出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：Hydrodynamic simulations of classical novae on ONe white dwarfs predict substantial production of 22Na. Observation of 22Na decay should be correlated with the corresponding nova because the half life of 22Na is only 2.6 years. The 1275-keV gamma ray from the b decay of 22Na is, therefore, an excellent diagnostic for the nova phenomenon and a long-sought target of gamma-ray telescopes. Nova simulations determine the maximum 22Na-detection distance to be < 1 kpc for the INTEGRAL spectrometer SPI, consistent with its non-observation to date. However, model estimates are strongly dependent on the thermonuclear rate of the 22Na(p; g)23Mg reaction, which destroys 22Na in novae. The 22Na(p; g)23Mg rate is expected to be dominated by narrow, isolated resonances with Ep < 300 keV. The currently employed rate is based two sets of direct measurements, only one of which was absolute. Recently, a new level has been found in 23Mg, which would correspond to a resonance at Ep = 198 keV that might dominate the reaction rate at nova temperatures. We have measured the 22Na(p; g) resonance strengths directly and absolutely. Proton beams were produced at the University of Washington and delivered to a specially designed beam line that included rastering and cold vacuum protection of the 22Na-implanted targets (fabricated at TRIUMF-ISAC). Measurements were made on known 22Na+p resonances and on the proposed new resonance at Ep = 198 keV.We measured the strengths of the known resonances to be inconsistent with previous measurements. Due to the resulting change in the 22Na(p; g) reaction rate, we expect the amount of 22Na produced by novae to differ significantly from current estimates, revising the prospects for its observation. Analysis of our results is presented.
