Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session FK: Mini-Symposium on Nuclear Reaction Rates Relevant to Stellar Evolution and Nucleosynthesis |
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Chair: Rebecca Surman, Union College Room: Queen's 6 |
Friday, October 10, 2014 9:00AM - 9:30AM |
FK.00001: Direct measurement of the $^{4}$He ($^{12}$C, $^{16}$O) $\gamma $ reaction cross section near stellar energies Invited Speaker: Kenshi Sagara The $^{12}$C$+^{4}$He$\to^{16}$O$+\gamma$ reaction is one of the key reactions in stellar He-burning, but its total cross section at stellar energy (Ecm $=$ 0.3 MeV) has not been measured yet, in spite of many experiments made in the world for about a half century. At Kyushu University Tandem accelerator Laboratory (KUTL), we have been making direct measurement of the $^{4}$He ($^{12}$C, $^{16}$O) $\gamma $ total cross section below Ecm $=$ 2.4 MeV for about 20 years. We have measured the total cross section at Ecm $=$ 2.4, 1.5 and 1.2 MeV. Now we are preparing to measure the cross section at 1.0 MeV. The direct measurement was made from Ecm $=$ 5 MeV down to 1.9 MeV at Ruhr University, Bochum. We use a pulsed $^{12}$C beam and a windowless $^{4}$He target, and detect all the $^{16}$O recoils in a charge state. A usually continuum $^{12}$C beam from our tandem accelerator is pulsed by a pre-buncher, a main buncher, and a beam chopper. Our tandem accelerator was designed to be used at the acceleration voltage of 6-10 MV. For the $^{4}$He ($^{12}$C, $^{16}$O) $\gamma $ experiment we need to use it at 1.3-1.8 MV where beam transmission is very low, then we have invented an acceleration-deceleration method for the tandem accelerator. We have developed a blow-in windowless He target based on an original idea. To separate $^{16}$O recoils from the $^{12}$C beam, we developed a recoil-mass separator. To reject $^{12}$C backgrounds, we developed a long-time chopper, and an ionization chamber. Now, we are preparing to measure time-of-flight of $^{16}$O recoils and $^{12}$C backgrounds. Many original instruments and the experimental results will be presented. Finally we discuss what are necessary for future direct measurement of the $^{4}$He ($^{12}$C, $^{16}$O) $\gamma $ total cross section below 1.0 MeV, down to 0.7 MeV. A dynamitron accelerator and hard-working researchers may be inevitable. [Preview Abstract] |
Friday, October 10, 2014 9:30AM - 9:45AM |
FK.00002: Nuclear astrophysics, BBN and neutrinos Carlo Gustavino Big Bang Nucleosynthesis (BBN) theory describes the formation of light isotopes such as $D$, $^3He$, $^4He$, $^6Li$ and $^7Li$ in the first minutes of cosmic time. Their abundance depends on the competition between the universal expansion rate and the yields of relevant nuclear reactions. As the universal expansion rate depends on the density of relativistic particles, the abundances of light isotopes allow to constrain the number of neutrinos species, provided that the knowledge of the relevant nuclear processes is accurate enough. The baryon density and the primordial abundance of deuterium (D/H) are presently measured with high accuracy, providing a suggestive, but still inconclusive, hint of the presence of dark radiation (i.e. extra neutrinos). The uncertainty of the $^2H(p,\gamma)^3He$ cross section at BBN energies represents the most important obstacle to improve the contraints on the existence of dark radiation. This reaction will be studied at the underground Gran Sasso Laboratory with the LUNA accelerator. The goal is to measure the $^2H(p,\gamma)^3He$ reaction cross section inside the BBN energy region, with an accuracy of less than $3\%$. The forthcoming LUNA measurement and its impact in cosmology, as well as in particle and nuclear physics, will be discussed. [Preview Abstract] |
Friday, October 10, 2014 9:45AM - 10:00AM |
