neutron fluence study

Hi Everyone,

I did a simulation involving a nozzle and a water phantom. The beam is
protons of 159 MeV kinetic energy. The beam passes through the nozzle
on to the phantom. I was looking at the neutron fluence at a surface
between the nozzle and the phantom. The protons coming out of the
nozzle are roughly 70 MeV.

In my results, I am seen lots of low energy neutrons(less 20 MeV) but
not really much high energy protons (~ 70 MeV). I have attached a
lin-log plot of (integral binned fluence)*energy versus energy. I am
guessing that I should be seen a peak between 10 Mev and 100 MeV.

I have attached the inp file and the output unit 81 in which I have
used USRBDX to calculate fluence. The plot is produced using the same
output.

I would appreciate any help. Sunil if u could also kindly take a look
and see I have made any mistake that would be great.

Thank you !!

Sharmalee Randeniya
Rice University