1. Coulomb breakup of 22 C and 31 Ne N. Kobayashi Department of Physics, Tokyo Institute of Technology

2. T. Nakamura, Y. Kondo, Y. Satou, S. Deguchi, Y. Kawada, K. N. Tanaka, N. Tanaka RIKEN Nishina Center for Accelerator-Based Science N. Aoi, H. Baba, N. Fukuda, N. Inabe, M. Ishihara, D. Kameda, T. Kubo, K. Kusaka, T. Motobayashi, T. Ohnishi, M. Ohtake, H. Otsu, H. Sakurai, M. Takechi, H. Takeda, E. Takeshita, S. Takeuchi, K. Tanaka, Y. Togano, Y. Yanagisawa, K. Yoneda, A. Yoshida, K. Yoshida LPC-ENSICAEN, IN2P3-CNRS et Université de Caen, France J. Gibelin, N. A. Orr International Atomic Energy Agency, NAPC/Nuclear Data Section, Austria A. Mengoni CNS, University of Tokyo A. Saito, S. Shimoura Department of Physics, University of Tokyo T. Sumikama Collaborators Halo Structure of the Island of Inversion Nucleus 31 Ne T. Nakamura, N. Kobayashi, Y. Kondo, Y. Satou et al. Phys. Rev. Lett. 103, 262501 (2009).

3. Outline Outline: Introduction > Exp. Setup > Analysis > Results > Discussion > Summary Introduction Halo nuclei Coulomb breakup / Inclusive Coulomb breakup E1 Cross section of halo nuclei Experimental setup @ RIBF Targets & detectors @ BigRIPS/ZDS Analysis Particle Identification Beam intensity Results Inclusive Coulomb breakup cross section σ(E1) of 20 C, 22 C, 31 Ne Discussion configuration of 31 Ne Summary

4. Interesting topics ・ neutron halo structure ( 22 C, 31 Ne) @ drip line ・ modification of magic number ・ island of inversion ( 31 Ne) Introduction Halo nuclei Z N Stable nuclei Unstable nuclei Magic number Halo nuclei Halo candidate nuclei in this experiment n 18 C 31 Ne S 1n =0.29(1.64) MeV 22 C S 2n =419(935) keV Island of inversion 19 C: heaviest halo nucleus known so far 19 C S 1n =577(94) keV 20 C S 1n =2.93(26) MeV

5. Introduction Coulomb breakup -- Method of extracting E1 strength 22 C Virtual photon 22 C * n 20 C n n n Pb E x (MeV) N E1 (E x ) E1 Virtual photon number n n 20 C Invariant mass method Exclusive Coulomb breakup measuredextracted Required beam intensity > about 100 cps measured Feasible even by a few cps Inclusive Coulomb breakup (present exp.) measured

6. ExEx 10 ～ 20MeV ～ 1MeV Introduction σ （ E1 ） of halo nuclei p n GDR (ordinary nuclei) soft E1 excitation (halo nuclei) halo nuclei σ(E1) is large ( > 0.5 barn) ordinary nuclei σ(E1) is small ( ~ 0.1 barn) T.Kobayashi et al., PLB 232, 51 (1989) 10 B n 18 C E1 cross section Large Small Signature of halo structure can be obtained

7. RI Beam Factory @ RIKEN New facility RIBF (RI Beam Factory) Completion in 2007 Former facility SRC Primary Beam: 48 Ca 345 MeV/u, 60 pnA BigRIPS ZDS

8. Experimental setup Secondary Beam 22 C 240 MeV/u ( 20 C, 19 C) 31 Ne 234 MeV/u TOF Primary Beam 48 Ca 60 pnA 345 MeV/u Bρ ΔE Bρ TOF ZDS Production Target @ F0 Be 3.62 g/cm 2 ( 22 C) 2.76 g/cm 2 ( 31 Ne) BigRIPS ΔE Reaction Target @ F8 Pb 6.74 g/cm 2 ( 22 C) 3.37 g/cm 2 ( 31 Ne) C 4.02 g/cm 2 ( 22 C) 2.54 g/cm 2 ( 31 Ne) Fragments 20 C 30 Ne

