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The heavy-ion radiative capture 12C(O16,γ28Si) was measured at the sub-Coulomb barrier bombarding energy Elab = 15.7 MeV, which corresponds to the lowest important resonance observed in the 12C+ O16 fusion excitation function. Thanks to combination of the bismuth germanate (BGO) γ-ray array and the 0° DRAGON electromagnetic spectrometer at TRIUMF, the γ-decay spectrum from the entrance channel down to the ground state of 28Si was measured. Comparisons of the experimental spectrum to γ spectrum extracted from Monte Carlo simulations of the complete setup suggest a Jπ = 2+ spin-parity assignment to the entrance channel and yield the radiative capture cross section ωRC = 0.22±0.04μb. Combining this present spin assignment with previous data on radiative capture, a J(J+1) systematics was constructed, and it indicated a moment of inertia commensurate with the 12C+O16 grazing angular momentum. Strong dipole transitions are observed from the entrance channel to T=1 states around 11.5 MeV and are found to result from enhanced M1IV transitions to states exhausting a large part of the M1 sum rule built on the ground state of 28Si. This specific decay was also reported at bombarding energies close to the Coulomb barrier in our previous study of the 12C(12C,γ24Mg) heavy-ion radiative capture reaction. Similarities between both systems are investigated. [ABSTRACT FROM AUTHOR]

The 1S(p,γ)34Cl 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 33S in oxygen-neon nova ejecta. This overproduction factor may, however, vary by orders of magnitude due to uncertainties in the 33S(p,γ)34Cl reaction rate at nova peak temperatures. Depending on this rate, 33S could potentially be used as a diagnostic tool for classifying certain types of presolar grains. Better knowledge of the 33S(p,γ)34Cl 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 33S(p,γ)34Cl 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 7 known states in 34Cl 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 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 33S(p,γ)34Cl rate, to explore the impact of the remaining uncertainty in this rate on nucleosynthesis in nova explosions. These calculations give a range of ~ 20-150 for the expected 33S overproduction factor, and a range of ~ 100-450 for the 32S/33S ratio expected in ONe novae. [ABSTRACT FROM AUTHOR]

The rate of the 18F(p,γ)19Ne reaction affects the final abundance of the γ-ray observable radioisotope 18F, produced in novae. However, no successful measurement of this reaction exists and the rate used is calculated from incomplete information on the contributing resonances. Of the two resonances thought to play a significant role, one has a radiative width estimated from the assumed analogue state in the mirror nucleus, 19F. The second does not have an analogue state assignment at all, resulting in an arbitrary radiative width being assumed. Here, we report the first successful direct measurement of the 18F(p,γ)19Ne reaction. The strength of the 665 keV resonance (Ex=7.076 MeV) is found to be over an order of magnitude weaker than currently assumed in nova models. Reaction rate calculations show that this resonance therefore plays no significant role in the destruction of 18F at any astrophysical energy. [ABSTRACT FROM AUTHOR]

In stars, 16O represents the endpoint of the helium burning sequence due to the low rate of 16O(α,γ)20Ne. We present a new direct measurement of the total cross section of 16O(α,γ)20Ne at Ec.m. = 1.69 MeV employing the DRAGON recoil separator. In addition, the branching ratios and strength of the Ec.m. = 2.426 MeV 3- resonance were determined. [ABSTRACT FROM AUTHOR]

The 17O(p,γ)18F reaction plays an important role in hydrogen-burning nucleosynthesis. Conflicting values for the low-energy behavior of its cross section exist in the literature. We present direct measurements of the astrophysical S factor of the 17O(p,γ)18F reaction at center-of-mass energies between 250 and 500 keV. These measurements were conducted in inverse kinematics at the DRAGON recoil separator. [ABSTRACT FROM AUTHOR]

