TheP +19Nes- wave resonant state in20Na at stellar energies

Abstract

The first excited state above the p + 19Ne threshold in 20Na has been identified at 2.637 MeV (+ 15 keV) with jx = 0 + or 1 + from the 20Ne(3He, t)20Na reaction, suggesting this state to be the s-wave resonance in the p + 19Ne scattering at stellar energies.In hydrogen-rich stellar sites with very high temperature, rapid proton process (rp-process) will take place, producing energy and heavier nuclides.Wallace and Woosley 1) have suggested that the rp-process will give a chance of breakout from the hot CNO (HCNO) cycle to the next cycle of heavier elements with higher rate.Specifically, 20Na is crucial for this breakoutl,2).However, the nuclear structure information on 20Na was insufficient3), especially about the spin-parities of the states above the p + 19Ne threshold.Several new states were reported 4) very recently, but no spin assignment was made for the states.We have performed an experiment of the 20Ne(3He,t)20Na reaction to determine the energies, spin parities of the states near and above the threshold in 20Na. A gas target of enriched 20Ne (99.95 %) of about 100 mmHg was bombarded by a 55.33-MeV 3He beam of about 0.5 -1.0 gA from the cyclotron of the Institute for Nuclear Study of the University of Tokyo.The reaction products tritons were measured by using a magnetic spectrograph and a position-sensitive gas counter placed on the focal plane.This system provides complete particle identification for tritons by using the energy loss, total energy and the time-offlight signals.The overall energy resolution (FWHM) is about 75 keV. The focal plane was carefully calibrated by using the known reactions 160(3He,t)16F and 14N(3He,t)140. The experimental uncertainties in excitation energies are mostly due to those of the reference peaks of 16F and 140 used, which are ranging from I0 to 60 keV, and partly due to the possible errors in fitting multiplet peaks. Figure 1 shows a typical momentum spectrum of tritons from the 20Ne(3He,t)20Na reaction.There are several states excited above the threshold of p + 19Ne, 2.199 MeV. Figure 2 shows the angular distributions for the ground state and the state at 2.637 MeV (+ 15 keV), which is the first excited state above the threshold. This excitation energy is consistent with 2.63 MeV derived by a recent precision 2~ (h, t) 2~

New direct study of theNe19(p,γ)Na20Couder1, Angulo2, Casarejos3 et al. 2004Phys. Rev. C212311View full textAdd to dashboardCite

“…This level was produced previously in nuclear reactions induced by stable beams, like 20 Ne͑ 3 He, t͒ 20 Na [3][4][5][6] or 20 Ne͑p , n͒ 20 Na [7]. Angular distributions of the tritons suggested a J =1 + assignment, while the ͑p , n͒ reaction data was consistent with a 3 + assignment.…”

Level structure above the proton threshold of20Na

“…The situation is not so clear for the region above the proton threshold. This region has attracted particular interest for some decades because the reaction sequence 15 O(α,γ ) 19 Ne(p,γ ) 20 Na is thought to represent the main breakout route between the hot CNO cycles and the rp process in x-ray bursters [3]. The purpose of the present Brief Report is to consider the level structure of 20 Na above the proton threshold and its relationship to known levels in 20 F [4], shown in Fig.…”

“…The most recent study of levels above the proton threshold of 20 Na was that of Wallace et al [5] from measurements of the β-delayed proton decay of 20 Mg. That paper focused on a search for a weak proton decay branch of the key astrophysical resonance for the 19 Ne(p,γ ) 20 Na reaction at ∼450 keV. For a detailed discussion of previous studies of the attempt to identify the spin-parity of this resonance, and to determine its strength, readers are referred to Ref.…”

“…[5] that combined the new high-precision proton threshold energy measurement of Ref. [1] with a precise relative energy difference measurement between this state and a neighboring 1 + resonance obtained in a high-resolution study of the 20 Ne( 3 He,t) 20 Na charge exchange reaction [7]. That information was used to derive a new more precise proton resonance energy of 457(3) keV and an excitation energy of 2647(3) keV in 20 Na.…”

“…A magnetic spectrometer was used in this study, with relative energies between the excited states reported as being measured to an accuracy of +/−2 keV [7]. Hence, using these values relative to the 2987 (2) 20 Na and 20 F. All footnotes refer to the present excitation energies in 20 Na. To the left-hand side of the table excitation energies in 20 Na from charge exchange reaction studies are given with references.…”