Measurement of Light Transmission in Radiation Damaged Glued Quartz Bars for Q weak

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. 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. 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: According to Fresnel’s 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 <1% 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 <1% of the light after being damaged from radiation.