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GPSAC 2017

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Poster Session A – 3:00-4:00PM, near NSH 202

A1 – Single-mode fibers and precision Radial Velocities, Andrew Bechter 

The capability of adaptive optics (AO) systems to deliver corrected starlight is well suited to efficiently couple light into single-mode fibers (SMFs). iLocater is a SMF-fed RV spectrograph that aims to achieve extremely precise RV measurements of late type stars. As part of the instrument development, on-sky fiber coupling measurements were taken in 2016 with one side of the Large Binocular Telescope (LBT). We present the SMF coupling efficiencies and analysis of simultaneous imaging on one target, Tania Australis (HD 89758). Using the results from this investigation, we aim to optimize SMF coupling efficiency to improve the throughput of iLocater which, in turn,will minimize RV errors by reducing photon noise and spectral profile modulations.

A2 – Correlations Between Hubble Residuals and Local Stellar Populations of Type Ia Supernovae, Benjamin Rose

There appears to be correlations between SN Ia Hubble diagram residuals and host galaxy mass, metallicity, and star formation history. An uncorrected bias may produce a systematic offset in cosmological measurements. Rigault et al. (2013) found that the local environment can correlate with Hubble residuals and possibly impact precision Hubble Constant measurements. Global properties are the luminosity average of local environments, therefore the properties of local environments may hold stronger correlations than their global counterparts. We analyze host galaxies from the SDSS-II survey using both ground-based and Hubble Space Telescope imaging. We generate local stellar environmental properties by selecting a best fit Flexible Stellar Population Synthesis model that matches the SDSS Scene Modeling data. The derived properties, such as metallicity, stellar age, and star formation history, are then compared to the SN Ia’s Hubble residual in the search for correlations.

A3 – Assessing the suitability of H4RG near infrared detectors for precise Doppler measurements, Eric Bechter

The first diffraction-limited Doppler spectrographs on large telescopes will operate at near-infrared (NIR) wavelengths in order to benefit from the imaging quality delivered by existing AO systems. Beyond the silicon cutoff, hybrid structured mercury-cadmium-telluride (HgCdTe) detectors show promise to provide sufficient sensitivity to enable extremely precise radial velocity (RV) measurements of late-type stars. The most advanced NIR detector commonly available is the Hawaii-2RG (H2RG) detector, manufactured by Teledyne. While the quantum efficiency (QE) of such devices has been shown to be ~ 90%, the noise characteristics of these devices, and how they relate to RV measurements, have yet to be quantified. We are characterizing the various noise sources generated by H4RG arrays using numerical simulations. We present recent results using our end-to-end spectrograph simulator in combination with the “HxRG Noise Generator,” which emulates the effects of read noise, residual bias drifts, pink (1/f) noise, alternating column noise, and picture frame noise. Our results have implications for RV error budgets and instrument noise floors that can be achieved with NIR Doppler spectrographs that utilize this kind of detector.

A4 – Study of the 7Li(α,γ)11B reaction, Gwenaelle Gilardy

At the end of its life, a massive star collapses into a neutron star. The neutrino flux released during the collapse is so significant that the probability of a neutrino interacting with a nucleus is enhanced enough to have an impact on nucleosynthesis. The origins of light elements, specifically 11B is not fully understood. The ν-process has been proposed as a candidate for 11B production. Neutrino triggered reactions lead to the creation of 11B, with the reaction 7Li(α,γ)11B as a component of the main reaction chain. This reaction was recently studied at Notre Dame and the preliminary results of this measurement will be presented.

A5 – Precision Half-life Measurements at the NSL, Jacob Long

In recent years, precision measurements have led to considerable advances in understanding in several areas of physics, including fundamental symmetry. The precise determination of ft values for superallowed mixed transitions between mirror nuclides could provide an avenue to test the theoretical corrections used to extract the Vud matrix element from superallowed pure Fermi transitions. The calculation of the ft value requires precise and accurate half-life, branching ratio, and Q value. To this end we recently started at the Nuclear Science Laboratory of the University of Notre Dame a program aimed at improving the lifetime of mirror transitions. Our first measurements on 17F and 25Al will be presented together with their impact on the ft-value determination of these isotopes.

