Stellar Electron-Capture Rates Accessed via the ( t , 3 He+ ) - PowerPoint PPT Presentation

Stellar Electron-Capture Rates Accessed via the ( t , 3 He+ γ ) Reactions Shumpei Noji (NSCL/MSU → ) RCNP/Osaka GRETINA at NSCL/MSU

Contents week ending P H Y S I C A L R E V I E W L E T T E R S PRL 112, 252501 (2014) 27 JUNE 2014 1. Stellar electron captures 
 β þ Gamow-Teller Transition Strengths from 46 Ti and Stellar Electron-Capture Rates & experimental approach S. Noji, 1,2,* R. G. T. Zegers, 1,2,3 Sam M. Austin, 1,2,3 T. Baugher, 1,3 D. Bazin, 1 B. A. Brown, 1,3 C. M. Campbell, 4 A. L. Cole, 5 H. J. Doster, 1,3 A. Gade, 1,3 C. J. Guess, 6,7 S. Gupta, 8 G. W. Hitt, 9 C. Langer, 1,2 S. Lipschutz, 1,3 E. Lunderberg, 1,3 R. Meharchand, 10 Z. Meisel, 1,2,3 G. Perdikakis, 11,1 J. Pereira, 1 F. Recchia, 1 H. Schatz, 1,2,3 M. Scott, 1,3 S. R. Stroberg, 1,3 2. ( t , 3 He+ γ ) experiments C. Sullivan, 1,2,3 L. Valdez, 1 C. Walz, 1 D. Weisshaar, 1 S. J. Williams, 1 and K. Wimmer 11,1 1 National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA 2 Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA 3 Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA 3. Gamow-Teller strengths 
 4 Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 5 Physics Department, Kalamazoo College, Kalamazoo, Michigan 49006, USA & electron-capture rates 6 Department of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, Massachusetts 01854, USA 7 Department of Physics and Astronomy, Rowan University, Glassboro, New Jersey 08028, USA 8 Indian Institute of Technology Ropar, Nangal Road, Rupnagar, Punjab 140001, India 9 Department of Applied Mathematics and Sciences, Khalifa University of Science, Technology, and Research, P.O. Box 127788 Abu Dhabi, UAE 10 Neutron and Nuclear Science Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA 11 Department of Physics, Central Michigan University, Mt. Pleasant, Michigan 48859, USA (Received 5 April 2014; published 25 June 2014) The Gamow-Teller strength in the β þ direction to 46 Sc was extracted via the 46 Ti ð t; 3 He þ γ Þ reaction at 115 MeV =u . The γ -ray coincidences served to precisely measure the very weak Gamow-Teller transition to a final state at 991 keV. Although this transition is weak, it is crucial for accurately estimating electron- PHYSICAL REVIEW C 92 , 024312 (2015) capture rates in astrophysical scenarios with relatively low stellar densities and temperatures, such as presupernova stellar evolution. Shell-model calculations with different effective interactions in the pf shell- Gamow-Teller transitions to 45 Ca via the 45 Sc( t , 3 He + γ ) reaction at 115 MeV / u and its application model space do not reproduce the experimental Gamow-Teller strengths, which is likely due to sd -shell to stellar electron-capture rates admixtures. Calculations in the quasiparticle random phase approximation that are often used in astrophysical simulations also fail to reproduce the experimental Gamow-Teller strength distribution, S. Noji, 1,2,* R. G. T. Zegers, 1,2,3 Sam M. Austin, 1,2 T. Baugher, 1,3, † D. Bazin, 1 B. A. Brown, 1,2,3 C. M. Campbell, 4 leading to strongly overestimated electron-capture rates. Because reliable theoretical predictions of A. L. Cole, 2,5 H. J. Doster, 1,3 A. Gade, 1,3 C. J. Guess, 6, ‡ S. Gupta, 7 G. W. Hitt, 8 C. Langer, 1,2,§ S. Lipschutz, 1,2,3 Gamow-Teller strengths are important for providing astrophysical electron-capture reaction rates for a E. Lunderberg, 1,3 R. Meharchand, 9, ∥ Z. Meisel, 1,2,3 G. Perdikakis, 1,2,10 J. Pereira, 1,2 F. Recchia, 1,¶ H. Schatz, 1,2,3 M. Scott, 1,3 broad set of nuclei in the lower pf shell, we conclude that further theoretical improvements are required to S. R. Stroberg, 1,3,# C. Sullivan, 1,2,3 L. Valdez, 11 C. Walz, 1,** D. Weisshaar, 1 S. J. Williams, 1 and K. Wimmer 1,10, †† match astrophysical needs. 1 National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA DOI: 10.1103/PhysRevLett.112.252501 PACS numbers: 23.40.-s, 25.55.Kr, 26.30.Jk, 27.40.+z 2 Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA 3 Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA 4 Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA Introduction. — Electron-capture (EC) rates on nuclei are strengths for nuclei in the lower pf shell [with the neutron 5 Physics Department, Kalamazoo College, Kalamazoo, Michigan 49006, USA essential ingredients for the modeling of core-collapse and ( N ) and proton number ( Z ) just exceeding the magic number 6 Department of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, Massachusetts 01854, USA thermonuclear supernovæ (SNe) [1]. In addition, EC rates 20]. It is shown that leading configuration-interaction 7 Indian Institute of Technology Ropar, Nangal Road, Rupnagar, Punjab 140001, India are important for the description of crustal heating [2] and models in which the model space is truncated to excitations 8 Department of Applied Mathematics and Sciences, Khalifa University of Science, Technology, and Research, cooling [3] processes in neutron stars. The estimation of EC within the pf shell fail to reproduce the data. Calculations P.O. Box 127788 Abu Dhabi, UAE rates requires detailed knowledge of Gamow-Teller (GT) 9 Neutron and Nuclear Science Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA in the quasiparticle random phase approximation (QRPA), transition strengths [ B ð GT Þ ] in the β þ direction, associated 10 Department of Physics, Central Michigan University, Mt. Pleasant, Michigan 48859, USA which are also frequently used for astrophysical purposes, SN, et al., PRL 112 , 252501 (2014) with the transfer of spin ( Δ S ¼ 1 ), isospin ( Δ T ¼ 1 ), and 11 Orange High School, Orange, New Jersey 07050, USA fail to reproduce the data as well. SN, et al., PRC 92 , 024312 (2015) no orbital angular momentum ( Δ L ¼ 0 ). ECs on a large GT strengths can be measured in β -decay experiments, (Received 19 March 2015; published 17 August 2015) number of nuclei, primarily with 40 ≤ A ≤ 120 , play a but they only provide access to a limited Q -value window.

