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

[postmaster at admin.triumf.ca]

Date/Time: Mon 2006-11-20 at 14:00

Location:  Auditorium          

Speaker:   Christof Vockenhuber (TRIUMF)

Title:     Ti-44 and Hf-182 – Two Nuclides in the World of Astrophysics

Abstract: One of the main fundamental questions in science is the origin of the elements. Nuclear astrophysics can provide some answers by a close interplay between astronomical observations, modeling of stars in their different stages and input from nuclear physics. Radioactive nuclides play an important role in that game: The reaction path in most of the processes follows short-lived nuclides. If the lifetime is long enough they are likely to survive the nucleosynthesis events and can be later traced to understand their origin. Two of them are Ti-44 and Hf-182 with half-lives of 58.9 years and 8.9 million years, respectively.

Ti-44 has been identified by space-based satellites in Cassiopeia A, the youngest known supernova remnant, and gives direct observational proof that nucleosynthesis is still ongoing. It also provides one of the best tools to understand the complexity of supernova explosions. At DRAGON we measured the main production via the alpha capture reaction on Ca-40. However, there are still large uncertainties coming from other key reactions with short-lived nuclides where no experimental data exist so far.

In contrast, Hf-182 is produced by neutron capture processes, as most of the heavy elements beyond iron. A high abundance of Hf-182 in the early solar system was found by tungsten isotopic anomalies in meteorites. This challenges stellar models, since Hf-182 can be produced by both, the s and the r process. In collaboration with the Forschungszentrum Karlsruhe we measured the destruction reaction of Hf-182 in the s process, which lead to a significant reduction in the uncertainty of contributions from AGB stars. This is particularly important since the dominant contribution by the less understood r process is inferred by subtracting the s process contribution from the solar system abundance.

In this talk I want to show with these two examples what we can learn in astrophysics by studying certain nuclides and will also present some future prospects for measurements of astrophysical relevance at ISAC.

The speaker is a candidate for a research scientist position in experimental nuclear astrophysics. Stimulants available 15 minutes before the talk.

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