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At temperatures below 0.1 GK, the $^{19}\mathrm{F}(p,\ensuremath{\gamma})^{20}\mathrm{Ne}$ reaction is the only breakout path out of the CNO cycle. Experimental studies of this reaction are challenging from a technical perspective due to copious $\ensuremath{\gamma}$-ray background from the far stronger $^{19}\mathrm{F}(p,\ensuremath{\alpha})^{16}\mathrm{O}$ reaction channel. Here, we present the first inverse kinematics study of the $^{19}\mathrm{F}(p,\ensuremath{\gamma})^{20}\mathrm{Ne}$ reaction, in which we measure the strength of the 323-keV resonance. We find a strength value of $\ensuremath{\omega}\ensuremath{\gamma}=3.{3}_{\ensuremath{-}0.9}^{+1.1}$ meV, which is a factor of two larger than the most recent previous study. The discrepancy is likely the result of a direct to ground state transition which previous studies were not sensitive to. We also observe the transition to the first ${2}^{\ensuremath{-}}$ state, which has not been observed for this resonance in previous studies. A new thermonuclear reaction rate is calculated and compared with the literature.

Nuclear reaction sensitivity studies have shown that the final isotopic abundance of O-Ne nova nucleosynthesis is dependent on the $^{34}\mathrm{S}(p,\ensuremath{\gamma})^{35}\mathrm{Cl}$ reaction at astrophysical energies corresponding to peak nova burning temperatures of 0.1--0.4 GK. Isotopic ratios of the S, Cl, and Ar products are all used in various methods of cosmochemical analysis of presolar meteoritic grains. Due to the lack of direct experimental data, the $^{34}\mathrm{S}+p$ reaction rate has been estimated using statistical modeling or information from indirect nucleon transfer experiments. In order to provide direct reaction information, the resonance strengths of several low energy resonances, ${E}_{\mathrm{c}.\mathrm{m}.}=272--495$ keV, in the $^{34}\mathrm{S}(p,\ensuremath{\gamma})^{35}\mathrm{Cl}$ reaction were measured for the first time in inverse kinematics using the DRAGON recoil separator located at TRIUMF, Canada's Particle Accelerator Centre in Vancouver.

The p-nuclei are the few stable nuclei heavier than iron on the neutron-deficient side of the valley of stability that cannot be produced through astrophysical neutron-capture reactions. The limited experimental data on reactions through which the p-nuclei might be produced leaves the origin of their production largely unknown. This work presents the first cross section measurements of the 76Se( α , γ )80Kr reaction. The rate of the time reversed reaction, 80Kr( γ , α )76Se, is one of the most uncertain of possible reactions which can occur at the 80Kr branching point on the γ-process photo-disintegration pathway. The reaction flow through 80Kr will directly affect the final abundance of the p-nuclide 78Kr. Experimental cross sections at two astrophysically relevant energies are reported and compared to cross sections calculated using Hauser-Feshbach codes talys , non-smoker , and smaragd . The success of these first ( α , γ ) cross section measurements performed in inverse kinematics in the energy region of the γ-process opens the door for future studies of reactions on radioactive γ-process nuclides.

In this Letter we report on the first inverse kinematics measurement of key resonances in the 22Ne(p, γ )23Na 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 22Ne(p, γ )23Na at Ec.m. = 149 keV, 181 keV, 248 keV and 458 keV. The strength of the important Ec.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, The authors thank the ISAC operations and technical staff at TRIUMF. TRIUMF's core operations are supported via a contribution from the federal government through the National Research Council Canada, and the Government of British Columbia provides building capital funds. DRAGON is supported by funds from the National Sciences and Engineering Research Council of Canada SAPPJ-2019-00039. The authors acknowledge support from the “ChETEC” COST Action (CA16117), supported by COST 116 (European Cooperation in Science and Technology). MW, AML, JR were supported by the UK Science and Technology Facilities Council (STFC) ST/P003885/1. UB acknowledges support from the European Research Council ERC-2015-STG Nr. 677497. J. José acknowledges support from the Spanish MINECO grant AYA2017-86274-P, the EU FEDER funds and the AGAUR/Generalitat de Catalunya grant SGR-661/2017. Authors from the Colorado School of Mines acknowledge funding via the U.S. Department of Energy grant DE-FG02-93ER40789.

