During the beta decay electrons are emitted, while the nucleus transforms itself to another nucleus. Becquerel discovered that the beta rays are negatively charged, and their charge to mass ratio is identical to that of the electrons. This way he identified the beta-particles as high velocity electrons. The negative beta-decay of a nucleus can be imagined as if a neutron of the nucleus would transform to a proton, while an electron and an antineutrino would be emitted. Therefore the atomic number of the nucleus increases by one, and the mass-number remains constant during the beta-decay. The range of the beta-rays is between the range of the alfa-particles and that of the gamma-rays. The beta-particles penetrate only a few millimetres into solid materials and metals, therefore it is relatively easy to shield them. | 
