Transcript ORCプロジェクトの提案 宇都宮弘章

Probing Nuclear Statistical Quantities by
Photodisintegration
光核反応による統計的核物理量の研究
H. Utsunomiya (Konan University)
RIKEN Workshop, 25-26 September 2008
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Outline
Japan synchrotron radiation facilities
Photodisintegration for nuclear statistical quantities
Systematic study of E1 & M1 g strength functions for
Zr isotopes
Pigmy E1 resonance for Sn isotopes
Nuclear level density
Summary
Collaborators
Konan U.
H. Utsunomiya, T. Kaihori, H. Akimune, T. Yamagata
AIST
K. Yamada, H. Toyokawa, T. Matsumoto, H. Harano
JAEA
H. Harada, F. Kitatani, S. Goko
RCNP
T. Shima
NewSUBARU
S. Miyamoto
Texas A&M, USA
Y.-W. Lui
ULB, Brussels, Belgium
S. Goriely
CEA-Bruyères-le-Châtel, France
S. Hilaire
ZG Petten, The Netherlands
A.J. Koning
この研究発表は、旧電源開発促進対策特別会計法及びに特別会計に関する法律
（エネルギー対策特別会計）に基づく文部科学省からの受託事業として、北海道大
学が実施した平成18年度、平成19年度および平成20年度「高強度パルス中性子
源を用いた革新的原子炉用核データの研究開発」の成果を含みます。
AIST Electron Accelerator Facility
Stroge Ring NIJI-IV
General-purpose Storage Ring
TERAS
・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
400MeV Electron Linear Acc.
TELL
S-band small linear acc.
・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
Small Storage Ring NIJI-II
・SRプロセス
Pulsed slow positron beam line
・ナノメートル～原子レベル空孔計測
Tsukuba Electron Ring for Acceleration and Storage (TERAS)
l=532 nm
2.4 eV
• Energy
Eg
Eg = 1 – 40 MeV
Inverse Compton Scattering
“photon accelerator”

L
Ee
Laser
g = Ee/mc2
e
Eg 
e
Electron Beam
L
1   cos    L 1  cos  L    E e
Neutron Detector System
Triple-ring neutron detector
20 3He counters (4 x 8 x 8 ) embedded in polyethylene
triple ring detectors
Monitor: NaI(Tl)
New SUBARU facility
SPring-8
1 GeV直線加速器
8 GeVシンクロトロン
NewSUBARU
兵庫県立大
高度研
Present: limited space
Beam
Shutter
Gamma
Targ
Detector
et
50
300
300
1650
450
1550
C r o s s S e c tio n [m b ]
Shima: JPS meeting at Yamagata (2008)
4He(g,p)3H
(preliminary)
2
1
0
20
25
30
35
E g [M eV ]
40
45
50
Future: Open-space beam line?
実効線量限度
6μSv/h以上の範囲
5000
3000
3000
実験中立ち入り禁止区域
8000
beam輸送管
輸送管内ガス:空気
実験ターゲット
（&中性子検出器）
NaI(Tl)検出器
Radiative Capture and Photodisintegration
Nuclear Statistical Quantities in the Hauser-Feshbach model
A(x, g)B (x= n, p, d, t, 3He, a)
x= n: s & r processes
Optical potential
Mass, deformation
continuum
Level density
A+x
g-ray strength function
Modified from RIPL1
Handbook/IAEA-TECDOC
http://www-nds.iaea.org/ripl/
Discrete levels
Ex, Jp
B
Neutron Capture and Photodisintegration
Brink hypothesis: GDR is built on excited states.
n(E)
GDR
(g,n)
(n,g)
Gamow peak
Sn
Ex
(Z, A-1)
Key issues
ng(E,T)
(g,g’)
Planck Distr.
lgn  c


0

n g ( E , T ) n ( E ) dE
(Z,A)
・E1, M1 g SF
above and below Sn
・NLD
Main ingredients in the Talys code
Talys code: Koning, Hilaire, Duijvestijn, Proc. Int. Conf. on Nuclear Data
for Science and Technology AIP Conf. Proc. 769, 1154 (2005).
 E1 g strength function
Lorentzian models:Axel, PR126 (1962), Kopecky & Uhl, PRC41 (1990)
HFB+QRPA model: Goriely, Khan, Samyn, NPA739 (2006)
 Nuclear Level density
HFB+ Combinatorial model: Hilaire & Goriely, NPA779 (2006)
 Spin-flip giant M1 g strength function by Bohr & Mottelson
Global systematics in RIPL Handbook
Lorentzian function : Eo=41A-1/3 MeV, Go = 4 MeV,
fM1=1.58 10-9 A0.47 MeV-3 at 7 MeV
(g,n) cross sections on Zr isotopes
91Zr(g,n)90Zr
Threshold behavior of (g,n) cross sections
is given by
92Zr(g,n)91Zr
94Zr(g,n)93Zr
 E  Sn
 ( E )   o 
 Sn




