Measurement of 4He(12C,16O)g reaction in Inverse Kinematics

Kunihiro FUJITAK. Sagara, T. Teranishi, M. Iwasaki, D. Kodama, S. Liu, S.

Matsuda, T. Mitsuzumi, J.Y. Moon, M.T. Rosary and H. Yamaguchi

Department of Physics, Kyushu University, Japan

Kyushu University Tandem Laboratory (KUTL)

2

Evolution of Stars

12C/16O abundance is determined

→ affects all of the posterior processes

H-burning

4p → 4Hevia

p-p chain &CNO cycle

He-burning

3 4He → 12C4He+12C → 16O+g

C-burning

O-burning Si-burning

3

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

– evolution of heavy stars – supernova or white dwarf?– abundance of element of universe

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

• Extrapolation with experimental data

Ecm (MeV) s (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

4

16O measurement① 4He beam + g measurement

② 16N decay measurement

③ direct 16O measurement with 12C beam and 4He target– high efficiency (~ 40%: charge fraction)– total 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 pmA

• Y(16O) ~ 5 counts/day

→ 1 month experiment for 10% error

Cross section (S=const.)

10-5

10-5

5

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

6

Windowless Gas Target

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

Differential pumping system (side view)

• center pressure: 24 Torr - post stripper is not necessary• effective length: 3.98 0.12 cm (measured by p+a elastic scattering)

→ target thickness is sufficient for our experiment (limited by energy loss of 12C beam)

24Torr

SSD: beam monitor4.5cm

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

beam

7

BG Reduction and 16O Detection 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

• Background reduction① RF deflector (Long-Time Chopper)

– background reduction ~10-3

② movable slits– combination with trajectory analysis

v dispersionm dispersion

8

Ecm=1.5 MeV experiment

• beam: 12C1+, frequency: 3.620MHz– energy: 6.0MeV, intensity: 60pnA

• target: 4He gas 15.0 Torr x 3.98 cm• observable: 16O3+, 4.5 ± 0.3 MeV– abundance = 40.9 ± 2.1 % = efficiency

95 hours data

16O

208 counts

Charge State Distribution of 16O

• Charge state after gas target– 16O has different charge state

• Our target is very thick

• Equilibrium charge distribution was measured• Comparison with theoretical calculation

2 4 6 8 10 12 140

10

20

30

40

50

60

70

14MeV

12MeV9.4MeV7.2MeVF

ract

ion

(%)

Energy(MeV)

4.5MeV

Line: the empirical formuladot: our data and triumf data

7+

6+5+

4+3+2+

10

Cross Section and S-factor

• 2.4MeV: • 1.5MeV:

• Background ratio NBG/N12C = 10-16

• Next experiment is Ecm=1.20 MeV

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

Our data (2009, 2010)

, 2010

stellar energy

Development of Ionization Chamber• BG reduction by 10-3 is necessary for

Ecm=0.7MeV measurement

Particle Identification by E-DE information → Ionization Chamber

• Gas: PR-Gas, 10~30 Torr• Effective area: 40Hx40Wx50tmm2

• Entrance Window: PET foil, 0.5mm, f45mm

• Voltage:– Cathode: GND, Grid: 100V, Anode: 150V

• Timing resolution of1ns is necessary

→ install Si-SSD at the end

f45mm

cathode

frish grid

anode

SSD

PETfoil

50mm

40mm

50mm

particle

Performance test by 12C+a

• Test experiment by Ecm=1.5MeV setting

– 6.0MeV, 12C beam: ~100nA– Pilot 16O - spontaneity generating from tandem acc.

– 16O(4.5MeV) and12C(3~6MeV) was separated by the ratio of 10-3(99.9%)– Energy resolution of Ionization Chamber was DE/E=9%(FWHM)

projection

12C

16O

Total E [MeV]

DE [

MeV

]

DE [MeV]

Test Experiment of Ecm=1.2MeV

• Update of Tandem acc. ~Accelerate Decelerate mode– successfully incremented for beam intensity

• Beam: 4.8MeV(1.2MV), 12C2+

• Observable: 3.6MeV, 16O3+ 5 hours data

14

Summary

• 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 x 3.98 cm was achieved

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

• Ecm= 2.4 MeV experiment

– s= 64.6 nb, S-factor = 89.0keV b• Ecm= 1.5 MeV experiment

– s= 0.900 nb, S-factor = 26.6 keV b• Now we start measurement at Ecm=1.2MeV

15

BACKUP

16

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

pass only reaction products (16O) which are spread in time.

f2=3×f1

V2=V1/9

f1=6.1MHzV1=±24.7kV

V3=23.7kV

reject BG

pass reaction products

+

Flat-bottom voltage

RF-Deflector (Long Time Chopper)

BG(12C)16O5+

500events

18

Trajectory Analysis• 12C backgrounds were rejected by slit

control based on trajectory analysis

16O3+ 4.5MeV (Ecm=1.5MeV)

12C3+ 6.0MeV

12C2+ 3.0MeVslits

target

ED D1 D2final focal plane(detector)

v dispersion

19

Ecm=2.4MeV experiment

• beam: 12C2+, frequency: 6.063MHz– energy: 9.6MeV , 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 data

941 counts

16O

Development of Ionization Chamber• BG reduction by 10-3 is necessary for Ecm=0.7MeV measurement

• Additional electric deflector? Or Wien-Filter?

→ difficult due to space boundary• Upgrade detector

DE information by Ionization Chamber

Simulation plot of E-DE

Ar Gas: 20Torrx5cm

16O (4.5MeV)

12C (1~6MeV)

Total E [MeV]

DE [

MeV

]

Resolution of Ionization Chamber

16O beam　　　　　　

Ionization Chamber

θ12 C,1

6 O

7μg/cm2 C-foil• Detector setting

– PR-gas: 20 Torr– Cathode: -150V, Grid: -50V

• Measurement of 16O+12C elastic scattering– Beam: 16O2+, 9.6MeV– Target: 12C(7 mg/cm2)

12C: 5.91MeV

16O: 4.75MeV

– Clearly separated for 16O(4.75MeV) and 12C(4.7MeV)

– Energy Resolution: DE/E=6%(FWHM)

Total E [ch]

DE [

ch]

45.0°37.5°

12C: 4.70MeV

Normal operation of tandem accelerator.

Accel-decel operation of tandem accelerator.

At low acceleration voltage, focusing becomes weak, and beam transmission decreases.

By alternative focus-defocus, Focusing becomes strong, and Beam transmission increases.

By the accel-decel operation, ・ 10 times higher beam transmission is obtained by strong focusing. ・ 17.5 times more intense beam can be injected, due to higher electric power

necessary for accel-decel operation.By a large aperture (12f) gas stripper, spread in beam energy and angle is

decreased, and beam transport to the target is ~3 times increased.

Totally, beam intensity is 300-500 times increased.

normal operation

accel-deceloperation

Al shorting bars for accel-decel operation