The irradiation of lithium and beryllium targets by a monoergic stream of protons reveals that the reaction

Question:

The irradiation of lithium and beryllium targets by a monoergic stream of protons reveals that the reaction Li7 (p, n) Be7 – 1.65MeV is initiated whereas the reaction Be9 (p, n) B9 – 1.85MeV does not take place. Find the possible values of kinetic energy of the protons.