Electron Captures in Supernovæ ‣ Stellar electron captures (EC) cf.) Terrestrial electron capture • Takes place in stellar interiors: high T A A Z X Z − 1 Y ν e e − free electrons in hot plasma bound (orbital) electrons ‣ Important process for supernovæ (SNe) • Neutronizes stellar core, decreases electron abundance • Reduces electron degeneracy pressure (which supports stars) → Leads to explosion Stellar EC is a key to supernova evolution.

Stellar Electron Captures E x ( A Y) ‣ Stellar electron captures (EC) E e (MeV) 10 ρ Y e = 10 9 g / cm 3 • Dominated by Gamow-Teller transitions GTGR T = 10 × 10 9 K - Δ L = 0 , Δ S = 1 , Δ T = 1 • Capture of free electrons in hot plasma k B T - Can get excited to high E x states incl. GTGR 5 U F - Electrons: Fermi-Dirac distribution A Z − 1 Y • Thermal ensemble of initial states - ECs take place from excited states A Z X 0 • Many nuclei play an important role - Majority are unstable nuclei Impossible to measure even a sizable fraction of cases • Accurate theory that constrains key model parameters • Experimental information for most crucial cases (importantly contributing nuclei) 
 to guide and test development of theory

Sensitivity Study: Importance for SN Collapse ‣ Time evolution of the electron fraction in CCSNe center arXiv:1508.07348v1, ApJ Chris Sullivan (NSCL) t - t b (msec) Evan O’Connor (NCSU) -100 -50-40 -30 -20 -10 Remco G. T. Zegers (NSCL) total 10 1 Thomas Grubb (NSCL) Sam M. Austin (NSCL) l l e h s g d s r e w 10 0 o l ~ 10 − 1 ~ sd + pf shells Most important are 10 − 2 n -rich pf & sdg -shell nuclei. ~upper sdg + h shell 10 − 3 ) 1 - c e s − 4 10 ( e Y 10 − 5 Sensitivity of late SN evolution to electron-capture rates 10 − 6 ~ s + p shells 10 − 7 Identify most critical experiments 
 10 − 8 Total 5< A ≤ 25 25< A ≤ 65 65< A ≤ 105 to be performed in the future 105< A ≤ 145 145< A ≤ 185 185< A ≤ 225 10 − 9 0.42 0.40 0.38 0.36 0.34 0.32 0.30 0.28 Y e


 
 
 
 Experimental Approach to Stellar Electron Captures E x ( A Y) E x ( A Y) ‣ β decays • Strength B (GT) from life time GTGR GTGR • Q -value restrictions ‣ Charge-exchange reactions • Accessible to high E x states CE • Reliable B (GT) extraction from cross section 
 A A Z − 1 Y Z − 1 Y → Proportionality 
 β decay β decay A A Z X Z X σ ∆ L =0 (0 ◦ ) ≈ ˆ σ GT B (GT) 50 unit cross section: calibrated for ( t , 3 He) extrapolated σ GT = 109 / A 0.65 ˆ 20 T. N. Taddeucci et al., Nucl. Phys. A469 (1987) 125 
 σ GT ( A ) (mb / sr) G. Perdikakis et al., Phys. Rev. C 83, 054614 (2011) 10 5 ˆ σ exp ( t , 3 He) at 115 A MeV ˆ CE reactions on important pf -shell nuclei 
 2 σ exp ( 3 He, t ) at 140 A MeV ˆ can be a powerful tool to study ECs σ exp ( 3 He, t ) at 140 A MeV Fit to ˆ 1 1 2 5 10 20 50 100200 A