Measurement of Light Transmission in Radiation Damaged

1
Measurement of Light Transmission in Radiation
Damaged Glued Quartz Bars for Qweak
KATIE KINSLEY (Department of Physics, Ohio
University, Athens, OH 45701) DAVID MACK
(Jefferson Lab, Newport News, VA 23606), JULIE
ROCHE (Ohio University, Athens, OH 45701)
ANALYSIS The transmission data collected was
analyzed using the following equation Where
Tuncor is the transmission percentage without
Fresnel correction factor included, Idark is the
output current of the dark rate, and Iin and Iout
are the output currents with the quartz sample in
and out, respectively.
INTRODUCTION The key objective of Qweak is to
compare the probability of scattering between
polarized electrons spinning in opposite
directions. In order to do this we take a
continuous beam of electrons and shoot it at a
hydrogen target. In doing this, the electrons
will sometimes come close to the electrically
charged parts of the target, causing the beam of
polarized electrons to scatter at different
angles. We used Cherenkov light detectors
consisting of large quartz bars and
photomultiplier tubes. These detectors are quite
large, therefore several large quartz bars must
be glued together using Shin-Etsu Silicones 406.
However, the continuous electron beam emits
powerful amounts of radiation, and the
transparency of the glue could be compromised due
to radiation damage. The ability of the glue to
withstand high levels of radiation needed to be
tested in order to ensure that the Cherenkov
light detectors could measure as much light as
possible, and that the glue would not absorb more
light with radiation damage.

SYSTEMATIC ERROR The transmission, especially at
low frequencies, is well over 100, which is
impossible. Because of this graph We
realized that this was because of a light leak in
our dark box, which was being analyzed by the
PMT. We used a piece of tape to cover different
slit sizes, and also added a collimator to block
room light from reaching the PMT. With this
change to the hardware, we measured the size of
the light leak and found that is was 0.2 nA of
room light leaking in. Our new equation accounts
for this error
METHODS USED BASIC SETUP The setup to measure
the radiation damaged quartz along with the
SES406 consists of a monochrometer that shoots a
beam of light with specified frequencies through
the sample bars. After the light travels through
the quartz, it goes though a collimator and then
into an integrating sphere. The integrating
sphere has a shutter that can be opened and
closed from outside the dark box. Once the light
passes through the shudder and into the
integrating sphere it bounces the light around
inside, and shoots it into a photomultiplier
tube. All of the equipment is connected to a
MS-DOS computer program, which displays the
output current for each run.
According to Fresnels correction factors,
different amounts of light are reflected at
different frequencies of light. Therefore, we
need to account for this reflection by
multiplying Tuncor by its appropriate correction
factor.
QUARTZ BAR SAMPLE
Qweak Detector at Jefferson Lab
CONCLUSION We resolved all the systematic issues
with the addition of the collimator and the
subtraction of stray light. Comparison of glued
and control slide show that glue causes lt1 loss
of transmission in the UV.
After accounting for Fresnel reflection, the
transmission data could be analyzed.
MONOCHROMETER
INTEGRATING SPHERE WITH PMT ATTACHED
PROCEDURE With the stated setup, the procedure
for measuring the transmission of light though
the quartz bars consisted of recording the
displayed output current at 250nm, 275nm, 300nm,
400nm, and 500nm. First we needed to measure the
dark rate of the box, so we closed the shudder to
prevent the monochrometer from shooting light
into the PMT. Usually the dark rate measured
around -14.500 nA. Additionally, it was
necessary to take with the sample in and out. In
order to do this, we would set the desired
frequency and high voltage, and then we would
take a total of 10 runs, alternating the quartz
bar sample being in and out of the beam of light,
providing 5 runs with the sample in and 5 runs
with the sample out. We would use this method
for a control sample and an experimental sample
glued together with SES406 that was exposed to 1
Mrad of radiation.
ABSTRACT Electron accelerators all over the world
are used to study particles at a subatomic level.
In the Qweak experiment, scientists are
attempting to learn more about scattering
probability for polarized electrons with opposite
spin. Detectors are being used in Qweak to
measure Cherenkov light. These detectors are
extremely large, and in order to build them
quartz bars must be glued together using SES406.
These quartz bars and glue will be exposed to
very high levels of radiation, and it is
essential to be sure that the glue will remain
transparent, even after high doses of radiation.
Using a monochrometer and a PMT, we took
measurements with control and experimental quartz
bar samples which had been exposed to 1 Mrad of
radiation. The final result showed that the
SES406 absorbed lt1 of the light after being
damaged from radiation.