The heavy-ion radiative capture reaction 12C(16O,γ)28Si has been studied at three energies Ec.m. = 8.5, 8.8, and 9 MeV which are close to the Coulomb barrier. The weak radiative capture process has been identified by measuring the 28Si recoils in the highly selective 0° spectrometer DRAGON at TRIUMF (Vancouver). The coincident γ rays have been recorded in the associated BGO array. This has allowed a complete measurement of the γ spectrum and the relative strength of all decay pathways. An important part of the decay through quasibound states close to the particle threshold and the feeding of bound states with particular deformation have been identified for the first time. Comparisons with Monte Carlo simulations allowed the extraction of the full experimental radiative capture cross section. Our results suggest an important contribution of spins Jπ = 5- and 6+ in the entrance channel. The surprisingly large cross sections from 12 μb at Ecm = 8.5 MeV to 25 μb at Ec.m.= 9.0 MeV for the heavy-ion radiative capture process are discussed in terms of the interplay between statistical and structural aspects of the process. [ABSTRACT FROM AUTHOR]

In stellar helium burning, 16O represents the endpoint of the helium-burning sequence due to the low rate of 16O(α,γ)20Ne. We present a new direct measurement of the total capture reaction rate of 16O(α,γ)20Ne at Ec.m.=2.26 MeV employing the DRAGON recoil separator. For the first time, the total S factor and its contributing direct capture transitions could be determined in one experiment. [ABSTRACT FROM AUTHOR]

Complete γ-decay in the 12C(12C,γ)24Mg and 12C(16O,γ)28Si reactions has been measured at energies close to the Coulomb Barrier using the DRAGON spectrometer and its associated BGO γ-array at the TRIUMF facility. The experimental data show an important feeding of doorway states around 10-11 MeV in both reactions. Comparisons with simulations allow to extract the full capture cross section and the main spin involved in the process. Different models are confronted to the results : completely statistical, semi-statistical with an unique entrance spin and cluster. The resolution of the BGO enables to eliminate a fully statistical scenario but is not enough to disentangle the two remaining scenarii. It is shown that the future PARIS array composed of the recently developed LaBr3 scintillators will have capabilities to distinguish between these two scenarii. [ABSTRACT FROM AUTHOR]

Gamma-ray telescopes in orbit around the earth are searching for evidence of the elusive radionuclide 22Na produced in novae. Previously published uncertainties in the dominant destructive reaction, 22Na(p,γ)23Mg, indicated new measurements in the proton energy range of 150 to 300 keV were needed to constrain predictions. We have measured the resonance strengths, energies, and branches directly and absolutely by using protons from the University of Washington accelerator with a specially designed beam line, which included beam rastering and cold vacuum protection of the 22Na implanted targets. The targets, fabricated at TRIUMF-ISAC, displayed minimal degradation over a ~20 C bombardment as a result of protective layers. We avoided the need to know the absolute stopping power, and hence the target composition, by extracting resonance strengths from excitation functions integrated over proton energy. Our measurements revealed that resonance strengths for Ep=213, 288, 454, and 610 keV are stronger by factors of 2.4-3.2 than previously reported. Upper limits have been placed on proposed resonances at 198, 209, and 232 keV. These substantially reduce the uncertainty in the reaction rate. We have re-evaluated the 22Na(p,γ) reaction rate, and our measurements indicate the resonance at 213 keV makes the most significant contribution to 22Na destruction in novae. Hydrodynamic simulations including our rate indicate that the expected abundance of 22Na ejecta from a classical nova is reduced by factors between 1.5 and 2, depending on the mass of the white-dwarf star hosting the nova explosion. [ABSTRACT FROM AUTHOR]

This paper discusses how the radiative capture process can shed light on the origin of the resonances observed in light heavy-ion collisions. The impact of resonant features on the fusion cross-sections is described from energies around the Coulomb barrier down to the Gamow energy in systems like 12C+12C and 12C+16O. [ABSTRACT FROM AUTHOR]

