The nucleus — Describe

Describe the processes of nuclear fission and nuclear fusion, including how mass and energy change.

Nuclear fission is the splitting of a large, unstable nucleus into two smaller nuclei (plus usually some neutrons), often triggered by the nucleus absorbing a neutron, e.g.: ^235_92 U + ^1_0 n -> ^141_56 Ba + ^92_36 Kr + 3 ^1_0 n. Nuclear fusion is the joining of two small, light nuclei to form one larger nucleus, e.g.: ^2_1 H + ^3_1 H -> ^4_2 He + ^1_0 n. In both fission and fusion, the total mass of the products is slightly less than the total mass of the original nuclei (mass is 'lost'); this lost mass is converted into a large amount of energy that is released.