Search

Background: Properties of proton-unbound $^{31}\mathrm{S}$ states determine the $^{30}\mathrm{P}(p,\ensuremath{\gamma})^{31}\mathrm{S}$ reaction rate, which has a significant impact on explosive hydrogen burning in classical novae and type-I x-ray bursts. Despite several previous studies, uncertainties still remain with respect to the nuclear structure of $^{31}\mathrm{S}$ near the proton threshold.Purpose: The level structure of $^{31}\mathrm{S}$ has been presently investigated via a charged-particle spectroscopy experiment using the $^{32}\mathrm{S}(p,d)^{31}\mathrm{S}$ reaction.Method: Deuterons corresponding to $^{31}\mathrm{S}$ excited states with $3.285\ensuremath{\le}\phantom{\rule{4pt}{0ex}}{E}_{x}\phantom{\rule{4pt}{0ex}}\ensuremath{\le}10.8$ MeV were momentum analyzed via an Enge split-pole spectrograph at six laboratory angles between ${10}^{\ensuremath{\circ}}$ and ${62}^{\ensuremath{\circ}}$. Differential cross sections of the $^{32}\mathrm{S}(p,d)^{31}\mathrm{S}$ reaction were measured at ${E}_{p}\phantom{\rule{4pt}{0ex}}=34.5$ MeV. Distorted-wave Born approximation calculations were performed to constrain the spin-parity assignments of several of the observed levels.Results: We have detected 72 excited states of $^{31}\mathrm{S}$, out of which 17 are within the astrophysical region of interest corresponding to the temperature range of 0.1--1.5 GK. We have resolved the discrepancy in the spin and parity of an excited state with ${E}_{x}\phantom{\rule{4pt}{0ex}}=6542$ keV, showing that is it not ${J}^{\ensuremath{\pi}}\phantom{\rule{4pt}{0ex}}=3/{2}^{\ensuremath{-}}$, and therefore the contribution of this state to the $^{30}\mathrm{P}(p,\ensuremath{\gamma})$ reaction rate is likely much less significant than previously thought owing to the larger angular-momentum transfer required to populate this excited state. Moreover, our measurement results help consolidate the spin-parity assignments for the 6377 and 6636 keV states in $^{31}\mathrm{S}$.Conclusions: This work presents the most comprehensive spin-parity assignments to date from a single-neutron transfer reaction on $^{32}\mathrm{S}$ to $^{31}\mathrm{S}$ excited states in the region between 6 to 7 MeV excitation energy. This region is significant for the determination of the $^{30}\mathrm{P}(p,\ensuremath{\gamma})^{30}\mathrm{S}$ reaction rate over the temperatures characteristic of explosive hydrogen burning in novae.

A systematic study of neutron-hole strength in the N = 81 nuclei 137Ba, 139Ce, 141Nd and 143Sm is reported. The single-neutron removal reactions (p,d) and (3He,) were measured at energies of 23 and 34 MeV, respectively. Spectroscopic factors were extracted from measured cross sectionsthrough a distorted-wave Born approximation analysis and centroids of single-particle strength have been established. The change in these centroid energies as a function of proton number have been compared to calculations of the monopole shift for the s1=2 and h11=2 orbitals, where the majorityof the strength has been observed. Signicant fragmentation of strength was observed for the d and g7=2 orbitals, particularly for the latter orbital which is deeply bound, with summed strengths that indicate a signicant amount lies outside of the measured excitation energy range.

