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

H-burning

4p → 4Hevia

p-p chain &CNO cycle

He-burning

3 4He → 12C

C-burning

O-burning Si-burning

Burning process in stars

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.

C. Rolfs (Ruhr Univ.) Kyushu U.

world

goal

20101970 1990

+ +

α 4α3α

~40 years

17 years

4He+12C → 16O+

4He+12C → 16O+γ experiment is very difficult.

4He + 12C → 16O +

E1 E2

Why is 4He+12C→16O+γ experiment so difficult?

Really low-energy experiments near 0.3MeV are necessary to make reliable extrapolation.

• At 0.3MeV 4He(12C,16O)Cross Section isvery small (~10-8 nb) due to Coulomb repulsion

Cross section (S=const.)

10-5

10-5

0.70.3 2.40.3

stellar energy

Coulomb-barrier effect

Extrapolation

Experiments

Experiment

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　

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

→ γ

Stellar energy

4He+12C→16O+γ experiment with γ 　 detection

S-factor has not been precisely determined yet.

Cross section (S=const.)

10-5

10-5

Coulomb barrier effectNo precise data at low energy due to ・ low detection-efficiency of γ-rays ・ huge Back Ground (BG) γ-rays

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　

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

high detection efficiency (~ 40%: charge fraction)total S-factor can be measured

③②①

Yield of 12C + 4He → 16O + γ

Y(16O) = ・ N(12C) ・ N(4He ) ・ Detection Efficiency ・ Beam Time

・ necessary components for Ecm=0.7MeV experiment- high intensity 12C beam: ~ 10 pA （ Limit of our tandem accelerator ）- Thick windowless 4He gas target : ~20 Torr x 4 cm　　　　　　　　　　　　 (Limit of E in the target ）- high detection efficiency (~40%)

・ Y(16O) ~ 5 counts/day at Ecm=0.7MeV → 1 month exp.

Background (BG) reductionN(16O)/N(12C) ~ 10-18 N(BG) / N(12C) < 10-19

beam target detect

Cross section (S=const.)

10-5

10-5

0.70.3 2.4

Increase the yield

at Ecm = 0.6 MeV → 　 10 month exp.at Ecm = 0.3 MeV → 　 7,000 year exp

Very hard to realize

Cross section is very small

extrapolate experiment

Setup for 4He(12C,16O)Experimentat Kyushu University Tandem Laboratory (KUTL)

Detector　(Si-SSD)

Sputterion source

12C beam

Tandem　Accelerator

Final focal plane(mass separation)

Blow　in　windowless4He　gas　target

Long-time chopper

chopperbuncher

16O

12C

Recoil　Mass　Separator(RMS)

Ecm = 2.4~0.7 MeVE(12C)=9.6~2.8 MeVE(16O)=7.2~2.1 MeV

Tandem

RMS

E-def

D-mag

D-mag

normal operation

accel-deceloperation

Al shorting bars for accel-decel operation

Accel-decel operation of tandem accelerator

Y(16O) = 　 ・ N(12C) ・ N(4He ) ・ Det.Efficiency ・ Beam Time

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.

①Increase the 12C beam

Totally, beam intensity is ~100 times increased

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　

RMS

TMP3

TMP4MBP2TMP2TMP5

MBP1

beam

TMP1

DP

1500 l/s

3000 l/s330 l/s

330 l/s520 l/s 520 l/s

520 l/s

350 l/s

Windowless Gas Target

Differential pumping system (side view)

• center pressure: 24 Torr center pressure: 24 Torr • effective length: 3.98 ± 0.12 cm (measured by p+α elastic scattering)effective length: 3.98 ± 0.12 cm (measured by p+α elastic scattering)

→ → target thickness is sufficient for our experimenttarget thickness is sufficient for our experiment (limited by energy loss of (limited by energy loss of 1212C beam)C beam)

SSD: beam monitor4.5cm

• Blow-In Gas Target (BIGT)– windowless & high confinement capability

beam

Y(16O) = 　 ・ N(12C) ・ N(4He ) ・ Det.Efficiency ・ Beam Time

②Increase the 4He gas target

Thickest in the world

24Torr

③②①

Recoil Mass Separator

All the 16O recoils(±2°) in a charge state (~40%) are detected.

