Radio morphology data have been collected for a sample of radio galaxies from the Revised 3rd Cambridge ( 3CR ) Catalog in the redshift range 0.15 < z < 0.65 .
Radio structure parameters including largest physical size , projected bending angle ( \beta ) , lobe length asymmetry ( Q ) and hot spot placement ( Fanaroff-Riley ratio ) have been measured from the highest quality radio maps available .
Combined with similar data for quasars in the same redshift range , these morphology data are used in conjunction with a quantification of the richness of the cluster environment around these objects ( the amplitude of the galaxy-galaxy spatial covariance function , B _ { gg } ) to search for indirect evidence of a dense intracluster medium ( ICM ) .
This is accomplished by searching for confinement and distortions of the radio structure that are correlated with B _ { gg } .

Correlations between physical size and hot spot placement with B _ { gg } show evidence for an ICM only at z \leq 0.4 , but there are no correlations at z \geq 0.4 , suggesting an epoch of z \sim 0.4 for the formation of the ICM in these Abell richness class 0-1 , FR2-selected clusters .
X-ray selected clusters at comparable redshifts , which contain FR1 type sources exclusively , are demonstrably richer than the FR2-selected clusters found in this study .
The majority of the radio sources with high B _ { gg } values at z \leq 0.4 can be described as “ fat doubles ” or intermediate FR2/FR1s .
The lack of correlation between B _ { gg } and \beta or B _ { gg } and Q suggests that these types of radio source distortion are caused by something other than interaction with a dense ICM .
Therefore , a large \beta can not be used as an unambiguous indicator of a rich cluster around powerful radio sources .
These results support the hypothesis made in Paper 1 that cluster quasars fade to become FR2s , then FR1s , on a timescale of 0.9 Gyrs ( for H _ { 0 } = 50 km s ^ { -1 } Mpc ^ { -1 } ) .