How to use this MCNP physics model?

[kg09889]

I am a student studying MCNP. I am designing a neutron inspector and planning to simulate it using MCNP. The design I am working on involves using a 14 MeV neutron generator to react neutrons with a target and then measure the gamma rays produced using an NaI detector. The energies I am particularly interested in are 2.2 MeV for H, 4.4 MeV for C, 6.1 MeV for O, and 10.8 MeV for N. Even though I have set the phys:n to the default values, it still shows that the physics model is disabled. How should I use the physics model in this situation I am designing?
Thank you for reading my message.

 

[Alex A]

Welcome to PhysicsForums!

The advanced physics models mostly relate to exotic particles, or things outside of table values. What you need should work with "mode n p". You probably won't need to turn on photonuclear physics, but if things definitely aren't working try that first on the phys p card.

 

[kg09889]

Thank you for welcoming me.
When I ran the simulation without using a physics model, I got a warning:
"no photon-production mt found in acegam. zaid = 7014.80c"
Additionally, the peak corresponding to the 10.8 MeV energy from nitrogen did not appear. At this point, I ran the simulation up to NPS = 748,377,421.
To resolve this issue, should I include a physics model in the phys:p card?
I appreciate your response and look forward to your reply.

 

[Alex A]

I'm not finished, but this is where I'm going....
The photon from neutron capture hitting the detector could be quite rare. With 10'000 energy bins they are ~1 kev wide, there is ~400kev of Gaussian broadening applied (this may be correct for an NaI detector) so that rare signal is blurred over hundreds of energy bins.

I think you won't see a clear peak.

I suggest you go default for all physics options. Reduce the number of energy bins to say 1000, remove GEB and run to see if the peak exists. Look out for the warning if that still exists.

 

[kg09889]

Thank you again for your response.
I will make the modifications right away and run the simulation.
I hope the results turn out well...
I will upload the modified file and the results after running the simulation.
4o

 

[kg09889]

I'm not finished, but this is where I'm going....
The photon from neutron capture hitting the detector could be quite rare. With 10'000 energy bins they are ~1 kev wide, there is ~400kev of Gaussian broadening applied (this may be correct for an NaI detector) so that rare signal is blurred over hundreds of energy bins.

I think you won't see a clear peak.

I suggest you go default for all physics options. Reduce the number of energy bins to say 1000, remove GEB and run to see if the peak exists. Look out for the warning if that still exists.

I ran the simulation as you suggested, but I still get the same warning:
"Warning. No photon-production MT found in acegam. ZAID = 7014.80c."
Also, I couldn't see the 10.8MeV peak for nitrogen... What should I do?

 

[Alex A]

Gamma production test
1 6 1 -1
2 0 1

*1 so 1

mode n p
imp:n 1 0
imp:p 1 0
sdef
c AN, NH4NO3, -1.720000
m6      1001 -0.050370 7014 -0.349978 8016 -0.599652 
f8:p 1
e8      0 1e-5 1000i 14 
nps 1e6

This is a very basic test and it essentially forces neutron capture for a clear result.
I see a peak in the output at 10.80 MeV (and others) so I take this as a success.

    1.0783E+01   4.90000E-04 0.0452
    1.0797E+01   1.68000E-04 0.0771
    1.0811E+01   1.13800E-03 0.0296
    1.0825E+01   8.40000E-05 0.1091
    1.0839E+01   1.43400E-03 0.0264
    1.0853E+01   7.00000E-05 0.1195
    1.0867E+01   1.77000E-04 0.0752

See what result you get. The warning is a concern.
Try specifying a different library. 80c is ENDF7.1 which is much newer than the ENDF6.8 that seems to be working here and you may already have that. ENDF8 is public and could be an option.
I will try some more tests here.

 

[kg09889]

Gamma production test
1 6 1 -1
2 0 1

*1 so 1

mode n p
imp:n 1 0
imp:p 1 0
sdef
c AN, NH4NO3, -1.720000
m6      1001 -0.050370 7014 -0.349978 8016 -0.599652
f8:p 1
e8      0 1e-5 1000i 14
nps 1e6

This is a very basic test and it essentially forces neutron capture for a clear result.
I see a peak in the output at 10.80 MeV (and others) so I take this as a success.

    1.0783E+01   4.90000E-04 0.0452
    1.0797E+01   1.68000E-04 0.0771
    1.0811E+01   1.13800E-03 0.0296
    1.0825E+01   8.40000E-05 0.1091
    1.0839E+01   1.43400E-03 0.0264
    1.0853E+01   7.00000E-05 0.1195
    1.0867E+01   1.77000E-04 0.0752

See what result you get. The warning is a concern.
Try specifying a different library. 80c is ENDF7.1 which is much newer than the ENDF6.8 that seems to be working here and you may already have that. ENDF8 is public and could be an option.
I will try some more tests here.

Thank you for your response.
I will try again.
I would appreciate it if you could let me know if you get any good results by running the code additionally.