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A Mineral Oil Monitoring System for the Daya Bay Neutrino Experiment
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Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 449 www.elsevier.com/locate/npbps
A Mineral Oil Monitoring System for the Daya Bay Neutrino Experiment Yanchang Lina,b,c , for the Daya Bay Collaboration a Department
of Physics, The University of Hong Kong, Hong Kong of Physics, The Chinese University of Hong Kong, Hong Kong c College of Nuclear Technology and Automation Engineering, Chengdu University of Technology, P.R. China b Department
Abstract The Daya Bay Reactor Neutrino Experiment expects to determine the neutrino mixing angle θ13 with a sensitivity of sin2 (2θ13 ) = 0.01 in a three-year run. Eight three-zone cylindrical Anti-neutrino Detector (AD) modules with Gddoped Liquid Scintillator are arranged in two near halls and a far hall. In the outermost zone of each AD, 192 PMTs are mounted in Mineral Oil (MO). The stability of the optical properties of the liquids is very important for controlling the systematic uncertainties of the experiment and thus will be monitored online. The design of a monitoring system for the MO and results from a prototype system is presented. To determine the neutrino mixing angle θ13 with a sensitivity of sin2 (2θ13 ) = 0.01, relative measurement by using eight three-zone Anti-neutrino Detector (AD) modules at three experimental sites will be performed in the Daya Bay experiment. The innermost zone of an AD is the Gd-doped Liquid Scintillator (LS) target. In the middle zone, pure LS is used as gamma catcher. The outermost zone, in which PMTs are mounted, is filled with Mineral Oil (MO) as buffer. To monitor the optical properties of the MO, an online monitoring system is designed. The MO monitoring system consists of a Clarity Box installed on the AD lid, a retro reflector near the bottom of the AD, as well as the Data Acquisition (DAQ) subsystem. The Clarity Box, in which a 2 inch PMT is installed, is made of acrylic. Near-monochromatic light pulses with wavelengths between 400 and 440 nm, which are generated by a LED and regulated by a monochromator with a bandwidth of 5 nm, are delivered into the AD via an optical fiber and a collimator. The light beam goes through the MO and is reflected by the retro reflector. Both the incoming light and the reflected photon will be picked up by the PMT. The output waveform will be digitalized with a flash ADC. The incoming light pulse is used as a reference signal, so that gain drifting from both the PMT and the DAQ subsys0920-5632/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2012.09.086
tem can be canceled. To evaluate the performance of the design, simulation using GEANT4 was done. The designed geometries are applied in the simulation. The mean path length of the light beam in the MO is 8.4 m. Simulated samples with default MO attenuation length, as well as attenuation lengths scaled by 80%, 90% and 110% are generated, each sample contains 300,000 events. Simulation results show that the relative deviation of the MO attenuation length can be monitored to better than 10% with a statistical error of about 0.05%, which meets the design requirement of 15%. As a double check, a prototype system was also developed. In the prototype, the Clarity Box and the retro reflector were installed at each end of a 4-m-long MOfilled PVC pipe. The long-term stability was better than 1.8% in a 31 h test. Experimental results also showed that the precision in monitoring the reflected light intensity was better than 4%. Both simulation and prototype study showed the design would meet the requirements of the Daya Bay experiment. The MO monitoring system is now under construction and will be installed in each AD. We acknowledge the support of an RGC Collaborative Research Grant CUHK 1/07C of the HKSAR govemment.
Nuclear Physics B (Proc. Suppl.) 229–232 (2012) 449 www.elsevier.com/locate/npbps
A Mineral Oil Monitoring System for the Daya Bay Neutrino Experiment Yanchang Lina,b,c , for the Daya Bay Collaboration a Department
of Physics, The University of Hong Kong, Hong Kong of Physics, The Chinese University of Hong Kong, Hong Kong c College of Nuclear Technology and Automation Engineering, Chengdu University of Technology, P.R. China b Department
Abstract The Daya Bay Reactor Neutrino Experiment expects to determine the neutrino mixing angle θ13 with a sensitivity of sin2 (2θ13 ) = 0.01 in a three-year run. Eight three-zone cylindrical Anti-neutrino Detector (AD) modules with Gddoped Liquid Scintillator are arranged in two near halls and a far hall. In the outermost zone of each AD, 192 PMTs are mounted in Mineral Oil (MO). The stability of the optical properties of the liquids is very important for controlling the systematic uncertainties of the experiment and thus will be monitored online. The design of a monitoring system for the MO and results from a prototype system is presented. To determine the neutrino mixing angle θ13 with a sensitivity of sin2 (2θ13 ) = 0.01, relative measurement by using eight three-zone Anti-neutrino Detector (AD) modules at three experimental sites will be performed in the Daya Bay experiment. The innermost zone of an AD is the Gd-doped Liquid Scintillator (LS) target. In the middle zone, pure LS is used as gamma catcher. The outermost zone, in which PMTs are mounted, is filled with Mineral Oil (MO) as buffer. To monitor the optical properties of the MO, an online monitoring system is designed. The MO monitoring system consists of a Clarity Box installed on the AD lid, a retro reflector near the bottom of the AD, as well as the Data Acquisition (DAQ) subsystem. The Clarity Box, in which a 2 inch PMT is installed, is made of acrylic. Near-monochromatic light pulses with wavelengths between 400 and 440 nm, which are generated by a LED and regulated by a monochromator with a bandwidth of 5 nm, are delivered into the AD via an optical fiber and a collimator. The light beam goes through the MO and is reflected by the retro reflector. Both the incoming light and the reflected photon will be picked up by the PMT. The output waveform will be digitalized with a flash ADC. The incoming light pulse is used as a reference signal, so that gain drifting from both the PMT and the DAQ subsys0920-5632/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2012.09.086
tem can be canceled. To evaluate the performance of the design, simulation using GEANT4 was done. The designed geometries are applied in the simulation. The mean path length of the light beam in the MO is 8.4 m. Simulated samples with default MO attenuation length, as well as attenuation lengths scaled by 80%, 90% and 110% are generated, each sample contains 300,000 events. Simulation results show that the relative deviation of the MO attenuation length can be monitored to better than 10% with a statistical error of about 0.05%, which meets the design requirement of 15%. As a double check, a prototype system was also developed. In the prototype, the Clarity Box and the retro reflector were installed at each end of a 4-m-long MOfilled PVC pipe. The long-term stability was better than 1.8% in a 31 h test. Experimental results also showed that the precision in monitoring the reflected light intensity was better than 4%. Both simulation and prototype study showed the design would meet the requirements of the Daya Bay experiment. The MO monitoring system is now under construction and will be installed in each AD. We acknowledge the support of an RGC Collaborative Research Grant CUHK 1/07C of the HKSAR govemment.