Measurement of the specific activity of Ar-39 in natural argon
  We report on the measurement of the specific activity of Ar-39 in natural argon. The measurement was performed with a 2.3-liter two-phase (liquid and gas) argon drift chamber. The detector was developed by the WARP Collaboration as a prototype detector for WIMP Dark Matter searches with argon as a target. The detector was operated for more than two years at Laboratori Nazionali del Gran Sasso, Italy, at a depth of 3,400 m w.e. The specific activity measured for Ar-39 is 1.01 +/- 0.02(stat) +/- 0.08(syst) Bq per kg of natural Ar. 
P. Benetti, F. Calaprice, E. Calligarich, M. Cambiaghi, F. Carbonara,   F. Cavanna, A.G. Cocco, F. Di Pompeo, N. Ferrari, G....