The large reported $E2$ strength between the ${2}^{+}$ ground state and ${1}^{+}$ first excited state of $^{8}\mathrm{Li}, B(E2;{2}^{+}\ensuremath{\rightarrow}{1}^{+})=55(15)\phantom{\rule{4pt}{0ex}}{e}^{2}{\mathrm{fm}}^{4}$, presents a puzzle. Unlike in neighboring $A=7--9$ isotopes, where enhanced $E2$ strengths may be understood to arise from deformation as rotational in-band transitions, the ${2}^{+}\ensuremath{\rightarrow}{1}^{+}$ transition in $^{8}\mathrm{Li}$ cannot be understood in any simple way as a rotational in-band transition. Moreover, the reported strength exceeds ab initio predictions by an order of magnitude. In light of this discrepancy, we revisited the Coulomb excitation measurement of this strength, now using particle-$\ensuremath{\gamma}$ coincidences, yielding a revised $B(E2;{2}^{+}\ensuremath{\rightarrow}{1}^{+})$ of $19{(}_{\ensuremath{-}6}^{+7})(2)\phantom{\rule{4pt}{0ex}}{e}^{2}{\mathrm{fm}}^{4}$. We explore how this value compares to what might be expected in the limits of rotational models. While the present value is about a factor of three smaller than previously reported, the current experimental data indicates that the $B(E2)$ value remains anomalously enhanced.

The large reported E 2 strength between the 2 + ground state and 1 + first excited state of 8 Li, B ( E 2; 2 + -> 1 + ) = 55(15) e 2 fm 4 , presents a puzzle. Unlike in neighboring A = 7-9 isotopes, where enhanced E 2 strengths may be understood to arise from deformation as rotational in -band transitions, the 2 + -> 1 + transition in 8 Li cannot be understood in any simple way as a rotational in -band transition. Moreover, the reported strength exceeds ab initio predictions by an order of magnitude. In light of this discrepancy, we revisited the Coulomb excitation measurement of this strength, now using particle- gamma coincidences, yielding a revised B ( E 2; 2 + -> 1 + ) of 19( + 7 - 6 )(2) e 2 fm 4 . We explore how this value compares to what might be expected in the limits of rotational models. While the present value is about a factor of three smaller than previously reported, the current experimental data indicates that the B ( E 2) value remains anomalously enhanced.

The ^24 Mg( α ,p) ^27 Al reaction was measured using the solenoid spectrometer for nuclear astrophysics at the University of the Notre Dame to study the astrophysical ^24 Mg( α ,p) ^27 Al reaction rate. Alpha beams from the 10-MV FN tandem accelerator impinged on ^24 Mg solid targets which were made using the vacuum evaporation method on ^12 C foils. A total of 43 beam energies were used. Recoiling protons from the ^24 Mg( α ,p) ^27 Al reaction were detected using a double-sided position sensitive silicon detector array mounted on the solenoid. Energies, times of flight, and flight distances of particles were measured for particle identification. Protons associated with a wide range of excitation energies E_x = 12.42–14.44 MeV in ^28 Si were identified.

Environmental detection of trace isotopes 233U and 236U are important forensic signatures for identifying uranium ore materials or tracking anthropogenic releases from weapons fallout or nuclear reprocessing. Currently, Accelerator Mass Spectrometry (AMS) is the only method sensitive enough to detect signatures of 233U/U and 236U/U at the natural level due to the molecular interferences of 232ThH and 235UH, respectively, often present in conventional mass spectrometry. In this work, we detail the AMS capabilities of actinides developed at the University of Notre Dame's Nuclear Science Laboratory (NSL). For the first time in our laboratory, we have measured isotopic ratios of 236U/U and explored additional signatures of 233U and decay chain products 231Pa and 230Th in both natural ore material and two National Bureau of Standards samples. In this work we estimate a system sensitivity for 236U/U of 1.4×10-11 and characterize the simultaneous detection of 233U, 231Pa, and 230Th.

The Mg-25,Mg-26(alpha, n)Si-28,Si-29 reactions have been shown to be influential to Al-26 production in massive stars. The previously measured data sets for these reactions have discrepant results, and further study is warranted. The first measurements are reported of the total reaction cross sections of these reactions using direct recoil detection. The results are in good agreement with previous data sets based upon differential cross section studies. Astrophysical reaction rates based on the experimental data are reported and are within a factor of 1.5 of previous statistical model estimates.

