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Direct measurement of astrophysically important resonances in ^(38)K(p,γ)^(39)Ca

Christian, G. and Lotay, G. and Ruiz, C. and Akers, C. and Burke, D. S. and Catford, W. N. and Chen, A. A. and Connolly, D. and Davids, B. and Fallis, J. and Hager, U. and Hutcheon, D. and Mahl, A. and Rojas, A. and Sun, X. (2018) Direct measurement of astrophysically important resonances in ^(38)K(p,γ)^(39)Ca. Physical Review C, 97 (2). Art. No. 025802. ISSN 2469-9985.

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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.

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Alternate Title:Direct measurement of astrophysically important resonances in 38K(p,γ)39Ca
Additional Information:© 2018 American Physical Society. Received 25 September 2017; revised manuscript received 1 December 2017; published 21 February 2018. The authors are grateful to the ISAC operations team and the technical staff at TRIUMF for their support during the experiment, in particular F. Ames for dedicated operation of the ECR charge state booster. We also thank R. Wilkinson for calculations of proton single-particle widths for the three resonances measured in this work. TRIUMF's core operations are supported via a contribution from the federal government through the National Research Council of 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. Authors from the Colorado School of Mines acknowledge support from the Department of Energy, Grant No. DE-FG02-93ER-40789. The UK authors acknowledge support by STFC. The authors acknowledge P. Denisenkov for assistance in running the nugrid code and for fruitful discussions. Support for nugrid is provided by the National Science Foundation through Grants No. PHY 02-16783/PHY 08-22648 and No. PHY-1430152, which fund the Joint Institute for Nuclear Astrophysics (JINA) and the JINA Center for the Evolution of the Elements, respectively. nugrid support is also provided by the European Union through Grant No. MIRG-CT-2006-046520. The nugrid Collaboration uses services of the Canadian Advanced Network for Astronomy Research (CANFAR) which in turn is supported by CANARIE, Compute Canada, University of Victoria, the National Research Council of Canada, and the Canadian Space Agency.
Funding AgencyGrant Number
National Research Council of CanadaUNSPECIFIED
Government of British ColumbiaUNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Department of Energy (DOE)DE-FG02-93ER-40789
Science and Technology Facilities Council (STFC)UNSPECIFIED
NSFPHY 02-16783
NSFPHY 08-22648
European UnionMIRG-CT-2006-046520
Canadian Network for the Advancement of Research, Industry and EducationUNSPECIFIED
University of VictoriaUNSPECIFIED
Canadian Space Agency (CSA)UNSPECIFIED
Record Number:CaltechAUTHORS:20180314-155855840
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85316
Deposited By: Tony Diaz
Deposited On:15 Mar 2018 03:27
Last Modified:15 Mar 2018 03:27

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