[Triumf-seminars] TRIUMF Colloquium today at 14:00

[TRIUMF Seminars]

Date/Time: Thu 2014-09-18 at 14:00

Location:  Auditorium          

Speaker:   Rob Hoffman (Livermore)

Title:     Reaction rate sensitivity of 44Ti production in massive stars and implications of a thick target yield measurement of 40Ca(alpha,gamma)44Ti

Abstract: The dynamic synergy between observation, theory, and experiment developed over many years around the field of gamma-ray astronomy has as its ultimate goal observations of specific radionuclides informing our understanding of stellar explosions and the theoretical models that predict nucleosynthesis. Of the radioactive species observed so far, those in the iron group and their decay products (Ni-56,57 -> Co-56,57) are used in many ways to constrain our current models of the core collapse explosion mechanism. The radionuclide 44Ti, made in the same explosive environment but in much lower amounts compared to the very abundant nickel isotopes, is hoped to one day serve as an even more sensitive diagnostic and a valuable probe of the conditions extant in some of the deepest layers to be ejected.

We evaluate two dominant nuclear reaction rates and their uncertainties that affect 44Ti production in explosive nucleosynthesis. Experimentally we develop thick-target yields for the 40Ca(alpha,gamma)44Ti reaction at alpha energies of 4.13, 4.54, and 5.36 MeV using gamma-ray spectroscopy. At the highest beam energy, we also performed an activation measurement which agrees with the thick target result. From the measured yields a stellar reaction rate was developed that is smaller than current statistical-model calculations and recent experimental results. Special attention has been paid to assessing realistic uncertainties of stellar reaction rates produced from a combination of experimental and theoretical cross sections. With such methods, we also develop a re-evaluation of the 44Ti(alpha,p)47V reaction rate. Using these two rates we carry out a sensitivity survey of 44Ti synthesis in eight expansions representing peak temperature and density conditions drawn from a suite of recent supernova explosion models. Our results suggest that the current uncertainty in these two reaction rates could lead to as large an uncertainty in 44Ti synthesis as that produced by different treatments of stellar physics.

Stimulants available 15 minutes before the talk.

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