Gamow-Teller strengths of the inverse beta transition Yb-176 -> Lu-176 for spectroscopy of proton-proton and other sub-MeV solar neutrinos

Discrete Gamow-Teller (GT) transitions Yb-176 --> Lu-176 at low excitation energies have been measured via the (He-3, t) reaction at 450 MeV and at 0 degrees. For Yb-176, two low-lying states are observed, setting low thresholds Q(nu) = 301 and 445 keV for neutrino (nu) capture. Capture rates estimated from the measured GT strengths, the simple two-state excitation structure, and the low Q(nu) in Yb-Lu indicate that Yb-based nu detectors are well suited for a direct measurement of the sub-MeV solar electron-neutrino (nu (e)) spectrum including pp neutrinos.