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Gamma-ray telescopes in orbit around the Earth are searching for evidence ofthe elusive radionuclide 22Na produced in novae. Previously publisheduncertainties in the dominant destructive reaction, 22Na(p,g)23Mg, indicatednew measurements in the proton energy range of 150 to 300 keV were needed toconstrain predictions. We have measured the resonance strengths, energies, andbranches directly and absolutely by using protons from the University ofWashington accelerator with a specially designed beamline, which included beamrastering and cold vacuum protection of the 22Na implanted targets. Thetargets, fabricated at TRIUMF-ISAC, displayed minimal degradation over a ~ 20 Cbombardment as a result of protective layers. We avoided the need to know thestopping power, and hence the target composition, by extracting resonancestrengths from excitation functions integrated over proton energy. Ourmeasurements revealed that resonance strengths for E_p = 213, 288, 454, and 610keV are stronger by factors of 2.4 to 3.2 than previously reported. Upperlimits have been placed on proposed resonances at 198-, 209-, and 232-keV. Wehave re-evaluated the 22Na(p,g) reaction rate, and our measurements indicatethe resonance at 213 keV makes the most significant contribution to 22Nadestruction in novae. Hydrodynamic simulations including our rate indicate thatthe expected abundance of 22Na ejecta from a classical nova is reduced byfactors between 1.5 and 2, depending on the mass of the white-dwarf starhosting the nova explosion.

Absolute Determination of the 22Na(p,g) Reaction Rate in Novae