classical novae, type I x-ray bursts, and ATLAS Alan Chen Department of Physics and Astronomy McMaster University

rare isotopes in stars: type I x-ray bursts model: binary star system accretion on neutron star thermonuclear runaway observations: light curves research areas: Breakout from the Hot-CNO cycles rp-process: path, endpoint, synthesis  p-process  key reactions experiments: proton-rich rare isotopes (p,  ) and ( ,p) reactions mass measurements

rp-process: beginnings explosive hydrogen-helium burning (T  0.5 GK)  breakout from the Hot-CNO cycles 15 O( ,  ) 19 Ne 19 Ne(p,  ) 20 Na 18 Ne( ,p) 21 Na 14 O( ,p) 17 F 17 F(p,  ) 18 Ne [figure adapted from C. Iliadis (2007)]

rp-process, cont’d after breakout from Hot-CNO cycles: ( ,p) and (p,  ) on proton-rich nuclei  production of heavier elements energy generation and timescale set by “waiting-point” nuclei: e.g., 30 S, 56 Ni, 64 Ge, 68 Se reaction flow: competition between  -decay and reactions ( ,p) and (p,  ) reaction rates: often calculated with statistical models (e.g., Hauser-Feshbach) need experimental verification

rp-process, cont’d [type I x-ray burst – neutron star: 1.3M sun, R = 8 km, T peak = 1.4 GK,  = 100 s]  p-process WP: 22 Mg, 26 Si, 30 S, 34 Ar ( ,p) cross sections rp-process WP: 56 Ni, 64 Ge, 68 Se, 72 Kr 57 Cu(p,  ) 58 Zn Q-values for 64 Ge(p,  ) 65 As 68 Se(p,  ) 69 Br [nucleosynthesis study: A. Parikh et al., Ap.J.Supp. Ser. (2008); PRC (2009)]

thermonuclear reaction: narrow resonances Breit-Wigner formula: partial widths of entrance and exit channels total width resonance energy resonance energy: needs to be measured precisely “resonance strength”  [broad resonances: widths are energy-dependent  calculate reaction rate analytically]

15 O( ,  ) 19 Ne Breakout reaction from the Hot CNO cycles Direct measurement not feasible Need B  for MeV state of 19 Ne

15 O( ,  ) 19 Ne B  for MeV state of 19 Ne: new technique ATLAS: 19 F beam gas cell catcher foil + wheel custom NaI detectors Approved for test run

( ,p) reactions Time-inverse measurements, so far 17 F(p,  ) 14 O, 21 Na(p,  ) 18 Ne, 25 Al(p,  ) 22 Mg, 29 P(p,  ) 26 Si, 33 Cl(p,  ) 30 S, 37 K(p,  ) 34 Ar  undetermined contributions from reactions to excited states Direct measurements are needed Approaches: AIRIS + HELIOS (inc. cryogenic gas cell and high-rate ionization chamber)

HELIOS Gas Target Multiple window flanges allow for different target thicknesses (1, 2 and 3 mm) For backward angle measurements: – upstream window: diameter = 0.31”  lab > 94° – downstream window: diameter = 0.25”  lab < 72° Effective target thicknesses of e.g. ~65  g/cm 2 for 700-mbar 3 He (2-mm gas cell) Best resolution: ~ 270-keV FWHM (using 1 mg/cm 2 Kapton window) lines for LN 2 cooling input/output gas lines fan for solid targets, FC, source, etc. entrance/exit window

HELIOS Ionization Chamber Alternating anode and grounded grids: – grid separation: 1.7 cm – wire spacing: 2-mm – x and y position sensitivity Commissioned Feb/March 2013: 28 Si+ 12 C, 28 Si+Au, 86 Kr(d,p), CARIBU beam, 14 C(d,p), 14 C( 3 He,d) Results: – rates of > 400 kHz (pileup ~ 10 – 30 %) – energy resolution better than 5%

18 Ne( ,p) 21 Na Breakout reaction from Hot-CNO cycles Experiments: transfer reactions time-inverse with RIBs

18 Ne( ,p) 21 Na with HELIOS Gamow window: E cm  1 – 2 MeV E( 18 Ne) = 1 – 1.5 MeV/A Gas cell: K: 25  g/cm 2 20% detection efficiency AIRIS: 10 5 pps Ecm  1.97 MeV: cross section  1 mb 40 – 50 counts in a week Matic, Mohr (2013)

( ,p) reactions Approaches: AIRIS + HELIOS (inc. cryogenic gas cell and high-rate ionization chamber) good energy resolution for protons limited solid angle coverage Alternative: use AGFA to detect recoils full angular coverage good separation of beam contaminant contributions no resolution

rare isotopes in stars: classical novae models: binary star system accretion on white dwarf thermonuclear runaway observations: ejecta spectroscopy presolar meteoritic grains research areas: Ne-Na, Mg-Al cycles reactions affecting synthesis of: -  -emitters (e.g., 18 F, 22 Na, 26 Al) - isotopes in meteoritic grains - elements in ejecta experiments: proton-rich rare isotopes (p,  ) and (p,  ) reactions 18 F(p,  ) 15 O, 25 Al(p,  ) 26 Si, 30 P(p,  ) 31 S [Nova Pyxidis]

the nuclear origin of galactic 26 Al important reactions: 26 Al(p,  ) 27 Si 25 Al(p,  ) 26 Si [Iliadis et al. Ap. J. (2002)] RHESSI

nova nucleosynthesis at phosphorus 29 P 30 P 27 Si 28 P 30 S 31 S 28 Si 29 Si 32 S 31 P 30 Si [p,  ] β+β+ [2.5 min] P(p,  ) 31 S [ 30 P(p,  ) 31 S: also important in x-ray bursts  reaction flow] [silicon abundances: competition between phosphorus (p,  ) and  + ]

nova nucleosynthesis at phosphorous (cont’d) variation in 30 P(p,  ) 31 S rate  changes A ≈ abundances by factors of 2 – 10 drives the nuclear activity toward heaviest elements produced (A ≈ 40)  reaction rate has large uncertainties (  x 20)  need more experiments, but direct measurement not feasible [José et al., Ap.J. (2001) and Iliadis et al., Ap.J. (2002)]

nova nucleosynthesis at ATLAS Use ( 3 He,d) as a surrogate for (p,  ): HELIOS Examples: 25 Al(p,  ) 26 Si  AIRIS: 10 7 pps 30 P(p,  ) 31 S  AIRIS: 10 7 pps