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The CNO cycle is the main energy source in stars more massive than our sun, it defines the energy production and the cycle time that lead to the lifetime of massive stars, and it is an important tool for the determination of the age of globular clusters. One of the largest uncertainties in the CNO chain of reactions comes from the uncertainty in the $^{14}$N$(p,\gamma)^{15}$O reaction rate. This uncertainty arises predominantly from the uncertainty in the lifetime of the sub-threshold state in $^{15}$O at $E_{x}$ = 6792 keV. Previous measurements of this state's lifetime are significantly discrepant. Here, we report on a new lifetime measurement of this state, as well as the excited states in $^{15}$O at $E_{x}$ = 5181 keV and $E_{x}$ = 6172 keV, via the $^{14}$N$(p,\gamma)^{15}$O reaction at proton energies of $E_{p} = 1020$ keV and $E_{p} = 1570$ keV. The lifetimes have been determined with the Doppler-Shift Attenuation Method (DSAM) with three separate, nitrogen-implanted targets with Mo, Ta, and W backing. We obtained lifetimes from the weighted average of the three measurements, allowing us to account for systematic differences between the backing materials. For the 6792 keV state, we obtained a $\tau = 0.6 \pm 0.4$ fs. To provide cross-validation of our method, we measured the known lifetimes of the states at 5181 keV and 6172 keV to be $\tau = 7.5 \pm 3.0$ and $\tau = 0.7 \pm 0.5$ fs, respectively, which are in good agreement with previous measurements., Comment: 10 pages, 13 figures

The predominant branch in the $\ensuremath{\beta}$ decay of $^{34}\mathrm{Ar}$ is the superallowed ${0}^{+}\ensuremath{\rightarrow}\phantom{\rule{0.16em}{0ex}}{0}^{+}$ transition to the ground state of $^{34}\mathrm{Cl}$. To determine its important branching ratio one must first establish the ratios for the competing Gamow-Teller branches based on the measured intensities of $\ensuremath{\gamma}$ rays subsequently emitted from the excited states they populate in $^{34}\mathrm{Cl}$. The strongest of these branches populates the ${1}^{+}$ state at 666 keV in $^{34}\mathrm{Cl}$, which has three possible $\ensuremath{\gamma}$-decay paths. We report here a measurement of the decay of this state, which we populated via resonant proton capture in the reaction $^{33}\mathrm{S}$($p,\ensuremath{\gamma}$)$^{34}\mathrm{Cl}$. We find that the intensity of the 519-keV $\ensuremath{\gamma}$-ray path is 1.46(19)% relative to that of the 666-keV path. This result is critical to new precise measurements of the superallowed decay of $^{34}\mathrm{Ar}$.

Nuclear reactions play a key role in the framework of the Big Bang Nucleosynthesis. A network of 12 principal reactions has been identified as the main path that drove the elemental nucleosynthesis in the first 20 min of the history of the Universe. Among them an important role is played by neutron-induced reactions, which, from an experimental point of view, are usually a difficult task to be measured directly. Nevertheless big efforts in the last decades have led to a better understanding of their role in the primordial nucleosynthesis network. In this work we apply the Trojan Horse Method to extract the cross section at astrophysical energies for the $$^3\text {He}$$ (n,p) $$^3\text {H}$$ reaction after a detailed study of the $$^2\hbox {H}$$ ( $$^3\text {He}$$ ,pt)H three-body process. Data extracted from the present measurement are compared with other published sets.

Quasi-elastic scattering measurements have been performed using 16O and 24Mg projectiles off 90Zr at energies around the Coulomb barrier. Experimental data have been analyzed in the framework of coupled channels (CC) calculations using the code CCFULL. The quasi-elastic scattering excitation function and derived barrier distribution for 16O + 90Zr reaction are well reproduced by the CC calculations using the vibrational coupling strengths for 90Zr reported in the literature. Using these vibrational coupling strengths, a Bayesian analysis is carried out for 24Mg + 90Zr reaction. The β 2 and β 4 values for 24Mg are determined to be + 0.43 ± 0.02 and − 0.11 ± 0.02 , respectively. The β 2 parameter determined in the present work is in good agreement with results obtained using inelastic scattering probes. The hexadecapole deformation of 24Mg has been measured very precisely for the first time. Present results establish that quasi-elastic scattering could provide a useful probe to determine the ground state deformation of atomic nuclei.

