1. Coulomb dissociation for astrophysics T. Gomi (RIKEN) 22Mg(p,γ)23Al
Outline
・ Reaction scheme, experimental setup
・ Relation with stellar reaction,
　　　Experimental advantage
・ Experimental results, astrophysical implications
・ General questions for C.D. exp.
Today, I would like to talk about coulomb dissociation for astrophysics.
using the case of 22Mg(p,g)23Al study,
I will introduce reaction scheme, and experimental setup.
And then, talk on relationship with stellar reaction and experimental advantage of this method.
And I will show experimental results and astrophysical implications.
Finally, I will show the general questions for
Coulomb dissociation experiment.

2. Collaborators
T. Gomi,1 T. Motobayashi,2 Y. Ando,1 N. Aoi,2 H. Baba,1 K. Demichi,1 Z. Elekes,3 N. Fukuda,2
Zs. Fulop,3 U. Futakami,1 H. Hasegawa,1 Y. Higurashi,2 K. Ieki,1 N.Imai,2 M. Ishihara,2 K. Ishikawa,4
N. Iwasa,5 H. Iwasaki,6 S. Kanno,1 Y. Kondo,4 T. Kubo,2 S. Kubono,7 M. Kunibu,1 K. Kurita,1
Y. U. Matsuyama,1 S. Michimasa,7 T. Minemura,2 M. Miura,4 H. Murakami,1 T. Nakamura,4 M. Notani,7
S. Ota,8 A. Saito,1 H. Sakurai,6 M. Serata,1 S. Shimoura,7 T. Sugimoto,4 E. Takeshita,1 S. Takeuchi,2
Y. Togano,1 K. Ue ,6 K. Yamada,1 Y. Yanagisawa,2 K. Yoneda,2 and A.Yoshida2
1 Rikkyo university Tohoku university
2 RIKEN University of Tokyo
3 ATOMKI (Hungary) CNS, University of Tokyo
4 Tokyo Institute of Tokyo 8 Kyoto University

3. γ Coulomb dissociation method
- measurement of the inverse reaction -
one of the indirect method
for study stellar reactions
22Mg(p,γ)23Al : stellar, radiative capture reaction
inverse reaction
23Al(γ,p)22Mg γ
23Al
High-Z
target (Pb)
22Mg p
23Al*
Incident beam
・ 2 particle in coincidence
・ momentum vector
Coulomb dissociation method,
It’s a measurement of the inverse reaction
of the stellar, radiative capture reaction.
the incident 23Al beam bombards a high-Z target , lead ,
and It’s Coulomb excited to an unbound state
that decay to the 22Mg plus proton channel.
This process is regarded as absorption of a photon.
Experimental requirement is
to measure 2 particles in coincidence
and
to measure the momentum vector of each particle.
And with invariant mass method,
we can deduce the relative energy.
This energy corresponds to the center of mass
Energy in stellar reaction
クーロン分解法では、２３Ａｌをビームとして、鉛などＺの大きい標的に入射し、
そこでのクーロン場、電磁相互作用により２３Ａｌを励起させ、分解片22Mg と陽子を測
定します。
・ invariant mass → relative energy
corresponds to the CM energy
in the stellar reaction
photo absorption

4. stellar 22Mg(p,γ)23Al reaction Resonant capture reaction through
the first excited state in 23Al
1st excited state is located near Gamow window in typical Novae.
Q: The influence is strong ?? or not ?? in stars.
Level structure
Strength ∝　Γγ
theoretical prediction
NO measurement !
Let me show the level structure of 23Al.
Present study focused on the resonant capture reaction
through the first excited state in 23Al.
First excited state is located at about 400 keV above proton threshold.
and near Gamow energy in typical nova
So question is that the effect is strong or not.
Excitation energy is already measured with
nucleon transfer reaction by MSU group.
This spin value is theoretical prediction.
Recently, some groups performed experiments.
Now it’s under disscition.
AND
Strength is also theoretical prediction.
No measurement.
So, we determined it by Coulomb dissociation.
ここに２３Ａｌと２２Ｍｇの現在わかっている準位構造をしめしました。
２３Ａｌの第一励起状態は、
天体での反応がもっとも盛んにおこるがもふエネルギーになおすと
温度が0.5Gk の時に相当します。
(Nova)
Coulomb dissociation

