  The China Dark Matter Experiment (CDEX) is a low background experiment at
China Jinping Underground Laboratory (CJPL) designed to directly detect dark
matter with a high-purity Germanium (HPGe) detector. In the second phase
CDEX-10 with a 10 kg Germanium array detector system, the liquid argon (LAr)
anti-compton active shielding and cooling system is proposed. For purpose of
studying the properties of LAr detector, a prototype with an active volume of 7
liters of liquid argon was built and operated. The photoelectron yields, as a
critically important parameter for the prototype detector, have been measured
to be 0.051-0.079 p.e./keV for 662 keV Gamma lines at different positions. The
good agreement between the experimental and simulation results has provided a
quite reasonable understanding and determination of the important parameters
such as the Surviving Fraction of the Ar2 excimers, the absorption length for
128 nm photons in liquid argon, the reflectivity of Teflon and so on.
