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We report the first mass measurement of the proton-halo candidate $^{22}$Al performed with the LEBIT facility's 9.4~T Penning trap mass spectrometer at FRIB. 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 [Phys. Rev. Lett. \textbf{125} 192503 (2020)]. The measured mass excess value of $\text{ME}=18\;093.6(7)$~keV, corresponding to an exceptionally small proton separation energy of $S_p = 99.2(1.0)$~keV, is compatible with the suggested halo structure. Our result agrees well with predictions from \textit{sd}-shell USD Hamiltonians. While USD Hamiltonians predict deformation in $^{22}$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., Comment: 9 pages, 4 figures

Linear gas stoppers are widely used to convert high-energy, rare-isotope beams and reaction products into low-energy beams with small transverse emittance and energy spread. Stopping of the high-energy ions is achieved through interaction with a buffer gas, typically helium, generating large quantities of He$^+$/e$^-$ pairs. The Advanced Cryogenic Gas Stopper (ACGS) was designed for fast, efficient stopping and extraction of high-intensity, rare-isotope beams. As part of the design process, a comprehensive particle-in-cell code was developed to optimize the transport and extraction of rare isotopes from the ACGS in the presence of space charge, including He$^+$/e$^-$ dynamics, buffer gas interactions including gas flow, RF carpets, and ion extraction through a nozzle or orifice. Details of the simulations are presented together with comparison to experiment when available.

Isobaric quintets provide the best test of the isobaric multiplet mass equation (IMME) and can uniquely identify higher order corrections suggestive of isospin symmetry breaking effects in the nuclear Hamiltonian. The Generalized IMME (GIMME) is a novel microscopic interaction theory that predicts an extension to the quadratic form of the IMME. Only the $A=20, 32$ $T=2$ quintets have the exotic $T_z = -2$ member ground state mass determined to high-precision by Penning trap mass spectrometry. In this work, we establish $A=36$ as the third high-precision $T=2$ isobaric quintet with the $T_z = -2$ member ground state mass measured by Penning trap mass spectrometry and provide the first test of the predictive power of the GIMME. A radioactive beam of neutron-deficient $^{36}$Ca was produced by projectile fragmentation at the National Superconducting Cyclotron Laboratory. The beam was thermalized and the mass of $^{36}$Ca$^+$ and $^{36}$Ca$^{2+}$ measured by the Time of Flight - Ion Cyclotron Resonance method in the LEBIT 9.4 T Penning trap. We measure the mass excess of $^{36}$Ca to be ME$ = -6483.6(56)$ keV, an improvement in precision by a factor of 6 over the literature value. The new datum is considered together with evaluated nuclear data on the $A=36$, $T=2$ quintet. We find agreement with the quadratic form of the IMME given by isospin symmetry, but only coarse qualitative agreement with predictions of the GIMME. A total of three isobaric quintets have their most exotic members measured by Penning trap mass spectrometry. The GIMME predictions in the $T = 2$ quintet appear to break down for $A = 32$ and greater.

We have developed and tested an experimental technique for the measurement of low-energy (p,n) reactions in inverse kinematics relevant to nuclear astrophysics. The proposed setup is located at the ReA3 facility at the National Superconducting Cyclotron Laboratory. In the current approach, we operate the beam-transport line in ReA3 as a recoil separator while tagging the outgoing neutrons from the (p,n) reactions with the low-energy neutron detector array (LENDA). The developed technique was verified by using the $^{40}$Ar(p,n)$^{40}$K reaction as a probe. The results of the proof-of-principle experiment with the $^{40}$Ar beam show that cross-section measurements within an uncertainty of $\sim$25\% are feasible with count rates up to 7 counts/mb/pnA/s. In this article, we give a detailed description of the experimental setup, and present the analysis method and results from the test experiment. Future plans on using the technique in experiments with the separator for capture reactions (SECAR) that is currently being commissioned are also discussed., Comment: Submitted to NIMA. Revised manuscript after referees' first review