Carbon and oxygen burning reactions, in particular, $^{12}\mathrm{C}+^{12}\mathrm{C}$ fusion, are important for the understanding and interpretation of the late phases of stellar evolution as well as the ignition and nucleosynthesis in cataclysmic binary systems such as type Ia supernovae and x-ray superbursts. A new measurement of this reaction has been performed at the University of Notre Dame using particle-$\ensuremath{\gamma}$ coincidence techniques with SAND (a silicon detector array) at the high-intensity 5U Pelletron accelerator. New results for $^{12}\mathrm{C}+^{12}\mathrm{C}$ fusion at low energies relevant to nuclear astrophysics are reported. They show strong disagreement with a recent measurement using the indirect Trojan Horse method. The impact on the carbon burning process under astrophysical scenarios will be discussed.

A new precision half-life measurement of $^{29}\mathrm{P}$ was conducted using the TwinSol $\ensuremath{\beta}$-counting station at the University of Notre Dame Nuclear Science Laboratory. The resulting value of ${t}_{1/2}^{\mathrm{new}}=4.1055(44)\phantom{\rule{0.28em}{0ex}}\mathrm{s}$ is the most precise $^{29}\mathrm{P}$ half-life measurement to date. Utilizing this measurement and reevaluating the world data leads to a new world average of ${t}_{1/2}^{\mathrm{world}}=4.1031(58)\phantom{\rule{0.28em}{0ex}}\mathrm{s}$, which improves the Birge ratio from 3.11 to 1.45 and is 2.3 times more precise than the previous world value. The new Cabibbo-Kobayashi-Maskawa matrix element ${V}_{\mathrm{ud}}$ for $^{29}\mathrm{P}$ shifts closer into agreement with the superallowed pure Fermi value. The uncertainty in the mixed transition value of ${V}_{\mathrm{ud}}$, however, is still dominated by the Fermi to Gamow-Teller mixing ratio $\ensuremath{\rho}$. Using the new world half-life and assuming the validity of the standard model, a new predicted value for $\ensuremath{\rho}$ and its associated correlation parameters have been evaluated in order to guide future determination of $\ensuremath{\rho}$.

Carbon and oxygen burning reactions, in particular, $^{12}$C+$^{12}$C fusion, are important for the understanding and interpretation of the late phases of stellar evolution as well as the ignition and nucleosynthesis in cataclysmic binary systems such as type Ia supernovae and x-ray superbursts. A new measurement of this reaction has been performed at the University of Notre Dame using particle-$\gamma$ coincidence techniques with SAND (a silicon detector array) at the high-intensity 5U Pelletron accelerator. New results for $^{12}$C+$^{12}$C fusion at low energies relevant to nuclear astrophysics are reported. They show strong disagreement with a recent measurement using the indirect Trojan Horse method. The impact on the carbon burning process under astrophysical scenarios will be discussed., Comment: accepted for publication in Phys. Rev. Lett

In the network of reactions present in the Big Bang nucleosynthesis, the 3He(n, p)3H has an important role which impacts the final 7Li abundance. The Trojan Horse Method (THM) has been applied to the 3He(d, pt)H reaction in order to extract the astrophysical S(E)-factor of the 3He(n, p)3H in the Gamow energy range. The experiment will be described in the present work together with the first preliminary results.

