Doubts about the output about the USRBDX card

Dear experts,
I hope this email finds you well.

I used USRBDX card to score the fluence of the proton, neutron and photon in particular position when 70,80,90,100 MeV proton beam hitting on Al and solid water target in turn.

The results of neutrons and photons are fine. But when I looked into the output of proton, there is no output when the energies of the proton beam are 70 and 80, while for the 90 and 100 MeV beams, there is output. As shown below


And I also read the sum.lis file, for 70 MeV proton beam, there is no response (Tot. resp.) at all as shown below

But for 100 MeV proton beam, there is response.
截屏2024-09-05 14.53.12
So I’m wondering why this happens because the difference between them is only the beam energy.
Another question is about the error of the Tot. resp. in the last picture, it is 49%. Does it means I need to increase the primary number?
Here are the input files for 70 and 100 MeV proton beam.
zhuozhou_70.inp (2.5 KB)

zhuozhou_100.inp (2.5 KB)

Best regards,
zhen