Improved study of the14O(?, p)17F reaction at stellar energies

Abstract

We have performed a study of the 140(a,p)17F reaction at stellar energies within the framework of the Generator Coordinate Method (GCM). Our calculation improves a previous study by enlargement of the model space.The mechanism of break-out from the hot CNO-cyele in novae and x-ray bursts, which subsequently leads to nucleosynthesis of elements up to the S~Ni region by rapid proton capture, is still an important problem in nuclear astrophysics [1]. Besides the 1sO (a,7) lONe re-140(2+) and p + 17F product states. The internal degrees of freedom of the a-cluster, the 140 ground state (140(0+)), the first excited 2 + state in 140 (140(2+)) and the ~7F ground state were all described by harmonic oscillator shell model states in jj-coupling. The relative wave functions between the various fragmentations have been determined from the coupled RGM-equations following along the lines of Res 3. The oscillator parameters for the cluster basis wave functions as weII as parameters in the nucleon-nucleon interaction were adjusted to reproduce the correct energy spUttkag between the proton channel and the a-channel as well as the energy positions of the two lSNe states close to the a-threshold (the 2 + state and the 3~ state at -24 keV). Our calculated lSNe level spectrum is shown in Fig. 1. Fig. 2 in terms of the astrophysical S-factor. Up to E < 300 keV, it is dominated by the tail of the 2 + resonance, exceeding the contribution arising from the high-energy wing of the 3~-bound state by about one order of magnitude. In the energy regime E g 0.3 -2.5 MeV the cross section is given by the contribution from the J = 1 partial wave which can be separated into a non-resonant direct transfer part and its interference with the 1-resonance at E = 3.6 MeV (not present in the previous study [3]). We find a constructive interference below the resonance energy. The 4 + resonance at 2.79 MeV yields an important contribution to the calculated S-factor at E = 2.7-3 MeV. There are experimentally known resonances in the a + 140 channel at E _> 1 The calculated transfer cross section is shown inMeV which are not present in our GCM study (see Fig. 1).The 140(a,p)l~F reaction rate can be derived at following the procedure discussed in Ref. 3. Comparing the present results to those of Ref. 3 we find the following conclusions which are important for the 140(a,p)l~F rate at astrophysical energies: i) The resonant contribution arising from the 2+ state is smaller in the present calculation by about a factor of 3.6. This can be traced back to a smaller a-width of this state, while its prcton-width Fp = ~ keV remains uneffected hy the inclusion of an a + 140(2+) configuration (experimental value P~ = 25 =k t0 keV). We now find F~ = 1.3 9 10 -~2 MeV which is in close agreement with the value deduced from the reduced a-width of its analogue-state in lsO (F~ = 1.1.5 9 10 -62 MeV, Ref.2). The reduction in the calculated a-width is caused by a stronger configuration mixing between the 2 + state with the 2 + state at -1.49MeV, whose energy splitting (and po...

Invariant-mass spectroscopy of Ne18, O16 , and CCharity1, Brown2, Elson3 et al. 2019Phys. Rev. C222420View full textAdd to dashboardCite

“…In order to reproduce the measured intrinsic widths of these states, Hahn et al [9] subsequently argued that the higher-energy state is J π =3 − 1 , while the lower-energy state is J π =2 + 3 . This is in contrast to Wiescher et al [41] and Funck et al [42,43] who put these states in reverse order in their 14 O(α,p) 17 F rate calculations for astrophysics.…”

Explosive Hydrogen Burning

“…In contrast, the latter calculation (59) accounts for the measured width of this state explicitly and finds a large effect. In fu rther studies with an enlarged model space (61), this enhancement is reduced by a factor of 3.6, but the high temperature reaction rate is essentially unchanged from that of Funck & Langanke (59).…”

“…At temperatures where the (u,p) reaction predominates, the calculations agree to within a factor of 2. At high temperatures, the rate calculated by Wiescher et al (56) includes a statistical-model estimate of the effects of high-energy resonances, a contribution to the cross section that was not examined by Funck & Langanke (59,61). Because the high-temperature reaction rate from Wiescher et al (56) may be the most reliable, it is used in the network calculations pre sented in Section 5.…”

Invariant-mass spectroscopy of $^{18}$Ne, $^{16}$O, and $^{10}$C excited states formed in neutron transfer reactions

“…In order to reproduce the measured intrinsic widths of these states, Hahn et al [9] subsequently argued that the higher-energy state is J π =3 − 1 , while the lower-energy state is J π =2 + 3 . This is in contrast to Wiescher et al [38] and Funck et al [39,40] who put these states in reverse order in their 14 O(α,p) 17 F rate calculations for astrophysics.…”

“…The neutron knockout cross section to the ground state of 8 C [3] is 3.8(3) mb, while the proton knockout cross sections to the first, second, and isobaric analog states of 8 B [5] are 12.0(20), 42.0(40), and 1.2(1) mb, respectively. Finally the inelastic scattering cross sections to first, second, and forth excited states of 9 C [7] are 3.74(20), 5.91 (40), and 4.12(40) mb, respectively.…”