What are massive positively charged particles emitted by some radioactive elements?

Answer 1

Alpha Particles

Named alpha because they were the first to be discovered, these particles are made up of 2 protons and 2 neutrons - the helium nucleus. Often, large atoms decay by releasing an alpha particle. These particles are relatively large and positively charged, and therefore do not penetrate through matter very well. A thin piece of paper can stop almost any alpha particle. However, the particles cause extreme damage of materials that they stop in by moving atoms as they slow down. Paper under continuous alpha irradiation would degrade.

Beta Particles

Beta particles are energetic electrons that are emitted from the nucleus of an atom. They are made when a neutron decays to a proton. Since neutrons are neutral particles and protons are positive, a negatively charged electron has to be emitted.

Gamma Rays

Gamma rays are photons that are emitted from the nucleus. Often an atom in an excited state will de-excite by emitting a gamma ray. Gamma rays are similar to light waves and x rays, except they are usually much higher frequency and consequently, more energetic. This radiation has no charge, and can penetrate most matter easily, requiring a lead brick for shielding.

Answer 2

Alpha Particle.