Radiation-Induced Changes in Optical Properties and Crystallinity of Polymers measured by Terahertz Time-Domain Spectroscopy, Differential Scanning Calorimetry, and X-Ray Diffraction
Author
Eskildsen, Katrine Gerassimovitch
Term
4. semester
Education
Publication year
2025
Submitted on
2025-05-29
Abstract
Dette speciale undersøger, om terahertz time-domain spektroskopi (THz-TDS) kan bruges som en ikke-destruktiv metode til at karakterisere strålingsinducerede ændringer i polymerer ved klinisk relevante, lave doser. Poly(methyl methacrylat) (PMMA) og høj densitet polyethylen (HD-PE) blev bestrålet i en lineær accelerator med doser fra 10 til 800 Gy ved en dosisrate på 6,00 Gy/min, hvorefter brydningsindekset blev målt med THz-TDS. Krystallinitet blev kvantificeret med differential scanning kalorimetri (DSC) for HD-PE og, for polyethylenprøver fra et semesterprojekt, med både DSC og røntgendiffraktion (XRD). Resultaterne viser, at PMMAs brydningsindeks stiger med dosis, mens HD-PEs brydningsindeks falder med dosis, og at % krystallinitet ved lave doser korrelerer svagt med brydningsindekset for HD-PE. For PE-prøverne gav XRD højere værdier for % krystallinitet end DSC, og der ses en svag lineær sammenhæng mellem brydningsindeks og krystallinitet. Et aldringsstudie viser desuden, at brydningsindekset for alle polymererne øges over tid efter bestråling, uafhængigt af dosis og polymertype. Samlet peger arbejdet på, at THz-TDS kan være en lovende tilgang til at følge materialers respons på bestråling og dermed støtte dosimetri, men at faktorer som aldring, lyspåvirkning og prøve renhed bør kontrolleres for at opnå høj nøjagtighed.
This thesis evaluates whether terahertz time-domain spectroscopy (THz-TDS) can serve as a non-destructive method to characterize radiation-induced changes in polymers at clinically relevant, low doses. Poly(methyl methacrylate) (PMMA) and high-density polyethylene (HD-PE) were irradiated using a linear accelerator with doses from 10 to 800 Gy at a dose rate of 6.00 Gy/min, and the refractive index was measured by THz-TDS. Crystallinity was quantified by differential scanning calorimetry (DSC) for HD-PE and, for polyethylene samples from a semester project, by both DSC and X-ray diffraction (XRD). The results show that PMMA’s refractive index increases with dose, whereas HD-PE’s refractive index decreases, and that at low doses the percent crystallinity in HD-PE correlates weakly with refractive index. For the PE samples, XRD yields higher percent crystallinity than DSC, and a slight linear relation between refractive index and crystallinity is observed. An ageing study further reveals that the refractive index of all polymers increases over time after irradiation, independent of dose and polymer type. Overall, the work indicates that THz-TDS is a promising approach for tracking materials’ response to irradiation and supporting dosimetry, while accuracy depends on controlling factors such as ageing, light exposure, and sample purity.
[This abstract was generated with the help of AI]
Documents