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
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, (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