5. Experimental Setup - RIKEN RIPS beamline - p Silicon telescope
Pb target 87mg/cm2 p
23Al
50AMeV 1m
22Mg
Silicon telescope
NaI(Tl) detector
(de-excitation γ-ray from 22Mg)
2.5m
0.5m
Plastic Hodoscope
Experimental setup.
Experiment was performed at RIKEN RIPS beamline.
The reaction products was measured by
suitable detectors for 2 particles,
silicon telescope and plastic hodoscope.
Silicon telescope is position-sensitive type
with 5mm width strips.
So we can measured the momentum vector of
each particles.
Additionally,
NaI detector surround the target
To measure the de-excitation gamma-ray
from 22Mg.
This information is used to confirm the final state
of this reaction.
was measured by silicon telescope
and plastic hodoscope.
They were set at 0.5m and 3m downstream from the target.
Silicon telescope is consisted of 4 layers.
Layer 1 and 2 have a striped electrode. X or Y
So we measured the position of proton and Mg22.
Mg22 stooped at layer4.
The total energy is measured.
Proton go punched through the silicon telescope and
Is measured by plastic
実験は理化学研究所のＲＩＰＳと呼ばれるビームラインで行いました。
鉛標的があって、２３Ａｌビームが入射してきます。
スピードは光速の約３０％です。
分解片の測定には、シリコン半導体検出器と
プラスチックシンチレータを使っています。
標的からの距離は５０ｃｍと３ｍで
全体を真空槽にいれています。
分解片それぞれの運動量を測定しました。
このシリコン検出器はそう特殊なものではないのですが、
今回、このプラスチック検出器と組み合わせたシステムを
作るあげることにより、先ほどいったように
測定領域を広げることができるようになりました。
15cm
・ suitable detectors for each particle
・ momentum vector
・ γ-ray detector (to confirm the final state)
Position-sensitive
（5mm width strips）

6. Coulomb dissociation reaction and stellar capture reaction
Relation between
Coulomb dissociation reaction
and stellar capture reaction
23Al + 208Pb
→ 22Mg + p + 208Pb : Coulomb dissociation
LARGE !
σC.D. = 4 mb
Virtual photon theory
σpeak = 30μb
23Al (γ,p) 22Mg : Photo absorption
Relationship between coulomb dissociation and
stellar capture reaction is the following.
Coulomb dissociation reaction is
connected to the photo absorption reaction
with virtual photon theory.
Photo absorption reaction is converted to
the proton capture reaction
using the detailed valance relation.
These relation enhance the cross-section
even if the original proton capture reaction has nano-barn order,
but Coulomb dissociation has milli-barn order.
Large cross section is
This is the one of the merit of Coulomb dissociation
Detailed valance
σpeak = 60 nb
22Mg ( p,γ) 23Al : Proton capture
Large cross section of C.D. is …

7. Advantage of Coulomb dissociation Exp.
Compared to the capture reaction measurement
Nuclear Structure
suitable or not ?
・ Large cross section ～ mb
・ Intermediate energy beam (50AMeV)
enable us to use thick target
(87mg/cm2 Pb)
easy difficult
23Al etc… A
B + p
・excited state below Sp
・can not simulate the inverse
of stellar reaction, exactly
・ 23Al has simple structure,
it’s suitable for C.D. exp.
400counts/3.5days with 104 cps
C.D. has Large yield !
even if WEAK beam !
Large cross section is
one of the merit of this method
compared to the capture reaction
and as other advantage,
Intermediate energy beam
enable us to use thick target.
On the other hand,
It is difficult to measure the nuclei,
which has the complex structure like this.
This nuclei has the excited state below the proton threshould.
In this case, we can not simulate the inverse reaction of stellar reaction exactly,
and it is hard to measure.
In the case of 23Al,
It has simple, easy structure.
So, from these advantage, Coulomb dissociation has
large yield even if weak beam intensity.
If, When you measure the capture reaction,
you should prepare 22Mg beam with 10 to the thirteenth cps.
I think it’s not attainable now.
Up to now,
When one measure the capture reaction,
one should prepare 22Mg beam with 1013 cps.
very intense beam, not attainable!!
Up to now,…

