  This paper presents the results of neutron flux measurements at two
irradiation facilities of the TRIGA Mark II reactor at ENEA Casaccia Research
Center, Italy. The goal of these measurements is to provide a complete
characterization of neutron irradiation facilities for accurate and precise
dose evaluation in radiation damage tests and, more generally, for all
applications that need a good knowledge of neutron flux in terms of intensity,
energy spectrum and spatial distribution. The neutron activation technique is
used to measure the activation rates of several reactions, chosen so to cover
the whole energy range of neutron flux spectrum. A multi-group neutron flux
measurement is obtained through an unfolding algorithm based on a Bayesian
statistical model. The obtained results prove that this experimental method
allows to measure the total neutron flux within 2% statistical uncertainty, and
to get at the same time a good description of its energy spectrum and spatial
distribution.
