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Direct measurement of 12 C + 4 He fusion cross section at Ecm=1.5MeV at KUTL

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. 2010. 1990. 1970.

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Direct measurement of 12 C + 4 He fusion cross section at Ecm=1.5MeV at KUTL

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  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. 2010 1990 1970 Burning process in stars He-burning 3 4He → 12C H-burning 4p → 4He via p-p chain & CNO cycle 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 C. Rolfs (Ruhr Univ.) goal g + +  Kyushu U. 17 years α 4α 3α

  3. Why is4He+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 Experiments Extrapolation Experiment Cross section (S=const.) stellar energy 10-5 0.3 10-5 E1 E2 Coulomb-barrier effect • Really low-energy experiments near 0.3MeV are necessary • to make reliable extrapolation. 0.7 2.4 0.3

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

  5. γ 4He+12C→16O+γ experiment with γdetection Cross section (S=const.) → 10-5 10-5 Stellar energy 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. Increase the yield Cross section is very small Yield of 12C + 4He → 16O + γ Y(16O) =s・ N(12C)・N(4He )・ Detection Efficiency ・ Beam Time beam target detect ③ ① ② • ・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 ・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 10-5 Background (BG)reduction N(16O)/N(12C) ~ 10-18 N(BG) / N(12C) < 10-19 0.3 0.7 2.4 Very hard to realize

  8. Setup for 4He(12C,16O)g Experiment at Kyushu University Tandem Laboratory (KUTL) Tandem Accelerator chopper buncher Blow in windowless 4Hegas target 12C beam RMS 12C Sputter ion source E-def D-mag Recoil Mass Separator (RMS) 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. 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 3000 l/s 520 l/s 330 l/s DP TMP3 MBP1 RMS beam TMP4 TMP2 TMP5 MBP2 TMP1 520 l/s 350 l/s 520 l/s 330 l/s 1500 l/s Y(16O) =s・N(12C)・N(4He )・ Det.Efficiency ・ Beam Time • Blow-In Gas Target (BIGT) • windowless & high confinement capability 24Torr beam SSD: beam monitor Differential pumping system (side view) 4.5cm • 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. Recoil Mass Separator All the 16O recoils(±2°) in a charge state (~40%) are detected. ③Increase the 16O detection efficiency 12C + 4He → 16O +γ 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 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 N(16O)/N(12C) ~ 10-18 at 0.7MeV Goal: N(BG)/N(12C) < 10-19 RF-Deflector E-def D mag LTC D mag At present: N(BG)/N(16O) become 10-16

  13. f1=6.1MHz V1=±24.7kV f2=3×f1 V2=V1/9 V3=23.7kV BG reduction Long-Time Chopper(RF deflector) pass only reaction products (16O) which are spread in time. reject BG + Pass 16O RF-Deflector Flat-bottom voltage with LTC without LTC BG(12C) 16O5+ 500events LTC 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: 16O5+ 7.2 ± 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 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 95 hours data 16O 208 counts

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

  18. Further BG reduction is necessary 95 hours data 16O 1.5MeV σ～0.7nb down to 0.7MeV Ecm=2.4MeV σ～65nb 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) ΔE of 16O is larger than 12C 16O PR Gas 30Torr cathode BG reject Si-SSD － E ΔE 16O,12C low energy DE e－ e－ e－ e－ 16O ＋ anode 12C We can separate 16O from BG (12C) 4He very thin foil (0.9μm) E+DE

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

  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= 0.900 nb, S-factor = 26.6 keV b Now we are developing an ionization chamber. Experiments of 4He+12C 16O+γ at Ecm = 1.51.151.00.850.7MeV will be made in a few years. , 2010 stellar energy Stellar energy future plan

  22. Assumed data Data from Ruhr university 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［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 1－ 2＋ S(0.3MeV) extrapolated = 190±15keV b Reliable theoretical curve will be necessary for extrapolation 0.3 g +  +

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