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Creators/Authors contains: "deBoer, R J"

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  1. Here we report on the direct measurement of the resonance strengths of the E R lab = 647 keV and 1842 keV resonances in the Ca 40 ( p , γ ) Sc 41 reaction. At novae temperatures, 0.2 < T 9 < 0.7 , the Ca 40 ( p , γ ) Sc 41 reaction is governed by the low energy resonance at E R lab = 647 keV , whereas the E R lab = 1842 keV resonance serves as a normalization standard for nuclear reaction experiments within the astrophysically relevant energy range. For the E R lab = 647 keV resonance, we obtain a resonance strength ω γ = ( 2.51 ± 0 . 09 stat ± 0 . 22 syst ) meV , with an uncertainty a factor of 2.5 smaller than the previous direct measurement value. For the E R lab = 1842 keV resonance, we obtain a resonance strength ω γ = ( 0.148 ± 0 . 006 stat ± 0 . 013 syst ) eV , which is consistent with previous studies but deviates by 2 σ from the most recent measurement. Our results suggest Ca 40 to be a strong waiting point in the nucleosynthesis path of oxygen-neon (ONe) novae. Published by the American Physical Society2025 
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    Free, publicly-accessible full text available February 1, 2026
  2. : The C 12 ( α , γ ) O 16 reaction, determining the survival of carbon in red giants, is of interest for nuclear reaction theory and nuclear astrophysics. A specific feature of the O 16 nuclear structure is the presence of two subthreshold bound states, (6.92 MeV, 2 + ) and (7.12 MeV, 1 ), that dominate the behavior of the low-energy S factor. The strength of these subthreshold states is determined by their asymptotic normalization coefficients (ANCs), which need to be known with high accuracy. : The objective of this research is to examine how the subthreshold and ground-state ANCs impact the low-energy S factor, especially at the key astrophysical energy of 300 keV . The S factors are calculated within the framework of the R -matrix method using the code. Our total S factor takes into account the E 1 and E 2 transitions to the ground state of O 16 including the interference of the subthreshold and higher resonances, which also interfere with the corresponding direct captures, and cascade radiative captures to the ground state of O 16 through four subthreshold states: 0 2 + , 3 , 2 + , and 1 . To evaluate the impact of subthreshold ANCs on the low-energy S factor, we employ two sets of the ANCs. The first selection, which offers higher ANC values, is attained through the extrapolation process [Blokhintsev , ]. The set with low ANC values was employed by deBoer []. A detailed comparison of the S factors at the most effective astrophysical energy of 300 keV is provided, along with an investigation into how the ground-state ANC affects this S factor. : The contribution to the total E 1 and E 2 S factors from the corresponding subthreshold resonances at 300 keV are ( 71 74 ) % and ( 102 103 ) % , respectively. The correlation of the uncertainties of the subthreshold ANCs with the E 1 and E 2 S ( 300 keV ) factors is found. The E 1 transition of the subthreshold resonance 1 does not depend on the ground-state ANC but interferes constructively with a broad ( 9.585 MeV ; 1 ) resonance giving (for the present subthreshold ANC) an additional 26 % contribution to the total E 1 S ( 300 keV ) factor. Interference of the E 2 transition through the subthreshold resonance 2 + with direct capture is almost negligible for small ground-state ANC of 58 fm 1 / 2 . However, its interference with direct capture for higher ground-state ANC of 337 fm 1 / 2 is significant and destructive, contributing 27 % . The low-energy S E 2 ( 300 keV ) factor experiences a smaller increase when both subthfreshold and the ground-state ANCs rise together due to their anticorrelation, compared to when only the subthreshold ANCs increase. Published by the American Physical Society2024 
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    Free, publicly-accessible full text available November 1, 2025
  3. Free, publicly-accessible full text available November 1, 2025
  4. Abstract The interplay and correlation between the $$^{22}$$ 22 Ne $$(\alpha ,\gamma )^{26}$$ ( α , γ ) 26 Mg and the competing $$^{22}$$ 22 Ne $$(\alpha ,n)^{25}$$ ( α , n ) 25 Mg reaction plays an important role for the interpretation of the $$^{22}$$ 22 Ne $$(\alpha ,n)^{25}$$ ( α , n ) 25 Mg reaction as a neutron source in the s - and n -processes. This paper provides a summary and new data on the $$\alpha $$ α -cluster and single-particle structure of the compound nucleus $$^{26}$$ 26 Mg and the impact on the reaction rate of these two competing processes in stellar helium burning environments. 
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  5. Abstract The20Ne(α,p)23Na reaction rate is important in determining the final abundances of various nuclei produced in type Ia supernovae. Previously, the ground state cross section was calculated from time reversal reaction experiments using detailed balance. The reaction rates extracted from these studies do not consider contributions from the population of excited states, and therefore, are only estimates. A resonance scan, populating both the ground and first excited states, was performed for the20Ne(α,p)23Na reaction, measuring between 2.9 and 5 MeV center of mass energies at the Nuclear Science Lab at the University of Notre Dame. Data analysis is underway and preliminary results show substantial contribution from the excited state reaction. 
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