The Large Underground Xenon (LUX) dark matter experiment aims to detect rare low-energy interactions from Weakly Interacting Massive Particles (WIMPs). The radiogenic backgrounds in the LUX detector have been measured and compared with Monte Carlo simulation. Measurements of LUX high-energy data have provided direct constraints on all background sources contributing to the background model. The expected background rate from the background model for the 85.3 day WIMP search run is $(2.6\pm0.2_{\textrm{stat}}\pm0.4_{\textrm{sys}})\times10^{-3}$~events~keV$_{ee}^{-1}$~kg$^{-1}$~day$^{-1}$ in a 118~kg fiducial volume. The observed background rate is $(3.6\pm0.4_{\textrm{stat}})\times10^{-3}$~events~keV$_{ee}^{-1}$~kg$^{-1}$~day$^{-1}$, consistent with model projections. The expectation for the radiogenic background in a subsequent one-year run is presented., 18 pages, 12 figures / 17 images, submitted to Astropart. Phys

© 2015 Published by Elsevier B.V. The LUX detector is currently in operation at the Davis Campus at the 4850' level of the Sanford Underground Research Facility (SURF) in Lead, SD to directly search for WIMP dark matter. Knowing the type and rate of backgrounds is critical in a rare, low energy event search, and LUX was designed, constructed, and deployed to mitigate backgrounds, both internal and external. An important internal background are decays of radon and its daughters. These consist of alpha decays, which are easily tagged and are a tracer of certain backgrounds, and beta decays, some of which are not as readily tagged and present a background for the WIMP search. We report on studies of alpha decay and discuss implications for the WIMP search.

We present the status and prospects of the LUX experiment, which employs approximately 300 kg of two-phase xenon to search for WIMP dark matter interactions. The LUX detector was commissioned at the surface laboratory of the Sanford Underground Research Facility in Lead, SD, between December 2011 and February 2012 and the detector has been operating underground since January, 2013. These proceedings review the results of the commissioning run as well as the status of underground data-taking through the summer of 2013.

A series of astrophysical measurements was recently completed at TRIUMF, related to the unknown total rate of the 21 Na(p, γ ) 22 Mg reaction. With a high intensity 21 Na beam from the ISAC facility, the DRAGON recoil mass spectrometer was used to directly measure seven resonances at center of mass energies from E c.m. = 200 to 1135 keV and determine their respective contributions to the 21 Na(p, γ ) 22 Mg reaction rate in novae and x-ray bursts, as well as their impact on 22 Na production in novae. This study also allowed the investigation of different excited states in 22 Mg; proposed decays and spin assignments are given for the 6246, 6329, and 6609 keV levels.

The 21Na(p,γ)22Mg reaction is an important link in the synthesis of 22Na in oxygenneon novae, and serves as one of the first steps of the rp-process in x-ray bursts. This reaction has recently been studied at the TRIUMF-ISAC radioactive beam facility with the new DRAGON recoil separator. Resonant contributions have been measured for seven 22Mg states, from near the proton threshold to about 6 MeV in excitation energy. We report the results and their impact on the 21Na(p,γ)22Mg reaction rate in novae and x-ray bursts.

The fusion of protons with radioactive nuclei is important in stellar explosions such as novae and X-ray bursts and for the production of neutrinos in the sun. The Daresbury Recoil Separator and a windowless gas target system have been installed at ORNL's Holifield Radioactive Ion Beam Facility (HRIBF) for measurements of proton capture reactions in inverse kinematics with radioactive ion beams. The performance of the system has been characterized with a number of experiments using stable ion beams. We report on results from these commissioning measurements and plans for measurements of the 1 H( 17 F, 18 Ne) and 1 H( 7 Be, 8 B) reactions.

The rates of the thermonuclear 18F(p, α)15O and 18F(p,γ)19Ne reactions in hot astrophysical environments are needed to understand gamma-ray emission from nova explosions. The rates for these reactions have been uncertain due to discrepancies in recent measurements, as well as to a lack of a comprehensive examination of the available structure information in the compound nucleus 19Ne. We have examined the latest experimental measurements with radioactive and stable beams, and made estimates of the unmeasured 19Ne nuclear level parameters, to generate new rates with uncertainties for these reactions. The rates are expressed as numerical values over the temperature range relevant for stellar explosions, as well as analytical expressions as functions of temperature in a format suitable for use in astrophysical simulations. Comparisons with the previous rate calculations are carried out, and the astrophysical implications are briefly discussed.

