Dear @raksha,
Thank you for sharing the source of the data.
I took the liberty to heavily modify one of your input files to try to reproduce the paper results. Here some warnings:
- The geometry used in the paper is not crystal clear to me. If we assume a cylindrical shape of the shielding and Fig. 4 to be a section of it, then I do not understand the statement in section 2.6 “…is housed in a HDPE container of height 47 cm and thickness 15 cm… ”. But anyway, I don’t think this is the origin of the issue.
- Material compositions are not specified, which could bring some uncertainties to the table, but I don’t think this is the issue either.
Here you can find a tgz file 20211213_forum.tgz (25.4 KB) with your modified input file together with the spectra sampling routine and the ISO 8529-1:2001(E) Am-Be spectra as provided in this other topic. This will allow you and anyone interested to give it a try using a more realistic neutron spectrum, as I unsuccessfully suggested you in my reply to your previous post. To make it work, you need to compile it by going to …/CERN-FLUKA-spectra-sampling/src/ in your terminal and type “make” (if an error about the FLUKA directory shows up, change FLUKA_DIR inside the Makefile to point to the directory where you have FLUKA installed and try again). Then you must use the generated executable for those runs using neutrons as primary particles in the Run tab of Flair (select in “Exe:”). Please refer to Sampling from energy spectra for details.
In the input file:
- Preprocessor directives allow you to chose between photons or neutrons as primary particles as well as a simulations considering the HDPE shielding or using air everywhere. Few examples are already setup in the Flair Run tab.
- Importance biasing is included when the shielding is used to easily gain statistics outside it.
- DOSE-EQ cylindrical scorings are used filtering the contribution of neutrons and photons. Note that in the simulation using neutrons as primary particles, we will also get a contribution to the dose by photons coming from neutron-induced reactions.
- In the Flair Geometry tab, some layers has been created to plot the USRBIN results in top of the geometry. Some normalization is already included, which assumes the numbers stated in the paper you provided, in section 2.1: 4.4e7 neutrons/s and 3.3e7 gamma/s for a 740 GBq source. Then I just scaled this values for the 185 GBq and 37 GBq samples used in the paper and converted the pSv/pr provided by FLUKA to uSv/h. Once the normalized USRBIN is plotted, you can make use of the “info” tool in the Geometry tab of Flair to check the results in the locations of interest.
- The source is a cylinder of 2 cm radius and 6 cm high.
Results:
- With neutrons as primary particles and air filling the whole geometry, we can reproduce the results of Tab. 5 in the paper.
- Combining the contribution to the dose rate of photons from the simulation using neutrons as primaries and the one using 4.43 gammas as primaries, we can reasonably reproduce the respective result in Table 6.
- Using neutrons as primaries and the HDPE shielding, I cannot reproduce the result in the paper either. I obtain about 120 uSv/h instead of the 21 uSv/h of the paper.
I encourage you and anyone interested to take a closer look to make sure I did not introduce some stupid error.
If none, I would recommend you to contact the corresponding author of the paper and see if he/she can shed some light. Special attention should be given to the scoring details: location and methodology. Unfortunately I am not an expert on MCNP so I cannot comment on the ring detector tally they mention to have used.
Hope this helps, do not hesitate to comment back.
Kind regards,
Francisco