APFB2011 by dffhrtcv3

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									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
     Burning process in stars
    H-burning               He-burning
                                                     C-burning
     4p → 4He            3 4He → 12C                                          Si-burning
                                                     O-burning
        via            4He+12C → 16O+g
    p-p chain &
    CNO cycle
                               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.
                             4He+12C   → 16O+γ experiment is very difficult.
4He     + 12C → 16O + g            world
                                                                ~40 years
                                  C. Rolfs                                         goal
    +                 +g         (Ruhr Univ.)      Kyushu U.
                                                                   17 years
α        3α       4α
                                          1970          1990                2010
    Why is 4He+12C→16O+γ experiment so difficult?
• At 0.3MeV 4He(12C,16O)g Cross Section is
  very small (~10-8 nb) due to Coulomb repulsion

            Cross section (S=const.)

                                                10-5
                              Experiments


                      10-5
     Extrapolation
                             Experiment
                                                             stellar
      0.3       0.7                                    2.4   energy
                                                                       0.3




                                          Coulomb-barrier effect             E1   E2

       Really low-energy experiments near 0.3MeV are necessary
       to make reliable extrapolation.
Experimental methods for 4He+12C→16O+γ cross section
4He+12C→16O+γ              experiment with γ detection


                                                           →        γ
Cross section (S=const.)

                               10-5




    10-5

                                                Stellar
                                                energy




                                                  No precise data at low energy
                           Coulomb barrier effect due to
                                                  ・low detection-efficiency of γ-rays
                                                  ・huge Back Ground (BG) γ-rays

                            S-factor has not been precisely determined yet.
Experimental methods for 4He+12C→16O+γ cross section



                high detection efficiency (~ 40%: charge fraction)
                total S-factor can be measured
Cross section is very small                        Increase the yield
Yield of    12C   + 4He → 16O + γ
           beam target   detect
Y(16O) = s・ N(12C)・N(4He )・ Detection Efficiency ・ Beam Time
                  ①      ②            ③
・necessary components for Ecm=0.7MeV experiment
   - high intensity 12C beam: ~ 10 pmA
                        (Limit of our tandem accelerator)
   - Thick windowless 4He gas target : ~20 Torr x 4 cm
                         (Limit of DE in the target)
   - high detection efficiency (~40%)
                                                         Cross section
・Y(16O)    ~ 5 counts/day at Ecm=0.7MeV                  (S=const.)
                                                                                      10-5
                     → 1 month exp.                 extrapolate          experiment

  at Ecm = 0.6 MeV → 10 month exp.
  at Ecm = 0.3 MeV → 7,000 year exp
                                                                  10-5

Background (BG) reduction
   N(16O)/N(12C) ~ 10-18                             0.3    0.7                          2.4
   N(BG) / N(12C) < 10-19         Very hard to realize
               Setup for 4He(12C,16O)g Experiment
                   at Kyushu University Tandem Laboratory (KUTL)

    buncher          Tandem Accelerator   chopper

                                                       Blow in windowless
                                                         4He gas target


             12C   beam
                                                                                          RMS


  Sputter                                       12C
ion source                                             E-def

                                                           D-mag
                                          Recoil
                                Tandem    Mass
                                          Separator                  Long-time chopper
                                          (RMS)              D-mag
       Ecm = 2.4~0.7 MeV                                              Final focal plane
       E(12C)=9.6~2.8 MeV                              16O           (mass separation)
       E(16O)=7.2~2.1 MeV                             Detector (Si-SSD)
①Increase the 12C beam                Accel-decel operation of tandem accelerator
           Y(16O) = s・N(12C)・N(4He )・ Det.Efficiency ・ Beam Time
                                  accel-decel
                                  operation



                                     normal
                                     operation

                                 Al shorting bars
                                 for accel-decel
                                 operation




 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.
                                      Totally, beam intensity is ~100 times increased
    ②Increase the 4He gas target Windowless Gas Target
            Y(16O) = s・N(12C)・N(4He )・ Det.Efficiency ・ Beam Time
•    Blow-In Gas Target (BIGT)
      – windowless & high confinement capability                  3000 l/s             520 l/s
                                                        330 l/s
                                                                   DP                  TMP3
                                                      MBP1
                             24Torr

                                      beam
                                                                                                 RMS


                                          TMP5 TMP2                          MBP2
                                                                                       TMP4
                                           350 l/s   520 l/s      TMP1       330 l/s   520 l/s

                                                                  1500 l/s

              4.5cm       SSD: beam monitor          Differential pumping system (side view)

•   center pressure: 24 Torr                                      Thickest in the world
•   effective length: 3.98 ± 0.12 cm (measured by p+α elastic scattering)
    → target thickness is sufficient for our experiment
           (limited by energy loss of 12C beam)
     ③Increase the 16O detection efficiency

   Recoil Mass Separator                                 12C   + 4He → 16O +γ
                                                                      Eject within 2°
     All the 16O recoils(±2°)
    in a charge state (~40%) are detected.
                             4He windowless
                                                           D mag
                             Gas target
                     12C beam           16O


