The third and fourth default spectra considered herein are provided by the Bayesian WINBUGS software (Spiegelhalter et al.,2003). A parametric model of the neutron spectrum considered in the cited software was a linear superposition of three components defined as follow: a Maxwellian for the thermal component; a 1/E for the epithermal part and a Watt (labeled spectrum-III) or evaporation (labeled spectrum-IV) for the fast component.