The Isobaric Multiplet Mass Equation (IMME) has been successful at predicting the masses of isobaric analogue states in the same multiplet, while its coefficients are known to follow trends as functions of mass number. The Atomic Mass Evaluation 2016 [Chin. Phys. C 41, 030003 (2017)] $^{44}$V mass value results in an negative $c$ coefficient for the IMME quadratic term. The $b$ and $c$ coefficients can provide constraints for construction of the isospin-nonconserving (INC) Hamiltonians for the $pf$ shell. The excitation energy of the $0^+, T=2$ level in $^{44}$V is currently unknown and can be used to constrain the $^{44}$Cr mass. The aim of the experiment was to perform high-precision mass measurements to resolve the difference between $^{44}$V isomeric and ground states, to test the IMME, and to provide ingredients for identifying the $0^+$, $T=2$ state in $^{44}$V. High-precision Penning trap mass spectrometry was performed at LEBIT, to measure the cyclotron frequency ratios of [$^{44g,m}$VO]$^+$ versus [$^{32}$SCO]$^+$, a reference mass, to extract both the isomeric and ground state masses of $^{44}$V. The mass excess of the ground and isomeric states in $^{44}$V were measured to be $-23\ 804.9(80)$ keV/$\text{c}^2$ and $-23\ 537.0(55)$ keV/$\text{c}^2$. This yielded a new proton separation energy of $S_p$ = 1\ 773(10) keV. The new mass values of $^{44}$V have been used to deduce the IMME $b$ and $c$ coefficients of the lowest $2^+$ and $6^+$ triplets in $A=44$. The $2^+$ $c$ coefficient is verified with the IMME trend and agrees with the shell-model predictions using charge-dependent Hamiltonians. The mirror energy differences were determined between $^{44}$V and $^{44}$Sc, in line with isospin-symmetry. The new value of the proton separation energy determined will be important for the determination of the $0^+$, $T=2$ state in $^{44}$V and for prediction of the mass of $^{44}$Cr., Comment: 9 pages, 5 figures

The variation in mean-square nuclear charge radius of xenon isotopes was measured utilizing a new method based on extreme ultraviolet spectroscopy of highly charged Na-like ions. The isotope shift of the Na-like D1 (3s $^{2}$S$_{1/2}$ - 3p $^2$P$_{1/2}$) transition between the $^{124}$Xe and $^{136}$Xe isotopes was experimentally determined using the electron beam ion trap facility at the National Institute of Standards and Technology. The mass shift and the field shift coefficients were calculated with enhanced precision by relativistic many-body perturbation theory and multi-configuration Dirac-Hartree-Fock method. The mean-square nuclear charge radius difference was found to be $\delta^{136, 124}$ = 0.269(0.042) fm$^2$. Our result has smaller uncertainty than previous experimental results and agrees with the recommended value by Angeli and Marinova [I. Angeli and K. P. Marinova, At. Data and Nucl. Data Tables {\bf 99}, 69-95 (2013)]., Comment: 6 pages, 3 figures

The region near Z=28, N=40 is a subject of great interest for nuclear structure studies due to spectroscopic signatures in $^{68}$Ni suggesting a subshell closure at N=40. Trends in nuclear masses and their derivatives provide a complementary approach to shell structure investigations via separation energies. Penning trap mass spectrometry has provided precise measurements for a number of nuclei in this region, however a complete picture of the mass surfaces has so far been limited by the large uncertainty remaining for nuclei with N > 40 along the iron and cobalt chains. Here we present the first Penning trap measurements of $^{68,69}$Co, performed at the Low-Energy Beam and Ion Trap facility at the National Superconducting Cyclotron Laboratory. In addition, we perform ab initio calculations of ground state and two-neutron separation energies of cobalt isotopes with the valence-space in-medium similarity renormalization group approach based on a particular set of two- and three-nucleon forces which predict saturation in infinite matter. We discuss the importance of these measurements and calculations for understanding the evolution of nuclear structure near $^{68}$Ni., Comment: 7 pages, 6 figures