A6 – Timing Resolution and Detection Efficiency of the St. George Detector System, Luis Morales

The St. George recoil mass separator at the University of Notre Dame will be used to study (α,γ) reactions of astrophysical interest. A detection system was developed for the St. George recoil mass separator, in collaboration with Indiana University South Bend, that will utilize energy and time-of-flight to separate reaction products from residual unreacted beam particles. The detection system uses two microchannel plate (MCP) detectors, perpendicular electric and magnetic field are used to bend secondary electrons from the surface of a parylene backed carbon foil to register timing measurements, and a silicon strip detector is used to measure the ion’s kinetic energy. The performance of the detection system will be presented.

A7 – Effects of Radiation and Heat on Boehmite, Patricia Huestis

The U.S. currently has approximately 300 million liters of highly radioactive wastes. Tanks containing the high-level waste (HLW) are difficult to deal with given the hostile environment that accompanies the ionizing radiation. Aluminum is prevalent in the tanks and removal requires leaching the tank sludge with caustic chemicals at an elevated temperature. The dissolution of aluminum is greatly complicated by the presence of aluminum oxides and hydroxides, and thus understanding how these solids age in the tank is essential for safe processing of HLW.

Initial tests were conducted on AlOOH (aluminum oxyhydroxide, boehmite), a major component of the solid tank waste. Boehmite has a sheet-like structure, where planes of aluminum and oxygen are held together by hydroxyl groups. This makes boehmite thermally unstable and prone to hydrogen formation within the material itself upon irradiation. Samples were irradiated up to 2 MGy using a 60Co γ-ray source and up to 175 MGy using stripped 4He nuclei simulating α-particles. Raman spectra did not show major alterations with radiation, even when given large doses. Pristine samples were heated and analyzed using Fourier Transform InfraRed (FTIR) spectroscopy and Temperature Programmed Desorption (TPD) which revealed a major transformation above 400°C, likely due to the material degrading into alumina. Hydrogen measurements were made on samples that were heated below the transformation temperature and compared to hydrogen measurements made on samples that were not heated. Heated samples released approximately 50% more hydrogen than non-heated samples, which indicates that hydrogen was made in the material and was trapped but able to diffuse out when given enough heat. Additional hydrogen measurements made on the previously mentioned samples show a decrease in hydrogen production for both samples, and a further decrease in hydrogen production for the sample that was heated. This is likely due to traps formed in the material which prevent excitons from reaching the material surface, though more work needs to be done to look at this.

A8 – Measuring Gamma Rays from Coulomb Excitation of 7Be and 7Li, Samuel Henderson
Ab-initio methods have been successful in describing the structure of light nuclei using realistic nucleon-nucleon interactions, but more experimental data is needed for light unstable nuclei. Recent no-core configuration interaction calculations have made predictions for transition strengths in 7Be. These include a value for the M1 and  E2 electromagnetic transition strength ratio for the gamma decay of the 7Li and 7Be 1st excited states. The E2 transition strength of 7Be has never before been measured while that of 7Li is known. To measure the E2 transition strength, a Coulomb Excitation experiment was performed using a radioactive beam of 7Be at the University of Notre Dame. 7Be was produced using the superconducting solenoids TwinSol, where 7Be was separated from other beam products made in the production reaction. A beam of 7Be ions were scattered off a gold target and the gamma rays from the inelastically scattered ions were detected using six clover Ge detectors. The most recent results for the E2 transition strength and its comparison to the no-core configuration interaction approach will be shown. In addition, an experiment on the mirror nucleus 7Li was performed using a stable beam. The E2 transition strength of 7Li has previously been measured and will provide an important benchmark for our 7Be analysis. Preliminary results of the 7Li compared to the 7Be will be presented, and extensions of this experimental method to further light unstable nuclei will also be discussed as well as the first stages of a Geant4 simulation to help account for anisotropies in our beam.
This work has been supported by US NSF grant no. PHY 14-19765 and DOE grant number DE-FG02-95ER-40934.

