Direct measurement of 4He(12C,16O)g reaction at KUTL* K. Fujita, K. Sagara, T. Teranishi, T. Goto, R. Iwabuchi, S. Matsuda, K. Nakano, N. Oba, M. Taniguchi and H. Yamaguchi Department of Physics, Kyushu University, Fukuoka, Japan *KUTL: Kyushu University Tandem Laboratory Physics Motivation Measurement of 16O Direct measurement of 16O with 12C beam and 4He target Detection efficiency is very high (≒100%) Total S-factor can be obtained directory necessary components for Ecm=0.7 MeV experiment background separation system: NBG/N12C ratio of 10-19 thick gas target : ~25 Torr × 3 cm high intensity beam: ~ 10 pmA Yield(16O) ~ 5 counts/day → 1 month experiment for 10% error Cross Section and S-factor of 4He(12C,16O)g reaction affects evolution of heavy stars – supernova or white dwarf abundance of element of universe Determine 12C/ 16O ratio after helium burning process C.S. is very small – coulomb barrier and varies drastically around 0.3 MeV – resonance state of 16O Extrapolation with experimental data Cross Section (S=const.) 10-5 Stellar energy Ecm 2.4 1.5 1.15 1.0 0.85 0.7 0.3 s(nbarn) 60 1 0.1 3x10-2 10-2 10-3 10-8 E1 E2 10-5 Our Experiment (within 10% accuracy) Extrapolation Experimental Layout Gas Target Kyusyu University Tandem Laboratory (KUTL) Window-less Gas Target any foil cannot used for gas confinement Blow-In Gas Target (BIGT) high confinement capability lower cost than gas-jet type To get higher pressure upgrade pumping speed small cylindrical bore beam buncher Tandem Accelerator Recoil Mass Separator chopper 45mm 12C beam Beam Monitor SSD (monitor target thickness x beam intensity) Center Pressure and Pressure Distribution beam line is segmented into 8 region 　 Blow-in windowless 4He gas target Sputter ion source Side view of Pumping System 3000l/s 330l/s DP 520l/s 12C P1 TMP3 MBP1 P2 P2 Long-time chopper beam P3 P3 P5 Recoil Mass Separator (RMS) ↓ P1 P6 pressure (Torr) P7 P2 P8 Tandem Accelerator Final focal plane (mass separation) P4 P4 P4 P3 16O P5 P6 TMP2 TMP4 TMP5 520l/s TMP1 520l/s Detector (Si-SSD) Center Pressure: 24 Torr ~18 times thicker for charge equilibrium of 16O → post stripper is not necessary Effective thickness is measured by 4He(p, p) reaction: ~4cm Thickness is sufficient for our experiment (limited by energy loss of 16O) length from target center (mm) 350l/s 1500l/s MBP2 Pulsed 12C beam is produced by buncher and chopper TOF information can be available for background reduction 330l/s Result Ecm = 2.4 MeV experiment beam: 12C2+, pulsed by 6.063MHz energy: 9.6MeV, tandem GV=3.2MV intensity: ~35pnA target: 4He gas ~ 23.9 Torr x 2.94 cm observable: 16O5+, 7.2±0.3 MeV abundance = 36.9±2.1 % = efficiency Ecm = 1.5 MeV experiment beam: 12C1+, pulsed by 3.620MHz energy: 6.0MeV, tandem GV=3.0MV intensity: ~150pnA target: 4He gas ~ 13.2 Torr x 2.94 cm observable: 16O5+, 4.5±0.3 MeV abundance = 40.9±2.1 % = efficiency Cross Section and S-factor D. Schurmann et al. Eur. Phys. J. A 26, 301-305 (2005) preliminary 10 hours data 29 hours data future plan 941 counts 16O 2.4MeV s=64.6±7.4 nbarn, S(2.4)= 89.0±10.2 keV･b large systematic error is remained : target thickness 1.5MeV S-factor is estimated to be 30 keV･b (preliminary) background reduction is in progress 16O E projection 30 counts of 16O were observed 12C B.G. events are generated from target, electric deflector, first focus point 16O events were separated clearly from 12C 941 events were obtained Conclusion Direct 16O measurement via 4He(12C, 16O)g reaction was proposed to determine 12C/16O abundance ratio in stars Blow-in type windowless gas target was developed, and thickness of 24 Torr × 4 cm was obtained Ecm= 2.4 MeV experiment s= 64.6 nb, S-factor of 89.0 keV･b was obtained Ecm= 1.5 MeV experiment 16O locus is observed cross section will be determined in the next experiment