Atomic Particles and Radiation

The main particles important in nuclear reactions are listed here. These can be released from the nucleus as radiation.

Neutron radiation is indirectly ionizing radiation. They don't directly ionize an atom when they are absorbed but, as a result of neutron collision, atoms frequently emit gamma radiation and that gamma radiation caused ionizion. Neutron radiation is more penetrating than alpha radiation or beta radiation. Neutron radiation causes materials to degrade through crystal dislocations, swelling, and embrittlement of metals.

Alpha radiation consists of helium nuclei. Because of their high mass relative to other particle radiation, alpha particles interact strongly with matter and are typically absorbed by a few centimeters of air. External to the body, alpha radiation is not harmful to humans because it is absorbed by the layer of dead skin cells.

Beta radiation consists of either electrons or positrons. This is ionizing radiation. When these two particals annihilate they form a gamma ray.
Non-particle radiation is released as gamma radiation. These rays have the shortest wavelength and highest energy in the electromagnetic spectrum and cause serious damage when they are absorbed by cells.



particle chargeweight (amu)
proton +11.00728
neutron 01.00866
electron -10.0009
positron +10.0009
alpha (He2+) +24.00153




Binding energy

Nuclear binding energy is the key to nuclear power. It is the difference in mass (converted to energy) of a nucleus from the sum of its masses of the protons and neutrons.

Consider the alpha partical with a total mass of 4.00153 amu. The sum of 2 protons and 2 neutrons is 4.03188 so 0.03035 amu was converted to energy when these particles came together.


1 amu = 1.66054 x 10-27 kg = 931.494 MeV/c2

1 MeV = 1.60 x 10-13 J

Energy released per particle= (0.03035)(931.494)/4 = 7.1 MeV or 1.13 x 10-12 J

The lighter nuclei release energy when they are formed from neutrons and protons but nuclei heavier than iron absorb energy. These heavier elements release energy when they are broken down into smaller particles.



Professor Shapley, University of Illinois, 2011