Shielding materials that are appropriate, economical, and easy to manufacture have become increasingly important to protect workers and the general public as demand for peaceful applications of nuclear and radiological technology grows. Radiotherapy is one of these peaceful applications, in which patients are given high doses of gamma radiation generated by high-energy electrons that can reach 24 MeV utilizing linear medical accelerators (linac(
Multi Leaves Collimators (MLCs) [1] are used in modern therapy protocols that rely on Intensity Modulated Radio Therapy (IMRT). These leaves move in a programmable manner so that the radiation field takes the shape of the tumor from a certain angle. When the tumor is irradiated from a different angle, the leaves are repositioned so that the field shape matches the shape of the tumor as seen from that angle. This process is repeated at various irradiation angles until the tumor receives the prescribed dose while the dose to surrounding normal tissue is minimized.
When photon beams greater than 10 MeV [2] are used in such a modern radiotherapy modality, a large quantity of energetic gamma radiation is stopped by the MLCs, resulting in the generation of significant neutron yield, which should be shielded together with gamma radiation. However, because the number of Monitoring Units (MU) delivered to the isocenter in such techniques is typically higher than that required for conventional radiotherapy, the neutron and gamma leakage radiations from the linac's head are extremely important, and shielding for such radiations has become a subject of great interest [3].
Light elements such as hydrogenous materials mixed with boron compounds are used in the construction of good shielding materials that attenuate fast neutrons because of their effectiveness of neutron moderation through elastic scattering process, which is significant for enhancing neutron reaction 10B5 (n,α) 7Li3 cross section [4, 5]. Secondary gamma radiations with energy of 2.2 MeV are created during neutron absorption, necessitating an increase in shielding thickness [6, 7]. As a result, the effective radiation shield must be made up of a mix of light hydrogenous elements that moderate fast neutron to thermal neutron and high-Z materials that absorb gamma rays.
Concrete is the most common and cost-effective shield for gamma and neutrons in high-energy linac-based radiotherapy treatment rooms, and it is utilized to build primary and secondary barriers, whereas BPE is typically used for doors. To protect personnel in radiotherapy facilities, the primary and secondary parries, as well as the door, must be of sufficient thickness [8].
Several studies and trials have been conducted in the past years to produce new forms of neutron and gamma radiation shields by modifying the characteristics of various materials [9–20]. Unfortunately, none of these studies propose a cost-effective alternative to the pricey BPE that could be used as a neutron/gamma shield in the door of the radiotherapy vault.
By examining several varieties of wood, a few trials were recently conducted to provide new sorts of economical shielding materials for neutron/gamma radiation. Elsersy 2016 [21] employed consecutive layers of beech wood and boron carbide (B4C) as a neutron shield and discovered that a B4C-to-wood thickness ratio of 0.5 to 1 is more convenient than borated wax as a neutron shield. In the case of gamma radiation, no information about shielding characteristics is provided. One drawback of this research is that the fabricated shield is anisotropic, requiring special caution in sample preparation.
K Ninyong et al. 2017 [22] investigated wood/natural rubber composites for thermal neutron shielding with the addition of either boron oxide (B2O3) or boric acid (H3BO3); he discovered that wood particles improved the dimensional stability and surface hardness of the wood/ natural rubber composites, while the B2O3 and H3BO3 worked as active thermal neutron shields. The same author investigated the same wood/natural rubber composites in 2019 [23], this time with the addition of lead (Pb) powder as gamma shielding materials. He discovered that whereas wood particles had no effect on radiation shielding, Pb powders successfully worked as a gamma protective shield.
Shamsuzzaman et al. 2019 [24] evaluated the neutron and gamma shielding capabilities of three different types of wood in their natural form to those of fiber reinforced polymer composite materials. In comparison to reinforced polymer composite materials, they discovered that wood samples are more (less) efficient in gamma (neutron) shielding capabilities.
Afrozi et al. 2020 [25] investigated the neutron shielding capabilities of a mixture composed of wood saw dust and borax at various thicknesses using neutron radiography techniques. The author discovered that adding 30% borax to wood increases neutron absorption ability to 20.24 percent and attenuation value to 0.53 cm− 1, compared to 19.05 percent and 0.36 cm− 1 for pure wood, respectively. The author did not include any information about gamma radiation shielding properties.
Robin et al 2022 [26] used different codes to investigate the radiation shielding characteristics features of eleven raw wood species in the energy range 1 KeV to 105 MeV for gamma radiation. The fast neutron effective removal cross section was also studied by the authors. The results of this study demonstrated that the main gamma shielding parameters, including minimum mean free path, HVL, and TVL, were highest at the lowest energy, increased with increasing energy, and decreased with increasing density, indicating that denser woods are more effective at lower energies. The findings of this study indicate that wood with a notable density and woods rich in hydrocarbons and low Z materials are better for fast neutrons shielding and less effective for gamma shielding. As could be noticed in this study, none of boron compounds were used to enhance the neutron shielding properties.
Nurul Awaliyah et al. 2022 [27] developed a flexible and transparent film for X-ray radiation shielding fabricated successfully from composite consists of wood, PVA, Gelatin, and BaCO3. The developed composite was primarily intended for use in medical applications. The author did not conduct any investigation into the properties of neutron shielding.
As is evident from the literature that has been presented, the studied compositions are not suitable to act as a cost-effective substitute for borated polyethylene, either because these materials are expensive or because they are difficult to use as neutron/gamma shields for doors of the radiotherapy treatment room. Accordingly, the goal of this research is to develop a new low-cost, easy-to-manufacture composite that can effectively attenuate both fast neutrons and gamma rays at the same time. For that purpose, dust wood is mixed with di-boron trioxide (B2O3) and styrene-butadiene rubber (SBR) in the proposed composite. The novel composite's major application is intended to replace the expensive BPE in the radiotherapy treatment room's door shielding.
This paper is organized as follows: Section 1 is devoted mainly to presenting the previous studies dealing with various materials, with an emphasis on wood as a neutron and/or gamma shielding material. The section ends with the main objective of this paper. Section 2 is subdivided into four subsections; the first one is dedicated to describing the constituents used in manufacturing the proposed new composite with insights on how the new composite’s samples are produced. The second subsection is devoted to presenting the experimental setup for measuring neutron/gamma shielding parameters, while such parameters are summarized in the third and fourth subsections. The experimental results along with theoretical ones are presented in section 3. A case study showing how the proposed new composite could be used in the door shielding of radiotherapy vault is depicted in section 4. Section 5 presents an economical evaluation of the new composite; Section 6 describes our ongoing plan for workability in producing the new composite. Finally, section 7 is dedicated to presenting the concluding remarks obtained from this work.