Scintillation light from gamma ray irradiation in liquid xenon is detected by two Hamamatsu R9288 photomultiplier tubes ( PMTs ) immersed in the liquid .
UV light reflector material , PTFE , is used to optimize the light collection efficiency .
The detector gives a high light yield of 6 photoelectron per keV ( pe/keV ) , which allows efficient detection of the 122 keV \gamma -ray line from ^ { 57 } Co , with a measured energy resolution of ( 8.8 \pm 0.6 ) % ( \sigma ) .
The best achievable energy resolution , by removing the instrumental fluctuations , from liquid xenon scintillation light is estimated to be around 6-8 % ( \sigma ) for \gamma -ray with energy between 662 keV and 122 keV .