H. Schatz

1
The rp process in X-ray bursts  astrophysics and
experiments with fast radioactive beams
H. Schatz Michigan State University National
Superconducting Cyclotron Laboratory Joint
Institute for Nuclear Astrophysics
2
(No Transcript)
3
X-ray bursts

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

• 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

4
Reality check Burst comparison with observations
Precision X-ray observations(NASAs RXTE)
Uncertain models due to nuclear physics
Galloway et al. 2003
Burst models withdifferent nuclear
physicsassumptions
? GS 1826-24 burst shape changes ! (Galloway
2003 astro/ph 0308122)
Woosley et al. 2003 astro/ph 0307425
Need much more precise nuclear data to make full
use of high quality observational data
For example to determine XH ? distance, EOS
5
More observables what about the produced
nuclei ?

• Crust composition
• ? Crust heating (Gupta et
  al. astro-ph/0609828)
• ? crust cooling
• ? superbursts

• Ejected composition (ltfew)
• (Weinberg et al. 06 astro-ph/0511247 )

?
Likely no nucleosynthesis contribution Goal
understand systems and neutron stars
6
Mass known lt 10 keV
Mass known gt 10 keV
Only half-life known
seen

• 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

Figure SchatzRehm, Nucl. Phys. A,
7
Why measuring excitation energies ?
32Cl(p,g)33Ar Reaction rate for T0.4 x 109
KExample contribution from one individual
resonance (5/2)
Boltzmann e-E/kT
Coulombpenetrability
8
n-removal related to astrophysical 32Clp ?
33Arg rate
Doppler corrected g-rays in coincidence with
33Ar in S800 focal plane
Focal planeidentify 33Ar
g-rays from predicted 3.97 MeV state
Beamblocker
33Ar
34Ar
SEGA
Radioactive 34Ar beam84 MeV/u T1/2844 ms(from
150 MeV/u 36Ar)
Plastic target 34Ar (p,d) 33Ar
9
New rates Clement et al. PRL 92 (2004) 2502,
Galaviz et al.
32Cl(p,g)33Ar
Ex by
SM (Brown)
x 3 uncertainty (from x 1000)
Exp
3970 5/2
-150(4) keV
3560 7/2
-104(6) keV
32Clp
Sp 3343(8)
reaction rate (cm3/s/mole)
Clement et al.
33Ar
33Ar
? Rate dominated by capture on low lying (90
keV) first excited state in 32Cl
10
H. Schatz
Stellar Enhancement Factor
stellar capture rate
SEF
ground state capture rate
MeV
1/2
4.190
5/2
Dominantresonance
3.819
this work
7/2
3.456
2
90 keV
5/2
3.364
1
3.343
NON Smoker
32Cl
33Ar

• direct measurement of this rate is not possible
  need indirect methods
• SEFs should be calculated with shell model if
  possible

11
Reach of method
Nuclei that can be studied at NSCL

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

Limitations - need g-decay branch
(d-spectroscopy being developed) - better for low
level density (match with shell model/mirror,
statistics limited for g-g) - has to be
coordinated with precision mass measurements
HIRA experimentswith particle detection(Famiano,
Lynch)
Clement et al. PRL92,17502 (2004) Schatz et al.
PRC72, 065804 (2005)
Program continued by D. Galaviz M. Amthor A. Chen
12
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)

13
NSCL Reacceleration Stage Options
A1900/ Cyclotron Stopper/ Charge Breeder/ RFQ/
LINAC
Stage I 1-2 MeV/u
Reaccelerated beam area
Stage II 12 MeV/u
14
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)
15
New rates Clement et al. PRL 92 (2004) 2502,
Galaviz et al.
Ex by
SM (Brown)
x 3 uncertainty (from x 1000)
Exp
3970 5/2
-150(4) keV
3560 7/2
-104(6) keV
32Clp
Sp (3343)
reaction rate (cm3/s/mole)
Clement et al.
32Cl(p,g)33Ar
33Ar
33Ar
16
Example understand bursts to constrain NS

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

(Ozel Nature 441 (2006) 1115)
17
Masses for key waiting points
NZ
160
100
Sp needed (withest. uncertaintyin keV from
Coulomb shift)
100
ISOLTRAP
160
100
180
CPT
150
LEBIT
Current effective lifetime uncertainties from
masses 64Ge up to x20 68Se up to x4 72Kr
up to x2

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

18
Nuclear physics needed for rp-process

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

(ok)
(in progress)
(just begun)
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 A63 but large
uncertainties (often x1000 -
x10000)
(Herndl et al. 1995, Fisker et al. 2001)
? Need radioactive beams
19
Opportunities for students
Summer research project of NSCL graduate student
Matt Amthor at LANLprior to his NSCL thesis
experiment to determine rp-process reaction rates
? Comparable to observed differences
Vary by factor 100
30S(p,g) 31Cl
36K(p,g) 37Ca
40Sc(p,g) 41Ti
46Cr(p,g) 47Mn
M. Amthor, A. Heger, H. Schatz, B. Sherrill
20
(No Transcript)
21
(No Transcript)
22
Observables of nuclear processes in X-ray bursts
Lightcurve
Precision X-ray observations(NASAs 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)