Search

The nature of the 1 − and 2 − excited states in Be 10 is studied using the Be 11 ( p , d ) transfer reaction in inverse kinematics at 10A MeV at TRIUMF ISAC-II, in particular to assess whether either of them can be considered as an excited halo state. The angular distributions for both states are extracted using deuteron- γ coincidences and analyzed using a transfer model taking into account one-step and two-step processes. A good fit of the angular distributions is obtained considering only the one-step process, whereby an inner p 3 / 2 neutron of Be 11 is removed, leaving the halo neutron intact. Higher-order processes however cannot be rejected. The small spectroscopic factors extracted suggest that the structure of both states is not uniquely halo-like, but rather display a more complex configuration mixing cluster and halo structures. Further insights are limited, as this experiment specifically probed the halo-like (but not cluster-like) Be 11 ( 1 / 2 + ) ⊗ ( ν p 3 / 2 ) − 1 configuration in both states.

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.

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

A recoil mass separator SECAR has been designed for the purpose of studying low-energy ( p , γ ) and ( α , γ ) reactions in inverse kinematics with radioactive beams for masses up to about A = 65. Their reaction rates are of importance for our understanding of the energy production and nucleosynthesis during explosive hydrogen and helium burning. The radiative capture reactions take place in a windowless hydrogen or He gas target at the entrance of the separator, which consists of four Sections . The first Section selects the charge state of the recoils. The second and third Sections contain Wien Filters providing high mass resolving power to separate efficiently the intense beam from the few reaction products. In the following fourth Section , the reaction products are guided into a detector system capable of position, angle and time-of-flight measurements. In order to accept the complete kinematic cone of recoil particles including multiple scattering in the target in the center of mass energy range of 0.2 MeV to 3.0 MeV, the system must have a large polar angle acceptance of ± 25 mrad. This requires a careful minimization of higher order aberrations. The present system will be installed at the NSCL ReA3 accelerator and will be used with the much higher beam intensities of the FRIB facility when it becomes available.

The normalized $^{238}$U(n,f)/$^{235}$U(n,f) cross section ratio has been measured using the NIFFTE fission Time Projection Chamber from the reaction threshold to $30$~MeV. The fissionTPC is a two-volume MICROMEGAS time projection chamber that allows for full three-dimensional reconstruction of fission-fragment ionization profiles from neutron-induced fission. The measurement was performed at the Los Alamos Neutron Science Center, where the neutron energy is determined from neutron time-of-flight. The $^{238}$U(n,f)/$^{235}$U(n,f) ratio reported here is the first cross section measurement made with the fissionTPC, and will provide new experimental data for evaluation of the $^{238}$U(n,f) cross section, an important standard used in neutron-flux measurements. Use of a development target in this work prevented the determination of an absolute normalization, to be addressed in future measurements. Instead, the measured cross section ratio has been normalized to ENDF/B-VIII.$\beta$5 at 14.5 MeV.

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.

A recoil separator SECAR has been designed to study radiative capture reactions relevant for the astrophysical rp-process in inverse kinematics for the Facility for Rare Isotope Beams (FRIB). We describe the design, layout, and ion optics of the recoil separator and present the status of the project.

The angular distributions of the elastic, inelastic scattering and break-up cross sections of the one neutron halo $^{11}$Be on a heavy-mass target ($^{197}$Au) have been measured at laboratory energies below (31.9 MeV) and around (39.6 MeV) the Coulomb barrier ($V_b \sim$ 40 MeV). The elastic, inelastic channel and break-up channels of the $^{11}$Be + $^{197}$Au reaction have been experimentally separated for the first time in this energy range. The experiment was performed at TRIUMF, using four Silicon detectors in telescope configuration to separate the $^{11}$Be from the $^{10}$Be fragments and the High-Purity Germanium Detector Array TIGRESS for $\gamma$-ray detection. The break-up and inelastic scattering contributions are observed to be relevant even at energies well below the Coulomb barrier. Data are compared with different models of increasing degree of sophistication: semiclassical, inert-core continuum discretised coupled channel (CDCC) calculations and CDCC including core deformation and excitations (XCDCC). XCDCC calculations are necessary to reproduce simultaneously elastic, inelastic and break-up scattering data. The results show that the reaction mechanism is sensible to the entanglement of core and halo degrees of freedom in $^{197}$Au.