Background: Globular clusters are known to exhibit anomalous abundance trends such as the sodium-oxygen anticorrelation. This trend is thought to arise via pollution of the cluster interstellar medium from a previous generation of stars. Intermediate-mass asymptotic giant branch stars undergoing hot bottom burning (HBB) are a prime candidate for producing sodium-rich oxygen-poor material, and then expelling this material via strong stellar winds. The amount of $^{23}\mathrm{Na}$ produced in this environment has been shown to be sensitive to uncertainties in the $^{22}\mathrm{Ne}(p,\ensuremath{\gamma})^{23}\mathrm{Na}$ reaction rate. The $^{22}\mathrm{Ne}(p,\ensuremath{\gamma})^{23}\mathrm{Na}$ reaction is also activated in classical nova nucleosynthesis, strongly influencing predicted isotopic abundance ratios in the Na-Al region. Therefore, improved nuclear physics uncertainties for this reaction rate are of critical importance for the identification and classification of pre-solar grains produced by classical novae.Purpose: At temperatures relevant for both HBB in AGB stars and classical nova nucleosynthesis, the $^{22}\mathrm{Ne}(p,\ensuremath{\gamma})^{23}\mathrm{Na}$ reaction rate is dominated by narrow resonances, with additional contribution from direct capture. This study presents new strength values for seven resonances, as well as a study of direct capture.Method: The experiment was performed in inverse kinematics by impinging an intense isotopically pure beam of $^{22}\mathrm{Ne}$ onto a windowless ${\mathrm{H}}_{2}$ gas target. The $^{23}\mathrm{Na}$ recoils and prompt $\ensuremath{\gamma}$ rays were detected in coincidence using a recoil mass separator coupled to a $4\ensuremath{\pi}$ bismuth-germanate scintillator array surrounding the target.Results: For the low-energy resonances, located at center of mass energies of 149, 181, and 248 keV, we recover stength values of $\ensuremath{\omega}{\ensuremath{\gamma}}_{149}=0.{17}_{\ensuremath{-}0.04}^{+0.05}, \ensuremath{\omega}{\ensuremath{\gamma}}_{181}=2.2\ifmmode\pm\else\textpm\fi{}0.4$, and $\ensuremath{\omega}{\ensuremath{\gamma}}_{248}=8.2\ifmmode\pm\else\textpm\fi{}0.7 \ensuremath{\mu}\text{eV}$, respectively. These results are in broad agreement with recent studies performed by the LUNA and TUNL groups. However, for the important reference resonance at 458 keV we obtain a strength value of $\ensuremath{\omega}{\ensuremath{\gamma}}_{458}=0.44\ifmmode\pm\else\textpm\fi{}0.02$ eV, which is significantly lower than recently reported values. This is the first time that this resonance has been studied completely independently from other resonance strengths. For the 632-keV resonance we recover a strength value of $\ensuremath{\omega}{\ensuremath{\gamma}}_{632}=0.48\ifmmode\pm\else\textpm\fi{}0.02$ eV, which is an order of magnitude higher than a recent study. For reference resonances at 610- and 1222-keV, our strength values are in agreement with the literature. In the case of direct capture, we recover an $S$ factor of 60 keV b, consistent with prior forward kinematics experiments.Conclusions: In summary, we have performed the first direct measurement of $^{22}\mathrm{Ne}(p,\ensuremath{\gamma})^{23}\mathrm{Na}$ in inverse kinematics. Our results are in broad agreement with the literature, with the notable exception of the 458-keV resonance, for which we obtain a lower strength value. We assessed the impact of the present reaction rate in reference to a variety of astrophysical environments, including AGB stars and classical novae. Production of $^{23}\mathrm{Na}$ in AGB stars is minimally influenced by the factor of 4 increase in the present rate compared to the STARLIB-2013 compilation. The present rate does however impact upon the production of nuclei in the Ne-Al region for classical novae, with dramatically improved uncertainties in the predicted isotopic abundances present in the novae ejecta.

