A5027038502- Nuclear physics research studies
- Nuclear Physics and Applications
- Astronomical and nuclear sciences
- Atomic and Molecular Physics
- X-ray Spectroscopy and Fluorescence Analysis
- Quantum Chromodynamics and Particle Interactions
- Neutrino Physics Research
- Advanced Chemical Physics Studies
- Particle physics theoretical and experimental studies
- Medical Imaging Techniques and Applications
- Gamma-ray bursts and supernovae
- Astro and Planetary Science
- Atomic and Subatomic Physics Research
- Stellar, planetary, and galactic studies
- Nuclear reactor physics and engineering
- Quantum, superfluid, helium dynamics
- Particle Accelerators and Free-Electron Lasers
- Radiation Detection and Scintillator Technologies
- Particle accelerators and beam dynamics
- Superconducting Materials and Applications
- Dark Matter and Cosmic Phenomena
- Inorganic Fluorides and Related Compounds
- Advanced NMR Techniques and Applications
- Astrophysics and Cosmic Phenomena
- Catalytic Processes in Materials Science
Triangle Universities Nuclear Laboratory
2012-2023
University of North Carolina at Chapel Hill
2013-2023
Duke University
1994-2022
Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Gran Sasso
2015
Joint Institute for Nuclear Astrophysics
2015
University of Notre Dame
2015
SLAC National Accelerator Laboratory
2013
Centre National de la Recherche Scientifique
2010
Institut National de Physique Nucléaire et de Physique des Particules
2010
Campus France
2010
We investigate the effects of thermonuclear reaction-rate uncertainties on nova nucleosynthesis. One-zone nucleosynthesis calculations have been performed by adopting temperature-density-time profiles hottest hydrogen-burning zone (i.e., region in which most takes place). obtain our from seven different, recently published, hydrodynamic simulations covering peak temperatures range Tpeak = 0.145 to 0.418 GK. For each these profiles, we individually varied rates 175 reactions within their...
Knowledge of the astrophysical rate ${}^{18}\mathrm{F}(p,\ensuremath{\alpha}{)}^{15}\mathrm{O}\mathrm{}$ reaction is important for understanding \ensuremath{\gamma}-ray emission expected from novae and heavy-element production in x-ray bursts. The this dominated at temperatures above $\ensuremath{\sim}0.4$ GK by a resonance near 7.08 MeV excitation energy ${}^{19}\mathrm{Ne}.$ ${}^{18}\mathrm{F}(p,\ensuremath{\alpha}{)}^{15}\mathrm{O}$ has been uncertain part because disagreements among...
The ${}^{17}\mathrm{F}(p,\ensuremath{\gamma}{)}^{18}\mathrm{Ne}$ reaction is important in stellar explosions, but its rate has been uncertain because of an expected ${3}^{+}$ state ${}^{18}\mathrm{Ne}$ that never conclusively observed. This would provide a strong $\ensuremath{\ell}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ resonance and, depending on excitation energy, could dominate the rate. We have observed this missing by measuring...
The 14N(p,gamma)15O reaction regulates the rate of energy generation in stellar CN cycle. Because discrepancies have been found analysis and interpretation previous capture data, we measured excitation function for energies range E(lab)(p)=155-524 keV. Fits these data using R-matrix theory yield a value S factor at zero 1.68+/-0.09(stat)+/-0.16(syst) keV b, which is significantly smaller than result. corresponding reduction has number interesting consequences, including an impact on...
We investigate the effects of thermonuclear reaction rate variations on 26 Al production in massive stars.The dominant sites such events were recently investigated by using stellar model calculations: explosive neon-carbon burning, convective shell carbon and core hydrogen burning.Post-processing nucleosynthesis calculations are performed for each these adopting temperature-density-time profiles from recent evolution models.For profile, we individually multiplied rates all relevant reactions...
Production of the radioisotope 18F in novae is severely constrained by rate 18F(p,alpha)15O reaction. A resonance at E(c.m.)=330 keV may strongly enhance reaction rate, but its strength has been very uncertain. We have determined this important measuring cross section on and off using a radioactive beam ORNL Holifield Radioactive Ion Beam Facility. find that 1.48+/-0.46 eV, it dominates over significant range temperatures characteristic ONeMg novae.
States near the ${}^{22}\mathrm{Ne}+p$ threshold in ${}^{23}\mathrm{Na}$ were investigated using ${}^{22}\mathrm{Ne}{(}^{3}\mathrm{He}{,d)}^{23}\mathrm{Na}$ reaction over angular range of $5\ifmmode^\circ\else\textdegree\fi{}<~{\ensuremath{\theta}}_{\mathrm{lab}}<~35\ifmmode^\circ\else\textdegree\fi{}$ at ${E(}^{3}\mathrm{He})=20 \mathrm{MeV}.$ Spectroscopic factors extracted for states corresponding to resonances ${}^{22}\mathrm{Ne}(p,\ensuremath{\gamma}{)}^{23}\mathrm{Na}$ reaction. Two...