8. Stellar reactions studied by Coulomb dissociation
using radioactive isotope beams
Steady burning
⇒ recent result
GSI (254AMeV)
RIKEN, MSU (50～80AMeV)
Notre Dome (3AMeV)
Solar neutrino
7Be(p,γ)8B
CNO cycle
14N(p,γ)15O RIKEN (100AMeV)
(Coulomb excitation, sub-threshold state)
Explosive burning
12C(p,γ)13N RIKEN (78AMeV)
13N(p,γ)14O RIKEN (88AMeV), GANIL (70AMeV )
hot CNO cycle
8B(p,γ)9C RIKEN (70AMeV)
11C(p,γ)12N GANIL,RIKEN (70AMeV)
12N(p,γ)13O RIKEN (84AMeV)
hot pp mode
22Mg(p,γ)23Al RIKEN (50AMeV)
26Si(p,γ)27P RIKEN (50AMeV)
Up to now,
Many Coulomb dissociation experiments
has been performed.
I listed here the experiment using radioactive isotope beam
related to stellar reaction.
For steady buruning,
7Be (p,gamma) reaction
at GSI, and RIKEN, MSU, and Notre Dome.
and N14 (p,g) reaction.
For explosive burning,
From the 12C (p,gamma) reaction
To 26Si (p,gamma) reaction are performed.
Of course, neutron capture reaction
can be measured with this method.
14C(n, gamma), 18C(n,gamma)
and so on.
Here, let me introduce
the resent result.
rp-process
r-process
8Li(n,γ)9Li MSU (40AMeV)
Neutron
capture
14C(n,γ)15C GSI (605AMeV), RIKEN (70AMeV),
MSU (35AMeV)
neutron induced
CNO cycle
r-process
18C(n,γ)19C RIKEN (67AMeV)
→ T.Nakamura

9. GSI experiment : 7Be(p,γ)8B by F. Shumann, K. Suemmerer, et al.
Lehrstuhl für Physik mit Ionenstrahlen (EP III)
Arbeitsgruppe Nukleare Astrophysik
Prof. Dr. C. Rolfs
Talk: 21st Brussels Meeting 2004
Monday,
Indirect determination of the
astrophysical S-factor of 7Be(p,g)8B
via high-energy
Coulomb Dissociation of 8B
Frank Schümann
GSI experiment for 7Be(p,g) reaction
Title yomu.
I will show the final result only

10. S17 - Factor Descouvemont modell leads to
S17(0)=20.4  1.2  1.0 eV-b.
Recently, the data is improved, blue one,
descuvemont model leads to S17 –factor.
It agrees with Junghans data, purpule triangle, from direct measurement.
C.D. is alternative method to determine S-factor
Recently, the experimental data was improved (blue circle) .
and Descouvemount model leads to S17 (0)-factor.
This agrees with the direct measurement data (triangle)
by Junghans et al. (S17 (0)=22.3±0.7±0.5 eV・b)
This results demonstrate that C.D. is an alternative method
to determine S17-factor.

11. Extension of the field of Coulomb dissociation experiment
p-shell region
sd-shell region
(p,γ) reaction
Far from the stability
22Mg(p,γ)23Al
About the (p,gamma) reaction,
the filed of experiment is extended
from p-shell nuclei to sd-shell nuclei.
And toward the far from stability.
OK, I will back to
the 23Al experiment.
Back to ….

