The 10 MV FN Tandem at the University of Notre Dame's Nuclear Science Laboratory has the option for a second foil stripper halfway down its high energy column. With its utilization, users are able to produce beams with higher energies and/or transmission than single foil stripping alone would be capable of achieving. A discussion of the Schiwietz-Grande, Nikolaev-Dmitriev, and Baudinet-Robinet semi-empirical models used to determine the resulting charge state abundances, as well as how they compare to measured charge state distributions is presented. The advantages of a second foil stripper are discussed alongside measurements of the charge state abundances produced. The potential for more interfering beam species of similar magnetic rigidity is also discussed. It was found that for most of the beams tested, second foil stripping allowed higher energies with higher yields than the single terminal foil stripping alone could achieve which can enhance the capabilities of other laboratories using similar accelerator systems.

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 radioisotopes of 43Sc and 44Sc are promising in the field of theranostics for their role as β+ emitters in theranostic pairs with 47Sc. Production of these isotopes through various nuclear reactions using either cyclotrons or linear accelerators is of particular interest and previous studies have provided results using accelerated beams of protons, deuterons, and alpha particles. A novel production technique, using an ion source cathode packed with natural calcium fluoride material and irradiated with a 3He beam, was tested at the Nuclear Science Laboratory at the University of Notre Dame in order to initially study the production of 41Ca. Gamma-ray spectrometry revealed presence of 43Sc and 44Sc in the target, and allowed for the first measurement of their yield due to reactions of 3He on natural calcium. The calculated thick target yields of 43Sc and 44gSc from the reactions natCa(3He,x)43Sc and natCa(3He,x)44gSc are compared to theoretical results using TALYS cross section models. Overall, results agree well with models at lower beam energies but tend to diverge at higher energies.

Deuteron-induced reactions on 6Li are important for nuclear structure studies and nuclear applications. A new experimental effort was dedicated to improve incomplete partial cross sections and the angular distribution information for d + 6Li reactions and to address the inconsistencies between various R-matrix evaluations of the 8Be system. The new measurements were performed over a deuteron energy range of 1.8 to 10 MeV with an angular distribution coverage of 20 degrees-170 degrees for outgoing particles. The experiment simultaneously measured neutrons, charged particles, and gamma rays from the various exit channels of the d + 6Li reaction. The cross sections for open reaction channels measured simultaneously are presented. In addition, results for the 6Li(d, n) 7Be total cross section using the activation method are also presented.

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 thermodynamical conditions and the neutron density produced in a laser-induced implosion of a deuterium-tritium (DT) filled capsule at the National Ignition Facility (NIF) are the closest laboratory analog of stellar conditions. We plan to investigate neutron-induced reactions on 40Ar, namely the 40Ar(n, 2n)39Ar(t1/2 =268 y), the 40Ar(n, γ)41Ar(110 min) and the potential rapid two-neutron capture reaction 40Ar(2n, γ)42Ar(33 y) in an Ar-loaded DT capsule. The chemical inertness of noble gas Ar enables reliable collection of the reaction products.

244Pu has recently been discovered in deep-sea deposits spanning the past 10 Myr, a period that includes two 60Fe pulses from nearby supernovae. 244Pu is among the heaviest r-process products, and we consider whether it was created in the supernovae, which is disfavored by nucleosynthesis simulations, or in an earlier kilonova event that seeded 244Pu in the nearby interstellar medium that was subsequently swept up by the supernova debris. We discuss how these possibilities can be probed by measuring 244Pu and other r-process radioisotopes such as 129I and 182Hf, both in lunar regolith samples returned to Earth by missions such as Chang'e and Artemis, and in deep-sea deposits.

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 detection of heavy (A > 127), long-lived trace radionuclides using accelerator mass spectrometry requires accelerator systems with high mass resolution and detectors with high efficiency, timing and energy resolution, and resistance to degradation. At the University of Notre Dame's Nuclear Science Laboratory, a two-anode gas ionization detector, similar to others employed at ETH Zurich, Vienna, and the Australia National University, has been built to be used with a time-of-flight system. This new detector is more robust than the existing Si detector, with two high resolution ΔE segments. This work describes the detector design and modifications to the time-of-flight system, summarizes the observed performance, and provides comparisons to a Geant4 model. The energy resolution (9% for 44 MeV 238U beams) was found to be better than the existing Si detector and its larger acceptance contributed a factor of five improvement (from 4% to 20%) in transmission through the detection system for uranium beams.