Oral Presentations – 4:00-5:30PM, NSH 118

4:00-4:15 – Accelerator Mass Spectrometry at the NSL, Adam Clark

Accelerator Mass Spectrometry (AMS) is a measurement technique that is used for a broad range of multidisciplinary applications such as art forgery detection, cross section measurements for stellar evolution, and environmental sampling for nuclear forensics. During this talk, I will briefly describe the basic principles of the AMS technique and the set up at the Nuclear Science Laboratory (NSL) following an upgrade to the low energy side of our accelerator. Additionally, previous work of both graduate and undergraduate students, as well as future developments, will be presented.

4:15-4:30 – Galactic Chemical Evolution in the Era of Narrow-band Photometric Surveys, Devin Whitten

With the advent of narrow-band photometric surveys such as Pristine, the Southern and Javalambre Photometric Local Universe Surveys, new opportunities are available for stellar parameter determination, stellar population study, and near-field cosmology from photometry alone. However, this area of observational astronomy requires a methodology to translate the multitude of photometric parameters into meaningful astronomical quantities, including chemical abundances, stellar parameters, and more.

4:30-4:45 – Updates on the Commissioning of the High Efficiency TOtal absorption spectrometeR (HECTOR), Orlando Gomez

No abstract provided

4:45-5:00 – “Hidden” CEMP Stars: The Impact of Warm Metal-Poor Stars on Galactic Chemical Evolution, Kaitlin Rasmussen

Carbon-Enhanced Metal-Poor (CEMP) stars are are crucial to studying early Galactic chemical evolution. Through spectroscopic abundance analysis, they can be used to probe the nature of primordial mini-halos, first star nucleosynthesis, and early star formation channels. Many ongoing medium-resolution programs to identify new CEMP stars are in place, but are limited by the detectability of carbon at high temperatures. We present new high-resolution measurements of carbon in a sample of warm, metal-poor stars and discuss the implications of a “hidden” warm CEMP population as well as insights into a solution to this problem.

5:00-5:15 – Improving r-process calculations for the rare-earth abundance peak via mass measurements, James Kelly

The rare-earth peak in the r-process abundance pattern depends sensitively both on the astrophysical site and on subtle changes in nuclear structure in the region. A series of precise atomic mass measurements at the JYFLTRAP double Penning trap help elucidate the nuclear structure and reduce the uncertainties in the r-process calculations. 158Nd, 160,162Pm, and 164−166Gd have been measured for the first time, and the precisions for 156Nd, 158Pm, 162-163Eu, 163Gd, and 164Tb have been improved considerably. The effects of the new mass values on the calculated r-process abundances, as well as the two-neutron separation energies and the possibility of a subshell closure at N=100, will be discussed. Further studies are anticipated to shed light on the underlying physics affecting the binding energies, and more mass measurements are planned to pin down r-process abundances.

Poster Session B – 5:30-6:30PM, near NSH 202

B1 – Search for supersymmetry in event with missing energy and two photons using CMS detector, Allison Hall

The CMS detector at the Large Hadron Collider is used to search for many possible extensions of the Standard Model. In this poster, the results of a search for gauge-mediated supersymmetry breaking in final states with photons and missing transverse momentum are reported. The study is based on a sample of proton-proton collisions collected at a center-of-mass energy of 13 TeV with the CMS detector in 2015, corresponding to an integrated luminosity of 2.3 fb-1. No excess is observed with respect to the standard model expectation, and the results are used to set limits on gluino pair production and squark pair production in the GGM SUSY framework. Gluino masses below 1.65 TeV and squark masses below 1.37 TeV are excluded at a 95% confidence level.

B2 – Extracting Statistican Properties of Samarium Isotopes Using the Oslo Method, Craig Reingold

The statistical model for nuclear reactions is one of the most quantitative theories in nuclear physics. In this model, two reacting nuclei fuse to form one compound nucleus in a highly excited state. At these high excitation energies, the spacing between nuclear resonances rapidly approaches the width of the resonances. Over this quasi-continuum, nuclear reactions cross sections can be treated as averaged functions, calculated using statistical factors. These factors include the nuclear level density (NLD) and γ-strength function (γSF).

