( ( ( ( ( Plutonium ( emits ( ( a ( low level ) ) ( of ( gamma rays ) ) ) ) ) , ) but ) ( ( its radioactivity ) ( is ( mainly ( due ( to ( ( the emission ) ( of ( what ( we ( call ( alpha particles ) ) ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (NNP Plutonium)) (VP (VBZ emits) (NP (NP (DT a) (JJ low) (NN level)) (PP (IN of) (NP (NN gamma) (NNS rays)))))) (, ,) (CC but) (S (NP (PRP$ its) (NN radioactivity)) (VP (VBZ is) (ADJP (RB mainly) (JJ due) (PP (TO to) (NP (NP (DT the) (NN emission)) (PP (IN of) (SBAR (WHNP (WP what)) (S (NP (PRP we)) (VP (VBP call) (ADJP (NN alpha) (JJ particles))))))))))) (. .)))
Plutonium emits a low level of gamma rays, but its radioactivity is mainly due to the emission of what we call alpha particles.
(ROOT (S (PP (IN Of) (NP (NP (DT the) (CD three) (JJ basic) (NNS types)) (PP (IN of) (NP (JJ radioactive) (NNS emissions))))) (, ,) (NP (DT the) (NN gamma) (NN particle)) (VP (VBZ is) (NP (DT the) (JJS most) (NN penetrating))) (. .)))