Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session E9: Nuclear Reactions |
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Sponsoring Units: DNP Chair: Shelly Lesher, University of Wisconsin at Lacrosse Room: 250A |
Saturday, April 16, 2016 3:30PM - 3:42PM |
E9.00001: Does the $\alpha $ Cluster Structure in Light Nuclei Persist Through the Fusion Process? Justin Vadas, Tracy Steinbach, Jon Schmidt, Varinderjit Singh, Sylvie Hudan, Romualdo deSouza, Lagy Baby, Sean Kuvin, Ingo Wiedenhover Despite the importance of light-ion fusion in nucleosynthesis, a limited amount of data exist regarding the de-excitation following fusion for such systems. The characteristics of $\alpha$ emission following the fusion of $^{18}$O and $^{12}$C nuclei have been explored. Alpha particles were detected in coincidence with evaporation residues (ER) and identified on the basis of their energy and time-of-flight. ERs were characterized by their energy spectra and angular distributions while the $\alpha$ particles were characterized by their energy spectra, angular distributions, and cross-sections. While the energy spectra and angular distributions for the $\alpha$ particles are relatively well reproduced by statistical model codes, the measured cross-section is substantially underpredicted by the models. Comparison of the measured relative $\alpha$ cross-section at low E$_{c.m.}$ for $^{18}$O+$^{12}$C, $^{16}$O+$^{12}$C, and $^{16}$O+$^{13}$C indicates that the $\alpha$ cluster structure of the initial projectile and target nuclei influences the $\alpha$ emission following fusion. The underprediction of the relative $\alpha$ emission by the statistical model codes suggests that the failure of these models to account for $\alpha$ cluster structure is significant. [Preview Abstract] |
Saturday, April 16, 2016 3:42PM - 3:54PM |
E9.00002: Measuring the Fusion Cross-Section of $^{\mathrm{18}}$O $+$ $^{\mathrm{12}}$C with Low-Intensity Beams near and below the Coulomb barrier Tracy Steinbach, Justin Vadas, Varinderjit Singh, Sylvie Hudan, Romualdo deSouza, Lagy Baby, Sean Kuvin, Ingo Wiedenhover, Sait Umar, Volker Oberacker Fusion between neutron-rich light nuclei in the crust of an accreting neutron star has been proposed as a heat source that triggers an X-ray superburst. To explore the probability of such fusion events and examine their decay characteristics an experimental program using beams of neutron-rich light nuclei has been initiated. The evaporation residues (ERs) that result from the fusion of $^{\mathrm{18}}$O and $^{\mathrm{12}}$C nuclei, are directly measured and distinguished from unreacted beam particles on the basis of their energy and TOF. Using an experimental setup developed for the measurement with low-intensity (\textless 10$^{\mathrm{5}}$ ions/s) radioactive beams the fusion excitation function for $^{\mathrm{18}}$O$+^{\mathrm{12}}$C has been measured in the sub-barrier domain down to the 820 $\mu $b level. The measured fusion excitation function is compared to the prediction of a density constrained TDHF model. In addition to the measured cross-section, the measured ER angular distributions provide insight into the relative importance of the different de-excitation channels. These ER angular distributions are compared to the predictions of a statistical model code, EVAPOR revealing an under-prediction of the de-excitation channels associated with $\alpha $ emission. The de-excitation channels associated with proton emission following fusion will also be investigated. [Preview Abstract] |
Saturday, April 16, 2016 3:54PM - 4:06PM |
E9.00003: Experimental evidence for a fusion enhancement in $^{19}$O$+^{12}$C at near barrier energies Varinderjit Singh, T.K. STEINBACH, J. Vadas, B.B. WIGGINS, S. Hudan, R.T. Desouza, L.T. Baby, V. TRIPATHI, S.A. KUVIN, I. WIEDENHOVER, A.S. Umar, V.E. Oberacker Fusion of neutron-rich light nuclei in the outer crust of an accreting neutron star has been proposed as responsible for triggering X-ray super-bursts. The underlying hypothesis in this proposition is that the fusion of neutron-rich nuclei is enhanced as compared to stable nuclei. To investigate this hypothesis, an experiment has been performed to measure the fusion excitation function for $^{18}$O and $^{19}$O nuclei incident on a $^{12}$C target. A beam of $^{19}$O was produced by the $^{18}$O(d,p) reaction at Florida State University and separated using the RESOLUT mass spectrometer. The resulting $^{19}$O beam bombarded a 100 $\mu $g/cm$^{2}$ $^{12}$C target at an intensity of 2-4 x 10$^{4\, }$p/s. Evaporation residues resulting from the de-excitation of the fusion product were distinguished by measuring their energy and time-of-flight. Evaporation residues were detected with high efficiency by measuring them in the angular range 4.4\textdegree $\le \theta_{lab}\le $11.7\textdegree . The fusion cross-section has been measured down to 170 mb level. As compared to $^{18}$O$+^{12}$C the fusion cross-section for $^{19}$O$+^{12}$C is enhanced by approximately a factor of 3 times at the lowest energy measured. The measured excitation function will be compared with theoretical calculations. [Preview Abstract] |
Saturday, April 16, 2016 4:06PM - 4:18PM |
E9.00004: Dynamical Coupling of Pygmy and Giant Resonances Carlos Bertulani, Nathan Brady, Thomas Aumann, James Thomas One of the effects overseen in studies of excitation of pygmy resonances is the fact that both pygmy and giant resonances are strongly coupled. This coupling leads to dynamical effects such as the modification of transition probabilities and and cross sections. We make an assessment of such effects by means of the relativistic coupled channels equations developed by our group. [Preview Abstract] |