Providing experimental constraints for the NLD and γSF for samarium isotopes is of utmost importance to nuclear astrophysics, nuclear security, and nuclear structure. Since many reaction cross sections have yet to be measured, Hauser Feshbach calculations are often employed. Furthermore, they can be used to predict photonuclear and inverse radiative-capture reaction cross sections of fission products. Constraining statistical factors is, therefore, imperative to nuclear security as well. In the field of nuclear structure, theorists predict an enhancement in the γSF at γ-ray energies. Experimental evidence shows that the enhancement is the result of dipole transitions, but the electromagnetic character has yet to be determined. This can be verified experimentally via observation of γ-ray scattering in segmented detectors.

In this work, the NLD and γSF were extracted using the STARLiTeR array at Texas A&M University. STARLiTeR consists of two segmented silicon detectors to identify charged reaction products, coupled with six BGO suppressed HPGe Clover detectors to measure γ-ray energies. Particle-gamma coincidence provide correlation matrices of excitation energy vs γ-ray energy, for which the Oslo method is employed to simultaneously extract the NLD and gSF. This analysis has been completed for 152,154Sm(p,d)151,153Sm reactions. In the future, we plan to analyze data from the (p,d) and (p,t) reaction channels of 148,150,152,154Sm and 160Dy.

B3 – Kinematic Studies of the Metastable Vortex Lattice Phases in MgB2, Elizabeth Louden

Small-angle neutron scattering (SANS) studies of the vortex lattice (VL) in the type-II superconductor MgBhave revealed an unprecedented degree of metastability that is demonstrably not due to vortex pinning.  Here, we report on detailed dynamic studies of the metastable (MS) to ground state (GS) VL transition.  The VL can be driven to the GS through successive application of an AC magnetic field and imaged using SANS.  This stop-motion technique revealed a power law behavior as a function of the number of applied cycles, a signature of granular jamming.  Further, two different MS VLs were examined:  a MS F phase prepared by “supercooling” across the phase boundary and a MS L phase by “superheating” across the same boundary.  These two different MS phases have qualitatively different single domain free energies, and exhibited a striking difference in the manner they returned to their respective GS, switching from a discontinuous transition to a continuous rotation.

B4 – Isotope Harvesting at the Facility for Rare Isotope Beams, John Wilkinson

No abstract provided.

B5 – Characterizing Dark Matter at the Large Hadron Collider Using Dilepton Distributions, Rodolfo Capdevilla

Spectral features in LHC dileptonic events may signal radiative corrections coming from new degrees of freedom, notably dark matter and mediators. Using simplified models, we show how these features can reveal the fundamental properties of the dark sector, such as self-conjugation, spin and mass of dark matter, and the quantum numbers of the mediator. Distributions of both the invariant mass “mee” and the Collins-Soper scattering angle “cosCS” are studied to pinpoint these properties. We derive constraints on the models from LHC measurements of mee and cosCS, which are competitive with direct detection and jets + Missing Energy searches. We find that in certain scenarios the cosCS spectrum provides the strongest bounds, underlying the importance of scattering angle measurements for non-resonant new physics.

B6 – Simulation of Nuclear Reactions in the HIPPO Gas-Jet target with GEANT4, Shane Moylan

No abstract provided.

B7 – Degree Preserving Growth of Networks, Sukhwan Chung & Shubha Kharel

We define a family of network growth models in which a newly arriving node of even degree attaches to the existing network without changing the degrees of the earlier nodes, by a process of cutting and joining edges. We discuss some of the properties of the graphs generated by this process, and provide the conditions for which the matching numbers of the graphs in the large network limit grows linearly with the graph order. We show that when the incoming degree is twice the matching number of the existing graph, the limit graph is a split graph or near split graph, with density 1/2. As an example, we consider the sequence of integers Sn = (1, g1, g2, …, gn), where gk = pk+1 – pk is the k-th prime gap and we show that if Legendre’s Conjecture holds then Sn is a graphical sequence for any finite n, which, with increasing n, defines a family of prime gap graphs. As another application, we show that this process can be used to build graphs with  power-law degree distributions without involving preferential attachment processes.

Dinner to follow!

This year’s sponsors:
Graduate Career ServicesGSUAPS PhysicsJINA-CEE