Study of the Destruction of 18 F in Novae with an Inverse (d,p) Reaction at the HRIBF Introduction/Motivation Experiment and Results Astrophysical Significance Conclusions and Future Work R. L. Kozub Tennessee Technological University RIBENS Collaboration Photo copyright: Steve Mandel HRIBF Workshop on Measurements for Nuclear Astrophysics 2006

Nova (RS Ophiuchi) Binary Companion Star Accretion and Explosion White Dwarf Hydrogen-Rich Material Nova Cygni 1992 Copyright David A. Hardy/astroart.org/PPARC

Reactions in Stellar Explosions (T ~ K, varying densities) Z N 1112 O N C F Ne 11Na ~0.01 GK ~0.2 GK ~0.5 GK ~1 GK 18 F 18 O ++ e-e-   110 min

Annihilation gamma rays detected using orbiting observatories  insights about nova mechanisms. GLAST (2007) Were ~7 resonances “missing” in 19 Ne in astro region (E x  MeV)…could be important to reaction rate. Also, structure of low-lying states important for p capture, nuclear models. INTEGRAL Observatory (Photo: ESA) Destruction of 18 F due mostly to 18 F+p  19 Ne*  15 O+ .

Mirror Assignments: Utku et al., PRC 57, 2731 (1998) Butt et al., PRC 58, R10 (1998) Fortune and Sherr, PRC 61, (2000) Mirror Pair: Levels missing in 19 Ne (prior to HRIBF work) Studied via 18 F+p resonances, but close to threshold and below, need p-transfer— difficult!

One-to-one correspondence of states having same, same J f , and ~same E x and wave function…new insights for astrophysics and new structure information on 18,19 F. 18 F J  =1 + p n 18 F J  =1 + (Deformed:  2 ~ ) But still requires a radioactive 18 F beam or target…. “STEPPING STONE EXPERIMENT”--Use Isospin Symmetry Look for 18 F+n mirror states in 19 F that have single neutron configurations with (stronger, easier) (d,p) reaction. Mirror analogs of =0 resonances should be enhanced: S n  S p ; estimate proton widths using.

ORIC p, d, or  Hot, fibrous production target HfO 2 : Create 18 F via 16 O( ,pn) 18 F RIB (300 keV) Mass analysis (Charge exchange) To experiments  E/E~10 -4 Ion source 25 MV tandem >100 RIBS available Holifield Radioactive Ion Beam Facility at ORNL

100  cm (mb/sr) 2s 1/2 2p 3/2 1d 3/  cm (deg.) 18 F(d,p) 19 F(6.6 MeV) DWBA  lab  116  -160   cm  7  - 29  ~ 3 days of data with 5 x F/s on target. DRS SIDAR Annular Strip Detector FP Strip Detector 18 F MeV 18 F 19 F 15 N 19 F 0.16 mg/cm 2 CD 2 2 H( 18 F,p) 19 F at the HRIBF (6 MeV/u)

 lab =147  SIDAR with FP g.s SIDAR-FP Coincidences (>70%) FP Position A=19 SIDAR Singles Spectra (One Detector “Wedge”)

Singles A=19 Coinc. 15 N/  Coinc. E p (MeV) 5.1* 4.4* 1.6* *Internal Energy Calibrations (16) [Tilley, et al., NP A595,1 (1995)] E p (MeV) (5/2 + ) (1/2 + ) (3/2 - ) (3/2 + ) (3/2 + ) (1/2 + ) 2 H( 18 F,p) 19 F:  lab =147  (strip #5), all detectors

Data DWBA 2s 1/2 DWBA 1p 1/2 DWBA 1d 5/2 Sum E meas = keV

Data Sum DWBA 2s 1/2 DWBA 1d 5/ keV 3/2 + E meas = 6497  10 keV 7262 keV 3/2 + and 7364 keV 1/2 + or/and a new 3/2 + ? E meas = 7306  10 keV 8014 keV 5/2 + and 8138 keV 1/2 + E meas = keV Analog may be important for novae at low temperatures!

From R. L. Kozub et al., PRC 71, (2005) Use extracted S n to calculate  p, using Woods-Saxon well with same radial parameters as for transferred neutron bound state in DWBA calculations, assuming S p =S n :

Stellar reaction rate calculations assume mirrors are and 6449-keV states seen in 19 F( 3 He,t) 19 Ne by Utku et al. S n (2s 1/2 )  0.12 for 6497 keV state  If mirror is 38-keV resonance in 19 Ne, it could dominate reaction rate for T 9 <0.27. However, =0 strength may be concentrated in 8-keV resonance, or even in a bound state. One of the latter would appear to be favored, owing to systematics of Thomas-Ehrman shifts for =0. (S n (2s 1/2 )<0.06 for 6528). If so, probably very little contribution to reaction rate by 19 Ne analog F+p 19 F 19 Ne 3/2 + Present E meas = 6497  10 keV * ? 3/2 + Doublet at 6.5 MeV: * Excitation energy disagrees with 0.78 MeV/u measurement [de Séréville, et al., PRC 67, (R) (2003)].

RECENT ASTRO WORK ON 18 F Before recent (p,p), (p,  ), (d,p) experiments, 18 F survival in novae was uncertain by factor of ~300, especially at lower temperatures; now much better constrained: less destruction of 18 F. Nucleosynthesis calculation [Smith et al.] using just new 18 F(d,p) 19 F data suggests a factor of 1.6 more 18 F than latest estimate should survive in novae, so gamma-ray observatories should be sensitive to a volume of space ~2x previous estimates-- good news for INTEGRAL, GLAST,,,,, However, the true location in 19 Ne of the mirror to the 6497-keV level is a critical issue--can resolve only with (very tough!) proton transfer experiments: (d,n), ( 7 Li, 6 He),….Brune et al. (next talk). [Kozub et al., Phys. Rev. C 71, (R) (2005) and references therein.] Now Coc et al., Astron. Astroph. 357, 561 (2000).

Summary Estimates of 18 F burning in novae constrained—good news for gamma ray observatories! New data for testing nuclear models, new mirror level associations, and NEW QUESTIONS: What are the mirror partners in 19 Ne, e. g., for the 7262-keV 3/2 + state, and especially the 6497-keV 3/2 + state? Is isospin symmetry still a useful tool at these higher excitation energies? Answer may come from proton transfer reactions, e.g., (d,n) (C. R. Brune et al.); maybe ( 7 Li, 6 He). Future experiments at HRIBF with 18 F beam (p,  ) measurements for E p = keV; >700 keV (missing resonances); (D. W. Bardayan, K. Y. Chae et al., RIB-099) 18 F(p,  ) 19 F? Low yield, very difficult. Similar (d,p) experiment at the HRIBF (for similar reasons) 26 Al(d,p) 27 Al to look for =0 analogs of 27 Si near 26 Al+p threshold; important for understanding nucleosynthesis of 26 Al (S. D. Pain et al., RIB-153)--more about 26 Al from Peter Parker.

Thanks! D. W. Bardayan, J. C. Batchelder, J. C. Blackmon, B. A. Brown, C. R. Brune, K. Y. Chae, † A. E. Champagne, J. A. Cizewski, D. J. Dean, U. Greife, C. J. Gross, C. C. Jewett, † R. J. Livesay, † Z. Ma, † D. J. Millener, B. H. Moazen, † C. D. Nesaraja, P. D. Parker, L. Sahin, J. P. Scott, † D. Shapira, M. S. Smith, J. S. Thomas, † P. J. Woods,….. † Students Many thanks to HRIBF staff! Research supported by the U. S. DOE and NSF.

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