Direct measurement of 4 He( 12 C, 16 O) g reaction at KUTL *

1. 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 E1 E2 10-5 Our Experiment (within 10% accuracy) Extrapolation Experimental Layout Gas Target • 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 • Kyusyu University Tandem Laboratory (KUTL) beam Recoil Mass Separator Tandem Accelerator buncher 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 3000l/s Side view of Pumping System 520l/s Sputter ion source DP 330l/s TMP3 P1 12C MBP1 P2 P2 beam Long-time chopper P5 P6 P1 ↓ P3 P3 Recoil Mass Separator (RMS) P7 pressure (Torr) P8 P2 P3 Final focal plane (mass separation) P4 Tandem Accelerator P4 P4 16O P6 P5 TMP2 TMP4 TMP5 TMP1 520l/s 520l/s length from target center (mm) 1500l/s 350l/s MBP2 • 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) Detector (Si-SSD) 330l/s Pulsed 12C beam is produced by buncher and chopper TOF information can be available for background reduction Result D. Schurmann et al. Eur. Phys. J. A 26, 301-305 (2005) • 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 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