Transcript Coulomb and Nuclear Breakup of Halo Nuclei

E1 Strength distribution of halo nuclei
observed via the Coulomb breakup
Takashi Nakamura
Tokyo Institute of Technology
Workshop on Statistical Nuclear Physics
and Applications in Astrophysics and Technology,
OHIO University, July 2008
Contents
1
Introduction
Soft E1 Excitation of 1n halo nucleus--Coulomb Breakup of 11Be
T.Nakamura et al.,PLB 331,296(1994).
N.Fukuda, TN et al.,PRC70, 054606 (2004).
2
Coulomb Breakup of 15C: Application to Astrophysics
Paper in preparation
3
Soft E1 Excitation of 2n halo nucleus
--Coulomb Breakup of 11Li
T. Nakamura, A.M.Vinodkumar et al.,PRL96, 252502 (2006).
4
SAMURAI Project @ RIBF
Photo- absorption of Nucleus
B(E1)
Ordinary (E1 Transition Probability)
Nucleus
Ex~80A-1/3MeV
n
Giant
Dipole
Resonance
(GDR)
p
g
10~20MeV
B(E1)
Ex
(=Eg)
(E1 Transition Probability)
n
9Li
g
n
9Li
1~2MeV
10~20MeV
Ex
(=Eg)
Soft E1 Excitation
Reaction Mechanism of Soft E1 Excitation?
?
E1
Soft Dipole Resonance
Direct Coulomb Breakup
core
n
dB(E1)
Z 1
2
exp(iqr)|
rY
|F

|
m
gs
dEx
A
Slow Vibration
of core against halo
c.f. Pigmy Resonance

Sn (Ex - Sn)3/2
Ex 4
8
Ex(Peak)  Sn B(E1) 1/Sn
5
Coulomb Breakup
11Be*
11Be
g
10Be
n
b> 0.3c
Heavy Target (Pb)
Excitation by a Virtual Photon
d C 16 3
dB( E1)

N E1 ( Ex )
dEx
9c
dEx
Cross Section = (Photon Number）x(Transition Probability)
Invariant Mass Spectroscopy
Excitation Energy
(=Photon Energy）
B(E1) Observed for Neutron-halo１１Be nucleus
11Be(70MeV/u)+Pb
B( E1)  1.05  0.06 e 2 fm 2
(3.29  0.06 W.u)
Huge E1 Probability
(usually B(E1) < 10-3)
T.Nakamura et al.,
PLB 331,296(1994)
N.Fukuda et al.,
PRC70, 054606 (2004)
No Resonance
But Huge Peak
Direct Breakup Model
dB(E1)
Z 1
2
exp(iqr)|
rY
|F

|
dEx
A m gs

Sn (Ex - Sn
Ex4
)3/2
core
n
Low-energy B(E1)---Very Sensitive
to Halo Wave Function !
dB(E1)
Z 1
2
exp(iqr)|
rY
|F

