Critical Role of Nuclear Data in Nuclear Astrophysics
Yasuki Nagai
RCNP, Osaka Univ.

Outline♦ Motive:
Nuclear-astrophysics & -physics view points♦ Experimental method:
photon-, α- and neutron-induced reactions with new methods♦ Results:♦ Summary:Observing Universe with Nuclear Telescope
Big Bang
Inflation
Cosmic Microwave Background

Quaser

0.4 MyAbundance

Stellar Generation & Elemental Abundance

1 Gy

Mass

Present

14 Gy
HSTSubaruAbundance

Galaxy Formation

Mass

Observation

View of evolution of universe

Stellar Evolution & Origin of Elements
Tool to trace the history of Galaxy1) Photoreaction of D, 3He & 4He at threshold region
with a newly developed method (focus on 4He)

Scenario of Super Nova ExplosionννCore collapse
ρc ~ 1010 g/cc
Tc ~ 1 MeV

ν-trappingρc ~ 1012 g/cc
Tc ~ 2 MeV

e-capture1000 kmννν Eν ~1053 erg

νExplosion
Core bounceρc ~ 1014 g/ccνTc ~ 5 MeVEmatter ~1051 erg

νShock wave

ν-heating

Neutronstar

ν R-process
10 km

4He:

rapid Process & Supernovae Explosion

1) Astrophysical site for r-process: remain open question !

♦ r-process induced by ν-driven wind from a nascent neutron starν interact with 4He:

4He(ν,ν’n)3He,4He(ν,ν’p)3H

Woosley et al. ApJ. (1990)

2) ν-heating in Delayed Explosion in Type II Supernovae
Energy Transfer by ν-Nucleus Interaction:
Influence the explosion process

Janka-Müller, A&A 306 (1996) 167

Neutrino induced breakup cross section for 4He:
Necessary to estimate the yield of the r-process elements & tostudy a role of the neutrino in the delayed supernovae explosion.
Point:

Woosley et al., Haxton et al.

ν-nucleus interaction & EM interaction with nuclei: similar
first forbidden & electric dipole

4He: Nuclear Physics Interest♦ 4He: Lightest self-conjugate nucleus with closed shell structure♦ 4He(γ,N) in the GDR region: Proceed mainly by electric dipole⇓
1) Ideal testing ground for theory on NN, 3N, collective structure
Efros, Leidemann et al.

2) Charge symmetry:
Florizone et al. Phys. Rev. Lett.(1994)

Ratio of the σ(γ,p) to σ(γ,n):Test the validity of charge symmetryof the strong interaction

Shaded region: recommended ratio (Caralco et al.)Experimental and theoretical situations on
the photodisintegration of 4He:
Complicated, despite the progresses madeby many researchers(γ,p) & (γ,n) Data21▲■▼◆

4He(γ,p)3H4He(γ,n)3He

Cross Section [mb]Cross Section [mb]4He(γ,p)3H

21▲ ■◆ ▼ ● 4 He(γ,n) 3 He○□△▽ 3H(p,γ)4He◇＋×0202530Eγ [MeV]

35○△40◆ Gorbunov 62 ▼ Arkatov 78 ▲ Bernabei 88■ Hoorebeke 93 ＋ Gardner 62 × Gemmell 62◇ Meyerhof 70 △ McBroom 82 ▽ Calarco 83○ Feldman 90□ Hahn 95

0202530E γ [M eV ]3He(n,γ) 4 He

35

◆ Gorbunov 62 ▲ Berman 80 ■ Malcom 73▼ Irish 73 ● Nilsson05△ Ward 81 ○ Komar 93

1) Measurement: separately for (γ,p) & (γ,n). {except few}
2) Large discrepancy between different data sets
3) Systematic uncertainty >> Statistical uncertainty

40

Develop a System with Small Systematic Uncertainty
Photon Probes and Measured Cross Sections
4He(γ,p)3H

Monochromatic γ
Bremsstrahlung
Radiative capture

Cross Section [mb]2104He(γ,n)3He210203040Eγ [MeV]

Data by Bremss. larger than data by monochro. below ~35 MeV50

Remarks of the (γ,N) Reaction Study at Low Energy1) γ-ray flux: low, ~104/s ⇒ pulsed photons to discriminate true
events from beam uncorrelated events
2) Energy of emitted particles: low, < a few MeV ⇒ active target,
to detect particles with 100 % efficiency
3) Cross section: small, a few mb ⇒ 4π detector

Our Method
1) Monoenergetic pulsed laser Compton backscattering photon2) Time projection chamber with active 4He gas target
3) Simultaneous measurement for 4He{(γ,p) & (γ,n)}:Essential to determine the ratio of σ(γ,p)/σ(γ,n)

