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Studies for a -induced astrophysical reactions at CRIB

Studies for a -induced astrophysical reactions at CRIB. Introduction of CRIB facility Method…Thick target method in inverse kinematics Experiments… 7 Li+ a / 7 Be+ a Summary. Hidetoshi Yamaguchi ( 山口英斉 ) T. Hashimoto, S. Hayakawa, D. Kahl, and S. Kubono

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Studies for a -induced astrophysical reactions at CRIB

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  1. Studies for a-induced astrophysical reactions at CRIB • Introduction of CRIBfacility • Method…Thick target method in inverse kinematics • Experiments…7Li+a / 7Be+a • Summary Hidetoshi Yamaguchi (山口英斉) T. Hashimoto, S. Hayakawa, D. Kahl, and S. Kubono Center for Nuclear Study, Univ. of Tokyo

  2. CRIB Introduction • CNS Radio-IsotopeBeam separator, operated by CNS (Univ. of Tokyo), located at RIBF (RIKEN Nishina Center). • Low-energy(<10MeV/u) RI beams by in-flight method. • Primary beam from K=70 AVF cyclotron. • Momentum (Magnetic rigidity) separation by “double achromatic” system, and velocity separation by a Wien filter. • Orbit radius: 90 cm, solid angle: 5.6 msr, momentum resolution: 1/850. Aizu Symposium

  3. Low-Energy RI beam Productions at CRIB Direct reactions such as (p,n), (d,p)and(3He,n)in inverse kinematics are mainly used for the production….large cross section Many RI beams have been produced at CRIB: typically 104-106pps RI beam at CRIB / Stable nuclei Aizu Symposium

  4. CRIB in RIBF • Iocated at RIBF (RIKEN Nishina Center) • Ion source / AVF/ CRIB…development under CNS-RIKEN collaboration (joint venture). AVF Aizu Symposium

  5. Intense secondary beam production using cryogenic gas target • H2 gas target of 760 Torr and 80 mm-long worked at 85Kstablyfor a7Li2+beam of 1.3 pμA. (which deposits heat of 7.4W). • Secondary beam: 7Be4+at 4.0 MeV/u, purity 75% (without degrader/ WF). 2x108 pps was achieved. H. Yamaguchi et al., NIMA (2008) Aizu Symposium

  6. International collaborations at CRIB • CRIB experiments performed in 2007-2009, by collaborated members of CNS and other institutes: Tohoku 7Be lifetime Aizu Symposium

  7. The “thick target” method • Inverse kinematics with a thick target: • Inverse kinematics… measurement is possible for short-lived RI which cannot be used as the target. • Simultaneous measurement of the excitation function for certain energy range.(Small systematic error.) • The beam can be stopped in the target…measurement at qcm=180 degrees (where the potential scattering is minimal) is possible. Resonance scattering Aizu Symposium

  8. Development of active target “GEM-MSTPC” Y position …drift time in the gas chamber • 10 cm X, Z positions…GEM+ ”Backgammon” pad Multiple-Sampling and Tracking Proportional Chamber with Gas Electron Multiplier • Acts as a gas target and a detector (TPC) at the same time. • Measurement of 3-dimensional trajectories of the particles at reaction ⇒ Reaction position can be measured directly! • Constructed at CNS, used for measurements of 18Ne(a,p) and 30S(a,p) in this year. Aizu Symposium

  9. Proton elastic resonant scattering with the thick target method Study the resonance states formed by a nucleus and a proton. Related to hydrogen burning… (p,g) reaction Recent results at CRIB : • 13N+p; T. Teranishi et al., Phys. Lett. B (2007). • 7Be+p;H. Yamaguchi et al., Phys. Lett. B (2009). • 21Na+p, 22Mg+p; J.J. He et al, Phys. Rev. C (2007) and Phys. Rev. C (2009). • 25Al+p; with McMaster Univ. group (A. Chen et al.). • 8B+p; with Kyushu Univ. (T. Teranishi). • 26Si+p; with Chung-Ang Univ. (J.Y. Moon et al.). Aizu Symposium