The National Ignition Facility (NIF) provides the opportunity to study nuclear reactions under controlled conditions at high temperatures and pressures at a level never before achieved. However, the timescale of the deuterium-tritium (DT) implosion is only a few nanoseconds, making data collection and diagnostics very challenging. One method that has been proposed for obtaining additional information about the conditions of the implosion is to activate a dopant material using the $\ensuremath{\alpha}$ particles produced from the DT fuel as a diagnostic. The yield of the activated material can give a measure of the mixing that occurs in the capsule. One of the reactions that has been proposed is $^{10}\mathrm{B}(\ensuremath{\alpha},n)\phantom{\rule{0.16em}{0ex}}^{13}\mathrm{N}$ as it produces a radioactive reactant product with a convenient half-life of $\ensuremath{\approx}10\phantom{\rule{0.16em}{0ex}}\mathrm{min}$. Although this reaction has several advantages for the application at hand, it has not seen much study in the present literature, resulting in large uncertainties in the cross section. Furthermore, for the current application, the cross section must be well characterized. With this motivation, the $^{10}\mathrm{B}(\ensuremath{\alpha},n)\phantom{\rule{0.16em}{0ex}}^{13}\mathrm{N}$ cross section has been remeasured for $2.2l{E}_{\ensuremath{\alpha}}l4.9\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ with the angle-integrated ground-state cross section reported for the first time. The present results, combined with previous measurements, allow for a determination of the cross section to a significantly higher degree of accuracy and precision than obtained previously and are shown to be consistent with thick-target measurements. Preliminary calculations are performed to test the feasibility of this reaction as a diagnostic for a NIF implosion.

Electromagnetic observables are able to give insight into collective and emergent features in nuclei, including nuclear clustering. These observables also provide strong constraints for ab initio theory, but comparison of these observables between theory and experiment can be difficult due to the lack of convergence for relevant calculated values, such as $E2$ transition strengths. By comparing the ratios of $E2$ transition strengths for mirror transitions, we find that a wide range of ab initio calculations give robust and consistent predictions for this ratio. To experimentally test the validity of these ab initio predictions, we performed a Coulomb excitation experiment to measure the $B(E2;3/{2}^{\ensuremath{-}}\ensuremath{\rightarrow}1/{2}^{\ensuremath{-}})$ transition strength in $^{7}\mathrm{Be}$ for the first time. A $B(E2;3/{2}^{\ensuremath{-}}\ensuremath{\rightarrow}1/{2}^{\ensuremath{-}})$ value of $26{(6)}_{\mathrm{stat}}{(3)}_{\mathrm{syst}}\phantom{\rule{0.16em}{0ex}}{e}^{2}{\mathrm{fm}}^{4}$ was deduced from the measured Coulomb excitation cross section. This result is used with the experimentally known $^{7}\mathrm{Li}\phantom{\rule{4pt}{0ex}}B(E2;3/{2}^{\ensuremath{-}}\ensuremath{\rightarrow}1/{2}^{\ensuremath{-}})$ value to provide an experimental ratio to compare with the ab initio predictions. Our experimental value is consistent with the theoretical ratios within $1\ensuremath{\sigma}$ uncertainty, giving experimental support for the value of these ratios. Further work in both theory and experiment can give insight into the robustness of these ratios and their physical meaning.

Proper understanding of the stellar nucleosynthesis processes requires information on a variety of capture reaction cross sections. Since these cross sections are typically very low, they require efficient measurement techniques. The High Efficiency Total Absorption Spectrometer (HECTOR) was designed to measure capture cross sections relevant for astrophysical processes. HECTOR is a $ \gamma$ -summing detector comprised of 16 separate NaI(Tl) segments. The detector design is presented, as well as a detailed study of the detector's summing efficiency and analysis procedure. The results of the commissioning of HECTOR are presented. The resonance strengths of the well-known resonances in the 27Al $ (\mathrm{p},\gamma)$28Si reaction measured with HECTOR are compared with the literature values.

The 14O(α,p)17F reaction is an important trigger reaction to the α-p process in X-ray bursts. The most stringent experimental constraints on its astrophysical rate come from measurements of the time-inverse reaction, 17F(p,α)14O. Previous studies of this inverse reaction have sufficiently characterized the high-energy dependence of the cross section but there are still significant uncertainties at lower energies. A new measurement of the 17F(p,α)14O cross section is underway at the Twin Solenoid (TwinSol) facility at the University of Notre Dame using an in-flight secondary 17F beam. The initial results are promising but improvements are needed to complete the measurement. The initial data and plans for an improved measurement are presented in this manuscript.

In the network of reactions present in the Big Bang nucleosynthesis, the 3He(n, p)3H reaction has an important role which impacts the final 7Li abundance. The Trojan Horse Method (THM) has been applied to the 3He(d, pt)H reaction in order to extract the astrophysical S(E)-factor of the 3He(n, p)3H reaction in the Gamow energy range. The experiment will be described in the present work together with the first preliminary results.

