Thesis Committee: Kate Scholberg, Haiyan Gao, Chris Walter, and Seog Oh (exofficio non-voting member)
Tyvek is a material that is used extensively in the outer detector of the Super-Kamiokande neutrino observatory. The Monte Carlo simulation of Super-Kamiokande has several routines that simulate the reflection of photons from the Tyvek. We have devised and built an experiment to measure the reflectivity of Tyvek in air and underwater on the plane of the incident light. The results from this experiment can be used to improve the Monte Carlo simulation of Super-K. It was found that the results in air fit very well the expected function, which is a combination of Lambert's Cosine Law (due to highly diffusive reflection) and a diffused specular component that still retains some angular dependence. The results in water also agree well with the fits for angles of incidence smaller than 40 degrees, while at larger angles of incidence the fit seems to miss the tail of the data. The reflectivity of Tyvek in the plane of the incident light seems to be much larger in water than in air (by a factor of 2.0-2.5, depending on the angle of incidence). This is consistent with the fact that, in water, the reflectivity functions appear to have a predominant diffused specular component. The current implementation of the reflection of photons from Tyvek in the Monte Carlo does not agree well with the experimental results. In the simulation, the number of photons that reflect according to Lambert's Cosine Law is too large compared to the number that reflect in a diffused specular fashion. This leads to large disagreements with the data, especially for results at large angles of incidence and in water, where the diffused specular component dominates.
Here is the thesis in PDF: Chavarria_thesis.pdf