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.