No, particles don't change their nature depending on their speed. Furthermore, you realize that speed is always relative to something (especially in open space, when there's no conventional reference system as it happens in day-to-day talking on Earth)? So, would you say that a particle can be a neutrino w.r.t. a galaxy and an alpha particle w.r.t. another remote galaxy?

Or that it can be an electron w.r.t. a star and a beta particle w.r.t. another? ;-)

> we have a technical term for an ionized helium nucleus travelling at roughly 2% of the speed of light—6000km/sec—we call it an alpha particle.

Technically, an helium nucleus is an alpha particle, independent of its speed.

Edit: an helium nucleus with two neutrons is an alpha particle. An helium nucleus can exist with just one neutron.