the structure of 30 s and the 29 p( p ,g ) 30 s reaction rate
DESCRIPTION
The structure of 30 S and the 29 P( p ,g ) 30 S reaction rate. Kiana Setoodehnia. 29 P( p ,g ) 30 S Reaction. P lays an important role in explosive hydrogen burning: At nova temperature regime (0.1 – 0.4 GK) : Influences the abundances of Si isotopes : linked to the - PowerPoint PPT PresentationTRANSCRIPT
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The structure of 30S and the 29P(p, )g 30S reaction rate
Kiana Setoodehnia
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29P(p, )g 30S Reaction
Plays an important role in explosive hydrogen burning:
• At nova temperature regime (0.1 – 0.4 GK):
Influences the abundances of Si isotopes: linked to the
presolar grains of nova origin.
• At X-ray burst temperature regime (0.4 – 1.5 GK):
Influences the energy generation, duration and the light-
curve structure of the burst.
C. Iliadis et al., Ap. J. Suppl. Ser. 142(2002)105J. José et al., Ap. J. 612(2004)414
J. José et al., Ap. J. Suppl. Ser. 189(2010)204
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29P(p, )g 30S Reaction Rate
30S00+
2210.6(5)
3404.6(8)
2+
(3+)
(2+)
(4+)
4733(40)
4888(40)
5136(2)
2+
5217.4(7)
5290(9)
5390(4)
3666(2)
3677(3)(1+)
(0+)
(3-, 2+)
3-At the temperature regime of astrophysical
interest (0.1 – 1.5 GK), the 29P(p,g)30S reaction
rate is dominated by:
• A 3+ state near 4.7 MeV and a 2+ state
near 4.8 MeV
The 29P(p,g)30S reaction rate is uncertain
over the temperature range of astrophysical
interest by 3 orders of magnitude.
Need to study the 29P+p states in 30S
29P+p
Q = 4399 keV
0.1
GK ≤
T ≤
1.5
GK
C. Iliadis et al., Ap. J. Suppl. Ser. 134(2001)151
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Spectroscopy of 30S
In recent years:
• Bardayan et al. 2007: 32S(p,t)30S• Galaviz et al. 2007: 31S(12C,12Cn)30S*( )g 30S • O’Brien et al. 2010: 32S(p,t)30S• Tan et al. 2010: 28Si(3He,n)30S
Some new states were discovered: 4704(5) keV – (3+),
but properties of the key resonances remained poorly
known.
PRC 76(2007)045803
Nucl. Phys. A834(2010)679c
AIP Conf. Proc. 1090(2009)288
J. Phys. Conf. Ser. 202(2010)012009
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Our Experiments
We studied 30S via:
• The 32S(p,t)30S reaction:
At Wright Nuclear Structure Laboratory using Enge spectrograph
• The 28Si(3He,ng)30S reaction:
At University of Tsukuba Tandem Accelerator Complex using Ge-detectors
Goals:
• Investigating Ex and J of 30S states above the proton threshold (4399 keV)
• Determining the 29P(p,g)30S reaction rate with more accuracy
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32S(p,t)30S Measurement at Yale
• Beam of protons accelerated with tandem Van de Graaff accelerator:
• Target: 250 μg/cm2 of CdS evaporated on a 20 μg/cm2
natural carbon backing
• Momentum analyzed the reaction products by the Enge magnetic spectrograph at Yale University
• Energy = 34.5 MeV• Intensity = 5 – 95 pnA• Tandem Terminal voltage = 17.3 MV
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32S(p,t)30S Measurement at YaleSpectrograph angles: 10˚, 20˚, 22˚ and 62˚
Target
1H-Beam
Detectors:
1- Gas-filled, position sensitive ionization drift chamber:
• Energy loss• momentum 2- plastic scintillator
• Residual energy
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30S Spectrum via 32S(p,t)30S
439
9
New
sta
te4
812
468
8
368
03
402
.6513
65
225
539
35
314
585
0
605
6634
4
653
5
676
832S(p,t)30Sθlab = 22˚Target: CdS
Triton EnergyExcitation Energy of 30S500 1000 1500 2000
Co
un
ts
60
40
20
0
Channel
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Energy Resolution
25˚
Resolution:
30 keV
Resolution:
80 – 120 keV
22˚
Bardayan et al. Phys. Rev. C 76(2007)045803
Co
un
ts
60
50
40
0
30
20
10
500 1000 1500 2000 Channel (arbitrary unit)
Setoodehnia et al. Phys. Rev. C 82(2010)022801(R) 4
81
24
68
8
36
80
34
02
.6
51
36
52
25
53
93
53
14
58
50
60
56
63
44
65
35
67
68
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Implanted Target vs. CdS
We fabricated a 32S implanted target to reduce the background:• 10.7 μg/cm2 of 32S implanted into a 60 μg/cm2 12C backing
Then, repeated the measurement at 22˚, 27.5˚ and 45˚.
Co
un
ts
10
0
100
1000 1500 2000Channel
Co
un
ts
32S(p,t)30S Target: CdS θlab = 22˚
32S(p,t)30S Implantedθlab = 22˚ target
4812
4688
4812
4688
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Jπ Assignment: 4688 keV
Jπ = 3+
Jπ = 2+
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Jπ Assignment: 4812 keV
Jπ of higher energy states are still under investigation
Jπ = 3+
Jπ = 2+
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The 29P(p, )g 30S Reaction Rate
The rate is substantially larger (4 – 20 times) than the previously
determined rate, and is dominated by the newly observed state from
0.3 – 1.5 GK
Setoodehnia et al. Phys. Rev. C 82(2010)022801(R)
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29P(p, )g 30S Rate Uncertainty
The uncertainty in the rate is reduced significantly (up to factors of 7
and 17) with respect to the previously determined uncertainties
Iliadis et al. Bardayan et al. New rate uncertainty
Setoodehnia et al. Phys. Rev. C 82(2010)022801(R)
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Summary
The existence and the Jπ assignment of the state near 4.7 MeV in 30S was confirmed.
A new state was observed in 30S at 4812(2) keV, whose existence was predicted by shell model calculations. Its Jπ assignment hasbeen determined to be most likely 2+.
The existence and the energy of the latter state is already confirmed by an in-beam γ-ray spectroscopy experiment via the 28Si(3He,nγ)30S reaction at University of Tsukuba Tandem Accelerator Complex.
The 29P(p,γ)30S rate is entirely dominated by these two resonances in the temperature range of 0.1 – 1.5 GK.