Recent measurement of the fusion excitation function for $^{17}\mathrm{O}+^{12}\mathrm{C}$ reported the significant suppression of the fusion cross section at ${E}_{\mathrm{c}.\mathrm{m}.}\ensuremath{\approx}14$ MeV. This suppression was hypothesized to signal the existence of a $^{16}\mathrm{O}+n+^{12}\mathrm{C}$ molecular configuration. Using the active-target detector MuSIC@Indiana provided an effective means of reexamining the fusion excitation function for $^{17}\mathrm{O}+^{12}\mathrm{C}$. The accuracy of this thick-target measurement is strengthened through comparison with the thin-target measurement of the excitation function for $^{17}\mathrm{F}+^{12}\mathrm{C}$. The result provides important information about the dependence of the average fusion cross section for the oxygen isotopic chain on neutron excess.

The rate of the final step in the astrophysical αp process, the ^{34}Ar(α,p)^{37}K reaction, suffers from large uncertainties due to a lack of experimental data, despite having a considerable impact on the observable light curves of x-ray bursts and the composition of the ashes of hydrogen and helium burning on accreting neutron stars. We present the first direct measurement constraining the ^{34}Ar(α,p)^{37}K reaction cross section, using the Jet Experiments in Nuclear Structure and Astrophysics gas jet target. The combined cross section for the ^{34}Ar,Cl(α,p)^{37}K,Ar reaction is found to agree well with Hauser-Feshbach predictions. The ^{34}Ar(α,2p)^{36}Ar cross section, which can be exclusively attributed to the ^{34}Ar beam component, also agrees to within the typical uncertainties quoted for statistical models. This indicates the applicability of the statistical model for predicting astrophysical (α,p) reaction rates in this part of the αp process, in contrast to earlier findings from indirect reaction studies indicating orders-of-magnitude discrepancies. This removes a significant uncertainty in models of hydrogen and helium burning on accreting neutron stars.

Experimentally determined cross sections are a critical input for accurately modeling the nuclear processes that take place in a variety of astrophysical environments. A new detector has been designed and constructed to measure the total cross section of nuclear reactions relevant for astrophysics. The Active Target High Efficiency detector for Nuclear Astrophysics (ATHENA) has been constructed and commissioned by a measurement of the 12C +12C fusion reaction. As an active target detector with a segmented anode, efficient measurements of total cross sections over a wide energy range are possible.

Accelerator Mass Spectrometry (AMS) with 53Mn has geological applications as a chronometer for exposure and burial times for discontinuously deposited sediments. It has also been used to search for evidence of recent supernovae events, and proposed as a proxy to monitor the variation in the galactic cosmic ray spectrum over time. The current sensitivity limit amongst active facilities is 53Mn/55Mn = 3 x 10-13 while a sensitivity of 53Mn/55Mn = 1 x 10-13 is necessary to fully exploit 53Mn's capabilities. At the University of Notre Dame's Nuclear Science Laboratory (NSL), a 10 MV tandem accelerator and a Browne-Buechner Spectrograph operated as a gas-filled magnet were used to separate 53Mn from 53Cr. Samples covering ranges of 53Mn/55Mn = 10-10 - 10-8 were measured for the first time at the NSL using various settings resulting in a background level of 53Mn/55Mn = 6.2(3) x 10-11. Analysis of the results, descriptions of experimental settings, and further explorations will be presented in this paper.

The rate of the final step in the astrophysical αp process, the ^{34}Ar(α,p)^{37}K reaction, suffers from large uncertainties due to a lack of experimental data, despite having a considerable impact on the observable light curves of x-ray bursts and the composition of the ashes of hydrogen and helium burning on accreting neutron stars. We present the first direct measurement constraining the ^{34}Ar(α,p)^{37}K reaction cross section, using the Jet Experiments in Nuclear Structure and Astrophysics gas jet target. The combined cross section for the ^{34}Ar,Cl(α,p)^{37}K,Ar reaction is found to agree well with Hauser-Feshbach predictions. The ^{34}Ar(α,2p)^{36}Ar cross section, which can be exclusively attributed to the ^{34}Ar beam component, also agrees to within the typical uncertainties quoted for statistical models. This indicates the applicability of the statistical model for predicting astrophysical (α,p) reaction rates in this part of the αp process, in contrast to earlier findings from indirect reaction studies indicating orders-of-magnitude discrepancies. This removes a significant uncertainty in models of hydrogen and helium burning on accreting neutron stars.

