“ … Image Source: NASA/JPL/Michael Carroll. Elise Liebow1, Heather C. Watson 1, George Shaw2 1 Department of Physics and … ”
Abstract
Europa has an icy crust with the possibility of a liquid ocean beneath the solid layer, which holds promise as a potentially habitable environment. A growing interest around Europa is evidenced by upcoming missions, including NASA's Europa Clipper and ESA's JUpiter's ICy moon Explorer (JUICE). One objective of these missions is to understand more about the crust/ocean and its ability to sustain life. Previous missions have shown that the predominant salts on Europa may be NaCl and MgSO4, however the effect of pressure and salinity on the melting / freezing points of ice under relevant conditions is less well constrained. Having insight about the phase relationships of the salt solutions could provide important constraints in interpreting mission-based data. We have experimentally determined the freezing point of NaCl solutions at pressures up to 700 bars with concentrations ranging up to 20% salt in distilled water. Our results align closely to other published results from past experiments for the known data, and we have new data for previously unexplored conditions. Overall, an addition of 20% NaCl can depress the freezing point of water by close to 20„ƒ at pressures that would represent a 70km thick crust on Europa. These results can be used to place constraints on current models of crustal thickness on icy moons like Europa
Pulsar dispersion measure (DM) quantifies the integrated electron column density along the line of sight. Electron density fluctuations produce DM variations that induce errors in high precision pulsar timing used by the Nanohertz Observatory for Gravitational Waves (NANOGrav). We analyze DM variations of two pulsars observed by NANOGrav, PSRs J1614-2230 and J1643-1224, to determine if the HII regions along their LOS enhance their DM variations. Both pulsars exhibit linear changes in DM that are due to the transverse motions of the LOS through density gradients in the interstellar medium (ISM). We calculate the motion of the pulsars' LOS through the HII regions and determine that the observed DM variations could trace density fluctuations on scales of astronomical units (AU) or less within the HII regions. J1614-2230 exhibits DM variations dominated by the solar wind, but both pulsars show additional periodic DM variations that are out of phase with the expected solar wind-induced fluctuations. These periodic DM variations are too large to be explained by the LOS motion through the HII regions, but could be induced by another local plasma structure that obstructs the LOS to both pulsars. Funded by the Summer 2020 Astronomy REU program at Cornell University under NSF award NST/AST-1950324. The NANOGrav Physics Frontiers Center is supported by NSF award number 1430284.
The purpose of this experiment was to craft an electron-positron annihilation spectrometer in order to conduct electron-positron annihilation lifetime spectroscopy (EPALS) in the Union College Ion Beam Analysis Laboratory. EPALS as a method of spectroscopy is tool used for analysis of atomic scale defects in crystalline materials. We constructed an apparatus to employ this as a method of crystalline defect analysis. Using EPALS, we obtained spectra for samples of pure iron and MgO crystals. We analyzed these spectra to make measurements of various positron lifetimes and thus various defect types within our samples. In this presentation, the preliminary results will be discussed.
“ … Ice Shell INTRODUCTION Samantha L. Rosenfeld, Prof. Heather Watson In the search for life beyond Earth, we look … ”
Abstract
Planetary science is the study of different physical, atmospheric, and geological properties of planetary bodies in our Solar System. We are specifically interested in studying Jupiter's moon Europa, because of its large quantity of ice and water. This surplus of H2O is an essential piece in the search for life beyond Earth, which means in order to understand how life could exist outside of Earth, we must first enhance our intuition about the conditions on this icy moon. In this project, we use computational analysis methods and a program called SeaFreeze to model and calculate the thermodynamic properties of water and ice to learn more about how different pressure and temperature conditions influence their molecular behavior and phase changes. Through this analysis, we find relationships for the thermodynamic properties across phase boundaries and for each type of ice. We apply this analysis to create a model for the interior of the ice layer on Europa, plotting properties such as density, p-wave velocity, and s-wave velocity as functions of depth. We find a semi-linear relationship for these properties, and require future analyses to study the effects of salt in order to gain a full picture of the interior of Europa.
