system
Given the following post, respond as if you're commenting on Reddit:
human
Does nuclear fusion produce radiation like nuclear fission?
gpt
There are two types of radioactivity that can come from fission/fusion.  The first is *prompt radiation* - this is particles given off instantaneously during the fission or fusion reaction.  For instance, fission of a U-235 nucleus leads to the emission of 2-3 neutrons, gamma rays, and two energetic fission products (which are just two smaller nuclei).  Fusion of deuterium and tritium (H-2 and H-3) gives off a neutron.  So both of these reactions lead to prompt radiation.  Prompt radiation is mitigated by shielding the reactor core.

The other component is due to the instability of the products of the reactions.  Due to some characteristics of the stability of atoms, the products of fission are almost always radioactive.  In other words, when the uranium nucleus splits into two pieces during fission, these pieces go on to decay later in other ways.  This is what causes spent nuclear fuel to be radioactive.

There are several different fusion reactions that could be theoretically used to produce power, but most of these don't lead to the creation of radioactive products.  For instance, in D-T fusion, the product is helium-4 (which is quite stable).  There are secondary ways in which the neutrons emitted by fusion can lead to the activation of materials within the reactor, but in general there is very little radioactivity in the products of nuclear fusion.