The new DRAGON recoil separator facility, designed and built to measure directly the rates of radiative proton and alpha capture reactions important for nuclear astrophysics, is now in operation at the TRIUMF-ISAC radioactive beams facility in Vancouver, Canada. Experiments have been conducted for the first time on the 21 Na(p,γ) 22 Mg reaction. The evolution of nova explosions, and particularly their 22 Na abundance, depends sensitively on this reaction rate. Commissioning studies using the well-known stable beam reactions 21 Ne(p,γ) 22 Na, 20 Ne(p,γ) 21 Na, and 24 Mg(p,γ) 25 Al have shown that the recoil separator performs within its design specifications both in suppression power and acceptance. The first radioactive beam studies were done using a beam of 5 × 10 8 21 Na atoms/s. Yield measurements recording simultaneously singles and coincident heavy-ion and gamma signals were performed, scanning in energy over the known resonance reported previously in 22 Mg at E cm = 212 keV, and in addition, over a strong resonance observed at E cm ≈822 keV.

The rate of the 21 Na(p,γ) 22 Mg reaction is expected to play a major role in the nucleosynthesis of 22 Na in Oxygen-Neon novae, leading to the emission of a characteristic 1.28 MeV gamma-line. This paper reports on preliminary results of the first direct measurements of this reaction and its astrophysical implications.

In the modelling of nucleosynthesis in nova explosions, temperature and density are important parameters to describe the hydrodynamics. Those parameters are not easy to observe, but specific gamma-ray emitters produced in the explosion provide constrains on the models, such as 22 Na, produced via 21 Na ( p , γ ) 22 Mg ( β + ) 22 Na . The new DRAGON recoil separator facility, designed and built to measure directly the rates of radiative proton and alpha capture reactions, important for nuclear astrophysics, is now operational. Experiments have been conducted on the 21 Na(p , γ) 22 Mg reaction using a radioactive 21 Na beam incident onto a windowless hydrogen gas target. Yield measurements have been performed detecting the prompt gamma and the reaction recoils at E cm ≈ 821 keV and 204 keV.

In a recent investigation of the development of leakage currents in Silicon Strip Detectors used in experiments with high intensity stable beams, anomalous behavior was observed. Over a very short period of time the leakage current rose to levels that could be damaging to the detectors. A discussion of this evidence and how the problem was solved, with a viable model, will be given, leading to guidelines for use of such detectors in a stable beam environment.

© 2014 Elsevier B.V. All rights reserved. The LUX (Large Underground Xenon) experiment aims at the direct detection of dark matter particles via their collisions with xenon nuclei. The 370 kg two-phase liquid xenon time projection chamber measures simultaneously the scintillation and ionization from interactions in the target. The ratio of these two signals provides very good discrimination between potential nuclear recoil and electronic recoil signals to search for WIMP-nucleon scattering. The LUX detector operates at the Sanford Underground Research Facility (Lead, South Dakota, USA) since February 2013. First results were presented in late 2013 setting the world's most stringent limits on WIMP-nucleon scattering cross-sections over a wide range of WIMP masses. A 300 day run beginning in 2014 will further improve the sensitivity and new calibration techniques will reduce systematics for the WIMP signal search.

The 29 P(p, γ ) 30 S reaction plays an important role in understanding the Si isotopic abundances in presolar grains of nova origin, which in turn provide us with information on the nature of the probable white dwarf progenitor's core, as well as the peak temperatures achieved during nova outbursts. This rate at nova temperatures is determined by two low-lying 3 + and 2 + resonances above the proton threshold at 4399 keV in 30 S. We have studied the 30 S nuclear structure via the 32 S(p,t) 30 S reaction at 5 laboratory angles between 9 ° to 62 ° . We have observed 14 states including two levels at 4692.7 ± 4.5 keV and 4813.8 ± 3.4 keV that are candidates for the 3 + and the previously “missing” 2 + state, respectively.

