This work demonstrated the feasibility and limitations of semiconducting {pi}-conjugated organic polymers for fast neutron detection via n-p elastic scattering. Charge collection in conjugated polymers in the family of substituted poly(p-phenylene vinylene)s (PPV) was evaluated using band-edge laser and proton beam ionization. These semiconducting materials can have high H/C ratio, wide bandgap, high resistivity and high dielectric strength, allowing high field operation with low leakage current and capacitance noise. The materials can also be solution cast, allowing possible low-cost radiation detector fabrication and scale-up. However, improvements in charge collection efficiency are necessary in order to achieve single particle detection with a reasonable sensitivity. The work examined processing variables, additives and environmental effects. Proton beam exposure was used to verify particle sensitivity and radiation hardness to a total exposure of approximately 1 MRAD. Conductivity exhibited sensitivity to temperature and humidity. The effects of molecular ordering were investigated in stretched films, and FTIR was used to quantify the order in films using the Hermans orientation function. The photoconductive response approximately doubled for stretch-aligned films with the stretch direction parallel to the electric field direction, when compared to as-cast films. The response was decreased when the stretch direction was orthogonal to the electric field. Stretch-aligned films also exhibited a significant sensitivity to the polarization of the laser excitation, whereas drop-cast films showed none, indicating improved mobility along the backbone, but poor {pi}-overlap in the orthogonal direction. Drop-cast composites of PPV with substituted fullerenes showed approximately a two order of magnitude increase in photoresponse, nearly independent of nanoparticle concentration. Interestingly, stretch-aligned composite films showed a substantial decrease in photoresponse with increasing stretch ratio. Other additives examined, including small molecules and cosolvents, did not cause any significant increase in photoresponse. Finally, we discovered an inverse-geometric particle track effect wherein increased track lengths created by tilting the detector off normal incidence resulted in decreased signal collection. This is interpreted as a trap-filling effect, leading to increased carrier mobility along the particle track direction. Estimated collection efficiency along the track direction was near 20 electrons/micron of track length, sufficient for particle counting in 50 micron thick films.
Strengthening the crystal lattice of lanthanide halides, which are brittle, anisotropic, ionic crystals, may prove to increase the availability and ruggedness of these scintillators for room-temperature gamma-ray spectroscopy applications. Eight aliovalent dopants for CeBr{sub 3} were explored in an effort to find the optimal aliovalent strengthening agent. Eight dopants, CaBr{sub 2}, SrBr{sub 2}, BaBr{sub 2}, ZrBr{sub 4}, HfBr{sub 4}, ZnBr{sub 2}, CdBr[sub 2}, and PbBr{sub 2}, were explored at two levels of doping, 500 and 1000 ppm. From each ingot, samples were harvested for radioluminescence spectrum measurement and scintillation testing. Of the eight dopants explored, only BaBr{sub 2} and PbBr{sub 2} were found to clearly decrease total light yield. ZnBr{sub 2} and CdBr{sub 2} dopants both affected the radioluminescence emission spectrum very little as compared to undoped CeBr{sub 3}. HfBr{sub 2}- and ZnBr{sub 4}-doped CeBr{sub 3} exhibited the highest light yields.