FK.00003: \textit{Ab initio} study of the $^3{\rm He}(\alpha,\gamma)^7{\rm Be}$ and $^3{\rm H}(\alpha,\gamma)^7{\rm Li}$ radiative captures J\'er\'emy Dohet-Eraly, Petr Navratil, Sofia Quaglioni, Wataru Horiuchi, Guillaume Hupin An \textit{ab initio} description of the $^3{\rm He}(\alpha,\gamma)^7{\rm Be}$ and $^3{\rm H}(\alpha,\gamma)^7{\rm Li}$ radiative captures from the no-core shell model with continuum (NCSMC)~[1] is presented. The study of the $^3{\rm He}(\alpha,\gamma)^7{\rm Be}$ reaction, complemented by the study of the $^3{\rm He}(^3{\rm He},2p)^4{\rm He}$ reaction, should enable one to determine the fractions of $pp$-chain terminations resulting in $^7{\rm Be}$ or ${^8}{\rm B}$ neutrinos~[2]. The NCSMC approach has the key feature to describe both bound and scattering states in a unified formalism and to deal with realistic nucleon-nucleon interactions. Within this approach, the bound-state properties of $^7{\rm Be}$ and $^7{\rm Li}$ are calculated and compared with the experiment. The scattering wave functions of $\alpha+^3{\rm H}/^3{\rm He}$ are also evaluated and tested by comparing the theoretical phase shifts and resonance properties with the experimental ones. From these bound and scattering wave functions, the astrophysical $S$ factors of the radiative captures are determined by considering the dominant $E1$ transitions.\\[4pt] [1] S. Baroni, P. Navratil, and S. Quaglioni, Phys. Rev. Lett 110 (2013) 022505;Phys. Rev. C 87 (2013) 034326.\\[0pt] [2] E. G. Adelberger et al., Rev. Mod. Phys. 70 (1998) [Preview Abstract] |
Friday, October 10, 2014 10:00AM - 10:15AM |
FK.00004: Monte Carlo Uncertainty Analysis of $^3$He$(\alpha,\gamma)^7$Be Richard deBoer, Joachim Goerres, Karl Smith, Ethan Uberseder, Michael Wiescher, Antonios Kontos, Gianluca Imbriani, Antonino Di Leva, Frank Strieder The $^{3}$He$(\alpha,\gamma)^{7}$Be reaction is of critical importance in determining the flux of solar neutrinos through the $pp$-II and $pp$-III chains. For this reason and others, the description of the cross section and its extrapolation towards low energy has always been a matter of intense debate. While large systematic differences have been present in the past, several recent measurements of the low energy cross section are all in excellent statistical agreement. The convergence of the recent individual experimental measurements prompts a global analysis of the reaction data. From the combined data, a more precise and accurate estimate of the low energy cross section can be determined. A global $R$-matrix fit is used to describe the $^{3}$He$(\alpha,\gamma)^{7}$Be data as well as scattering data over a similar energy range. The fit is then subjected to a Monte Carlo analysis to extract the uncertainties on the cross section and corresponding reaction rate. By combining several recent measurements, the combined data yield a low energy $S$ factor of $S(0)$ = 0.542$\pm$2.0\%(capture)$^{+1.0\%}_{-1.4\%}$(model)$^{+3.9\%}_{-2.0\%}$(phase shifts) keV b giving a total uncertainty in $S(0)$ of +4.5\%/-3.0\%. [Preview Abstract] |
Friday, October 10, 2014 10:15AM - 10:30AM |
FK.00005: Feasibility study to search for the rare $\gamma $-decay mode in $^{12}$C Miho Tsumura, Takahiro Kawabata, Satoshi Adachi, Tatsuo Baba, Tatsuya Furuno, Yuki Ishii, Motoki Murata, Atsushi Tamii, Takashi Hashimoto, Kichiji Hatanaka, Yohei Matsuda, Kenjiro Miki, Chihiro Iwamoto, Takeshi Ito, Masaki Miura, Juzo Zenihiro, Shigeru Kubono, Masatoshi Itoh, Shun Ando, Yukie Maeda, Satoshi Sakaguchi, Hidetoshi Akimune, Hisako Fujimura, Iwa Ou The triple $\alpha $ reaction plays a very important role in the $^{12}$C synthesis in the universe. Gamma-decay widths of excited states in $^{12}$C are the key parameters to determine the triple $\alpha $ reaction rate. The triple $\alpha $ process proceeds via the 0$_{2}^{+}$ state (Hoyle state) at normal stellar temperature. However, at high temperature T$_{9}$ \textgreater 1, the highly excited states such as the 3$_{1}^{-}$ and 2$_{2}^{+}$ states become dominant. Unfortunately, the $\gamma $-decay widths of these states are still unknown. We proposed to measure the $^{1}$H($^{12}$C, $^{12}$Cp) reaction to determine the radiative widths of the highly excited states in $^{12}$C. Recoil protons will be measured in coincidence with scattered $^{12}$C instead of $\gamma $-rays. The test experiment was carried out at the cyclotron facility in RCNP. In the present talk, we will report this result. [Preview Abstract] |
Friday, October 10, 2014 10:30AM - 10:45AM |
