We report precision mass measurements of Sb-133, Te-133g,Te-m, and I-133g,I-m, produced at CARIBU at Argonne National Laboratory's ATLAS facility and measured using the Canadian Penning Trap mass spectrometer. These masses clarify an anomaly in the Te-133 beta-decay. The masses reported in the 2020 Atomic Mass Evaluation (M. Wang et al., 2021) produce Q(beta-) (Te-133)=2920(6) keV; however, the highest-lying I-133 level populated in this decay is observed at E-i = 2935 . 83(15) keV, resulting in an anomalous Q(beta-)(i) = -16(6) keV. Our new measurements give Q(beta-) (Te-133) = 2934.8(11) . 8(11) keV, a factor of five more precise, yielding Q(beta)(i) = -1 . 0(12) keV, a 3 sigma shift from the previous results. This resolves this anomaly, but indicates further anomalies in our understanding of the structure of this isotope.

Studies aiming to determine the astrophysical origins of nuclei produced by the rapid neutron capture process (r process) rely on nuclear properties as inputs for simulations. The solar abundances can be used as a benchmark for such calculations, with the r-process rare-earth peak (REP) around mass number (A) 164 being of special interest due to its presently unknown origin. With the advancement of rare isotope beam production over the last decade and improvement in experimental sensitivities, many of these REP nuclides have become accessible for measurement. Masses are one of the most critical inputs as they impact multiple nuclear properties, namely the neutron-separation energies, neutron capture rates, β-decay rates, and β-delayed neutron emission probabilities. In this work, we report masses of 20 neutron-rich nuclides (along the Ba, La, Ce, Pr, Nd, Pm, Gd, Dy and Ho isotopic chains) produced at the CAlifornium Rare Isotope Breeder Upgrade (CARIBU) facility at Argonne National Laboratory. The masses were measured with the Canadian Penning trap (CPT) mass spectrometer using the Phase-Imaging Ion-Cyclotron-Resonance (PI-ICR) technique. We then use these new masses along with previously published CPT masses to inform predictions for a Markov Chain Monte Carlo (MCMC) procedure aiming to identify the astrophysical conditions consistent with both solar data and mass measurements. We show that the MCMC responds to this updated mass information, producing refined results for both mass predictions and REP abundances.

Atomic masses are a foundational quantity in our understanding of nuclear structure, astrophysics, and fundamental symmetries. The longstanding goal of creating a predictive global model for the binding energy of a nucleus remains a significant challenge, however, and prompts the need for precise measurements of atomic masses to serve as anchor points for model developments. We present precise mass measurements of neutron-rich Ru and Pd isotopes performed at the Californium Rare Isotope Breeder Upgrade facility at Argonne National Laboratory using the Canadian Penning Trap mass spectrometer. The masses of 108Ru, 110Ru, and 116Pd were measured to a relative mass precision delta m/m approximate to 10(-8) via the phase-imaging ion-cyclotron-resonance technique, and represent an improvement of approximately an order of magnitude over previous measurements. These mass data were used in conjunction with the physically interpretable machine learning (PIML) model, which uses a mixture density neural network to model mass excesses via a mixture of Gaussian distributions. The effects of our new mass data on a Bayesian-updating of a PIML model are presented.

For many fission products, the $\ensuremath{\gamma}$ rays emitted following $\ensuremath{\beta}$ decay provide an easily detectable signature that can be used to identify their quantities and distributions in a sample. As a result, $\ensuremath{\gamma}$-ray spectroscopy is often exploited to study fission-product yields, provided sufficiently accurate information on the $\ensuremath{\gamma}$-ray intensities is available. In many cases, the uncertainties in the existing nuclear data are large enough that they compromise the precision achievable for modern experiments and applications. In this paper, we present high-precision results for the absolute $\ensuremath{\gamma}$-ray emission intensities for the most intense transitions in the $\ensuremath{\beta}$ decays of $^{144}\mathrm{Ce}$ and $^{147}\mathrm{Nd}$. We measured these intensities to $\ensuremath{\lesssim}1%$ accuracy by producing radiopure samples with fission-product beams at CARIBU and detecting the emitted radiation with a $4\ensuremath{\pi}\ensuremath{\beta}$ counter and a meticulously efficiency-calibrated high purity germanium detector at Texas A University.

