Measurement of 4 He( 12 C, 16 O)  reaction in Inverse Kinematics Kunihiro FUJITA K. 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)

Evolution of Stars 12 C/ 16 O abundance is determined → affects all of the posterior processes 2 H-burning 4p → 4 He via p-p chain & CNO cycle He-burning 3 4 He → 12 C 4 He+ 12 C → 16 O+  C-burning O-burning Si-burning

3 Introduction 12 C/ 16 O ratio after helium burning process –evolution of heavy stars – supernova or white dwarf? –abundance of element of universe Cross Section of 4 He( 12 C, 16 O)  –very small (~10 -8 nb) – coulomb barrier –varies drastically around stellar energy(0.3MeV) Extrapolation with experimental data E cm (MeV)  (nbarn) x our experiment ( 10% accuracy) extrapolation stellar energy E1 E2

4 16 O measurement ① 4 He beam +  measurement ② 16 N decay measurement ③ direct 16 O measurement with 12 C beam and 4 He target –high efficiency (~ 40%: charge fraction) –total S-factor can be obtained necessary components for E cm =0.7MeV experiment –background separation system: N BG /N 12 C ratio of –thick gas target : ~25 Torr x 3 cm –high intensity beam: ~ 10 p  A Y( 16 O) ~ 5 counts/day → 1 month experiment for 10% error Cross section (S=const.) 10 -5

5 Experimental Setup Layout of Kyushu University Tandem Laboratory (KUTL) Detector (Si-SSD) Sputter ion source 12 C beam Tandem Accelerator Final focal plane (mass separation) Blow in windowless 4 He gas target Long-time chopper chopper buncher 16 O 12 C Recoil Mass Separator (RMS) E cm = 2.4~0.7 MeV E( 12 C)=9.6~2.8 MeV E( 16 O)=7.2~2.1 MeV Tandem RMS

6 Windowless Gas Target RMS TMP3 TMP4 MBP2 TMP2 TMP5 MBP1 beam TMP1 DP 1500 l/s 3000 l/s 330 l/s 520 l/s 350 l/s Differential pumping system (side view) 24 Torr SSD: beam monitor 4.5cm Blow-In Gas Target (BIGT) –windowless & high confinement capability beam

7 BG Reduction and 16 O Detection v dispersion m dispersion

8 E cm =1.5 MeV experiment beam: 12 C 1+, frequency: 3.620MHz –energy: 6.0MeV, intensity: 60pnA target: 4 He gas 15.0 Torr x 3.98 cm observable: 16 O 3+, 4.5 ± 0.3 MeV –abundance = 40.9 ± 2.1 % = efficiency 95 hours data 16 O 208 counts

Charge State Distribution of 16 O Charge state after gas target – 16 O has different charge state Our target is very thick Equilibrium charge distribution was measured Comparison with theoretical calculation

10 Cross Section and S-factor future plan D. Schurmann et al. Eur. Phys. J. A 26, (2005) Our data (2009, 2010), 2010 stellar energy

Development of Ionization Chamber BG reduction by is necessary for E cm =0.7MeV measurement Particle Identification by E-  E information → Ionization Chamber Gas: PR-Gas, 10~30 Torr Effective area: 40 H x40 W x50 t mm 2 Entrance Window: PET foil, 0.5  m,  45mm Voltage: –Cathode: GND, Grid: 100V, Anode: 150V Timing resolution of1ns is necessary → install Si-SSD at the end  45mm cathode frish grid anode SSD PET foil 50mm 40mm 50mm particle

Performance test by 12 C+  Test experiment by E cm =1.5MeV setting –6.0MeV, 12 C beam: ~100nA –Pilot 16 O - spontaneity generating from tandem acc. – 16 O(4.5MeV) and 12 C(3~6MeV) was separated by the ratio of (99.9%) –Energy resolution of Ionization Chamber was  E/E=9%(FWHM) projection 12 C 16 O Total E [MeV]  E [MeV]

Test Experiment of E cm =1.2MeV Update of Tandem acc. ~Accelerate Decelerate mode –successfully incremented for beam intensity Beam: 4.8MeV(1.2MV), 12 C 2+ Observable: 3.6MeV, 16 O 3+ 5 hours data

14 Summary

15 BACKUP

16 Charge State Fraction of 16 O Our data W. Liu et al. / Nucl. Instr. and Meth. A 496 (2003) 198–214

pass only reaction products ( 16 O) which are spread in time. f 2 =3×f 1 V 2 =V 1 /9 f 1 =6.1MHz V 1 =±24.7kV V 3 =23.7kV reject BG pass reaction products + Flat-bottom voltage RF-Deflector (Long Time Chopper) BG( 12 C) 16 O events

18 Trajectory Analysis 12 C backgrounds were rejected by slit control based on trajectory analysis 16 O MeV (E cm =1.5MeV) 12 C MeV 12 C MeV slits target EDD1D2 final focal plane (detector) v dispersion

19 E cm =2.4MeV experiment beam: 12 C 2+, frequency: 6.063MHz –energy: 9.6MeV, intensity: ~35pnA target: 4 He gas ~ 23.9 Torr x 3.98 cm observable: 16 O ± 0.3 MeV –abundance = 36.9 ± 2.1 % = efficiency 29hours data 941 counts 16 O

Development of Ionization Chamber BG reduction by is necessary for E cm =0.7MeV measurement Additional electric deflector? Or Wien-Filter? → difficult due to space boundary Upgrade detector  E information by Ionization Chamber Simulation plot of E-  E Ar Gas: 20Torrx5cm 16 O (4.5MeV) 12 C (1~6MeV) Total E [MeV]  E [MeV]

Resolution of Ionization Chamber 16 O beam Ionization Chamber θ 12 C, 16 O 7μg/cm 2 C-foil Detector setting –PR-gas: 20 Torr –Cathode: -150V, Grid: -50V Measurement of 16 O+ 12 C elastic scattering –Beam: 16 O 2+, 9.6MeV –Target: 12 C(7  g/cm 2 ) 12 C: 5.91MeV 16 O: 4.75MeV –Clearly separated for 16 O(4.75MeV) and 12 C(4.7MeV) –Energy Resolution:  E/E=6%(FWHM) Total E [ch]  E [ch] 45.0° 37.5° 12 C: 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 (12 f ) gas stripper, spread in beam energy and angle is decreased, and beam transport to the target is ~3 times increased. Totally, beam intensity is times increased. normal operation accel-decel operation Al shorting bars for accel-decel operation