                                                                               detect
                                                  E-def             D mag        16O5+




       12C   + 4He → 16O +γ yield has been increased
       Y(16O) = s・N(12C)・N(4He )・ Detection Efficiency ・ Beam Time
                       ①       ②              ③
              BG reduction

 Goal: N(BG)/N(12C) < 10-19           N(16O)/N(12C) ~ 10-18 at 0.7MeV


• Background 12C are produced by                          RF-Deflector
   multiple scattering
   charge exchange                         E-def        D mag


                                                            LTC
                                                                  D mag
• Background reduction
   ・Recoil Mass Separator
     background reduction ~10-11
   ・ TOF with Pulsed beam ~10-2
                                          At present:
   ・Long-Time Chopper(RF deflector)
                              ~10-3       N(BG)/N(16O) become 10-16
   BG reduction                   Long-Time Chopper(RF deflector)
pass only reaction products (16O)
which are spread in time.
     f1=6.1MHz          f2=3×f1
     V1=±24.7kV         V2=V1/9                                       reject BG
                   +
                                                                  Pass
                                                                    16O

                                            Flat-bottom voltage
  V3=23.7kV

     without LTC                                     with LTC

                                            RF-Deflector

                                                                  BG(12C)
                                                                            16O5+

                                                                            500events

                                               LTC



                  Measurement of 4He(12C,16O)γ at Ecm = 2.4 MeV
4He(12C,16O)g                 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 data



                                                 941 counts

                        16O




                                                         14
4He(12C,16O)g              at Ecm=2.4MeV experiment
                       Ruhr univ.




                                       Our data




•   2.4MeV
     – s  64.6  2.7 nb, S(2.4)  89.0  3.8 keV  b
4He(12C,16O)g               at Ecm=1.5 MeV experiment
•   beam: 12C1+, frequency: 3.620MHz        •   target: 4He gas 15.0 Torr x 3.98 cm
     – energy: 6.0MeV, intensity: 60pnA     •   observable: 16O3+, 4.5 ± 0.3 MeV
                                            –   abundance = 40.9 ± 2.1 % = efficiency

                                     95 hours data



                               16O

                                                                208 counts
           Cross Section and Stot-factor

                extrapolation

                         Our exp. plan

             Stellar
             energy




                          Kyushu U.                   Ruhr U.




•   1.5MeV
     – s  0.900  0.09 nb, S(1.5)  26.6  2.8 keV  b

• Next experiment is Ecm=1.151.00.850.7 MeV
Further BG reduction is necessary
                                                   95 hours data


                                             16O




   Ecm=2.4MeV                   1.5MeV                  down to
                Increased BG                            0.7MeV
   σ~65nb                       σ~0.7nb

                   In order to go to low energy
                   further BG Reduction is necessary!
    further BG reduction
                   16O    and 12C separation by Ionization chamber
 • measure the ΔE (∝energy loss) by the ionization chamber (and E by the SSD)


          PR Gas 30Torr                                     ΔE of 16O is larger than 12C

                               cathode                 DE
                                         Si-SSD                            16O
                                                   -                                   16O
16O,12C                   ΔE              E
low energy
                     e- e- e- e-
                                                                                 12C
                                                                                        BG
                                                   +                                   reject
                                                                            4He
                               anode

  very thin foil                                                                       E+DE
  (0.9μm)
                                                  We can separate 16O from BG (12C)
  BG reduction by Ionization Chamber
Huge 12C-BG will be eliminated using the ionization chamber.


                      95 hours data
                                       DE
                                                          16O
                                                                       16O
                16O


                                                                 12C
                                                                        BG
                                                                       reject
                                                           4He



                                                                       E+DE




       Ionization chamber will be available from October 2011.
                             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.
                                                                    , 2010

• Ecm= 2.4 MeV experiment                          stellar energy
   – s= 64.6 nb,
   – S-factor = 89.0 keV b              Stellar
                                        energy

• Ecm= 1.5 MeV experiment
   – s= 0.900 nb,                                    future plan
   – S-factor = 26.6 keV b

• Now we are developing an ionization chamber.

• Experiments of 4He+12C 16O+γ at Ecm = 1.51.151.00.850.7MeV
  will be made in a few years.
A rehearsal for extrapolation using R-matrix theory
                        |     [g/l2 2 /( El  E )] |2
                                     1      1/

s El         (2l + 1)                         l
                                                                   R.Kuntz, M.Fey, M.Jaeger, A.Mayer, W.Hammer
         k                 | 1  ( Sl  Bl ) Rl  iPl Rl |   2
                                                                   Astrophysical J. 567. (2002) 643-650
Rl    [l /( El  E )]
                         Assumed data (±10%)
                        Ecm[MeV] S-factor[keV b]
                           0.70        70.0±7.0
                           0.85        50.0±5.0
                           1.00        45.0±4.5
                           1.15        35.0±3.5
                           1.50        30.0±3.0
  2+ 1-
                    S(0.3MeV) extrapolated = 190±15 keV b




                             Assumed data             Data from
                                                    Ruhr university
              0.3

								
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