Neutrons, as the most penetrating particles, have found applications in many sectors nuclear including but not limited to nuclear power plants, medical hospitals, radiography and aerospace. To safely take advantage of these highly ionizing radiations, proper shielding materials need to be developed to protect the personals and properties. The currently available shielding materials mainly consist of water and concrete. Although these materials are efficient neutrons shields, they cannot be adapted to provide wearable and lightweight protective gears for personal working in the vicinity of these radiations.

Among low Z materials, polymeric fibers have gained a lot of attention in the field of nuclear shielding due to their exceptional lightweight and ease of transformation into various shapes. Among these remarkable fillers, Ultra High Molecular Weight (UHMWPE) fibers have been proven to provide outstanding neutrons screening performances for various energies. Indeed, these fibers contain a high proportion of hydrogen atoms that are known for their moderating effect toward incoming neutrons. For instance, UHMWPE reinforced epoxy/boron carbide hybrid composites displayed remarkable performances against fast neutrons with a macroscopic cross-section of 0.188 cm⁻¹ equivalent to a mean free path of 3.7 cm [1]. Similarly, against thermal neutrons a macroscopic cross-section of 0.313 cm⁻¹ equivalent to a mean free path of 2.2 cm, was recorded [2]. It is also important to specify that boron particles were added because of their ability to absorb the energy of thermalized neutrons [3]. Furthermore, Toyen et al. developed durable thermal neutron shields from samarium oxide (Sm₂O₃) grafted UHMWPE fibers [4]. On the other hand, the low melting point (around 120°C) of these fibers is a major drawback hindering the full exploitation of their shielding ability [5–8].

Para-aramid (Kevlar) fibers, similarly to UHMWPE fibers are mainly used in the field of ballistic to shield against various high velocity projectiles [9, 10]. Kevlar fibers start to decompose at temperatures in excess of 400°C and their atomic composition is somehow close to that of the UHMWPE fibers [11–13]. Thus, it came to our attention the study of the neutrons shielding properties of Kevlar based materials. Another objective is to develop, for the first time ever, a dual ballistic and nuclear protection designed for soldiers and personnel working in contact of theses radiations. In another words, the present work unravels the combination of the ballistic and nuclear shields into one hybrid composite capable of stopping high velocity projectiles and thermal neutrons.

Before assessing the neutron shielding efficiency of the Kevlar/Epoxy/B₄C hybrids, the number of neutrons passing through a thin Cadmium layer (0.5 mm) was counted. The obtained value was then subtracted from those obtained with the prepared hybrids. The next step consists on counting the number of neutrons passing through different thicknesses of the samples. The obtained results were then used to calculate the neutron attenuation coefficient (Σ), according to Equation 1 and the obtained results are shown in Figure 2. Meanwhile, Figure 3A illustrates the variations of the screening ratio as a function of the fillers loading and Figure 3B shows the values of the neutrons attenuation coefficient Σ.

From the obtained results the neat Kevlar fibers showed remarkable shielding performances with a screening ratio of about 40% for a 12 mm thick sample. This is attributed to the atomic composition of these fibers containing a large proportion of low Z atoms, especially hydrogens which are well-known for their high interaction with neutrons of various energies. The addition of the epoxy resulted in better shielding performances. For instance, the screening ratio reached about 71% for a 12 mm thick sample. Besides providing lower Z atoms for higher interactions with neutrons, the epoxy resin allows the preparation of structural composites with improved mechanical properties. Meanwhile, with the addition of the B₄C particles, the λ reached the outstanding value of 0.191 cm for the 20 wt.% B₄C loading. The boron atoms were added for their absorbing effect toward incoming neutrons. Indeed, boron atoms have a large macroscopic cross-section and mainly interact with neutrons by absorption. Therefore, this study confirmed that the combination of hydrogen and boron atoms in different forms can synergistically produce high performance shields.

To better asses the efficiency of the studied materials, a comparative study was conducted with practically all the available thermal neutrons shields [14–20]. The Σ values obtained, in this work, as well as those gathered from various references are listed in Table 1. As clearly seen from this table, the developed shields surpass the majority of the already available shields. For instance, neat Kevlar fibers provided similar performances than Boric acid/EPDM composites [19]. Meanwhile, epoxy/Kevlar composite displayed comparable thermal neutron shielding than Epoxy/Clay/B₄C [13]. Additionally, the hybrid compositions offered the best results with a record value of 3.638 cm⁻¹ for the hybrid Kevlar/Epoxy/20% B₄C. More importantly, the Kevlar-based materials can provide supplementary protections against high velocity projectiles and stab threats for an optimal multi-threats protection.

In this study, Kevlar fibers were introduced, for the first time ever, as interesting fillers for the development of advanced ballistic and nuclear shields. In fact, the obtained results confirmed to great potential of these materials to shield against thermal neutrons, directly originating from the NUR nuclear reactor. The lightweight and flexibility can be used to produce wearable ballistic and neutrons protections for soldiers and personals working in the vicinity of these radiations. The present study also opens up the way for further researches as high performance polymeric fibers can be seen as the future of the nuclear shielding materials.