H. Schatz Michigan State University National Superconducting Cyclotron Laboratory Joint 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 Precision X-ray observations (NASA’s RXTE) Woosley et al astro/ph Need much more precise nuclear data to make full use of high quality observational data Uncertain models due to nuclear physics Burst models with different nuclear physics assumptions  GS burst shape changes ! (Galloway 2003 astro/ph ) Reality check: Burst comparison with observations For example to determine X H  distance, EOS

Ejected composition (<few%) (Weinberg et al. 06 astro-ph/ ) Crust composition  Crust heating (Gupta et al. astro-ph/ )  crust cooling  superbursts More observables – what about the produced nuclei ? KS NASA/Chandra/Wijnands et al. Likely no nucleosynthesis contribution Goal: 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 experiments use (p,d  ) to determine level structure ISOLTRAP Rodriguez et al. NSCL Lebit Bollen et al. ANL CPT Savard et al. Recent progress in mass measurements JYFL Trap Kankainen et al. SHIPTRAP Measure:  decay properties  gs masses  level properties  rates/cross sections

Why measuring excitation energies ? Coulomb penetrability Boltzmann e -E/kT + _ 100 KeV Shell model (OXBASH) 32 Cl(p,g) 33 Ar Reaction rate for T=0.4 x 10 9 K Example: contribution from one individual resonance (5/2+)

Focal plane: identify 33 Ar Plastic target 34 Ar (p,d) 33 Ar Radioactive 34 Ar beam 84 MeV/u T 1/2 =844 ms (from 150 MeV/u 36 Ar) 33 Ar 34 Ar Beam blocker n-removal related to astrophysical 32 Cl+p  33 Ar+  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. 33 Ar S p 3343(8) SM (Brown) Exp /2 +  104(6) keV  150(4) keV /2 + reaction rate (cm 3 /s/mole) Clement et al. E x by 32 Cl+p  Rate dominated by capture on low lying (90 keV) first excited state in 32 Cl 32 Cl(p,  ) 33 Ar

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 keV Ar 32 Cl 5/2 + 7/2 + 5/2 + 1/2 + MeV Dominant resonance

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, (2005) Program continued by D. Galaviz M. Amthor A. Chen HIRA experiments with 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) (

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. 33 Ar S p (3343) SM (Brown) Exp 32 Cl(p,  ) 33 Ar /2 +  104(6) keV  150(4) keV /2 + reaction rate (cm 3 /s/mole) Clement et al. E x by 32 Cl+p 29 P+p  Other reactions in preparation 30 S S p (4399) reaction rate (cm 3 /s/mole) Temperature (GK) X ~2.5 uncertainty (from x 10) 29 P(p,  ) 30 S 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) T c /F cool (  ~surface area) Eddington luminosity X-ray bursts from EXO0748−676: O,Fe absorption lines (  redshift) T c /F cool (  ~surface area) Eddington luminosity X H = erg/g/s/1e17 X H =0.55 X H =0.29 Mass uncertainties within AME95 Brown et al. 2002

Masses for key waiting points 150 Sp needed (with est. uncertainty in keV from Coulomb shift) ISOLTRAP CPT LEBIT  Future trap measurements: 65 As, 66 Se, 70 Kr, 74 Sr  Mass measurements with reactions: 69 Br, 73 Rb  Future trap measurements: 65 As, 66 Se, 70 Kr, 74 Sr  Mass measurements with reactions: 69 Br, 73 Rb Current effective lifetime uncertainties from masses: 64 Ge: up to x20 68 Se: up to x4 72 Kr: up to x2 Current effective lifetime uncertainties from masses: 64 Ge: up to x20 68 Se: up to x4 72 Kr: up to x2 N=Z

Nuclear physics needed for rp-process: some experimental information available (most rates are still uncertain) Theoretical reaction rate predictions difficult near drip line as single resonances dominate rate: Hauser-Feshbach: not applicable Shell model: available up to A~63 but large uncertainties (often x 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 LANL prior to his NSCL thesis experiment to determine rp-process reaction rates Opportunities for students 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

Precision X-ray observations (NASA’s RXTE) Need precise nuclear data to 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 burst shape changes ! (Galloway 2003 astro/ph ) Observables of nuclear processes in X-ray bursts: Lightcurve