Dear Fluka Experts,

I want to show a neutron detection of the SiC+LiF. When I add the DETECT card to my Flair input, I could not get any graph regarding count. How can I solve this problem?
My Flair is attached below.

basic.flair (5.8 KB)

Well… This is a plot from a simulation I ran with the file you attached. I stopped in the middle of run because I was busy, (20000000/1000000000) but should there be a plot like this?

Hello,
Could you please explain how you did it? Did you change the input values in FLUKA?
In addition, I am not sure how the spectrum that LiF+SiC looks like but mine was definitely wrong.

Dear @EzgiUslan

Further details on what you are trying to achieve exactly would have been very useful, luckily they were provided in a complementary short-lived post.

There are few things preventing you from getting meaningful results:

• FLUKA’s default energy unit is GeV, not MeV, as I guess you assumed. So the energy of you neutron beam is currently 25.3 eV, and the energy range in your DETECT card is [~0,100] GeV. I believe this was not your intention.

• Most probably you want the DETECT card to be linked to your detector region. Right now it is linked to the target region.

• You also need the correlated generation of alpha and triton from the Li-6(n,alpha) reaction, to obtain it you have to activate the neutron pointwise treatment for Li-6. And for doing this you need to create a monoisotopic material for Li-6 and use it in the definition of your LiF compound. Please see note 5 of LOW-NEUT and How to set the low energy neutron cross sections for further details. Attention to the naming of the material!

Hope this helps,
Francisco

Hello Francisco Ogallar Ruiz,

I made the edits to the FLUKA input file with the information you provided and got the spectrum. Thank you!

However, I still have some questions. I would be glad if you could help me.

1. When we click on the ‘regions’ part of the DETECT card, the values ​​1,6 and 11 are seen. I don’t know which of these to use. But right now I’m using 1. What does region 1-6-11 mean? Would you help me, please?

2. I selected a PHOTON particle option for alpha particle tracking in USRBIN. I’m not sure if my usage is correct. Should I use HEAVYION for tracking alpha particles?

3. As you mentioned in your previous email, I created a monoisotopic material (LOW-MAT) for Lithium. Do I need to do this for fluoride as well? If necessary, do I need to write A = 19 to the atomic weight in the LOW-MAT for Fluoride? You can see the card in the inp file.

4. When I changed the delta p and delta phi values ​​in the Beampos card, I got the result. If I didn’t add them I couldn’t generate the spectrum. I took these values ​​from another random input file. But I don’t know why I use them and what values ​​are suitable for me. Can you help me with this? What does delta p and delta phi mean? How can I select the proper number for my application? I read the manual but I couldn’t understand.
basic.inp (2.2 KB)

5. Do I also need to use a LOW-NEUT card? Or is Fluka already activating it as stated in the manual? I don’t know what the LOW-NEUT variables are.

6. My goal is to observe the energy efficiency of thermal neutrons and simulate the neutron detector. Therefore, do you have any other card recommendations that I should add to the program other than USRBIN and DETECT?

7. The spectrum I obtained is not a continuous line but rather peak after peak. Is it because I use a low number of samples? If I increase the number of samples, can I get better results? A more realistic spectrum like shown in the photo below?

Sorry for the long message, and thanks in advance for your time and effort.

Best Regards,
Ezgi

I’m not changing anything :0… but I use extension ‘40’ to draw plot. Your plot may be use extension ‘17’ and using log-scale on x-axis. I use linear-scale on x-axis. It seems to me that there are only two differences.

1. extension 40 vs extension 17
2. linear scale vs log scale

Dear @EzgiUslan,

I will try to tackle your questions in the coming days. In the meanwhile I think you could really profit from taking a look to the presentations of the last FLUKA beginners course: 2022 FLUKA.CERN course - Brussels (16-20 May 2022): Timetable · Indico. In fact, some of your questions will be solved after doing so.

Kind regards,
Francisco

Dear @EzgiUslan

Indeed you got a spectrum, but it is not the one you were looking for. Please see my answers below, in particular number 3 and 4.

1. What does region 1-6-11 mean?

This is only an upper limit for the number of regions you that you can specify in the DETECT card. If you choose 6 you will see that 6 fields become available to you. In your case you only need one region but there are cases in which a detector may be composed by several regions and/or one needs to define trigger regions. See DETECT for further info.

2. Should I use HEAVYION for tracking alpha particles?

If you are interested in the DETECT results, you do not need a USRBIN. The DETECT card has nothing to do with it. If you introduce both, you are simply asking for two independent scorings for two different things. For further info on this see USRBIN and SCORING I. Using scorings such as USRBINs does not affect the tracking of particles in FLUKA.

3. As you mentioned in your previous email, I created a monoisotopic material (LOW-MAT) for Lithium. Do I need to do this for fluoride as well?