We used the $^{16}\mathrm{O}$${(}^{3}$He,n${)}^{18}$Ne, $^{12}\mathrm{C}$${(}^{12}$C${,}^{6}$He${)}^{18}$Ne, and $^{20}\mathrm{Ne}$(p,t${)}^{18}$Ne reactions to study $^{18}\mathrm{Ne}$ states up an excitation energy of 10 MeV, with emphasis on levels corresponding $^{14}\mathrm{O}$(\ensuremath{\alpha},p${)}^{17}$F $^{17}\mathrm{F}$(p,\ensuremath{\gamma}${)}^{18}$Ne resonances that could strongly affect these reaction rates in hot stellar environments. Excitation energies, widths, absolute...
States near the $^{23}\mathrm{Na}+p$ threshold in $^{24}\mathrm{Mg}$ were investigated using $^{23}\mathrm{Na}(^{3}\mathrm{He},d)^{24}\mathrm{Mg}$ reaction over angular range of $5\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\leqslant}{\ensuremath{\theta}}_{\mathrm{lab}}\ensuremath{\leqslant}35\ifmmode^\circ\else\textdegree\fi{}$ at $E(^{3}\mathrm{He})=20\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. Spectroscopic factors extracted for states corresponding to resonances...
Hydrogen burning of the oxygen isotopes takes place in low-mass stars, asymptotic giant branch and classical novae. Observations elemental isotopic abundances stellar spectra or presolar grains provide strong constraints for models if reliable thermonuclear reaction rates hydrogen are available. We present results a new measurement ${}^{17}\mathrm{O}{(p,\ensuremath{\gamma})}^{18}\mathrm{F}$ laboratory bombarding energy range $170--530$ keV. The is performed with significantly higher beam...
The energy derived from the CN cycle at low stellar temperatures is regulated by 14N(p,gamma)15O reaction. A previous direct measurement of this reaction has been interpreted as showing evidence for a subthreshold resonance which makes major contribution to rate temperatures. This resonance, E(c.m.) = -504 keV would correspond known Ex 6793-keV state in 15O. We have measured mean lifetime 1.60(+0.75)(-0.72) fs (90% C.L.) using Doppler-shift attenuation method. factor 15 longer than that...
The $^{17}\mathrm{O}(p,\ensuremath{\gamma})^{18}\mathrm{F}$ and $^{17}\mathrm{O}(p,\ensuremath{\alpha})^{14}\mathrm{N}$ reactions have a profound influence on hydrogen-burning nucleosynthesis in number of stellar sites, including red giants, asymptotic giant branch (AGB) stars, massive classical novae. Previously evaluated thermonuclear rates for both carry large uncertainties. We investigated the proton-capture reaction $^{17}\mathrm{O}$ bombarding energy range...
Knowledge of the ${}^{17}\mathrm{F}(p,\ensuremath{\gamma}{)}^{18}\mathrm{Ne}$ reaction rate is important for understanding stellar explosions, but it was uncertain because properties an expected previously unobserved ${3}^{+}$ state in ${}^{18}\mathrm{Ne}$ were not known. This would provide a strong s-wave resonance ${}^{17}\mathrm{F}+p$ system and, depending on its excitation energy, could dominate at temperatures above 0.2 GK. We have observed this missing by measuring...
A measurement of the $\ensuremath{\beta}$-delayed $\ensuremath{\alpha}$ decay $^{16}\mathrm{N}$ using a set twin ionization chambers is described. Sources were made by implantation, beam produced via In-Flight Technique. The energies and emission angles $^{12}\mathrm{C}$ particles measured in coincidence very clean spectra, down to $450$ keV, obtained. structure spectra from this experiment good agreement with results previous measurements. An analysis our data same input parameters as used...
We have studied natural parity states in $^{26}\mathrm{Mg}$ via the $^{22}\mathrm{Ne}$($^{6}\mathrm{Li}$, $d$)$^{26}\mathrm{Mg}$ reaction. Our method significantly improves energy resolution of previous experiments and, as a result, we report observation state $^{26}\mathrm{Mg}$. Possible spin-parity assignments are suggested on basis published \ensuremath{\gamma}-ray decay experiments. The stellar rate $^{22}\mathrm{Ne}$($\ensuremath{\alpha},\ensuremath{\gamma}$)$^{26}\mathrm{Mg}$ reaction...
The $^{22}\mathrm{Ne}(p,\ensuremath{\gamma})^{23}\mathrm{Na}$ reaction is one of the most uncertain reactions in NeNa cycle and plays a crucial role creation $^{23}\mathrm{Na}$, only stable Na isotope. Uncertainties low-energy rates this other lead to ambiguities nucleosynthesis predicted from models thermally pulsing asymptotic giant branch (AGB) stars. This turn complicates interpretation anomalous Na-O trends globular cluster evolutionary scenarios. Previous studies...
This paper summarizes our present understanding of nuclear reactions with short–lived particles, which are relevant for the nucleosynthesis and energy generation in explosive stellar scenarios. It discusses need data on far off stability presents a short description possibilities measurements radioactive beams. The an overview aspects different burning possible influence proton capture nuclei discussed hydrogen novae X–ray bursts. Also various weak–interaction processes during collapse phase...
In astrophysical environments, the long-lived (t1/2 = 0.72 Myr) ground state of 26Al can communicate with its short-lived 6.35 s) first excited through thermal excitations. The result is that half-life for be much shorter than laboratory value, which have an impact on amount produced at high temperatures. We reexamined equilibration process using results new calculations some key transition rates. addition, we discuss a simple way describing behavior in stellar plasma and use this to better...