  10. Studies on alpha-induced reactions with thick helium target Heavy-ion(RI) beam + thick helium target • Alpha particle channel… Alpha elastic resonance scattering…related to (a, g) reactions. • Proton channel….Direct measurement of (a, p) reactions. Interests at CRIB: • 7Li+α; measured in 2009 (mirror of 7Be+α.) • 7Be+α; measured in Apr, 2010. • 14O+α; Notani et al. (2004), also measured in 2008. Break-out from CNO. • 21Na+α; measured in 2008. 22Ne enrichment, galactic g-ray. • 11C+α ; measured in 2009, break out from hot-pp. • 18Ne+α;measured in 2010 (active target), break out from CNO. • 30S+α ; measured in 2010 (active target), XRB. Aizu Symposium

  11. 7Li+a experiment; Purpose Stable-stable nuclei elastic scattering, however, Feasibility test of the 7Be+a experiment. New measurement of the excitation functions of 7Li+a elastic/inelastic scatterings for Ex=10-13 MeV at 180 deg in c.m. angle, using thick target method in inverse kinematics. Better determination for the resonant widths than the previous data [Cusson et al. Nucl. Phys (1966)]. Alpha-cluster structure of 11B (α+α+t).

  12. Exotic cluster structure • 2a+t / 2a+3He cluster state in 11B/11C, similar to the dilute cluster structure in 12C: Y.K. En’yo (2007), T. Kawabata et al. (2007). ⇒ A rotational band is expected in higher excited energy region. • Near the 2a+3He(t) threshold…developedcluster-condensed state with Jp=1/2+ is expected (T. Yamada et al.), but not found yet. • a width ⇔ spectroscopic factor of a-cluster configuration ⇔ evidence of cluster structure Aizu Symposium

  13. Astrophysical interests • Related to 7Li(a,g), directly measured only at resonances: • Paul et al., PR 164 (1967) 1332. • Hardie et al., PRC, 29 (1984)1199. • T<< 1 GK; 7Li(p,a)4He (p-p chain).7Be(a,g)11C(b+n)11B is more important. • High temperature: triple-a should be fast, but may play important role in some environments: • 11B/7Li ratio in supernovae…the n-process 11B is produced mainly through the 7Li(a,g)11B reaction.(Some are via 12C(n,n’p) and 12C (n,e+n).) The ratio of 11B/7Lican be sensitive to the neutrino mixing parameter, q13. (T. Yoshida et al., PRL2006.) • Boron production in inhomogeneous big-bang nucleosynthesis. _ Aizu Symposium

  14. 7Li+a elastic scattering exc. function • Cusson et al,. 1966 • Structure consistent with previous measurements (Cusson et al., elastic scat. at qCM=159°and Soic et al, break up) was successfully observed. Aizu Symposium

  15. 7Li+alpha result • Alpha resonances were clearly observed, widths (Ga) were determined with a better precision. T=3/2? 1/2? Is Jp really 9/2-? New! Aizu Symposium

  16. 7Be+a study • 7Be(a,g)11C …reaction in the hot p-p chain Important at high temperature (Wiesher et al.,1986) • Supermassive objects, pop-III stars (Fuller et al., Mitalas), Novae (Hernanz et al.), Big bang nucleosynthesis (Andouze and Reeves),… • Reaction rate … resonances of 11C must be studied. Wiesher et al.(1986) Aizu Symposium

  17. 7Be+a online spectrum • Measurement performed in April, 2010. • Several peaks were observed in the energy spectrum…alpha resonances Aizu Symposium

  18. Summary • CRIB is a facility which provides low-energy RI beams with good intensity and purity. • Developments: cryogenic gas target for intense RI beam, active target (GEM-MSTPC) etc. • Experiments based on interests of nuclear astrophysics and nuclear structure have been performed at CRIB, forming international collaborations. Some of the recent experimental results are presented: • 7Li+a(11B structure, Boron production in high-T environment); Strong alpha resonances were observed. New information on the alpha widths and other resonance parameters. • 7Be+a(11C structure, hot p-p chain); measured in April. Aizu Symposium

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