( ( When ( fission occurs ) ) ( , ( ( ( ( neutrons , ) ( which ( are ( particles ( in ( ( the nucleus ) ( of ( the atom ) ) ) ) ) ) ) ) , ) ( ( are released ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NN fission)) (VP (VBZ occurs)))) (, ,) (NP (NP (NNS neutrons)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBP are) (ADJP (JJ particles) (PP (IN in) (NP (NP (DT the) (NN nucleus)) (PP (IN of) (NP (DT the) (NN atom))))))))) (, ,)) (VP (VBP are) (VP (VBN released))) (. .)))
When fission occurs, neutrons, which are particles in the nucleus of the atom, are released.
(ROOT (S (NP (DT A) (NN neutron)) (VP (VBZ collides) (PP (IN with) (NP (NP (DT an) (NN atom)) (PP (IN of) (NP (ADJP (JJ u-235) (PP (IN during) (NP (DT the) (JJ basic) (JJ nuclear) (NN fission)))) (NN process)))))) (. .)))
A neutron collides with an atom of u-235 during the basic nuclear fission process.