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