direct measurement of 12 c + 4 he fusion cross section at ecm=1.5mev at kutl h.yamaguchi k. sagara,...
TRANSCRIPT
Direct measurement of 12C + 4He fusion cross section at Ecm=1.5MeV at KUTL
H.Yamaguchi K. Sagara, K. Fujita, T. Teranishi, M. taniguchi, S .Liu, S. Matsua, Maria T. Rosary, T. Mitsuzumi, M. Iwasaki
Kyushu University Tandem accelerator Laboratory
H-burning
4p → 4Hevia
p-p chain &CNO cycle
He-burning
3 4He → 12C
C-burning
O-burning Si-burning
Burning process in stars
12C/16O ratio affects widely further nuclear synthesis.
4He+12C → 16O+γ cross section has not been determined yet, in spite of 40 years efforts in the world.
C. Rolfs (Ruhr Univ.) Kyushu U.
world
goal
20101970 1990
+ +
α 4α3α
~40 years
17 years
4He+12C → 16O+
4He+12C → 16O+γ experiment is very difficult.
4He + 12C → 16O +
E1 E2
Why is 4He+12C→16O+γ experiment so difficult?
Really low-energy experiments near 0.3MeV are necessary to make reliable extrapolation.
• At 0.3MeV 4He(12C,16O)Cross Section isvery small (~10-8 nb) due to Coulomb repulsion
Cross section (S=const.)
10-5
10-5
0.70.3 2.40.3
stellar energy
Coulomb-barrier effect
Extrapolation
Experiments
Experiment
Experimental methods for 4He+12C→16O+γ cross section
→ γ
Stellar energy
4He+12C→16O+γ experiment with γ detection
S-factor has not been precisely determined yet.
Cross section (S=const.)
10-5
10-5
Coulomb barrier effectNo precise data at low energy due to ・ low detection-efficiency of γ-rays ・ huge Back Ground (BG) γ-rays
Experimental methods for 4He+12C→16O+γ cross section
high detection efficiency (~ 40%: charge fraction)total S-factor can be measured
③②①
Yield of 12C + 4He → 16O + γ
Y(16O) = ・ N(12C) ・ N(4He ) ・ Detection Efficiency ・ Beam Time
・ necessary components for Ecm=0.7MeV experiment- high intensity 12C beam: ~ 10 pA ( Limit of our tandem accelerator )- Thick windowless 4He gas target : ~20 Torr x 4 cm (Limit of E in the target )- high detection efficiency (~40%)
・ Y(16O) ~ 5 counts/day at Ecm=0.7MeV → 1 month exp.
Background (BG) reductionN(16O)/N(12C) ~ 10-18 N(BG) / N(12C) < 10-19
beam target detect
Cross section (S=const.)
10-5
10-5
0.70.3 2.4
Increase the yield
at Ecm = 0.6 MeV → 10 month exp.at Ecm = 0.3 MeV → 7,000 year exp
Very hard to realize
Cross section is very small
extrapolate experiment
Setup for 4He(12C,16O)Experimentat 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
E-def
D-mag
D-mag
normal operation
accel-deceloperation
Al shorting bars for accel-decel operation
Accel-decel operation of tandem accelerator
Y(16O) = ・ N(12C) ・ N(4He ) ・ Det.Efficiency ・ Beam Time
At low acceleration voltage, focusing becomes weak, and beam transmission decreases.By alternative focus-defocus, focusing becomes strong, and beam transmission increases. ・ 10 times higher beam transmission is obtained by strong focusing. ・ 10 times more intense beam can be injected.
①Increase the 12C beam
Totally, beam intensity is ~100 times increased
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 • effective length: 3.98 ± 0.12 cm (measured by p+α elastic scattering)effective length: 3.98 ± 0.12 cm (measured by p+α elastic scattering)
→ → 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)
SSD: beam monitor4.5cm
• Blow-In Gas Target (BIGT)– windowless & high confinement capability
beam
Y(16O) = ・ N(12C) ・ N(4He ) ・ Det.Efficiency ・ Beam Time
②Increase the 4He gas target
Thickest in the world
24Torr
③②①
Recoil Mass Separator
All the 16O recoils(±2°) in a charge state (~40%) are detected.
