The ²⁶Al(p,γ)²⁷Si Reaction: Stellar Origins of Galactic ²⁶Al

Citation

Vogelaar, Robert Bruce (1989) The ²⁶Al(p,γ)²⁷Si Reaction: Stellar Origins of Galactic ²⁶Al. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/vbh6-nk69. https://resolver.caltech.edu/CaltechTHESIS:08262013-145328209

Abstract

To explain the ²⁶Mg isotopic anomaly seen in meteorites (²⁶Al daughter) as well as the observation of 1809-keV γ rays in the interstellar medium (live decay of ²⁶Al) one must know, among other things, the destruction rate of ²⁶Al. Properties of states in ²⁷Si just above the ²⁶Al + p mass were investigated to determine the destruction rate of ²⁶Al via the ²⁶Al(p,γ)²⁷Si reaction at astrophysical temperatures.

Twenty micrograms of ²⁶Al were used to produce two types of Al₂O₃ targets by evaporation of the oxide. One was onto a thick platinum backing suitable for (p,γ) work, and the other onto a thin carbon foil for the (³He,d) reaction.

The ²⁶Al(p,γ)²⁷Si 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 Eₚ = 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 ωγ less than 0.02 µeV.

By arranging four large NaI detector as a 47π calorimeter, the 196-keV proton resonance, and one at 247 keV, were observed directly, having ωγ = 55 ± 9 and 10 ± 5 µeV, 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.

Thesis Files