Upload
norma-haviland
View
217
Download
1
Embed Size (px)
Citation preview
Photodisintegration and nuclear statistical quantities in astrophysics
H. Utsunomiya (Konan University)
SNP2008, Ohio University, July 8-11, 2008
Outline
1. Photodisintegration and nuclear statistical quantities 2. Case 1: E1 strength function in 181Ta(,n)180Ta 3. Case 2: Nuclear level density in 181Ta(,n)180Tam
4. Case 3: M1 strength function in 91,92,94Zr(,n) 90,91,93Zr5. Summary
Konan U. H. Utsunomiya, T. Yamagata, H. Akimune AIST H. Toyokawa, T. Matsumoto, H. Harano JAEA H. Harada, S. Goko RCNP T. Shima NewSUBARU S. Miyamoto Texas A&M, USA Y.-W. Lui
ULB, Brussels, Belgium S. GorielyCEA-Bruyères-le-Châtel, France S. HilaireZG Petten, The Netherlands A.J. Koning
Collaborators
What can we do with real photons?
r-processp-process s-p
rocess
Photonuclear reactions are an excellent electromagnetic probe. The universal role of photonucelar reactions is to investigate the
strength function and nuclear level density that are key nuclear ingredients for the p-, s-, and r-process.
Nucleosynthesis of heavy elements through SF and NLD ・ p-process ・ s-process ・ r-process
Nucleosynthesis of light elements by the detailed balance
Nuclear Statistical Quantities in the Hauser-Feshbach model
A(x, )B (x=n, p, d, t, 3He, )
A + x
B
Optical potential
continuum
Discrete levels Ex, J
Level densityMass, deformation
Common to Radiative Capture and Photodisintegration
RIPL Handbook/IAEA-TECDOChttp://www-nds.iaea.org/ripl/
-ray strength function
Photoreaction rates for nuclei in state
Ex
n(E,T)
Gamow peakSn
(Z,A)
(Z, A-1)
(,n)(n,)
・ E1, M1 strength functions above and below Sn・ Nuclear level densities
(,’)
n c n0
(E,T) n (E)dE
Planck Distr.
Brink hypothesisGDR is built on excited states.
GDR
n(E)
Key issues
Neutron channel (,n)
181Ta180m
178Hf177Hf176Hf180g
180W 182W 183W
s process
r process
181W
179Ta180g
182Ta
179Hf 180m 181Hf
p process
s process
Origin of 180Tam
Only naturally occurring isomer and nature’s rarest nuclide
1+
9–
0
75 keV180Tag
> 1.2 x 1015 y
8.15 h
180Tam
mediating excited states Ex > 1 MeV
Incident -ray
181Ta (Target)
181Ta(,n)180Ta
180Ta
p-process production of 180Tam
180Tags and 180Tam are equilibrated under stellar conditionthrough mediating excited states above 1 MeV.Total cross sections are needed.
total
s-process production of 180Tam
180Ta1+
2+
9- 75.3
42
0
181Ta7/2+
9/2-, 7/2-, 5/2-
E1
T1/2 > 1.2×1015y
T1/2=8.152h
4+, 3+
…
5-, 4-, 3-, 2-
…
8+
6+
7-
5-(7/2+)
T1/2=1.82y179Ta
s wave neutron s wave
neutron
Nuclear Level Density
(9-) = total - gs
・ VUV-IR自由電子レーザー
・レーザー逆コンプトン光・偏光アンジュレータ光・放射光
S-band small linear acc.S-band small linear acc.
General-purpose Storage Ring TERAS
Stroge Ring NIJI-IV
Pulsed slow positron beam line
・レーザーコンプトン散乱 準単色 ps-fsⅩ線・コヒーレントテラヘルツ波
AIST Electron Accelerator FacilityAIST Electron Accelerator Facility
400MeV Electron Linear Acc. TELL
・ナノメートル~原子レベル空孔計測
Small Storage Ring NIJI-II・ SRプロセス
EE
L
L L e
1 1cos cos
e
e
E
L
Ee
•• EnergyEnergy
Laser Electron Beam
Inverse Compton Scattering
E = 1 – 40 MeV
= Ee/mc2
“photon accelerator”
Neutron Detector System
triple ring detectors
Monitor: NaI(Tl)
Triple-ring neutron detector20 3He counters (4 x 8 x 8 ) embedded in polyethylene
Experimental Set-up for direct neutron detection and photoactivation
Target Sample ; 181Ta 3He Proportional Counter ×20
Neutron Moderator ; Polyethylene
Target Sample ; 197Au
NaI(Tl) Scintillator
1
10
100
8 9 10 11 12 13
IAEA [8]Utsunomiya et al. (2002)QRPAHybridLorentzian
(,
n) [
mb]
E [MeV]
181Ta(,n)180Ta
Utsunomiya et al., PRC(2003)
181Ta(,n)180Ta : total
Extra E1 -ray strength near Sn
Experimental results, and comparison with theoretical models
Present work (2006)
Systematic uncertainties
10 ~ 26%
0.1
1
10
100
7 8 9 10 11 12 13 14
Cross Section [mb]
E[MeV]
181Ta(,n)180Ta
181Ta(,n)180Tam
Goko et al. Phys. Rev. Lett. 96, 192501 (2006)
IAEA : Lee et al. (1998)Statistical NLD model
Combinatorial NLD modelHilaire & Goriely, NPA779 (2006)
10-2
10-1
100
101
102
103
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 0.1 1 10
Cro
ss S
ecti
on [m
b]
m/
tot
En[MeV]
Present results
for the s-process production of 180Tam
30keV(s-process)
0.04
Previous Predictions
0.02 ~ 0.09 (K.Yokoi, K.Takahashi ;1983)
0.043±0.008 (Zs. Nèmeth, F.Käppeler, G.Reffo ;1992)
Combinatorial NLD model
m/tot :
m : 44mb (Zs. Nèmeth, F.Käppeler, G.Reffo ;1992)
Goko et al. Phys. Rev. Lett. 96,
192501 (2006)
Statistical NLD model
mbmn 2290
at 30 keV
01.004.0 totn
mn
mTanTa 180179 ),(
totn
mn
mn
M1 strength in Zr isotopes
Crawley et al., PRC26, 87 (1982)
Sn
(e,e’) weak & fragmented
(p,p’): giant M1 resonance
’): giant M1 resonance
Anantaraman et al., PRL46 (1981)
Bertrand et al., PL103B (1981)
Meuer et al., NPA 1980
Nanda et al., PRL51 (1982)
Laszewski et al., PRL59 (1987)
Sn
Sn
Sn
GDRM1
M1
M1
M1
E1
E1
E1
E1
Excitation Energy
Strong M1 strength of giant-resonance type was observed in (p,p’) below GRD. The M1 strength lies over the neutron separation energy for 92,94,96Zr.