The first complete measurement of the β-decay strength distribution of _{17}^{45}Cl_{28} was performed at the Facility for Rare Isotope Beams (FRIB) with the FRIB Decay Station Initiator during the second FRIB experiment. The measurement involved the detection of neutrons and γ rays in two focal planes of the FRIB Decay Station Initiator in a single experiment for the first time. This enabled an analytical consistency in extracting the β-decay strength distribution over the large range of excitation energies, including neutron unbound states. We observe a rapid increase in the β-decay strength distribution above the neutron separation energy in _{18}^{45}Ar_{27}. This was interpreted to be caused by the transitioning of neutrons into protons excited across the Z=20 shell gap. The SDPF-MU interaction with reduced shell gap best reproduced the data. The measurement demonstrates a new approach that is sensitive to the proton shell gap in neutron rich nuclei according to SDPF-MU calculations.

For many fission products, the gamma rays emitted following beta decay provide an easily detectable signature that can be used to identify their quantities and distributions in a sample. As a result, gamma-ray spectroscopy is often exploited to study fission-product yields, provided sufficiently accurate information on the gamma-ray intensities is available. In many cases, the uncertainties in the existing nuclear data are large enough that they compromise the precision achievable for modern experiments and applications. In this paper, we present high-precision results for the absolute gamma-ray emission intensities for the most intense transitions in the beta decays of Ce-144 and (147) Nd. We measured these intensities to less than or similar to 1% accuracy by producing radiopure samples with fission-product beams at CARIBU and detecting the emitted radiation with a 4 pi beta counter and a meticulously efficiency-calibrated high purity germanium detector at Texas A&M University.

Nuclear isomer effects are pivotal in understanding nuclear astrophysics, particularly in the rapid neutron-capture process where the population of metastable isomers can alter the radioactive decay paths of nuclei produced during astrophysical events. The beta-decaying isomer Sb-128m was identified as potentially impactful since the beta-decay pathway along the A = 128 isobar funnels into this state bypassing the ground state. We report the first direct mass measurements of the Sb-128 isomer and ground state using the Canadian Penning Trap mass spectrometer at Argonne National Laboratory. We find mass excesses of -84564.8(25) keV and -84608.8(21) keV, respectively, resulting in an excitation energy for the isomer of 43.9(33) keV. These results provide the first key nuclear data input for understanding the role of Sb-128m in nucleosynthesis, and we show that it will influence the flow of the rapid neutron-capture process.

The boundaries of the Chart of Nuclides contain exotic isotopes that possess extreme proton-toneutron asymmetries. Here we report on strong evidence of 9N, one of the most exotic proton-rich isotopes where more than one half of its constitute nucleons are unbound. With seven protons and two neutrons, this extremely proton-rich system would represent the first-known example of a ground-state five-proton emitter. The invariant-mass spectrum of its decay products can be fit with two peaks whose energies are consistent with the theoretical predictions of an open-quantum-system approach, however we cannot rule out the possibility that only a single resonance-like peak is present in the spectrum.

Production cross sections were measured for fragments produced by an 85 MeV/u 198Pt beam incident on a beryllium target. Event-by-event particle identification of A, Z, and q for the reaction products was performed by employing energy loss, time-of-flight, magnetic rigidity, and total kinetic energy measurements. Over 70 nuclei in the Hf-Pt region were identified, including three isotopes first observed in this work: 191,192Hf and 189Lu. Due to the existence of multiple charge states between H-like and C-like ions, a new analysis method was introduced, incorporating Monte Carlo calculations of charge state fractions for a given charge state of the projectile residue just after the reaction. For the first time, charge-state probability distribution functions after the reaction have been deduced from experimental data. This study provides insight into how to produce key nuclides near N=126 and the ability of a fragmentation residue to retain electrons from the primary beam.

Information on the $^{38}$S level scheme was expanded through experimental work utilizing a fusion-evaporation reaction and in-beam $γ$-ray spectroscopy. Prompt $γ$-ray transitions were detected by the Gamma-Ray Energy Tracking Array (GRETINA) and recoiling $^{38}$S residues were selected by the Fragment Mass Analayzer (FMA). Tools based on machine-learning techniques were developed and deployed for the first time in order to enhance the unique selection of $^{38}$S residues and identify any associated $γ$-ray transitions. The new level information, including the extension of the even-spin yrast sequence through $J^π = 8^{(+)}$, was interpreted in terms of a basic single-particle picture as well shell-model calculations which incorporated the empirically derived FSU interaction. A comparison between the properties of the yrast states in the even-$Z$ $N=22$ isotones from $Z=14$ to $20$, and for $^{36}$Si-$^{38}$S in particular, was also presented with an emphasis on the role and influence of the neutron $1p_{3/2}$ orbital on the structure in the region.

