Direct measurement of 4He(12C,16O) reaction near stellar

energy

Kunihiro FUJITAK. Sagara, T. Teranishi, T. Goto, R. Iwabuchi, S. Matsuda, K. Nakano, N. Oba, M. Taniguchi

and H. Yamaguchi

Department of Physics, Kyushu UniversityKyushu University Tandem Laboratory (KUTL)

2

Introduction• 12C/ 16O ratio: after helium burning process

– affects evolution of heavy stars – supernova or white dwarf

– abundance of element of universe

• Cross Section of 4He(12C,16O) – very small (~10-8 nbarn) – coulomb barrier – varies drastically around 0.3MeV

• Extrapolation with experimental dataEcm (MeV) (nbarn)

2.4 601.5 1

1.15 0.11.0 3x10-2

0.85 10-2

0.7 10-3

0.3 10-8

our experiment( 10% accuracy)

extrapolation

stellar energy

E1

E2

3

16O measurement① 4He beam + measurement② 16N decay measurement

③③ direct direct 1616O measurement with O measurement with 1212C beam and C beam and 44He targetHe target– high efficiency (~ 40%: charge fraction)high efficiency (~ 40%: charge fraction)– total S-factor can be obtainedtotal S-factor can be obtained

• necessary components for Ecm=0.7MeV experiment

– background separation system: NBG/N12C ratio of 10-19

– thick gas target : ~25 Torr x 3 cm– high intensity beam: ~ 10 pA

• Y(16O) ~ 5 counts/day→ 1 month experiment for 10% error

Cross section (S=const.)

10-5

10-5

4

Experimental Setup• Layout of Kyushu University Tandem Laboratory (KUTL)

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)

Ecm = 2.4~0.7 MeVE(12C)=9.6~2.8 MeVE(16O)=7.2~2.1 MeV

Tandem

RMS

5

RMS

TMP3

TMP4MBP2TMP2TMP5

MBP1

beam

TMP1

DP

1500 l/s

3000 l/s330 l/s

330 l/s520 l/s 520 l/s

520 l/s

350 l/s

Windowless Gas Target

Differential pumping system (side view)

• center pressure: 24 Torr - center pressure: 24 Torr - post stripper is not necessary post stripper is not necessary• effective length: 3.98 ± 0.12 cmeffective length: 3.98 ± 0.12 cm

→ → target thickness is sufficient for our experimenttarget thickness is sufficient for our experiment

(limited by energy loss of (limited by energy loss of 1212C beam)C beam)

24Torr

SSD: beam monitor4.5cm

• Blow-In Gas Target (BIGT)– windowless & high confinement

capability

beam

6

16O Detection System

movable slits

v dispersionm dispersion

Recoil Mass Separator– 12C/16O separation : ratio of 10-11

– angular acceptance: ±1.9deg 100% 16O can be observed

• Background 12C– charge exchange– multiple scattering p/q value is nearly equal to 16O

• Background reduction① RF deflector (Long-Time Chopper)

– background reduction ~10-3 ② movable slits

– combination with trajectory analysis

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Ecm=2.4MeV experiment• beam: 12C2+, pulsed by 6.063MHz

– energy: 9.6MeV, tandem GV=3.2MV– 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 data29hours data

941 counts

16O

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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 3.98 cm

1cycle=276.2ns

• 30 counts of 30 counts of 1616O were O were observedobserved

• B.G. events are generated from– target– Electric Deflector– RF Deflector

10hours data10hours data

• observable: 16O3+, 4.5 ± 0.3 MeV– abundance = 40.9 ± 2.1 % =

efficiency

16O

16O

+4.734m: LTC2

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Trajectory Analysis• Trajectory of 16O and 12C backgrounds in RMS

16O3+ 4.5MeV

12C3+ 6.0MeV

12C2+ 3.0MeVslits

target

ED D1 D22nd focus(detector)

1st focus

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Result of BG Reduction

• BGs from electric deflector and from target was reduced• some BG events can be seen at 16O region

16O

16O

0.5 hour data0.5 hour data

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Cross Section and S-factor

• 2.4MeV–

• 1.5MeV– S(1.5) is obtained to be ~30 keV b (very preliminary)– background reduction is not sufficient

bkeV 3.889.0S(2.4) nbarn, 2.764.6

preliminary

preliminary

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

Our data (2009, 2010)

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Summary

• Direct 16O measurement via 4He(12C, 16O) reaction was proposed to determine 12C/16O abundance ratio in stars

• Blow-in type windowless gas target was developed, and thickness of 24 Torr x 3.98 cm was achieved

• Background reduction was performed by using RMS, RF deflector and movable slits

• Ecm= 2.4 MeV experiment– = 64.6 nb, S-factor of 89.0 keV b

• Ecm= 1.5 MeV experiment– 16O locus is observed– cross section will be determined in the next experiment

BACKUP

13

14

Charge State Fraction of 16O

0

10

20

30

40

50

60

70

2 4 6 8 10 12 14

Frac

tion

[%

]

Energy [MeV]

5+4+3+ 6+2+

7+

Our dataW. Liu et al. / Nucl. Instr. and Meth. A 496 (2003) 198–214