1. Direct measurement of 12C + 4He fusion cross section at Ecm=1
Direct measurement of 12C + 4He fusion cross section at Ecm=1.5MeV at KUTL
H.Yamaguchi
K. Sagara, K. Fujita, T. Teranishi, M. taniguchi, S .Liu,
S. Matsua, Maria T. Rosary, T. Mitsuzumi, M. Iwasaki
Kyushu University Tandem accelerator Laboratory

2. Burning process in stars
H-burning
4p → 4He
via
p-p chain &
CNO cycle
He-burning
3 4He → 12C
C-burning
O-burning
Si-burning
4He+12C → 16O+g
12C/16O ratio affects widely further nuclear synthesis.
4He+12C → 16O+γ cross section has not been determined yet,
in spite of 40 years efforts in the world.
4He+12C → 16O+γ experiment is very difficult.
4He + 12C → 16O + g
world
~40 years +  g α 4α 3α
C. Rolfs
(Ruhr Univ.)
goal
Kyushu U.
17 years
2010
1970
1990

3. Why is 4He+12C→16O+γ experiment so difficult?
At 0.3MeV 4He(12C,16O)g Cross Section is
very small (~10-8 nb) due to Coulomb repulsion E1 E2
Cross section (S=const.)
10-5
0.7
0.3
2.4
Experiments
Extrapolation
Experiment
stellar
energy
0.3
Coulomb-barrier effect
Really low-energy experiments near 0.3MeV are necessary
to make reliable extrapolation.

4. Experimental methods for 4He+12C→16O+γ cross section

5. γ S-factor has not been precisely determined yet.
4He+12C→16O+γ experiment with γ　detection → γ
Stellar energy
Cross section (S=const.)
10-5
No precise data at low energy
due to
・low detection-efficiency of γ-rays
・huge Back Ground (BG) γ-rays
Coulomb barrier effect
S-factor has not been precisely determined yet.

6. Experimental methods for 4He+12C→16O+γ cross section
high detection efficiency (~ 40%: charge fraction)
total S-factor can be measured

7. Background (BG) reduction
Cross section is very small
Increase the yield
Yield of 12C + 4He → 16O + γ
Y(16O) = s・ N(12C)・N(4He )・ Detection Efficiency ・ Beam Time
beam
target
detect ① ② ③
・necessary components for Ecm=0.7MeV experiment
high intensity 12C beam: ~ 10 pmA
（Limit of our tandem accelerator）
Thick windowless 4He gas target : ~20 Torr x 4 cm
　　　　　　　　　　　　 (Limit of DE in the target）
- high detection efficiency (~40%)
Cross section (S=const.)
10-5
0.7
0.3
2.4
・Y(16O) ~ 5 counts/day at Ecm=0.7MeV
→ 1 month exp.
extrapolate
experiment
at Ecm = 0.6 MeV →　10 month exp.
at Ecm = 0.3 MeV →　7,000 year exp
Background (BG) reduction
N(16O)/N(12C) ~ 10-18
N(BG) / N(12C) < 10-19
Very hard to realize

8. Setup for 4He(12C,16O)g Experiment
at Kyushu University Tandem Laboratory (KUTL)
Tandem Accelerator
buncher
chopper
Blow in windowless
4He gas target
12C beam
RMS
12C
Sputter
ion source
E-def
D-mag
Recoil
Mass
Separator
(RMS)
This is the setup for this experiment.
Ion source produce the C beam.
The beam is accelerated by the Tandem accelerator and injected to the windowless He gas target
The recoil O is saparated from C beam by the Recoil Mass Separator, .
The O is detected here.
Using the beam chopper and buncher, we produce a pulsed beam, and measure Time Of Flight to reduce background.
Tandem
Long-time chopper
D-mag
Ecm = 2.4~0.7 MeV
E(12C)=9.6~2.8 MeV
E(16O)=7.2~2.1 MeV
Final focal plane
(mass separation)
16O
Detector (Si-SSD)

9. Accel-decel operation of tandem accelerator
①Increase the 12C beam
Accel-decel operation of tandem accelerator
Y(16O) =　s・N(12C)・N(4He )・ Det.Efficiency ・ Beam Time
accel-decel
operation
normal
operation
Al shorting bars
for accel-decel operation
At low acceleration voltage, focusing becomes weak, and
beam transmission decreases.
By alternative focus-defocus, focusing becomes strong, and
beam transmission increases.
・10 times higher beam transmission is obtained by strong focusing.
・10 times more intense beam can be injected.
Totally, beam intensity is ~100 times increased

10. ②Increase the 4He gas target
Windowless Gas Target
②Increase the 4He gas target
Y(16O) =　s・N(12C)・N(4He )・ Det.Efficiency ・ Beam Time
Blow-In Gas Target (BIGT)
windowless & high confinement capability
RMS
TMP3
TMP4
MBP2
TMP2
TMP5
MBP1
beam
TMP1 DP
1500 l/s
3000 l/s
330 l/s
520 l/s
350 l/s
24Torr
beam
4.5cm
SSD: beam monitor
Differential pumping system (side view)
center pressure: 24 Torr
effective length: 3.98 ± 0.12 cm (measured by p+α elastic scattering)
→ target thickness is sufficient for our experiment
(limited by energy loss of 12C beam)
Thickest in the world

