Glue content and mixing angle of the eta - eta' system. The effect of   the isoscalar 0- continuum
  Masses and topological charges of the eta and eta' mesons are expressed in terms of the singlet-octet mixing angle theta. Contributions of the pseudoscalar 0- continuum are evaluated in a model independant way. Applications to the decay eta --> 3pi and to the radiative decay of vector mesons involving eta and eta' are considered. Agreement with experiment is in general good and the results quite stable for -30.5 <= theta <= -18.5 
N. F. Nasrallah