Can a 1cm-thick concrete wall absorb so many photons and photoneutrons?

Dear all,

I have simulated an accelerator,the source of which is photon with
enengy=18MeV.Therefore,photoneutrons are produced.In my work,the flux of
these photons and photoneutrons can be detected before they cross a
1cm-thick concrete wall(the REGION is INRCC,see details in the input
file),while none can be detected in this 1cm-thick concrete wall(the
REGION is OUTRCC,also see details in the input file).But I don't think
this wall can absorb these particles so much,or just there are something
wrong with my work?
I appreciate all help from you.

Yours,
Danny