Sodium 22

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 structure of the radionuclide ²²Mg has received much attention in recent years by both experimentalists and theorists because of its role in determining the properties of astrophysical reaction rates relating to the production of ²²Na in explosive stellar scenarios.
 

related papers-2005-ruiz_phys_rev.pdf

Author: See Paper Document

Journal: Phys. Rev. C 71 025802 (2005)