12C + 4He → 16O +γ yield has been increased
Y(16O) = ・ N(12C) ・ N(4He ) ・ Detection Efficiency ・
Beam Time
③Increase the 16O detection efficiency
12C + 4He → 16O +γ
12C beam
4He windowless Gas target
Eject within 2°
16O
E-def
D mag
D magdetect 16O5+
RF-Deflector
BG reduction
• Background 12C are produced bymultiple scatteringcharge exchange
• Background reduction ・ Recoil Mass Separator background reduction ~10-11
・ TOF with Pulsed beam ~10-2
・ Long-Time Chopper(RF deflector) ~10-3 N(BG)/N(16O) become 10-16
Goal: N(BG)/N(12C) < 10-19
At present:
N(16O)/N(12C) ~ 10-18 at 0.7MeV
E-def D mag
D magLTC
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
16O
+
Flat-bottom voltage
Long-Time Chopper(RF deflector)
BG(12C)16O5+
500events
Measurement of 4He(12C,16O)γ at Ecm = 2.4 MeV
BG reduction
RF-Deflector
LTC
without LTC with LTC
14
4He(12C,16O)at 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 data29hours data
941 counts
16O
• 2.4MeV–
4He(12C,16O)at Ecm=2.4MeV experiment
Our data
bkeV 3.889.0S(2.4) nb, 2.764.6
Ruhr univ.
4He(12C,16O)at 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
208 counts208 counts
95 hours data95 hours data
16O
Ruhr U.Kyushu U.
extrapolation
Cross Section and Stot-factor
• 1.5MeV–
• Next experiment is Ecm=1.151.00.850.7 MeV
bkeV 2.826.6S(1.5) nb, 0.090.900
Stellar energy
Our exp. plan
preliminary
Further BG reduction is necessary95 hours data95 hours data
16O
In order to go to low energy further BG Reduction is necessary!
Ecm=2.4MeVσ ~ 65nb
Increased BG 1.5MeVσ ~ 0.7nb
down to 0.7MeV
• measure the ΔE (∝ energy loss) by the ionization chamber (and E by the SSD)
further BG reduction
We can separate 16O from BG (12C)
16O
12C
4He
16O
BG reject
16O and 12C separation by Ionization chamber
-
+
cathode
anode
PR Gas 30Torr
very thin foil (0.9μm)
16O,12Ce -
Si-SSD
e - e - e -
ΔE E
low energy
ΔE of 16O is larger than 12C
BG reduction by Ionization Chamber
95 hours data95 hours data
Huge 12C-BG will be eliminated using the ionization chamber.
Ionization chamber will be available from October 2011.
16O
12C
4He
16O
BG reject
16O
Summary• Direct measurement of 4He+12C 16O+γ cross section (total S-factor) is in
progress at KUTL (Kyushu Univ. Tandem Lab.)
• Many new instruments and methods have been developed for this experiment.
• Ecm= 2.4 MeV experiment– = 64.6 nb, – S-factor = 89.0 keV b
• Ecm= 1.5 MeV experiment– = 0.900 nb,– S-factor = 26.6 keV b
• Now we are developing an ionization chamber.
• Experiments of 4He+12C 16O+γ at Ecm = 1.51.151.00.850.7MeV will be made in a few years.
future plan
, 2010
stellar energy
Stellar energy
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R.Kuntz, M.Fey, M.Jaeger, A.Mayer, W.Hammer Astrophysical J. 567. (2002) 643 - 650
A rehearsal for extrapolation using R-matrix theory
Ecm [ MeV ]0.700.851.001.151.50
S-factor [ keV b ]70.0±7.050.0±5.045.0±4.535.0±3.530.0±3.0
Assumed data (±10%)
Data from Ruhr university
Assumed data
S(0.3MeV) extrapolated = 190±15 keV b1 -2 +
0.3
Reliable theoretical curve will be
necessary for extrapolation
++