Salim Siddiqui

Effect of particle size, filler loadings and x-ray tube voltage on the transmitted x-ray transmission in tungsten oxide—epoxy composites

The effect of particle size, filler loadings and x-ray tube voltage on the x-ray transmission in WO(3)-epoxy composites has been investigated using the mammography unit and a general radiography unit. Results indicate that nano-sized WO(3) has a better ability to attenuate the x-ray beam generated by lower tube voltages (25-35 kV) when compared to micro-sized WO(3) of the same filler loading. However, the effect of particle size on x-ray transmission was negligible at the higher x-ray tube voltages (40-120 kV).

Characterisation of micro-sized and nano-sized tungsten oxide-epoxy composites for radiation shielding of diagnostic X-rays

Characteristics of X-ray transmissions were investigated for epoxy composites filled with 2-10 vol% WO3 loadings using synchrotron X-ray absorption spectroscopy (XAS) at 10-40 keV. The results obtained were used to determine the equivalent X-ray energies for the operating X-ray tube voltages of mammography and radiology machines. The results confirmed the superior attenuation ability of nano-sized WO3-epoxy composites in the energy range of 10-25 keV when compared to their micro-sized counterparts. However, at higher synchrotron radiation energies (i.e., 30-40 keV), the X-ray transmission characteristics were similar with no apparent size effect for both nano-sized and micro-sized WO3-epoxy composites. The equivalent X-ray energies for the operating X-ray tube voltages of the mammography unit (25-49 kV) were in the range of 15-25 keV. Similarly, for a radiology unit operating at 40-60 kV, the equivalent energy range was 25-40 keV, and for operating voltages greater than 60 kV (i.e., 70-100 kV), the equivalent energy was in excess of 40 keV. The mechanical properties of epoxy composites increased initially with an increase in the filler loading but a further increase in the WO3 loading resulted in deterioration of flexural strength, modulus and hardness.

Learning Optics with Multiple Representations: Not as Simple as Expected

Researchers have shown the importance of adopting multiple representations when teaching and learning science. In this study, we investigated how effectively students represented their understanding of optics concepts and the difficulties they faced when using multiple representations in an introductory university physics course. To this end, we observed the teaching of a physics course in an Australian university for four semesters, developed and administered an instrument to assess students’ use of written descriptions, diagrams, formula and graphs and compared conceptual pre-test and post-test data. We also interviewed students for their perceptions of the use of multiple representations when learning optics with this instrument. Prior to instruction, most items were answered with two representations – word and diagram. The instructor integrated all four representations into his lectures. After instruction, many more students adopted formula in their responses and the three-representations of word, diagram, and formula were the most frequent combination. In interviews, the majority of students commented that the question items with explicit emphasis on multiple representations were beneficial in improving their understanding of the optics concepts. We discuss students’ perceived difficulties and provide suggestions for future instruction with multiple representations in optics.