What's the difference between fluscw and fluscw+ in the userweight card? How to record the photons when cooling time change bigger? Which one is the proper secondary source?

Source Definition
1

Dear experts,
I met a problem when I want to define a secondary source when doing the shielding calculation. The background is in my case: firstly, a target is interacted by electron beam, and then the target will emit photons after the electron beam stops. I would like to use the activated target at different cooling time as the secondary source, and then calculate the proper shielding width. I have two ways to solve the problem, described as below:
1. I just used a usrbdx card to calculate the photons emitted at different time, and then use the photon spectrum as secondary source to calculated the shielding width.
2. I used a fluscw.f function to record the photons emitted from the target and then use it as the secondary source.
But there are problem in both two ways. In the first way, the secondary source are defined isotropic, I think that’s not good; In the second way, it’s likely that fluscw can not record the particles when there is DCYSCORE defining the cooling time, and also the data from fluscw and fluscw+ are quite different(what’s the difference? I can not understand it by the fm.pdf file).

I don’t know which one is right and can be used as the secondary source. So, how can I solve this problem? Attached are the input file. Great thanks for your kind help.

step111.inp (23.7 KB)
step111.flair (13.9 KB)
fluscw.f (2.0 KB)

step1 with way 1
direct.flair (15.5 KB)
direct.inp (24.3 KB)
step2 with way 1
step2.flair (15.7 KB)
step2.inp (24.2 KB)

Merry Christmas!

Best regard,
Yours Wan

3

Hi Wan,

Thank you for your question. I will have a look into it at the beginning of next week.

Cheers,
Jerzy

4

Hi Wan,

There are quite a few things to unravel here.
First of all, if you just want to score the effective or the ambient dose for different cooling times to calculate your shielding, you don’t really need to split your simulation in two steps. I encourage you to have a look at the lecture on Radiation Protection calculations from the last FLUKA Beginner’s course:

To dig deeper into the topic of radiation protection calculations with FLUKA, and you can go through the materials of the FLUKA topical course on radiation protection:

To get an idea on where you would actually use the fluscw user routine, the presentation on Activation gives some useful details:

For a better understanding of how you should design your shielding and plan interventions in the irradiated area, have a look at these two presentations:

RPtopical_CERN2024_PromptRadiation_and_ShieldingDesign.pdf

Below, I am attaching a modified version of your direct file which is a good starting point to tackle your problem.

direct.flair (9.2 KB)
direct.inp (12.1 KB)

The cooling times that I am defining are 0, 1h, 10h, 1 day, 1 week and 1 month. Each of these cooling times has an assigned USRBIN scoring. Additionally, you have a scoring for the prompt radiation.
After looking at your files I have the impression that maybe this detail confused you. The cooling time of 0 is not equivalent to the scoring without any assigned DCYSCORE. If you assign a DCYSCORE with a cooling time of 0, you will get residual radiation from the activated materials, but the prompt radiation from the primary beam will not be present in the scoring.
You introduced an irradiation profile of 20h with 1.25E16 electrons/second. This is actually a quite intense beam which will give you very high dose from the prompt radiation. However, due to the low energy of electrons of only 35 MeV, activation will be rather rare and therefore I introduced a LAM-BIAS card to increase the probability of photonuclear interaction. You may want to play with the parameters there.

I will not go into details explaining why the methods that you were trying to use are wrong. The same for the difference between fluscw and fluscw+ in your case, you can find the explanation how these options differ in the description of the USERWEIG card:

https://flukafiles.web.cern.ch/manual/chapters/description_input/description_options/userweig.html#userweig

Generally speaking, there are problems that require more sophisticated weighting schemes or actually splitting the simulation in two steps, but your case is a very typical RP calculation which can be easily performed using only the built-in FLUKA cards.

Please read carefully the materials that I pointed you to and come back if you have any further questions. There, you can also find simple exercises that will surely help you understand better the concepts regarding the material activation and varying cooling time.

Best,
Jerzy