The low-lying structure of 13Be has remained an enigma for decades. Despite numerous experimental and theoretical studies, large inconsistencies remain. Being both unbound and one neutron away from 14Be, the heaviest bound beryllium nucleus, 13Be is difficult to study through simple reactions with weak radioactive-ion beams or more complex reactions with stable-ion beams. Here, we present the results of a study using the 12Be(d, p)13Be reaction in inverse kinematics using a 9.5 MeV per nucleon 12Be beam from the ISAC-II facility. The solid deuteron target of IRIS was used to achieve an increased areal thickness compared to conventional deuterated polyethylene targets. The Q-value spectrum below -4.4 MeV was analyzed using a Bayesian method with GEANT4 simulations. A three-point angular distribution with the same Q-value gate was fit with a mixture of s- and p-wave, s- and d-wave, or pure p-wave transfer. The Q-value spectrum was also compared with GEANT simulations obtained using the energies and widths of states reported in four previous works. It was found that our results are incompatible with works that revealed a wide 5/2+ resonance but shows better agreement with ones that reported a narrower width.

The low-lying structure of $^{13}\mathrm{Be}$ has remained an enigma for decades. Despite numerous experimental and theoretical studies, large inconsistencies remain. Being both unbound and one neutron away from $^{14}\mathrm{Be}$, the heaviest bound beryllium nucleus, $^{13}\mathrm{Be}$ is difficult to study through simple reactions with weak radioactive-ion beams or more complex reactions with stable-ion beams. Here, we present the results of a study using the $^{12}\mathrm{Be}(d,p)^{13}\mathrm{Be}$ reaction in inverse kinematics using a 9.5 MeV per nucleon $^{12}\mathrm{Be}$ beam from the ISAC-II facility. The solid deuteron target of IRIS was used to achieve an increased areal thickness compared to conventional deuterated polyethylene targets. The $Q$-value spectrum below $\ensuremath{-}4.4$ MeV was analyzed using a Bayesian method with geant4 simulations. A three-point angular distribution with the same $Q$-value gate was fit with a mixture of $s$- and $p$-wave, $s$- and $d$-wave, or pure $p$-wave transfer. The $Q$-value spectrum was also compared with geant simulations obtained using the energies and widths of states reported in four previous works. It was found that our results are incompatible with works that revealed a wide $5/{2}^{+}$ resonance but shows better agreement with ones that reported a narrower width.

Recent measurement of the fusion excitation function for 17O + 12C reported the significant suppression of the fusion cross section at Ec.m. & AP; 14 MeV. This suppression was hypothesized to signal the existence of a 16O +n + 12C molecular configuration. Using the active-target detector MuSIC@Indiana provided an effective means of reexamining the fusion excitation function for 17O + 12C. The accuracy of this thick-target measurement is strengthened through comparison with the thin-target measurement of the excitation function for 17F + 12C. The result provides important information about the dependence of the average fusion cross section for the oxygen isotopic chain on neutron excess.

Measurement of fusion excitation functions for stable nuclei has largely been restricted to nuclei with significant natural abundance. Typically, to investigate neighboring nuclei with low natural abundance has required obtaining isotopically enriched material. This restriction often limits the ability to perform such measurements. We report the measurement of a high quality fusion excitation function for a $^{17}$O beam produced from unenriched material with 0.038\% natural abundance. The measurement is enabled by using an active thick-target approach and the accuracy of the result is validated using its mirror nucleus $^{17}$F and resonances. The result provides important information about the average fusion cross-section for the oxygen isotopic chain as a function of neutron excess.

The detailed study of radioactive nuclei has resulted in opportunities for addressing many open questions in low-energy nuclear physics. For over three decades, the TwinSol separator at the University of Notre Dame has produced high-quality in-flight radioactive beams at low-energy for light isotopes that have been used in experiments aimed at nuclear structure, astrophysics, and fundamental symmetries studies. We have recently upgraded the TwinSol separator by adding additional elements: a dipole magnet, and a third solenoid. This new TriSol separator will improve the quality and purity of future radioactive beams. This improvement will enable the use of heavier beams and address beam contamination that has hindered past experiments. The current status of TriSol and its science program will be presented along with the role the TriSol program plays in the current landscape of nuclear physics user facilities. The TriSol program includes plans for studies of 11C(p, p)11C reaction for investigating the nature of the first stars, 14O(α, p)17F and its influence on reaction networks in X-ray bursts, the measurement of fusion reactions on Ne isotopes important for pycnonuclear reactions, precision half-life measurements for fundamental symmetries studies, and the use of TriSol as a magnetic spectrometer.

