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Investigation of Stellar 26 Si(p, g ) 27 P Reaction via Coulomb Dissociation

This study investigates the 26Si(p,g)27P reaction, which is important for nucleosynthesis models. The decay of 26Al to 26Mg is observed in the interstellar medium. Experimental data on the reaction and resonances in 26Si are needed. The astrophysical reaction rate and competition with 26Si beta-decay are also studied.

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Investigation of Stellar 26 Si(p, g ) 27 P Reaction via Coulomb Dissociation

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  1. Investigation of Stellar 26Si(p,g)27P Reaction via Coulomb Dissociation Yasuhiro Togano Rikkyo University

  2. 26Al: constraint for nucleosynthesis models • Ground state of 26Al decays to 26Mg with 1.8 MeV g-line. • This g-ray is observed in the interstellar medium. Nuclear database around 26Al is needed including the unstable nuclei

  3. 26Si(p,g)27P reaction • Proton capture reaction of the unstable nuclei26Si. • One of the reactions which occur in the rp-process. • 26Si predominantly b decays to the isomeric state of 26Al (26Alm). • 26Al in high temperature (T9~0.4): thermal equilibrium between isomeric state and ground state. 26Si destruction by proton capture is important to estimate the amount of 26Alm and the effect of equilibrium.

  4. Resonances in 26Si(p,g)27P reaction • Level structure at low energy was studied via transfer reactions. • 28Si(7Li,8He)27P, 32S(3He,8Li)27P • No experimental information on Gg. (p,g) cross section Coulomb Dissociation 772 keV 340 keV

  5. Coulomb dissociation • Inverse reaction of (p,g) reactions : (g,p) • Large cross section : 104 ~ 105 times larger than the (p,g) • Higher beam energies : thicker target available • One can determine Gg values from CD cross sections Photodisintegration by virtual photons

  6. Production of 27P beam: RIPS • 36Ar 115 MeV/u • 462 mg/cm2 Be target Fragmentation • 27P 57 MeV/u • Purity: ~1% • Intensity: ~2.8kcps Experimental Area

  7. Setup for 27P dissociation • Lead target: 125 mg/cm2 • Relative energy between 26Si nuclei and protons were measured • Momentum vectors of products 278cm F2 F3 48.2cm

  8. Relative energy between 26Si and proton • Relative energy = collision energy in (p,g) reaction

  9. Gamma decay width of the states • 1st excited state • g.s.(1/2+) 1st (3/2+) • Gg = Gg(E2) + Gg(M1) • GgC.D. = Gg(E2) = (9.3 ± 1.7) × 10-5 eV • Gg(M1) = Gg(E2) × d2 d2: E2/M1 mixing ratio • d2: based on shell model: ambiguity = 60% • Gg(1st)=(4.6±2.7)×10-3eV • 2nd , 3rd excited states • g.s.(1/2+) 2nd, 3rd(5/2+) • GgC.D. = Gg • Gg(2nd)=(2.7 ± 0.5) × 10-4eV • Gg(3rd)=(3.4 ± 0.9) × 10-4eV E2/M1 E2

  10. Astrophysical reaction rate for 26Si(p,g)27P Resonant capture through 1st excited state in 27P is dominant at T > 0.08 GK

  11. Competition of 26Si(p,g) and 26Si b-decay Novae Heavy : 26Si(p,g)27P reaction dominates at around peak temperature Xp=0.5 J. Jose et al. ApJ 520, 347 C. Iliadis et al. ApJ Supl. 142, 105

  12. Reaction flow around 26Si and its effect on 26Al • 25Al(p,g)26Si: No experimental determination of cross section. • Estimate by Parpottas et al. (PRC 70, 065805) ×

  13. Summary • We have performed an experiment to study the 26Si(p,g)27P reaction by Coulomb dissociation method. • The g-decay width of three states below 1.5 MeV were determined. • Astrophysical reaction rate of the 26Si(p,g)27P was estimated using experimental results. • Resonant capture via the first excited state is the dominant process in most of the stellar environment. • Most of 26Si is destructed by the proton capture and 26Alm is mainly synthesized by 25Mg(p,g)26Alm reaction.

  14. Collaborators list T. Gomi, T. Motobayashi, Y. Ando, N. Aoi, H. Baba, K. Demichi, Z. Elekes, N. Fukuda, Zs. Fulop, U. Futakami, H. Hasegawa, Y. Higurashi, K. Ieki, N. Imai, M. Ishihara, K. Ishikawa, N. Iwasa, H. Iwasaki, S. Kannno, Y.Kondo, T. Kubo, S. Kubono, M. Kunibu, K. Kurita, Y. U. Matsuyama, S. Michimasa, T. Minemura, M. Miura, H. Murakami, T. Nakamura, M. Notani, S. Ota, A. Saito, H. Sakurai, M. Serata, S. Shimoura, T. Sugimoto, E. Takeshita, S. Takeuchi, K. Ue, K. Yamada, Y. Yanagisawa, K. Yoneda, and A. Yoshida Rikkyo Univ., RIKEN, ATOMKI, TITECH, Tohoku Univ. Univ. of Tokyo, CNS, Kyoto Univ.

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