Direct measurement of 12 C + 4 He 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 K yushu U niversity T andem accelerator L aboratory

H-burning 4p → 4 He via p-p chain & CNO cycle He-burning 3 4 He → 12 C C-burning O-burning Si-burning Burning process in stars 12 C/ 16 O ratio affects widely further nuclear synthesis. 4 He+ 12 C → 16 O+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   α4α 3α ~40 years 17 years 4 He+ 12 C → 16 O+  4 He+ 12 C → 16 O+γ experiment is very difficult. 4 He + 12 C → 16 O + 

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

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

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

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

③ ② ① Yield of 12 C + 4 He → 16 O + γ Y( 16 O) =  ・ N( 12 C) ・ N( 4 He ) ・ Detection Efficiency ・ Beam Time ・ necessary components for E cm =0.7MeV experiment -high intensity 12 C beam: ~ 10 p  A （ Limit of our tandem accelerator ） -Thick windowless 4 He gas target : ~20 Torr x 4 cm (Limit of  E in the target ） - high detection efficiency (~40%) ・ Y( 16 O) ~ 5 counts/day at Ecm=0.7MeV → 1 month exp. Background (BG) reduction N( 16 O)/N( 12 C) ~ N(BG) / N( 12 C) < beamtargetdetect Cross section (S=const.) 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 extrapolateexperiment

Setup for 4 He( 12 C, 16 O)  Experiment at Kyushu University Tandem Laboratory (KUTL) Detector (Si-SSD) Sputter ion source 12 C beam Tandem Accelerator Final focal plane (mass separation) Blow in windowless 4 He gas target Long-time chopper chopper buncher 16 O 12 C Recoil Mass Separator (RMS) E cm = 2.4~0.7 MeV E( 12 C)=9.6~2.8 MeV E( 16 O)=7.2~2.1 MeV Tandem RMS E-def D-mag

normal operation accel-decel operation Al shorting bars for accel-decel operation Accel-decel operation of tandem accelerator Y(16O) =  ・ N( 12 C) ・ N( 4 He ) ・ 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. ① Increase the 12 C beam Totally, beam intensity is ~100 times increased

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 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 experiment (limited by energy loss of 12 C beam) (limited by energy loss of 12 C beam) SSD: beam monitor 4.5cm Blow-In Gas Target (BIGT) –windowless & high confinement capability beam Y(16O) =  ・ N( 12 C) ・ N( 4 He ) ・ Det.Efficiency ・ Beam Time ② Increase the 4 He gas target Thickest in the world 24Torr

③② ① Recoil Mass Separator All the 16 O recoils(±2°) in a charge state (~40%) are detected. 12 C + 4 He → 16 O +γ yield has been increased Y( 16 O) =  ・ N( 12 C) ・ N( 4 He ) ・ Detection Efficiency ・ Beam Time ③ Increase the 16 O detection efficiency 12 C + 4 He → 16 O +γ 12 C beam 4 He windowless Gas target Eject within 2° 16 O E-def D mag detect 16 O 5+

RF-Deflector BG reduction Background 12 C are produced by multiple scattering charge exchange Background reduction ・ Recoil Mass Separator background reduction ~ ・ TOF with Pulsed beam ~10 -2 ・ Long-Time Chopper(RF deflector) ~10 -3 N(BG)/N( 16 O) become Goal: N(BG)/N( 12 C) < At present: N( 16 O)/N( 12 C) ~ at 0.7MeV E-defD mag LTC

pass only reaction products ( 16 O) which are spread in time. f 2 =3×f 1 V 2 =V 1 /9 f 1 =6.1MHz V 1 =±24.7kV V 3 =23.7kV reject BG Pass 16 O + Flat-bottom voltage Long-Time Chopper(RF deflector) BG( 12 C) 16 O events Measurement of 4 He( 12 C, 16 O)γ at Ecm = 2.4 MeV BG reduction RF-Deflector LTC without LTC with LTC

14 4 He( 12 C, 16 O)  at E cm =2.4MeV experiment beam: 12 C 2+, frequency: 6.063MHz – energy: 9.6MeV, intensity: ~35pnA target: 4 He gas ~ 23.9 Torr x 3.98 cm observable: 16 O ± 0.3 MeV – abundance = 36.9 ± 2.1 % = efficiency 29hours data 941 counts 16 O

2.4MeV – 4 He( 12 C, 16 O)  at E cm =2.4MeV experiment Our data Ruhr univ.

4 He( 12 C, 16 O)  at E cm =1.5 MeV experiment beam: 12 C 1+, frequency: 3.620MHz – energy: 6.0MeV, intensity: 60pnA target: 4 He gas 15.0 Torr x 3.98 cm observable: 16 O 3+, 4.5 ± 0.3 MeV –abundance = 40.9 ± 2.1 % = efficiency 208 counts 95 hours data 16 O

Ruhr U. Kyushu U. extrapolation Cross Section and S tot -factor 1.5MeV – Next experiment is E cm =1.15  1.0  0.85  0.7 MeV Stellar energy Our exp. plan preliminary

Further BG reduction is necessary 95 hours data 16 O In order to go to low energy further BG Reduction is necessary! Ecm=2.4MeV σ ～ 65nb Increased BG 1.5MeV σ ～ 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 16 O from BG ( 12 C) 16 O 12 C 4 He   16 O BG reject 16 O and 12 C separation by Ionization chamber － ＋ cathode anode PR Gas 30Torr very thin foil (0.9μm) 16 O, 12 C e－e－ Si-SSD e－e－ e－e－ e－e－ ΔE E low energy ΔE of 16 O is larger than 12 C

BG reduction by Ionization Chamber 95 hours data Huge 12 C-BG will be eliminated using the ionization chamber. Ionization chamber will be available from October O 12 C 4 He   16 O BG reject 16 O

Summary Direct measurement of 4 He+ 12 C  16 O+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. E cm = 2.4 MeV experiment –  = 64.6 nb, – S-factor = 89.0 keV b E cm = 1.5 MeV experiment –  = nb, – S-factor = 26.6 keV b Now we are developing an ionization chamber. Experiments of 4 He+ 12 C  16 O+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

R.Kuntz, M.Fey, M.Jaeger, A.Mayer, W.Hammer Astrophysical J (2002) 643 － 650 A rehearsal for extrapolation using R-matrix theory Ecm ［ MeV ］ S-factor ［ keV b ］ 70.0± ± ± ± ±3.0 Assumed data (±10%) Data from Ruhr university Assumed data S(0.3MeV) extrapolated = 190±15 keV b 1－1－ 2＋2＋ 0.3 Reliable theoretical curve will be necessary for extrapolation + +  