Unable to get the initital photon energy while using ISOTOPE card along with source.f

Dear FLUKA Experts,

I created a test flair project where I have used ISOTOPE card along with source.f. I have not defined energy in source.f because I believed the energy will be taken from ISOTOPE card depending upon which radionuclide I am using. Here I put Z = 27 and A = 60, so it represents Co - 60. To verify what are the initial photon energies considered in the simulation I added the line WRITE (,) TKEFLK (NPFLKA), so that I can see the values 1.17 MeV and 1.33 MeV in the log file. But I am unable to get those values.
Am I missing something ?

test.inp (1.1 KB)
source.f (9.3 KB)

Regards,
Riya

** UPDATE**

In continuation of the above matter, I added in the previous input one USRBIN and one USRTRACK to verify, but it seems it is not reading ISOTOPE.
Here are the updated files:
test.inp (1.6 KB)
source.f (9.3 KB)

Regards,
Riya

Dear Riya,

Please, have a look at this post that contains all the information you need:

Keep in mind that the energy of the decay photons is set after the source routine is called. In addition, take into account that an isotropic direction sampling overwrites the particle direction set in the source routine.

If you want to check the source energy, you can include a USRBDX card around the source location or implement the mgdraw user routine.

I hope this helps you.

Marta

From the manual (BEAM card):

In this [ISOTOPE] case WHAT(1) [energy] and WHAT(2) [momentum spread] are meaningless.

A radioactive nucleus is not supposed to have any kinetic energy, rather to decay at rest. Therefore, there is no direction to set in addition. As Marta pointed out, the photon energies will be defined by FLUKA itself after loading the isotope in the source routine, where in case of an ISOTOPE source no photon is there (rather its parent nucleus only).
The option of loading the daughter photons in the source routine is an alternative method, as well explained by David in the quoted post, where there is no ISOTOPE to deal with, since one starts the simulation directly with the decay particles.

Thank you for the responses @msabateg @ceruttif ,

Yes, I followed that discussion and hence tried to implement it, but I am unable to reproduce it in the output. I tried adding a RPP geometry surrounding the source, and added USRBDX but in the output tab.lis file all entries are zero. It will be helpful if you can confirm if there is any mistake in the input or the source file. Here is the input with the USRBDX card.

test.flair (1.9 KB)
test.inp (1.8 KB)
source.f (9.3 KB)

I am extremely sorry that I am unable to understand the solution of it. I will try to explain the doubt.

What changes are required in my present input or in the source file to implement the the following source that I tried to create here?:

Situation: A parallel beam of initial particles coming from the decay of Co - 60 (in other words I want a parallel beam of 1.17 MeV photons and 1.33 MeV photons, but instead of assigning these values directly, I tried to reproduce the same situation using ISOTOPE card)

Also does this mean that when we are using ISOTOPE card, the emitted particles will always be isotropic in nature, no matter whether we have assigned any values of TXFLK, TYFLK and TZFLK in the source routine ?

Also, I am unable to understand why USRBDX results are zero in my present input.

Regards,
Riya

Exactly.

No way, as the first answer indicates. To reproduce this situation, you need to select PHOTON and not ISOTOPE in the BEAM card and sample explicitly in the source routine the desired energies as well as set the photon direction (that can also be done just in the BEAMPOS card if it’s fixed).

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Thank you @ceruttif for clearing the doubts. But then, since the ISOTOPE card has overwritten the direction in source.f, hence the direction is isotropic in the simulation, so why does USRBDX still give zero result in the RPP placed surrounding the source ? Isn’t it producing any photon ?

Regards,
Riya

Dear Riya,

you are missing the DCYSCORE cards. See slide 24 at

Cheers,
David

1 Like

Thank you @horvathd .

Regards,
Riya