why can you find different features at an oceanic-continental convergent zone than those found at a continental-continental convergent zone?

Continental plates are much thicker that Oceanic plates. At the convergent boundaries the continental plates are pushed upward and gain thickness. The rocks and geological layers are much older on continental plates than in the oceanic plates. The Continental plates are much less dense than the Oceanic plates.

No. an alpha particle is a pair of protons and a pair of neutrons, i.e. a helium