10,12 Be におけるモノポール遷移

1. 10,12Beにおけるモノポール遷移 Makoto Ito1 and K. Ikeda2 1Department of Pure and Applied Physics, Kansai University 2RIKEN Nishina Center for Accelerator based Science, RIKEN 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. 10,12BeにおけるIsoscalar, Isovector monopole transitions IV. まとめと今後の課題

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

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

4. 10,12Beにおける化学結合構造の形成機構 10Be 12Be 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

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

6. Generalized Two-center Cluster model 12Be=a+a+4N Ionic or atomic a 8He 6He 7He 6He 5He Covalent connection Unified model of covalent, atomic, ionic configurations ... S + + Y = C2 C3 C1 S, Ci: Variationalp.r.m. 0Pi (i=x,y,z) Coupled channels of atomic orbits Absorbing BC Scattering BC Tr. density <Yf | r| Yi> Resonance width PTP113 (05) 12Be(01+)→12Be(0ex+) Monopole transition a+8He Cross sections PRC78(R) (08) ｰi W(R)

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

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

9. IsoscalarvsIsovector excitations in 12Be There are clear enhancements in Isoscalar⇒ Cluster excitation (03+) Isovector⇒ Neutron excitations (02+, 05+) Monopole strength are comparable to a single particle strength !

10. EWSR fraction of the isoscalar monopole transitions in 12Be Mono. Tr. 01+ 02+ 03+ 04+ 05+ 06+ (0pR)(0pL)(s+)2 (p-)2 (s+)2 (p-)2 (p-)2 a+8He 6He+6He 5He+7He 2.4% 21.6% 1.8% 4.8% 8.0% ～26% Exp. By Chinese Group, ～12% Analog to Hoyle state in 12C (23%) Total～40%

11. ( α+6He(2+) ) + ( α+6Heg.s. ) Monopole tr. in 10Be Isoscalar transitions Strength (Arb. Unit.) Transition to ionic state Is strongly enhanced. Ex. ( MeV ) (p1/2-)2 (p3/2+)2 Isovector transitions Strength (Arb. Unit.) Transition to MO states Is relatively enhanced. Ex. ( MeV )

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