The low-lying structure of $^{13}$Be has remained an enigma for decades. Despite numerous experimental and theoretical studies, large inconsistencies remain. Being both unbound, and one neutron away from $^{14}$Be, the heaviest bound beryllium nucleus, $^{13}$Be is difficult to study through simple reactions with weak radioactive ion beams or more complex reactions with stable-ion beams. Here, we present the results of a study using the $^{12}$Be(d,p)$^{13}$Be reaction in inverse kinematics using a 9.5~MeV per nucleon $^{12}$Be beam from the ISAC-II facility. The solid deuteron target of IRIS was used to achieve an increased areal thickness compared to conventional deuterated polyethylene targets. The Q-value spectrum below -4.4~MeV was analyzed using a Bayesian method with GEANT4 simulations. A three-point angular distribution with the same Q-value gate was fit with a mixture of $s$- and $p$-wave, $s$- and $d$-wave, or pure $p$-wave transfer. The Q-value spectrum was also compared with GEANT simulations obtained using the energies and widths of states reported in four previous works. It was found that our results are incompatible with works that revealed a wide $5/2^+$ resonance but shows better agreement with ones that reported a narrower width.

Active-target detectors have the potential to address the difficulties associated with the low intensities of radioactive beams. We have developed an active-target detector, the Notre Dame Cube (ND-Cube), to perform experiments with radioactive beams produced at TwinSol and to aid in the development of active-target techniques. Various aspects of the ND-Cube and its design were characterized. The ND-Cube was commissioned with a 7Li beam for measuring 40Ar+7Li fusion reaction cross sections and investigating 7Li(α,α)7Li scattering events. The ND-Cube will be used to study a range of reactions using light radioactive ions produced at low energy.

Multi-Sampling Ionization Chambers (MuSIC) provide an efficient means of measuring nuclear reactions with low beam rates (< 10(6) pps). However, in comparison to thin-target measurements, prior measurements using MuSIC detectors all manifest fusion excitation functions with wide error bars in the energy dimension. This uncertainty limits the applicability of these devices in measuring near and sub-barrier fusion cross-sections. Key to overcoming this limitation is spatial localization of the fusion in the detector. By comparing the measured ionization in the MuSIC detector with accurate energy loss calculations the position of the fusion in the detector is determined. The analysis not only provides the desired improvement in energy resolution, but it also allows extraction of the atomic number of the evaporation residues following fusion. The effectiveness of this approach is demonstrated for O-18+C-12 measured with MuSIC@Indiana.

A new precision half-life measurement of 13N has been conducted using the TwinSol n-counting station at the University of Notre Dame. The measured value of t1/2new = 597.05(19) s differs from the previous world value by about 2.8 sigma. An evaluation of the 13N half-life results in a tworld 1/2 = 597.19(22) s. Updated standard model predictions for the Fermi to Gamow-Teller mixing ratio rho and its associated correlation parameters have been calculated using the new 13N world half-life in preparation for a future measurement of the mixing ratio. Finally, an ab initio no-core configuration interaction (NCCI) calculation for the B(GT) of this decay, carried out using the Daejeon16 interaction, has been performed, revealing the need for higher-order chiral corrections.

Monte Carlo simulations are widely used in nuclear physics to model experimental systems. In cases where there are significant unknown quantities, such as energies of states, an iterative process of simulating and fitting is often required to describe experimental data. We describe a Bayesian approach to fitting experimental data, designed for data from a $^{12}$Be(d,p) reaction measurement, using simulations made with GEANT4. Q-values from the $^{12}$C(d,p) reaction to well-known states in $^{13}$C are compared with simulations using BayesOpt. The energies of the states were not included in the simulation to reproduce the situation for $^{13}$Be where the states are poorly known. Both cases had low statistics and significant resolution broadening owing to large proton energy losses in the solid deuterium target. Excitation energies of the lowest three excited states in $^{13}$C were extracted to better than 90 keV, paving a way for extracting information on $^{13}$Be.