Direct measurement of 12 C 4 He fusion

Direct measurement of 12 C + 4 He fusion cross section at Ecm=1. 5 Me. V 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

Burning process in stars H-burning He-burning 4 p → 4 He via p-p chain & CNO cycle 3 4 He → 12 C 4 He+12 C → 16 O+g C-burning Si-burning O-burning 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. 4 He+12 C 4 He + 12 C → 16 O + g + +g α 3α → 16 O+γ experiment is very difficult. world C. Rolfs (Ruhr Univ. ) 4α 1970 ~40 years goal Kyushu U. 1990 17 years 2010

Why is 4 He+12 C→ 16 O+γ experiment so difficult? • At 0. 3 Me. V 4 He(12 C, 16 O)g Cross Section is very small (~10 -8 nb) due to Coulomb repulsion Cross section (S=const. ) 10 -5 Experiments 10 -5 Extrapolation 0. 3 0. 7 Experiment 2. 4 stellar energy 0. 3 Coulomb-barrier effect Really low-energy experiments near 0. 3 Me. V are necessary to make reliable extrapolation. E 1 E 2

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

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

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

Increase the yield Cross section is very small Yield of 12 C + 4 He → 16 O + γ beam target detect Y(16 O) = s・ N(12 C)・N(4 He )・ Detection Efficiency ・ Beam Time ① ② ③ ・necessary components for Ecm=0. 7 Me. V experiment - high intensity 12 C beam: ~ 10 pm. A （Limit of our tandem accelerator） - Thick windowless 4 He gas target : ~20 Torr x 4 cm 　　　　　　 (Limit of DE in the target） - high detection efficiency (~40%) ・Y(16 O) ~ 5 counts/day at Ecm=0. 7 Me. V → 1 month exp. Cross section (S=const. ) extrapolate at Ecm = 0. 6 Me. V →　10 month exp. at Ecm = 0. 3 Me. V →　7, 000 year experiment 10 -5 Background (BG) reduction N(16 O)/N(12 C) ~ 10 -18 N(BG) / N(12 C) < 10 -19 0. 3 Very hard to realize 0. 7 2. 4

Setup for 4 He(12 C, 16 O)g Experiment at Kyushu University Tandem Laboratory (KUTL) buncher Tandem Accelerator chopper Blow in windowless 4 He gas target 12 C beam RMS 12 C Sputter ion source Tandem Ecm = 2. 4~0. 7 Me. V E(12 C)=9. 6~2. 8 Me. V E(16 O)=7. 2~2. 1 Me. V Recoil Mass Separator (RMS) E-def D-mag 16 O Long-time chopper Final focal plane (mass separation) Detector (Si-SSD)

①Increase the 12 C beam Accel-decel operation of tandem accelerator Y(16 O) =　s・N(12 C)・N(4 He )・ 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

②Increase the 4 He gas target Windowless Gas Target • Y(16 O) =　s・N(12 C)・N(4 He )・ Det. Efficiency ・ Beam Time Blow-In Gas Target (BIGT) – windowless & high confinement capability 3000 l/s 330 l/s MBP 1 DP 520 l/s TMP 3 bea m 24 Torr beam RMS TMP 5 TMP 2 350 l/s 520 l/s TMP 1 MBP 2 330 l/s TMP 4 520 l/s 1500 l/s 4. 5 cm SSD: beam monitor Differential pumping system (side view) center pressure: 24 Torr Thickest in the world • 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) •

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

BG reduction N(16 O)/N(12 C) ~ 10 -18 at 0. 7 Me. V Goal: 　N(BG)/N(12 C) < 10 -19 • Background 12 C are produced by multiple scattering charge exchange RF-Deflector E-def D mag LTC • Background reduction ・Recoil Mass Separator D mag 　　　　 background reduction ~10 -11 ・ TOF with Pulsed beam ~10 -2 ・Long-Time Chopper(RF deflector) ~10 -3 At present: N(BG)/N(16 O) become 10 -16

BG reduction Long-Time Chopper(RF deflector) pass only reaction products (16 O) which are spread in time. f 1=6. 1 MHz V 1=± 24. 7 k. V + f 2=3×f 1 V 2=V 1/9 reject BG Pass　　　　　　　 　　　　 Flat-bottom voltage 16 O V 3=23. 7 k. V with LTC without LTC RF-Deflector BG(12 C) 16 O 5+ 500 events LTC Measurement of 4 He(12 C, 16 O)γ at Ecm = 2. 4 Me. V

4 He(12 C, 16 O)g • • • at Ecm=2. 4 Me. V experiment beam: 12 C 2+, frequency: 6. 063 MHz – energy: 9. 6 Me. V , intensity: ~35 pn. A target: 4 He gas ~ 23. 9 Torr x 3. 98 cm observable: 16 O 5+ 7. 2 ± 0. 3 Me. V – abundance = 36. 9 ± 2. 1 % = efficiency 29 hours data 941 counts 16 O 14

4 He(12 C, 16 O)g at Ecm=2. 4 Me. V experiment Ruhr univ. Our data • 2. 4 Me. V –

4 He(12 C, 16 O)g • at Ecm=1. 5 Me. V experiment beam: 12 C 1+, frequency: 3. 620 MHz – energy: 6. 0 Me. V, intensity: 60 pn. A target: 4 He gas 15. 0 Torr x 3. 98 cm • observable: 16 O 3+, 4. 5 ± 0. 3 Me. V – abundance = 40. 9 ± 2. 1 % = efficiency • 95 hours data 16 O 208 counts

Cross Section and Stot-factor extrapolation Our exp. plan Stellar energy ary n i m reli p Kyushu U. • Ruhr U. 1. 5 Me. V – • Next experiment is Ecm=1. 15 1. 0 0. 85 0. 7 Me. V

Further BG reduction is necessary 95 hours data 16 O Ecm=2. 4 Me. V σ～ 65 nb Increased BG 1. 5 Me. V σ～ 0. 7 nb In order to go to low energy further BG Reduction is necessary! down to 0. 7 Me. V

further BG reduction 16 O and 12 C separation by Ionization chamber • measure the ΔE (∝energy loss) by the ionization chamber (and E by the SSD) PR Gas 30 Torr ΔE of 16 O is larger than 12 C cathode 16 O, 12 C low energy ΔE Si-SSD E DE － e－ e－ very thin foil (0. 9μm) 16 O 12 C ＋ anode 16 O 4 He BG reject E+DE We can separate 16 O from BG (12 C)

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

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. • Ecm= 2. 4 Me. V experiment – s= 64. 6 nb, – S-factor = 89. 0 ke. V b , 2010 stellar energy Stellar energy • Ecm= 1. 5 Me. V experiment – s= 0. 900 nb, – S-factor = 26. 6 ke. V b future plan • 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. 7 Me. V will be made in a few years.

A rehearsal for extrapolation using R-matrix theory R. Kuntz, M. Fey, M. Jaeger, A. Mayer, W. Hammer Astrophysical J. 567. (2002) 643－650 Assumed data (± 10%) Ecm［Me. V］ S-factor［ke. V b］ 0. 70 70. 0± 7. 0 0. 85 50. 0± 5. 0 1. 00 45. 0± 4. 5 1. 15 35. 0± 3. 5 1. 50 30. 0± 3. 0 S(0. 3 Me. V) extrapolated = 190± 15 ke. V b 2＋ 1－ will be e v r u c etical olation r o e h t Reliableary for extrap necess g + Assumed data 0. 3 + Data from Ruhr university