12. Relative energy spectrum
Experimental result
Relative energy spectrum
22Mg(p,γ)23Al
Higher excited state
1st excited state
(objective state)
Counts /150keV
continuum component: E1 ,
constant astrophysical S -factor
So , this figure is relative energy spectrum.
This peak corresponds to the first excited state
and objective of present study.
We can see the another peak,
from higher excited state.
We take into account the continuum component.
Assuming the E1 transition and constant s-factor,
we obtained this shape .
And amplitude is decided by fitting.
The width of this spectrum is due to the experimental resolution,
at 400keV, 170keV.
So, we identify the reaction through the first excited state.
得られた相対エネルギースペクトルを示します。
今回目的とする第一励起状態を経由した反応はこの赤いピークになります。
この幅は検出器の分解能で説明できます。
こちらはこのあたりからの分解過程だと考えれられます。
共鳴反応に相当する反応反応に対してはガウス分布で、
直接反応に相当する反応過程に対しては予想される関数を使って
ふぃってんぐしてあります。
このように目的とする第一励起状態からの分解過程が
特定できます。
1000
2000
3000
4000
Relative energy [keV]
・ energy resolution 170keV (Erel = 400keV)
・ identify the reaction through the first excited state clearly.

13. Angular distribution P l = 2 l = 1 consistent 23Al l = 2
22Mg P
23Al *
Coulomb + Nuclear
l = 2
l = 1
23Al
g.s.
(5/2+ : shell model)
0.528
(1/2+ : shell model)
consistent
“βC” = “βN”
distorted-wave calculation
optical potential : 17O+208Pb (84AMeV)
collective (vibrational) model
Small “Nuclear” component : 8 %
l = 2
Coulomb ONLY
Coulomb and nuclear response is considered
as same deformation parameter.
This is the angular distribution
When the 23Al is excited to the first excited state.
Solid circle is experimental data.
Solid curve is L=2 , dashed curve is L=1 transition.
predicted by distorted wave calculation
with this optical potential.
This result is consistent with the spin value
predicted by the standard shell model.
Let me show this small nuclear component
In this experiment. like this .
The influence for final gamma-gamma value is only 8 %.
From the cross section,
Radiative width, gamma-gamma, is determined
to be to the seventh eV.
This value has direct effect
on the resonant reaction strength.
Let me show that, in this experiment,
nuclear excitation is small.
In this figure, I assumed the Coulomb plus Nuclear response.
And these response is same magnitude as deformation parameter.
Then,
In this figure, artificially,
I change the nuclear response.
This deviation is only 8 % .
The reason is small nuclear response.
It is sure that
Coulomb dissociation experiment.
Next, I will show
the astrophysical implication of this result.
これが実験データで、この線は、DWBAを用いた反応理論からの予想を
実験装置の応答を考慮した値をむすんだものです。
移行角運動量を２とした場合と、１とした場合をそれぞれ実線と破線で示します。
このようにＬ＝２であることがしめされます。
次にこれなんですが、
本研究では、クーロン力による分解過程を想定していますが、
核力に対する応答が気になるので、わざと、
核力にたいする敏感さをクーロン力に対する敏感さに対して
３０％増やしたり、へらしたりしてみます。
この範囲は、まわりの原子核から考えて妥当な範囲です。
その結果、角度分布の変動はこの点線のように変化します。
こちらのＬ＝１にたいして同様なことをおこなっても
この線の太さ以内の変化です。
これらの結果からも移行角運動量が２であることが支持されます。
= (7.2 ±1.7) × 10-7 eV
Coulomb + Nuclear
Compatible with the predicted value
by J.A. Caggiano et.al.
5.49×10-7 eV
Nuclear ONLY
Astrophysical implications

