Radiation Physics and Engineering
A peer-reviewed journal published by K. N. Toosi University of Technology

Design of neutron beam for neutron radiography base on the use of TRR thermal column

Document Type : Research Article

Authors

Saeed Sabouri 1
Yaser Kasesaz 2
Mohsen Kheradmand Saadi 1

1 Department of Nuclear Engineering, SR.C, Islamic Azad University, Tehran, Iran

2 Nuclear Science and Technology Research Institute, Tehran, Iran

https://doi.org/10.22034/rpe.2026.579704.1349
Abstract
In this study, a thermal neutron beam suitable for neutron radiography (NR) was designed based on the thermal column of the Tehran Research Reactor (TRR). The existing air-filled channel inside the graphite thermal column was utilized to implement a dedicated beamline consisting of a gamma filter slab, a boron carbide thermal neutron absorber with a central aperture, and a conical collimator. A comprehensive parametric optimization was performed using the MCNPX Monte Carlo code. A total of 144 configurations were evaluated by varying the gamma filter material, aperture thickness, aperture radius and the distance between the aperture and image position. Bismuth demonstrated superior performance compared with lead due to its lower neutron absorption and effective gamma attenuation. The optimized configuration, employing 5 cm of Bi filter and a 5 cm B₄C aperture with a 2 cm radius, achieved a thermal neutron flux of 1.0×106 n·cm-2·s-1 at L/D = 114 under full-core simulation conditions at reactor full power. The neutron-to-gamma ratio and fast neutron suppression were significantly improved, while the gamma dose rate was substantially reduced compared with the existing E-beam tube NR facility at TRR. A secondary surface-source methodology was implemented to accelerate the parametric study and was subsequently validated against full-core simulations. Although the simplified model overestimated absolute flux values, it accurately reproduced relative performance trends, confirming its suitability for design optimization. The results demonstrate that the TRR thermal column can provide an efficient and high-quality neutron beam for advanced NR applications with enhanced beam purity and radiation safety.

Highlights

  • 144 configurations have been investigated using MCNPX, varying gamma shield material to maximize beam purity.
  • Bismuth significantly outperforms Lead as a gamma shield due to its lower neutron absorption cross-section.
  • The optimized design achieves a thermal neutron flux of 1.0×106 n.cm−2.s−1 at L/D = 114 under full-core conditions.

Keywords

Neutron Radiography
Tehran Research Reactor
Thermal column
MCNPX Monte Carlo code

Copyright
RPE is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0).

Conflict of Interest
The authors declare no potential conflict of interest regarding the publication of this work‎.

Funding
‎The authors declare that no funds‎, ‎grants‎, ‎or other financial support were received during the preparation of this manuscript‎.

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Radiation Physics and Engineering
Volume 7, Issue 3
Summer 2026
Pages 27-37

  • Receive Date 27 April 2026
  • Revise Date 14 June 2026
  • Accept Date 16 June 2026

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