The nucleosynthesis path of the γ-process is predominantly governed by the branching points at which the flow of the initial (γ,n) is redirected by either (γ,p) or (γ,α) reactions. In this work, the inverse reactions, proton and α capture on 108Cd were studied in order to aid in verification of the 112Sn isotope as a potential branching point in the γ-process. The results of the first measurement with a γ-summing detector, HECTOR, are compared with previous measurements found in the literature and with NON-SMOKER predictions. The results of this work will provide input for Hauser-Feshbach calculations to obtain the γ induced reaction rates.

We report a new precision half-life measurement of $^{20}\mathrm{F}$, performed using the $\ensuremath{\beta}$-counting station of the University of Notre Dame's Nuclear Science Laboratory. The measured half-life of $11.0160{(41)}_{\text{stat}}{(155)}_{\text{sys}}$ s resulting from this work will help resolve the longstanding discrepancy between two earlier sets of high-precision half-life measurements.

A direct test of nova explosion models comes from the observation of γ rays created in the decay of radioactive isotopes produced in the nova. One such isotope, 18F, is believed to be the main source of observable γ rays at and below 511 keV. The main destruction mechanism of 18F is thought to be the 18F(p,α)15O reaction, and uncertainties in the reaction rate arise from uncertainties in the energies, spins, and parities of the nuclear levels in 19Ne above the 18F+p threshold. To measure the properties of these levels, the 19F(3He,t)19Ne∗(γ) reaction was studied at Argonne National Laboratory and the Nuclear Science Laboratory at the University of Notre Dame.A direct test of nova explosion models comes from the observation of γ rays created in the decay of radioactive isotopes produced in the nova. One such isotope, 18F, is believed to be the main source of observable γ rays at and below 511 keV. The main destruction mechanism of 18F is thought to be the 18F(p,α)15O reaction, and uncertainties in the reaction rate arise from uncertainties in the energies, spins, and parities of the nuclear levels in 19Ne above the 18F+p threshold. To measure the properties of these levels, the 19F(3He,t)19Ne∗(γ) reaction was studied at Argonne National Laboratory and the Nuclear Science Laboratory at the University of Notre Dame.

The influence of high-energy (1.6 MeV) Ar2+ irradiation on the interfacial interaction between cerium oxide thin films (∼15 nm) with a SiO2/Si substrate is investigated using transmission electron microscopy, ultrahigh vacuum x-ray photoelectron spectroscopy (XPS), and a carbon monoxide (CO) oxidation catalytic reaction using ambient pressure XPS. The combination of these methods allows probing the dynamics of vacancy generation and its relation to chemical interactions at the CeO2/SiO2/Si interface. The results suggest that irradiation causes amorphization of some portion of CeO2 at the CeO2/SiO2/Si interface and creates oxygen vacancies due to the formation of Ce2O3 at room temperature. The subsequent ultra-high-vacuum annealing of irradiated films increases the concentration of Ce2O3 with the simultaneous growth of the SiO2 layer. Interactions with CO molecules result in an additional reduction of cerium and promote the transition of Ce2O3 to a silicate compound. Thermal annealing of thin films exposed to oxygen or carbon monoxide shows that the silicate phase is highly stabile even at 450 °C.

