Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session H12: Nuclear Reactions and Astrophysics I |
Hide Abstracts |
Sponsoring Units: DNP Chair: Sanjay Reddy, Univ. of Washington Room: Roosevelt 4 |
Sunday, January 29, 2017 8:30AM - 8:42AM |
H12.00001: Simualting the Phase Separated rp-ash Matthew Caplan, Chuck Horowitz, Donald Berry The composition and phase separation of rp-ash on accreting neutron stars determine the thermal properties of the crust which must be understood to interpret observations of crust cooling in X-ray bursts. In this work, we report on recent large scale molecular dynamics simulations of the outer crust. Using the crust compositions calculated by Mckinven et al. 2016, we study the structure of the crystal that forms, as well as diffusion and thermal properties of the crust. [Preview Abstract] |
Sunday, January 29, 2017 8:42AM - 8:54AM |
H12.00002: Development of a Neutron Long Counter Detector for ($\alpha$, n) Cross Section Measurements at Ohio University Kristyn Brandenburg, Zach Meisel, Carl R Brune, Thomas Massey, Doug Soltesz, Shiv Subedi The origin of the elements from roughly zinc-to-tin $(30{<}Z{<}50)$ has yet to be determined. The neutron-rich neutrino driven wind of core collapse supernova (CCSN) is a proposed site for the nucleosynthesis of these elements. However, a significant source of uncertainty exists in elemental abundance yields from astrophysics model calculations due to the uncertainty for $(\alpha,n)$ reaction rates, as most of the relevant cross sections have yet to be measured. We are developing a neutron long counter tailored to measure neutrons for $(\alpha,n)$ reaction measurements performed at The Ohio University Edwards Accelerator Laboratory. The detector design will be optimized using the Monte-Carlo N-Particle transport code (MCNP6). Details of the optimization process, as well as the present status of the detector design will be provided. The plans for first $(\alpha,n)$ cross section measurements will also be briefly discussed. [Preview Abstract] |
Sunday, January 29, 2017 8:54AM - 9:06AM |
H12.00003: A New Open-Source Nuclear Equation of State Framework based on the Liquid-Drop Model with Skyrme Interactions Andre da Silva Schneider, Luke Roberts, Christian Ott The equation of state (EOS) of dense matter is an essential ingredient for numerical simulations of many astrophysical phenomena. We implement a modular open-source Fortran 90 code to construct the EOS of hot dense matter for astrophysical applications. For high density matter we use a non-relativistic liquid-drop description of nuclei that includes surface effects in a single nucleus approximation (SNA). The model is based on the work of Lattimer and Swesty [Nucl. Phys. A 535, 331 (1991)] and has been generalized to accommodate most Skyrme parametrizations available in the literature. Low density matter is described as an ensemble of nuclei in nuclear statistical equilibrium (NSE). The transition between the SNA and NSE regimes is performed via a continuous function that smoothly blends their Helmholtz free energy. To account for the existence of 2 solar mass neutron stars, we extend the formalism to allow for a stiffening of the EOS at densities above 3 times nuclear saturation density, where the properties of matter are presently poorly constrained. We study how different Skyrme parametrizations affect the EOS, neutron star mass-radius relationships, and the spherically symmetric collapse and post-bounce supernova evolution of massive stars. [Preview Abstract] |
Sunday, January 29, 2017 9:06AM - 9:18AM |
H12.00004: Report on an improved calculation of the Beryllium-7 + proton $\rightarrow$ Boron-8 + photon cross section at stellar energies X. Zhang, Kenneth M. Nollett, D. R. Phillips The radiative capture reaction, 7Be+p $\rightarrow$ 8B+photon, is a subject of long-standing interest for nuclear astrophysics. Its cross section needs to be known at low energies (about 20 keV in our Sun), which unfortunately is too small to be directly measured in lab. Therefore, theories are used to extrapolate the higher-energy measurements down to the low energies. The previous studies, including microscopic and phenomenological models, face difficulties with estimating theoretical uncertainties. In this talk, I will present our studies [Phys.Lett.B.751.535(2015)] based on the Halo-Effective-Field-Theory framework, which provides a systematic expansion for the reaction amplitude in terms of the low energy to the high energy scale ratio. Our next-to-leading-order formula can parameterize other existing results with sub-percent discrepancy in the relevant energy region, which is consistent with our theoretical uncertainty estimation based on the size of ignored higher order contributions. We then applied Bayesian analysis to constrain the theory parameters based on the direct capture data, and got a stringent constraint on the zero energy S factor, S(0)=21.3 ± 0.7 (eV b). The error is less than half of the previously recommended value, S(0)=20.8 ± 1.6 (eV b). [Preview Abstract] |
Sunday, January 29, 2017 9:18AM - 9:30AM |
