Vol. 7, Issue 1, Part C (2025)

Neutron moderation plays a vital role in sustaining controlled and efficient reactions in thermal nuclear reactors. This study provides a comparative evaluation of the neutron moderating characteristics of various elemental and compound materials based on three key parameters: Energy loss per collision (ξ), Slowing-Down Power (SDP), And Moderating Ratio (MR). While previous studies have focused on specific moderator materials, an integrated analysis based on these fundamental physical parameters remains limited. This gap hinders the optimal selection of moderator materials, particularly in modern reactor designs that require high neutron efficiency and fuel flexibility.
In this study, the values for ξ, SDP, and MR for each material were calculated using scientifically established equations related to these parameters, which are documented in trusted scientific references. Computer programs were used to calculate the values, and the results were analyzed with the help of Origin 6 software. Elements such as hydrogen, carbon, and beryllium demonstrated excellent moderating performance due to their ideal combination of high energy loss and low neutron absorption cross-sections. Hydrogen had a Moderating Ratio (MR) of approximately (61.8), carbon around (212.4), and beryllium about (171.2). In contrast, heavy elements such as gadolinium, samarium, dysprosium, and uranium showed very poor performance due to low ξ and high absorption, making them unsuitable as moderators (MR ≪ 1).
Among the compound materials, heavy water (D₂O) stood out with its extremely high moderating ratio (MR=6925) due to its very low neutron absorption, despite having a moderate slowing-down power. Hydrogen-rich materials such as polyethylene, paraffin, methane (CH₄), and lithium hydride (LiH) exhibited strong moderation capabilities by combining high ξ with low absorption, making them effective and economically viable options. Although beryllium oxide (BeO) had a lower MR (≈ 11.6), it remains valuable for high-temperature applications due to its excellent thermal and radiation stability.