We present the first direct measurement of an astrophysical reaction using a radioactive beam of isomeric nuclei. In particular, we have measured the strength of the key 447-keV resonance in the 26mAl(p,γ)27Si reaction to be 432+146-226 meV and find that this resonance dominates the thermally averaged reaction rate for temperatures between 0.3 and 2.5 GK. This work represents a critical development in resolving one of the longest standing issues in nuclear astrophysics research, relating to the measurement of proton capture reactions on excited quantum levels, and offers unique insight into the destruction of isomeric 26Al in astrophysical plasmas. [ABSTRACT FROM AUTHOR]

The radiative capture process of the 12C+12C and 12C+16O reactions has been studied using the very selective 0° Dragon spectrometer at Triumf and its associated BGO γ-array. The experiments have been performed at energies around the Coulomb barrier where resonances in the process have been reported. Our results show previously unobserved γ-decay to doorway states in the 24Mg and 28Si respectively around 10 to 12 MeV. The nature of the states is discussed and two scenarii are proposed. [ABSTRACT FROM AUTHOR]

Abstract: The Nuclear Astrophysics program at TRIUMF, particular the one centered around the DRAGON and TUDA facilities, as well as some additional experiments will be discussed. In particular, measurements of the 12C(α,γ)16O, the 26Al(p,γ)27Si and the 40Ca(α,γ)44Ti reactions at DRAGON will be described. For the TUDA facility a measurement of 10B(α,p)13C as a test for the 18Ne(α,p)21Na measurement is presented. The development of the new cylindrical, large solid angle gas detector TACTIC will be described. In addition, new measurements refuting a temperature dependence of radioactive decay times in metals will be presented as well as GEANT4 simulations regarding the β-delayed α-spectrum of 16N will be given. [Copyright &y& Elsevier]

Abstract: We report here on experiments with radioactive 21Na and 7Be beams performed by Colorado School of Mines students at the ISAC facility of TRIUMF and the Holifield Radioactive Ion Beam Facility (HRIBF) of ORNL. At TRIUMF, the DRAGON recoil separator and its segmented BGO array were used to investigate higher energy resonances in the reaction H(21Na,γ)22Mg. Using the HRIBF we performed an experiment with a 7Be ion beam to measure scattering off Hydrogen and Carbon. Both elastic 7Be+p scattering and for the first time resonant inelastic scattering 7Be(p,p′)7Be∗ were observed. [Copyright &y& Elsevier]

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

Resonant scattering studies were performed using radioactive 20,21Na beams at ISAC between energies of 0.5 keV/u and 1.5 keV/u. Intensities of up to 1 × 108 /sec were used with thick CH2 targets, and elastic and inelastic proton resonances were observed corresponding to states in 21,22Mg by detecting recoil protons using the LEDA silicon array. A multichannel R-Matrix formalism was used to fit the excitation functions leading to the deduction of partial widths and spin-parity assignments. In certain cases definite spin-parity assignments could be made without fitting angular distributions due to the constraining nature of Coulomb-interfering resonances. Where possible, analogue assignments are made in the A=22, T=1, system based on the 21Na+p analysis. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

In this Letter we report on the first inverse kinematics measurement of key resonances in the Ne 22 (p , γ) 23 Na reaction which forms part of the NeNa cycle, and is relevant for 23Na synthesis in asymptotic giant branch (AGB) stars. An anti-correlation in O and Na abundances is seen across all well-studied globular clusters (GC), however, reaction-rate uncertainties limit the precision as to which stellar evolution models can reproduce the observed isotopic abundance patterns. Given the importance of GC observations in testing stellar evolution models and their dependence on NeNa reaction rates, it is critical that the nuclear physics uncertainties on the origin of 23Na be addressed. We present results of direct strengths measurements of four key resonances in Ne 22 (p , γ) 23 Na at E c. m. = 149 keV, 181 keV, 248 keV and 458 keV. The strength of the important E c. m. = 458 keV reference resonance has been determined independently of other resonance strengths for the first time with an associated strength of ωγ = 0.439(22) eV and with higher precision than previously reported. Our result deviates from the two most recently published results obtained from normal kinematics measurements performed by the LENA and LUNA collaborations but is in agreement with earlier measurements. The impact of our rate on the Na-pocket formation in AGB stars and its relation to the O-Na anti-correlation was assessed via network calculations. Further, the effect on isotopic abundances in CO and ONe novae ejecta with respect to pre-solar grains was investigated. [ABSTRACT FROM AUTHOR]