FK.00006: Imaginary time approach for reaction rate of triple-alpha process Kazuhiro Yabana, Takahiko Akahori, Yasuro Funaki We propose a new theoretical approach for the radiative capture reaction rate, which we call the imaginary-time theory. In the theory, inverse temperature is identified with the temperature. Since reaction rates can be calculated without solving any scattering problem in the theory, it is ideally suited for the triple-alpha process in which scattering problem of three charged particles has caused difficulties. Using the imaginary-time theory, we obtain the triple-alpha reaction rate in the quantum three-body model treating alpha particles as structureless point particles. The calculated rate is almost identical to the standard NACRE rate. We have also found that the reaction mechanism of the triple-alpha process changes at exactly the same temperatures as those in empirical theories. We may show that it is possible to derive an analytical formula close to that of the NACRE rate, if we introduce some assumptions in the three-body model. We demonstrate that, if we introduce a coupled-channel expansion with a truncation, reaction rate is substantially overestimated. This finding may help to explain the very different reaction rates obtained so far using different theoretical approaches. [Preview Abstract] |
Friday, October 10, 2014 10:45AM - 11:00AM |
FK.00007: Proton Capture on $^{12}$C Joachim Goerres, Karl-Ulrich Kettner, Hans-Werner Becker, Richard J. deBoer, Ethan Uberseder, Michael C. Wiescher During explosive Hydrogen burning the $^{12}$C(p,$\gamma$)$^{13}$N reaction is the entry point which injects $^{12}$C, newly produced by the triple $\alpha$-process, into the hot CNO cycle. At solar temperatures this reaction is one of the two sources for neutrinos within the CNO cycle whose observation would provide a test for the SSM. The capture cross section is determined by 2 resonances, the direct capture to the ground state as well as interferences between these components. To investigate uncertainties found in the literature for the 1.7 MeV resonance we have measured this reaction in the energy of 1.2 to 2.5 MeV. Detailed excitation functions were measured at 0$^\circ$ and 55$^\circ$ and complemented by angular distributions measured in 100 keV steps. The results of this experiment will be reported together with R-matrix fits over the entire energy range of astrophysical interest. [Preview Abstract] |
Friday, October 10, 2014 11:00AM - 11:15AM |
FK.00008: Measurement of the 14O(a,p)17F reaction at Ecm $=$ 2.2 $\sim$ 5.3 MeV Kevin Hahn, Aram Kim The direct measurement of the astrophysically important 14O(a,p)17F reaction was performed using a low-energy 14O beam at the Center for Nuclear Study, University of Tokyo. The excitation function for \textit{Ex }$=$ 7.3 $\sim$ 10.4 MeV in 18Ne was measured with the thick target method and several new states as well as previously known states have been observed. In this study, we did not observe strong double proton decay events, compared to a previous study by Fu \textit{et al. }We analyzed single proton decay events using the TOF (Time of Flight) information of the recoiled protons. Consequently, we report the excitation function of 14O(\textit{\textunderscore ; p})17F, when we consider that two channels, which are decaying to the ground and 1st excited states of 17F, are mixed. [Preview Abstract] |
Friday, October 10, 2014 11:15AM - 11:30AM |
FK.00009: Spectroscopy of Low-Lying Proton-Resonances using the $(d,n)$ Reaction in Inverse Kinematics Ingo Wiedenhoever, Lagy T. Baby, Sean Kuvin, Jessica Baker, Jeff Blackmon, Catherine Deibel, Kevin Macon, Dennis Gay, Kayla Colbert, Nathan Quails Studies of rp-process nucleosynthesis in stellar explosions show that establishing the lowest $l=0$ and $l=1$ resonances is the most important step to determine reaction rates in the astrophysical $rp$--process path. In order to establish the $(d,n)$ reaction as a standard technique for the spectroscopy of astrophysical resonances, we have developed a compact setup of low-energy Neutron-detectors, {\sc resoneut} and tested it with the stable beam reaction $\mathrm{^{12}C(d,n)^{13}N}$ in inverse kinematics. At the {\sc resolut} in-flight radioactive beam facility, we have used the new detector system to investigate the $l=0$ and $l=1$ resonance spectrum in $^{18}$Ne and $^{26}$Si. Results from these experiments and the implications on proton-induced nucleosynthesis rates will be discussed. [Preview Abstract] |
