The ultra-low background facility
The ultra-low background facility is dedicated to the material screening for frontier physics experiments such as dark matter direct detection, neutrino-free double beta decay search and nuclear astrophysics experiments. The facility consists of 19 low background γ spectrometers (GeTHU), an Ultra-low background γ spectrometer (ARGUS) and an ultra-low background liquid scintillator spectrometer in the underground space of CJPL. And two ultra-low background α spectrometers and two ICPMS spectrometers are constructed in the auxiliary laboratory in Xichang city. The above facilities form a “above ground / underground” dual-center, multi-technology layout with the ability to analyze multiple kinds of samples and nuclides with high sensitivity.
Low background gamma spectrometer (GeTHU)
The Germanium γ-ray spectrometer of TsingHua University (GeTHU) low-background γ spectrometers consists of a total of 19 high-purity germanium γ spectrometers. The GeTHU-I prototype was developed and put into trial operation in the first phase of the laboratory (CJPL-I) in 2012. The performance of GeTHU-I reaches an advance level among the other low-background γ spectrometers worldwide, and it is also the first deep underground ultra-low background γ spectrometer in China. At present, three GeTHU series (GeTHU 1/2/3) are currently in operation in CJPL-I to provide material measurement services for cutting-edge physics experiments such as CDEX, PandaX, JUNA, and Jiangmen neutrino experiments.
Other 16 low-background high-purity germanium γ spectrometers are currently under construction and are located in the world's largest polyethylene shielded chamber in Hall C2 of CJPL-II. Those spectrometers including 14 coaxial high-purity germanium detectors, one well-type high-purity germanium detector, and one ultra-low-energy high-purity germanium detector. The spectrometer uses 15 cm high-purity copper, 15 cm lead, and 1 m polyethylene as the passive shielding, and their sensitivities will reach mBq/kg.
ARray of GermaniUm γ-ray Spectrometer (ARGUS)
Located in the world's largest polyethylene shielded chamber in Hall C2 of the CJPL-II, the ARGUS ultra-low background γ spectrometer consists of five low-background high-purity germanium detectors, and a multilayer shielding of 20 cm low-background copper, 5 cm low-background lead and 15 cm ordinary lead. The background level of ARGUS will reach <20 cpkd @60-2700 keV, and the sensitivity will reach the order of μBq/kg.
Ultra-low background liquid scintillator spectrometer
The laboratory has built two AccuFLEX LSC-LB7 ultra-low background liquid scintillator spectrometers produced by HITACHI-ALOKA for the analysis of trace amounts of 3H and 14C. The LSC-LB7 measures β-emitters by the detection of its scintillation light in the liquid scintillator, its sensitivity for 3H can reach 0.36 Bq/L, which is the highest among other commercial products.
Ultra-Low background α spectrometer
Two UltraLo-1800 ultra-low background α spectrometers produced by XIA are built in the Auxiliary Laboratory in Xichang to measure the trace α radioactivity on the surface of a sample. UltraLo-1800 uses Dual Channel Ion Chamber technology to measure α radioactivity on the sample surface via active background suppression method. It can reach a < α/cm2/hr background count rate level and a sensitivity of 10-3 μBq/cm2.
ICPMS spectrometer
Two Element-XR ICPMS spectrometers produced by Thermo Fisher are built in the Auxiliary Laboratory in Xichang to measure the trace Th/U radioactivities in samples. The ICPMS spectrometers are in 1000 grade clean room with two 100 grade clean platform. The sensitivity of the Element-XR ICPMS spectrometer is expected to reach 10-12 g/g (ppt) ~10-6 g/g (ppm) U/Th in a copper sample.
Measurement service
The ultra-low background facility provides measurement services to the society. For those apply to our service, please send all the information requested to the email cjpl@tsinghua.edu.cn. After receiving the email, we will evaluate the application and after the application is accepted, we will contact the applicant by email to further confirm and measurement. The application with incomplete information or does not meet the requirements will not be accepted.
Request form: 
CJPL Assay request form.docx
