Be同位体におけるモノポール励起

10,12Beにおけるモノポール遷移
Makoto Ito1 and K. Ikeda2
1Department
2RIKEN
of Pure and Applied Physics, Kansai University
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
Global subject: Unified studies of structure and reaction in N-rich systems
Low-lying
Molecular Orbital :
p ―、s＋‥
Unbound Nuclear Systems
Ex. energy
Slow RI beam
Is Threshold
Rule valid ??
Decays in
Continuum
Structural
Change
N
( N,Z ) : Two Dimensions
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
中性子励起
殻模型に近い状態
共有結合
a-a 間の相対
運動が励起する
xHe
yHe
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
12C=3α, 16O=α+12C,
Interests in monopole
4α, T. Yamada et al.
Development of cluster structure ⇒ Enhancement of Isoscalar Monopole Transition
M IS   G.S .
A
r
i 1
i
2

Cluster  G.S . Arel
(2 ) Cluster
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
8He
G.S.
(p-)2 (s+)2
6He
6He
5He
7He
Isoscalar
Isovector
Excited 0+ states (Unbound)
Are there characteristic features in Isoscalar vs Isovector ?
Contents of Today’s report
We investigate the competition between the isoscalar transitions
and the isovector transitions in 10,12Be.
Generalized Two-center Cluster model
12Be=a+a+4N
Ionic or atomic
a
Covalent
8He
6He
6He
5He
7He
connection
Unified model of covalent, atomic, ionic configurations
...
S
Y
C1
+
C2
+
C3
0Pi (i=x,y,z) Coupled channels of atomic orbits
Absorbing BC
S, Ci : Variational p.r.m.
Scattering BC
Tr. density
<Yf | r| Yi>
Resonance width
PTP113 (05)
ｰi W(R)
a+8He Cross sections
PRC78(R) (08)
→12Be(0ex+)
Monopole transition
12Be(0 +)
1
Monopole operators
1. Neutrons and Protons monopole operators
Mˆ ( N ) 
A

i 1
2 1   3i 
r
i
2
Mˆ ( P ) 
A
r
i 1
2
1   3i 
i
2. Isoscalar and Isovector monopole operators
A
Isoscalar:
Mˆ ( IS )  Mˆ  N   Mˆ P    ri 2
i 1
A
Isovector:
2
ˆ
ˆ
ˆ
M ( IV )  M  N   M P    ri  3i
i 1
2
Monopole transition in 12Be： 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
M ( IS )  0 f
12
2

r
0
i 1
i 1
Enhanced
2. Isovector monopole transition → sensitive to neutron excitations
M ( IV )  0 f
12
2

r

0
 i zi 1
i 1
α－α part is vanished !
MO excitations
Isoscalar vs Isovector excitations in 12Be
There are clear enhancements in
Isoscalar ⇒ Cluster excitation (03+)
Isovector ⇒ Neutron excitations
(02+, 05+)
M IS , IV 
M s. p.
Monopole strength are comparable to a single particle strength !
EWSR fraction of the isoscalar monopole transitions in 12Be
Sf  Ef 0
01+
(p-)2 (s+)2
Mono. Tr.

f
2
A
r
i 1
02+
(p-)2 (p-)2
2.4%
i
2

1
0
03+
a+8He
21.6%
 2 A r


m

2
2
04+
6He+6He
1.8%




1
05+
(0pR)(0pL) (s+)2
4.8%
06+
5He+7He
8.0%
～26%
Analog to Hoyle
state in 12C (23%)
Exp. By Chinese
Group, ～12%
Total～40%
Monopole tr. in
(80α+6He(2+) ) + ( α+6Heg.s. )
10Be
Isoscalar transitions
Transition to ionic state
Is strongly enhanced.
Strength (Arb. Unit.)
70
60
50
40
30
20
10
0
Ex. ( MeV )
Isovector transitions
Transition to MO states
Is relatively enhanced.
Strength (Arb. Unit.)
4
3.5
3
(p1/2-)2
(p3/2+)2
2.5
2
1.5
1
0.5
0
Ex. ( MeV )
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 Be isotopes
⇒ Covalent, ionic and atomic structures appears in excited states
⇒ Excited states are generated by the excitation of a-a or 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.

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