In nuclear and particle physics, plastic scintillators are probably one of the most widely used for detectors. Plastic scintillator materials are used in many applications for the detection of radioactive material, primarily due to the sensitivity per unit cost compared to other detection materials. Plastic scintillators are solutions of organic scintillators but in a solid plastic solvent. Plastics offer an extremely fast signal with a decay constant of about 2-3 ns and high light output. However, the resolution and lack of full-energy peaks in the plastic scintillator material prohibits detailed spectroscopy. Therefore, other doped materials are used for spectroscopic applications.
Colloidal semiconductor nano-crystals, so-called quantum dots (QDs), heavy generated tremendous interest both for fundamental research and tech- nical applications such as light emitting diodes (LEDs), bio-imaging and solar cells. Because of their size-dependent photoluminescence related to quantum-size effect tunable across the wide visible spectrum. CdSe QDs, have become the most extensively investigated QDs.
Photomultiplier (PMT) have maximum quantum efficiency around 400 nm but photodiode have maximum quantum efficiency around 600 nm. The standard secondary scintillators have emission wavelength around 400 nm because 400 nm is mostly maximum quantum-efficiency of PMT. Thus it isn’t suitable for photodiode application. Emission wavelength of quantum- dot depends on size effect. So I fabricate quantum-dot doped plastic scintil- lator in order to change emission wavelength for standard plastic scintillator.
I studied luminescence property of different concentration quantum-dot doped plastic scintillator by using X-ray, photon and 45-MeV proton beam. I measured X-ray, photo- and proton-induced luminescence of different con- centrations quantum-dot doped plastic scintillators. Among them, quantum- dot doped plastic scintillator (styrene + PPO + quantum-dot) emitted a siz- able luminescence.
Also I measured proton pulse-height spectrum of quantum-dot doped plastic scintillator by using 45-MeV proton beams at Korea Institute of Radiological and Medical Sciences (KIRAMS).
And I measured fluorescence decay time for studying mechanism of scintillation.
Thesis Advisor: Prof. Hongjoo Kim