China Jinping Underground Laboratory

The China Jinping Underground Laboratory (Chinese: 中国锦屏地下实验室; pinyin: Zhōngguó jǐn píng dìxià shíyàn shì) is a deep underground laboratory in the Jinping Mountains of Sichuan, China. The cosmic ray rate in the laboratory is under 0.2 muons/m²/day, placing the lab at a depth of 6720 m.w.e.:2 and making it the best-shielded underground laboratory in the world.:17 The actual depth of the laboratory is 2,400 m (7,900 ft), yet there is horizontal access so equipment may be brought in by truck. The China Jinping Underground Laboratory (Chinese: 中国锦屏地下实验室; pinyin: Zhōngguó jǐn píng dìxià shíyàn shì) is a deep underground laboratory in the Jinping Mountains of Sichuan, China. The cosmic ray rate in the laboratory is under 0.2 muons/m²/day, placing the lab at a depth of 6720 m.w.e.:2 and making it the best-shielded underground laboratory in the world.:17 The actual depth of the laboratory is 2,400 m (7,900 ft), yet there is horizontal access so equipment may be brought in by truck. Although the marble through which the tunnels are dug is considered 'hard rock', at the great depth it presents greater geotechnical engineering challenges:16–27:16–19 than the even harder igneous rocks in which other deep laboratories are constructed.:13–14 The 10 MPa (1500 psi; 99 atm) water pressure in the rock is also inconvenient. But marble has the advantage for radiation shielding of being low in radionuclides, such as 40K, 226Ra, 232Th,:17 and 238U.:16 This in turn leads to low levels of radon (222Rn) in the atmosphere.:5 The laboratory is in Liangshan in southern Sichuan, about 500 km (310 mi) southwest of Chengdu.:3 The closest major airport is Xichang Qingshan Airport, 120 km (75 mi) away by road.:5 The Jinping-II Dam hydroelectric power project involved excavating a number of large tunnels under the Jinping Mountains: four large 16.7 km (10.4 mi) headrace tunnels carrying water east,:30 two 17.5 km (10.9 mi) vehicular access tunnels,:1 and one water drainage tunnel. Hearing of the excavation in August 2008, physicists at Tsinghua University determined that it would be an excellent location for a deep underground laboratory, and negotiated with the hydropower company to excavate laboratory space in the middle of the tunnels. A formal agreement was signed on 8 May 2009, and excavation was promptly started.:29 The first phase CJPL-I, consisting of a 6.5 × 6.5 × 42 m (21 × 21 × 138 ft) main hall,:8 plus 55 m (180 ft) of access tunnel (4,000 m³ total excavation):15 was excavated by May 2010,:7 and construction completed 12 June 2010.:7 A formal laboratory inauguration was held 12 December 2010.:37