H12.00005: Reaction Mechanism Dependence Of The Population And Decay Of $^{\mathrm{10}}$HE Han Liu, Thomas Redpath, Michael Thoennessen Measurements of neutron unbound systems allow for stringent tests of theoretical nuclear structure models at extreme neutron-to-proton ratios. It was recently suggested that the decay of broad neutron unbound states would be sensitive to the incoming channel wavefunction. Thus, the extended wavefunctions of halo nuclei could significantly affect the observed decay energy spectra for broad neutron unbound resonances. Experimental evidence for such an effect had been suggested in the case of $^{\mathrm{10}}$He. Its ground state resonance decaying to $^{\mathrm{8}}$He$+$n$+$n exhibited a shift of about 500 keV when populated in a proton removal reaction from $^{\mathrm{11}}$Li compared to the transfer reaction $^{\mathrm{8}}$He(t,p). In order to test this effect we measured the $^{\mathrm{10}}$He ground state resonance in two reactions using beams with different wavefunctions. We compared the decay energy spectrum of $^{\mathrm{10}}$He populated in a three-proton removal reaction from the (non-halo) nucleus $^{\mathrm{13}}$B with the spectrum from the one-proton removal reaction using the halo-nucleus $^{\mathrm{11}}$Li. The decay energy spectra were reconstructed from the measured momenta of the $^{\mathrm{8}}$He fragment and two coincident neutrons. The experiments were performed at the Coupled Cyclotron Facility of the NSCL with the Sweeper magnet and the MoNA-LISA array. [Preview Abstract] |
Sunday, January 29, 2017 9:30AM - 9:42AM |
H12.00006: Lifetime Measurement of $^{26}$O Thomas Redpath An interesting property of some neutron-unbound systems is true two-neutron emission where the neutrons are emitted simultaneously as opposed to a sequential decay through an intermediate state. Since neutrons are only affected by the angular momentum barrier, the timescale for this process is much shorter than for two proton emission which is dominated by the Coulomb barrier. One such case is $^{26}$O where a very low decay energy was measured and the two valence neutrons are expected to occupy $d$-wave orbitals. Also, the ground state of $^{25}$O is located 700 keV higher. In a first experiment, the MoNA collaboration extracted a lifetime of $4.5 ^{+1.1} _{-1.5} \mathrm{(stat)} \pm 3 \mathrm{(syst)}$ ps with a confidence level of 82\%. Recently, an experiment dedicated to measuring the $^{26}$O lifetime in order to improve the confidence level of the measurement was performed at NSCL. The experiment utilized a newly developed segmented target which increased the statistics without degrading the resolution. Preliminary results will be presented. [Preview Abstract] |
Sunday, January 29, 2017 9:42AM - 9:54AM |
H12.00007: Enhancement of fusion at near-barrier energies for neutron-rich light nuclei: $^{\mathrm{19}}$O $+ \quad^{\mathrm{12}}$C Varinderjit Singh, J. Vadas, T. K. Steinbach, B. B. Wiggins, S. Hudan, R. T. deSouza, L. T. Baby, S. A. Kuvin, Vandana Tripathi, I. Wiedenhover, A. S. Umar Measuring the fusion excitation function for an isotopic chain of projectile nuclei provides a sensitive test of a microscopic description of fusion. To investigate the theoretically predicted fusion enhancement for neutron-rich light nuclei, an experiment was performed to measure the fusion excitation functions for $^{\mathrm{19}}$O $+ \quad^{\mathrm{12}}$C and $^{\mathrm{18}}$O $+ \quad^{\mathrm{12}}$C. Using the $^{\mathrm{18}}$O(d,p) reaction and the RESOLUT mass spectrometer at Florida State University, a beam of $^{\mathrm{19}}$O was produced with an intensity of 2-4 x 10$^{\mathrm{3}}$ p/s. This beam bombarded a 100 $\mu $g/cm$^{\mathrm{2}}$ carbon target. Using an approach optimized for the measurement of fusion with a low-intensity beam, evaporation residues (ERs) resulting from the de-excitation of the fusion product were measured. The ERs were identified by measuring their energy and time-of-flight. At near-barrier energies, an enhancement of fusion by a factor of three has been observed for $^{\mathrm{19}}$O $+ \quad^{\mathrm{12}}$C in comparison to $^{\mathrm{18}}$O $+ \quad^{\mathrm{12}}$C. Comparison of the experimental results with the predictions of a density constrained time-dependent Hartree-Fock (DC-TDHF) model provide evidence for the importance of pairing in the fusion process. [Preview Abstract] |
Sunday, January 29, 2017 9:54AM - 10:06AM |
H12.00008: Measuring the fusion cross-section of $^{39,47}$K + $^{28}$Si at near barrier energies Justin Vadas, Varinderjit Singh, Blake Wiggins, Jacob Huston, Sylvie Hudan, Romualdo deSouza, Abdou Chbihi, Dieter Ackermann, Kyle Brown The outer crust of an accreting neutron star provides an interesting environment for nuclear reactions to occur. In particular, the enhancement of fusion between neutron-rich nuclei relative to their $\beta$-stable counterparts has been suggested as a trigger for an X-ray superburst. Recently, nuclei in the mass range of A=20-40 have been proposed as the most likely candidates for this process. To investigate this question, comparing the fusion excitation functions for both neutron-rich and $\beta$-stable nuclei at energies near the fusion barrier is necessary. The development of a $^{47}$K radioactive beam at NSCL’s ReA3 facility makes such a comparison possible for the first time. An approved experiment to measure the fusion excitation functions for $^{39,47}$K + $^{28}$Si will be described. This experiment utilizes a technique optimized for measuring the total fusion cross-section of reactions involving low-intensity (10$^{3}$ - 10$^{6}$ ions/s) radioactive beams. In addition, protons and $\alpha$ particles emitted by the compound nucleus as it de-excites are measured. Preliminary results will be presented. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700