Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session HC: Nuclear Astrophysics III |
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Chair: Alfredo Estrade, Central Michigan University Room: Salon 3 |
Friday, October 27, 2017 8:30AM - 8:42AM |
HC.00001: Investigating and reducing the impact of nuclear reaction rate uncertainties on $^{44}$Ti production in core-collapse supernovae. Shiv Subedi, Zach Meisel Recent observational advances have enabled high resolution mapping of $^{44}$Ti in core-collapse supernova (CCSN) remnants. Comparisons between observations and 3D models provide stringent constraints on the CCSN mechanism. However, recent work has identified several uncertain nuclear reaction rates that influence $^{44}$Ti production in model calculations. We are using MESA (Modules for Experiments in Stellar Astrophysics) as a tool to investigate the previously identified sensitivities of $^{44}$Ti production in CCSN to varied reaction rates. MESA is a code for modeling stellar evolution and stellar explosions in one-dimension. We will present the simulation results and our plans to reduce or remove the most significant uncertainties from $(\alpha,n)$, $(\alpha,p)$, $(\alpha,\gamma)$, $(p,n)$ and $(p,\gamma)$ reaction rates using direct and indirect measurement techniques at Edwards Accelerator Lab at Ohio University. [Preview Abstract] |
Friday, October 27, 2017 8:42AM - 8:54AM |
HC.00002: Penning trap mass measurement of $^{56}$Cu A.A. Valverde, M. Brodeur, G. Bollen, M. Eibach, K. Gulyuz, A. Hamacker, C. Izzo, W.-J. Ong, D. Puentes, M. Redshaw, R. Ringle, R. Sandler, S. Schwarz, C.S. Sumithrarachchi, J. Surbrook, A.C.C. Villari, I.T. Yandow The doubly-magic nucleus $^{56}$Ni is one of the most important waiting point nuclei in the rp-process. While we now know that it is not the endpoint of the rp-process, which continues to the Sn-Sb-Te cycle, the flow around this nucleus is still not well understood. A pathway bypassing $^{56}$Ni through the $^{55}$Ni(p,$\gamma$)$^{56}$Cu reaction exists, but the rate depends on the $Q$ value of this reaction, which has not been experimentally determined. Mass measurements were undertaken using the LEBIT 9.4T Penning trap mass spectrometer at the National Superconducting Cyclotron Laboratory to rectify this situation. [Preview Abstract] |
Friday, October 27, 2017 8:54AM - 9:06AM |
HC.00003: Development of a Neutron Long Counter Detector for ($\alpha$, n) Cross Section Measurements at Ohio University Kristyn Brandenburg, Zachary Meisel, Carl R Brune, Thomas M 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 winds of core collapse supernovae (CCSN) are 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] |
Friday, October 27, 2017 9:06AM - 9:18AM |
HC.00004: Nuclear level density and gamma strength function in $^{64}$Fe M. K. Smith, A. Spyrou, T. Ahn, A. C. Dombos, S. N. Liddick, F. Montes, F. Naqvi, D. Richman, H. Schatz, J. Brown, K. Childers, B. P. Crider, C. J. Prokop, E. Deleeuw, P. A. DeYoung, C. Langer, R. Lewis, Z. Meisel, J. Pereira, S. J. Quinn, K. Schmidt, A. C. Larsen, M. Guttormsen The Fe-Cd mass region exhibits enhanced collectivity and an unexpected increased in gamma-decay probability at low energies. These effects could be significant for r-process nucleosynthesis, where masses, beta-decay probabilities, and neutron capture cross sections are among the most important inputs. Neutron capture is notoriously difficult to measure; so the recent development of an indirect technique to constrain neutron-captures far from stability is especially valuable. This is the beta-Oslo method, which allows the extraction of the nuclear level density and gamma-ray strength function to compute neutron-capture cross sections. This work reports on 64Fe, populated via beta-decay of 64Mn at the National Superconducting Cyclotron Laboratory and measured with the 4pi Summing NaI (SuN) total gamma-ray spectrometer. [Preview Abstract] |
Friday, October 27, 2017 9:18AM - 9:30AM |
HC.00005: Towards an experimental constraint for the $ ^{56} $Ni(n,p)$ ^{56} $Co reaction rate which is key for the astrophysical $\nu p$~process. Georgios Perdikakis, Panagiotis Gastis, Carla Frohlich, Mihai Horoi, Antonios Kontos, Sean Liddick, Ling-Ying Lin, Fernando Montes, Stelios Nikas, Thomas Redpath, Matthew Redshaw, Roman Senkov, Artemis Spyrou, Antonio Villari, Kathrin Wimmer, Remco Zegers Neutrino-driven winds in core-collapse supernovae, are an important site for the production of elements heavier than iron. If the neutrino-driven wind is slightly proton-rich as predicted by modern hydrodynamics simulations, then some of the elements heavier than Fe could be synthesized by the $ \nu $p-process making it a reasonable candidate for the Lighter Element Primary Process (LEPP), and a possible contributor to the abundances of light p-nuclei. The key $ ^{56} $Ni(n,p)$ ^{56} $ Co reaction rate for the neutrino-p process will be constrained experimentally through the $ ^{56} $Co(p,n)$ ^{56} $Ni cross section measurement in ReA3. This new experimental technique that enables the measurement of (p,n) reactions at low energies with radioactive beams and the corresponding proof-of-principle experiment using the $ ^{85} $Rb(p,n) reaction will be discussed. [Preview Abstract] |
Friday, October 27, 2017 9:30AM - 9:42AM |
