Photonuclear reactions in astrophysics

1 Nucleosynthesis of heavy elements2 Photonuclear reactions in stars3 Laboratory studies: 12 nuclei D, Be-9, Se-80, Zr-90,94, Pd-108, La-139,

Pr-141, Ta-181,W-186, Re-187, Os-188

4 Conclusions

中日 NP2006: 上海 (Shanghai), May 16 - 20, 2006

H. Utsunomiya (Konan Univ)

Collaborators

1) <Konan> S. Goko, A. Makinaga, H. Akimune, T. Kaihori, S. Hohara

2) <AIST> H. Toyokawa, K. Kudo, A. Uritani, H. Harano, T. Matsumoto

3) <Kyoto> H. Ohgaki4) <Numazu> K. Sumiyoshi5) <NAO> T. Kajino6) <Darmstadt> P. Mohr7) <SPring-8> H. Yonehara, K. Soutome, N. Kumagai, H.

Ohkuma, 8) <Texas A&M> Y.W. Lui9) <Univ. Libre de Bruxelles> M. Arnould, S. Goriely, M.

Rayet10) <Orsay> E. Khan11) <JAEA> H. Harada, F.Kitatani, K.Y. Hara, T. Hayakawa,

H. Shizuma

Solar abundances of heavy elements

10-610-510-410-310-210-1100101102

80100120140160180200A180Ta

180W

r

p

s

138La

H: 71% He: 27%Metal: 2%

(mass %) 3W (what, where, when) & 1H (how)

Who? (Nature or God)

Nucleosynthesis of heavy elements

p-nuclei 35 neutron-deficient nuclei with small solar abundances:74Se - 196Hg

GSI Darmstadt

Arnould & Goriely (2003)

Temperature ： (1.5 ～ 3.5) x 109 K

Promising sites:

O/Ne-rich layer of massive stars during their explosions as Type II(core collapse)-supernovae or in pre-supernova phase

Type Ia-supernovae

Arnould (1976)Woosley & Haward (1978)Rayet et al. (1995)Rauscher et al. (2002)

2000 nuclei ， 20000 reactions :

Photodisintegration: (,n)(,p)(,) Capture reactions: (n,)(p,)(,) Weak transformation: -decays, e±-captures,

(anti)neutrino-captures

Stellar Model of the p-process

Photoreaction rate for nuclei in the ground state

€

λ j = c nγ0

∞

∫ (E,T )σ γ j (E)dE j= n, p,

€

nγ (E,T )dE=1

π 2

1

(hc)3

E2

exp(E / kT )−1dE Planck distribution

neutron channel

GDR cross sectionPlanck distribution

Gamow peak

Stellar Photoreaction Rate

Z, A-1

Z, ANuclei are thermalizedunder stellar conditions

(nucleus in state

€

λ*γ n =

(2Jμ +1)λμγ n(T )exp(−ε μ / kT )

μ∑

(2Jμ +1)exp(−ε μ / kT )μ

∑

Hauser-Feshbach model

transmission coefficient

Particle (n,p,) transmission coefficient

Level density

€

σ n = π Dj

2 1

2(2JIμ +1)

(2J +1)Tγ

μ (J π )Tnμ (J π )

Ttot(J π )J π

∑

€

Tk(J π )= Tkμ

ν =0

ω

∑ (J π )+ Tkν (ε ν ,J π )ρ(ε ν ,J π ,π ν )dε ν dJ π d

Jν , π ν∫ε ω

ε max

∫ π ν (k = γ ,n)

3 important nuclear parameters

AIST

National Institute of Advanced Industrial Science and Technology

産総研

Inverse Compton Scattering

E = 1 – 40 MeV

= Ee/mc2

“photon accelerator”

AIST ( 産総研 )Experimental Setup

TERAS:Tsukuba Electron Ring for Accelerating and storage

Laser System

TERAS

lens

mirror

depolarizer+expander

LaserNd:YVO4

mirror

Triple Ring Neutron Detector System

triple ring detectors

Monitor: NaI(Tl)

Triple ring detector: 20 3He counters (4 x 8 x 8 )

181Ta179Ta180g

180m

179Hf178Hf177Hf176Hf180g

180m 181Hf

182Ta

180W 182W 183W181W

s process

r process

p process origin of 180Tam : σtot at 109 KArnould, Goriely

s process origin of 180Tam : σm at 108 KKaeppeler

Unknown σm : 179Ta(n,)180Tam

180Ta (odd-odd p-nucleus)Nature’s rarest isotopeThe one and only naturally-occurring isomer

H. Utsunomiya et al. 2003Phys. Rev. C63, 018801

181Ta(,n)180Ta

Extra E1-strength at low energy

1

10

100

8 9 10 11 12 13

IAEA [8]Utsunomiya et al. (2002)QRPAHybridLorentzian

E [MeV]

181Ta(γ,n)180Ta

Novel probe of Nuclear Level Density of 180Ta

181Ta

180Ta

180Tam 9−

1−

75 keV

7/2+

9/2 ー 7/2 ー 5/2ー

s-wave neutron

E1

5 ー 4 ー 3 ー 2ー

Selective multistep transitions between high spin states5 ー → 6 ＋ → 7 ー → 8 ＋ → 9 ー

8.152 h

> 1015 y

Partial cross sections for the isomeric state: σm(E) for 181Ta(,n)180Tam

181Ta197Au

Total cross sections: σtot(E) for 181Ta(,n)180Ta Direct neutron counting

Partial cross sections: σgs(E) for 181Ta(,n)180Tags

Photoactivation

σm(E)= σtot (E) - σgs(E)

Photoactivation

180Hf KX rays

181Ta(,n)180Tags(EC)180Hf

σgs(E):partial cross section for the ground state

Partial cross sections for the isomeric state: σm(E) for 181Ta(,n)180Tam

Combinatorial NLD: Hilaire et al. 2001: Goriely & Hilaire 2006

HFBCS pot. model: Demetriou & Goriely 2001

S. Goko et al. Phys. Rev. Lett. May-2006 issue, in press

σm(E)

σtot (E)

Partial neutron capture cross section179Ta(n,)180Tam

σm = 90 ± 22 mb at 30 keV: Statistical Model Calculation with the combinatorial NLD

Previously,σm = 44 mb

Conclusions

Astrophysical photo-reactions and disintegrations (APHRODITE) constitute an important research field in connection with the origin of heavy elements by probing

・ E1 strength function above/below neutron thresholds ・ nuclear level density

The following three research activities are important: (1) Photonuclear reaction experiments (,n) (,p) ()

(,’) (2) Nuclear theory and astrophysical modeling (3) New photon sources in the MeV region

Yonehara, Soutome & Kumagai

SPring-8

10 tesla Super-Conducting Wiggler

10T- SCW synchrotron radiation

Utsunomiya et al., 2005NIMA538, 225

Determination of Laboratory reaction rates for (,n), (,p), and (,) reactions

Black-body radiation at billions of Kelvin