Direct measurement of the 448 keV level in the 19Nep,20Na reaction

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Direct measurement of the 448 keV level in the
19Ne(p,?)20Na reaction

• M. Couder, C. Angulo, E. Casarejos, P. Leleux,
  F. Vanderbist

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Status

• In X-ray bursts, possible escape of the hot-CNO
  cycles to the rp-process through
• 18F(p,a)15O(a,g)19Ne(p,g)20Na
• 18F(p,g)19Ne(p,g)20Na
• 18F(b)18Ne(a,p)21Na
• Reaction rate of 19Ne(p,g)20Na dominated by a
  resonant level at 448 keV above threshold.
• Jp assignment
• 1 from 20Ne(3He,t)20Na and 20Ne(p,n)20Na angular
  distribution measurement (wg6 meV) predicted
  (Kubono et al.)
• 1- from GCM calculation (wg33 meV) (Baye and
  Descouvemont)
• 3 from assignment to the 3 level at 2.966 MeV
  in 20F (wggt16 meV) (Brown)

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Previous measurement in Louvain-la-Neuve with
19Ne beam

• Detection of the delayed a-decays following the
  b of the 20Na decay.
• Detector
• Double-sided silicon strip detectors
• Solid state nuclear track detectors
• Efficiency 1.5
• Background from 19Ne(d,n)
• wg lt 21 meV(90 CL)

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Direct detection of the recoils 20Na using the
recoil separator ARES.

• Detection of the recoil product.
• The recoil and the ion beam are contained in a
  small cone (q1/2 20 mrad) behind the target (1
  recoil /1011 ion beam)
• ARES exploits the fact that the recoil and the
  beam have the same momentum.
• Selection in velocity.
• Charge selection.
• Detection.

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Characterisation of ARES

• Study of 19F(p,g)20Ne (Er635 keV, ??1.6 eV).
• Global efficiency 4 (11.5 transmission of
  20Ne7)
• Well reproduced by the simulation.
• Rejection factor 5. 10-7

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Study of 19Ne(p,g)

• Measure the strength of the 448 keV level using
  the ARES spectrometer.
• Normalisation to the 19Ne(p,p) elastic scattering.

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Normalisation
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Normalisation
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Study of 19Ne(p,g)

• Measure the strength of the 448 keV level using
  the ARES spectrometer.
• Normalisation to the 19Ne(p,p) elastic
  scattering.
• 19Ne beam
• Limited to 108 pps to limit the counting rate in
  the final detector.
• A 19F contamination of 2?10-3 was found.

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DE-ESpectrum
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Study of 19Ne(p,g)

• Measure the strength of the 448 keV level using
  the ARES spectrometer.
• Normalisation to the 19Ne(p,p) elastic
  scattering.
• 19Ne beam
• Limited to 108 pps to limit the counting rate in
  the final detector.
• A 19F contamination of 2?10-3 was found.
• Result
• Global efficiency 2.7 (7.2 transmission of
  20Na7).
• ??lt 15.2 meV (90 confidence level).