This Week at Physics

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This Week at Physics

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Events on Thursday, May 3rd, 2018

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Fission and the formation of the r-process rare-earth abundance peak in neutron star mergers
Time: 2:30 pm
Place: 5280 Chamberlin Hall
Speaker: Nicole Vassh, University of Notre Dame
Abstract: The recent observations of the GW170817 electromagnetic counterpart
suggest lanthanides were produced in this neutron star merger event.
However many questions regarding heavy element production in mergers
remain: can such events account for all the r-process lanthanide material
observed in the galaxy? are precious metals such as gold produced in
sufficient amounts? are actinides produced? where within the merger
environment does nucleosynthesis occur and under what specific conditions?
Such questions can only be answered with careful studies of the nuclear
physics uncertainties affecting r-process calculations. Here I will
discuss recent extended calculations of beta-delayed fission and their
implications for r-process nucleosynthesis. The influence of fission
fragment distributions will also be addressed with a particular emphasis
on the unknown origin of the r-process rare-earth peak at A~164. Since the
rare-earth peak is formed as the r-process path begins to draw closer to
stability, the rare-earth nuclei contributing to peak formation will soon
be within reach of nuclear physics experiments performed at, for example,
the CPT at CARIBU and the upcoming FRIB. Here I will present the latest
results for the masses found to produce the rare-earth peak in a low
entropy accretion disk wind scenario and compare directly with recent mass
measurements from the CPT at CARIBU. Such collaborative efforts between
theory and experiment could soon be in a position to make definitive
statements regarding the mechanism of rare-earth peak formation and thus
the astrophysical site of the r process.
Host: Baha Balantekin
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Astronomy Colloquium
Can we send relativistic-speed nanocrafts to nearby exoplanets? Challenges and Solutions?
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and Cookies 3:30 PM, Talk begins at 3:45 PM
Speaker: Thiem Hoang, University of Toronto
Abstract: The Breakthrough Starshot initiative aims to launch gram-scale spacecraft to relativistic speeds of v ~ 0.2 c, capable of reaching the closest Earth-like exoplanet, Proxima b, in 20 years. One of the most critical challenges facing this ambitious project originates from the interactions of relativistic nanocrafts with the interstellar medium during its journey to Proxima b. In this talk, I will first present our quantitative evaluation of the damage to a relativistic nanocraft by interstellar gas and dust. Second, I will discuss the deflection and oscillation of a charged nanocraft due to the interstellar magnetic field. Third, I will discuss the gas drag force at high energy regime and quantify its effect on the deceleration of a relativistic lightsail. Finally, I will discuss practical strategies to mitigate the impacts of the interstellar medium, and to control the nanocraft attitude in order for the spacecraft to reach an intended exoplanet.
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