The new DRAGON facility at TRIUMF is designed to measure alpha and proton capture reactions with radioactive ion beams in inverse kinematics. For nucleo-synthesis in astrophysical scenarios, the relevant energies lie in the 0.15–1 MeV/u range, where very low cross sections are expected. Therefore the separation of the recoil products from the beam particles will be a difficult task. This paper focuses on the end detectors, which will be used to distinguish recoils from beam particles at the end of the DRAGON separator. [Copyright &y& Elsevier]

Background: Nucleosynthesis of mid-mass elements is thought to occur under hot and explosive astrophysical conditions. Radiative α capture on 34S has been shown to impact nucleosynthesis in several such conditions, including core and shell oxygen burning, explosive oxygen burning, and type Ia supernovae. Purpose: Broad uncertainties exist in the literature for the strengths of three resonances within the astrophysically relevant energy range (ECM=1.94-3.42MeV at T=2.2GK). Further, there are several states in 38Ar within this energy range which have not been previously measured. This work aimed to remeasure the resonance strengths of states for which broad uncertainty existed as well as to measure the resonance strengths and energies of previously unmeasured states. Methods: Resonance strengths and energies of eight narrow resonances (five of which had not been previously studied) were measured in inverse kinematics with the DRAGON facility at TRIUMF by impinging an isotopically pure beam of 34S ions on a windowless 4He gas target. Prompt γ emissions of de-exciting 38Ar recoils were detected in an array of bismuth germanate scintillators in coincidence with recoil nuclei, which were separated from unreacted beam ions by an electromagnetic mass separator and detected by a time-of-flight system and a multianode ionization chamber. Results: The present measurements agree with previous results. Broad uncertainty in the resonance strength of the ECM=2709keV resonance persists. Resonance strengths and energies were determined for five low-energy resonances which had not been studied previously, and their strengths were determined to be significantly weaker than those of previously measured resonances. Conclusions: The five previously unmeasured resonances were found not to contribute significantly to the total thermonuclear reaction rate. A median total thermonuclear reaction rate calculated using data from the present work along with existing literature values using the STARLIB rate calculator agrees with the NON-SMOKER statistical model calculation as well as the REACLIB and STARLIB library rates at explosive and nonexplosive oxygen-burning temperatures (T=3-4GK and T=1.5-2.7GK, respectively). [ABSTRACT FROM AUTHOR]

Background: Classical novae are cataclysmic nuclear explosions occurring when a white dwarf in a binary system accretes hydrogen-rich material from its companion star. Novae are partially responsible for the galactic synthesis of a variety of nuclides up to the calcium (A∼40) region of the nuclear chart. Although the structure and dynamics of novae are thought to be relatively well understood, the predicted abundances of elements near the nucleosynthesis endpoint, in particular Ar and Ca, appear to sometimes be in disagreement with astronomical observations of the spectra of nova ejecta. Purpose: One possible source of the discrepancies between model predictions and astronomical observations is nuclear reaction data. Most reaction rates near the nova endpoint are estimated only from statistical model calculations, which carry large uncertainties. For certain key reactions, these rate uncertainties translate into large uncertainties in nucleosynthesis predictions. In particular, the 38K(p,γ)39Ca reaction has been identified as having a significant influence on Ar, K, and Ca production. In order to constrain the rate of this reaction, we have performed a direct measurement of the strengths of three candidate ℓ=0 resonances within the Gamow window for nova burning, at 386±10 keV, 515±10 keV, and 689±10 keV. Method: The experiment was performed in inverse kinematics using a beam of unstable 38K impinged on a windowless hydrogen gas target. The 39Ca recoils and prompt γ rays from 38K(p,γ)39Ca reactions were detected in coincidence using a recoil mass separator and a bismuth-germanate scintillator array, respectively. Results: For the 689 keV resonance, we observed a clear recoil-γ coincidence signal and extracted resonance strength and energy values of 120-30+50(stat.)-60+20(sys.)meV and 679+2-1(stat.)±1(sys.)keV, respectively. We also performed a singles analysis of the recoil data alone, extracting a resonance strength of 120±20(stat.)±15(sys.) meV, consistent with the coincidence result. For the 386 keV and 515 keV resonances, we extract 90% confidence level upper limits of 2.54 meV and 18.4 meV, respectively. Conclusions: We have established a new recommended 38K(p,γ)39Ca rate based on experimental information, which reduces overall uncertainties near the peak temperatures of nova burning by a factor of ∼250. Using the rate obtained in this work in model calculations of the hottest oxygen-neon novae reduces overall uncertainties on Ar, K, and Ca synthesis to factors of 15 or less in all cases. [ABSTRACT FROM AUTHOR]