During the slow neutron capture process in massive stars, reactions on light elements can both produce and absorb neutrons thereby influencing the final heavy element abundances. At low metallicities, the high neutron capture rate of 16-O can inhibit s-process nucleosynthesis unless the neutrons are recycled via the 17O(a,n)20Ne reaction. The efficiency of this neutron recycling is determined by competition between the 17O(a,n)20Ne and 17O(a,g)21Ne reactions. While some experimental data are available on the former reaction, no data exist for the radiative capture channel at the relevant astrophysical energies. The 17O(a,g)21Ne reaction has been studied directly using the DRAGON recoil separator at the TRIUMF Laboratory. The reaction cross section has been determined at energies between 0.6 and 1.6 MeV Ecm, reaching into the Gamow window for core helium burning for the first time. Resonance strengths for resonances at 0.63, 0.721, 0.81 and 1.122 MeV Ecm have been extracted. The experimentally based reaction rate calculated represents a lower limit, but suggests that significant s-process nucleosynthesis occurs in low metallicity massive stars., 7 pages, 5 figures

Radiative capture reactions play a pivotal role for our understanding of the origin of the elements in the cosmos. Recoil separators provide an effective way to study these reactions, in inverse kinematics, and take advantage of the use of radioactive ion beams. However, a limiting factor in the study of radiative capture reactions in inverse kinematics is the momentum spread of the product nuclei, which can result in an angular spread larger than the geometric acceptance of the separator. The DRAGON facility at TRIUMF is a versatile recoil separator, designed to study radiative capture reactions relevant to astrophysics in the A ∼ 10–30 region. In this work we present the first attempt to study with DRAGON a reaction, 6 Li( α , γ ) 10 B, for which the recoil angular spread exceeds DRAGON’s acceptance. Our result is in good agreement with the literature value, showing that DRAGON can measure resonance strengths of astrophysically important reactions even when not all the recoils enter the separator.

The production of the p–nuclei is one of the unsolved puzzles in nuclear astrophysics. A possible mechanism is the nucleosynthesis in the neutrino–driven winds of core–collapse supernovae (νp–process), but it carries uncertainties, mostly in the supernova dynamics and the nuclear physics input. The pp-chain breakout reaction 7Be(α,γ)11C, which occurs prior to the supernova explosion, was identified as an important link which can influence the nuclear flow of the z/p-process and the final abundances of the p-nuclei. Nevertheless, its reaction rate is poorly known over the relevant energy range (T=1.5-3 GK). To improve the 7Be(α,γ)11C rate for vp-process nucleosynthesis temperatures, the first measurement of the strengths of two important resonances with unknown strength was recently performed at TRIUMF. A radioactive 7Be beam (t1/2 = 53.24 d) beam and the DRAGON recoil separator were used. The experimental details and preliminary results for the resonance strengths will be discussed.

International audience; The origin of the p-nuclei, has been a long-standing puzzle in nuclear astrophysics. The $\nu $ p-process is a candidate for the production of the light p-nuclei, but it presents high sensitivity to both supernova dynamics and nuclear physics. It has been recently shown that the breakout from pp-chains through the$^{7}$Be $(\alpha ,\gamma )^{11}$C reaction, which occurs prior to $\nu $ p-process, can significantly influence the reaction flow, and subsequently the production of p-nuclei in the $90

Background: Nucleosynthesis of mid-mass elements is thought to occur under hot and explosive astrophysical conditions. Radiative α capture on S34 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 Ar38 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 S34 ions on a windowless He4 gas target. Prompt γ emissions of de-exciting Ar38 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).

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 38 K ( p , γ ) 39 Ca 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 38 K impinged on a windowless hydrogen gas target. The 39 Ca recoils and prompt γ rays from 38 K ( p , γ ) 39 Ca 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 + 50 − 30 ( stat . ) + 20 − 60 ( 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 38 K ( p , γ ) 39 Ca 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.