9. Particle identification Z A/Z Z 31 Ne Z A/Z Reaction Target Pb / C Particle ID @ BigRIPS Particle ID @ ZDS 30 Ne Coulomb breakup 20 C ~ 80 counts/s @ RIBF 22 C ~ 6 counts/s @ RIBF 31 Ne ~ 5 counts/s @RIBF c.f. 31 Ne ~ 4 counts/d @ RIPS H.Sakurai et al.,PRC54,2802R(1996) This experiment became possible for the first time by RIBF 20 C ~ 80 counts/s @ RIBF 22 C ~ 6 counts/s @ RIBF 31 Ne ~ 5 counts/s @RIBF ×10 5 31 Ne ~ 4 counts/d @ RIPS H.Sakurai et al.,PRC54,2802R(1996) This experiment became possible for the first time by RIBF BigRIPS ZDS Reaction: 31 Ne + Pb (3.37 g/cm 2 ) → 30 Ne 31 Ne, 30 Ne are clearly separated from other nuclei

10. Energyσ(Pb) (barn) σ(C) (barn) σ(E1) (barn) 22 C -> 20 C240 MeV/u1.46(5)0.21(7)0.92(18) 31 Ne -> 30 Ne234 MeV/u1.07(1) 0.11(1)0.78(13) 19 C -> 18 C242 MeV/u0.917(2)0.128(3)0.58(2) Results Established Halo 19 C Expected value from known B(E1) σ(E1)~0.6 barn halo structure Energyσ(Pb) (barn) σ(C) (barn) σ(E1) (barn) 20 C -> 19 C241 MeV/u0.23(2)0.048(5)0.10(2) 22 C -> 20 C240 MeV/u1.46(5)0.21(7)0.92(18) 31 Ne -> 30 Ne234 MeV/u1.07(1) 0.11(1)0.78(13) 19 C -> 18 C242 MeV/u0.917(2)0.128(3)0.58(2) E1 σ(E1) = σ(Pb) – Γσ(C) Γ = R(Pb)/R(C) ~ 2.2 halo

11. Energyσ(Pb) (barn) σ(C) (barn) σ(E1) (barn) 22 C -> 20 C240 MeV/u1.46(5)0.21(7)0.92(18) 31 Ne -> 30 Ne234 MeV/u1.07(1) 0.11(1)0.78(13) 19 C -> 18 C242 MeV/u0.917(2)0.128(3)0.58(2) Configuration of 31 Ne Energyσ(Pb) (barn) σ(C) (barn) σ(E1) (barn) 20 C -> 19 C241 MeV/u0.23(2)0.048(5)0.10(2) 22 C -> 20 C240 MeV/u1.46(5)0.21(7)0.92(18) 31 Ne -> 30 Ne234 MeV/u1.07(1) 0.11(1)0.78(13) 19 C -> 18 C242 MeV/u0.917(2)0.128(3)0.58(2) Measured σ -1n (E1) = 540(70) barn Channel: 31 Ne → 30 Ne Low-l configuration (2p 3/2, 2s 1/2 ) is supported

12. Momentum distribution of 30 Ne fragment Low-l (2p 3/2 ) is supported. 3p-2h intruder configuration High-l (1f 7/2 ) is excluded. (island of inversion) Red lines are calculated by CSC_GM based on Glauber model. Reaction: 31 Ne + C (2.54 g/cm 2 ) → 30 Ne B. Abu-Ibrahim et al., Comp. Phys. Comm. 151, 369 (2003) Resolution(σ) ~ 22 MeV/c Γ (FWHM) ~ MeV/c

13. Summary The signature of halo structure for 22 C and 31 Ne is obtained Low-l configuration is dominant in 31 Ne g.s. Inclusive Coulomb breakup cross section of 22 C and 31 Ne was measured for the first time at RIBF Outlook γ-ray spectrum & momentum distribution → Configuration of 22 C g.s & 31 Ne g.s Halo Structure of the Island of Inversion Nucleus 31 Ne T. Nakamura, N. Kobayashi, Y. Kondo, Y. Satou et al. Phys. Rev. Lett. 103, 262501 (2009).

14. Thank you.