On the relative ages of galactic globular clusters. A new observable, a semi-empirical calibration and problems with the theoretical isochrones
Journal article published in 1998 by
R. Buonanno,
Ce E. Corsi,
L. Pulone 
,
F. Fusi Pecci,
M. Bellazzini
,
F. Fusi Pecci,
M. Bellazzini
