Assessment of New Composites Containing Polyamide-6 and Lead Monoxide as Shields against Ionizing Photonic Radiation based on Computational and Experimental Methods

This study aimed to introduce new composites, containing polyamide-6 (PA6) and lead monoxide (PbO), to protect against ionizing photon sources used for diagnostic and therapeutic purposes. Five composites, containing various weight percentages of PbO filler (0, 5, 10, 20, and 50%), were developed in this study. Initially, the numerical attenuation value was estimated using XMuDat program by calculating the mass attenuation coefficients at different energy levels. Next, the samples were synthesized based on the melt-mixing method in a laboratory mixing extruder, and their characteristics were determined by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Finally, experimental radiation attenuation tests were carried out. Based on the SEM results, the acceptable filler weight percentage was up to 20%; however, substantial aggregates formation was observed at the highest weight percentage. The results of XRD analysis showed a higher tendency for crystallization by decreasing the amorphous area, while increasing the filler weight percentage. Moreover, the amount of mass loss was monitored at different temperatures, revealing that the filler incorporation improved the thermal durability of the samples. According to the radiation results, a good agreement was observed between the experimental and computational data, except when aggregates formation was substantial. According to the experimental data, by increasing the lead weight percentage from 0% (crude PA6) to 50%, the half-value layer decreased from 3.13 to 0.17 cm at an energy level of 59 keV and from 7.28 to 4.97 cm at an energy level of 662 keV. Considering these promising results, the applicability of PA6/PbO composites for protection against low- and medium-energy ionizing photon sources must be investigated in future studies.

High-Pressure Phases of SnO and PbO: A Density Functional Theory Combined with an Evolutionary Algorithm Approach

Tin monoxide, SnO, and its analog, lead monoxide, PbO, have the same tetragonal P4/nmm structure, shaped by nonbonding dispersion forces and lone pairs. The high-pressure phases of SnO and PbO have been explored in several experimental and theoretical studies, with conflicting results. In this study, the high-pressure structures of SnO and PbO are investigated using density functional theory calculations combined with an evolutionary algorithm to identify novel high-pressure phases. We propose that the monoclinic P21/m SnO and orthorhombic Pmmn PbO phases, which are metastable at 0 GPa, are a slight rearrangement of the tetragonal P4/nmm-layered structure. These orthorhombic (and their closely related monoclinic) phases become more favored than the tetragonal phase upon compression. In particular, the transition pressures to the orthorhombic γ-phase Pmn21of SnO/PbO and the monoclinic phase P21/m of SnO are found to be consistent with experimental studies. Two new high-pressure SnO/PbO polymorphs are predicted: the orthorhombic Pbcm phase of SnO and the monoclinic C2/m of PbO. These phases are stabilized in our calculations when P > 65 GPa and P > 50 GPa, respectively. The weakening of the lone pair localization and elastic instability are the main drivers of pressure-induced phase transitions. Modulations of the SnO/PbO electronic structure due to structural transitions upon compression are also discussed.

Performance evaluation of lead-monoxide dosimeter with parylene coating for quality assurance of brachytherapy devices

The source position of irradiation is identified using a method that uses rulers and films for quality assurance (QA) in brachytherapy. However, this method involves a high probability of errors, because the scales are checked using the naked eye, and QA is indirectly performed using photographs. Lead monoxide (PbO) is widely used as a semiconductor dosimeter, because it is a photoconductor that generates electrons in response to electromagnetic waves. Moreover, PbO has excellent sensitivity to reflected rays, owing to its high atomic number (Z Pb: 82, Z O: 8) and density (ρPbO: 9.53 g/cm3). We applied PbO to a dosimeter for QA in a brachytherapy device and attempted to increase the signal stability with a parylene coating for performance improvement. Subsequently, a comparative analysis was performed with a PbO dosimeter that was not coated with parylene to determine whether the fabricated dosimeter is applicable as a dosimeter for QA of the brachytherapy device, by analyzing the reproducibility, linearity, percentage interval distance (PID), and angular dependence in the 192Ir source used for brachytherapy. The RSD of the non-parylene PbO dosimeter was 0.85%, and the RSD of the parylene PbO dosimeter was 0.40% in the reproducibility results. In the linearity evaluation results, the R 2 value of the non-parylene PbO dosimeter was 0.9996, and that of the parylene PbO dosimeter was 0.9997 In the PID evaluation results, the difference in the intensity distribution measured according to the distance due to the dose was attenuated at the coated parylene in the case of the parylene PbO dosimeter. Therefore, adjustments using correction coefficients are required for suitable performance. In the angular dependence evaluation results, the parylene PbO dosimeter had 3.44% less angular dependence than the non-parylene dosimeter at an angle of 45°. The parylene-coated PbO dosimeter showed better performance than the non-parylene-coated PbO dosimeter in terms of the reproducibility, linearity, and angular dependence. Therefore, it is considered that the parylene-coated PbO dosimeter can be implemented for QA of brachytherapy devices.

Lead monoxide: a promising two-dimensional layered material for applications in nonlinear photonics in the infrared band

Lead monoxide (PbO), a novel few-layer two-dimensional (2D) material, was theoretically predicted to have an excellent optical response.