Design and construction of a new neutron radiography system at Tehran Research Reactor

In order to achieve a thermal neutron beam for neutron radiography applications, a new neutron collimator has been designed, installed and characterized at Tehran Research Reactor (TRR). TRR is a 5 MW, open pool and light water coolant reactor with seven beam tubes. Neutron collimator that is an important part of neutron radiography system was installed in the six inch E beam tube. Collimator design was performed using MCNPX code. To improve the beam quality, polycrystalline bismuth as gamma filter and graphite as fast neutron moderator were used. Based on this design, the L/D of the system ranges between 150 to 250. The neutron flux at the image plane can be varied from 2.6x106 n cm-2 s-1 to 6.5x106 n cm-2 s-1. Preliminary measurements of the neutron beam were performed using foil activation method and TLD700 dosimeter for measuring neutron flux and gamma dose rate respectively after installation of the collimator in the beam tube. Results show that the measurements are in a good similarity with calculations and also the obtained beam has a good quality for neutron radiography applications and the parameters of this beam is comparable with other neutron radiography systems around the world.