Study of ionization signals in a TPC filled with a mixture of liquid   Argon and Nitrogen
  In this paper we report on the evidence for ionization track signals from cosmic ray muons and Compton electrons in a Time Projection Chamber (TPC) filled with liquid Argon and doped with different fractions of Nitrogen. This study has been conducted in view of the possible use of liquid Argon/Nitrogen TPCs for the detection of gamma rays in the resonant band of the Nitrogen absorbtion spectrum, a promising technology for security and medical applications. 
A. Ereditato, M. Hess, S. Janos, I. Kreslo, L. Martinez, M. Messina,   U. Moser, B. Rossi, H.-U. Shuetz, M. Zeller