Subject	isotope
Predicate	be useful as
Object	tracers
Modality	Modality Occurrences some[subj/radioactive] 1
Polarity	POSITIVE
Plausibility	0.0006
Neighborhood Sigma	0.0006
Local Sigma	0.0200
Example Sentences	Sentence Occurrences Source radioactive isotopes are useful as tracers 1 Google Autocomplete