All electromagnetic radiation with a wavelength below 0.1 ≈ (Ângstrˆm) is called gamma radiation. Gamma radiation is produced in radioactive decay and nuclear reactions.
Neutron stars are powerful gamma radiators. The penetration power of gamma particle resulting from radioactive decay is strong; it can penetrate very deep into a substance (for example, through a 10 cm thick aluminium sheet) before being absorbed.
Gamma rays cannot penetrate the Earth's atmosphere, so gamma ray observations have to be conducted on satellites.
One nm (nanometre) equals 10 ≈ (Ângstrˆm) = 10-10 metres.
