The production of (26)Al in the early solar system by the (16)O((16)O,x)(26)Al(gs) and (14)N((16)O,x)(26)Al(gs) reactions

The astrophysically short half life (0.74 Myr) of {dollar}sp{lcub}26{rcub}{dollar}Al isotope makes it one of the more important extinct nuclides whose abundances in the early solar system can be used as a probe of the environment in which the solar system formed. The abundance of {dollar}sp{lcub}26{rcub}{dollar}Al in the present galaxy deduced from the gamma ray observations ( (Mah84) and (Die95)) is about an order of magnitude lower than its meteoritic abundances measured in the form of an enhancement in the abundance of {dollar}sp{lcub}26{rcub}{dollar}Mg (daughter of {dollar}sp{lcub}26{rcub}{dollar}Al) over the solar system level (Was85). The existence of {dollar}sp{lcub}26{rcub}{dollar}Al in the meteorites is an indication that some sort of nucleosynthesis event occurred less than a few million years before the collapse of the proto-solar cloud, perhaps during that collapse. The most widely accepted explanation is that a nearby stellar explosion (such as a supernova) injected large amounts of {dollar}sp{lcub}26{rcub}{dollar}Al and some other extinct nuclides into the proto-solar cloud, possibly triggering the collapse of the cloud in the process (e.g., (Cam77), (Cam92) and (Cam95)). Motivated by the COMPTEL observation (Blo94) of unexpectedly high fluxes of gamma rays in the energy range of 3-7 MeV from the direction of the Orion complex, Clayton and Jin ( (Cla94), (Cla95a) and (Cla95b)) proposed several cosmic-ray scenarios for the production of {dollar}sp{lcub}26{rcub}{dollar}Al in the early solar system. One of their scenarios is that the meteoritic {dollar}sp{lcub}26{rcub}{dollar}Al was produced by the irradiation of the proto-solar material by oxygen-rich cosmic rays (with energies up to 10 MeV/nucleon) through the {dollar}rmsp{lcub}12{rcub}C(sp{lcub}16{rcub}O,x)sp{lcub}26{rcub}Alsb{lcub}gs{rcub}{dollar} reaction. In order to test this proposal Bateman et al. (Bat96b) measured the yield of the {dollar}rmsp{lcub}12{rcub}C(sp{lcub}16{rcub}O,x)sp{lcub}26{rcub}Al{dollar} reaction and determined that the yield of this reaction alone is not large enough to produce the meteoritic abundances of {dollar}sp{lcub}26{rcub}{dollar}Al. Even though Clayton and Jin (Cla95a) assumed the contribution to the yield from the {dollar}rmsp{lcub}16{rcub}O(sp{lcub}16{rcub}O,x)sp{lcub}26{rcub}Alsb{lcub}gs{rcub}{dollar} would not be significant, the yield of this reaction was measured in the experimental work of this thesis. Due to higher solar system abundance of oxygen compared to carbon, this reaction turned out to have the highest contribution to the yield. For completeness, the yield of the {dollar}rmsp{lcub}14{rcub}N(sp{lcub}16{rcub}O,x)sp{lcub}26{rcub}Alsb{lcub}gs{rcub}{dollar} reaction was also measured, because this reaction is another possibility for the production of the meteoritic {dollar}sp{lcub}26{rcub}{dollar}Al by the incident oxygen-rich cosmic rays. Due to lower solar system abundances of nitrogen compared to carbon as well as a smaller cross section, the yield of this reaction found to be negligible as expected. For the experimental work, thick BeO samples were irradiated with beams of {dollar}sp{lcub}16{rcub}{dollar}O and {dollar}sp{lcub}14{rcub}{dollar}N ions, and the resulting activities were counted off-line using a Compton suppressed HPGe detector. The number of produced {dollar}rmsp{lcub}26{rcub}Alsb{lcub}gs{rcub}{dollar} atoms was determined by counting the 1809 keV gamma rays resulting from the decay of {dollar}rmsp{lcub}26{rcub}Alsb{lcub}gs{rcub}.{dollar} If {dollar}sp{lcub}26{rcub}{dollar}Al was uniformly distributed throughout the proto-solar cloud, then the abundance ratio of {dollar}rmsp{lcub}26{rcub}Al/sp{lcub}16{rcub}O=1.8times10sp{lcub}-7{rcub}{dollar} could be calculated for the entire cloud. This abundance ratio could be produced by oxygen-rich cosmic rays only if more than 30% of the solar system oxygen was injected into the proto-solar cloud as cosmic rays that had...