These figures show also a marked depression in the flux intensities
at neutrons energy around 3.5 MeV which means that the attenuation factor at this certain energy is high. This can be attributed
to the initial depression in the leakage fast neutron spectrum
emitted directly from the reactor core around this energy range,
due to the presence of 7 cm water reflector and 9.5 cm thick lead
filter placed inside the reactor channel and before the beam
collimator. In our experiment fast neutron spectra have two maxima
at energy ranges from 1.6 to 3 MeV and from 4 to 6 MeV with a
minimum value of the effective removal cross section. At the range
of energy from 6 to 11 MeV the effective removal cross section may
be considered constant.