|
m
gs
dEx
A
 a2
Sn (Ex - Sn)3/2
Ex4
Low-energy B(E1)
11Be
ground state
r~ a2 |exp(-r/l)/r|2
Halo State
-Sn
Halo State
Fourier Transform
Non-Halo State
| Fgs (1/2+)  = a |10Be(0+)2s1/2 b |10Be(2+)1d5/2 
a2 ,b2 : Spectroscopic factor
a2= 0.72±0.04 N.Fukuda, TN et al., PRC70, 054606 (2004)
a2= 0.61±0.05 R.Palit et al., PRC68, 034318 (2003).
2
Coulomb Breakup of
15C
Application to Astrophysics
Neutron Capture Reaction  Coulomb Dissociation
15C(g,n)14C
14C(n,g)15C
Burning zone in Low mass Asymptotic Giant Branch(AGB) stars
Neutrons from 13C(a,n) reaction
14C(n,g)15C(b-)15N(n,g)16N(b-)16O(n,g)17O(n,a)14C M.Wiescher et al., ApJ, 363,340
Inhomogeneous Big Bang Model
r-process model
Terasawa,Sumiyoshi,Kajino, ApJ562,470(2001).
Previous Experiments
14C(n,g)15C:
Beer et al.(Karlsruhe), 1/5 of Direct Capture,
APJ387,258 (1992)
R.Reifarth et al.(Karlsruhe), Consitent with Direct Capture PRC77,015804(2008)
15C(g,n)14C:
Coulomb breakup
Horvath et al.(MSU), Inconsistent with Direct breakup
D. Pramanik et al.(GSI), Consistent with Direct breakup
APJ570, 926(2001)
PLB551,63(2003)
Neutron Capture Reaction vs. Coulomb Dissociation
14C(n,g)15C
Neutron Capture
15C(g,n)14C
Coulomb Dissociation
(2 I A  1) Eg
 n ,g ( Erel ) 
 g ,n ( Eg )
2
(2 I A-1  1) 2c Erel
2
The principle of detailed balance
Advantages of Coulomb Dissociation
Phase Factor ~100, Photon Number ~500
Target(Thick, Stable), Kinematical Focusing
Results: Coulomb Breakup of 15C
15C:
moderate neutron-halo 1/2+ gs, Sn=1.27MeV
14
+
15C(g.s)= a14C(0+)2s
1/2 b C(2 )1d5/2 
15C+Pb@68MeV/u
a2=0.75(4)
r0=1.25 fm
a=0.65 fm
Consistent with GSI (a2=0.73)
(D.Pramanik et al) Data
But not with MSU data
Neutron Capture Cross Section
From the data with b>20fm
 n ,g ( Erel ) 
Eg
2
c Erel
2
 g ,n ( Eg )
Consistent with Direct Capture Measurement 14C(n,g)15C
By R.Reifarth et al., PRC77,015804(2008)
s-wave capture vs. p-wave
capture
A(n,g)B(Normal)
S-wave capture dominant
A(n,g)B(Halo)
p-wave capture dominant
 ng
 ng  1/ v  1/ Erel
 ng  Erel
p-wave
s-wave
En
18C(n,g)19C
Case
Experimental Input
Coulomb Breakup of 19C
T.Nakamura et al.,PRL83,1112(1999).
Conventional Calculation(HF)
Theoretical Results: T.Sasaqui, T.Kajino, G.J.Mathews,
K.Otsuki, T.Nakamura, Astrophys.J. 634, 1173 (2005).
3
Coulomb Breakup of halo nuclei 11Li
T. Nakamura, A.M.Vinodkumar et al.,
Phys. Rev. Lett. 96, 252502 (2006).
One neutron halo nucleus vs. Two neutron halo nucleus
n
n
10Be
Sn=504 keV
Motion between
core and 1 valence neutron
9Li
n
S2n=300 keV
Motion between
1. Core and neutron
2. Core and neutron
3. Two valence neutrons
(neutron-neutron correlations)
Coulomb Breakup of 11Li
(Summary of Previous Results)
MSU@ 28MeV/nucleon
PRL 70 (1993) 730.
PRC 48(1993) 118.
RIKEN @ 43MeV/nucleon
PLB348 (1995) 29.
GSI @280MeV/nucleon
NPA 619 (1997) 151.
Experimental Setup
NEUT
@RIPS at RIKEN
n
n
Pb Target
9Li
HOD
DC
DALI
11Li
70MeV/nucleon
BOMAG
Elimination of Cross-Talk events
Examine Different Wall Events
Condition:
b1  b12
Almost no bias
t1
b1
b12
b2
Eth=6MeVee to avoid any gamma related events
t2
Coulomb Dissociation Spectrum of 11Li
Angular Distribution
  2.34  0.05(stat.)  0.28( syst.) b
for Erel  3 MeV
Comparison with
Previous results
Comparison with a 3-body
theory
Calculation
H.Esbensen and G.F. Bertsch
NPA542(1992)310.
“Soft dipole excitations in 11Li”
Non-energy weighted
E1 Cluster Sum Rule
B( E1)  

0
2
 
dB( E1)
3  Ze  2
2
dEx 
  r1  r2  2(r1  r2 )
dEx
4  A 
r2
2

3  Ze 
2
r
  c-2n
 A
9Li
rc-2n
n
r1
B( E1)  1.42  0.18 e 2 fm 2 ( Erel  3MeV)
 1.78(22) e 2 fm 2(Extrapolated value)

rc - 2 n
2
 5.01 0.32 fm
~70% largerthan
 non-correlated
strength r1  r2  0
(
)
14
12  48-18
deg
Implication of the Narrow Opening Angle
Simple two-neutron shell model
r2
9Li
rc-2n

