Design and fabrication of a Nano-based neutron shield for fast neutrons from medical linear accelerators in radiation therapy

Background

Photo-neutrons are produced at the head of the medical linear accelerators (linac) by the interaction of high-energy photons, and patients receive a whole-body-absorbed dose from these neutrons. The current study aimed to find an efficient shielding material for fast neutrons.

Methods

Nanoparticles (NPs) of Fe₃O₄ and B₄C were applied in a matrix of silicone resin to design a proper shield against fast neutrons produced by the 18 MeV photon beam of a Varian 2100 C/D linac. Neutron macroscopic cross-sections for three types of samples were calculated by the Monte Carlo (MC) method and experimentally measured for neutrons of an Am-Be source. The designed shields in different concentrations were tested by MCNPX MC code, and the proper concentration was chosen for the experimental test. A shield was designed with two layers, including nano-iron oxide and a layer of nano-boron carbide for eliminating fast neutrons.

Results

MC simulation results with uncertainty less than 1% showed that for discrete energies and 50% nanomaterial concentration, the macroscopic cross-sections for iron oxide and boron carbide at the energy of 1 MeV were 0.36 cm^− 1 and 0.32 cm^− 1, respectively. For 30% nanomaterial concentration, the calculated macroscopic cross-sections for iron oxide and boron carbide shields for Am-Be spectrum equaled 0.12 cm^− 1 and 0.15 cm^− 1, respectively, while they are 0.15 cm^− 1 and 0.18 cm^− 1 for the linac spectrum. In the experiment with the Am-Be spectrum, the macroscopic cross-sections for 30% nanomaterial concentration were 0.17 ± 0.01 cm^− 1 for iron oxide and 0.21 ± 0.02 cm^− 1 for boron carbide. The measured transmission factors for 30% nanomaterial concentration with the Am-Be spectrum were 0.71 ± 0.01, 0.66 ± 0.02, and 0.62 ± 0.01 for the iron oxide, boron carbide, and double-layer shields, respectively. In addition, these values were 0.74, 0.69, and 0.67, respectively, for MC simulation for the linac spectrum at the same concentration and thickness of 2 cm.

Conclusion

Results achieved from MC simulation and experimental tests were in a satisfactory agreement. The difference between MC and measurements was in the range of 10%. Our results demonstrated that the designed double-layer shield has a superior macroscopic cross-section compared with two single-layer nanoshields and more efficiently eliminates fast photo-neutrons.

Block Copolymer-Assisted Solvothermal Synthesis of Hollow Bi2MoO6 Spheres Substituted with Samarium

Hollow spherical structures of ternary bismuth molybdenum oxide doped with samarium (Bi_2-xSm_xMoO₆) were successfully synthesized via development of a Pluronic P123 (PEO₂₀-PPO₇₀-PEO₂₀)-assisted solvothermal technique. Density functional theory calculations have been performed to improve our understanding of the effects of Sm doping on the electronic band structure, density of states, and band gap of the material. The calculations for 0 ≤ x ≤ 0.3 revealed a considerably flattened conduction band minimum near the Γ point, suggesting that the material can be considered to possess a quasi-direct band gap. In contrast, for x = 0.5, the conduction band minimum is deflected toward the U point, making it a distinctly indirect band gap material. The effects of a hollow structure as well as Sm substitution on the absorbance and fluorescence properties of the materials produced increased emission intensities at low Sm concentrations (x = 0.1 and 0.3), with x = 0.1 displaying a peak photoluminescence intensity 13.2 times higher than for the undoped bulk sample. Subsequent increases in the Sm concentration resulted in quenching of the emission intensity, indicative of the onset of a quasi-direct-to-indirect electronic band transition. These results indicate that both mesoscale structuring and Sm doping will be promising routes for tuning optoelectronic properties for future applications such as catalysis and photocatalysis.

Catalytic performance of bismuth pyromanganate nanocatalyst for Biginelli reactions

Bi₂Mn₂O₇ nano-powders were synthesized via a stoichiometric 1 : 1 Bi : Mn molar ratio hydrothermal method at 180 °C for 48 h in a 1 M NaOH aqueous solution.

A controlled solvothermal synthesis of CuS hierarchical structures and their natural-light-induced photocatalytic properties

A solvothermal synthesis of CuS hierarchical structures for the photodegradation of methylene blue (MB).

Sol–gel synthesis, characterization, and optical properties of Gd3+-doped CdO sub-micron materials

Highly crystalline Gd3+-doped cadmium oxide micro-structure was synthesized by calcining the obtained precursor of a sol–gel reaction. The reaction was carried out with cadmium nitrate (Cd(NO3)2·4H2O), gadolinium oxide, and ethylene glycol (C2H6O2) reactants without any additives at 80°C for 2 h. The resulting gel was calcined at 900°C with increasing temperature rate of 15°C/min for 12 h in a furnace. As a result of heating, the organic section of the gel was removed, and the Gd3+-doped cadmium oxide micro-structure was produced. The obtained compound from the sol–gel technique possesses a cubic crystalline structure at a micro scale. XRD study indicates that the obtained Gd3+-doped CdO has a cubic phase. Also, the SEM images showed that the resulting material is composed of particles with cluster structure. Also, FT-IR spectroscopy was employed to characterize the Gd3+-doped CdO micro-structures.

Hydrothermal synthesis and characterization of straw bundle-like lithium sodium disilicate (silinaite) micro-rods

Highly mono-shaped straw bundle-like silinaite micro-rods have been synthesized using an aqueous mixture of silicic acid, lithium sulfate, and sodium hydroxide under hydrothermal conditions at 180°C. The synthesized materials were characterized by powder X-ray diffraction technique and Fourier transform infrared spectroscopy. The morphologies of the synthesized materials were studied by field emission scanning electron microscopy technique. The synthesized micro-rods are composed of long, fine nanosheets. Electronic absorption and photoluminescence spectra of the synthesized materials were also studied. With increasing reaction time, a blueshift was observed in the UV–vis electronic absorption and emission spectra of the synthesized materials.

Lithium metasilicate and lithium disilicate nanomaterials: optical properties and density functional theory calculations

UV–vis and photoluminescence spectra of the hydrothermally synthesized crystalline lithium metasilicate (Li2SiO3) and lithium disilicate (Li2Si2O5) nanomaterials are studied. The intensity of the bands in the emission spectra increases with increasing reaction time in both compounds. The electronic band structure along with density of states calculated by the density functional theory (DFT) method indicates that Li2SiO3 and Li2Si2O5 have an indirect energy band gap of 4.575 and 4.776 eV respectively. The optical properties, including the dielectric, absorption, reflectivity, and energy loss spectra of the compounds, are calculated by DFT method and analyzed based on the electronic structures.

Hydrothermal synthesis, characterization, and investigation of optical properties of Sb3+-doped lithium silicates nanoparticles

The hydrothermal synthesis and optical properties of undoped and Sb3+-doped lithium metasilicate and lithium disilicate nanomaterials were investigated. The microstructures and morphologies of the synthesized Li2−2x Sb2x SiO3 and Li2−2x Sb2x Si2O5 nanoparticles were studied with powder X-ray diffraction and scanning electron microscopy techniques, respectively. The synthesized undoped and doped lithium metasilicate and lithium disilicate nanomaterials, respectively, are isostructural with the standard bulk Li2SiO3 (space group Cmc21) and Li2Si2O5 (space group Ccc2) materials. The electronic absorption and photoluminescence spectra of the synthesized materials are studied. The measured optical properties show dependence on the dopant amounts in the structure.