the phenomenon of radioactivity was first discivered by a scientist called henri becquerel and was later confirm by another scientist marie curie and her husband perry curie. radioactivity is the spontaneous decay or disintergration of the nuclie of a atom of an element. radioactivity radiation is of three types which are 1. alpha particle 2. beta particle 3. gamma ray. apha particles are positively charged particles with high ionization energy, low pnetrating power and can be stop by a tin sheet of paper. beta particles are negatively charged particles with lower ionization energy and higher penetrating power which can be stop by a tin sheet of aluminium. Gamma rays are also known as electromagnetic radiation. they have the lowest ionization energy but the highest penetrating power and can be stopped by a tin sheet of lead.... a radioactive element is a substance or element which gives out radiation. half life is the time taken for half of the nucleus of an atom to decay in half.