And used LAM-BIAS.
Have the following question for you:
1, I don’t know if this is the correct setting?
2, The simulation time is too long. I’m running 1e8 primary particles, 20 spawns and 10 cycles and it took about 2-3 days and the uncertainty is still very high. I wonder if there could be a better way to speed it up?
Many thanks in advance for any help anyone can provide!
thank you for posting, I will be looking into this.
It looks like the files failed to upload properly, can you upload them again?
perhaps this will be clear when I see the input, but in case you have multiple scoring cards, which scoring card are you specifically looking at (region, any associate score modifiers, etc)
the input as you sent it cannot be run, there is a DCYSCORE card is trying to modify a detector that does not exis (w_CL74). Make sure this is solved on your end.
you are looking at a quite rare event, the activity of Eu152 from a concrete that only contains a tiny fraction of europium (~1e-6). That is not an issue of course, but does mean that longer run times and biasing techniques are inevitable
it looks like your proton beam is not on axis with the copper target, which is resulting in only a small amount of neutrons (approximately 0.017 neutrons per primary protons, as you can see in the run summary of the .out file)
Please check the above points and let me know if it is all intentional. I tried with 1e7 primary particles, 20 spawns, and 2 cycles, and I have achieved satisfactory statistics. Of course you will need to decide according to your requirements and resources. Please let me know which of the scoring card you were evaluating when you encountered low statistics after the long run, as well as any cuts or projections you applied.
Regarding, the LAM-BIAS card, low-energy neutrons (En < 20 MeV) use a tabulated approach for their cross section and the biasing card does not apply to them, unfortunately. See this post and its reply.
I’m so sorry, please ignore the DCYSCORE about w_CL74.
Yes, I scored the activity of Eu-152 in concrete. This is the Eu-152 result of my run, the data from Z-axis 580-590cm bin, where the uncertainty is really too high and may be different from your result.
The result file is too big to upload. You will need to rename the .lis file to .rar, then unzip it and get a .lis file. r58063Eu-152.txt (169.8 KB) cy_21.bnn (2).lis (2.2 MB)
The angle between the Beam and the target was deliberately placed, thanks for the heads up.
And I also scored several other activations that may be higher, such as 27Co-60, 73Ta-182, 21Sc-46, 11Na-22, etc., but the other settings have not been changed, only the scorecard has been added. The fact that all of them have very high uncertainties just confuses me a lot. It doesn’t look like it will work if I just addition primary particles because the run times are so long.
I use a computer that runs 1e8 primary particles , 20 spawns and 10 cycles and took about 2-3 days.
Is it possible that I can effectively reduce the run time by using the 2-step method?
I understand; the statistics are indeed quite low because of the rarity of the events involved. The main issue (I assume) for this lack of production is that the main mechanism for the production of the Eu152 isotope is neutron interactions with the Eu in the concrete; there are too few neutrons in the simulation, and too few Eu atoms in the target.
To bias the number of neutrons, you can use LAM-BIAS on the protons interacting with all materials (beginning with the target and concrete) in the simulation. This will ensure a larger production of neutrons, among other products. I would suggest biasing the interaction length between 0.01 and 0.1. The weight re-normalization is made by the code internally, so you don’t need to change anything after setting that.
Right now, Eu represents only 1e-7 of the concrete composition. You could imagine scaling this by a factor of 100-1000 (I would tend towards the lower end, to maintain accuracy), such that the probability of a neutron interacting with a Eu is significantly larger, but overall the effect in the neutron fluence would barely be noticeable. Take care, of course, to then scale all your activation by the inverse of the same factor.
Combined, these two factors should boost the number of interactions by between 1000 and 100’000 times. I hope this helps you achieve the level of precision you need,