 (11 Li )  Core  a (1s ) 2  b (0 p) 2
n
r1

Melting of s(+ parity) and p(-parity) orbitals
H.Simon et al. PRL83,496(1999).
N. Aoi et al. NPA616,181c(1997).
cos 12  a 2 (1s ) 2 cos 12 (1s ) 2  b 2 (0 p) 2 cos 12 (0 p ) 2  2ab (0 p ) 2 cos 12 (1s ) 2
 2ab (0 p) 2 cos 12 (1s) 2
If only
(1s)2
or
(0p)2
If full overlap (1s)2 & (0p)2
If 50% overlap integral
14
12  48-18
deg
cos12  0,
12  90
cos12  1 / 3,
12  55
cos12  1 /(2 3 ),
12  73
Mixture of different parity states is essential !
Mixture of higher L orbitals More correlated
Further Correlation?
E(9Li-n)
Experimental Result
Simulation (Phase Space)
E(9Li-n)
E(9Li-n)
1MeV
9Li
n
E(9Li-n)
E(9Li-n)
preliminary
1MeV
E(9Li-n)
p-wave?
10Li
s-wave
Virtual state
Obataind from
11Li+C9Li+n
spectrum
F(11 Ligs )  a F(9 Ligs )  (s1/ 2 ) 2  b F(9 Ligs )  ( p1/ 2 ) 2  ...
O( E1) | F(11 Ligs )  g F(9 Ligs )  (s1/ 2 )1 ( p1/ 2 )1  ...
1MeV
n
E(n-n)
n
E(9Li-nn)
E(n-n)
9Li
E (n - n)  E ( 9Li - nn )
E(9Li-nn)
1MeV
preliminary
4
SAMURAI Project at RI Beam Factory
RIBF
For the future
(RIKEN RI Beam Factory)
Samurai
K=2400MeV
E/A=350MeV
Facility
before 2007 New
100MeV/nucleon
Facility
8Tm
6%, 100mrad
Completed in 2007
World Largest RI-beam facility
350MeV/nucleon, ~1pA
Heavy ions up to U beam
SAMURAI
Superconducting Analyser for MUlti-particles from RAdio-Isotope Beam
Funded! 2008-2011 1.5GJPY~15MUSD~10MEuro
Superconducting
Magnet
To let neutron(s) pass
through the gap
Sweep Beam and
Charged Fragments
Good Mass Resolution
for PID @ A~100
+NEBULA
(NEutron Detection
System for Breakup of
Unstable Nuclei with
Large Acceptance)
Bending Power
BL=7Tm (B=3Tesla, 60deg bending)
Summary
1 Soft E1 Excitation of 1n halo nucleus---Coulomb Breakup of 11Be
T.N et al.,PLB 331,296(1994); N.Fukuda, TN et al.,PRC70, 054606 (2004).
• Large E1 strength ~3W.u. at low excitation energies
• Direct Breakup Mechanism– Reflecting Large amplitude of Halo state
• Coulomb Breakup---Spectroscopic Tool (spectroscopic factors)
2
Coulomb Breakup of 15C: Application to Astrophysics
• 14C(n.g)15C can be studied by Coulomb breakup of 15C
• P-wave direct capture Direct breakup of Halo (s-wave)
3
Soft E1 Excitation of 2n halo nucleus --Coulomb Breakup of 11Li
T. Nakamura, A.M.Vinodkumar et al., Phys. Rev. Lett. 96, 252502 (2006).
• Strong B(E1) at very low excitation energy
B( E1)  1.42  0.18e2 fm2 (~4W.u)
• neutron-neutron spatial correlation from E1 sum rule
4
SAMURAI Project
nn~50deg
R301n Collaboration: (Coulomb Breakup of 11Li)
T.Nakamura1, A.M. Vinodkumar1,T.Sugimoto1,N.Aoi2,
H.Baba2, D.Bazin4, N.Fukuda2, T.Gomi2, H.Hasegawa3,
N. Imai5, M.Ishihara2, T.Kobayashi6, Y.Kondo1, T.Kubo2,
M.Miura1, T.Motobayashi2, H.Otsu6, A.Saito7, H.Sakurai2,
S.Shimoura7, K.Watanabe6, Y.X.Watanabe5, T.Yakushiji6,
Y. Yanagisawa2, Y.Yoneda2
1. Tokyo Inst. of Technology
2. RIKEN
3. Rikkyo Univ
4. NSCL, MSU
5. KEK,
6. Tohoku University
7. CNS, Univ. of Tokyo
 gn
d C 16 3
dB( E1)

N E1 ( E x )
 N E1 ( E x )
dEx
9c
dEx
Ex
dB( E1)
 gn  Eg
dEx
 ng 
Eg
2
c Erel
2
 gn 
Eg
3
c Erel
2
Erel
dB( E1)

dEx
( Erel  S n )
Peak at Erel=Sn
MACS(Maxwellian-averaged neutron capture cross section)
= 7.4(4) b