  A low background germanium gamma ray spectrometer, GeTHU, has been installed
at China JinPing underground Laboratory. The integral background count rate
between 40 and 2700 keV was 0.6 cpm, and the origin was studied by Monte Carlo
simulation. Detection limits and efficiencies were calculated for selected
gamma peaks. Boric acid and silica sand samples were measured and 137Cs
contamination was found in boric acid. GeTHU will be mainly used to measure
environmental samples and screen materials in dark matter experiments.