“ … E. Villeneuve, Scott M. LaBrake, Michael F. Vineyard, and Heather C. Watson Introduction Electron-positron annihilation … ”
Abstract
Electron-Positron Annihilation Lifetime Spectroscopy (EPALS) is an analytical method for characterizing physical atomic scale defects in materials. The goal of this project is to expand on the use of this spectroscopy method in order to characterize defects in crystalline materials and develop a standard method and procedure for such a task. In order to accomplish this, I procured the necessary electronics and radioactive material source. This spring, I plan to spend time setting up and performing preliminary experiments in order to ensure the effectiveness of this analytical method. This method will ideally be able to provide insight into the characteristics of crystalline defects as it pertains to radioactive diffusion, which can aid in radioactive waste containment and put constraints on radiometric dating systems.
“ … Modeling and Saltwater Experiments Samantha L. Rosenfeld1, Heather C. Watson 1 1Union College, Schenectady, NY Freezing … ”
Abstract
We explore the properties of the hydrosphere on Europa involving both a modeling technique and experimental methods. We perform a computational analysis of the thermodynamic properties for an ideal, pure-water Europan ice shell using a Python programming framework called SeaFreeze. We create four models assuming surface temperatures of either 50 K or 140 K and ice shell thicknesses of either 3 km or 30 km. We observe mostly linear trends for the density and seismic wave velocities with respect to depth, and find that surface temperatures have the greatest effect on the models. Simultaneously, we experimentally investigate the phase diagram of different saltwater concentrations in an attempt to further constrain the ice shell properties. We determine the freezing-melting points of 5%, 10%, and 20% by-weight NaCl-water solutions under constant pressures from 0 MPa to 70 MPa. We find that increasing the salt concentration, the pressure, or both decreases the freezing point temperature with a freezing point temperature depression of about -20 ¬?C from that of pure water at zero pressure. Based on our experimental results, we expect that adding NaCl to the pure-water computational models would cause them to have lower temperatures at the ice-water boundary, assuming saltwater has similar density and seismic wave velocity trends as pure-water. Areas of future development include continuing to explore the phase diagrams of different saltwater concentrations, including MgSO4, KCl, and varying combinations of all three salts, extending the pure-water SeaFreeze models to analyze Europa's subsurface ocean layer, implementing various new techniques to make our experiments more precise, and finally applying our results to the other icy moons, such as Ganymede or Callisto.
“ … Denmark (2018). J. Feinstein and H. Watson, “Introducing positron annihilation spectroscopy to … ”
Abstract
This experiment crafted an electron-positron annihilation spectrometer in order to conduct electron-positron annihilation lifetime spectroscopy (EPALS) in the Union College Ion Beam Analysis Laboratory. EPALS, as a method of spectroscopy, is tool used for material analysis. We constructed an apparatus to employ this as a method of crystalline defect analysis. Using EPALS, we obtained spectra for samples of pure iron and MgO crystals. We analyzed these spectra to make measurements of various positron lifetimes and thus various defect types within our samples. In this thesis, the preliminary results will be discussed.
“ … Temperature of Iron Meteorites John Schlater Professor Heather Watson Submitted in Partial Fulfillment of the … ”
Abstract
Accurate constraints of the diffusion closure temperature in radioisotope thermal-chronometers of early Solar System allow for greater accuracy in the dating of rocky bodies. These closure temperatures can be estimated based on the composition and geometry of the body, along with information about the diffusion coefficient and activation energy of the specific radioisotopes inside the body. Thin film diffusion experiments were performed on nine samples of pure iron pellets coated with 100nm of lead. These samples were subjected to heating at either 600°C for up to ten days, or 750°C for up to twenty-three hours, allowing for sufficient diffusion of the coating into the medium. The diffused samples were analysed at the University of Albany Ion Beam Laboratory using Rutherford Backscattering spectrometry (RBS). RBS spectra were processed using SIMNRA, an ion beam analysis program for Windows, to generate concentration profiles of the diffused lead. These profiles were fit to the thin-film solution to Fick's Second Law linear diffusion equation, returning diffusion coefficients for Pb in Fe 600°C and 750°C. Our results give an activation energy of 364±53 kJ/mol, within reason of expected values for diffusion in metals. This information can be used in tandem with other work in this ongoing project.