Experiment at AIST (Tsukuba)
Laser-Compton backscattered γ-ray : Eγ = 2~32MeV, Φγ =104 /sec
Storage ring TERAS
e-(800MeV), 6ns, 100MHzγ - collimator

150 ns, 1kHz
Nd-YLF Laser( λ = 1053nm, 527nm, 351nm)

MirrorBGO γ-ray monitor

Time Projection
Chamber( He + CH4 mixture )Key Points to obtain real events with large S/N:1) Real events: produced (i) along LCS-beam path with 2 mm φ(ii) when pulsed LCS-beam enters TPC

Time Projection Chamber
Target gas :He + CH4 (CD4)

Kii, Shima, Baba,Nagai, NIM (2005)

Key Points :1) Track shape, dE/dx, reaction point ⇒ event identification,dσ/dΩ, asymmetry(Note: we detect a charged fragment)

2) Solid angle: ~ 4π, Detection efficiency : ∼100%3) E(ion) decreases, energy deposited in the TPC by ion increases,differs from other detectors, powerful for (γ,N) near threshold.

How to Identify Events
Background (electron, natural) and True Events (4He, 12C)Counts104x [mm]1) Electron: small pulse heightthreshold level(offline analysis)

30

103

02-3001010150100150200250z [mm]Track of scattered electron

100010203040
Pulse Height [channel]502) True Events of 4He and 12C:
path length, tack width, pulse height, reaction kinematics

Track Shape & Pulse Height for 4He

30

4He(γ,n)3(a)x [mm]

x [mm]

4He(γ,p)H0γ-beam-30
250

200150p100-30250

500z [mm]

He

200

150

100

500z [mm]30(b)observed
Monte Carlo calc.
(χ 2=1.11)(b)

20CountsCounts3(a)0γ-beam

30

10030observed
Monte Carlo calc.
(χ 2=1.08)

201010203040
Pulse Height [channel]

50010203040
Pulse Height [channel]50

D(γ,p)n : Critical Test of the System♦Why we used it to test the system
1) Use He+CD4 instead of He+CH42) Energy deposit by proton in the TPC< energy deposit by 3He

0.56 ± 0.04 ± 0.03
⇔ 0.55 mb (theo.)

1.2
Cross Sction [mb]σ(γ,p: mb) =He+CD4 mixture in TPC

Highly sensitive method:Experimentally demonstrated○ Present△ Skopik 74○ Bernabei 86○ Leleux 79, 85
× Michel 89

0.8

Theory0.401015202530Eγ [MeV]3540

σ(γ,p) & σ(γ,n) for 4HeShima et al. PR C72(2005)

He(γ,p)3H42102025303540Eγ [MeV]

Efros et al.,Lorentz Integ. Trans.

4550

Cross Section [mb]Cross Section [mb]4He(γ,n)3He

21020

ResultSandhas et al.,Faddeev-AGS formalism

25303540Eγ [MeV]4550

Londergan & Shakin
Shell model with tensor1) σ(γ,p) & σ(γ,p) monotonically increase with energy up to 30 MeV2) σ(γ,p) differ from old data & recent theoretical cal.
3) σ(γ,n) agree with Berman’s data & Sandhas’s cal. up to 26 MeV.
4) Tensor force play a role? Open question!

Result for 3He

31He(γ,p)dNaito et al. Phys. Rev. C73 (2006)

Cross Section [mb]

0.5
0
1.5

Present

3He(γ,pp)n1

Faddeev (AV18)

0.5

Faddeev(AV18+Urbana-IX)

02

Total

(Krakow, Bochum, Julich, Kyusyu)

10510152025Eγ [MeV]30351) At 16 MeV, present data agree with old data, & with cal. values.
2) At 10.2 MeV, measured σ(γ,p) is ∼20% & σ(γ,pp) is ∼ factor 3smaller than the calculated values.

１２C(α,γ）16O reaction study at Ec.m.=300 keV

Aim:Key points: １２C(α,γ）16O cross section at Ec.m.≤ 1.5 MeV* Cross section < 1 nbarn

SE2 [keV b]

Astrophysical SE2 factor

101

100

11.5

22.5

Ecm [MeV]

33.5keV Neutrons Radiative Capture Reaction
neutronprompt discrete γ-ray

Comparison of (n,γ) to (γ,N) studies(γ,N)
ground & continuum(n,γ)
ground + continuum+ excited bound states

Essential point:
Detect discrete γ-rays from the (n,γ) to low-lying states

Experimental Setup
Proton beam: 3.2 MV Pelletronat Tokyo Inst. Tech.

