Fluorine-18 decays into oxygen-18 with the release of a positron (β+\beta^+β+) and an electron neutrino (νe\nu_eνe).
State the change of quark character in β+\beta^+β+ decay.
Figure 1 shows the distribution of kinetic energies of β+\beta^+β+ particles from the decay of fluorine-18. 
Explain how Figure 1 supports the existence of the neutrino.
The existence of the neutrino is also confirmed by interactions with nuclei. In one such interaction: νe+n→e−+Y\nu_e + \text{n} \rightarrow \text{e}^- + \text{Y}νe+n→e−+Y. Identify particle Y.
The positron released in the decay is annihilated when it encounters an electron in surrounding matter. A pair of gamma photons of equal energy is then produced. During an experiment, three gamma photons are detected: G1 with energy 4.8×10−14 J4.8 \times 10^{-14}\text{ J}4.8×10−14 J, G2 with energy 7.2×10−14 J7.2 \times 10^{-14}\text{ J}7.2×10−14 J, and G3 with energy 9.5×10−14 J9.5 \times 10^{-14}\text{ J}9.5×10−14 J. Deduce which of the three gamma photons could have been produced by this positron annihilation.