Coulomb dissociation for astrophysics

T. Gomi (RIKEN)

Outline ・ Reaction scheme, experimental setup ・ Relation with stellar reaction, 　　　 Experimental advantage ・ Experimental results, astrophysical implications

・ General questions for C.D. exp.

22Mg(p,γ)23Al

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 5 Tohoku university2 RIKEN 6 University of Tokyo 3 ATOMKI (Hungary) 7 CNS, University of Tokyo4 Tokyo Institute of Tokyo 8 Kyoto University

Collaborators

Coulomb dissociation method - measurement of the inverse reaction -

inverse reaction

22Mg(p,γ)23Al : stellar, radiative capture reaction

23Al(γ,p)22Mg

γ

23Al

High-Z target (Pb)

22Mg

p

23Al*

Incident beam

・ 2 particle in coincidence・ momentum vector

photo a

bsorp

tion

)()()( 22pmgpMgpMgrel mmPPEEE

・ invariant mass → relative energy corresponds to the CM energy in the stellar reaction

one of the indirect methodfor study stellar reactions

stellar 22Mg(p,γ)23Al reaction

Resonant capture reaction through the first excited state in 23Al

Level structure

Strength ∝ 　 Γγ

theoretical prediction NO measurement !

Coulomb dissociation(Nova)

1st excited state is located near Gamow window in typical Novae. Q: The influence is strong ?? or not ?? in stars.

23Al50AMeV

Silicon telescope

22Mg

p

2.5m0.5m

1m

Plastic Hodoscope

15c

m

Experimental Setup - RIKEN RIPS beamline -

Position-sensitive（ 5mm width strips ）

・ suitable detectors for each particle・ momentum vector ・ γ-ray detector (to confirm the final state)

NaI(Tl) detector(de-excitation γ-ray from 22Mg)

Pb target 87mg/cm2

Relation between Coulomb dissociation reaction and stellar capture reaction

Virtual photon theory

Detailed valance

22Mg ( p,γ) 23Al : Proton capture

LARGE ! σC.D. = 4 mb

σpeak = 60 nb

σpeak = 30μb

23Al + 208Pb → 22Mg + p + 208Pb : Coulomb dissociation

23Al (γ,p) 22Mg : Photo absorption

d

dN

QEdEd

d

cmcm

12

),()12(2

)12)(12(),( 2

2

23

22

pk

k

j

jjp p

Al

pMg

Large cross section of C.D. is …

Advantage of Coulomb dissociation Exp.

・ Large cross section ～ mb・ Intermediate energy beam (50AMeV) enable us to use thick target (87mg/cm2 Pb)

400counts/3.5days with 104 cps

C.D. has Large yield !even if WEAK beam !

Compared to the capture reaction measurement

easy difficult23Al etc…

A

B + p

A

B + p

Nuclear Structure suitable or not ?

When one measure the capture reaction,one should prepare 22Mg beam with 1013 cps. very intense beam, not attainable!!

Up to now,…

・ excited state below Sp・ can not simulate the inverse of stellar reaction, exactly・ 23Al has simple structure, it’s suitable for C.D. exp.

Stellar reactions studied by Coulomb dissociation using radioactive isotope beams

22Mg(p,γ)23Al RIKEN (50AMeV) 26Si(p,γ)27P RIKEN (50AMeV)

8B(p,γ)9C RIKEN (70AMeV)11C(p,γ)12N GANIL,RIKEN (70AMeV)12N(p,γ)13O RIKEN (84AMeV)

7Be(p,γ)8B

12C(p,γ)13N RIKEN (78AMeV)13N(p,γ)14O RIKEN (88AMeV), GANIL (70AMeV )

14N(p,γ)15O RIKEN (100AMeV) (Coulomb excitation, sub-threshold state)

14C(n,γ)15C GSI (605AMeV), RIKEN (70AMeV), MSU (35AMeV)

18C(n,γ)19C RIKEN (67AMeV)

hot CNO cycle

Solar neutrino

hot pp mode

CNO cycle

rp-process

neutron induced CNO cycle

Steady burning

Explosive burning

GSI (254AMeV)RIKEN, MSU (50 ～ 80AMeV)Notre Dome (3AMeV)

8Li(n,γ)9Li MSU (40AMeV) Neutron capture

r-process

r-process

⇒ recent result

→ T.Nakamura

Indirect determination of the astrophysical S-factor of 7Be(p,)8B

via high-energyCoulomb Dissociation of 8B

Ruhr-Universität Bochum Lehrstuhl für Physik mit Ionenstrahlen (EP III)Arbeitsgruppe Nukleare AstrophysikProf. Dr. C. Rolfs

Talk: 21st Brussels Meeting 2004Monday, 13.12.2004

Frank Schümann

GSI experiment : 7Be(p,γ)8B by F. Shumann, K. Suemmerer, et al.

I will show the final result only

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.410

15

20

25

30

35

40

45

Descouvemont (MN*0.84) Typel*0.82

GSI-II (previous) GSI-I Davids Kikuchi GSI-II (actual)

S 17 [e

V-b

]

Ecm

[MeV]

S17 - Factor

Descouvemont modell leads to

S17(0)=20.4 1.2 1.0 eV-b.

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.

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.410

15

20

25

30

35

Descouvemont (MN*0.84) Typel*0.82

Hammache Strieder Junghans Baby GSI-II (actual)

S 17 [

eV-b

]

Ecm

[MeV]

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

Back to ….

0 1000 2000 3000 4000

Relative energy [keV]

Cou

nts

/150

keV

Experimental result Relative energy spectrum

・ energy resolution 170keV (Erel = 400keV)・ identify the reaction through the first excited state clearly.

continuum component: E1 , constant astrophysical S -factor

22Mg(p,γ)23Al

1st excited state(objective state)

Higher excited state

= (7.2 ±1.7) × 10-7 eV

Small “Nuclear” component : 8 %

23Al g.s. (5/2+ : shell model)

0.528 (1/2+ : shell model)

l = 2

l = 1

“βC” = “βN”

Coulomb + Nuclear

Coulomb ONLY l = 2

Nuclear ONLY

distorted-wave calculationoptical potential : 17O+208Pb (84AMeV)collective (vibrational) model

Angular distribution

consistent

Astrophysical implications

Coulomb + Nuclear

23Al

22Mg

P

23Al *

Coulomb and nuclear response is consideredas same deformation parameter.

Compatible with the predicted value by J.A. Caggiano et.al. 5.49×10-7 eV

Cosmic γ-emitter

Ne novaM.Wiescher et.al. Phil. Trans. R. Soc. Lond. (1998)

Astrophysical implication

0.1 0.2 0.5 1.0 2.0 T [GK]

106

104

102

100

ρ [

g/c

m3]

βdecay is favored rather than (p,γ) reaction

Which?

22Mg(p,γ)23Al

Nucleosynthesis in explosive hydrogen burning(Novae, X-ray bursts)

our experimental data → 　 reaction rate → competition with βdecay

Nova Model M1 : J.Jose et al Astrophys. J. 520 347 (1999) M2 : C. Iliadis et.al. Astrophys. J. Supp. 142 105 (2002)

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…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

Theory Experiment

Reaction mechanism etc.. → K. Ogata 　

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.