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.