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+5−2 keV with an associated strength of 17+7−5 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.

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_{c.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 (^{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.

Background: The rate of the F18(p,γ)Ne19 reaction affects the final abundance of the radioisotope F18 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, F19, 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 F18 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 Ne19 reaction products. A radioactive F18 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 F18(p,γ)Ne19 reaction with the reevaluation of several detector efficiencies and the use of an updated Ne19 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 F18 at nova temperatures.

We have performed the first direct measurement of the 38Kðp; γÞ39Ca reaction using a beam of radioactive 38K. A proposed l ¼ 0 resonance in the 38K þ p system has been identified at 679(2) keV with an associated strength of 120 þ50 −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 ¼ 0 resonances at 386 and 515 keV, respectively. The present results have reduced uncertainties in the 38Kðp; γÞ39Ca 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 38Kðp; γÞ39Ca path is unlikely to be responsible for the production of Ar and Ca in significantly enhanced quantities relative to solar abundances.

The DRAGON facility for the study of radiative capture reactions has an extended gas target, surrounded by an array of BGO detectors. The distribution of detected gamma rays amongst the segmented array permits an estimate of the reaction position and consequently of the resonance energy. We report a study of the technique, using the 24 Mg(p, γ ) 25 Al reaction. Energy determination to better than 0.5% has been demonstrated.

The DRAGON (Detector of Recoils And Gammas Of Nuclear reactions) is used to measure radiative proton and alpha capture reaction rates involving both stable and radioactive, heavy-ion reactants at the TRIUMF-ISAC high intensity radioactive beam facility. Completed in 2001 it has been used for several challenging studies for nuclear astrophysics, e.g. 12 C(α, γ) 16 O, 21 Na(p, γ) 22 Mg, 26g Al(p, γ) 27 Si and 40 Ca(α, γ) 44 Ti. Since initial operation, a number of improvements have been incorporated which are described here. These include a beam centering monitor based on a CCD camera, a mechanical iris to skim of beam halo, a solid state stripper acting as a charge state booster for beams with A ≳ 30, beta and gamma detectors to monitor beam intensity and to determine beam contamination in experiments with radioactive beam and the ionization chamber for both recoil identification and isobar separation.

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 12 C( α , γ ) 16 O, the 26 Al(p, γ ) 27 Si and the 40 Ca( α , γ ) 44 Ti reactions at DRAGON will be described. For the TUDA facility a measurement of 10 B( α ,p) 13 C as a test for the 18 Ne( α ,p) 21 Na 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 16 N will be given.

We report here on experiments with radioactive 21 Na and 7 Be 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( 21 Na, γ) 22 Mg. Using the HRIBF we performed an experiment with a 7 Be ion beam to measure scattering off Hydrogen and Carbon. Both elastic 7 Be + p scattering and for the first time resonant inelastic scattering 7 Be(p, p′) 7 Be ∗ were observed.

Nuclear reactions play a key role in understanding nucleosynthesis in stars. Recoil mass spectrometers such as DRAGON are well suited to study reactions with respect to astrophysical production because of direct detection of reaction products. Here we present the first stage of an experiment running at the recoil mass spectrometer DRAGON at the ISAC/TRIUMF facility in Vancouver, Canada, to study the reaction 40Ca(α, γ)44Ti at astrophysically relevant energies. This reaction is one of the key reactions for production of 44Ti, which has been identified in young supernova remnants by space based γ-ray telescopes onboard COMPTEL and INTEGRAL. In this paper we focus on technical upgrade of DRAGON for 40Ca(α, γ)44Ti and preliminary results at resonances at Ex ∼ 9.2 MeV.

We present new measurements of the charge-state distribution (CSD) of a 1.068 MeV/u C beam in He and of the 6+:5+ charge-state population ratio in the recoils of the 12C(α, γ)16O reaction, both measured at the DRAGON recoil mass spectrometer. A computer simulation to model the CSD of both beam and recoil particles in inverse-kinematics experiments is compared to data from this work and from previous work at ERNA. The simulation provides good agreement with both data sets. The results suggest that, for this fusion reaction on the Jπ = 4+ resonance at Ebeam = 1.064 MeV/u, immediately after fusion, the recoil ions contain only the nucleons and not the electrons of the target He atom.

