230 likes | 349 Views
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.
E N D
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
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
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
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.
Experimental methods for 4He+12C→16O+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 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
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)
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
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
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
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
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
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
4He(12C,16O)g at Ecm=2.4MeV experiment Ruhr univ. Our data • 2.4MeV
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
Cross Section and Stot-factor 1.5MeV Next experiment is Ecm=1.151.00.850.7 MeV extrapolation Our exp. plan Stellar energy preliminary Kyushu U. Ruhr U.
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!
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
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
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 = 1.51.151.00.850.7MeV will be made in a few years. , 2010 stellar energy Stellar energy future plan
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 + +