First strength measurements of low-energy resonances in the $^{45}$Sc($p,γ$)$^{46}$Ti reaction and its astrophysical implications
The $^{45}$Sc($p,γ$)$^{46}$Ti reaction plays an important role in both hydrostatic and explosive nucleosynthesis. During hydrostatic oxygen and silicon burning in massive stars, including dynamic processes such as convective carbon-oxygen (C-O) shell mergers, it acts as a bottleneck that regulates the reaction flow in the Sc-Ti mass region. In oxygen-neon (ONe) novae, the ejecta indicate the production of elements up to the Fe group, as observed in V1974 Cygni, and the $^{45}$Sc($p,γ$)$^{46}$Ti reaction links nuclei above Ca to the Fe region. In core-collapse supernovae (CCSNe), it influences the production of the radioactive isotope $^{47}$Sc. At present, the thermonuclear reaction rate is based on statistical model calculations. In this work, we report on measurements of the $^{45}$Sc($p,γ$)$^{46}$Ti reaction performed using the 5~MV accelerator at the Nuclear Science Laboratory, University of Notre Dame, over a laboratory proton energy range of 526--1275~keV. We present the first direct measurements of the resonance strengths for six resonances at $E^{\rm lab}_{\rm R} = 917.4$, 1026.0, 1031.1, 1049.7, 1059.4 and 1257.5~keV, together with integrated resonance strengths at $E^{\rm lab} = 555$, 630, 700, 761 and 871~keV. For resonance energies below the lowest directly measured energy, available transfer-reaction data were used to estimate the resonance strengths. An updated thermonuclear reaction rate is derived, and its astrophysical implications are discussed.