11. ③Increase the 16O detection efficiency
12C + 4He → 16O +γ
Recoil Mass Separator
All the 16O recoils(±2°)
in a charge state (~40%) are detected.
Eject within 2°
4He windowless
Gas target
D mag
12C beam
16O
detect
16O5+
E-def
D mag
12C + 4He → 16O +γ yield has been increased
Y(16O) =　s・N(12C)・N(4He )・ Detection Efficiency ・ Beam Time ① ② ③

12. BG reduction Background 12C are produced by Background reduction
Goal: 　N(BG)/N(12C) < 10-19
N(16O)/N(12C) ~ at 0.7MeV
Background 12C are produced by
multiple scattering
charge exchange
Background reduction
・Recoil Mass Separator
　　　　 background reduction ~10-11
・ TOF with Pulsed beam ~10-2
・Long-Time Chopper(RF deflector)
~10-3
RF-Deflector
E-def
D mag
LTC
D mag
Another big problem is BG reduction.
Our final goal is 10 (-19).
By Recoil Mass Separator, BG are reduced to 10 (-11) level.
By Time-Of-Flight technique with pulsed beam, BG are reduced to 10 (-2) .
By Long-Time-Chopper, BG are reduced to 10 (-3) . I will explain Long-Time-Chopper soon.
Totally, BG are reduced to 10(-16), at present.
At present:
N(BG)/N(16O) become 10-16

13. Long-Time Chopper(RF deflector)
BG reduction
Long-Time Chopper(RF deflector)
pass only reaction products (16O) which are spread in time.
f2=3×f1
V2=V1/9
f1=6.1MHz
V1=±24.7kV
V3=23.7kV
reject BG +
Pass　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　
　　　　16O
Flat-bottom voltage
with LTC
without LTC
RF-Deflector
LTC
BG(12C)
16O5+
500events
Measurement of 4He(12C,16O)γ at Ecm = 2.4 MeV

14. 4He(12C,16O)g at Ecm=2.4MeV experiment
beam: 12C2+, frequency: 6.063MHz
energy: 9.6MeV , intensity: ~35pnA
target: 4He gas ~ 23.9 Torr x 3.98 cm
observable: 16O ± 0.3 MeV
abundance = 36.9 ± 2.1 % = efficiency
29hours data
941 counts
16O

15. 4He(12C,16O)g at Ecm=2.4MeV experiment
Ruhr univ.
Our data
2.4MeV

16. 4He(12C,16O)g at Ecm=1.5 MeV experiment
target: 4He gas Torr x 3.98 cm
observable: 16O3+, 4.5 ± 0.3 MeV
abundance = 40.9 ± 2.1 % = efficiency
beam: 12C1+, frequency: 3.620MHz
energy: 6.0MeV, intensity: 60pnA
95 hours data
16O
208 counts .

17. Cross Section and Stot-factor
extrapolation
Our exp. plan
Stellar energy
preliminary
Kyushu U.
Ruhr U.
1.5MeV
Next experiment is Ecm=1.151.00.850.7 MeV

18. Further BG reduction is necessary
95 hours data
16O
Ecm=2.4MeV
σ～65nb
1.5MeV
σ～0.7nb
down to
0.7MeV
Increased BG
In order to go to low energy
further BG Reduction is necessary!

19. further BG reduction 16O and 12C separation by Ionization chamber
measure the ΔE (∝energy loss) by the ionization chamber (and E by the SSD) － ＋
cathode
anode
PR Gas 30Torr
very thin foil (0.9μm)
16O,12C e－
Si-SSD ΔE E
low energy
ΔE of 16O is larger than 12C
16O
12C
4He
E+DE DE BG
reject
We can separate 16O from BG (12C)

20. BG reduction by Ionization Chamber
Huge 12C-BG will be eliminated using the ionization chamber.
95 hours data
16O
12C
4He
E+DE DE BG
reject
16O
Ionization chamber will be available from October 2011.

21. Summary
Direct measurement of 4He+12C 16O+γ cross section (total S-factor) is in progress at KUTL (Kyushu Univ. Tandem Lab.)
Many new instruments and methods have been developed for this experiment.
Ecm= 2.4 MeV experiment
s= 64.6 nb,
S-factor = 89.0 keV b
Ecm= 1.5 MeV experiment
s= nb,
S-factor = 26.6 keV b
Now we are developing an ionization chamber.
Experiments of 4He+12C 16O+γ at Ecm = 1.51.151.00.850.7MeV will be made in a few years.
future plan
, 2010
stellar energy
Stellar energy

22. A rehearsal for extrapolation using R-matrix theory
R.Kuntz, M.Fey, M.Jaeger, A.Mayer, W.Hammer
Astrophysical J (2002) 643－650
Ecm［MeV］
0.70
0.85
1.00
1.15
1.50
S-factor［keV b］
70.0±7.0
50.0±5.0
45.0±4.5
35.0±3.5
30.0±3.0
Assumed data (±10%) 2＋ 1－
S(0.3MeV) extrapolated = 190±15 keV b
Data from
Ruhr university
Assumed data
Reliable theoretical curve will be necessary for extrapolation +  g
0.3