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.

The cross-section of the thermal neutron capture 41 Ar(n,γ) 42 Ar( t 1/2 =32.9 y) reaction was measured by irradiating a 40 Ar sample at the high-flux reactor of Institut Laue-Langevin (ILL) Grenoble, France. The signature of the two-neutron capture has been observed by measuring the growth curve and identifying the 1524.6 keV γ-lines of the shorter-lived 42 K(12.4 h) β − daughter of 42 Ar. Our preliminary value of the 41 Ar(n,γ) 42 Ar thermal cross section is 240(80) mb at 25.3 meV. For the first time, direct counting of 42 Ar was performed using the ultra-high sensitivity technique of noble gas accelerator mass spectrometry (NOGAMS) at Argonne National Laboratory, USA.

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.

Background: A multitude of broad interfering resonances characterize the $^{10}\mathrm{B}(p,\ensuremath{\alpha})^{7}\mathrm{Be}$ cross section at low energies. The complexity of the reaction mechanism, as well as conflicting experimental measurements, have so far prevented a reliable prediction of the cross section over the energy ranges pertinent for a boron-proton fusion reactor environment.Purpose: To improve the evaluated cross section of the $^{10}\mathrm{B}(p,\ensuremath{\alpha})^{7}\mathrm{Be}$ reaction, this study targets the proton energy region from 0.8 to 2.0 MeV, where kinematic overlap of the scattered protons and reaction $\ensuremath{\alpha}$ particles have made past measurements very challenging.Method: New detailed studies of the reaction have been performed at the Edwards Accelerator Laboratory at Ohio University and the Nuclear Science Laboratory at the University of Notre Dame using time-of-flight and degrader foil techniques, respectively.Results: Proton and $\ensuremath{\alpha}$-particle signals were clearly resolved using both techniques, and 16 point differential cross sections were measured over an angular range of ${\ensuremath{\theta}}_{\text{lab}}={45}^{\ensuremath{\circ}}$ and $157.{5}^{\ensuremath{\circ}}$. A comprehensive $R$-matrix analysis of the experimental data, including data from previous low-energy studies of the $^{10}\mathrm{B}(p,\ensuremath{\alpha})^{7}\mathrm{Be}, ^{10}\mathrm{B}(p,p)^{10}\mathrm{B}$, and $^{10}\mathrm{B}(p,\ensuremath{\gamma})^{11}\mathrm{C}$ reactions, was achieved over the region of measurement. Using a representative set of previous data, the fit was extended to very low energies.Conclusions: On the basis of this data and $R$-matrix analysis, a more reliable and consistent description of the $^{10}\mathrm{B}(p,\ensuremath{\alpha})^{7}\mathrm{Be}$ cross section has been established. The uncertainty over the energy range of this study has been reduced from $\ensuremath{\approx}20%$ to $\ensuremath{\approx}10%$, and the level structure over this region has been clarified considerably.

Background: A multitude of broad interfering resonances characterize the B-10(p, alpha) Be-7 cross section at low energies. The complexity of the reaction mechanism, as well as conflicting experimental measurements, have so far prevented a reliable prediction of the cross section over the energy ranges pertinent for a boron-proton fusion reactor environment. Purpose: To improve the evaluated cross section of the (10) B(p, alpha) Be-7 reaction, this study targets the proton energy region from 0.8 to 2.0 MeV, where kinematic overlap of the scattered protons and reaction a particles have made past measurements very challenging. Method: New detailed studies of the reaction have been performed at the Edwards Accelerator Laboratory at Ohio University and the Nuclear Science Laboratory at the University of Notre Dame using time-of-flight and degrader foil techniques, respectively. Results: Proton and alpha-particle signals were clearly resolved using both techniques, and 16 point differential cross sections were measured over an angular range of theta(lab) = 45 degrees and 157.5 degrees. A comprehensive R-matrix analysis of , the experimental data, including data from previous low-energy studies of the B-10(p , alpha)Be-7 B-10 (p, p) B-10 and B-10 (p, gamma) C-11 reactions, was achieved over the region of measurement. Using a representative set of previous data, the fit was extended to very low energies. Conclusions: On the basis of this data and R-matrix analysis, a more reliable and consistent description of the B-10 (p, alpha) Be-7 cross section has been established. The uncertainty over the energy range of this study has been reduced from approximate to 20% to approximate to 10% and the level structure over this region has been clarified considerably.

