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 air without any interaction. Neutron radiation is highly penetrating.
- In order to absorb them, neutrons must be first slowed down. This point can be fulfilled only by material containing light nuclei (e.g. hydrogen nuclei).
- An absorption of neutron (one would say shielding) causes initiation of certain nuclear reaction (e.g. radiative capture or even fission), which is accompanied by a number of 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).
- Mean lifetime of a free neutron is 882 seconds (i.e. half-life is 611 seconds ).
- A natural neutron background of free neutrons exists everywhere on Earth and it is caused by muons produced in the atmosphere, where high energy cosmic rays collide with particles of Earth’s atmosphere.