The 26Al(p,γ)27Si reaction: Stellar origins of galactic 26Al
Abstract
To explain the 26 Mg isotopic anomaly seen in meteorites ( 26Al daughter) as well as the observation of 1809-keV gamma rays in the interstellar medium (live decay of ^ {26}Al) one must know, among other things, the destruction rate of 26 Al. Properties of states in ^{27 }Si just above the ^{26 }Al + p mass were investigated to determine the destruction rate of 26 Al via the 26Al(p, gamma)27 Si reaction at astrophysical temperatures. Twenty micrograms of ^{26 }Al were used to produce two types of Al _2O_3 targets by evaporation of the oxide. One was onto a thick platinum backing suitable for (p,gamma) work, and the other onto a thin carbon foil for the (^3He,d) reaction. The 26Al(p, gamma)27 Si excitation function, obtained using a germanium detector and voltage-ramped target, confirmed known resonances and revealed new ones at 770, 847, 876, 917, and 928 keV. Possible resonances below the lowest observed one at E_ p = 286 keV were investigated using the 26Al(^3He,d) 27Si proton-transfer reaction. States in 27Si corresponding to 196- and 286-keV proton resonances were observed. A possible resonance at 130 keV (postulated in prior work) was shown to have a strength of omega gamma < 0.02 mueV. By arranging four large NaI detector as a 4 pi calorimeter, the 196-keV proton resonance, and one at 247 keV, were observed directly, having omega gamma = 55 +/- 9 and 10 +/- 5 mueV. respectively. Large uncertainties in the reaction rate have been reduced. At novae temperatures, the rate is about 100 times faster than that used in recent model calculations, casting some doubt on novae production of galactic 26Al.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1989
- Bibcode:
- 1989PhDT.........3V
- Keywords:
-
- Physics: Astronomy and Astrophysics, Physics: Nuclear;
- Aluminum Isotopes;
- Anomalies;
- Astrophysics;
- Evaporation;
- Excitation;
- Interstellar Matter;
- Magnesium Isotopes;
- Novae;
- Proton Resonance;
- Reaction Kinetics;
- Stars;
- Aluminum Oxides;
- Calorimeters;
- Helium Isotopes;
- Meteorites;
- Oxides;
- Platinum;
- Silicon Isotopes;
- Astrophysics