12C + 4He → 16O +γ yield has been increased

Y(16O) = 　 ・ N(12C) ・ N(4He ) ・ Detection Efficiency ・

Beam Time

③Increase the 16O detection efficiency

12C + 4He → 16O +γ

12C beam

4He windowless Gas target

Eject within 2°

16O

E-def

D mag

D magdetect 16O5+

RF-Deflector

BG reduction

• Background 12C are produced bymultiple scatteringcharge exchange

• Background reduction ・ Recoil Mass Separator background reduction ~10-11

・ TOF with Pulsed beam ~10-2

・ Long-Time Chopper(RF deflector) ~10-3 N(BG)/N(16O) become 10-16

Goal: 　 N(BG)/N(12C) < 10-19

At present:

N(16O)/N(12C) ~ 10-18 at 0.7MeV

E-def D mag

D magLTC

pass only reaction products (16O) which are spread in time.

f2=3×f1

V2=V1/9

f1=6.1MHzV1=±24.7kV

V3=23.7kV

reject BG

Pass

16O

+

Flat-bottom voltage

Long-Time Chopper(RF deflector)

BG(12C)16O5+

500events

Measurement of 4He(12C,16O)γ at Ecm = 2.4 MeV

BG reduction

RF-Deflector

LTC

without LTC with LTC

14

4He(12C,16O)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: 16O5+ 7.2 ± 0.3 MeV

– abundance = 36.9 ± 2.1 % = efficiency

29hours data29hours data

941 counts

16O

• 2.4MeV–

4He(12C,16O)at Ecm=2.4MeV experiment

Our data

bkeV 3.889.0S(2.4) nb, 2.764.6

Ruhr univ.

4He(12C,16O)at Ecm=1.5 MeV experiment• beam: 12C1+, frequency: 3.620MHz

– energy: 6.0MeV, intensity: 60pnA

• target: 4He gas 15.0 Torr x 3.98 cm• observable: 16O3+, 4.5 ± 0.3 MeV

– abundance = 40.9 ± 2.1 % = efficiency

208 counts208 counts

95 hours data95 hours data

16O

Ruhr U.Kyushu U.

extrapolation

Cross Section and Stot-factor

• 1.5MeV–

• Next experiment is Ecm=1.151.00.850.7 MeV

bkeV 2.826.6S(1.5) nb, 0.090.900

Stellar energy

Our exp. plan

preliminary

Further BG reduction is necessary95 hours data95 hours data

16O

In order to go to low energy further BG Reduction is necessary!

Ecm=2.4MeVσ ～ 65nb

Increased BG 1.5MeVσ ～ 0.7nb

down to 0.7MeV

• measure the ΔE (∝ energy loss) by the ionization chamber (and E by the SSD)

further BG reduction

We can separate 16O from BG (12C)

16O

12C

4He

16O

BG reject

16O and 12C separation by Ionization chamber

－

＋

cathode

anode

PR Gas 30Torr

very thin foil (0.9μm)

16O,12Ce －

Si-SSD

e － e － e －

ΔE E

low energy

ΔE of 16O is larger than 12C

BG reduction by Ionization Chamber

95 hours data95 hours data

Huge 12C-BG will be eliminated using the ionization chamber.

Ionization chamber will be available from October 2011.

16O

12C

4He

16O

BG reject

16O

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– = 64.6 nb, – S-factor = 89.0 keV b

• Ecm= 1.5 MeV experiment– = 0.900 nb,– S-factor = 26.6 keV b

• Now we are developing an ionization chamber.

• Experiments of 4He+12C 16O+γ at Ecm = 1.51.151.00.850.7MeV will be made in a few years.

future plan

, 2010

stellar energy

Stellar energy

)]/([

|)(1|

|)]/([|)12(

2

22/12/1

EER

RiPRBS

EEl

k

lll

lllll

lllEl

R.Kuntz, M.Fey, M.Jaeger, A.Mayer, W.Hammer Astrophysical J. 567. (2002) 643 － 650

A rehearsal for extrapolation using R-matrix theory

Ecm ［ MeV ］0.700.851.001.151.50

S-factor ［ keV b ］70.0±7.050.0±5.045.0±4.535.0±3.530.0±3.0

Assumed data (±10%)

Data from Ruhr university

Assumed data

S(0.3MeV) extrapolated = 190±15 keV b1 －2 ＋

0.3

Reliable theoretical curve will be

necessary for extrapolation

++