We have performed a direct measurement of the 19Ne(p,γ)20Na reaction in inverse kinematics using a beam of radioactive 19Ne. The key astrophysical resonance in the 19Ne+p system has been definitely measured for the first time at Ec.m.=456-2+5 keV with an associated strength of 17-5+7 meV. The present results are in agreement with resonance strength upper limits set by previous direct measurements, as well as resonance energies inferred from precision (³He, t) charge exchange reactions. However, both the energy and strength of the 456 keV resonance disagree with a recent indirect study of the 19Ne(d, n)20Na reaction. In particular, the new 19Ne(p,γ)20Na reaction rate is found to be factors of ∼8 and ∼5 lower than the most recent evaluation over the temperature range of oxygen-neon novae and astrophysical x-ray bursts, respectively. Nevertheless, we find that the 19Ne(p,γ)20Na reaction is likely to proceed fast enough to significantly reduce the flux of 19F in nova ejecta and does not create a bottleneck in the breakout from the hot CNO cycles into the rp process. [ABSTRACT FROM AUTHOR]

Background: The rate of the 18F(p,γ)19Ne reaction affects the final abundance of the radioisotope 18F ejected from novae. This nucleus is important as its abundance is thought to significantly influence the first-stage 511-keV and continuum γ-ray emission in the aftermath of novae. No successful measurement of this reaction existed prior to this work, and the rate used in stellar models had been calculated based on incomplete information from contributing resonances. Purpose: Of the two resonances thought to provide a significant contribution to the astrophysical reaction rate, located at Ec.m.=330 and 665 keV, the former has a radiative width estimated from the assumed analog state in the mirror nucleus, 19F, while the latter resonance does not have an analog state assignment, resulting in an arbitrary radiative width being assumed. As such, a direct measurement was needed to establish what role this resonance plays in the destruction of 18F at nova temperatures. This paper extends and takes the place of a previous Letter which reported the strength of the Ec.m.=665 keV resonance. Method: The DRAGON recoil separator was used to directly measure the strength of the important 665-keV resonance in this reaction, in inverse kinematics, by observing 19Ne reaction products. A radioactive 18F beam was provided by the ISAC facility at TRIUMF. R-matrix calculations were subsequently used to evaluate the significance of the results at astrophysical energies. Results: We report the direct measurement of the 18F(p,γ)19Ne reaction with the reevaluation of several detector efficiencies and the use of an updated 19Ne level scheme in the reaction rate analysis. The strength of the 665-keV resonance (Ex=7.076 MeV) is found to be an order of magnitude weaker than currently assumed in nova models. An improved analysis of the previously reported data is presented here, resulting in a slightly different value for the resonance strength. These small changes, however, do not alter the primary conclusions. Conclusions: Reaction rate calculations definitively show that the 665-keV resonance plays no significant role in the destruction of 18F at nova temperatures. [ABSTRACT FROM AUTHOR]

