Title: Low energy scattering cross section ratios of ${}^{14}\mathrm{N}(p,p){}^{14}\mathrm{N}$

Abstract

Background: The slowest reaction in the first CNO cycle is ¹⁴N(p, γ) ¹⁵O, therefore its rate determines the overall energy production efficiency of the entire cycle. The cross section presents several strong resonance contributions, especially for the ground-state transition. Some of the properties of the corresponding levels in the ¹⁵O compound nucleus remain uncertain, which affects the uncertainty in extrapolating the capture cross section to the low energy range of astrophysical interest. Purpose: The ¹⁴N (p, γ) ¹⁵O cross section can be described by using the phenomenological R matrix. Over the energy range of interest, only the proton and γ-ray channels are open. Since resonance capture makes significant contributions to the ¹⁴N (p, γ) ¹⁵O cross section, resonant proton scattering data can be used to provide additional constraints on the R-matrix fit of the capture data. Methods: A 4 MV KN Van de Graaff accelerator was used to bombard protons onto a windowless gas target containing enriched ¹⁴N gas over the proton energy range from E_p =1.0 to 3.0 MeV. Scattered protons were detected at θ_lab = 90,120°,135 °,150°, and 160° using ruggedized silicon detectors. In addition, a 10 MV FN Tandem Van de Graaff accelerator was used to acceleratemore » protons onto a solid Adenine ( C 5 H 5 N 5 ) target, of natural isotopic abundance, evaporated onto a thin self-supporting carbon backing, over the energy range from E p = 1.8 to 4.0 MeV. Scattered protons were detected at 28 angles between θ lab = 30. 4° and 167. 7° by using silicon photodiode detectors. Results: Relative cross sections were extracted from both measurements. While the relative cross sections do not provide as much constraint as absolute measurements, they greatly reduce the dependence of the data on otherwise significant systematic uncertainties, which are more difficult to quantify. The data are fit simultaneously using an R-matrix analysis and level energies and proton widths are extracted. Even with relative measurements, the statistics and large angular coverage of the measurements result in more confident values for the energies and proton widths of several levels; in particular, the broad resonance at E_c.m. = 2.21 MeV, which corresponds to the 3/2⁺ level at E_x = 9.51 MeV in ¹⁵O. In particular, the s - and d -wave angular-momentum channels are separated. Conclusion: The relative cross sections provide a consistent set of data that can be used to better constrain a full multichannel R-matrix extrapolation of the capture data. It has been demonstrated how the scattering data reduce the uncertainty through a preliminary Monte Carlo uncertainty analysis, but several other issues remain that make large contributions to the uncertainty, which must be addressed by further capture and lifetime measurements.« less

Authors:

deBoer, R. J. ^[1]; Bardayan, D. W. ^[1]; Görres, J. ^[1]; LeBlanc, P. J. ^[1]; Manukyan, K. V. ^[1]; Moran, M. T. ^[1]; Smith, K. ^[1]; Tan, W. ^[1]; Uberseder, E. ^[1]; Wiescher, M. ^[1]; Bertone, P. F. ^[2]; Champagne, A. E. ^[2]; Islam, M. S. ^[3]

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+ Show Author Affiliations

1. Univ. of Notre Dame, IN (United States). Joint Inst. for Nuclear Astrophysics
2. Univ. of North Carolina, Chapel Hill, NC (United States); Triangle Universities Nuclear Lab., Durham, NC (United States)
3. Ball State Univ., Muncie, IN (United States)

Publication Date:

Mon Apr 20 00:00:00 EDT 2015

Research Org.:

University of North Carolina, Chapel Hill, NC (United States); Duke Univ., Durham, NC (United States). Triangle Universities Nuclear Laboratory

Sponsoring Org.:

USDOE Office of Science (SC), Nuclear Physics (NP)

OSTI Identifier:

1600481

Alternate Identifier(s):

OSTI ID: 1178478

Grant/Contract Number:  

FG02-97ER41041

Resource Type:

Accepted Manuscript

Journal Name:

Physical Review C, Nuclear Physics

Additional Journal Information:

Journal Volume: 91; Journal Issue: 4; Journal ID: ISSN 0556-2813

Publisher:

American Physical Society (APS)

Country of Publication:

United States

Language:

English

Subject:

73 NUCLEAR PHYSICS AND RADIATION PHYSICS; experimental nuclear astrophysics