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Title: Absolute determination of the {sup 22}Na(p,{gamma}){sup 23}Mg reaction rate in novae

Journal Article · · Physical Review. C, Nuclear Physics
; ; ; ; ;  [1]; ; ; ; ; ;  [2];  [3]
  1. Department of Physics, University of Washington, Seattle, Washington 98195-1560 (United States)
  2. TRIUMF, Vancouver, BC V6T 2A3 (Canada)
  3. Departament Fisica i Enginyeria Nuclear (UPC) and Institut d'Estudis Espacials de Catalunya (IEEC), E-08034 Barcelona (Spain)

Gamma-ray telescopes in orbit around the earth are searching for evidence of the elusive radionuclide {sup 22}Na produced in novae. Previously published uncertainties in the dominant destructive reaction, {sup 22}Na(p,{gamma}){sup 23}Mg, 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 {sup 22}Na implanted targets. The targets, fabricated at TRIUMF-ISAC, displayed minimal degradation over a {approx}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{sub 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 {sup 22}Na(p,{gamma}) reaction rate, and our measurements indicate the resonance at 213 keV makes the most significant contribution to {sup 22}Na destruction in novae. Hydrodynamic simulations including our rate indicate that the expected abundance of {sup 22}Na 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.

OSTI ID:
21499505
Journal Information:
Physical Review. C, Nuclear Physics, Vol. 83, Issue 3; Other Information: DOI: 10.1103/PhysRevC.83.034611; (c) 2011 American Institute of Physics; ISSN 0556-2813
Country of Publication:
United States
Language:
English