 1 / 2
.
In the E1 photo-excitation,   1
is allowed. However, the
experimental cross sections are
strongly enhanced from the
expected   1 behavior.
The Lorentzian parametrization of the
E1 g-ray strength function
91Zr(n,g)92Zr
92Zr(g,n)91Zr
8
10
12
14
E [MeV]
16
The generalized Lorentzian parametrization of the E1 g-ray
strength function significantly underestimates the cross sections .
The standard Lorentzian parametrization of the E1 g-ray strength
function for 92Zr can fit the (g,n) data, but strongly overestimates
(n,g) cross sections.
M1 strength in Zr isotopes in the photoneutron channel
91Zr(g,n)90Zr
H. Utsunomiya et al., PRL100 (2008)
91Zr(n,g)92Zr
M1
E1
92Zr(g,n)91Zr
M1
E1
94Zr(g,n)93Zr
M1
E1
The HFB+QRPA E1 gSF
Plus
M1 resonance
Eo= 9 MeV, σ0=7.5mb, G=2.5MeV
in Lorentz shape.
M1 strength in Zr isotopes
(p,p’): giant M1 resonance
Crawley et al., PRC26, 87 (1982)
Nanda et al., PRL51 (1982)
Anantaraman et al., PRL46 (1981)
Bertrand et al., PL103B (1981)
Other probes
M1
GDR
Sn
E1
M1
E1
Sn
E1
g,g’): giant M1 resonance
Sn
Laszewski et al., PRL59 (1987)
(e,e’) weak & fragmented
Meuer et al., NPA 1980
M1
E1
M1
Sn
Excitation Energy
96Zr(g,n)95Zr
g-ray strength functions
E1 : HFB+QRPA, Goriely et al. (2004)
M1 resonance in Lorentz shape
Eo = 8.5 MeV (9.0 MeV for 91,92,94Zr)
0 =7.5mb
G=2.5 MeV
Preliminary
96Zr(g,n)95Zr
NLD
HFB+ Combinatorial
Goriley & Hilaire (2008)
Optical potential
Koning & Delaroche (2003)
95Zr(n,g)96Zr
95Zr(n,g)96Zr
96Zr
=64
d](n,
g)
1/2
s-process branching
95Zr[T
Uncertainties : 30 – 40%
in 0.01 – 1 MeV
Preliminary
Sources of uncertainties
NLD models
1.HFB+Combinatorial
2.BSFG
3.CT (Constant Temp.)
4.GSM (Gen. Superfluid)
5.HFBCS+statisticales
Optical potential models
1.KD (Koning & Delaroche 2003)
2.JLM (Bauge et al. 2001)
93Zr(n,g)94Zr
93Zr(n,g)94Zr
×106 y](n, g)94Zr
Transmutation of nuclear waste
93Zr known as LLFP (long-lived
fission products)
93Zr[T
1/2=1.5
Preliminary
Uncertainties : 40 – 50%
in 0.01 – 1 MeV
Sources of uncertainties
NLD & Optical pot. models
Pigmy E1 resonance in 117Sn
117Sn(g,n)116Sn
断面積のしきい値振る舞い（1点鎖線、l=1）に
 1 / 2
従わない。
 E  Sn 


 Sn 
 ( E )   o 
116Sn(n,g)117Sn
Lorentz型のガンマ線強度関数（破線）で
117Sn(g,n)断面積はフィットできるが、
116Sn(n,g)断面積はoverestimateする。
Solution： HFB+QRPAガンマ線強度関数（点線）に Pigmy resonance
（Eo=8.5 MeV, G=2 MeV, so=7 mb in Gaussian shape）を導入すれば、117Sn(g,n)断面積
だけでなく116Sn(n,g)断面積もほぼ再現できる。
Pigmy resonance in 116Sn
しきい値が高いeven-A核である116Snの場合は、pigmy resonanceの
high energy partが(g,n)断面積に寄与していると考えられる。
g-ray SF for 117,116Sn
Comparison with Oslo data
117Sn
116Sn
s-process production of 180Tam
5-,
4-,
3-,
…
(7/2+)
179Ta
3+
…
s wave
neutron
4+,
5-
2-
9/2-, 7/2-, 5/2-
s wave
neutron
T1/2=1.82y
6+
Nuclear Level Density
E1
7-
(9-) = total - gs
8+
T1/2 > 1.2×1015y
T1/2=8.152h
9-
75.3
2+
42
1+
0
180Ta
7/2+
181Ta
Experimental results, and comparison with
theoretical models
Goko et al. Phys. Rev. Lett. 96, 192501 (2006)
Cross Sect ion [mb]
181
Ta(g,n)
180
Ta
100
Combinatorial NLD
Hilaire & Goriely, NPA779 (2006)
10
HF + BCS NLD
1 81
1
Ta( g,n)
1 80
Ta
m
0.1
7
8
9
10
11
12
13
14
E [MeV]
g
Present work (2006)
IAEA : Lee et al. (1998)
High-spin states with J
needed in Ex < 5 MeV.
5
are
Summary
 The gSF and NLD are key nuclear statistical quantities in the
Hauser-Feshbach model calculations of reaction rates of
direct relevance to the nucleosynthesis of heavy elements.
 Systematic studies of extra g-ray strength arising from M1
and pigmy E1 resonance in the low-energy tail of GDR are
important to improve the predictive power of the HauserFeshbach model for the nucleosynthesis of heavy elements.
 The unique spin and parity of isomeric states can be a good
probe of NLD by measuring relevant partial cross sections