PhD Projects
Improving Material Properties of Plastic Scintillators
Problem: Plastic scintillators for can discriminate between neutrons and gamma rays. However, the high concentration of small molecule dopant required leads to undesirable plasticizing effects such as softening, low glass transition temperature, and dopant aggregation and leaching.
Hypothesis: Cross-linking and polymerizable dopants may mitigate plasticizing effects by increasing the rigidity and covalently bonding the dopant with the polymer matrix.
Summary of Results:
Identified a commercial and synthesized cross-linker structure-property relationships developed in collaboration with physicists and nuclear engineers
Fabricated cross-linked samples with 10x higher Shore-D hardness and equivalent radiation detection capabilities.
Synthesized novel polymerizable dopants and co-polymerized with vinyl toluene to eliminate dopant leaching. Two synthetic dopants retained radiation detection capabilities.
Photopolymerized Plastic Scintillators Capable of Pulse Shape Discrimination
Problem: Plastic scintillators are fabricated via a thermally initiated radical bulk polymerization. This process is air sensitive and time and energy intensive (5-7 days in academic settings).
Hypothesis: Adapting technology and chemistry from the dental industry may allow for a quicker photopolymerization of plastic scintillators.
Summary of Results:
A two part photo-initiating system used in the dental industry combined with a dimethacrylate cross-linker allowed from bulk polymerization of 20g plastic scintillators.
Photo-polymerized plastic scintillators were fabricated by a 2 hour light exposure followed by a 70C post-cure, in air.
Despite the shorter fabrication time in air (5 fold reduction), photo-polymerized plastic scintillators performed comparable to thermally initiated analogs.
Polysiloxane Scintillators Capable of Pulse Shape Discrimination
Problem: Traditional plastic scintillators capable of pulse shape discrimination (PSD) are based on thermoplastics. This limits their potential applications.
Hypothesis: Polysiloxanes with high phenyl content may provide an elastomeric matrix for PSD capable plastic scintillators, meeting requirements for flexible applications.
Summary of Results:
A high phenyl content polysiloxane matrix was identified from Wacker.
A commercial and synthesized dopant were loaded up to 5 wt% .
Even at low dopant loadings, polysiloxane scintillators performed as well or better than traditional analogs. This is the first time polysiloxanes, or any other polymer, has been shown to have comparable PSD to polystyrene or poly(vinyl toluene).
Bismuth Dopants for Gamma Ray Spectroscopy in Plastic Scintillators
Problem: Plastic scintillators can detect neutrons or gamma rays and even distinguish the two via PSD. However, they are not able to determine source, or radioactive isotope, that emitted the radiation. Gamma ray spectroscopy would allow plastic scintillators to identify the source of radiation - for example, whether the gamma ray came from potassium (bananas) or uranium (nuclear materials...).
Hypothesis: Incorporating high Z elements into plastic scintillators will lead to the photoelectric effect, allowing plastic scintillators to be used for gamma ray spectroscopy. Bismuth dopants are a good candidate due to bismuth's low toxicity, compared to tin and lead, and wide range of organobismuth molecules available.
Summary of Results:
Three types of bismuth dopants, triarylbismuth, trialkoxybismuth, and bismuth oxide dopants were synthesized.
Triarylbismuth dopants were soluble but not stable under polymerization conditions.
Trialkoxybismuth dopants were stable under polymerization conditions but insoluble in vinyl toluene.
Bismuth oxide nanoparticles did not disperse in vinyl toluene, but could be functionalized to improve dispersion.