A=27, T=3/2$ quartet. The normal quadratic form of the IMME using the latest data yields a reduced $\chi^2$ of 2.9. The cubic term required to generate an exact fit to the latest data matches theoretical attempts to predict this term.

The single-ion Penning trap (SIPT) at the Low-Energy Beam Ion Trapping Facility has been developed to perform precision Penning trap mass measurements of single ions, ideal for the study of exotic nuclei available only at low rates at the Facility for Rare Isotope Beams (FRIB). Single-ion signals are very weak—especially if the ion is singly charged—and the few meaningful ion signals must be disentangled from an often larger noise background. A useful approach for simulating Fourier transform ion cyclotron resonance signals is outlined and shown to be equivalent to the established yet computationally intense method. Applications of supervised machine learning algorithms for classifying background signals are discussed, and their accuracies are shown to be ≈65% for the weakest signals of interest to SIPT. Additionally, a deep neural network capable of accurately predicting important characteristics of the ions observed by their image charge signal is discussed. Signal classification on an experimental noise dataset was shown to have a false-positive classification rate of 10.5%, and 3.5% following additional filtering. The application of the deep neural network to an experimental 85Rb+ dataset is presented, suggesting that SIPT is sensitive to single-ion signals. Lastly, the implications for future experiments are discussed.

Gas stoppers have been used for a long-standing successful science program at Michigan State University with stopped and rare-isotope beams produced by projectile fragmentation. The National Superconducting Cyclotron Laboratory's Coupled Cyclotron Facility has recently transitioned into the Facility for Rare Isotope Beams (FRIB) laboratory to provide rare isotopes using a high-power superconducting linear accelerator and new production facilities. To allow the science program with stopped and reaccelerated beams to continue during the transition period, a stand-alone capability was added. The Batch Mode Ion Source (BMIS) was built and has been providing beams of long-lived and stable isotopes of a variety of elements for successful user experiments. The BMIS system is described and results from the production of various beams are presented.