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 in ${}^{18}\mathrm{Ne}$ that has never been conclusively observed. This state would provide a strong $\ensuremath{\ell}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ resonance and, depending on its excitation energy, could dominate the stellar reaction rate. We have observed this missing ${3}^{+}$ state by measuring the ${}^{1}\mathrm{H}{(}^{17}\mathrm{F},p{)}^{17}\mathrm{F}$ excitation function with a radioactive ${}^{17}\mathrm{F}$ beam at the ORNL Holifield Radioactive Ion Beam Facility. We find that the state lies at a center-of-mass energy of ${E}_{r}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}599.8\ifmmode\pm\else\textpm\fi{}1{.5}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{2.0}_{\mathrm{sys}}\phantom{\rule{0ex}{0ex}}\mathrm{keV}$ ( ${E}_{x}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4523.7\ifmmode\pm\else\textpm\fi{}2.9\mathrm{keV}$) and has a width of $\ensuremath{\Gamma}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}18\ifmmode\pm\else\textpm\fi{}{2}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{1}_{\mathrm{sys}}\phantom{\rule{0ex}{0ex}}\mathrm{keV}$.

A method has been developed that can provide beams of many short-lived nuclei of interest in nucleosynthesis along the rp process path. With a {sup 17}F beam (T{sub 1/2}=64 s ) the excitation function of the {sup 17}F( p,thinsp{alpha}){sup 14} O reaction was measured to determine properties of excited states in {sup 18}Ne . These states influence the rate of the {sup 14}O( {alpha},thinspp){sup 17} F reaction which is important for understanding energy generation and nucleosynthesis in x-ray bursts. The present direct measurements yield a pattern of resonances and cross sections which differ substantially from previous estimates. {copyright} {ital 1999} {ital The American Physical Society}

We have studied the properties of low-lying ${}^{18}\mathrm{F}+p$ resonances as excited states in ${}^{19}\mathrm{Ne}.$ Three new levels have been found in the range $0l~{E}_{\mathrm{c}.\mathrm{m}.}l~1 \mathrm{MeV}$ just above the ${}^{18}\mathrm{F}+p$ threshold, and partial decay widths and isospin-mirror connections are suggested to known states in ${}^{19}\mathrm{F}$ for each of the nine states in this energy range. The properties of these resonances have been used to calculate the reaction rate ${N}_{A}〈\ensuremath{\sigma}v〉$ for the ${}^{18}\mathrm{F}(p,\ensuremath{\gamma}{)}^{19}\mathrm{Ne}$ and ${}^{18}\mathrm{F}(p,\ensuremath{\alpha}{)}^{15}\mathrm{O}$ reactions in the temperature range ${10}^{8}lTl{10}^{9}.$ A comparison of these rates indicates that in this temperature range, the ${}^{14}\mathrm{O}(\ensuremath{\alpha}{,p)}^{17}\mathrm{F}(p,\ensuremath{\gamma}{)}^{18}\mathrm{Ne}{(e}^{+}\ensuremath{\nu}{)}^{18}\mathrm{F}(p,\ensuremath{\gamma}{)}^{19}\mathrm{Ne}$ reaction sequence is not as fast as the ${}^{15}\mathrm{O}(\ensuremath{\alpha},\ensuremath{\gamma}{)}^{19}\mathrm{Ne}$ reaction.

Clayton and Jin have proposed that {sup 26}Al in the early solar system was made by oxygen-rich cosmic rays through the {sup 12}C({sup 16}O,x){sup 26}Al{sub g.s.} reaction. To test their proposal we have measured the yield of {sup 26}Al{sub g.s.} from this reaction using the activation method. We find that the yield is too low to explain the {sup 26}Al/{sup 27}Al ratio that has been observed in carbonaceous chondrite meteorites. {copyright} {ital 1998} {ital The American Physical Society}

Clayton and Jin[1] have proposed that the meteoritic 26 Al was produced by low energy cosmic rays in the early solar system through the 12 C( 16 O,x) 26 Al reaction. We have measured the yield of 26 Al from this reaction and find that it is too low to explain the meteorite observations.

