Experimental Investigation of the Ne19(p,γ)20Na

Abstract

The ^{19}Ne(p,γ)^{20}Na reaction is the second step of a reaction chain which breaks out from the hot CNO cycle, following the ^{15}O(α,γ)^{19}Ne reaction at the onset of x-ray burst events. We investigate the spectrum of the lowest proton-unbound states in ^{20}Na in an effort to resolve contradictions in spin-parity assignments and extract reliable information about the thermal reaction rate. The proton-transfer reaction ^{19}Ne(d,n)^{20}Na is measured with a beam of the radioactive isotope ^{19}Ne at an energy around the Coulomb barrier and in inverse kinematics. We observe three proton resonances with the ^{19}Ne ground state, at 0.44, 0.66, and 0.82 MeV c.m. energies, which are assigned 3^{+}, 1^{+}, and (0^{+}), respectively. In addition, we identify two resonances with the first excited state in ^{19}Ne, one at 0.20 MeV and one, tentatively, at 0.54 MeV. These observations allow us for the first time to experimentally quantify the astrophysical reaction rate on an excited nuclear state. Our experiment shows an efficient path for thermal proton capture in ^{19}Ne(p,γ)^{20}Na, which proceeds through ground state and excited-state capture in almost equal parts and eliminates the possibility for this reaction to create a bottleneck in the breakout from the hot CNO cycle.

Direct Measurement of the Key Ec.m.=456 keV Resonance in the Astrophysical Wilkinson1, Lotay2, Lennarz3 et al. 2017Phys. Rev. Lett.

“…The reported resonance strength in Ref. [22] is in complete contradiction with earlier direct measurements [16][17][18], and the reported resonance energy is in disagreement with previous indirect studies [12,21]. Because of the significantly enhanced strength and considerable reduction in resonance energy, the rate of the 19 Neðp; γÞ 20 Na reaction was found to be a factor of ∼20 higher than previous evaluations [5,12].…”

“…−5 ðstatÞ þ3 −3 ðsystÞ meV. Both the presently observed resonance energy and resonance strength are in disagreement with the most recent indirect study of the 19 Neðp; γÞ 20 Na reaction [22]. However, the newly reported energy is in excellent agreement with that of Ref.…”

“…Under ONe novae and x-ray burst conditions, the 19 Neðp; γÞ 20 Na reaction is thought to be dominated by the contributions of a single low-energy resonance located ∼450 keV above the proton-emission threshold energy of 2190.1 (11) keV in 20 Na [9], corresponding to an excited state at E x ∼ 2650 keV. However, the strength of this resonance has remained the subject of intense debate for over two decades [10][11][12][13][14][15][16][17][18][19][20][21][22] and, in recent years, its energy has come into question as well [21,22]. Previous direct measurements of the 19 Neðp; γÞ 20 Na reaction have been performed using radioactive beams of 19 Ne [ [14][15][16][17][18].…”

“…Most recently, Belarge et al used a radioactive beam of 19 Ne to populate proton-unbound levels in 20 Na via the 19 Neðd; nÞ reaction, while resulting proton decays were detected using silicon strip detectors [22]. In that work, strong proton decay branches at 440 and 200 keV to the ground and first excited state of 19 Ne, respectively, were reported for the key resonance in the 19 Neðp; γÞ 20 Na reaction.…”

Studies of X-ray burst reactions with radioactive ion beams from RESOLUT

“…We studied the properties of unbound states in 20 Na using the 19 Ne(d,n) 20 Na reaction [28]. The experimental configuration and approach were similar to that in the study of unbound levels in 18 Ne.…”