“ … design and fab- rication of a number of instruments, Prof. Heather Watson … ”
Abstract
We collected samples of soil from along the East River in Queens, New York, near the Hell Gate Bridge, on the Astoria Park side of the bridge in 2019 and on the Randall's Island Park side in 2021. We performed proton-induced X-ray emission (PIXE) analysis on the samples and found that soil closer to the Hell Gate Bridge contained higher concentrations of heavy metals, specifically lead and zinc. Many of the soil samples contained lead concentrations greater than the EPA standard of 400 ppm. We also performed PIXE analysis on a sample of the paint used on the bridge and found similar enhancements of lead and zinc. Our results indicate that the paint used on the Hell Gate Bridge is the cause of enhancements of heavy metals in the surrounding soil.
“ … of Physics and Astronomy, June 2022. ADVISOR: Dr. Heather C. Watson We explore the properties of the … methods. We perform a computational … , thank you to HeatherWatson, for her support and guidance throughout the entire … ”
Abstract
We explore the properties of the hydrosphere on Europa involving both a modeling technique and experimental methods. We perform a computational analysis of the thermodynamic properties for an ideal, pure-water Europan ice shell using a Python programming framework called SeaFreeze. We create four models assuming surface temperatures of either 50 K or 140 K and ice shell thicknesses of either 3 km or 30 km. We observe mostly linear trends for the density and seismic wave velocities with respect to depth and find that surface temperature has the greatest effect on the models. Simultaneously, we experimentally investigate the phase diagram of different saltwater concentrations in an attempt to further constrain the ice shell properties. We determine the freezing temperatures of 5%, 10%, and 20% by-weight NaCl-water solutions under constant pressures from 0 MPa to 70 MPa. We find increasing the salt concentration, the pressure, or both decreases the freezing point temperature with a depression at our most extreme conditions of about -20 °C from that of pure water at zero pressure. Based on our experimental results, we expect that adding NaCl to the pure-water models would lower their ice-water boundary temperatures. Areas of future development include continuing to explore the phase diagrams of different saltwater concentrations, including MgSO<sub>4</sub>, KCl, and varying combinations of all three salts, extending the pure-water SeaFreeze models to analyze Europa's subsurface ocean layer, implementing various new techniques to make our experiments more precise, and finally applying our results to the other icy moons, such as Ganymede or Callisto.
“ … of Physics and Astronomy, June 2022. ADVISOR: Dr. Heather C. Watson Radiation is a form of energy that can … ”
Abstract
Radiation is a form of energy that can damage materials at an atomic level. This has implications for the mobility of radioactive waste through containment materials. We are characterizing atomic defects in materials by using Electron-Positron Annihilation Lifetime Spectroscopy (EPALS). When an electron and positron come into contact with each other, they annihilate and release two antiparallel 511-keV gamma rays. In a pristine crystalline sample, positrons can easily annihilate with electrons, but in a sample with vacancies/defects in the crystal structure, positrons take longer to annihilate. Therefore, the more vacancies in a sample, the longer the average lifetime of a positron in the sample. We measure the lifetime by detecting the time between the emission of a 1274-keV gamma ray when the positron is created and the emission of the 511-keV gamma ray. We have experimentally measured pure, single-crystal MgO samples and found that our results are within the range of past published results (120 ps - 280 ps) with average lifetimes at 258±34.8 ns and 266±12.1 ns. We have also made measurements that span over the course of 1-3 days, resulting in similar lifetimes of 265±2.62 ns. In future experiments, we plan on analyzing pure Fe and Aluminum-doped MgO and then comparing these positron lifetimes with radiation-damaged versions of the same samples.