Friday, October 10, 2014 11:30AM - 11:45AM |
FK.00010: $^{20}$Ne(p,$\gamma$)$^{22}$Na and $^{22}$Ne(p,$\gamma$)$^{23}$Na Reaction Study with 5U-4 St. Ana Accelerator Stephanie Lyons, Joachim Goerres, Hyo Soon Jung, Dan Robertson, Kiana Setoodehnia, Ed Stech, Michael Wiescher, Antonios Kontos Hydrogen burning can proceed via the NeNa cycle in stars whose stellar temperature is greater than 0.05GK. The NeNa cycle is important for the nucleosynthesis of Ne, Na, and Mg isotopes. Direct capture and the high energy tail of a subthreshold resonance dominate the stellar reaction rate for $^{20}$Ne(p,$\gamma$)$^{21}$Na. The strength of the non-resonant contributions were measured\footnote{C. Rolfs et al., \textbf{Nuclear Physics A}241, 480 (1975)} relative to the resonance at 1.17MeV. Due to conflicting results,\footnote{J. Keinonen et al., \textbf{Phys. Rev. C}15, 579 (1977)} we have remeasured the strength of this resonance relative to the 1.28 MeV resonance in $^{22}$Ne(p,$\gamma$)$^{23}$Na using implanted neon targets. Study of this reaction has continued using the newly commissioned 5U-4 St. Ana Accelerator and re-furbished Rhinoceros Gas Target.\footnote{C. Rolfs et al., \textbf{NIM} 157, 19 (1978)} [Preview Abstract] |
Friday, October 10, 2014 11:45AM - 12:00PM |
FK.00011: Direct measurement of $^{38}$K$(p,\gamma)^{39}$Ca in inverse kinematics Gavin Lotay, Gregory Christian, Devin Burke, Alan Chen, Devin Connolly, Barry Davids, Jennifer Fallis, Ulrike Hager, Dave Hutcheon, Adam Mahl, Alex Rojas, Chris Ruiz, Xuan Sun Sensitivity studies have identified $^{38}$K$(p, \gamma)^{39}$Ca as one of a handful of significant reactions in ONe novae, with the potential to change $^{38}$Ar, $^{39}$K, and $^{40}$Ca abundances in ONe ejecta by factors of $\sim$18, $\sim$17 and $\sim$24, respectively. We have performed the first ever measurement of this reaction using the DRAGON recoil mass separator at TRIUMF. The experiment was performed in inverse kinematics using a beam of radioactive $^{38}$K. To date, this is the most massive projectile ever used in a radiative capture experiment. The astrophysical reaction rate is expected to be dominated by low-$\ell$ resonances inside the Gamow window. Hence we have focused our efforts on the resonances at $E_{\textrm{c.m.}}$ = 386, 515, and 689 keV. In this talk, I will present an overview of the experiment and data analysis and show preliminary resonance strengths (or upper limits) measured at each of the three energies. Finally, I will discuss the astrophysical implications of the measurements as they relate to ONe novae. [Preview Abstract] |
Friday, October 10, 2014 12:00PM - 12:15PM |
FK.00012: Density functional theory of direct neutron capture cross section for the r-process nucleosynthesis Masayuki Matsuo The neutron capture is one of the fundamental nuclear processes relevant to the r-process nucleosynthesis. The direct (radiative) neutron-capture process is expected to dominate over another process via the compound states as the neutron separation energy in many of the r-process nuclei are very low ($S_n \le 2$ MeV). Previous theories often employ single-particle models, but such models hardly describe the correlation, e.g. the pygmy dipole mode. We propose a new microscopic theory of the direct neutron capture, which is based on a re-formulation of the continuum quasiparticle random phase approximation (the linear response theory) for the Skyrme-Bogoliubov energy density functional model. This theory allows us to take into account collective correlations in the capture of low-energy neutron (from 10 keV to 1 MeV) and associated photo-emission. In this presentation, I shall discuss essential ingredients and new facets of this capture theory, and illustrate them by numerical examples. The examples are shown for neutron-rich Sn isotopes with A=134-150, which are expected to line along the r-process path. We shall discuss roles of the neutron pair correlation which becomes important as the neutron separation energy becomes lower. [Preview Abstract] |
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