We measured the Zn57 β-delayed proton (βp) and γ emission at the National Superconducting Cyclotron Laboratory. We find a Zn57 half-life of 43.6±0.2 ms, βp branching ratio of (84.7±1.4)%, and identify four transitions corresponding to the exotic β-γ-p decay mode, the second such identification in the fp-shell. The p/γ ratio was used to correct for isospin mixing while determining the Zn57 mass via the isobaric multiplet mass equation. Previously, it was uncertain as to whether the rp-process flow could bypass the textbook waiting point Ni56 for astrophysical conditions relevant to Type-I X-ray bursts. Our results definitively establish the existence of the Ni56 bypass, with 14-17% of the rp-process flow taking this route.

Background: Isomeric states in atomic nuclei are a sensitive probe of their underlying microscopic structure and can be used to study the evolution of shell structure far from stability. Recent studies have identified and provided detailed spectroscopy of isomers in neutron-rich nuclei with Z = 28-50. Isomeric states in the odd-odd gallium isotopes have been reported for all gallium isotopes from A = 72 to A = 80 with the exception of Ga-76. Purpose: The purpose of this experiment was to observe short-lived isomeric states in the vicinity of Ni-78. Methods: In-beam fragmentation of a Kr-86 primary beam at the National Superconducting Cyclotron Laboratory produced radioactive ions which were delivered to and deposited in a CeBr3 scintillator coupled to a position-sensitive photomultiplier tube. Beta-delayed gamma rays were measured by ancillary HPGe clover and LaBr3 detectors which surrounded the implantation detector. Results: The previously observed J(pi) =1(+), 199-keV level in Ga-76, populated following the beta decay of Zn-76, was identified as isomeric with a half-life of 34(1)(stat)(8)(sys.) ns. Shell-model calculations suggest this state is formed by the coupling of protons in negative-parity configurations to 1/2(-) neutron configurations. Transition strengths assuming a ground-state spin of J = 2 and J = 3 were determined from the experimental data.

Nuclei in the vicinity of the N = Z line provide many sensitive probes of isospin symmetry. One example concerns the character and sequence of low-lying states of the T = 1/2 mirror pair 71Kr and 71Br which has been under debate for several decades. In this paper we report a new measurement of the absolute beta-branching to ground and excited states which, taken with our precise lifetime of T1/2 = 94.9(4) ms, gives a superallowed ground state-to-ground state log(ft) value of 3.64(4). This is only consistent with both 71Br and 71Kr having the same spin and parity, J pi = 5/2-, as expected from mirror symmetry. The beta-delayed proton emission to the first-excited state in 70Se was observed for the first time which also strongly supports this assignment.

The products of the 203,205Tl(50Ti, 2n) fusion-evaporation reactions were studied using the recently commissioned Argonne Gas-Filled Analyzer at Argonne National Laboratory. Two alpha-decay activities with energies of 9210(19) and 9246(19) keV and half-lives of 42+42-14 and 24.4+7.0 -4.5 ms were observed which were followed by the known alpha decays of 247Md and 243Es. They are interpreted as originating from the 1/2-[521] and 7/2-[514] single-proton Nilsson states in the hitherto unknown isotope 251Lr. From the measured Q alpha values the 1/2- level was placed 117(27) keV above the 7/2- level in 251Lr in contrast to 255Lr where the 1/2- level is the lowest. Also, the alpha decay of 253Lr was studied in more detail and a new alpha line at 8660(20) keV was found and a new half-life value of 2.46(32) s for an isomeric state in 253Lr was measured. The 251,253,255Lr Q alpha values were compared with predictions of various mass models. The relative energies of the 1/2-[521] and 7/2-[514] single-proton Nilsson states in 251,253,255Lr isotopes were compared with results of the cranking shell model with pairing treated using the particle-number-conserving method. The level separation and, in particular, the level order change between 251Lr and 255Lr was reproduced only when the hexacontetrapole deformation epsilon 6 was included in the calculations.

Background: The evolution of nuclear shell structure far from stability can be explored by identifying and measuring the properties of isomers. Neutron-rich nuclei between the $Z=28$ and the $Z=50$ closed shells have been the subject of recent studies which have identified a number of $0.1--10\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}$ isomers and measured detailed spectroscopic properties.Purpose: The purpose of this analysis was to identify and measure the properties of short-lived isomeric states populated following $\ensuremath{\beta}$ decay in $Z\ensuremath{\approx}30,\phantom{\rule{0.28em}{0ex}}N\ensuremath{\approx}50$ nuclei near the doubly magic nucleus $^{78}\mathrm{Ni}$.Methods: Radioactive ions produced by beam fragmentation at the National Superconducting Cyclotron Laboratory were implanted into a ${\mathrm{CeBr}}_{3}$ scintillator coupled to a pixelated photomultiplier tube. Ancillary arrays of HPGe clover and ${\mathrm{LaBr}}_{3}$ detectors were positioned around the implantation detector to measure $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ rays.Results: The previously observed 2634-keV level in $^{76}\mathrm{Zn}$, populated following the $\ensuremath{\beta}$ decay of $^{76}\mathrm{Cu}$, was identified as isomeric with a half-life of 25.4(4) ns. A combination of timing and $\ensuremath{\gamma}$-ray spectroscopy was used to confirm this assignment. Shell-model calculations were performed and indicate that this state may be a negative-parity state formed by the occupation of the $\ensuremath{\nu}0{g}_{9/2}$ orbital.Conclusions: A new isomeric state in $^{76}\mathrm{Zn}$ has been identified, and its half-life was measured. Ambiguity about the structure of this state could be resolved with further experiments.

