The structure of 30 S and the 29 P( p ,g ) 30 S reaction rate
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Transcript of The structure of 30 S and the 29 P( p ,g ) 30 S reaction rate
The structure of 30S and the 29P(p, )g 30S reaction rate
Kiana Setoodehnia
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
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
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
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
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
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
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
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
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
Jπ Assignment: 4688 keV
Jπ = 3+
Jπ = 2+
Jπ Assignment: 4812 keV
Jπ of higher energy states are still under investigation
Jπ = 3+
Jπ = 2+
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)
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)
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.