The ${}^{33}$S($p,\ensuremath{\gamma}$)${}^{34}$Cl reaction is important for constraining predictions of certain isotopic abundances in oxygen-neon novae. Models currently predict as much as 150 times the solar abundance of ${}^{33}$S in oxygen-neon nova ejecta. This overproduction factor may vary by orders of magnitude due to uncertainties in the ${}^{33}$S($p,\ensuremath{\gamma}$)${}^{34}$Cl reaction rate at nova peak temperatures. Depending on this rate, ${}^{33}$S could potentially be used as a diagnostic tool for classifying certain types of presolar grains. Better knowledge of the ${}^{33}$S($p,\ensuremath{\gamma}$)${}^{34}$Cl rate would also aid in interpreting nova observations over the S-Ca mass region and contribute to the firm establishment of the maximum endpoint of nova nucleosynthesis. Additionally, the total S elemental abundance which is affected by this reaction has been proposed as a thermometer to study the peak temperatures of novae. Previously, the ${}^{33}$S($p,\ensuremath{\gamma}$)${}^{34}$Cl reaction rate had only been studied directly down to resonance energies of 432 keV. However, for nova peak temperatures of $0.2--0.4$ GK there are seven known states in ${}^{34}$Cl both below the 432-keV resonance and within the Gamow window that could play a dominant role. Direct measurements of the resonance strengths of these states were performed using the DRAGON (Detector of Recoils And Gammas of Nuclear reactions) recoil separator at TRIUMF. Additionally two new states within this energy region are reported. Several hydrodynamic simulations have been performed, using all available experimental information for the ${}^{33}$S($p,\ensuremath{\gamma}$)${}^{34}$Cl rate, to explore the impact of the remaining uncertainty in this rate on nucleosynthesis in nova explosions. These calculations give a range of $\ensuremath{\approx}$20--150 for the expected ${}^{33}$S overproduction factor, and a range of $\ensuremath{\approx}$100--450 for the ${}^{32}$S/${}^{33}$S ratio expected in ONe novae.

Measurements of neutron-adding, neutron-removing, and proton-adding reactions were carried out for the four stable even Ni isotopes. Particular attention was paid to obtaining precise values of the cross sections at the peaks of the angular distributions. Tests with sum rules for the neutron data indicate that the results are self-consistent at the level of a few tenths of a nucleon. Data on proton-adding reactions were also obtained and analyzed with a slightly different method—while these data are also consistent, the ambiguities are larger. The occupancies of the neutron orbits derived from the data, the proton vacancies, and the energy centroids of the neutron, neutron-hole, and proton single-particle excitations are obtained. The data also provide some estimate about the closure of the 0 f 7 / 2 shell. The results are compared to shell-model calculations and may serve as a reference point for future exploration. ispartof: Physical Review C, Nuclear Physics vol:87 issue:3 pages:1-15 status: published

The single-neutron properties of N = 51 nuclei have been studied with the ( d , p )and( α , 3 He) reactions, at beam energies of 15 and 50 MeV respectively, on 88 Sr, 90 Zr, and 92 Mo targets. The light reaction products were momentum analyzed using a conventional magnetic spectrometer. Additionally, the 2 H( 86 Kr ,p ) reaction was measured at a beam energy of 10 MeV / u, where outgoing light ions were analyzed using a helical-orbit spectrometer. Absolute cross sections and angular distributions corresponding to the population of different final states in the heavy product were obtained for each reaction. Spectroscopic factors were extracted and centroids of the single-particle strength were deduced. The observations appear consistent with calculations based on an evolution of single-particle structure driven by the nucleon-nucleon forces acting between valence protons and neutrons. ispartof: Physical Review C, Nuclear Physics vol:87 issue:1 status: published

