H. Schatz Michigan State University

National Superconducting Cyclotron LaboratoryJoint Institute for Nuclear Astrophysics

The rp process in X-ray bursts  astrophysics and experiments with fast radioactive beams

X-ray bursts

• Many new observations by Beppo-SAX, RXTE, Chandra, XMM-Newton lots of open questions

• Can learn about neutron stars• increase in mass, spin, temperature compared to isolated NS

• Bright and frequent (most common thermonuclear explosion in the universe)

Galloway et al. 2003

97-98

2000

Precision X-ray observations(NASA’s RXTE)

Woosley et al. 2003 astro/ph 0307425

Need much more precise nuclear data to make full use of high quality observational data

Uncertain models due to nuclear physics

Burst models withdifferent nuclear physicsassumptions

Burst models withdifferent nuclear physicsassumptions

GS 1826-24 burst shape changes ! (Galloway 2003 astro/ph 0308122)

Reality check: Burst comparison with observations

For example to determine XH distance, EOS

• Ejected composition (<few%) (Weinberg et al. 06 astro-ph/0511247 )

• Crust composition Crust heating (Gupta et al. astro-ph/0609828)

crust cooling superbursts

More observables – what about the produced nuclei ?

KS 1731-260

NASA/Chandra/Wijnands et al.

Likely no nucleosynthesis contributionGoal: understand systems and neutron stars

?

Mass known < 10 keV

Mass known > 10 keV

Only half-life known

seen

Figure: Schatz&Rehm, Nucl. Phys. A,

Reaction rates:• direct measurements difficult• “indirect” methods:

• Coulomb breakup• (p,p)• transfer reactions stable beams and RIBS

Guide direct measurements Huge reduction in uncertainties If capture on excited states matters only choice

NSCL Set of experimentsuse (p,d) to determinelevel structure

ISOLTRAPRodriguez et al.NSCL Lebit

Bollen et al.

ANL CPTSavard et al.

Recent progress in mass measurements

JYFL TrapKankainen et al.

SHIPTRAPMeasure: decay properties gs masses level properties rates/cross sections

Why measuring excitation energies ?

Coulombpenetrability

Boltzmann e-E/kT

+_100 KeV

Shellmodel(OXBASH)

32Cl(p,g)33Ar Reaction rate for T=0.4 x 109 KExample: contribution from one individual resonance (5/2+)

mole s

cmeMeV][)(1054.1

39T

MeV][rE605.11

2/39

11

ATvN A1

2 1

(2 1)(2 1)pr

T

J

J J

Focal plane:identify 33Ar

Plastic target34Ar (p,d) 33Ar

Radioactive 34Ar beam84 MeV/u T1/2=844 ms(from 150 MeV/u 36Ar)

33Ar

34Ar

Beamblocker

n-removal related to astrophysical 32Cl+p 33Ar+rate

-rays from predicted 3.97 MeV state

Doppler corrected -rays in coincidence with 33Ar in S800 focal plane:

SEGA

x 3 uncertainty(from x 1000)

New rates: Clement et al. PRL 92 (2004) 2502, Galaviz et al.

33Ar 33Ar

Sp 3343(8)

SM (Brown) Exp

3970 5/2+

104(6) keV150(4) keV

3560 7/2+

reac

tion

rate

(cm

3/s

/mol

e)

Clement et al.

Ex by

32Cl+p

Rate dominated by capture on low lying (90 keV) first excited state in 32Cl

Rate dominated by capture on low lying (90 keV) first excited state in 32Cl

32Cl(p,)33Ar

H. Schatz

Stellar Enhancement Factor

SEF = stellar capture rate

ground state capture rate

this work

NON Smoker

direct measurement of this rate is not possible – need indirect methods SEF’s should be calculated with shell model if possible

1+

2+90 keV

3.364

3.456

3.819

4.190

33Ar

32Cl

5/2+

7/2+

5/2+

1/2+MeV

3.343

Dominantresonance

Advantages of method:• reach as beam is less n-deficient (see chart) and thick targets can be used (fast beams, ’s)• measure isotones simultaneously• precise energies due to -detection

Limitations:- need -decay branch (d-spectroscopy being developed)- better for low level density (match with shell model/mirror, statistics limited for ) - has to be coordinated with precision mass measurements

Reach of method

Nuclei that can be studied at NSCL

Clement et al. PRL92,17502 (2004)Schatz et al. PRC72, 065804 (2005)

Program continued by D. GalavizM. AmthorA. Chen

HIRA experimentswith particle detection(Famiano, Lynch)

Summary

• Fast beams are important tool for rp-process reaction rate studies especially when reach to most exotic nuclei is required (p,d) in inverse kinematics is a useful method

a wide range of reactions is within reach at the NSCL

• Other tools are also needed low energy beams for direct rate measurements

New facility at MSU/NSCL is planned (gas stopping and reacceleration to astrophysical energies)

stable beams interdisciplinary environment Joint Institute for Nuclear Astrophysics (JINA) (www.jinaweb.org)

NSCL Reacceleration Stage Options

A1900/ Cyclotron Stopper/ Charge Breeder/ RFQ/ LINAC

Reaccelerated beam area

Stage I 1-2 MeV/u

Stage II 12 MeV/u

NSCL Layout with Stopping Station

At this stage, the lay-out of the low energy arena is for illustration only and requires significant user input (incl. user provided equipment)

x 3 uncertainty(from x 1000)

New rates: Clement et al. PRL 92 (2004) 2502, Galaviz et al.

