Isotopic Ratio Measurements of 135Cs/137Cs Using Resonance Ionization Mass Spectrometry

135Cs/137Cs isotopic ratios were measured in the presence of high levels of 133Cs using Resonance Ionization Mass Spectrometry (RIMS). Single- and double-resonance excitation of Cs with high-resolution continuous-wave (cw) lasers along 6s 2S1/2→6p 2P3/2, 6s 2S1/2→6p 2P3/2→7d 2D5/2, and 6s 2S1/2→6p 2P3/2→8s 2S1/2 pathways were followed by photoionization with an Ar ion laser. The age of a standard burn-up sample was determined using RIMS and compared to Thermal Ionization Mass Spectrometry (TIMS). The efficiency, selectivity and isobar suppression for TIMS and RIMS has been compared. The overall RIMS efficiency was found to be ≈2×10−6 with a combined selectivity of ≈1010 for both 135Cs and 137Cs against 133Cs using the preferred single-resonance excitation scheme.