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_{-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.

ITO International Research Center, on the campus of the University of Tokyo, June 1 to 6, 2014; http://ribf.riken.jp/ARIS2014/index.html

The performance of the DRAGON recoil spectrometer at TRIUMF-ISAC has been studied using radiative capture reactions with stable beams of 12C, 20Ne, 21Ne, 23Na, 24Mg and 26Mg. Calibration of the deflection magnet measuring the beam energy was established and the beam suppression factors of the separator were investigated. Yields from six narrow resonances were measured and compared with previous results. For the 1,112.6 keV resonance in Ne 20 ( p , γ ) Na 21 our result is in disagreement with the NACRE database assignment but agrees with another previous result.

Resonant scattering studies were performed using radioactive 20,21 Na beams at ISAC between energies of 0.5 keV/u and 1.5 keV/u. Intensities of up to 1 × 10 8 /sec were used with thick CH 2 targets, and elastic and inelastic proton resonances were observed corresponding to states in 21,22 Mg 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 21 Na+p analysis.

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.

Preliminary studies in preparation for an absolute cross-section measurement of the radiative capture reaction 3 He( α , γ ) 7 Be with the DRAGON recoil separator have demonstrated beam suppression > 10 14 at the 90% confidence level. A measurement of this cross section by observation of 7 Be recoils at the focal plane of the separator should be virtually background free.

The DRAGON facility at TRIUMF-ISAC has been used to study the radiative capture of hydrogen by unstable 21 Na, at energies of interest in nuclear astrophysics. The strength of the reaction was measured for resonant capture through five excited states of 22 Mg and a limit set for one other state. Yields ranging between 10 -12 and 10 -10 per incident beam particle were observed. Only the state at 5.714 MeV makes a significant contribution to 22 Na production by explosive burning in Oxygen-Neon novae. Careful comparison of the beam energy for capture through the 5.714 MeV state against the beam energy for a well-studied stable-beam resonance indicates the need for a re-adjustment of the 22 Mg mass.

The DRAGON (detector of recoils and gamma-rays of nuclear reactions) setup at the ISAC radioactive ion beam facility of TRIUMF, Vancouver, was used to measure the energy loss of stable neon and magnesium as well as of radioactive sodium ions (energy range 200–1150 keV/u) in hydrogen gas. Stopping power values were determined and (as no previous experimental data around the stopping power maximum existed) compared to the available semi-empirical codes SRIM 2000, SRIM 2003, ATIMA and MSTAR. The experimental data seems to favor the new SRIM 2003 approach and will hopefully provide input to a further improvement of the parameter set.

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.

Important ion beam parameters like energy spread and stability of the new isotope separator and accelerator accelerator at TRIUMF were determined during the first beamtime with the detector of recoils and gammas of nuclear gas target and BGO array. For this purpose a variation of the nuclear resonance method, using a geometrical scan over the resonance as placed in an extended gas target cell, as well as time-of-flight correlations were employed.

A facility for measuring cross-sections (resonance strengths) for reactions of astrophysical importance involving short-lived, radioactive reactants has been designed, built and installed at the new TRIUMF-ISAC Radioactive Beams Laboratory in Canada. Named DRAGON (Detector of Recoils And Gamma-rays of Nuclear reactions), it has been successfully commissioned with stable and radioactive heavy ion beams from ISAC. This report presents the main components of the facility, namely, the windowless gas target, the surrounding g detector array, the subsequent electromagnetic recoil mass separator, the focal plane detectors for recoils, the detection system for elastics, and the modular electronics and computer software used for the data acquisition. Examples of the operation of the facility for both stable beam reactions and the first radioactive beam reaction study, 21 Naðp;gÞ 22 Mg are also presented, along with future plans for the program. r 2003 Elsevier Science B.V. All rights reserved. PACS: 29.0

Studies of the charge state distribution of low energy (< 1.5 MeV/u), low Z (< 13) heavy ions passing through hydrogen and helium gas of varying target pressure have been performed using separate windowless gas target systems at TRIUMF and the University of Naples. Semi-empirical relationships have been deduced to estimate the equilibrium charge state distributions as a function of beam energy. From these distributions, cross-sections for the relevant charge changing reactions have been deduced. (C) 2002 Elsevier Science B.V. All rights reserved.

