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

Physics Motivation

Experimental Layout

Result

•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

•Kyusyu University Tandem Laboratory (KUTL)

Gas Target

Center Pressure and Pressure Distribution

•beam line is segmented into 8 region 　

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

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

Detector (Si-SSD)

Sputterion

source

12C beam

Tandem Accelerator

Final focal plane(mass

separation)

Blow-in windowless4He gas target

Long-time chopper

chopperbuncher

16O

12C

Recoil Mass Separator(RMS)

Pulsed 12C beam is produced by buncher and chopperTOF information can be available for background reduction

Tandem Accelerator

Recoil Mass Separator

*KUTL: Kyushu University Tandem Laboratory

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

Conclusion

•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)

45mmBeam Monitor SSD

(monitor target thickness x beam intensity)

beam

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

D. Schurmann et al.Eur. Phys. J. A 26, 301-305 (2005)

•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

DP

TMP1TMP2

TMP5TMP4

TMP3MBP1

MBP21500l/s

3000l/s 520l/s

520l/s520l/s350l/s

330l/s

330l/s

beam

Side view of Pumping SystemP1

P2

P3

P4P5 P6

P4

P2

P3P6P5

P4 P3P2

P1↓

Ecm 2.4 1.5 1.15 1.0 0.85 0.7 0.3s(nbar

n)60 1 0.1 3x10-2 10-2 10-3 10-8

Our Experiment (within 10% accuracy)

Stellar energy

Extrapolation

E1 E210-5

10-5

Cross Section (S=const.)

•30 counts of 16O were observed•12C B.G. events are generated from

–target, electric deflector, first focus point

29 hours data

16O

16O

941 counts

E projection

•16O events were separated clearly from 12C

•941 events were obtained

preliminary

future plan

pres

sure

(To

rr)

length from target center (mm)

•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 experiments= 64.6 nb, S-factor of 89.0 keV ･ b was obtained

•Ecm= 1.5 MeV experiment16O locus is observedcross section will be determined in the next experiment

10 hours data

P8P7