Angular distributions of the elastic, inelastic, and breakup cross sections of the halo nucleus ^{11}Be on ^{197}Au were measured at energies below (E_{lab}=31.9 MeV) and around (39.6 MeV) the Coulomb barrier. These three channels were unambiguously separated for the first time for reactions of ^{11}Be on a high-Z target at low energies. The experiment was performed at TRIUMF (Vancouver, Canada). The differential cross sections were compared with three different calculations: semiclassical, inert-core continuum-coupled-channels and continuum-coupled-channels ones with including core deformation. These results show conclusively that the elastic and inelastic differential cross sections can only be accounted for if core-excited admixtures are taken into account. The cross sections for these channels strongly depend on the B(E1) distribution in ^{11}Be, and the reaction mechanism is sensitive to the entanglement of core and halo degrees of freedom in ^{11}Be.

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.

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.

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.

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.

An in-depth characterization of the TACTIC detector was performed using data from a 148Gd alpha source and some test runs with a stable ion beam. The detector is an active target time-projection chamber with a blind central region for maximizing beam tolerance and GEM-based electron amplification, equipped with a modern digitizing data acquisition system allowing the recording of full signals. The system was developed to study the reaction 8Li(α,n)11B, which is important for bridging the mass 8 gap in scenarios of low 4He density like Inhomogeneous Big Bang Nucleosynthesis and the production of r-process seeds in supernovae. Both energy resolution and tracking accuracy were found to agree with theoretical predictions and Geant4 simulations. The 8Li beam rate capability of the system is predicted to be of the order of 105s-1, several orders of magnitude higher than most previous measurements of the same reaction, while still maintaining a high detection efficiency of 70% to 80 %.

The front end of the Jyvaskyla IGISOL facility was upgraded in 2003 by increasing its pumping capacity and by improving the radiation shielding. In late 2005, the skimmer electrode of the mass separator was replaced by a sextupole ion guide, which improved the mass separator efficiency up to an order of magnitude. The current design of the facility is described. The updated yield data, achieved with and without the additional JYFLTRAP purification, using both fusion evaporation reactions and particle induced fission is presented to give an overview of the capability of the facility. These data have been determined either by radioactivity measurements or by direct ion counting after the Penning trap system.

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

International audience; The changing of the nuclear shells for light, neutron-rich nuclei, and the single-particle nature of 26Na, has been explored by studying 25Na(d, p)26Na in inverse kinematics, using a beam of 25Na ions at 5 MeV per nucleon, provided by the ISAC-II facility at TRIUMF, Vancouver. Charged particles were detected with a highly-segmented silicon array that surrounded the 0.5 mg/cm2 (CD2)n target. Gamma rays from the recoiling 26Na nucleus were detected using eight Compton-suppressed HPGe clover detectors. Recoil tagging was provided by an in-beam scintillation foil, downstream of the germanium array. A novel technique of utilising pγ- and pγγ-gating to extract proton angular distributions from states populated close in energy was employed with success. New states in 26Na that are populated directly have been identified, using γ-decay patterns. Shell model calculations for comparison to experimental results are ongoing, using different model bases.

JYFLTRAP is a Penning trap system at the accelerator laboratory in Jyvaskyla, Finland that enables high-precision experiments with stored, exotic species that are produced at the IGISOL facility. On one hand, these can be performed within the trap itself, like e.g. mass spectrometry. On the other hand, the trap can be used to provide the highly purified species for further experiments, e.g. for trap-assisted nuclear decay spectroscopy. This contribution focuses on these two possible applications with the presentation of some recent results on superallowed beta decays.

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.

This work reports on the scattering of 11Be on 197Au at energies around and below the Coulomb barrier. By experimentally identifying the elastic scattering, inelastic scattering and breakup channels, and comparing them with different calculations, valuable information on the 11Be structure and its B(E1) distribution to the continuum are obtained. On top of that, a deeper understanding of the scattering process at low energies is achieved for reactions of this kind, making these studies extendable to other loosely-bound systems like 17,19C Gobierno de España FPA2015-64969-P, FIS2014-53448-C2-1-P, FPA2013-47327-c02-01-R, FPA2012-32443, FIS2013-41994-P, CSD2007-00042 EUROCORES EUI-2009-04162 European Union 654002

