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VIEWS: 19 PAGES: 10

									  Lifetimes of the astrophysically
      important states in 19Ne


                   Wanpeng Tan
              University of Notre Dame
Collaborators:
J. Görres, M. Wiescher, J. Daly, M. Couder, A.
Couture, H.Y. Lee, E. Stech, E. Strandberg,
and C. Ugalde

                           JINA Frontiers 2005
                                              Motivation
     15O(a,g)19Neis one of the two routes to                                              4U1728-34
     break out CNO cycles and trigger rp-                                                 Rossi X-ray Timing Explorer
     process                                                                              Picture: T. Strohmeyer, GSFC

      –   Energy production
      –   Nucleosynthesis
     X-ray bursts: 10-100s, 1039 erg
     Superbursts: 1000x stronger and
     longer

Wiescher et al., J. Phys. G 25, R133 (1999)
Fisker et al., astro-ph/0410561 (2005)




                                                               Superburst 4U 1636-53
                                                               Picture: T. Strohmayer, GSFC




                                               JINA Frontiers 2005
       Breakout of the Hot CNO Cycles

T9<0.08 Cold CNO cycles

T9<0.3 Hot CNO cycles
                                                                  Mg (12)
T9>0.3-0.4, breakout leads to                                     Na (11)                 13 14




                                      Proton Number
the rp-process                                                Ne (10)
                                                              F (9)                   11 12
Two routes:                                               O (8)
15O(a,g)19Ne                                              N (7)                9 10
18Ne(a,p)21Na                                         C (6)                            15O(a,g)19Ne
                                                              3 4 5 6 7 8              18Ne(a,p)21Na

                                                                      3a process

                                                                        Neutron Number


                                JINA Frontiers 2005
The importance of 4.03MeV state of 19Ne
Reaction rate of resonances
                                                                                  2J R  1
N A  v  T         3 / 2
                               g e    E R / kT
                                                   where            g 
                                                                           (2 J P  1)( 2 J T  1)
                                                                                                   Ba g

Three quantities for nuclear                          rat e ωγfrom Langanke et al, Ap. J. 301, 629(1986)

physicists to measure: ER, Γγ, Bα
besides J                                                  1
                                                                    4.03MeV
Γγ of α-unbound states of 19Ne are                      0. 8                               4.55MeV
unmeasured.
                                                        0. 6
4.03 MeV level dominates the rate
at temperatures T9 < 0.6.                                                                      4.71MeV
 – Very small Bα                                        0. 4                4.38MeV
 <4.3x10-4 by Davids et al, PRC2003                                                             4.60MeV
 – Only upper/lower limits on lifetime
 τ<50fs by Davidson et al, NPA1973                      0. 2
 Γ<440 meV by Hackman et al, PRC2000                                                T9
                                      JINA Frontiers 2005 0
                                                               -2              -1
Doppler-Shift Attenuation Method (DSAM)

Measure lifetime to obtain decay width                 /
Traditional method                                              γ

    Eg  Eg 0 (1  F ( )  cos )                             19Ne

 – Easy to apply and good for poorly resolved peaks           target
 – Not sufficient for asymmetric peaks and feeding effects from
   higher lying states

Full line shape analysis
 – Realistic Geant4 simulation
 – Details of the peak shape, especially for double peak structure
   and tailing effects
 – Dealing with the feeding from higher lying states


                              JINA Frontiers 2005
                          17O(3He,n-γ)19Ne


                     HPGe
                                                  Doppler shifts and geometry
                               45o                uncertainty are cancelled.
                                                      => energy measurement
3He   3MeV

                 17O/Ta
                                      n det
             135o                                                HPGe


                                        3He   3MeV                        28.5o
      maximize Doppler shift of gamma
      energies by measuring gammas                           17O/Ta
      emitted along the same direction as
      19Ne travels.
                                                       90o
           => lifetime measurement
                                                                  n det
                                 JINA Frontiers 2005
     19Ne   related gamma spectra in coincidence with neutrons



                                45o


                               135o


                                 0o




Gamma peaks are not only shifted but also broadened.
Simple DSAM approach is insufficient to study more complicated shapes
Full line-shape analysis is necessary for precise measurements
 –   Details of the peak shape, especially for double peak structure and tailing effects
 –   Dealing with the feeding from higher lying states

                                      JINA Frontiers 2005
      4034keV state


     Unshifted




Measured Ex = 4034.5±0.8 keV
        JINA Frontiers 2005
4034keV state of 19Ne


                                  13 fs   Best Geant4 fit
                                   4 fs
                                          2sigma uncertainties
                                  29 fs
                                  50 fs   Upper limit by Davidson et al




                                             Measured lifetime
                                             τ= 13±96 fs
                                             or Γ=51±43 21 meV




            JINA Frontiers 2005
                Summary of our results
             Compilation (TUNL)                               Present work
  E* [keV]             Jπ            τm [fs]            E*[keV]             τm[fs]
1507.56±0.3     5/2-          1.4 0..5  10 3
                                  0 6              1507.51±0.35       1.7±0.4x103
1536.0±0.4      3/2+          28±11                 1536.05±0.36       16 ±6
1615.6±0.5      3/2-          143 ±31               1615.4±0.4         80 ±25
2794.7±0.6      9/2+          140 ±35               2794.2±0.4        102 ±16
4032.9±2.4      3/2+          <50                   4034.5±0.8          13 16
                                                                           9
4140±4          (9/2)-        <300                  4143.5±0.6          18 4
                                                                           5

4197.1±2.4      (7/2)-        <350                  4200.3±1.1          43 14
                                                                            
                                                                             21


4379.1±2.2      7/2+          <120                  4377.8±0.6           5 6
                                                                           4
4549±4          (1/2,3/2)-    <80                   4547.7±1.0          15 10
                                                                           
                                                                             21


4600±4          (5/2+)        <160                  4601.8±0.8           7 9
                                                                           6
4635±4          13/2+         >1x103                4634.0±0.9        >1x103

    Errors of mean lifetimes of present work are given at the 95% confidence level.


                                  JINA Frontiers 2005

								
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