HC.00006: Evidence of n-$\gamma$ Competition in $^{69,71}$Co Decay Stephanie Lyons, A. Spyrou, S. N. Liddick, F. Naqvi, R. Surman, B. P. Crider, A. C. Dombos, D. L. Bleuel, B. A. Brown, A. Couture, L. Crespo Campo, M. Guttormsen, A. C. Larsen, R. Lewis, P. Moller, S. Mosby, M. R. Mumpower, G. Perdikakis, C. J. Prokop, T. Renstrom, S. Siem, S. J. Quinn, S. Valenta The r-process is known to produce roughly half of the isotopes of heavy elements. Sensitivity studies have shown that the final abundance distributions of r-process nuclei are affected by various input parameters, including nuclear masses and $\beta$-delayed neutron-emission probabilities. While it is expected that neutron capture dominates above the neutron threshold, recent measurements of $\beta$-decay on r-process nuclei have observed $\gamma$-emission above the neutron threshold. This may have an effect on the final abundances of r-process nuclei. For this reason, $\beta$-decay intensities for $^{69,71}$Co were measured using the technique of total absorption spectroscopy at the NSCL. The experimental results reveal another case of neutron-$\gamma$ competition. The implications on r-process nucleosynthesis will be discussed. [Preview Abstract] |
Friday, October 27, 2017 9:42AM - 9:54AM |
HC.00007: Using Two-Proton Transfer to Study H and He Burning Reactions of Type-1 X-Ray Bursts Douglas Soltesz, Thomas N. Massey, Alexander Voinov, Zach Meisel The reaction rate of the $^{\mathrm{59}}$Cu(p,$\gamma )^{\mathrm{60}}$Zn has been identified to have a significant impact on the light curve of X-ray bursts, controlling the reaction flow out of the Ni-Cu cycle impacting the late-time light curve. Using two proton transfer, $^{\mathrm{58}}$Ni($^{\mathrm{3}}$He,n)$^{\mathrm{60}}$Zn can be used to study the $^{\mathrm{59}}$Cu(p,$\gamma )^{\mathrm{60}}$Zn reaction. We are currently using the neutron evaporation spectrum from $^{\mathrm{58}}$Ni($^{\mathrm{3}}$He,n)$^{\mathrm{60}}$Zn in order to extract the level density of $^{\mathrm{60}}$Zn and constrain $^{\mathrm{59}}$Cu(p,$\gamma )^{\mathrm{60}}$Zn. To augment the ($^{\mathrm{3}}$He,n) technique for lower level-density compound nuclides, a silicon detector array is currently being developed for use in determining charged-particle decay branching ratios from discrete states. The present status of data analysis and detector development will be discussed, as well as future plans. [Preview Abstract] |
Friday, October 27, 2017 9:54AM - 10:06AM |
HC.00008: Comparison of neutron capture cross sections obtained from two Hauser-Feshbach statistical models on a short-lived nucleus using experimentally constrained input Rebecca Lewis, Sean Liddick, Artemis Spyrou, Benjamin Crider, Alexander Dombos, Farheen Naqvi, Christopher Prokop, Stephen Quinn, Ann-Cecilie Larsen, Lucia Crespo Campo, Magne Guttormsen, Therese Renstrom, Sunniva Siem, Darren Bleuel, Aaron Couture, Shea Mosby, George Perdikakis A majority of the abundance of the elements above iron are produced by neutron capture reactions, and, in explosive stellar processes, many of these reactions take place on unstable nuclei. Direct neutron capture experiments can only be performed on stable and long-lived nuclei, requiring indirect methods for the remaining isotopes. Statistical neutron capture can be described using the nuclear level density (NLD), the $\gamma$ strength function ($\gamma$SF), and an optical model. The NLD and $\gamma$SF can be obtained using the $\beta$-Oslo method. The NLD and $\gamma$SF were recently determined for $^{74}$Zn using the $\beta$-Oslo method, and were used in both TALYS and CoH to calculate the $^{73}$Zn(n,$\gamma$)$^{74}$Zn neutron capture cross section. The cross sections calculated in TALYS and CoH are expected to be identical if the inputs for both codes are the same, however, after a thorough investigation into the inputs for the $^{73}$Zn(n,$\gamma$)$^{74}$Zn reaction there is still a factor of two discrepancy between the two codes. [Preview Abstract] |
Friday, October 27, 2017 10:06AM - 10:18AM |
HC.00009: Constraining the cross section of $^{82}$Se(n,$\gamma$)$^{83}$Se to validate the $\beta$-Oslo method K. Childers, S.N. Liddick, B.P. Crider, A.C. Dombos, R. Lewis, A. Spyrou, A. Couture, S. Mosby, C.J. Prokop, F. Naqvi, A.C. Larsen, M. Guttormsen, L.C. Campo, T. Renstrom, S. Siem, D.L. Bleuel, G. Perdikakis, S. Quinn Neutron capture cross sections of short-lived nuclei are important for a variety of basic and applied nuclear science problems. However, because of the short half-lives of the nuclei involved and the nonexistence of a neutron target, indirect measurement methods are required. One such method is the $\beta$-Oslo method. The nuclear level density and $\gamma$ strength function of a nucleus are extracted after $\beta$-decay and used in a statistical reaction model to constrain the neutron capture cross section. This method has been used previously, but must be validated against a directly measured neutron capture cross section. The neutron capture cross section of $^{82}$Se has been measured previously, and $^{83}$Se can be accessed by the $\beta$-decay of $^{83}$As. The $\beta$-decay of $^{83}$As to $^{83}$Se was studied using the SuN detector at the NSCL and the $\beta$-Oslo method was utilized to constrain the neutron capture cross section of $^{82}$Se, which is compared to the directly measured value. [Preview Abstract] |
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