Excited states in O-13 were investigated using inelastic scattering of an E/A = 69.5 MeV O-13 beam off of a Be-9 target. The excited states were identified in the invariant-mass spectra of the decay products. Both single-proton and sequential two-proton decays of the excited states were examined. For a number of the excited states, the protons were emitted with strong anisotropy where emissions transverse to the beam axis are favored. The measured proton-decay angular distributions were compared to predictions from distorted-wave Born-approximation calculations of the spin alignment which was shown to be largely independent of the excitation mechanism. The deduced O-13 level scheme is compared to ab initio no-core shell model with continuum predictions. The lowest-energy excited states decay isotropically consistent with predictions of strong proton 1s(1/2) structure. Above these states in the level scheme, we observed a number of higher-spin states not predicted within the model. Possibly these are associated with rotational bands built on deformed cluster configurations predicted by antisymmetrized molecular dynamics calculations. The spin alignment mechanism is shown to be useful for making spin assignments and may have widespread use.

Background: The evolution of nuclear shell structure far from stability can be explored by identifying and measuring the properties of isomers. Neutron-rich nuclei between the Z = 28 and the Z = 50 closed shells have been the subject of recent studies which have identified a number of 0.1-10 mu s isomers and measured detailed spectroscopic properties. Purpose: The purpose of this analysis was to identify and measure the properties of short-lived isomeric states populated following beta decay in Z approximate to 30, N approximate to 50 nuclei near the doubly magic nucleus 78Ni. Methods: Radioactive ions produced by beam fragmentation at the National Superconducting Cyclotron Laboratory were implanted into a CeBr3 scintillator coupled to a pixelated photomultiplier tube. Ancillary arrays of HPGe clover and LaBr3 detectors were positioned around the implantation detector to measure beta-delayed gamma rays. Results: The previously observed 2634-keV level in 76Zn, populated following the beta decay of 76Cu, was identified as isomeric with a half-life of 25.4(4) ns. A combination of timing and gamma -ray spectroscopy was used to confirm this assignment. Shell-model calculations were performed and indicate that this state may be a negative-parity state formed by the occupation of the nu 0g9/2 orbital. Conclusions: A new isomeric state in 76Zn has been identified, and its half-life was measured. Ambiguity about the structure of this state could be resolved with further experiments.

The $^{24}\mathrm{Mg}+^{12}\mathrm{C}$ fusion reaction was used to perform a detailed $\ensuremath{\gamma}$-ray spectroscopy study of the astrophysically important nucleus $^{34}\mathrm{Ar}$. In particular, an experimental setup, coupling the advanced $\ensuremath{\gamma}$-ray tracking array GRETINA with the well-established Argonne fragment mass analyzer (FMA), was employed to obtain excitation energies and spin-parity assignments for excited states in $^{34}\mathrm{Ar}$, both above and below the proton separation energy. For the first time, an angular distribution analysis of in-beam $\ensuremath{\gamma}$ rays from fusion-evaporation reactions, using a tracking array, has been performed and Coulomb energy differences of analog states in the $T=1,$ $A=34$ mirror system, explored from 0 to 6 MeV. Furthermore, we present a comprehensive discussion of the astrophysical $^{33}\mathrm{Cl}(p,\ensuremath{\gamma})$ stellar reaction rate, together with implications for the identification of nova presolar grains from sulfur isotopic abundances.

A ^{13}F resonance was observed following a charge-exchange reaction between a fast ^{13}O beam and a ^{9}Be target. The resonance was found in the invariant-mass distribution of 3p+^{10}C events and probably corresponds to a 5/2^{+} excited state. The ground state was also expected to be populated, but was not resolved from the background. The observed level decays via initial proton emissions to both the ground and first 2^{+} state of ^{12}O, which subsequently undergo 2p decay. In addition, there may also be a significant proton decay branch to the second 2^{+} level in ^{12}O. The wave function associated with the observed level may be collectivized due to coupling to the continuum as is it located just above the threshold for proton decay to the 2_{2}^{+} state of ^{12}O.