It decreases far more rapidly with distance than an electrostatic force. The strong force exerted by one nucleon on another nucleon falls to zero within the nucleus. The strong force between two adjacent nucleons, therefore, does not contribute anything to the binding of the nucleons on the other side of the nucleus. Fission is a possible consequence of this instability only in U-235 and other fissile material.
Alpha particles are very massive in comparison with the other types of radioactive particles below.
Within a few centimetres of travelling through the air the alpha particle will collide with the air molecules, lose kinetic energy in the collisions, pick up electrons and become a neutral stable helium atom. Alpha particles cannot penetrate skin, although enough exposure will cause a severe skin burn. The particle also emits gamma radiation which sheds excess energy leaving a more stable isotope. Beta particles arise from the decay of a neutron. It did not exist before decay occurred.