Annihilation Radiation Gauge for Relative Density and Multiphase Fluid Monitoring A. Vidal, G. Viesti, F. Pino, H. Barros and L. Sajo-Bohus EPJ Web of Conferences, 66 (2014) 10017 Published online: 20 March 2014 DOI: 10.1051/epjconf/20146610017