Optimization of thermal neutron flux in an irradiator assembly with different isotopic sources

• The aim of this work, is to evaluate the thermal neutron distribution in an irradiator assembly.
• Thermal neutron distribution were determined experimentally and calculated by MCNP.
• The calculated and experimental results were in good agreement.

This work aimed to determine the distribution of thermal neutron flux in an irradiator assembly to study the possibility of use this irradiator for Neutron Activation Analysis; NAA. To establish the facility specifications, the thermal neutron flux values of 252Cf and Pu-Be isotopic neutron sources along the horizontal irradiator axis were determined experimentally and calculated by Monte Carlo N-Particle; MCNP transport code. The irradiator assembly characterized by supplying a stable neutron flux for a long period, eliminating the need to use standard material i.e. comparative method, so that the process becomes efficient, compact, economical and more reliable. The measurements were carried out at different position inside the irradiator assembly using proportional 3He-detector and gold foil activation method. As well as, these measurements were performed without and with two types of neutron reflector such as water and steel to determine the thermal neutron distribution along the irradiation points. The experimental results were compared to the calculations performed with MCNP Code. The calculated and experimental results were in reasonable agreement for both 252Cf and Pu-Be sources. This indicated that the material and geometrical properties of the irradiator were modeled well.