Browsing by Author "Hassan, Amna"

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Towards low dose retrospective dosimetry on shelled species
(2020-08-01) Hassan, Amna; Waller, Ed
This work investigates calcified tissues of shelled species for retrospective dosimetry using electron paramagnetic resonance (EPR) spectroscopy. To determine applicable samples for low dose studies, shells of crustacean and mollusc species were irradiated to 10 Gy using a 137Cs source. Reference dosimetry was performed with alanine powder using a specifically developed calibration curve. Characteristic Mn2+ signals were present in the EPR spectra of all studied species. Radiation induced peaks were not detected in shells of any species except terrestrial snails. A dose-response curve for terrestrial snails was developed by irradiating shells to 2, 10, and 20 Gy. However, Mn2+ signals caused limitations in resolving radiation induced peaks below 2 Gy. Environmental factors were assessed, and it was found that shell structure and habitat characteristics contribute to Mn2+ signals in EPR spectra. Since high-intensity Mn2+ signals obscured radiation-induced peaks, shells of the studied aquatic species were deemed unsuitable for low dose retrospective dosimetry.
Yeast-based impedance biodosimetry for retrospective assessment of radiation exposures
(2024-07-01) Hassan, Amna; Atkinson, Kirk
In the event of a radiological accident, conventional dosimeters are not always present or available to provide dose estimates. As such, retrospective dosimetry techniques can be used to determine the radiation dose to populations and the environment. This work investigates the feasibility of Saccharomyces cerevisiae yeast cells as fortuitous dosimeters for retrospective assessments of exposures following radiological accidents using impedance biodosimetry. The radiation response of S. cerevisiae was examined by using cellular metabolic activity and impedance as a means to evaluate dose. A novel dosimeter design was developed to allow impedance measurements to be performed on yeast samples. Simulations with Geant4 Monte Carlo code were conducted to explain the significance of the local environment and its impact on impedance measurements. It was found that yeast irradiated in the presence of various adjacent materials yield different impedance responses and the local environment influences the radiative energy deposition in yeast cells. This is due to the primary and secondary photoelectrons and Compton electrons that are produced within these materials, which contribute to additional energy deposition and increase damage to cells. This effect was exploited by adding an intermediate material in yeast samples to amplify the impedance signals. In this current work, aluminum grains were utilized as the standard intermediate material in yeast dosimeters as a controlled proxy for real world situations and for the purposes of mechanistic analysis and sensitivity assessments. To evaluate the feasibility of impedance biodosimetry, a dose-response curve was produced by irradiating yeast cells from 0:5 Gy to 8 Gy using a ¹³⁷Cs gamma source. The dose-response curve exhibited a linear relationship of dose with changes in the impedance response. Additionally, the lowest detectable dose that could be measured using this methodology was determined to be 300mGy. Fading of the impedance signal was also investigated, where no noticeable fading over a 7-month period was observed. Finally, the impedance response of Fleischmann's ® yeast was examined, and it was found that commercially available yeast cells exhibit a similar response to laboratory-grade yeast, as well as a radiation response. Based on these experimental findings, yeast cells were determined to be suitable to use for retrospective dosimetry applications since these samples are widely available and require no additional processing. Yeast-based impedance biodosimetry was determined to be an inexpensive technique that could be used in the event of a radiological accident to evaluate initial dose estimates to exposed areas. However, since the local environment considerably influences the energy deposition in cells, knowledge of materials that may be adjacent to yeast samples during the exposure is necessary to provide accurate dose assessments.