Thanks to Dr. Sarah Eno, Post-Doc Geng-Yuan, Thomas O'Bannon,
and others from the High Energy Physics Group for helping me with
this project. Thanks to Dr. Alan Peel for allowing this research
project to be conducted for credit.
• The Compact Muon Solenoid (CMS) detector is located at the
Large Hadron Collider (LHC), which is the largest and most powerful
particle accelerator ever built.
• The LHC is a 27-kilometer underground laboratory located on
the Swiss-French border.
• CMS is one of the four experiments at the LHC. • CMS is quite
compact for all the materials it contains,
it detects particles known as muons, and is the world’s most
powerful solenoid magnet.
• The CMS detector consists of 6 main components.• The detector
will be upgraded in preparation for the
High Luminosity LHC starting in 2025.• UMD’s High Energy Physics
(HEP) investigates
methods for better measuring the energies of hadrons in order to
prepare for the detector’s upgrade.
There are two important types of radiation damage that can occur
in plastic scintillators: Production of new stable absorption
centers and the deterioration of fluormolecules. In the German
physicist Wick’s paper "Strong reduction of radiation damage in
plastic scintillators by illumination with visible light," he shows
that for polystyrene (PS) base substrates, the so-called
"permanent" damage due to the color centers formed during
irradiation can be reduced by exposure to blue light (Figure 2).
The purpose of this project is to investigate whether a similar
reduction can happen in a polyvinyltoluene (PVT) base substrate.
Light pulses from blue, green, and red LED’s will be used to
measure the optical transmission and to illuminate the
scintillators. Some PVT samples will be kept in the dark while
other samples will be illuminated during irradiation with blue
(460-470 nm), green (515-530 nm), and red (613-618 nm) light by the
LEDS. To measure the light output of each sample, an alpha source
test will be performed. An alpha source (Pu-239) will be placed on
top of the sample and a photomultiplier tube, which produces an
electric current proportional to the intensity of detected light.
The mean value of the permanent induced absorption Δμperm can then
be plotted as a function of the wavelength to determine if any of
the three colored LEDS reduces the irradiation damage in the PVT
scintillator samples.
About CMS
Radiation Damage in Plastic Scintillators
Ruhi [email protected]
Science Discovery and the Universe Physics and Computer
Science
• Plastic Scintillators are used in the field of high energy
physics to detect particles.
• Advantages of using plastic scintillators as oppose to other
types (liquid, organic, etc.) of scintillators are that it is
cheaper, has a fast time response, and there is more experience
with this material.
• Modern scintillators use either polystyrene (PS) or
polyvinyltoluene (PVT) as the base material.
• Scintillators are comprised of a substrate (PVT or PS) and two
wave-length-shifting dopants.
• Particles passing through the scintillator excites the valence
electrons in the molecules of the substrate, causing the electrons
to fall from energetic orbitals to emit light.
• This light output is then measured by the photon detectors in
the scintillator (for this project, a photomultiplier tube will be
used as the photodetector).
• Light output decreases as the plastic is exposed to ionizing
radiation (radiation damage).
• There is an exponential light loss characterized by a decay
constant D:
L/Lo ∝ e− L/D
For this project, I built my own alpha source test, which
consisted of a photomultiplier tube (PMT), a PMT circuit board, and
an alpha source. I was able to use the ExpressPCB and ExpressSCH
software in order to create my PMT circuit board and to design the
schematic. I learned useful technical skills and was trained to
help take alpha source, absorption, and emission measurements.
Coding in python and C++ was necessary to create the plots and is
very useful in any field of physics, not just in high energy
physics. I also created a circuit board with LEDS that connected
with a pulsar in order to illuminate the plastic.I am now more
familiar with circuitry and the software used to create boards. In
addition, I now better understand the interactions among particles
and the scintillation phenomenon.Although the project is not
finished (I still have no results on whether blue light can reduce
radiation damage in a PVT base substrate), I plan to continue with
this project, possibly over the summer.
Background on Project/ Methodology
What I learned/Future work
Plastic Scintillators
Figure 2: Results obtained from 3 polystyrene
samples when illuminated by three different
colored LEDS (red, green, and blue). For
wavelengths above 380nm, this plot shows that
the illumination with blue light during irradiation
reduced strongly the permanent absorption
damage. K. Wick, Inst. fur Exp., Hamburg Univ., Germany
Figure 4: Alpha source measurements (NIST set
1 samples). Can be compared to demonstrate
irradiation effects to plastic scintillators.Geng Yuan Jeng, UMD
HEP-CMS
Acknowledgments
Figure 1:
Compact Muon Solenoid cross-section CMS collaboration, CERN
ETH Institute of Particle Physics
Figure 3: PMT circuit board created
using ExpressPCB.Ruhi Perez-Gokhale, UMD HEP-CMS
