We have measured the radiative decays phi --> etagamma, phi --> eta'gamma selecting pi(+)pi(-)gammagammagamma final state in a sample of similar to 5 x 10(7) phi-mesons produced at the Frascati phi-factory DAPhiNE. We obtain Gamma(phi --> eta'gamma)/Gamma(phi --> etagamma) = (4.70 +/- 0.47 +/- 0.31) x 10(-3). From this result we derive new accurate values for the branching ratio BR(phi --> eta'gamma) = (6.10 +/- 0.61 +/- 0.43) x 10(-5) and the mixing angle of pseudoscalar mesons in the flavour basis phi(P) = (41.8(-1.6)(+1.9))degrees. (C) 2002 Elsevier Science B.V. All rights reserved. RI Gauzzi, Paolo/D-2615-2009; valente, paolo/A-6640-2010; ANTONELLI, ANTONELLA/C-6238-2011; Di Domenico, Antonio/G-6301-2011; De Lucia, Erika/D-2250-2011; Passalacqua, Luca/F-5127-2011; branchini, paolo/A-4857-2011; Murtas, Fabrizio/B-5729-2012
