Physics Colloquium Feb 1, 2019: Dr. Alis Rodriguez Manso

Friday, Feb 1, 2019 at 2 pm in Physics 148.  Refreshments to be served in 148 at 1:45 pm
Speaker: Dr. Alis Rodriguez Manso, Texas A&M University
Title: Neutron-proton equilibration in heavy-ion dynamically deformed nuclear systems, and, Particle Induce γ-ray and X-ray Emission experiments for contamination and elemental composition studies.
Heavy ion (HI) collisions exhibit a complex and beautiful variety of behavior which arrises from the dynamic interplay of competing forces. The nuclear equation of state (EoS) governs this behavior. The low-density neck which is very pronounced in HI collisions below the balance energy play many roles. The neck acts as a sink for neutrons, but also acts as a bridge to allow neutron-proton equilibration and mass exchange between the reaction partners. The material in the neck can be released as free nucleons, or can aggregate into clusters. The neck will rupture at least once as the reaction partners re-separate, but can rupture in multiple places with measurable delay between the ruptures. 
At Texas A&M University we have recently characterized neutron-proton (NZ) equilibration in HI reactions. We examine the measured composition of the remnant of the projectile and the largest (and second largest) remnant of the neck. These compositions both show a clear dependence with rotation angle. The rotation angle is interpreted as a measure of the duration of contact; not only is a timescale extracted for NZ equilibration but it is seen that the composition changes exponentially in time, consistent with a process following first-order kinetics. The results are robust with respect to the impacts of secondary decay, the background of statistical decay, and choice of alignment angle definition. The equilibration is seen for a broad range of final states, and for beam and target combinations with varying initial neutron richness.
On the second part of the seminar I will focus on a more applied matter. Contamination of soils and waters by Per- and polyfluoroalkyl substances (PFAS) from Aqueous Film Forming Foam (AFFF) formulations used by the U.S. Department of Defense (DoD) to extinguish fuel-based fires (due to either training or fire suppression), is an ongoing problem that may have on the order of thousands of sites contaminated with PFAS. The AFFF formulations used by the DoD contained significant quantities of Perfluorooctane Sulfonate (PFOS), Perfluorooctanoic Acid (PFOA) and other PFAS. The U.S. Environmental Protection Agency’s (EPA’s) drinking water Health Advisory Levels for PFOS and PFOA have consequently prompted critical research on AFFF sites, since the contamination sources can be derived from DoD and non-DoD sources. All PFAS contain elements of different numbers of carbon (C) and fluoride (F) based on their chemical formula, but some PFAS contain varies numbers of sulfur (S), nitrogen (N), or phosphorus (P).  For example, recent discovery of 40 classes of PFAS in historical AFFFs and AFFF-impacted groundwater do not contain phosphorus; while, the phosphorus-containing PFAS are used in food-contact papers or other commercial products. Accordingly, it is possible to use techniques that are capable of fingerprinting the abundance of the element composition in PFAS as a means to allocate and track the source. Accelerator-based Ion Beam Analysis (IBA) as PIXE (Particle Induced X-ray Emission) and PIGE (Particle Induced Gamma-ray Emission) are traditional techniques commonly used for elemental analysis in biological and environmental samples, however, these techniques have not been adapted for PFAS forensic and allocation purposes. 
Both PIXE and PIGE experiments have been assembled and actively used in the past two years at the K150 Cyclotron Institute (CI) at Texas A&M University (TAMU) with the intention of collaborating with other departments and universities in the study of contaminants’ pathways to the environment and characterization of materials and, in addition, contribute didactically to undergraduates/graduates involved in the project. 
I will discuss our recent projects and the impact they have on the research program and on undergraduate/graduate education.

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