14. Astrophysical implication
22Mg(p,γ)23Al
Astrophysical implication
our experimental data
→　reaction rate
→ competition with βdecay
Nucleosynthesis
in explosive hydrogen burning
(Novae, X-ray bursts)
T [GK]
106
104
102
100
ρ [g/cm3]
Which?
This reaction is related to Nucleosyntheis
In explosive hydrogen burning such as Nova
or X-ray burst.
Reaction flow ,reaction path,
have a effect on the final abundance of these nuclei.
Using our experimental data,
Reatcion rate is calculated,
We can the competition with beta-decay
in each temparature and density condition.
This orange curve indicated that
p,gamma reaction balanced with beta-decay.
I also plotted the profile
predicted by some nova models.
In this condition,
Beta-decay is favored rather than
(p,g) reaction.
Nucleosynthesis in explosive hydrogen burning,
such as nove or X-ray bursts.
Heavier nuclei and cosmic gamma ray-emitter,
like a 22Na or 26Al is generated.
Reaction path, network path have
the effect on the final abundance
of these nuclei.
With our experimental data,
I calculated the astrophysical reaction rate,
then, consider the competition with beta-decay.
This orange line indicate that
p,gamma reaction balanced with beta-decay
in each density and temperature.
Typical nova condition is dashed line.
So in nova like this,
Beta-decay is favored,
and p,gamma reaction may occur
in more high temperature and density condition.
Nova Model
M1 : J.Jose et al Astrophys. J (1999)
M2 : C. Iliadis et.al. Astrophys. J. Supp (2002)
Cosmic
γ-emitter
Ne nova
M.Wiescher et.al.
Phil. Trans. R. Soc. Lond. (1998)
βdecay is favored
rather than (p,γ) reaction

15. for Coulomb dissociation in general
Questions
for Coulomb dissociation in general
・ Sensitivity depends on the transition type (E1, E2, M1,….)
due to different fluxes of photons
・ For low-Z nuclei, “nuclear” component is not small.
・ Higher order processes (post acceleration, ….)
To solve…
Reaction
mechanism etc..
→ K. Ogata　
Experiments give various data.
・ incident beam with different energy
ex: 3AMeV– 250AMeV
・ Low-Z target (probe) instead of Pb
ex: p,α,C,…
・ angular or momentum distribution
・ selection of impact parameter
・ and so on.
→　T. Nakamura
Finally, I would like to talk on
questions for Coulomb dissociation in general.
Sensitivity depends on the transition type. E1,E2,M1 and so on.
Due to different fluxes of photons.
In the 23Al case, it’s OK, but
Low-Z nuclei, nuclear response is not small.
And
Higher order process like a post acceleration and so on.
To understand these character,
experiment will give various data
with wide range for incident beam energy,
using the low-Z target instead of Pb.
Angular or momentum distribution
and selection of impact parameter
and so on.
Some of them will be presented
by Nakamura-san this evening.
of course,
Reaction mechanism theory
Is also.
This detail will be mentioned by Ogata-san
this afternoon.
Of course,
need strong relationship with theory,
reaction mechanism, which may be presented by Ogata-san,
Theory
Experiment

16. Coulomb dissociation method is useful
Summary
Coulomb dissociation method is useful
to study astrophysical (p,γ), (n,γ) reactions.
・ measurement of the inverse reaction of the stellar reaction
・ advantage (large cross section, thick target)
→ large yields
→ we can access stellar reactions
which direct measurement cannot.
・ 22Mg(p,γ)23Al rp-process –
resonant reaction rate through the first excited state
reaction network (competition with βdecay)
・ This method has some questions
theory + experiment will give the solution.
I summarized my talk.
Coulomb dissociation method is useful
to study astrophysical (p,gamma),(n,gamma) reactions
It’s the measurement of the inverse reaction of the stellar reaction.
It has advantage, large cross section, use of thick target,
and the good yields.
So this method can access stellar reactions,
Which direct measurement cannot access.
I introduced the experiment for 22Mg(p,gamma) reaction
related to rp-process.
We determined the resonant reaction rate
through the first excited state,
and the reaction network competition with beta-decay.
This method has some questions
theory and experiment collaboration give the solution.