We have performed the first direct measurement of the 38K(p,γ)39Ca reaction using a beam of radioactive 38K. A proposed ℓ=0 resonance in the 38K+p system has been identified at 679(2) keV with an associated strength of 120+50−30  meV. Upper limits of 1.16 (3.5) and 8.6 (26) meV at the 68% (95%) confidence level were also established for two further expected ℓ=0 resonances at 386 and 515 keV, respectively. The present results have reduced uncertainties in the 38K(p,γ)39Ca reaction rate at temperatures of 0.4 GK by more than 2 orders of magnitude and indicate that Ar and Ca may be ejected in observable quantities by oxygen-neon novae. However, based on the newly evaluated rate, the 38K(p,γ)39Ca path is unlikely to be responsible for the production of Ar and Ca in significantly enhanced quantities relative to solar abundances. [ABSTRACT FROM AUTHOR]

Background and study aim: Endoscopic therapy of brisk upper gastrointestinal bleeding remains challenging. A proprietary nanopowder (TC-325) has been proven to be effective in high pressure bleeding from external wounds. The efficacy and safety of TC-325 were assessed in a survival gastrointestinal bleeding animal model. Method: 10 animals were randomized to treatment or sham. All animals received intravenous antibiotics, H2-blockers and heparin (activated clotting time 2 � normal). In a sterile laparotomy the gastroepiploic vessels were dissected, inserted through a 1-cm gastrotomy, and freely exposed in the gastric lumen, and the exposed vessel lacerated by needle knife. The treatment group received TC-325 by a modified delivery catheter while the sham group received no endoscopic treatment. Time to hemostasis, and mortality at 60 minutes, 24 hours, 48 hours, and 7 days were noted. Necropsy was performed in all animals. Results: Spurting arterial bleeding was achieved in all animals. No control animal showed hemostasis within the first hour compared with 100 % (5 / 5) in the treatment arm (mean 13.8 minutes, P < 0.0079). Durable hemostasis was achieved with no evidence of rebleeding after 1 and 24 hours in 80 % (4 / 5) of the treated animals compared with none in the control group (P < 0.0098). None of the control animals survived more than 6 hours. Necropsy at 1 week in treated animals revealed healed gastrotomy without foreign body granuloma or embolization to the lung or brain. Conclusion: TC-325 is safe and highly effective in achieving hemostasis in an anticoagulated severe arterial gastrointestinal bleeding animal model. [ABSTRACT FROM AUTHOR]

We have performed the first direct measurement of two resonances of the ^{7}Be(α,γ)^{11}C reaction with unknown strengths using an intense radioactive ^{7}Be beam and the DRAGON recoil separator. We report on the first measurement of the 1155 and 1110 keV resonance strengths of 1.73±0.25(stat)±0.40(syst)  eV and 125&#95;{-25}^{+27}(stat)±15(syst)  meV, respectively. The present results have reduced the uncertainty in the ^{7}Be(α,γ)^{11}C reaction rate to ∼9.4%-10.7% over T=1.5-3  GK, which is relevant for nucleosynthesis in the neutrino-driven outflows of core-collapse supernovae (νp process). We find no effect of the new, constrained reaction rate on νp-process nucleosynthesis.

We present the first direct measurement of an astrophysical reaction using a radioactive beam of isomeric nuclei. In particular, we have measured the strength of the key 447-keV resonance in the ^{26m}Al(p,γ)^{27}Si reaction to be 432&#95;{-226}^{+146}  meV and find that this resonance dominates the thermally averaged reaction rate for temperatures between 0.3 and 2.5 GK. This work represents a critical development in resolving one of the longest standing issues in nuclear astrophysics research, relating to the measurement of proton capture reactions on excited quantum levels, and offers unique insight into the destruction of isomeric ^{26}Al in astrophysical plasmas.