Background: The precise determination of the $\mathcal{F}t$ value in $T=1/2$ mixed mirror decays is an important avenue for testing the standard model of the electroweak interaction through the determination of ${V}_{ud}$ in nuclear $\ensuremath{\beta}$ decays. $^{11}\mathrm{C}$ is an interesting case, as its low mass and small ${Q}_{EC}$ value make it particularly sensitive to violations of the conserved vector current hypothesis. The present dominant source of uncertainty in the $^{11}\mathrm{C}\phantom{\rule{4pt}{0ex}}\mathcal{F}t$ value is the half-life.Purpose: A high-precision measurement of the $^{11}\mathrm{C}$ half-life was performed, and a new world average half-life was calculated.Method: $^{11}\mathrm{C}$ was created by transfer reactions and separated using the TwinSol facility at the Nuclear Science Laboratory at the University of Notre Dame. It was then implanted into a tantalum foil, and $\ensuremath{\beta}$ counting was used to determine the half-life.Results: The new half-life, ${t}_{1/2}=1220.27(26)$ s, is consistent with the previous values but significantly more precise. A new world average was calculated, ${t}_{1/2}^{\text{world}}=1220.41(32)$ s, and a new estimate for the Gamow-Teller to Fermi mixing ratio $\ensuremath{\rho}$ is presented along with standard model correlation parameters.Conclusions: The new $^{11}\mathrm{C}$ world average half-life allows the calculation of a $\mathcal{F}{t}^{\text{mirror}}$ value that is now the most precise value for all superallowed mixed mirror transitions. This gives a strong impetus for an experimental determination of $\ensuremath{\rho}$, to allow for the determination of ${V}_{ud}$ from this decay.

Ab-initio calculations have been able to reproduce emergent phenomena such as the formation of clusters in nuclei, a prominent feature in light nuclei. A number of ab-initio methods have made predictions for the B(E2; 3/2− → 1/2−) transition strength in the radioactive nucleus 7Be where a prominent α-3 He structure is expected. In order to test and guide these ab-inito methods, we have performed a Coulomb excitation experiment to measure the B(E2; 3/2− → 1/2−) in 7Be. Our current results point to the importance of reproducing cluster features in our nuclear models.Ab-initio calculations have been able to reproduce emergent phenomena such as the formation of clusters in nuclei, a prominent feature in light nuclei. A number of ab-initio methods have made predictions for the B(E2; 3/2− → 1/2−) transition strength in the radioactive nucleus 7Be where a prominent α-3 He structure is expected. In order to test and guide these ab-inito methods, we have performed a Coulomb excitation experiment to measure the B(E2; 3/2− → 1/2−) in 7Be. Our current results point to the importance of reproducing cluster features in our nuclear models.

A new precision half-life measurement of $^{25}\mathrm{Al}$ was conducted using the TwinSol $\ensuremath{\beta}$-counting station at the University of Notre Dame. The new measured value of ${t}_{1/2}^{\mathrm{new}}=7.1657(24)$ s is in good agreement with the most recent measurement, while being 3 times more precise. Using these new measurements, an evaluation of the $^{25}\mathrm{Al}$ half-life has been performed, leading to an average half-life of ${t}_{1/2}^{\mathrm{world}}=7.1665(26)$ s, which is 5 times more precise than it's predecessor and has a more satisfactory Birge ratio of 1.1. To aid in future measurements of correlation parameters, a new Fermi to Gamow-Teller mixing ratio $\ensuremath{\rho}$ and correlation parameters for this mixed transition have been calculated assuming the standard model validity using the new world half-life.

The first measurements of the capture reactions for the astrophysical γ-process using HECTOR, a total absorption spectrometer are presented. Two reactions: 102Pd(p,γ)103Ag and 90Zr(α,γ)94Mo were measured using the γ-summing technique. The results are compared with the previous measurements found in the literature and with the NON-SMOKER predictions. The results from the current work are in a good agreement with the data found in the literature and serve as a test of the newly developed detector.

The reflection and transmission Salecker-Wigner-Peres clock times averaged over the post-selected reflected and transmitted sub-ensembles, respectively, are investigated for the one dimensional scattering of a localized wave packet through an asymmetric barrier. The dwell time averaged over the same post-selected sub-ensembles is also considered. The emergence of negative average reflection times is examined and we show that while the average over the reflected sub-ensemble eliminates the negative peaks at resonance for the clock time, it still allows negative values for transparent barriers. The saturation of the average times with the barrier width (Hartman effect) is also addressed., Comment: 10 pages, 15 figures. Accepted for publication in European Physical Journal Plus

Many astrophysical events, such as novae and X-ray bursts, are powered by reactions with radioactive nuclei. Studying the properties of these nuclei in the laboratory can therefore further our understanding of these astrophysical explosions. The TwinSol separator at the University of Notre Dame has recently been used to produce intense (~106 pps) beams of 17F. In this article, some of the first measurements with these beams are discussed.