Key characteristics of neutron radiation are summarized in few following points:
- Neutrons are neutral particles – no net electric charge.
- Neutrons cannot directly cause ionization. Neutrons ionize matter only indirectly.
- Neutrons scatter with heavy nuclei very elastically. Heavy nuclei very hard slow down a neutron, let alone absorb a fast neutron.
- Neutrons can travel hundreds of feet in the air without any interaction. Neutron radiation is highly penetrating.
- Neutrons must be first slowed down to absorb them. This point can be fulfilled only by a material containing light nuclei (e.g.,, hydrogen nuclei).
- An absorption of neutron (one would say shielding) causes the initiation of certain nuclear reactions (e.g.,, radiative capture or even fission), accompanied by many other types of radiation. In short, neutrons make matter radioactive. Therefore with neutrons, we have to shield also the other types of radiation.
- Free neutrons (outside a nucleus) are unstable and decay via beta decay. The decay of the neutron involves the weak interaction and is associated with a quark transformation (a down quark is converted to an up quark).
- The mean lifetime of a free neutron is 882 seconds (i.e., the half-life is 611 seconds ).
- A natural neutron background of free neutrons exists everywhere on Earth. It is caused by muons produced in the atmosphere, where high-energy cosmic rays collide with particles of Earth’s atmosphere.