We have performed a direct measurement of the ^{19}Ne(p,γ)^{20}Na reaction in inverse kinematics using a beam of radioactive ^{19}Ne. The key astrophysical resonance in the ^{19}Ne+p system has been definitely measured for the first time at E&#95;{c.m.}=456&#95;{-2}^{+5}  keV with an associated strength of 17&#95;{-5}^{+7}  meV. The present results are in agreement with resonance strength upper limits set by previous direct measurements, as well as resonance energies inferred from precision (^{3}He, t) charge exchange reactions. However, both the energy and strength of the 456 keV resonance disagree with a recent indirect study of the ^{19}Ne(d, n)^{20}Na reaction. In particular, the new ^{19}Ne(p,γ)^{20}Na reaction rate is found to be factors of ∼8 and ∼5 lower than the most recent evaluation over the temperature range of oxygen-neon novae and astrophysical x-ray bursts, respectively. Nevertheless, we find that the ^{19}Ne(p,γ)^{20}Na reaction is likely to proceed fast enough to significantly reduce the flux of ^{19}F in nova ejecta and does not create a bottleneck in the breakout from the hot CNO cycles into the rp process.

We have performed the first direct measurement of the ^{38}K(p,γ)^{39}Ca reaction using a beam of radioactive ^{38}K. A proposed ℓ=0 resonance in the ^{38}K+p system has been identified at 679(2) keV with an associated strength of 120&#95;{-30}^{+50}  meV. Upper limits of 1.16 (3.5) and 8.6 (26) meV at the 68% (95%) confidence level were also established for two further expected ℓ=0 resonances at 386 and 515 keV, respectively. The present results have reduced uncertainties in the ^{38}K(p,γ)^{39}Ca reaction rate at temperatures of 0.4 GK by more than 2 orders of magnitude and indicate that Ar and Ca may be ejected in observable quantities by oxygen-neon novae. However, based on the newly evaluated rate, the ^{38}K(p,γ)^{39}Ca path is unlikely to be responsible for the production of Ar and Ca in significantly enhanced quantities relative to solar abundances.

The radionuclide 22Na is a potential astronomical observable that is expected to be produced in classical novae in quantities that depend on the thermonuclear rate of the 22Na(p,γ)23Mg reaction. We have measured the strengths of low-energy 22Na(p,γ)23Mg resonances directly and absolutely using a radioactive 22Na target. We find the strengths of resonances at Ep=213, 288, 454, and 610 keV to be higher than previous measurements by factors of 2.4-3.2, and we exclude important contributions to the rate from proposed resonances at Ep=198, 209, and 232 keV. The 22Na abundances expected in the ejecta of classical novae are reduced by a factor of ≈2.

Radiative alpha-particle capture into the first excited, J(pi)=0+ state of 16O at 6.049 MeV excitation energy has rarely been discussed as contributing to the 12C(alpha,gamma)16O reaction cross section due to experimental difficulties in observing this transition. We report here measurements of this radiative capture in 12C(alpha,gamma)16O for center-of-mass energies of E=2.22 MeV to 5.42 MeV at the DRAGON recoil separator. To determine cross sections, the acceptance of the recoil separator has been simulated in GEANT as well as measured directly. The transition strength between resonances has been identified in R-matrix fits as resulting both from E2 contributions as well as E1 radiative capture. Details of the extrapolation of the total cross section to low energies are then discussed [S6.0(300)=25(-15)(+16) keV b] showing that this transition is likely the most important cascade contribution for 12C(alpha,gamma)16O.

The strength of the Ec.m. = 184 keV resonance in the 26gAl(p, gamma)27 reaction has been measured in inverse kinematics using the DRAGON recoil separator at TRIUMF's ISAC facility. We measure a value of omega gamma = 35 +/- 7 microeV and a resonance energy of Ec.m. = 184 +/- 1 keV, consistent with p-wave proton capture into the 7652(3) keV state in 27Si, and discuss the implications of these values for 26GAl nucleosynthesis in typical oxygen-neon white-dwarf novae.

The forward-backward asymmetry in np-->dpi(0), which must be zero in the center-of-mass system if charge symmetry is respected, has been measured to be [17.2+/-8.0(stat)+/-5.5(syst)]x10(-4), at an incident neutron energy of 279.5 MeV. This observable is compared to recent chiral effective field theory calculations, with implications regarding the du quark mass difference.