USRBIN neutron fluence

Dear Fluka users,
           I give in attachmet my input file; the problem is the
evaluation of neutron fluence on a concrete bunker shielding a UC2
target. Near the point of coordinates (400, 500, 370) a small portion
of the concrete shielding is created at a mesoscale: aggregates and
paste. It is a parallelepiped of dimension X: 3,5cm Y: 3,5cm Z: 7cm.
The USRBIN cards investigate this volume with a resolution 0,2mm, in
order to catch the thin zone around aggregates, which is 0,3mm order
of thickness.
I obtained the plots I give in attachment; I expected, however, to
catch a different behavior of the materials corresponding to the
aggregates and the thin area around them, because of different
chemical composition and density.

Do I have to better the statistics to have results more acceptable?
Thank you
kind regards,

Beatrice

**************************************************
Ing. Beatrice Pomaro

Universita' degli Studi di Padova
Dipartimento di Costruzioni e Trasporti
Via F. Marzolo, 9 - 35131 Padova (Italy)
tel.: +39 049 8275605
e-mail: pomaro_at_dic.unipd.it