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

=532 nm2.4 eV

Tsukuba Electron Ring for Acceleration and Storage (TERAS)

Laser : INAZUMA

expander

mirror

mirror lens

Laser system

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.

22222

22

)(

EEE

E

oo

o=7.5mb, =2.5 MeVEo=9 MeV

Lorentz shape

92Zr94Zr

91Zr

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.