We report the first direct measurement of the $^{14}\text{O}$ superallowed Fermi $\beta$-decay $Q_{EC}$-value, the last of the so-called "traditional nine" superallowed Fermi $\beta$-decays to be measured with Penning trap mass spectrometry. $^{14}$O, along with the other low-$Z$ superallowed $\beta$-emitter, $^{10}$C, is crucial for setting limits on the existence of possible scalar currents. The new ground state $Q_{EC}$ value, 5144.364(25) keV, when combined with the energy of the $0^+$ daughter state, $E_x(0^+)=2312.798(11)$~keV [Nucl. Phys. A {\bf{523}}, 1 (1991)], provides a new determination of the superallowed $\beta$-decay $Q_{EC}$ value, $Q_{EC}(\text{sa}) = 2831.566(28)$ keV, with an order of magnitude improvement in precision, and a similar improvement to the calculated statistical rate function $f$. This is used to calculate an improved $\mathcal{F}t$-value of 3073.8(2.8) s., Comment: 5 pages, 5 figures

We report on direct time-of-flight based mass measurements of 16 light neutron-rich nuclei. These include the first determination of the masses of the Borromean drip-line nuclei $^{19}$B, $^{22}$C and $^{29}$F as well as that of $^{34}$Na. In addition, the most precise determinations to date for $^{23}$N and $^{31}$Ne are reported. Coupled with recent interaction cross-section measurements, the present results support the occurrence of a two-neutron halo in $^{22}$C, with a dominant $\nu2s_{1/2}^2$ configuration, and a single-neutron halo in $^{31}$Ne with the valence neutron occupying predominantly the 2$p_{3/2}$ orbital. Despite a very low two-neutron separation energy the development of a halo in $^{19}$B is hindered by the 1$d_{5/2}^2$ character of the valence neutrons., Comment: 5 pages

The root-mean-square (rms) nuclear charge radius of ^8He, the most neutron-rich of all particle-stable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of ^6He was measured to be 2.068(11) fm, in excellent agreement with a previous result. The significant reduction in charge radius from ^6He to ^8He is an indication of the change in the correlations of the excess neutrons and is consistent with the ^8He neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations.

The possibility of observing neutrinoless double beta decay offers the opportunity of determining the neutrino mass IF the nuclear matrix element were known. Theoretical calculations are uncertain and measurements of the occupations of valence orbits by nucleons active in the decay can be important. The occupation of valence neutron orbits in the ground states of 76Ge and 76Se were determined by precisely measuring cross sections for both neutron-adding and removing transfer reactions. Our results indicate that the Fermi surface is much more diffuse than in theoretical (QRPA) calculations. We find that the populations of at least three orbits change significantly between these two ground states while in the calculations the changes are confined primarily to one orbit., Comment: 4 pages, 3 figures

Precision measurements were carried out to test the similarities between the ground states of 76Ge and 76Se. The extent to which these two nuclei can be characterized as consisting of correlated pairs of neutrons in a BCS-like ground state was studied. The pair removal (p,t) reaction was measured at the far forward angle of 3 degrees. The relative cross sections are consistent (at the 5% level) with the description of these nuclei in terms of a correlated pairing state outside the N=28 closed shells with no pairing vibrations. Data were also obtained for 74Ge and 78Se.

Dedicated ionization chamber was built and installed to measure the energy loss of very heavy nuclei at 2.7 MeV/u produced in fusion reactions in inverse kinematics (beam of 208Pb). After going through the ionization chamber, products of reactions on 12C, 18O targets are implanted in a Si detector. Their identification through their alpha decay chain is ambiguous when their half-life is short. After calibration with Pb and Th nuclei, the ionization chamber signal allowed us to resolve these ambiguities. In the search for rare super-heavy nuclei produced in fusion reactions in inverse or symmetric kinematics, such a chamber will provide direct information on the nuclear charge of each implanted nucleus., Comment: submitted to NIMA, 10 pages+4 figures, Latex, uses elsart.cls and grahpicx