  We discuss the isolation of prompt photons in hadronic collisions by means of
narrow isolation cones and the QCD computation of the corresponding cross
sections. We reconsider the occurence of large perturbative terms with
logarithmic dependence on the cone size and their impact on the fragmentation
scale dependence. We cure the apparent perturbative violation of unitarity for
small cone sizes, which had been noticed earlier in next-to-leading-order (NLO)
calculations, by resumming the leading logarithmic dependence on the cone size.
We discuss possible implications regarding the implementation of some hollow
cone variants of the cone criterion, which simulate the experimental difficulty
to impose isolation inside the region filled by the electromagnetic shower that
develops in the calorimeter.