Clayton & Jin have proposed that the high abundance of 26Al found in meteorites was produced by cosmic rays in the early solar system through the 12C(16O, x)26Algs reaction. We have measured the yield of 26Al in the ground state (i.e.,26Algs) from this reaction and find that, if this mechanism produced the meteoritic 26Al, a substantial fraction of the solar system oxygen must have entered the solar system as low-energy cosmic rays. This does not seem plausible. If the proto-Sun itself was the source of the oxygen cosmic rays, they must have carried off some 5% of the power of the protosolar wind for 1 Myr. This too seems unlikely. Although we do not address the role of other cosmic-ray species in the production of 26Al, it appears that 26Al was produced in a stellar environment, and not by cosmic rays.

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 to an excitation energy of 10 MeV, with emphasis on levels corresponding to $^{14}\mathrm{O}$(\ensuremath{\alpha},p${)}^{17}$F and $^{17}\mathrm{F}$(p,\ensuremath{\gamma}${)}^{18}$Ne resonances that could strongly affect these reaction rates in hot stellar environments. Excitation energies, widths, absolute cross sections, and angular distributions were measured. We found previously unidentified states at ${\mathit{E}}_{\mathit{x}}$=6.15\ifmmode\pm\else\textpm\fi{}0.01 MeV, 7.12\ifmmode\pm\else\textpm\fi{}0.02 MeV, 7.35\ifmmode\pm\else\textpm\fi{}0.02 MeV, 7.62\ifmmode\pm\else\textpm\fi{}0.02 MeV, 8.30\ifmmode\pm\else\textpm\fi{}0.02 MeV, (8.45\ifmmode\pm\else\textpm\fi{}0.03 MeV), 8.55\ifmmode\pm\else\textpm\fi{}0.03 MeV, 8.94\ifmmode\pm\else\textpm\fi{}0.02 MeV, and 9.58\ifmmode\pm\else\textpm\fi{}0.02 MeV. We combined level width, cross section, and angular distribution data to infer ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$ values for a number of the new levels as well as for the previously known 5.1-MeV doublet. Using information from our experiments, we recalculated the $^{14}\mathrm{O}$(\ensuremath{\alpha},p${)}^{17}$F reaction rate, which constitutes a possible path out of the hot CNO cycle into the rp process and could play an important role in transforming nuclei involved in the hot CNO cycle into heavier nuclei with Z\ensuremath{\ge}10. \textcopyright{} 1996 The American Physical Society.

The ^(26)Al(^3He,d)^(27)Si reaction was measured from 0°≤θ_(c.m.)≤35° at E(^3He)=20 MeV using a quadrupole-dipole-dipole-dipole magnetic spectrometer. States in ^(27)Si were observed above the background at 7652 and 7741 keV and upper limits were set for the state at 7592 keV. Implications for the ^(26)Al(p,γ)^(27)Si stellar reaction rate are discussed.

The reaction sequences governing the reaction flow in the rp process are important for the understanding of the energy generation and nucleosynthesis of heavy elements in hot and explosive stellar hydrogen burning. Of considerable interest are (p,\ensuremath{\alpha}) reactions along the process path which lead to the formation of reaction cycles rather than to chains of proton capture processes and \ensuremath{\beta} decays. Previous direct attempts to measure the low-energy reaction cross sections for $^{31}\mathrm{P}$(p,\ensuremath{\alpha}${)}^{28}$Si and $^{35}\mathrm{Cl}$(p,\ensuremath{\alpha}${)}^{32}$S resulted only in upper limits for the strengths of possible low-energy resonances which may dominate the reaction rates. In this paper an indirect experimental approach is presented to study the structure of the low-energy unbound states in the compound nuclei $^{32}$ S and $^{36}\mathrm{Ar}$. The results allow a more accurate determination of the contributions of these low-energy levels in the (p,\ensuremath{\alpha}) reaction channel.

