10,12 Be におけるモノポール遷移 Makoto Ito 1 and K. Ikeda 2 1 Department of Pure and Applied Physics, Kansai University I. 導入：研究の大域的目的とこれまでの研究成果 II. 今回の目的：モノポール遷移への興味 III. 10,12 Be における Isoscalar, Isovector monopole transitions IV. まとめと今後の課題 2 RIKEN Nishina Center for Accelerator based Science, RIKEN

Global subject: Unified studies of structure and reaction in N-rich systems ( N,Z ) : Two Dimensions Ex. energy Structural Change Low-lying Molecular Orbital :  ― 、  ＋ ‥ Unbound Nuclear Systems Slow RI beam Decays in Continuum Is Threshold Rule valid ?? N

Be 同位体の結果：多様な化学結合様構造 8 Be 10 Be 12 Be 14 Be 16 Be 発達した α クラスター 殻模型に近い状態  -  間の相対 運動が励起する イオン構造 y He x He 中性子励起 α + α 共有結合

10,12 Be における化学結合構造の形成機構 10 Be 12 Be α クラスターの相対運動＋中性子の一粒子運度が励起して多様な結合状態が発現 基底状態から励起状態への動的励起に何か面白い現象はあるか ? ⇒ 単極遷移

Interests in monopole We investigate the competition between the isoscalar transitions and the isovector transitions in 10,12 Be. Isoscalar Development of cluster structure ⇒ Enhancement of Isoscalar Monopole Transition Variety of clusters in a neutron-rich system 12 Be =  +  + 4N : Various clusters appear with a variation of excitation energy (  - ) 2 (  + ) 2 Contents of Today’s report 8 He 6 He 7 He 5 He G.S. Excited 0 + states (Unbound) Are there characteristic features in Isoscalar vs Isovector ? 12 C=3α, 16 O=α+ 12 C, 4α, T. Yamada et al. クラスター相対 運動の励起 Isovector

Generalized Two-center Cluster model Unified model of covalent, atomic, ionic configurations C1 C2C3  0Pi (i=x,y,z) Coupled channels of atomic orbits Covalent  8 He Resonance width PTP113 (05)  + 8 He Cross sections PRC78(R) (08) 12 Be=  +  +4N ｰ i W(R) S, Ci : Variational p.r.m. S connection Absorbing BCScattering BCTr. density 12 Be(0 1 + )  → 12 Be(0 ex + ) Monopole transition 7 He 5 He 6 He Ionic or atomic

Monopole operators 1. Neutrons and Protons monopole operators 2. Isoscalar and Isovector monopole operators Isoscalar: Isovector:

Monopole transition in 12 Be ： Isoscalar vs Isovector excitations There is a possibility to identify the excitation degrees of freedom in the excitation by monopole fields. 1. Isoscalar monopole transition → responsible to a cluster excitation 2. Isovector monopole transition → sensitive to neutron excitations Enhanced MO excitations α － α part is vanished !

Isoscalar vs Isovector excitations in 12 Be Isoscalar ⇒ Cluster excitation (0 3 + ) Isovector ⇒ Neutron excitations (0 2 +, ) There are clear enhancements in Monopole strength are comparable to a single particle strength !

EWSR fraction of the isoscalar monopole transitions in 12 Be Mono. Tr. (  - ) 2 (  + ) (  - ) 2 (  - ) 2 (0p R )(0p L ) (  + ) 2  + 8 He 6 He+ 6 He 5 He+ 7 He 2.4%21.6%1.8%4.8%8.0% Analog to Hoyle state in 12 C (23%) ～ 26% Exp. By Chinese Group, ～ 12% Total ～ 40%

Monopole tr. in 10 Be ( α+ 6 He(2 + ) ) + ( α+ 6 He g.s. ) (  1/2 - ) 2 (  3/2 + ) 2 Ex. ( MeV ) Strength (Arb. Unit.) Isoscalar transitions Isovector transitions Transition to ionic state Is strongly enhanced. Transition to MO states Is relatively enhanced.

Present studies Results of the studies We have studied the chemical-bonding-structure in Be isotopes and the monopole transition from the ground state to the excited states. 1. Chemical-bonding-structures in Be isotopes 2. Monopole transitions in 10,12 Be Feature studies We are now studying 18 O=  + 12 C+2N. These properties will appear systematically in other light neutron excess system. ⇒ Covalent, ionic and atomic structures appears in excited states M. Ito et al., PRC83(11), PRC84(11), PRC85(12),RRC85(12) ⇒ Excited states are generated by the excitation of  -  or the excess neutrons ⇒ Isoscalar monopole is strongly enhanced for the  -  excitation ⇒ Isovector monopole is responsible the excess-neutrons’ excitations