91Zr(n)90Zr
92Zr(n)91Zr
94Zr(n)93Zr
(,n) cross sections on Zr isotopes
Threshold behavior of (,n) cross sections isgiven by
.)(2/1
n
no S
SEE
In the E1 photo-excitation, is allowed. However, the experimental cross sections are strongly enhanced from the expected behavior.
1
1
The generalized Lorentzian parametrizationof the E1 -ray strength function significantly underestimates the cross sections .
Main ingredients in the Talys code
E1 strength functionLorentzian models:Axel, PR126 (1962), Kopecky & Uhl, PRC41 (1990)
HFB+QRPA model: Goriely, Khan, Samyn, NPA739 (2006)
Nuclear Level densityHFB+ Combinatorial model: Hilaire & Goriely, NPA779 (2006)
Spin-flip giant M1 strength function by Bohr & MottelsonGlobal systematics in RIPL Handbook
Lorentzian function : Eo=41A-1/3 MeV, o = 4 MeV,
fM1=1.58 10-9 A0.47 MeV-3 at 7 MeV
Talys code: Koning, Hilaire, Duijvestijn, Proc. Int. Conf. on Nuclear Data for Science and Technology AIP Conf. Proc. 769, 1154 (2005).
91Zr(n,)92Zr
8 10 12 14 16 E [MeV]
92Zr(n)91Zr
The Lorentzian parametrization of the E1 -ray strength function for 92Zr can fit the (,n) data, but strongly overestimates (n,) cross sections.
The Lorentzian parametrization of the E1 -ray strength function
91Zr(n,)92Zr
M1 strength in Zr isotopes in the photoneutron channel
91Zr(n)90Zr
92Zr(n)91Zr
94Zr(n)93Zr
M1
M1
M1
E1
E1
E1
H. Utsunomiya et al., PRL100 (2008)
If we employ the HFB+QRPA E1 -ray strength function supplemented with extra M1 strengthassumed at 9 MeV with σ0=7.5mb and =2.5 MeVin Lorentz shape, the cross sections are well reproduced.
The M1 strength is about 75% larger than the strength predicted by the global systematics.
Major shell gaps associated with spin-flip M1 excitations
Z,N=28 1f7/2 → 1f5/2
50 1g9/2 → 1g7/2
82 1h11/2 → 1h9/2
126 1i13/2 → 1i11/2
1g9/2
1g7/2
2d5/2
50
isotopesZr 54,52,5194,92,9140
J= 5/2+ for 91,93Zrgs means that excess neutrons occupy the 2d5/2 shell.
Spin-flip M1
M1 strength can be similar for 91,92,94Zr.
Medium-range plan 1: E1, M1 -ray strength functions
Systematic measurements of (,n) cross sections for as many stable nuclei as possible around the magic numbers 50, 82 and 126
1. Zr isotopes (Zr-90,91,92,94,96)
2. Mo isotopes (Mo-92,94,95,96,97,98,100)
3. Sn isotopes (Sn-116,117, Sn-118,119,120,122,124)
4. Nd isotopes (Nd-142,143,144,145,146,148,150)
5. Pb isotopes (Pd-206,207,208)
H. Utsunomiya et al., PRL100 (2008)
Partial cross section for Isomers and total cross sections
5. 196Pt(,n)195Ptm(13/2+, 259.30 keV, 4.02d)
6. 187Re(,n)186Rem((8+), 149 keV, 2.0x105y) 187Re(,n)186Regs(1-, 90.64h)
7. 178Hf(,n)177Hfm(37/2-, 2740.0 keV, 51.4m)
8. 176Lu(,’)176Lum(1-, 123.0 keV, 3.64h)
Medium-range plan 2: Level densities
S. Goko et al., PRL96 (2006)
Summary
The SF and NLD are key nuclear statistical quantities in the Hauser-Feshbach model calculations of neutron capture and photoreaction rates in nuclear astrophysics.
Photonuclear reactions are an excellent electromagnetic probe of SF and NLD of direct relevance to the p-, s-, and r-process nucleosynthesis of heavy elements.