Neutron
7Li(p,n)
En=10-90keV

C o u nt s /1 k e V(´ 1 0 6)

15keV90keV

0 .5

0197Au: Normalization of the cross section

well known within 3% uncertainty

0204060

Neutron Energy [keV]80100

Weak Component: bottle-neck reaction 62Ni(n,γ)63Ni
From onset of central H-burning through explosion as Type II SNPopulation I stars of 15 ∼ 25 M~

Rauscher et al. 2002
Overproduction
factorMass number A• Overproduction of 62Ni
compared to the solar abundance• σ(n,γ:62Ni) affects overallcalculated abundance forweak s-process elements♦ Previous data on σ(n,γ:62Ni) at a stellar temperature• well known at thermal energy• MACS (Maxwellian averaged capture cross section) at 30 keV

26(5) mb Beer (74), 35.5(4) mb Bao (87), 12.5(4) mb Bao (00)• assume s-wave capture & apply a 1/v law ?

at -0.077 keV andthe near threshold resonance at 4.5 keV ?

4.51+/20.07
7.s.

c.s.

1+/2

Problems in obtaining σ(n,γ:62Ni) at keV• contribution of the sub-threshold resonance1+/262Ni

3−/2518

1−/2063Ni

♦ γ-ray spectrum for 62Ni(n,γ)63Ni
Tomyo et al. ApJ.(2005) Lett.

1+/2

4.5

1+/20.07
7.s.

c.s.

1+/262Ni

3−/2518

1−/2063Ni♦ Characteristic point of the γ-ray spectrum:• Partial cross section for the 6.8 MeV γ-ray fromthe neutron capture by 62Ni to the ground state:~ half of the total cross section.
→ reaction proceed a non-resonant s-wave capture• Ratio Yγ(c.s.→3/2-)/Yγ(c.s.→1/2-) is very small?

Measured γ-ray branching ratio as a function of En :

4.5

c.s.

100

1+/20.07
7.s.

50

ratio [%]

1+/21+/262Ni

3−/2518

1−/2063Ni

Iγ(c.s. → 3/2- )Iγ(c.s. → 1/2- )

10

1020

4060

Neutron Energy [keV]80Summary1) Method for photonuclear reaction study: developed→ allow to measure observables with high precision2) Method for 12C(α,γ)16O reaction study: developed→ allow to determine σ(α,γ) down to Ec.m.≤1.0 MeV3) Method for (n,γ) reaction study: improve Igashira Gr.
→ allow to measure very small σ(n,γ) of ∼1 µb4) Method for (n,n’) and (n,n’γ) reaction study: developed.
→ provide crucial information to calculate σ(n,γ) forthe excited nuclear state in stellar environments
Open New Generation of Nuclear Astrophysics StudyColleague
RCNP: T. Shima, S. Naito, A. Tomyo, H. Makii, K. Mishima, M. Segawa, E. Sano,
H. Ueda, Y. Temma, T. Masaki, T. Ohta, A. Nakayoshi, S. Fujimoto
Tokyo Inst. Tech. (Research Lab. Nucl. Reactors):
M. Igashira, T. Ohsaki, J. Nishiyama
Tokyo Inst. Tech. (Dept. Applied Phys.):K. Takeda, S. Motoyama, K. Senoo, K. Watanabe, T. Irie, S. Seino, T. Suzuki,T. Kikuchi, T. Kii, T. Baba, T. Kobayashi, Y. Nobuhara, M. Kinoshita
AIST:

H. Ohgaki (Kyoto Univ.), H. Toyokawa

γ-ray Pulse Height & LCS Photon FluxE γ (max)=22.4M eV
3000

CountsExperim entAverage flux ~104 /s⇔ Pulse rate 1~5kHzSim ulation(M γ =5.2)

2000

Photon counting by
pile-up analysis
10000400
800
1200
1600
Pulse Height [channel]

2000

LCS Photon Flux Φγ :Φγ = Mγ × R.

Mγ : photon multiplicity

R : laser pulse rate

Charge Symmetry
Ratio of two body cross sections, R= σ(γ,p)/σ(γ,n)
32.5Rγ21.5△◆×●

10.5
020

2224

2628Eγ [MeV]30

Londergan & Shakin
Halderson & Philpott
H. & P. with CSB×3
Unkelbach & Hofmann
Gorbunov 1974
Balestra et al. 1977Florizone et al. 1994
PresentPresent (fit)32♦ First simultaneous measurement with 4 π geometry♦ Consistent with an expected value without CSB.

Kunz et al., Phys. Rev. Lett. (2001)

Assuncao et al. Phys. Rev. C (2006)