Laser resonance ionization mass spectrometry measurements of cesium in nuclear burn-up and sediment samples

Isotopic ratio measurements of 135Cs to 137Cs were performed using both resonance ionization mass spectrometry (RIMS) and thermal ionization mass spectrometry (TIMS) to determine the chronological age of nuclear fuel burn-up samples. Initial measurements on a lake sediment sample are being performed at NIST for determination of cesium content in the sample. Atomization behavior of the graphite furnace source, the overall efficiency and selectivity were measured for different sample preparations. Single-resonance excitation 6s 2S1/2 (F=4) → 6p 2P3/2 (F′=5) with an extended cavity diode laser followed by photoionization with the 488 nm line of an argon ion laser yielded optical selectivity for 135Cs and 137Cs of more than two orders of magnitude against stable 133Cs and overall selectivity of 108. An overall efficiency of 5×10−7 was measured for standard 133Cs solutions and for the nuclear fuel burn-up samples.