Bismuth Sulfide Nanoflowers for Detection of X-rays in the Mammographic Energy Range

Nambiar, S., Osei, E. K., & Yeow, J. T. W. (2015). Bismuth Sulfide Nanoflowers for Detection of X-rays in the Mammographic Energy Range. Scientific Reports, 5, 9440. DOI: 10.1038/srep09440The increased use of diagnostic x-rays, especially in the field of medical radiology, has necessitated a significant demand for high resolution, real-time radiation detectors. In this regard, the photoresponse of bismuth sulfide (Bi2S3), an n-type semiconducting metal chalcogenide, to low energy x-rays has been investigated in this study. In recent years, several types of nanomaterials of Bi2S3 have been widely studied for optoelectronic and thermoelectric applications. However, photoresponse of Bi2S3 nanomaterials for dosimetric applications has not yet been reported. The photosensitivity of Bi2S3 with nanoscale “flower-like” structures was characterized under x-ray tube-potentials typically used in mammographic procedures. Both dark current and photocurrent were measured under varying x-ray doses, field sizes, and bias voltages for each of the tube potentials – 20, 23, 26 and 30 kV. Results show that the Bi2S3 nanoflowers instantaneously responded to even minor changes in the dose delivered. The photoresponse was found to be relatively high (few nA) at bias voltage as low as +1 V, and fairly repeatable for both short and long exposures to mammographic x-rays with minimal or no loss in sensitivity. The overall dose-sensitivity of the Bi2S3 nanoflowers was found to be similar to that of a micro-ionization chamber.This project was funded by the Waterloo Institute for Nanotechnology (University of Waterloo, Canada) as part of a collaboration program with Prof. C.N.R. Rao's laboratory at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR, Bangalore, India)

Application of Nanomaterials for X-ray Shielding and Dosimetry in Diagnostic Radiology

Lead is commonly used in medical radiology departments as a shielding material against X-rays. Lead-based protective materials are also routinely used by clinical personnel and patients during radiological examinations or procedures. However, lead is extremely toxic and prolonged exposure to it can result in serious health concerns. In this thesis, a novel, lead-free, cost-effective nanocomposite was developed for X-ray protection applications. Conformable polymer nanocomposites from polydimethylsiloxane (PDMS) were fabricated using different weight percentages (wt%) of bismuth oxide (BO) nanopowder. BO has a relatively high atomic-number which allowed increased X-ray interactions required for the X-ray photons to deposit energy within the PDMS/BO nanocomposite. The attenuation properties of the nanocomposites were characterized using diagnostic X-ray energies from 40 to 150 kV. The results showed that the PDMS/BO nanocomposite (44.44 wt% of BO and 3.73 mm thick) was capable of attenuating all the scattered X-rays generated at a tube potential of 60 kV. Another aspect of my thesis-work involves X-ray detection using bismuth sulfide (Bi2S3) nanoflowers and organic polymer nanocomposite. There is an increasing demand for real-time, large-area, flexible dosimeters, especially in the biomedical industry. In this thesis, photoelectric response of hydrothermally synthesized Bi2S3 nanoflowers was measured under both low X-ray energies (20 to 30 kV), and higher diagnostic X-ray energies (40 to 100 kV). The photoresponse of the nanoflowers clearly showed high sensitivity to changes in X-ray intensities, the capability to operate at relatively low bias voltages (+1 and +1.5 V under X-rays in the mammographic and higher diagnostic energies respectively), and the potential to perform as a reliable dosimetric material for instantaneous dose measurements over a wide range of diagnostic X-rays. Finally, the nanoflowers were incorporated into a p-type, semiconducting organic polymer (P3HT). The photoelectric response of the both pure P3HT and P3HT/Bi2S3-nanocomposite devices was measured under X-rays in the diagnostic energy range. The P3HT/Bi2S3-nanoflower composite showed significantly higher sensitivity (~4 times under 100 kV X-rays) compared to that of pure polymer. In summary, the flexible P3HT/Bi2S3-nanoflower device could potentially be used over an uneven surface for real-time detection of diagnostic X-rays at a minimal operating voltage of -40 mV