A direct measurement of the 19Ne(p, γ)20 Na reaction has been performed in inverse kinematics at the DRAGON recoil separator, at an energy ∼ 10 keV higher than previous measurements. The key resonance in the 19 Ne + p system relevant for ONe novae and Type-I X-ray burst temperatures have been successfully measured for the first time. Preliminary estimates of the resonance energy and strength are reported as Ec.m. ≠458 keV and ωγ ≠18 meV. These results are consistent with previous direct measurements, but disagree with the most recent study of the 19Ne(p, γ)20 Na reaction rate. These preliminary results will be finalised after a forthcoming negative log-likelihood analysis.

A segmented neutron detector has been constructed and used for recoil neutron (6–13 MeV) measurements of the reaction γp→nπ+ very close to threshold. BC-505 liquid scintillator was used to allow pulse shape discrimination between neutrons and photons. A measurement of the absolute efficiency of the detector was performed using stopped pions in the reaction π−p→nγ. Results of the efficiency calibration are compared to a Monte Carlo simulation.

Inclusive measurements of the pion differential cross sections and analyzing powers have been carried out for the $p\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{pn}{\ensuremath{\pi}}^{+}$ reaction at 420 and 500 MeV using the SASP spectrometer at TRIUMF. Pion energies from the onset of the continuum down to about 25 MeV were covered in the angular range from $23\ifmmode^\circ\else\textdegree\fi{}$ to $100\ifmmode^\circ\else\textdegree\fi{}$ (lab). Total cross sections of $0.750\ifmmode\pm\else\textpm\fi{}0.075 \mathrm{mb}\mathrm{}$ and $2.77\ifmmode\pm\else\textpm\fi{}0.28 \mathrm{mb}$ were determined for the $p\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{pn}{\ensuremath{\pi}}^{+}$ reaction at 420 and 500 MeV, respectively. The experimental results are presented and discussed within the framework of a partial wave analysis. Theoretical predictions from a covariant one-boson-exchange model that includes final state interactions, provide a good description of the data. The pion spectra, in the region corresponding to low relative $\mathrm{np}$ energies, are also well described by a final state interaction model that uses the $p\stackrel{\ensuremath{\rightarrow}}{p}d{\ensuremath{\pi}}^{+}$ cross sections as input. Details of the determination of the background corrections and detector efficiencies will be discussed.

Analyzing powers for $\stackrel{\ensuremath{\rightarrow}}{p}n\ensuremath{\rightarrow}\mathrm{pp}(^{1}S_{0}){\ensuremath{\pi}}^{\ensuremath{-}}$ were measured at beam energies 353, 404, and 440 MeV by extracting the quasifree process from $\stackrel{\ensuremath{\rightarrow}}{p}d\ensuremath{\rightarrow}\mathrm{ppp}{\ensuremath{\pi}}^{\ensuremath{-}}$. Partial wave amplitude analysis yields a significant contribution from the isospin 1, $s$-wave channel. This contribution is relatively much larger than that expected from theoretical models which have been successful in describing the isospin 1, $s$-wave channel behavior of $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{pp}{\ensuremath{\pi}}^{0}$ cross sections at threshold.