The 17 F( p ,γ) 18 Ne direct capture cross section is important for understanding nucleosynthesis in novae. We have measured cross sections for the proton-transfer reaction 14 N( 17 F, 18 Ne) 13 C in order to determine asymptotic normalization coefficients for the 17 F+ p system and hence the 17 F( p ,γ) 18 Ne direct capture cross section. The technique and preliminary results are presented.

Production of the radioisotope 18F in novae is severely constrained by the rate of the 18F(p,α)15O reaction. A resonance at Ec.m. = 330 keV may strongly enhance the 18F(p,α)15O reaction rate, but its strength has been very uncertain. We have determined the strength of this important resonance by measuring the 18F(p,α)15O cross section on- and off-resonance using a radioactive 18F beam at ORNL's Holifield Radioactive Ion Beam Facility. We find that its resonance strength is 1.48 ± 0.46 eV, and that it dominates the 18F(p,α)15O reaction rate over a significant range of temperatures characteristic of nova outbursts occuring on ONeMg white dwarfs.

Galactic 26Al is the first radioactive nucleus to be positively identified by -ray astronomy with detection of the 1.809 MeV ray associated with its decay. This nucleus is destroyed in astrophysical environments in the 26Al(p, )27Si and inelastic 26Al+p scattering reactions where properties of 27Si levels determine reaction rates. To investigate these properties, elastic and inelastic 26Al+p scattering reactions were measured between Ec.m. = 0.5 1.5 MeV at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL). A candidate for a new resonance in the 26Al(p, )27Si reaction was identified. Upper limits were also set on the strengths of postulated resonances and on the cross section of the inelastic reaction, but there is little effect on current reaction rate calculations.

The uncertainty in the 29P(p,gamma)30S reaction rate over the temperature range of 0.1 - 1.3 GK was previously determined to span ~4 orders of magnitude due to the uncertain location of two previously unobserved 3+ and 2+ resonances in the 4.7 - 4.8 MeV excitation region in 30S. Therefore, the abundances of silicon isotopes synthesized in novae, which are relevant for the identification of presolar grains of putative nova origin, were uncertain by a factor of 3. To investigate the level structure of 30S above the proton threshold (4394.9(7) keV), a charged-particle spectroscopy and an in-beam gamma-ray spectroscopy experiments were performed. Differential cross sections of the 32S(p,t)30S reaction were measured at 34.5 MeV. Distorted wave Born approximation calculations were performed to constrain the spin-parity assignments of the observed levels. An energy level scheme was deduced from gamma-gamma coincidence measurements using the 28Si(3He,n-gamma)30S reaction. Spin-parity assignments based on measurements of gamma-ray angular distributions and gamma-gamma directional correlation from oriented nuclei were made for most of the observed levels of 30S. As a result, the resonance energies corresponding to the excited states in 4.5 MeV - 6 MeV region, including the two astrophysically important states predicted previously, are measured with significantly better precision than before. The uncertainty in the rate of the 29P(p,gamma)30S reaction is substantially reduced over the temperature range of interest. Finally, the influence of this rate on the abundance ratios of silicon isotopes synthesized in novae are obtained via 1D hydrodynamic nova simulations., Comment: 22 pages, 12 figures

The ${}^{31}\mathrm{S}{(p,\ensuremath{\gamma})}^{32}$Cl reaction is expected to provide the dominant break-out path from the SiP cycle in novae and is important for understanding enrichments of sulfur observed in some nova ejecta. We studied the ${}^{32}\mathrm{S}{{(}^{3}\mathrm{He},t)}^{32}$Cl charge-exchange reaction to determine properties of proton-unbound levels in ${}^{32}$Cl that have previously contributed significant uncertainties to the ${}^{31}\mathrm{S}{(p,\ensuremath{\gamma})}^{32}$Cl reaction rate. Measured triton magnetic rigidities were used to determine excitation energies in ${}^{32}$Cl. Proton-branching ratios were obtained by detecting decay protons from unbound ${}^{32}$Cl states in coincidence with tritons. An improved ${}^{31}\mathrm{S}{(p,\ensuremath{\gamma})}^{32}$Cl reaction rate was calculated including robust statistical and systematic uncertainties.