At low stellar temperatures the energy release due to the CN cycle is regulated by its slowest reaction ${}^{14}\mathrm{N}(p,\ensuremath{\gamma}){}^{15}\mathrm{O}$, the rate of which strongly depends on the subthreshold resonance at ${E}_{\mathrm{c}}.\mathrm{m}.=\ensuremath{-}504\phantom{\rule{0.28em}{0ex}}\mathrm{keV}$, which corresponds to the 6.79 MeV state in ${}^{15}\mathrm{O}$. By using the Doppler-shift attenuation method and the ${}^{3}\mathrm{He}({}^{16}\mathrm{O},\ensuremath{\alpha}){}^{15}\mathrm{O}$ reaction to populate the state, we obtained an upper limit on the lifetime of this state of $\ensuremath{\tau}l1.8\phantom{\rule{0.28em}{0ex}}\mathrm{fs}$ [68.3% confidence level (C.L.)]. In addition we measured the lifetimes of the 6.18 and 6.86 MeV states to be $\ensuremath{\tau}l2.5$ and $\ensuremath{\tau}=13.{3}_{\ensuremath{-}1.2}^{+0.9}\phantom{\rule{0.28em}{0ex}}\mathrm{fs}$, respectively (68.3% C.L.), in good agreement with the literature.

Radiative capture reactions involving the fusion of hydrogen or helium are ubiquitous in the stellar history of the universe, and are some of the most important reactions in the processes that govern nucleosynthesis and energy generation in both static and explosive scenarios. However, radiative capture reactions pose some of the most difficult experimental challenges due to extremely small cross sections. With the advent of recoil separators and techniques in inverse kinematics, it is now possible to measure radiative capture reactions on very short-lived radioactive nuclei, and in the presence of high experimental backgrounds. In this paper we review the experimental needs for making measurements of astrophysical importance on radiative capture reactions. We also review some of the important historical advances in the field of recoil separators as well as describe current techniques and performance milestones, including descriptions of some of the separators most recently working at radioactive ion beam facilities, such as DRAGON at TRIUMF and the DRS at the Holifield Radioactive Ion Beam Facility. We will also summarize some of the scientific highlight measurements at the RIB facilities.

The reaction mechanisms of the two-neutron transfer reaction ${}^{12}$C(${}^{6}$He,${}^{4}$He) have been studied at ${E}_{\mathrm{lab}}=30$ MeV at the TRIUMF ISAC-II facility using the Silicon Highly-segmented Array for Reactions and Coulex (SHARC) charged-particle detector array. Optical potential parameters have been extracted from the analysis of the elastic scattering angular distribution. The new potential has been applied to the study of the transfer angular distribution to the 2${}_{2}^{+}$ 8.32 MeV state in ${}^{14}$C, using a realistic three-body ${}^{6}$He model and advanced shell-model calculations for the carbon structure, allowing to calculate the relative contributions of the simultaneous and sequential two-neutron transfer. The reaction model provides a good description of the 30-MeV data set and shows that the simultaneous process is the dominant transfer mechanism. Sensitivity tests of optical potential parameters show that the final results can be considerably affected by the choice of optical potentials. A reanalysis of data measured previously at ${E}_{\mathrm{lab}}=18$ MeV, however, is not as well described by the same reaction model, suggesting that one needs to include higher-order effects in the reaction mechanism.

The DRAGON recoil separator is located at the ISAC facility at TRIUMF, Vancouver. It is designed to measure radiative alpha and proton capture reactions of astrophysical importance. Over the last years, the DRAGON collaboration has measured several reactions using both radioactive and high-intensity stable beams. For example, the 160(a, g) cross section was recently measured. The reaction plays a role in steady-state helium burning in massive stars, where it follows the 12C(a, g) reaction. At astrophysically relevant energies, the reaction proceeds exclusively via direct capture, resulting in a low rate. In this measurement, the unique capabilities of DRAGON enabled determination not only of the total reaction rates, but also of decay branching ratios. In addition, results from other recent measurements will be presented.

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.

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 ^{18}F at any astrophysical energy.

The $\ensuremath{\beta}$-feeding probabilities for three important contributors to the decay heat in nuclear reactors, namely ${}^{102,104,105}$Tc, have been measured using the total absorption spectroscopy technique. For the measurements, sources of very high isobaric purity have been obtained using a Penning trap (JYFLTRAP). A detailed description of the data analysis is given and the results are compared with high-resolution measurements and theoretical calculations.

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 ^{18}F at any astrophysical energy.

