Thesis Committee: Kate Scholberg, Haiyan Gao, Chris Walter, and Seog Oh (exofficio non-voting member)
ABSTRACT:
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