  We have computed correlation functions for nucleons and extracted the masses
for positive- and negative-parities. Use of group theory plays an important
role in obtaining sources that have good overlap to higher spin states and
minimum contamination from unwanted states. In the simulation three distinct
sources and corresponding sinks that transform according to the $G_1$
irreducible representations are tested and used to form matrices of correlation
functions. Diagonalizations give us clear mass splittings between low-lying
states and excited states for both parities.
