1. Radiation-Resistant Scintillators Zachary H. Thomas, zthomas@umd.edu Science, Discovery and the Universe Physics and Government and Politics High Energy Physics Group Compact Muon Solenoid Collaboration At CERN, the European Organization for Nuclear Research, physicists investigate the fundamental structure of the universe The Large Hadron Collider (LHC), the world’s largest and most powerful particle accelerator, is the last link in CERN’s chain of particle accelerators The Compact Muon Solenoid (CMS) is one of the four detectors built into the LHC, with programs ranging from studying the Standard Model of particle interactions to searching for particles that make up dark matter. The component of the CMS detector that measures the energy of hadrons, or strongly interacting particles, is the hadron calorimeter (HCAL) UMD’s High Energy Physics (HEP) group investigates methods for better measuring the energies of hadrons, in order to prepare for the detector’s next upgrade in 2025 About UMD HEP-CMS What I learned HCAL is made of scintillators and brass absorbers Valence electrons in a scintillator are excited by particles passing through, then fall from energetic orbitals to emit light The light output is measured by photon detectors on the periphery of each scintillator The photon count is proportional to the energy of the passing particle, which can be analyzed using Poisson statistics (for counting) Doping materials in the scintillator affect the wavelength, lifetime, and total yield of emitted light Due to radiation, the light yield of the scintillators is getting reduced UMD HEP-CMS is investigating how different concentrations of dopants can make scintillators more radiation-resistant Scintillators All research was conducted under Sarah Eno and Alberto Belloni of the High Energy Physics group, Compact Muon Solenoid Collaboration, University of Maryland, College Park. Thanks to Dr. Alan Peel, Sarah Eno, and the University for enabling this research to be completed for credit hours. Experiment In order to compare the light yield of scintillators with different bases and dopant concentrations, we calculated a dose constant for each sample Since the light yield of a scintillator decays exponentially as a function of dose rate immediately after irradiation, the dose constant (D) represents the dose rate (d) at which the ratio of original light yield (L 0 ) to post-irradiation light yield (L) is 1/e L(d)=L 0 e -d/D A higher dose constant means better light yield after irradiation, and a lower dose constant means worse light yield after irradiation We found that low dose rates, in general, resulted in a lower dose constant after recovery from irradiation, and that the green-spectrum base has a marginally better light output after low-dose irradiation (Figure 3) Since the scintillators in HCAL experience low rates of radiation from collisions, we are looking for scintillating plastic that has a higher dose constant at low levels of irradiation Results We had two types of scintillator base: one emits light in the blue spectrum and one emits light in the green spectrum Each base had nine possible concentrations of two dopants: one, two, or four times the primary dopant with one, two, or four times the secondary dopant We irradiated samples of each base type and dopant concentration at different radiation rates, total dose, temperatures, and oxygen levels To measure the light output of each sample, we placed an alpha source (Pu-239) on top of the sample and a photomultiplier tube, which produces an electric current proportional to the intensity of detected light (Figure 1) Acknowledgements Figure 3 Compact Muon Solenoid cross-section CMS collaboration, CERN Figure 2 Dose constants as a function of dose rate Geng Yuan Jeng, UMD HEP-CMS Figure 1 Alpha source measurements Scintillator measured after cold irradiation Zach Thomas, UMD HEP-CMS I learned a lot of technical skills in order to successfully work on my various projects. Python and C++ programming were necessary for making these plots. The dose constant plot, for example, was made by fitting the peak of the alpha measurement plot to a Gaussian distribution. Coding skills will be particularly useful in any field of physics, and it is not a primary focus of this physics department. I also better understand interactions between particles, like hadrons in scintillating material. I am still getting familiar with CMS’s method of data collection, which involves weighting data based on the likelihood of certain interactions, so that the resulting data looks “cleaner”.