Saturday, April 16, 2016 4:18PM - 4:30PM |
E9.00005: Differential (p,p') and (p,d) Cross Sections of $^{89}$Y and $^{92}$Zr Molly Wakeling, Jason Burke, Johnathon Koglin, John McClory Differential cross sections for the (p,p') and (p,d) reactions on $^{89}$Y and $^{92}$Zr were measured using a 28.5-MeV proton beam at the 88-inch cyclotron at Lawrence Berkeley National Laboratory. Angular distributions were obtained for the ground state and several excited states of each isotope using silicon detector telescopes over angles 10$^{\circ}$ to 140$^{\circ}$ in the reaction plane. Angular distributions for unresolved higher-energy states up to 22 MeV were also obtained. These data were obtained by fitting a Gaussian function to each peak in the energy spectra using the ROOT toolkit and integrating the number of counts under each peak. The cross sections will be included in nuclear structure models so that neutron and other particle reaction cross sections can be predicted for other isotopes, including eventually those farther from stability and those whose half-lives are too short to measure experimentally. [Preview Abstract] |
Saturday, April 16, 2016 4:30PM - 4:42PM |
E9.00006: Feeding of isomers of stable Rh, Ag, Ir and Au isotopes in fast-neutron-induced reactions. N. Fotiades, M. Devlin, R.O. Nelson, J.J. Carroll The GEANIE spectrometer, comprised of 20 high-purity Ge detectors coupled to the broad-spectrum pulsed neutron beam of the Los Alamos Neutron Science Center's (LANSCE) WNR facility, has been used to determine partial $\gamma$-ray cross sections in $(n,xn)$ fast-neutron-induced reactions. In ($n,n^{\prime}$) reactions on stable Ir and Au isotopes the $\gamma$-ray feeding, as established with GEANIE, for the isomers relative to the feeding of the corresponding ground states increases with increasing neutron energy up to the neutron energy where the ($n,2n$) reaction channel opens and then decreases. The behavior in mass $A = 100$ region of the $\gamma$-ray feeding of isomers and ground states was also studied with GEANIE in fast-neutron-induced reactions on stable Rh and Ag isotopes. The feeding of the isomers was found to be very similar in the corresponding reaction channels and it was compared to the feeding determined for the ground states. The opening of higher-neutron-emitting reaction channels remove angular momentum from the compound system and reduce the population of higher-spin isomers relative to the feeding of lower-spin ground states in all cases studied. [Preview Abstract] |
Saturday, April 16, 2016 4:42PM - 4:54PM |
E9.00007: Theoretical study of isotopic production cross-sections in proton-nucleus reactions at 200MeV Mohammad S. Sabra As NASA's future plans are likely to include extended human missions in deep space, protections from space radiation take on increased importance. When galactic cosmic rays, mainly protons, interacts with the material of spacecraft, secondary fragments are produced, which contribute substantially to the dose and dose equivalent received by the crew inside. A detailed understanding of the reaction mechanism, as well as a knowledge of cross sections are needed. We analyze energy spectra, angular distributions, and isotopic cross-sections of intermediate-mass fragments (IMFs) from the interaction of $^{27}$Al, $^{59}$Co, and $^{197}$Au with 200 MeV protons. Calculations within the modified statistical model with final state interaction were performed using SAPTON code. General agreement is obtained with the experiment which suggests that most of the IMFs are emitted after equilibrium is reached (i.e. in the evaporation stage). [Preview Abstract] |
Saturday, April 16, 2016 4:54PM - 5:06PM |
E9.00008: Isospin-dependent phase diagram of nuclear matte Jorge Lopez, Sergio Terrazas-Porras This investigation uses results from classical molecular dynamics studies of infinite nuclear systems with varying density, temperature and isospin content to extricate the isospin-dependent phase diagram of nuclear matter. [Preview Abstract] |
Saturday, April 16, 2016 5:06PM - 5:18PM |
E9.00009: Rydberg phases of Hydrogen and low energy nuclear reactions Sveinn Olafsson, Leif Holmlid For over the last 26 years the science of cold fusion/LENR has been researched around the world with slow pace of progress. Modest quantity of excess heat and signatures of nuclear transmutation and helium production have been confirmed in experiments and theoretical work has only resulted in a large flora of inadequate theoretical scenarios. Here we review current state of research in Rydberg matter of Hydrogen that is showing strong signature of nuclear processes. In the presentation experimental behavior of Rydberg matter of hydrogen is described. An extensive collaboration effort of surface physics, catalysis, atomic physics, solid state physics, nuclear physics and quantum information is need to tackle the surprising experimental results that have so far been obtained. Rydberg matter of Hydrogen is the only known state of matter that is able to bring huge collection of protons to so short distances and for so long time that tunneling becomes a reasonable process for making low energy nuclear reactions. Nuclear quantum entanglement can also become realistic process at theses conditions. [Preview Abstract] |
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