The quantitative consistency of nucleon transfer reactions as a probe of the occupancy of valence orbits in nuclei is tested. Neutron-adding, neutron-removal, and proton-adding transfer reactions were measured on the four stable even Ni isotopes, with particular attention to the cross section determinations. The data were analyzed consistently in terms of the distorted wave Born approximation to yield spectroscopic factors. Valence-orbit occupancies were extracted, utilizing the Macfarlane-French sum rules. The deduced occupancies are consistent with the changing number of valence neutrons, as are the vacancies for protons, both at the level of

Reduced uncertainty in the thermonuclear rate of the {sup 33}S(p,{gamma}){sup 34}Cl reaction would help to improve our understanding of nucleosynthesis in classical nova explosions. At present, models are generally in concordance with observations that nuclei up to roughly the calcium region may be produced in these explosive phenomena; better knowledge of this rate would help with the quantitative interpretation of nova observations over the S-Ca mass region, and contribute towards the firm establishment of a nucleosynthetic endpoint. As well, models find that the ejecta of nova explosions on massive oxygen-neon white dwarfs may contain as much as 150 times the solar abundance of {sup 33}S. This characteristic isotopic signature of a nova explosion could possibly be observed through the analysis of microscopic grains formed in the environment surrounding a nova and later embedded within primitive meteorites. An improved {sup 33}S(p,{gamma}){sup 34}Cl rate (the principal destruction mechanism for {sup 33}S in novae) would help to ensure a robust model prediction for the amount of {sup 33}S that may be produced. Finally, constraining this rate could confirm or rule out the decay of an isomeric state of {sup 34}Cl(E{sub x} = 146 keV, t{sub 1/2} = 32 m) as a source formore » observable gamma-rays from novae. We have performed several complementary experiments dedicated to improving our knowledge of the {sup 33}S(p,{gamma}){sup 34}Cl rate, using both indirect methods (measurement of the {sup 34}S({sup 3}He,t){sup 34}Cl and {sup 33}S({sup 3}He,d){sup 34}Cl reactions with the Munich Q3D spectrograph) and direct methods (in normal kinematics at CENPA, University of Washington, and in inverse kinematics with the DRAGON recoil mass separator at TRIUMF). Our results will be used with nova models to facilitate comparisons of model predictions with present and future nova observables.« less

We have determined the [gamma]-ray branching ratio [Gamma][sub [gamma]]/[Gamma][sub tot] for the first excited state in [sup 14]O ([ital E][sub [ital x]]=5.17 MeV) to be (3.1[plus minus]1.7)[times]10[sup [minus]4], corresponding to a [gamma] width of 12[plus minus]7 eV. This value was determined by measuring the ratio of the [sup 14]N([ital p],[ital n])[sup 14]O[sub 0] to [sup 14]N([ital p],[ital n])[sup 14]O[sub 1] cross sections via neutron time of flight, and the ratio of [sup 14]N([ital p],[ital n])[sup 14]O[sub 0] to [sup 14]N([ital p],[ital n])[sup 14]O[sub 1]([gamma])[sup 14]O[sub 0] cross sections at the same center-of-mass energy by bombarding a hydrogen target with a [sup 14]N beam and kinematically distinguishing the [sup 14]O[sub 0] recoils from the two reaction channels. The present value for [Gamma][sub [gamma]] is consistent with other measurements at the 2-[sigma] level; a weighted mean of all measurements is used to calculate the stellar [sup 13]N([ital p],[gamma])[sup 14]O reaction rate, and thereby determine the temperatures and densities at which the stellar carbon-nitrogen-oxygen (CNO) cycle is converted to the hot CNO cycle.