Study On Attenuation Length Of Liquid Scintillator And High Purity Germanium Detector In Jiangmen Underground

Neutrino oscillation is the only observed phenomenon beyond the particle standard model and is considered to be the breakthrough point of new physics.The exact value was measured in three of the six parameters of the neutrino oscillation.In August 2012,the Daya Bay experiment provedsin² 2?₁₃=0.89?0.010?7?st at?8??0.005?7?sy st?8?as?₁₃central value with a standard deviation of 7.7 times with 139 days of data.The Jiangmen Neutrino Experimental Station,which will be completed in 2020,aims to measure the neutrino quality sequence.In order to achieve measurement accuracy,Jiangmen detector requires great detection performance and a large amount of extremely low background materials.The stability of liquid scintillator?LS?,especially gadolinium-doped liquid scintillator?GdLS?,is one of the key properties for reactor neutrino experiments,and the stability of LS and GdLS is monitored in terms of the attenuation length.At the same time,based on the investigation of the high-performance low background high purity germanium?HPGe?gamma spectrometer around the world,with the optimal detector performance as the design goal,the measurement accuracy of HPGe gamma spectrometer for natural radioactivity was studied to meet the requirement of measuring low background material for jiangmen detector.Therefore,this paper studies the attenuation length of liquid scintillator will be used in Jiangmen neutrino experiment and designs a Jiangmen underground ultra-low background HPGe gamma spectrometer with an anti-Compton detector.It provides design basis for jiangmen neutrino experiment and other low background experiments,such as neutrino double beta experiment,dark matter experiment and neutrino oscillation experimentA relative measurement is performed to cancel systematic uncertainties from PMT responses.The result shows the attenuation length is decreasing in the past six years,consistent with the detector energy scale decrease.This result is very important for the design of jiangmen neutrino detector.Using the Geant4,the peak to Compton ratio of HPGe gamma spectrometer with Bismuth germanium oxide?BGO?as an anti-Compton detector was studied.The results showed that after adding 50mm anti-Compton detector,the peak to Compton ratio of gamma of 1.46 MeV and natural radioactivity ²³⁸U,²³²Th,⁴⁰K were increased by about 28 times and 10 times,respectively,comparing the two cases of anti-Compton and non-anti-Compton and using the generator to simulat decay process of natural radioactivity.The detector's peak-to-Compton ratio is further increased to 5044 by using a 5 inch probe and a sample with a height and side thickness of 250 mm.Based on the investigation of the high-performance low background HPGe gamma spectrometer around the world,a reasonable shield and its radioactivity were set up,as well as a reasonable natural radioactive background and cosmic rays were set up according to Jiangmen environment.Research shows that in the underground laboratory of jiangmen,the Integral background count rate?100keV²700keV?of the HPGe gamma spectrometer without anti-compton detector can reach less than 0.111 count/min,and the detection limit of the detector is mBq/kg.With the addition of an anti-compton detector,the integral background can be reduced by more than 10 times and the detection limit can be reduced to?Bq/kg.The research results provide the design basis and performance reference for the construction of HPGe gamma spectrometer in jiangmen underground laboratory in the future.