41Ca (t1/2 = 9.94 x 104 yrs) is an important stellar radionuclide and its production in the Early Solar System from various irradiation scenarios can help determine the viability of models of early stellar processes. A novel re-action technique has been under development and recently tested at the Nuclear Science Laboratory at the University of Notre Dame. This technique utilizes an "in-cathode" reaction method, where natural CaF2 material is packed into an ion source sample holder (cathode) and then irradiated and subsequently measured using Accelerator Mass Spectrometry (AMS) without the need for chemical processing afterward. The setup for the irradiation was performed using a 3He beam to measure the reaction natCa(3He,x)41Ca. Initial AMS results suggest additional complexity due to ion source sputtering rates and geometry, which will need to be explored further.

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.

The CNO cycle is the main energy source in massive stars during their hydrogen burning phase, and, for our sun, it contributes at the approximate to 1% level. As the14N(p, gamma)15O reaction is the slowest in the cycle, it determines the CNO energy production rate and thus the CNO contribution to the solar neutrino flux. These CNO neutrinos are produced primarily from the beta decay of 15O and, to a lesser extent, from the decay of 13N. Solar CNO neutrinos are challenging to detect, but they can provide independent new information on the metallicity of the solar core. Recently, CNO neutrinos from 15O have been identified for the first time with the Borexino neutrino detector at the INFN Gran Sasso underground laboratory. There are, however, still some considerable uncertainties in the 14N(p, gamma)15O reaction rate under solar temperature conditions. The low energy reaction data presented here, measured at the CASPAR underground accelerator, aim at connecting existing measurements at higher energies and attempts to shed light on the discrepancies between the various data sets, while moving towards a better understanding of the 14N(p, gamma )15O reaction cross section. The present measurements span proton energies between 0.27 and 1.07 MeV, closing a critical gap in the existing data. A multichannel R-matrix analysis was performed with the entire new and existing data sets and is used to extrapolate the astrophysical S factors of the ground state and the 6.79 MeV transition to low energies. The extrapolations are found to be in agreement with previous work, but find that the discrepancies between measured data and R-matrix fits, both past and present, still exist. We examine the possible reasons for these discrepancies and thereby provide recommendations for future studies.

As the scope of Accelerator Mass Spectrometry (AMS) expands, there is an increased need to extend the capability of isobaric separation to the medium-heavy mass region. Existing AMS facilities are limited in their ability to separate radioactive nuclei in the A = 100-200 range of interest from their neighboring stable isobars, as such measurements require higher energies than available in most facilities. ATLAS is one of the highest energy system used for AMS based experiments and has enabled isobaric discrimination for medium to heavy nuclides, notably via the Gas-Filled Magnet technique. A preparatory experiment performed in November, 2019, successfully demonstrated isobaric separation of 92Zr-92Mo using the Argonne Gas-Filled Analyzer (AGFA) with high magnetic rigidity. Since that time, MONICA, an eight-anode ionization chamber that measures both energy loss and position with two sets of split anodes, has been developed to aid in AMS experiments at AGFA and has undergone four commissioning runs at the Nuclear Science Laboratory at the University of Notre Dame utilizing Si, Fe/Ni, and Mn beams. This report presents the AGFA AMS run (November 2019) and the subsequent commissioning runs of the MONICA detector, including preliminary measurements on the long-lived isotopes 39Ar (268 y) and for the first time on 42Ar (33 y).