The point of doing it for Li-6 is to activate the neutron pointwise treatment, which allows for the proper emision of alpha and tritium as products of the Li-6(n,\alpha)t reaction. So you do not need to do it for Fluorine but you need to get it right for Li-6. Your current input is not correct. Please stick to the instructions in note 5 of LOW-NEUT in what refer to the naming of your monoisotopic Li-6 material (i.e. name it LITHIU-6). The name you chose (LITHIUM) for the monoisotopic Li-6 is already the name used by FLUKA for natural Li (see here), so please avoid it. Once you have named your material LITHIU-6, then FLUKA already knows which cross-section to use without the need of a LOW-MAT card (you can remove it).
Attention: in your current input you are now using only Li-6 in your LiF compound. I doubt this is what you want. Most probably you want to have the natural composition of Li, so you need to define also a Li-7 material and use it in the right proportion when defining the LiF compound. See the Materials lecture if you need help when defining a material/compound.

4. I took these values ​​from another random input file.

And as a consequence you simulated a neutron beam with energies ranging from 0 to few GeV! Choosing random numbers for the fields of your input will never help you, in fact it tricked you by providing a completely wrong spectrum. Please read carefully BEAM and the Simple Sources lecture. If you struggle with the meaning of whats and cards, please take a look to this entry of the manual Note that the “proper number” needs to be defined by you in accordance with how you want the simulated beam to be. To obtain a monoenergetic pencil beam of thermal neutrons you just need to leave those fields empty.

5. Do I also need to use a LOW-NEUT card?

No, you do not.

6. do you have any other card recommendations that I should add to the program other than USRBIN and DETECT?

I do not have any particular recommendation. What we have discussed here is enough for obtaining the spectrum you were looking for and, as mentioned before, a USRBIN is not needed for that.

7. The spectrum I obtained is not a continuous line but rather peak after peak. Is it because I use a low number of samples? If I increase the number of samples, can I get better results?

The spectrum you obtained is not the one you were aiming for because of the reasons explained above. But indeed, if you need to reduce your statistical fluctuations you can increase the number of primary particles simulated. Keep an eye on the error bars of your spectrum to decide whether you need more primaries or not, rather than in its shape.

Hope things are clearer now.

Kind regards,
Francisco

Hello Francisco Ogallar Ruiz,

Thanks for your answer! It helped a lot! I believe I finally received the desired spectrum. You can see the final input file below.

If you don’t mind, could you please verify that all is well? I added several comments and also used some other cards.

Lastly, I have two more questions. (If this is too much for a single thread I can make a new post.)

How can I convert the Y axis of the DETECT card into an actual count? In the manual, it says to detect Scores of energy deposition on an event-by-event basis. Event means the deposited energy count on the detector region. Therefore, to get the actual count value I should multiply the total number of events with the Y-axis coefficients. How can I find the total number of these events?

The second question is, I would like to calculate the absolute detector efficiency of SiC. Is it possible to calculate that in FLUKA?

The formula for the efficiencies is:
Absolute efficiency = number of pulses recorded / number of radiation quanta emitted by the source
Intrinsic efficiency = number of pulses recorded / number of radiation quanta incidents
on a detector

I believe intrinsic efficiency calculation is not possible, as the detect card scores every energy deposition event. However, how can I measure Absolute efficiency? Is the number of recorded pulses equal to the event numbers mentioned in the first question and the number of radiation quanta emitted by the source equal to the number of primaries selected on the START card?

Thank you so much for all your efforts and time.
Best Regards,
Ezgi
basic2.inp (3.4 KB)

Dear @EzgiUslan,

Regarding your input, I will not go through the comments you left inside since it is not clear to me if they are actual questions or not. If you have specific questions feel free to open further threads in this forum. I just have a couple of comments:

• You are still using only Li-6, please see my reply above, I believe you have missed the part preceded with the bold word Attention.
• As mentioned above, scorings do not affect particle tracking in FLUKA. Therefore, your RESNUCLE scoring does not affect the tracking of nuclei, it only affect their scoring.

How can I find the total number of these events?

The DETECT results are normalized per primary particle. Therefore your results are already counts/primary. To get counts you just need to multiply by the total number of neutrons (primaries) that you want to consider.

I would like to calculate the absolute detector efficiency of SiC. Is it possible to calculate that in FLUKA? […] how can I measure Absolute efficiency?

You must keep in mind that you are simulating an ideal detector, but both quantities you mention can be easily obtained in your simulation according to the definition you have provided.

The number of pulses recorded would be the addition of all entries in the result of the DETECT card. The FLUKA results are given per primary particle, in your own terms this is per quanta emitted by the source , so this comes for free. You just need to add all entries of the DETECT card to get the absolute efficiency as you defined it.

The intrinsic efficiency will be equal to the absolute one in your simulation, because (almost) all primary neutrons hit your detector, given the characteristics of the beam you have defined. But let’s imagin that your beam is different, and not all neutrons hit your detector, then to get the intrinsic efficiency you need to get the number of neutrons hitting the detector. This can be done, for instance, using a USRBDX scoring. There is plenty of info on how to use this scoring in the manual and lectures I linked before, as well as in this forum.

Hope this helps.

Kind regards,
Francisco