As the end of the fall semester
comes closer, something else draws near: the deadlines to apply for internships
for this coming summer. You might think summer is still far away, but you need
to start now if you want to make the most of it. There are so many options for
doing research over the summer, whether to buff up your resume or just start
getting involved in your field. You can apply for a Science
Undergraduate Laboratory Internship (SULI), or for a Research
Experience for Undergraduates (REU) program. If you
are curious whether doing an internship over the summer is worth it, I have to
tell you that it truly is.
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| Me with parts for lead glass electromagnetic calorimeter. |
I applied for the SULI program in
late 2015, I found out that I had been accepted into the program during the
early spring of 2016. I was allowed to work at Jefferson Labs during the summer,
helping Bogdan Wojtsekhowski to construct a new calorimeter.
Calorimeters are a key instrument
for studying particles, and a variety of different calorimeters are used in
institutions all over the world. Different calorimeters have their advantages
and disadvantages, based on the materials used, the geometry or design of the
calorimeter, etc. At Jefferson Labs, work is being done to mitigate the
disadvantages of a specific type of calorimeter: a homogeneous electromagnetic
calorimeter, constructed from lead glass.
A homogenous electromagnetic
calorimeter constructed from lead glass is needed for investigating the nucleon
structure via the study of a proton elastic electric form factor. However,
there is a problem with using lead glass in calorimeters. Over time, as the
lead glass is exposed to radiation, it becomes discolored. This discoloration
negatively impacts the performance of the calorimeter. When the lead glass is
heated up, though, it becomes clear once again.
Bogdan Wojtsekhowski of Jefferson
Labs came up with the novel idea of operating the calorimeter at a high
temperature in order to prevent discoloration to the lead glass. The new, high
temperature EM calorimeter is still being tested, with small prototypes being
made first to make sure the idea works. Each prototype is constructed larger
than the previous, to ensure that the designs can be scaled up without any
undesirable effects.
My role at Jefferson Labs was to
resolve the two main problems being encountered while constructing the
calorimeter. First, the light guides which were glued to the lead-glass were
developing strain and snapping off. This led to the second problem: when the
light guides broke off from the lead-glass, the residual epoxy was extremely
resilient and difficult to remove.
The epoxy removal was the easier issue to resolve. The adhesive, Eccobond F202 Bipax, had a max service temperature of approximately 240°C. Since the lead-glass and light guides do not soften until reaching temperatures in excess of 500°C, I placed the materials with residual epoxy in an oven set to 340°C for 6 hours. This caused the adhesive to become discolored and brittle, making it easy to chip off using a razor blade and blunt object. This was done after applying alcohol to the epoxy to prevent the chips from flying, and the razor blade was kept at a shallow angle to prevent damage to the glass.
Preventing strain in the light
guides required more work. Strain develops in glass as a result of improper
cooling. If the outer part of the glass is allowed to cool too quickly, it
solidifies around the still soft middle. Then, when the middle cools, it
expands into to already solid out part. This is what causes the glass to
develop strain. In order to fix this, the light guides had to be annealed, a
process which involves reheating the glass to relieve stress within the glass
and then cooling it down uniformly. The light guides, being made of
Borosilicate +33, needed to be annealed according to the parameters in the
table to the left while using a ramp rate of 10°C/min. In order to heat large
quantities of light guides at these temperatures, I had to design an apparatus
to hold the light guides inside the oven, and get permission for them to be put
through an ultra-high vacuum, or UHV, oven. In order to prevent contamination
of the oven, I had to wipe down every light guide that would be heated, as well
as the apparatus that they would be stored in.
As part of my internship, I was
required to create a poster
regarding my work, and write a more in-depth paper detailing what I had done. More
in depth information on the work regarding the high-temp. EM calorimeter, can
be found in Bogdan
Wojtsekhowski’s February 11, 2016 report. The calorimeter is part
of Jefferson Lab’s Super Bigbite Spectrometer, and you can find more information
on it at their website.
Through the SULI program, I got
hands-on experience in an actual lab, learned a lot from professional
physicists, and met many other undergraduates from around the world who shared
a passion for physics.
