Dear fluka experts and colleagues:
I have tried to simulate directly the photons produced by the electron beam hitting the tungsten target, but since the photons produced by Bremsstrahl radiation are in all directions, only a few of them are useful to me. If I want to increase the number of effective photons, I have to keep increasing the number of primary electrons, which wastes a lot of calculation time.
So I now want to directly define a continuous spectrum photon source, or by simulating Bremsstrahl radiation, save the resulting continuous spectrum photon beam as a particle source to load into my other calculations
is there any advice?
Thanks
1 Like
You can define your own source using a source routine.
Have a look at the source routine lecture from the last Fluka course.
Dear @chen2019 !
For example, you can use SpekPy tool to create your desired X-ray spectrum and use it in the calculations. This is not mandatory, you can use spectrum from any other source, but they need to be in the format described below. Here I will try to describe the workflow with the SpekPy:
- Create three columns of the desired spectrum data in a format:
| Emin (keV) | Emax (keV) | dF/dE (keV^-1 cm^-2) |
These columns can be constructed from the SpekPy data spectrum. So, your data will look like this:
Spectrum data
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Name this file e.g. test.spec and put in the spectra directory along with your flair and input file.
- Link and compile executable with the attached source routine (18.7 KB)
- In the Flair define the preprocessor card as
spec = "test" - Define
SOURCEcard, where in the sdum field write:=spec - In the
BEAMcard define your preferred location and direction of the source (divergence etc). Note, that energy will be sampled from the provided spectrum file!
If you wish to add other spectra data follow the same procedure, but change the spec value accordingly to sample from another spectrum.
Hope this will help!
Regards,
Ivan
1 Like
Dear @Ivan
Thank you very much for your advice,Meanwhile, I am very sorry for the late reply,because I have been studying the manual of source routine these days.
I believe your advice will be very effective and I will go back to practice and learn the SpekPy tool,But I am afraid that there will be something I don’t understand, so I may ask you for advice.In order to save resources for the community, I will close this post first.
Thank you again
Best regard
Thank you @amario
Yes, I have been studying the manual on the souce routine.However, it seems that I still need to find out whether fluka can preserve the photon spectrum generated by the electron beam hitting the tungsten target that I want, and how
Dear @chen2019 ,
you don’t necessarly need to use SpekPy to obtain spectra, you can also divide your problem on two steps: the first step is to calculate spectrum with FLUKA (or any preferred tool) bombarding electrons on tungsten, the second is to use this generated spectrum following my previously provided guide. To obtain this spectrum with FLUKA on a first step you need to define USRTRACK or USRYIELD cards. This is a general workflow, you can ask for specific question, but it is always better to study all the basics yourself first.
Kind regards,
Ivan
Dear @Ivan
I did a test where I generated a spectrum using SpekPy’s sample program and exported the spectral data, spectrum01.txt file.And then, i loaded the generated spectral data into the source_newgen.f program and scored the output spectra with a usrbdx card.
I got some results, but I have a question,although the spectral graph plot by usrbdx is similar to the spectral image generated by SpekPy, the longitudinal data of the two are still somewhat different,why?
The unit of usrbdx is part/Gev/cm²/pri, and the unit of SpekPy is photons/cm²/keV (mAs=1.0),I have tried for a long time to convert the two to the same unit, but always failed. Can you tell me why this spectrum difference is.
Thank you
spectrum01.txt (9.1 KB)
mysource_ng1.f (19.0 KB)
PhotonSpectrum003.flair (5.4 KB)
Dear @chen2019 !
The normalization case is a bit off-topic and usually it is up to user how to normalize the results (depending on your particular problem). But I will try to make a few comments below.
In your case FLUKA results of USRBDX are normalized per photon, in the SpekPy it is per mAs, so, if you know how many photons (for you specific setup) come after mAs electrons hit anode, then you can get the normalization factor. For your case the total normalization to compare with SpekPy is \approx 1.427568e5 (see pic below), from this value 1e-6 factor arises due to conversion from 1/GeV to 1/keV, after this, your photons/cm2/keV/primary multiplied by a factor of \approx 1.427568e11 will give photons/cm2/keV/mAs, in other words \approx 1.427568e11 photons/mAs are coming in your region of interest (1 mAs is a 1e-3/1.602e-19 \approx 6.242197e15 number of electrons striking anode per second). This was obtained from this calculation! And purpose is to only demonstrate relations. Originally, this norm factor is up to you to define!
However, going back to your initial post in this thread: from this calculation you can see why you need so huge amount of primary electrons to simulate spectrum of X ray photons directly. Only a tiny fraction of total electrons bombarding anode give us a desired photons (after filtering etc): 1.427568e11/6.242197e15*100 \approx 0.00228% — efficiency of production of X rays for your case (in terms of intensity). A more classical definition of production of X rays is energy efficiency = KV x Z x 10e-6, so, for your case is about 0.65% (briefly looking I can’t find efficiency in terms of intensity to compare).
Also, see a bit modified flair file attached (3.6 KB) where a few fixies were made (USRBDX area defined, bin number changed etc)
Hope this will be helpfull!
Regards,
Ivan
2 Likes
Dear @Ivan
Thank you again for your comments, which were very useful to me and helped me better understand the conversion efficiency of X-ray.By the way,I just want to make sure that ,the kv is the voltage of the tube and Z is the atomic number of the target material, right?
Regards，
chen
Dear @Ivan
I sincerely appreciate you. You have provided me with a lot of help and research references, all of which have been very valuable.
Thank you
1 Like