# Doubt regarding beam intensity (p/s) in IRRPROFI card

Dear expert,

I have a doubt regarding the p/s value in IRRPROFI card. Does beam intensity refer to the one experienced by target or the one released from the source ?
In case of neutron activation, generally neutron fields are given in terms of fluence (neutrons per cm2 per s). If source dimension is large as compared to the target, some source particle will miss the target. For example, in the attached figure, what should be p/s value? Should I multiply the fluence value by A or B (ref. from the figure) to incorporate in IRRPROFI card?

Regards,
Riya

The beam intensity shall be the one of the beam you simulate.
Since you simulate a source of area A, where some particles miss the target and so reduce the resulting dose/fluence per beam particle in the target, you have to multiply by A.
The results in the target need to be the same as the ones from the simulation of a source of area B, where values per beam particle are higher and compensated by a lower normalization factor.

Dear @ceruttif

I am sorry that I could not understand the solution. Let me explain the situation with an example that I carried out.

The fluence considered = 1E+14.

Case 1: I considered a planar source of dimension 40 cm x 80 cm, area = 3200 cm^2, p/s = 3200 *1E+14. With this criteria, the activity of Mo in the output is 8.242E+13 Bq.

2nd case, planar source dimension is 40 cm x 40 cm, area = 1600 cm^2, p/s = 1600*1E+14. With this criteria, the activity of Mo in the output is 4.1268E+13 Bq.

In both the cases, all parameters are same except source dimension. I kept fluence value constant in both the cases, so I multiplied the source area accordingly into p/s term.

I have included the input files if needed. Am I missing anything about the unit of output of RESNUCLE? The manual said the unit is in Bq. Do I have to include any normalization in the output ?

source_newgen_plane.f (19.0 KB)
Mo1.inp (2.0 KB)
Mo1.flair (2.4 KB)

Regards,
Riya

I suggest you repeat the same exercise assigning VACUUM to your VOID region, such as to verify that the resulting activity is identical (and not different by a factor 2) in the two cases, as expected. Thermal neutron scattering in your huge air region can dramatically change the picture.

Dear @ceruttif ,

I repeated the exercise with vacuum, but still got a difference by a factor of 2.

Here are the necessary files.

Mo1.inp (2.2 KB)
Mo1.flair (2.5 KB)
Mo1_22_tab.lis (52.6 KB)
source_newgen_plane.f (19.0 KB)
Mo1_21_tab.lis (52.6 KB)

Regards,
Riya

Dear Riya,

there is a problem with your source routine. If you set up an USRBIN scoring to see the primary neutron beam, you get the following result:

The cause it that you are reusing the random_prob variable both for the `x` and `z` coordinate of the plane, thus creating a line.

After fixing this I got approximately the same result in both cases.

Cheers,
David

P.S.: you should add a PHYSICS card with Type: COALESCE turned on if you are simulating activation.

2 Likes

Hi @horvathd ,

This is what I did, but still got a difference of factor of 2. Is this what you meant in the source routine ?

Mo1.inp (2.5 KB)
Mo1.flair (3.1 KB)
source_newgen_plane.f (19.1 KB)

Regards,
Riya

Dear Riya,

yes, that is one correct way to fix it. (You donâ€™t need to duplicate the xdummy variable. Each call to the `FLRNDM(xdummy)` function will return a different random number.)

I ran your Flair file again, and I still got equal results in both cases. By any change did you forget to recompile after modifying the source routine?

Cheers,
David

1 Like

Thank you @horvathd for the help.

Regards,

Riya