The antiparticle of an alpha particle is called an antialpha particle. An alpha particle is composed of two protons and two neutrons, which is essentially a helium-4 nucleus. The antialpha particle would have the same mass as an alpha particle but would consist of two antiprotons and two antineutrons.
It's important to note that while particles and their antiparticles have opposite electric charges, they have the same mass. In the case of the alpha particle and antialpha particle, they would both have a mass of approximately 4 atomic mass units (AMU). The primary difference between the two is the presence of antiparticles instead of particles, resulting in opposite charge properties.