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The structure of 30 S and the 29 P(p  30 S reaction rate Kiana Setoodehnia.

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Presentation on theme: "The structure of 30 S and the 29 P(p  30 S reaction rate Kiana Setoodehnia."— Presentation transcript:

1 The structure of 30 S and the 29 P(p  30 S reaction rate Kiana Setoodehnia

2 29 P(p  30 S 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)105 J. José et al., Ap. J. 612(2004)414 J. José et al., Ap. J. Suppl. Ser. 189(2010)204

3 29 P(p  30 S Reaction Rate 30 S (5) (8) 2+2+ (3 + ) (2 + ) (4 + ) 4733(40) 4888(40) 5136(2) (7) 5290(9) 5390(4) 3666(2) 3677(3) (1 + ) (0 + ) (3 -, 2 + ) 3-3- At the temperature regime of astrophysical interest (0.1 – 1.5 GK), the 29 P(p  ) 30 S reaction rate is dominated by: A 3 + state near 4.7 MeV and a 2 + state near 4.8 MeV The 29 P(p  ) 30 S reaction rate is uncertain over the temperature range of astrophysical interest by 3 orders of magnitude. Need to study the 29 P+p states in 30 S 29 P+p Q = 4399 keV 0.1 GK ≤ T ≤ 1.5 GK C. Iliadis et al., Ap. J. Suppl. Ser. 134(2001)151

4 Spectroscopy of 30 S In recent years: Bardayan et al. 2007: 32 S(p,t) 30 S Galaviz et al. 2007: 31 S( 12 C, 12 Cn) 30 S   30 S O’Brien et al. 2010: 32 S(p,t) 30 S Tan et al. 2010: 28 Si( 3 He,n) 30 S Some new states were discovered: 4704(5) keV – (3 + ), but properties of the key resonances remained poorly known. PRC 76(2007) Nucl. Phys. A834(2010)679c AIP Conf. Proc. 1090(2009)288 J. Phys. Conf. Ser. 202(2010)012009

5 Our Experiments We studied 30 S via: The 32 S(p,t) 30 S reaction: At Wright Nuclear Structure Laboratory using Enge spectrograph The 28 Si( 3 He,n  ) 30 S reaction: At University of Tsukuba Tandem Accelerator Complex using Ge-detectors Goals: Investigating E x and J  of 30 S states above the proton threshold (4399 keV) Determining the 29 P(p  ) 30 S reaction rate with more accuracy

6 32 S(p,t) 30 S Measurement at Yale Beam of protons accelerated with tandem Van de Graaff accelerator: Target: 250 μg/cm 2 of CdS evaporated on a 20 μg/cm 2 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

7 32 S(p,t) 30 S Measurement at Yale Spectrograph angles: 10˚, 20˚, 22˚ and 62˚ Target 1 H-Beam Detectors: 1- Gas-filled, position sensitive ionization drift chamber: Energy loss momentum 2- plastic scintillator Residual energy

8 30 S Spectrum via 32 S(p,t) 30 S 4399 New state S(p,t) 30 S θ lab = 22˚ Target: CdS Triton EnergyExcitation Energy of 30 S Counts Channel

9 Energy Resolution 25˚ Resolution: 30 keV Resolution: 80 – 120 keV 22˚ Bardayan et al. Phys. Rev. C 76(2007) Counts Channel (arbitrary unit) Setoodehnia et al. Phys. Rev. C 82(2010)022801(R)

10 Implanted Target vs. CdS We fabricated a 32 S implanted target to reduce the background: 10.7 μg/cm 2 of 32 S implanted into a 60 μg/cm 2 12 C backing Then, repeated the measurement at 22˚, 27.5˚ and 45˚. Counts Channel Counts 32 S(p,t) 30 S Target: CdS θ lab = 22˚ 32 S(p,t) 30 S Implanted θ lab = 22˚ target

11 J π Assignment: 4688 keV J π = 3 + J π = 2 +

12 J π Assignment: 4812 keV J π of higher energy states are still under investigation J π = 3 + J π = 2 +

13 The 29 P(p  30 S 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)

14 29 P(p  30 S 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)

15 Summary The existence and the J π assignment of the state near 4.7 MeV in 30 S was confirmed. A new state was observed in 30 S at 4812(2) keV, whose existence was predicted by shell model calculations. Its J π assignment has been 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 28 Si( 3 He,n γ ) 30 S reaction at University of Tsukuba Tandem Accelerator Complex. The 29 P(p, γ ) 30 S rate is entirely dominated by these two resonances in the temperature range of 0.1 – 1.5 GK.


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