Upcoming Seminars & Lectures

Date	Time		Speaker	Location	Title
Today, 2024-04-18	14:00	Colloquium	Mike Wieser U Calgary	Auditorium / Hybrid	Tales told by the Atomic Weights: Unraveling the stories of the chemical elements
Abstract:		We are most familiar with the atomic weight of a chemical element as the average atomic mass of the occurrence of this element. At first glance, this number may seem rather mundane, but the digits encode much deeper meaning. As early as 1919, T. W. Richards (a Nobel prize winner in chemistry) recognized that atomic weights "tell in a language of their own the story of the birth or evolution of all matter". We now know that atomic weights are not constants of Nature. Indeed, the variability in atomic weight for an element is the result of subtle, but significant, variations in the relative numbers of isotopes of that element. Changes in the distribution of the isotopes depends on the history of the atoms and these variations provide unique insights into physical, chemical, and biological processes involving the element. In this talk, I will describe how decoding the differences in the relative numbers of isotopes can provide unique insights into the mechanisms responsible for changing isotopic composition. We will explore some recent applications of isotope abundance data to detect the dysregulation of trace metals in living systems as the result of disease, to detect the accumulation of radioactive decay products in human tissues, and to place constraints on the probability of double beta decay to eventually understand neutrino properties. At the heart of the determination of isotopic composition is the mass spectrometer and significant developments over the past two decades are creating research opportunities in new areas. I will present our work at the University of Calgary over the past two decades and recent work at TRIUMF to enable high sensitivity and high-resolution isotope abundance measurements on TITAN. **************************** https://uvic.zoom.us/j/81903315109?pwd=T0RTOEJCUVppMnFWQzRkNzV1UUs3UT09 Meeting ID: 819 0331 5109 Password: 183359 ****************************

Wed , 2024-05-01	13:00	Theory	Tim Tait UC Irvine	Remote	Hints for New Physics from the Primordial He-4 Abundance?
Abstract:		Some of the earliest information about the evolution of the cosmos comes from big bang nucleosynthesis, which predicts the primordial abundances of light nuclei. Recently, measurements of He-4 from 10 new extremely metal-poor galaxies discovered by the Subaru telescope puts tension on the fit to the cosmological parameters, and may be the first hints of physics beyond the Standard Model operating during BBN. I'll discuss this new result, and show that postulating a primordial asymmetry of the neutrinos can resolve it. I will also discuss our new python-based tool, PRyMordial, which is publicly-available and allows one to easily and flexibly study the physics of BBN. --- Remote Connection: https://ubc.zoom.us/j/68146558315?pwd=UnE3U051OWk2cHZXUXBtNGRNRUpxQT09 Meeting ID: 681 4655 8315 Passcode: 398279

Thu , 2024-05-02	14:00	Colloquium	Pavel Denissenkov University of Victoria	Auditorium/ Hybrid	Numerical simulations of i-process nucleosynthesis in stars constrained by nuclear physics experiments and astrophysical observations
Abstract:		Most of the trans-iron elements in the Solar System were produced in the slow (s-) and rapid (r-) neutron-capture processes in stars and their explosions, which are both relatively well studied. On the other hand, abundances of heavy elements and their isotopes measured in some of the so-called carbon-enhanced metal-poor (CEMP) stars and presolar dust grains can be better explained as a result of i-process nucleosynthesis that occurred at neutron densities intermediate between those characteristic for the s- and r-processes. The most likely site of the i process is a helium convective zone that entrains hydrogen from an adjacent H-rich envelope. This may happen in rapidly-accreting white dwarfs (RAWDs) in close binary systems, like those considered to lead to Supernova Ia explosions in the single-degenerate channel, or in asymptotic giant branch (AGB) stars at low metallicities. I will present and compare results of numerical simulations of i-process nucleosynthesis in a simple one-zone model for a range of constant neutron densities as well as in more realistic multi-zone models of RAWDs and AGB stars. The abundances of heavy elements and their isotopes obtained in those models will be compared with elemental and isotopic abundance ratios measured in CEMP stars and presolar dust grains. On the chart of nuclides the i process path extends from 3 to 8 isotopes beyond the valley of stability, for most of which only theoretical neutron-capture reaction rates computed using the Hauser-Feshbach method are available. Uncertainties of these rates are likely to be responsible for some discrepancies between the predicted and observed abundances. Which of these uncertainties may have the strongest impact on the predicted abundances of selected elements and isotopes can be revealed in Monte Carlo (MC) simulations, in which all rates are varied within their limits estimated from Hauser-Feshbach computations, followed by a statistical analysis of their results. I will present and compare results of such MC simulations and their analysis obtained for the one- and multi-zone models of i-process nucleosynthesis, in particular an updated list of reactions whose rates need to be constrained experimentally and their uncertainties reduced for the predicted abundances to better agree with the observed ones. Finally, I will advertise the CaNPAN i-process computational tools that can be used to conduct reaction rate uncertainty studies for one-zone nucleosynthesis models.

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