33Ar 33Ar

Sp (3343)

SM (Brown) Exp

32Cl(p,)33Ar32Cl(p,)33Ar

3970 5/2+

104(6) keV150(4) keV

3560 7/2+

reac

tion

rate

(cm

3/s

/mol

e)

Clement et al.

Ex by

32Cl+p

29P+p

Other reactions in preparation Other reactions in preparation

30S 30S

4888 2+

4733 3+Sp (4399)

reac

tion

rate

(cm

3/s

/mol

e)

Temperature (GK)

X ~2.5 uncertainty(from x 10)

29P(p,)30S29P(p,)30S

Galaviz et al.

Preliminary

(Ozel Nature 441 (2006) 1115)

Example: understand bursts to constrain NS

X-ray bursts from EXO0748−676:• O,Fe absorption lines ( redshift)• Tc/Fcool ( ~surface area)• Eddington luminosity

X-ray bursts from EXO0748−676:• O,Fe absorption lines ( redshift)• Tc/Fcool ( ~surface area)• Eddington luminosity

XH=0.661

2

erg/

g/s/

1e1

7

XH=0.55

XH=0.29

Mass uncertaintieswithin AME95Brown et al. 2002

Masses for key waiting points

150

Sp needed (withest. uncertaintyin keV from Coulomb shift)

ISOLTRAP

CPT

LEBIT

Future trap measurements: 65As,66Se,70Kr,74Sr Mass measurements with reactions: 69Br, 73Rb

Future trap measurements: 65As,66Se,70Kr,74Sr Mass measurements with reactions: 69Br, 73Rb

180

160

100

100

100

160

Current effective lifetime uncertainties from masses:64Ge: up to x2068Se: up to x472Kr: up to x2

Current effective lifetime uncertainties from masses:64Ge: up to x2068Se: up to x472Kr: up to x2

N=Z

Nuclear physics needed for rp-process:

0 12

3 45 6

7 8

9 10

11 12 13

14

15 16

17 18 19 20

21 22

23 24

25 26 27 28

29 30

31 32

33 34 35 36

37 38 39 4041

42 43 44

45 46 47 48

49 5051 52

5354 55

56

57 58

n (0) H (1)

H e (2)L i (3)

Be (4) B (5) C (6) N (7)

O (8) F (9)

N e (10)N a (11)

M g (12)A l (13)S i (14) P (15)

S (16)C l (17)

A r (18) K (19)

C a (20)Sc (21)

Ti (22) V (23)

C r (24)M n (25)

Fe (26)C o (27)

N i (28)C u (29)

Zn (30)G a (31)

G e (32)As (33)

Se (34)B r (35)K r (36)R b (37)

S r (38) Y (39)

Zr (40)N b (41)

M o (42)Tc (43)

R u (44)R h (45)Pd (46)Ag (47)

C d (48)In (49)

Sn (50)Sb (51)

Te (52) I (53)

Xe (54)

some experimental information available(most rates are still uncertain)

Theoretical reaction rate predictions difficult neardrip line as single resonances dominate rate:

Hauser-Feshbach: not applicable

Shell model: available up to A~63 but large uncertainties (often x1000 - x10000)

(Herndl et al. 1995, Fisker et al. 2001)

Need radioactive beams

• -decay half-lives• masses• reaction rates mainly (p,), (,p)

(ok)

(in progress)

(just begun)

Summer research project of NSCL graduate student Matt Amthor at LANLprior to his NSCL thesis experiment to determine rp-process reaction rates

Opportunities for students

Simulated Light Curves from Kepler

0.5

0.7

0.9

1.1

1.3

1.5

1.7

0 5 10 15 20 25 30

Time from start of Burst (s)

Bu

rst

Lu

min

os

ity

(1

0^

38

erg

/s)

Low Rates/Burst 2

High Rates/Burst 2

Simulated Light Curves from Kepler

0.5

0.7

0.9

1.1

1.3

1.5

1.7

0 5 10 15 20 25 30

Time from start of Burst (s)

Bu

rst

Lu

min

os

ity

(1

0^

38

erg

/s)

Low Rates/Burst 2

High Rates/Burst 2

30S(p,g)* 31Cl

36K(p,g)** 37Ca

40Sc(p,g) 41Ti

46Cr(p,g) 47Mn

Vary by factor 100

M. Amthor, A. Heger, H. Schatz, B. Sherrill

Comparable to observed differences

97-98

2000

Precision X-ray observations(NASA’s RXTE)

Need precise nuclear datato make full use of high quality observational data

Example: determine accreted hydrogen mass fraction by comparing model with observations distance estimate Stringent EOS constraints (Oezel 2006)

GS 1826-24 burst shape changes ! (Galloway 2003 astro/ph 0308122)

Observables of nuclear processes in X-ray bursts: Lightcurve