First strength measurements of low-energy resonances in the 45 Sc(p, gamma) 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 lab R = 917.4, 1026.0, 1031.1, 1049.7, 1059.4 and 1257.5 keV, together with integrated resonance strengths at E 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.