Peer Reviewed

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.

ruiz_epja_2014.pdf

Author: C. Ruiz, U. Greife, U. Hager

Journal: European Physical Journal A

The available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production are summarized and critically evaluated. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for 8B solar neutrinos. Opportunities for further increasing the precision of key rates are also discussed, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Seattle, in January 2009, is intended as a 10-year update and supplement to 1998, Rev. Mod. Phys. 70, 1265.

adelberger11.pdf

Author: Adelberger, E. G.; García, A.; Robertson, R. G. Hamish; Snover, K. A.; Balantekin, A. B.; Heeger, K.; Ramsey-Musolf, M. J.; Bemmerer, D.; Junghans, A.; Bertulani, C. A.; Chen, J.-W.; Costantini, H.; Prati, P.; Couder, M.; Uberseder, E.; Wiescher, M.; Cyburt, R.; Davids, B.; Freedman, S. J.; Gai, M.; Gazit, D.; Gialanella, L.; Imbriani, G.; Greife, U.; Hass, M.; Haxton, W. C.; Itahashi, T.; Kubodera, K.; Langanke, K.; Leitner, D.; Leitner, M.; Vetter, P.; Winslow, L.; Marcucci, L. E.; Motobayashi, T.; Mukhamedzhanov, A.; Tribble, R. E.; Nollett, Kenneth M.; Nunes, F. M.; Park, T.-S.; Parker, P. D.; Schiavilla, R.; Simpson, E. C.; Spitaleri, C.; Strieder, F.; Trautvetter, H.-P.; Suemmerer, K.; Typel, S.

Journal: Review of Modern Physics, vol. 83, Issue 1, pp. 195-246

The radionuclide Na22 is a potential astronomical observable that is expected to be produced in classical novae in quantities that depend on the thermonuclear rate of the Na22(p,γ)Mg23 reaction. We have measured the strengths of low-energy Na22(p,γ)Mg23 resonances directly and absolutely using a radioactive Na22 target. We find the strengths of resonances at E_p=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 E_p=198, 209, and 232 keV. The Na22 abundances expected in the ejecta of classical novae are reduced by a factor of ≈2.

physrevlett.105.152501.pdf

Author: Sallaska, A. L.; Wrede, C.; García, A.; Storm, D. W.; Brown, T. A. D.; Ruiz, C.; Snover, K. A.; Ottewell, D. F.; Buchmann, L.; Vockenhuber, C.; Hutcheon, D. A.; Caggiano, J. A.

Journal: Physical Review Letters, vol. 105, Issue 15, id. 152501 (2010)

Gamma-ray telescopes in orbit around the earth are searching for evidence of the elusive radionuclide Na22 produced in novae. Previously published uncertainties in the dominant destructive reaction, Na22(p,γ)Mg23, 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 Na22 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 E_p=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 Na22(p,γ) reaction rate, and our measurements indicate the resonance at 213 keV makes the most significant contribution to Na22 destruction in novae. Hydrodynamic simulations including our rate indicate that the expected abundance of Na22 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.

physrevc.83.034611.pdf

Author: Sallaska, A. L.; Wrede, C.; García, A.; Storm, D. W.; Brown, T. A. D.; Ruiz, C.; Snover, K. A.; Ottewell, D. F.; Buchmann, L.; Vockenhuber, C.; Hutcheon, D. A.; Caggiano, J. A.; José, J.

Journal: Physical Review C, vol. 83, Issue 3, id. 034611 (2011)

The ¹⁸F(p,α)¹⁵O reaction rate is crucial for understanding the final abundance of ¹⁸F predicted by nova models. The γ-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 ¹⁸F, 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.

physrevc.83.042801_2.pdf

Author: C. E. Beer, A. M. Laird, A. St. J. Murphy, M. A. Bentley, L. Buchman, B. Davids, T. Davinson, C. A. Diget, S. P. Fox, B. R. Fulton, U. Hager, D. Howell, L. Martin, C. Ruiz, G. Ruprecht, P. Salter, C. Vockenhuber, and P. Walden

Journal: Phys. Rev. C 83, 042801(R) (2011) [4 pages]

The lowest-energy resonance in the ²³Mg(p,γ)²⁴Al reaction, which is dominant at classical nova temperatures, has been measured directly for the first time using the DRAGON recoil spectrometer. The experiment used a radioactive ²³Mg beam (mixed within a significantly stronger ²³Na beam) of peak intensity 5×10⁷ s^-1, at the ISAC facility at TRIUMF. We extract values of E_R=485.7_-1.8^+1.3keV and ωγ=38_-15⁺²¹ meV from our data (all values in the center-of-mass frame unless otherwise stated). In addition, the experiment prompted a recalculation of the Q value for this reaction based on a revision of the ²⁴Al mass. The effect on the uncertainties in the quantities of ejected ²²Na and ²⁶Al from oxygen-neon classical novae is discussed.

erikson_23mgpg_2010.pdf

Author: Erikson, L. et al.

Journal: Physical Review C

The short-lived nuclide 44 Ti is an important nuclide for the understanding of explosive nucle-osynthesis. The main production reaction, 40 Ca(α, γ)44 Ti, has been studied in inverse kinematics with the recoil mass spectrometer DRAGON located at the TRIUMF-ISAC facility in Vancouver, Canada. The temperature range relevant for α-rich freeze-out during a core-collapse supernova has been covered entirely with a 40 Ca beam of 0.60 to 1.15 MeV/nucleon. All relevant quantities for the calculation of the astrophysical reaction rate have been measured directly. Due to many previously undiscovered resonances, the reaction rate derived from the energy dependent 44 Ti yield is higher than the one based on previous prompt γ-ray studies commonly used in supernova models. The presented new rate results in an increased 44 Ti production in supernovae.

VockenhuberPRC2007_40Ca_ag_44Ti_preprint.pdf

Author: See Paper Document

Journal: Phys. Rev. C 76 035801 (2007).