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Large excesses of Ca44 in certain presolar graphite and silicon carbidegrains give strong evidence for Ti44 production in supernovae. Furthermore,recent detection of the Ti44 gamma-line from the Cas A SNR by CGRO/COMPTELshows that radioactive Ti44 is produced in supernovae. These make the Ti44abundance an observable diagnostic of supernovae. Through use of a nuclearreaction network, we have systematically varied reaction rates and groups ofreaction rates to experimentally identify those that govern Ti44 abundance incore-collapse supernova nucleosynthesis. We survey the nuclear-rate dependenceby repeated calculations of the identical adiabatic expansion, with peaktemperature and density chosen to be 5.5xE9 K and 1E7 g/cc, respectively, toapproximate the conditions in detailed supernova models. We find that, forequal total numbers of neutrons and protons (eta=0), Ti44 production is mostsensitive to the following reaction rates: Ti44(alpha,p)V47,alpha(2alpha,gamma)C12, Ti44(alpha,gamma)Cr48, V45(p,gamma)Cr46. We tabulatethe most sensitive reactions in order of their importance to the Ti44production near the standard values of currently accepted cross-sections, atboth reduced reaction rate (0.01X) and at increased reaction rate (100X)relative to their standard values. Although most reactions retain theirimportance for eta > 0, that of V45(p,gamma)Cr46 drops rapidly for eta >=0.0004. Other reactions assume greater significance at greater neutron excess:C12(alpha,gamma)O16, Ca40(alpha,gamma)Ti44, Al27(alpha,n)P30, Si30(alpha,n)S33.Because many of these rates are unknown experimentally, our results suggest themost important targets for future cross section measurements governing thevalue of this observable abundance.Comment: 37 pages, LaTex, 17 figures, 8 table

Nuclear Reactions Governing the Nucleosynthesis of44Ti

Nuclear Reactions Governing the Nucleosynthesis of⁴⁴Ti