The double differential cross section for $\mathrm{pn}\ensuremath{\rightarrow}\mathrm{pp}{(}^{1}{S}_{0}){\ensuremath{\pi}}^{\ensuremath{-}}$ at three beam energies has been extracted from the quasifree process $\mathrm{pd}\ensuremath{\rightarrow}\mathrm{ppp}{\ensuremath{\pi}}^{\ensuremath{-}}$. A comparison is carried out with single differential cross section measurements for ${}^{3}\mathrm{He}({\ensuremath{\pi}}^{\ensuremath{-}},pn)n$, where the pion is thought to be absorbed onto a $\mathrm{pp}{(}^{1}{S}_{0})$ ``diproton'' state. A significant difference is observed in the shape of the angular distribution between the production and absorption data. This difference is ascribed to the effects of the ${}^{3}\mathrm{He}$ nuclear environment characterizing the absorption process; however, an adequate theoretical explanation is not available.

Exclusive measurements of the analyzing power and two spin-transfer observables for nucleon knockout from an 16 O target are presented, at kinematic conditions chosen to emphasize interactions in the nuclear interior. The analyzing power data are substantially reduced in comparison with values calculated in the distorted wave impulse approximation ~DWIA! using the free nucleon-nucleon interaction, particularly for knockout of the deeply bound 1s 1/2 nucleons. Inclusion of density dependence for the interaction in the calculations improves the agreement with the data, but does not provide a satisfactory description for nucleon knockout from 16 O. Spin-orbit distortions are shown to strongly affect the DWIA predictions of the 1 s 1/2 analyzing powers over most of the experimental kinematic range, but notably not near the points of negligible recoil momentum. Hence these data offer constraints on the optical potentials and independently on the two-body effective interaction. @S0556-2813~98!02104-9# PACS number~s!: 25.40.Ep, 24.70.1s, 24.10.Eq, 13.75.2n

The measurement of low energy fusion reactions of importance to nuclear astrophysics scenarios are a prime objective of the physics program of the new ISAC facility, located at TRIUMF in Vancouver, Canada. Intense radioactive beams of 19 Ne, 14,15 O, 20,21 Na, 17,18 F and other low Z species with energies in the range of 0.15 to 1.5 MeV/mass unit will be available to measure cross sections and resonance strengths of alpha and proton induced reactions. An important component of the experimental configuration will be a new Reaction Products Detection Facility (RPDF) consisting of a windowless gas target, surrounded by a gamma array, while the recoils are separated from the intense radioactive beam using a Recoil Mass Spectrometer (RMS). The RMS will be based on a Wien filter. The recoiling reaction products will then be detected using either a Si μ-strip array or a gas filled detector. Using these devices along with coincidence requirements and time of flight conditions a background reduction factor of the order of 10 +15 is the present goal.

A search for narrow, deeply bound pionic atom states via atomic radiative capture of negative pions in a target of {sup 208}Pb was carried out for pion kinetic energies of 20 and 25 MeV. Although no clear signature of any such gamma ray emission could be observed in the data, fits of the gamma ray spectra between the energies of 12 and 42 MeV involving a quadratic background together with a pair of peaks (1s, 2p) whose relative intensity was taken from theory yielded an overall strength for the peaks which are consistent (to a 67{percent} confidence level) with radiative capture whose integrated cross section is 20.0 {plus_minus} 10.0 {mu}b/sr at 90{degree} for 20 MeV incident pions. A lower probability (40{percent} confidence level) result was obtained when the fit was carried out without the peaks included, just the continuum background. {copyright} {ital 1997} {ital The American Physical Society}

The measurement of low energy fusion reactions of importance to nuclear astrophysics scenarios are a prime objective of the physics program of the new ISAC facility, located at TRIUMF in Vancouver, Canada. Intense radioactive beams of 19 Ne, 14,15 O, 20,21 Na, 17,18 F and other low Z species with energies in the range of 0.15 to 1.5 MeV/mass unit will be available to measure cross sections and resonance strengths of alpha and proton induced reactions. An important component of the experimental configuration will be a new Recoil Product Detection Facility (RPDF) consisting of a windowless gas target, surrounded by a gamma array, while the recoils are separated from the intense radioactive beam using a Electro-Magnetic Separator (EMS) employing Wien filters. The recoiling reaction products will then be detected using either a Si μ-strip array or a gas filled detector. Using these devices along with coincidence requirements and time-of-flight conditions a background reduction factor of the order of 10 +15 is the present goal.

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.