AmBe source simulation

[raksha (RAKSHA RAJPUT)]

Dear Experts,

I wish to learn neutron transport using Fluka.

1. The source is Am-Be source. I started with an alpha particle at (0,0,0) and target is Be-9.
   How should I score neutron dose rate in air at 1m ? I tried scoring but the results are not matching with literature data. Say, o/p from USRBDX when multiplied with neutron yield and flux to dose rate conversion factor (for average neutron energy 4.4 MeV), i should obtain the neutron dose rate - am I doing it correct ? As I intend to further solve neutron shielding problem, I chose to use a single energy (average for Am-Be source, from literature). (i/p: alpha1ambe.flair)
2. I tried starting with 4.4 MeV neutron in BEAM, I could score neutron dose rate in air. But with HDPE as shield material, I could not get the expected neutron dose rate. (i/p: 2511ambe2b.flair)

Secondly, how to get the gamma dose rate as the decay of C-12* will give 4.43 MeV gamma, how to obtain this gamma and associated gamma dose rate at 1m ?
I refered some Fluka inputs which attempted the same, but could not follow them completely.
Please suggest/help.
PFA my input files.
Regards,
Raksha Rajput
alpha1ambe.flair (1.8 KB)
alpha1ambe_22_sum.lis (4.2 KB)
alpha1ambe_21_sum.lis (81.4 KB)
2511ambe2b.flair (6.3 KB)
2511ambe2b_21.bnn.lis (4.6 KB)

[fogallar (Francisco Ogallar Ruiz)]

Dear @raksha,

Please take a look to the following posts, which may be of help:

AmBe Neutron Spectrum

Dear FLUKA experts, I am trying to simulate neutron spectrum from an Americium-Beryllium source. I am using an alpha source distributed over a cylindrical volume (filled with Am-Be material). I have also used LAM-BIAS card to bias nuclear inelastic interactions by He-4. I have tried to score resultant neutron spectrum using USRBDX and USRTRACK scorers. Following is the resultant neutron spectrum as USRBDX output: [AmBe_Source_21_plot] Similar results were obtained from USRTRACK card as well. …

Comparison of results for validation

As part of my study concerned about shielding design, I need to prove that I validated code installation by reproducing some standard setup for which results were published. I picked this article (https://bit.ly/335flGu) and tried to obtain similar or close results using the details of their simulation. However, they used MCNP and different dose conversion coefficients. I get a high dose rate value different from those of the reference article. I am wondering if it is appropriate to compare the…

As mentioned in one of them, for simulations involving an Am-Be source, the recommended approach is to start the simulation directly from the neutron spectrum. To learn how to sample from a given spectrum take a look to

Sampling from energy spectra

For more complex simulations one often needs a beam that is not mono-energetic but follows a specific energy distribution. This feature is provided “out-of-the box” for CERN FLUKA by the CERN-FLUKA-spectra-sampling.tgz (21.8 KB) user routine package (version 1.4) that can be fully configured via the input file. IMPORTANT NOTICE: With the release of FLUKA 4.0.0 the package had to be upgraded. In order to use it with FLUKA version >= 4.0.0 please re-download from the link above. The provided c…

Then, seems that you are interested in dose equivalent (correct me if I am wrong), you can simply set an USRBIN scoring DOSE-EQ, whose results will be in pSv/primary. To transform to equivalent dose rate you just need to properly normalize using the activity of your sample.

Not sure what you mean by “I could not get the expected neutron dose rate”, could you elaborate?

Regarding the gamma, it is generated when you start from the alpha particle in the Be target but, since I just recommended to start from the neutron spectrum, you could run a second simulation, this time with a 4.43 MeV photon beam (instead of a neutron one). The dose can be obtained as in the previous case (USRBIN).

Hope this helps.

Kind regards,
Francisco