New radioactive ion beam (RIB) facilities, like FRIB in the US or FAIR in Europe, will push further away from stability and enable the next generation of nuclear physics experiments. Thus, the need for improved RIB targets is more crucial than ever: developments in exotic beams should coincide with developments in targets for use with those beams, in order for nuclear physics to remain on the cutting edge. Of great importance to the future of RIB physics are scattering, transfer and capture reaction measurements of rare, exotic, and unstable nuclei on light targets such as hydrogen and helium. These measurements require targets that are dense, highly localized, and pure, and conventional targets often suffer too many drawbacks to allow for such experimental designs. Targets must also accommodate the use of large area, highly-segmented silicon detector arrays, high-efficiency gamma arrays, and novel heavy ion detectors to efficiently measure the reaction products. To address this issue, the Jet Experiments in Nuclear Structure and Astrophysics (JENSA) Collaboration led by the Colorado School of Mines (CSM) is in the process of designing, building and testing a supersonic gas jet target for use at existing and future RIB facilities. The gas jet target provides a high density and high purity of target nuclei within a tightly confined region, without the use of windows or backing materials. The design also enables the use of multiple state-of-the-art detection systems.

In stars, ${}^{16}$O represents the endpoint of the helium burning sequence due to the low rate of ${}^{16}$O($\ensuremath{\alpha}$,$\ensuremath{\gamma}$)${}^{20}$Ne. We present a new direct measurement of the total cross section of ${}^{16}$O($\ensuremath{\alpha}$,$\ensuremath{\gamma}$)${}^{20}$Ne at ${E}_{\mathrm{c}.\mathrm{m}.}=1.69\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ employing the DRAGON recoil separator. In addition, the branching ratios and strength of the ${E}_{\mathrm{c}.\mathrm{m}.}=2.426\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ ${3}^{\ensuremath{-}}$ resonance were determined.

The ${}^{17}$O($p,\phantom{\rule{-0.16em}{0ex}}\ensuremath{\gamma}$)${}^{18}$F 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 ${}^{17}$O($p,\phantom{\rule{-0.16em}{0ex}}\ensuremath{\gamma}$)${}^{18}$F reaction at center-of-mass energies between 250 and 500 keV. These measurements were conducted in inverse kinematics at the DRAGON recoil separator.

4 pags., 2 figs. -- Nuclear Physics in Astrophysics V 3–8 April 2011, Eilat, Israel, We present our initial efforts with the DRAGON separator at TRIUMF facility towards obtaining the energy dependence of the astrophysical S-factor for 3He(¿, ¿)7Be reaction in the energy range of Ecm = 2 to 3 MeV that was recommended by the recent evaluations. A comparison between the existing data and our new complementary Madrid data, together with the recent theoretical calculations, is also given in the context of our ongoing work., This work has been supported by the UK STFC.

In a recent experiment performed at Triumf using the Dragon 0° spectrometer and its associated BGO array, the complete γ-decay of the radiative capture channel below the Coulomb barrier has been measured for the first time. This measurement has been performed at two energies Ec.m. = 6.6 and 7.2 MeV. A selective contribution of the entrance spins 2+ and 3− has been evidenced which is consistent with existing results above the barrier.

In stellar helium burning, ${}^{16}$O represents the endpoint of the helium-burning sequence due to the low rate of ${}^{16}$O($\ensuremath{\alpha}$,$\ensuremath{\gamma}$)${}^{20}$Ne. We present a new direct measurement of the total capture reaction rate of ${}^{16}$O($\ensuremath{\alpha}$,$\ensuremath{\gamma}$)${}^{20}$Ne at ${E}_{\mathrm{c}.\mathrm{m}.}=2.26\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ 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.

We have performed a heavy ion radiative capture reaction between two light heavy ions, $^{12}$C and $^{16}$O, leading to $^{28}$Si. The present experiment has been performed below Coulomb barrier energies in order to reduce the phase space and to try to shed light on structural effects. Obtained $\gamma$-spectra display a previously unobserved strong feeding of intermediate states around 11 MeV at these energies. This new decay branch is not fully reproduced by statistical nor semi-statistical decay scenarii and may imply structural effects. Radiative capture cross-sections are extracted from the data., Comment: 4 pages, 7 figures, to appear as proceedings of FUSION 2011 conference at St-Malo, France

The {sup 18}F(p,{alpha}){sup 15}O reaction rate is crucial for understanding the final abundance of {sup 18}F predicted by nova models. The {gamma}-ray emission in the first few hours after a nova outburst is expected to be dominated by 511 keV annihilation photons from the decay of {sup 18}F, and so understanding its production can provide important constraints on the conditions during the outburst when compared with observations. Results are presented from the lowest-energy direct measurement to date, performed at the Isotope Separator and Accelerator radioactive beam facility at the TRIUMF laboratory, Canada. Cross section measurements at center-of-mass energies of 250, 330, 453, and 673 keV are obtained and the results compared to previous data and R-matrix calculations. The implications for the overall reaction rate in the context of nova explosions have been discussed.