Transcript Hot CNO Cycle Breakout via 15O(alpha,gamma)19Ne

Lifetimes of the astrophysically
19
important states in Ne
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)19Ne
is one of the two routes to
break out CNO cycles and trigger rpprocess
–
–
4U1728-34
Rossi X-ray Timing Explorer
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
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Breakout of the Hot CNO Cycles
T9<0.08 Cold CNO cycles
T9>0.3-0.4, breakout leads to
the rp-process
Two routes:
15O(a,g)19Ne
18Ne(a,p)21Na
Proton Number
T9<0.3 Hot CNO cycles
Mg (12)
Na (11)
13 14
Ne (10)
F (9)
11 12
O (8)
N (7)
9 10
C (6)
3 4 5 6 7 8
15O(a,g)19Ne
18Ne(a,p)21Na
3a process
Neutron Number
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The importance of 4.03MeV state of 19Ne
Reaction rate of resonances
N A  v  T
3 / 2
g e
 ER / kT
Three quantities for nuclear
physicists to measure: ER, Γγ, Bα
besides J
where
g 
2J R  1
Ba g
(2 J P  1)(2 J T  1)
rate
ωγfrom Langanke et al, Ap. J. 301, 629(1986)
Γγ of α-unbound states of 19Ne are
unmeasured.
4.03 MeV level dominates the rate
at temperatures T9 < 0.6.
– Very small Bα
1
4.03MeV
4.55MeV
0.8
0.6
<4.3x10-4 by Davids et al, PRC2003
4.71MeV
4.38MeV
4.60MeV
– Only upper/lower limits on lifetime
τ<50fs by Davidson et al, NPA1973
Γ<440 meV by Hackman et al, PRC2000
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0.4
T9
Doppler-Shift Attenuation Method (DSAM)
Measure lifetime to obtain decay width
   /
γ
Traditional method
Eg  Eg 0 (1  F ( ) cos )
19Ne
target
– Easy to apply and good for poorly resolved peaks
– 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
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17O(3He,n-γ)19Ne
HPGe
Doppler shifts and geometry
uncertainty are cancelled.
=> energy measurement
45o
3He
3MeV
17O/Ta
n det
HPGe
135o
3He
28.5o
3MeV
maximize Doppler shift of gamma
energies by measuring gammas
emitted along the same direction as
19Ne travels.
=> lifetime measurement
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17O/Ta
90o
n det
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
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4034keV state
Unshifted
Measured Ex = 4034.5±0.8 keV
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4034keV state of 19Ne
13 fs
4 fs
29 fs
50 fs
Best Geant4 fit
2sigma uncertainties
Upper limit by Davidson et al
Measured lifetime
τ= 13±96 fs
or Γ=51±43 21 meV
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Summary of our results
Compilation (TUNL)
Jπ
E* [keV]
Present work
τm [fs]
E*[keV]
τm[fs]
1507.56±0.3
5/2-
1.4 00..56  10 3
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
4140±4
(9/2)-
<300
4143.5±0.6
4197.1±2.4
(7/2)-
<350
4200.3±1.1
4379.1±2.2
7/2+
<120
4377.8±0.6
4549±4
(1/2,3/2)-
<80
4547.7±1.0
4600±4
(5/2+)
<160
4601.8±0.8
13 16
9
4
18 5
21
43 14
5 64
21
15 10
7 96
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